i^^B 


Ji 


Jff 


COMMERCIAL       ORGANIC      ANALYSIS 

Allen's 
Commercial   Organic  Analysis 

A  Treatise  on  the  Properties,  Proximate  Analytical  Examination  and  Modes  of 
Assaying  the  Various  Organic  Chemicals  and  Products  Employed  in  the  Arts,  Manu- 
factures, Medicine,  etc. ,  with  Concise  Methods  for  the  Detection  and  Determination 
of  their  Impurities,  Adulterations,  and  Products  of  Decomposition.  By  ALFRED 
H.  ALLEN,  F.I.C.,  F.C.S.,  Public  Analyst  for  the  West  Riding  of  Yorkshire  and 
the  City  of 'Sheffield;  Past  President  of  the  Society  of  Public  Analysts  of  Great 
Britain,  etc. 

Vol.  I. — Preliminary  Examination  of  Organic  Bodies.  Alcohols,  Neutral  Alcoholic 
Derivatives,  Ethers,  Starch  and  its  Isomers,  Sugars,  Acid  Derivatives  of  Alcohols 
and  Vegetable  Acids,  etc.  Third  Edition,  with  numerous  additions  by  the 
author,  and  revisions  and  additions  by  DR.  HENRY  LEFFMANN,  Professor  of 
Chemistry  in  the  Woman's  Medical  College  of  Pennsylvania,  and  in  the  Wagner 
Free  Institute  of  Science,  Philadelphia,  etc.  With  many  useful  tables.  8vo, 
illustrated,  557  pages.  Cloth,  net  $4.50 

Vol.  II. — PART   I.     Fixed  Oils,   Fats,  Waxes,    Glycerin,  Soaps,    Nitroglycerin, 
Dynamite  and  Smokeless  Powders,  Wool-Fats,  Degras,  etc.      Third  Edition,  with 
many  useful  tables.     Revised  by  DR.  HENRY  LEFFMANN,  with  numerous  addi- 
tions by  the  author:     8vo,  illustrated,  387  pages.  Cloth,  ^$3.50 
Vol.  II. — PART  II.     Hydrocarbons,  Mineral  Oils,  Lubricants,  Asphalt,  Benzene 
and   Naphthalene,    Phenols,    Creosote,    etc.      Third  Edition,    Revised   by    DR. 
HENRY  LEFFMANN,  with  numerous  additions   by  the  author.       8vo,  illustrated, 
330  pages.  Cloth,  net  $3. 50 
Vol.  II. — PART   III.       Terpenes,    Essential   Oils,    Resins,    Camphors,    Aromatic 
Acids,  etc.      Third  Edition,  Cloth,  net  $5.00 
Vol.  III.— PART  I.     Tannins,  Dyes,  Coloring  Matters,  and  Writing  Inks.      Third 
Edition,  Revised,  Rewritten,  and  Enlarged,  by  J.  MERRITT  MATTHEWS,  Pro- 
fessor of  Chemistry  and  Dyeing  at  the  Philadelphia  Textile  School.     8vo,  illus- 
trated, 589  pages.  Cloth,  net  $4.50 
Vol.  III. — PART  II.     The  Amines  and  Ammonium  Bases,   Hydrazines  and  De- 
rivatives.    Bases  from  Tar.     The  Antipyretics,  etc.     Vegetable  Alkaloids,    Tea, 
Coffee,  Cocoa,  Kola,  Cocaine,   Opium,  etc.     Second  Edition.     8vo,  illustrated, 
593  Pages.  Cloth,  ^$4.50 
Vol.  III.— PART  III.     Vegetable  Alkaloids  concluded,  Non-basic  Vegetable  Bitter 
Principles.     Animal  Bases,  Animal  Acids,  Cyanogen    and    Its    Derivatives,  etc. 
Second  Edition.     8vo,  illustrated,  534  pages.                                      Clothj  net  $4.50 
Vol.  IV.     Proteids  and  Albuminous  Principles.     Milk  and  Milk  Products,  Meat 
.  and    Meat    Products,  Haemoglobin   and   its   Allies.     Proteoids  or   Albuminoids. 
Second  Edition,  with  elaborate  appendices  and  a  large  number  of  useful  tables. 
8vo,  illustrated,  584  pages.  Cloth,  net  $4.50 

•'The  general  excellence  of  the  work  is  such  as  to  make  it  almost  indispensable  to  any 
chemist  working  in  this  field.  *  *  *  It  is  particularly  satisfactory  tc  find,  along  with  care- 
ful consideration  given  to  the  work  of  others,  so  much  evidence  of  individual  laboratory 
experience  on  the  part  of  the  author  himself.  Mr.  Allen's  book  deserves  its  well  established 
place  as  one  of  the  standard  classics  of  the  working  chemical  library."— American  Chemical 
Journal. 


CHEMISTRY 
INORGANIC  AND  ORGANIC 

WITH  EXPERIMENTS 


BY 

CHAELES  LOUDON  BLOXAM 


NINTH    EDITION,    REWRITTEN   AND   REVISED 
BY 

JOHN  MILLAR  THOMSON,   LL.D.,   F.K.S, 

PROFESSOR  OF  CHEMISTRY,  KING'S  COLLEGE,  LONDON 
AND 

ARTHUR  G.   BLOXAM,   F.I.C. 

CONSULTING    CHEMIST  AND  CHARTEEED  PATENT  AGENT 


OF  THE 

UNIVERSITY 


PHILADELPHIA 
P.   BLAKISTON'S   SON  &  CO 

1012   WALNUT  STREET 
1907 


P  E  E  F  A  C  E. 


NOTWITHSTANDING  the  many  competitors  for  public  favour  that 
have  appeared  during  the  past  few  years,  the  continued  popularity 
of  Bloxam's  "  Chemistry  "  indicates  that  its  particular  qualities  are 
not  to  be  met  with  in  other  works.  Under  the  conviction  that  one 
of  the  chief  claims  of  the  book  for  attention  is  the  constant 
reference  to  experiment,  more  especially  in  the  earlier  part,  the 
Editors  have  retained  this  feature  in  the  Ninth  Edition. 

The  treatment  of  the  Inorganic  and  Organic  portions  of  the 
work  in  the  one  volume  becomes  increasingly  more  difficult,  but 
this  arrangement  is  undoubtedly  convenient  to  those  who  use  the 
book  for  the  purpose  of  reference,  and  the  temptation  to  divide 
the  volume  into  two  to  admit  of  the  fuller  treatment  of  the 
Organic  portion  has  been  resisted.  In  the  Editors'  opinion  the 
main  objection  to  the  condensed  character  of  this  part  of  the  book 
is  the  necessary  omission  of  many  structural  formulae  which  are 
useful  aids  to  students.  It  is  believed,  however,  that  sufficient 
explanation  is  given  to  enable  the  reader  to  construct  the  formulas 
for  himself  ;  and  the  attempt  to  do  so  will  prove  far  more  instruc- 
tive than  the  mere  inspection  of  a  printed  formula. 

A  change  has  been  made  in  the  present  edition  in  the  order 
of  treatment  of  the  non-metallic  elements,  the  place  of  Carbon 
having  been  changed  so  that  its  consideration  occurs  after  that 
of  the  three  other  typical  elements,  Hydrogen,  Oxygen,  and 
Nitrogen. 

Many  of  the  old  illustrations  which  had  become  obsolete  have 


Ti  PKEFACE. 

been  removed  from  the  work  and  several  new  illustrations,  some 
in  the  division  devoted  to  Organic  Chemistry,  have  been  intro- 
duced. 

The  plan  adopted  throughout  several  editions  of  making  no 
•division  in  the  Organic  portion  between  the  treatment  of  the  Fatty 
and  Aromatic  Compounds,  being  advantageous,  has  been  again 
followed. 

Due  allowance  being  made  for  the  time  occupied  in  printing  a 
book  of  this  size,  the  Editors  trust  that  their  revision  has  brought 
the  work  up  to  date  and  that  the  present  edition  will  be  as 
favourably  received  as  the  two  which  have  previously  left  their 
hands. 

KING'S  COLLEGE,  LONDON. 
August  1903. 


TABLE   OF   CONTENTS. 


INORGANIC  CHEMISTRY. 

INTRODUCTION. — NON-METALS.  PARAGRAPHS 

Water      .............  i-  10 

HYDROGEN n-  16 

OXYGEN 17-^30 

Water 31-  48 

Hydrogen  peroxide 49 

Ozone       .............  50 

Air 51-  52 

NITROGEN,  Argon,  Helium 53 

Ammonia  ............  54-  57 

Nitric  acid         . 58-  60 

Oxides  of  nitrogen.     Hydrazine.     Hydrogen  nitride         .         .         .  61-  66 

CARBON  .............  67-  70 

Carbon  dioxide          ..........  71-  77 

Carbon  monoxide      ..........  78-  85 

Acetylene 86-  87 

Ethylene 88 

Marsh-gas.     Flame 89-  92 

Fuel 93-94 

Types  of  Chemical  Compounds           .......  95 

CHLORINE        ..,.-.• 96-100 

Hydrochloric  acid loi-io^ 

Hypochlorous  acid     .......         .,        .         .  105-106 

Chloride  of  lime                                                     t         ,  107 

Chloric  a"cid       ,...«,,..„.  108-109 
Perchloric  acid          .         .         .         .         .         .         .         .         .         .no 

Chlorine  dioxide        .....                  ....  ni-H2 

Chlorides  of  carbon  ..........  113-114 

Chloride  of  nitrogen .         .         •  H5 

Aqua  regia.     Nitrosyl  chloride           .        „ 116 

BROMINE.     Hydrobromic  acid         ........  117-118 

ODINE.     Hydriodic  acid          .........  119-123 

FLUORINE.    Hydrofluoric  acid 124-126 


Tiii  TABLE  OF  CONTENTS. 

PARAGRAPHS 

Beriew  of  the  halogens 127 

SULPHUR 128-129 

Hydrogen  sulphides I3°-I3I 

Oxides  of  sulphur 132-133 

Sulphuric  acid I34-T35 

Thiosulphuric  acid I36 

Thionic  acids    . 137-140 

Carbon  disulphide     .         .         .         .         .         .         .         .         •         .141 

Chlorides  and  iodides  of  sulphur 142 

SELENIUM  AND  TELLURIUM 143-144 

KEVIEW  OF  THE  SULPHUR  GROUP 145 

BORON 146-147 

PHOSPHORUS 148-151 

Phosphoric  acids 152 

Phosphorous  and  hypophosphorous  acids 1 53-154 

Structure  of  acids 155 

Phosphides  of  hydrogen    .         .         .         .         .         .         .         .         .156 

Chlorides  and  sulphides  of  phosphorous    ......  157-158 

Amides 159 

ARSENIC 160 

Arsenious  and  arsenic  acids 161-162 

Hydrides  and  sulphides  of  arsenic 163-166 

KEVIEW  OF  NITROGEN  GROUP        .        .        .  .        .        .        .167 

SILICON 168-175 

Eeview  of  the  carbon  group      .         .         .         .         .         .         .         .176 

GENERAL  PRINCIPLES.     Atoms  and  Molecules.     Chemical  Affinity 

Molecular  Structure.     Spectrum  Analysis          .         .         .         -177 
METALS. 

Potassium         ...........  178-181 

Sodium 182-185 

Ammonium 186-190 

Lithium.     Kubidiurn.     Csesium 191-192 

Keview  of  alkali-metals 193 

Barium 194  3  S"° 

Strontium 195 

Calcium 196-198 

Glass         .............  199 

Review  of  alkaline  earth  metals         .......  200 

Magnesium 201 

Zinc .  202 

Cadmium ...  203 

Beryllium 204 

Aluminium 205-207 

Pottery,  Porcelain  and  Bricks 208 

Gallium 209 


TABLE  OF  CONTENTS.  ix 

METALS— (continued.)  PARAGRAPHS 

Indium 210 

Ee view  of  the  aluminium  metals        .         .         .         .         .         .         .211 

Scandium .         .         .         .212 

Yttrium 213 

Lanthanum       .         .         . .214 

Ytterbium 215 

Bare  earths 216-217 

Iron 218-229 

Cobalt 230 

Nickel 231 

Manganese 232-234 

Chromium          ...........  235 

Keview  of  iron  metals        .........  236 

Molybdenum 237 

Tungsten 238 

Uranium 239 

Bismuth    ............  240-242 

Antimony  ;  Vanadium  ;  Tantalum    .......  243-247 

Tin 248-253 

Titanium 254 

Zirconium  ;  Thorium 255 

Germanium  ;  Cerium         .........  256-257 

Lead 258-268 

Thallium 269 

Copper      ...         270-283 

Silver 284-287 

Mercury 288-295 

Platinum 296-298 

Palladium 299 

Khodium 300 

Osmium    ............  301 

Euthenium        ...........  302 

Iridium ' 303 

Eeview  of  platinoid  metals        ........  304 

Gold 305-307 

OEGANIC  CHEMISTEY. 

Ultimate  organic  analysis  ........  308 

Calculation  of  formulae      .........  309-312 

Classification  of  organic  compounds 313 

HYDROCARBONS. 

Paraffin  hydrocarbons       .........  314-316 

Olefine  hydrocarbons         .         .         .         .         .         .         .         .         •  3J7 

Acetylene  hydrocarbons  .         .         .         .         .         .         .         .318 

Benzene  hydrocarbons  and  their  constitution.     Position  isomerism  .  319-328 


x  TABLE  OF  CONTENTS. 

OKGANIC  CHEMISTKY— (continued.)  PARAGRAPHS 

Terpene  hydrocarbons  ;  Camphors  ;  Kesins       .....  329~333 
ALCOHOLS. 

Monohydric  alcohols  ;  Isomeric  alcohols 334-34^ 

Dihydric  alcohols  or  Glycols -347 

Polyhydric  alcohols  ;  Glycerols,  &c •  34^-349 

ALDEHYDES 35°~356 

ACIDS. 

Monobasic  ;  Acetic,  Acrylic,  Benzoic  series  ;  Stereo-isomerism         .  357~383 

Dibasic 3^4-396 

Polybasic                            :                 •  397-398 

KETONES 399-4°! 

ETHERS 402-409 

HALOGEN  DERIVATIVES.  Hydrocarbons  ;  Alcohols  ;  Aldehydes  ;  Acids  410-417 

ETHEREAL  SALTS 418-433 

Sulphonic  acids         . 434 

Nitre-compounds       ..........  435 

ORGANO-MINERAL  COMPOUNDS      .        .        .-                       .        .        .  436-445 
AMMONIA  DERIVATIVES. 

Amines  ;  Amides  ;  Amido-acids        .......  446-479 

Diazo-  and  Azo-compounds  ;  Hydrazines  ;  Azo-imides     .         .         .  480-485 

CYANOGEN  COMPOUNDS  .                486-505 

PHENOLS 506-518 

QUINONES.     Triphenylmethane  dyestuffs          .         .         .                  .         .  519-522 

CARBOHYDRATES 523-546 

GTLUCOSIDES.    Vegetable  colouring-matters 547-553 

ALBUMINOID  COMPOUNDS.     Animal  colouring-matters  ....  554-561 
HETERONUCLEAL  COMPOUNDS. 

Pyrrol ;  Pyridine ;  Quinoline 562-577 

Uric  acid  and  the  Alkaloids 578-591 

PHYSICAL  PROPERTIES  OP  ORGANIC  COMPOUNDS. 

Fusing-  and  Boiling-Points       .......         .  592-594 

Specific  Volumes 595 

Optical  Properties     ..........  596 

Absorption  Spectra 597 

APPLIED  OKGANIC  CHEMISTKY. 

DISTILLATION  OP  COAL 598 

DYEING  AND  CALICO-PRINTING 599 

TANNING 600 

OILS  AND  FATS 601 

SOAP  ;  CANDLES 602-  603 

STARCH  ;  MALTING 604-605 

BREWING  ;  WINE  AND  SPIRITS 606-607 

BREAD 608 

TEA,  COFFEE,  COCOA 609 


TABLE  OF  CONTENTS.  xi 

APPLIED  OKGANIC  CHEMISTKY— (continued.)  PARAGRAPHS 

ANIMAL  CHEMISTRY^ 

Milk,  blood,  flesh,  urine    .........      610-614 

CHEMISTKY  OF  VEGETATION. 

Soils,  manures  .         .         .         .         .         .         .         .         .         .         .615 

Kotation  of  crops 616 

Chemical  changes  in  plants 617-619 

NUTKITION  OF  ANIMALS 620-621 

CHANGES  AFTER  DEATH .    622 


INDEX .827 


ATOMIC  WEIGHTS.* 


Aluminium    . 

Al'" 

26.9 

Neon    . 

. 

19.9 

Antimony      . 

.    Sb'"orSbv 

II9-3 

Nickel  . 

.  Ni"orNi'" 

58.3 

Argon   . 

. 

39-6 

Niobium 

.      Nbv 

93-3 

Arsenic 

.   As"'orAsv 

744 

Nitrogen 

.  N"'  or  NV 

13-9 

Barium 

.       Ba" 

136.4 

Osmium 

.        Osviii 

189.6 

Beryllium     .. 

.        Be" 

9 

Oxygen 

.        0" 

15-9 

Bismuth 

.    Bi'"  or  Biv 

206.9 

Palladium     . 

.  Pd"orPdiv 

105.7 

Boron    . 

.       B'" 

10.9 

Phosphorus    . 

.    P'"orPv 

30.8 

Bromine 

.        Br' 

794 

Platinum 

.    Pt'  or  Ptiv 

J93-3 

Cadmium 

.       Cd" 

iii.6 

Potassium 

.       K' 

3^-9 

Caesium 

.       Cs' 

132 

Praseodymium 

. 

1394 

Calcium 

.       Ca" 

39-8 

Kadium 

. 

223.3 

Carbon  . 

.       Civ 

11.9 

Khodiurn 

.      Ro'" 

102.2 

Cerium  . 

.       Ce" 

139 

Kubidium 

.      Kb' 

84.8 

Chlorine 

Cl' 

35-2 

Kuthenium    . 

.      Ruiv 

IOO.9 

Chromium     . 

.    Cr'"  or  Crvi 

5i-7 

Samarium     . 

.      Sm 

148.9 

Cobalt  . 

.    Go"  or  Co'" 

58.5 

Scandium 

.      Sc 

43-8 

Copper  . 

.    Cu'  or  Cu" 

63-1 

Selenium 

.      Se" 

78.6 

Erbium 

.       E" 

164.8 

Silicon 

.      Siiv 

28.2 

Fluorine 

.      F' 

18.9 

Silver    . 

.         •  .   Ag' 

107.1 

Gadolinium  . 

. 

155 

Sodium 

.      Na' 

22.9 

Gallium 

.       Ga'" 

69.5 

Strontium 

.      Sr" 

87 

Germanium    . 

.    Ge"orGeiv 

71.9 

Sulphur 

.     S"  or  S* 

31-8 

Gold      . 

.      Au'" 

195-7 

Tantalum 

.      Taiv 

181.6 

Helium 

. 

4 

Tellurium 

.      Te" 

126.6 

Hydrogen 

.       H' 

i 

Terium 

. 

158-8 

Indium 

.      In'" 

113.1 

Thallium 

.      Tl' 

202.6 

Iodine   . 

.      I' 

125.9 

Thorium 

.      Th" 

230.8 

Iridium 

.       Iriv 

I9I-5 

Thulium 

. 

169.7 

Iron 

.  Fe"  or  Fe'" 

55-5 

Tin        . 

.  Sn"  or  Sniv 

II8.I 

Krypton 

81.2 

Titanium 

.      Ti*v 

47-7 

Lanthanum   . 

.      La" 

137-9 

Tungsten 

.      Wvi 

182.6 

Lead     . 

.      Pb" 

205.4 

Uranium 

.    U"  or  U'" 

236.7 

Lithium 

.      Li' 

7 

Vanadium     . 

.    V'orVv 

50.8 

Magnesium    . 

.      Mg" 

24.2 

Xenon  . 

. 

127 

Manganese    . 

.  Mn"  or  Mniv 

54-6 

Ytterbium     . 

. 

I7I.7 

Mercury 

.  Hg'  or  Hg" 

198.5 

Yttrium 

.      Y" 

88.3 

Molybdenum 

.       Mo* 

95-3 

Zinc       . 

.       Zn" 

64.9 

Neodymiuui 

. 

142.5 

Zirconium     . 

.       Zr^ 

89.9 

*  The  accent  or  index  affixed  to  each  symbol  expresses  the  number  of  atoms  of  hydrogen 
for  which  the  atomic  weight  of  the  element  is  usually  exchangeable  in  chemical  combinations. 
Tne  numbers  given  are  referred  to  the  standard  H  =  1. 


INTRODUCTION. 


THE  special  province  of  Chemistry  is  the  study  of  such  changes  in  the 
properties  of  matter  as  are  typified  by  the  rusting  of  iron. 

When  the  rust  is  examined  it  is  found  to  be  essentially  different 
from  the  iron,  which  may  be  said  to  have  changed  its  nature  in 
becoming  rust. 

The  melting  of  iron  when  it  is  very  strongly  heated  is  also  a  change 
in  the  nature  of  the  metal,  for  the  properties  of  a  liquid  are  palpably 
different  from  those  of  a  solid. 

The  two  changes  are,  however,  dissimilar  in  character ;  for  the  rust 
does  not  again  become  iron  when  left  to  itself,  whereas  the  liquid  iron 
again  becomes  solid  when  allowed  to  cool,  and  the  cold  mass  in  no  way 
differs  from  the  original  iron. 

Both  phenomena  are  accompanied  by  an  alteration  of  the  iron  from 
the  grey,  solid  form  in  which  it  generally  exists,  but  the  phenomenon 
of  rusting  produces  a  change  which  is  permanent,  whilst  that  of  lique- 
faction produces  a  change  which  is  only  temporary. 

A.  distinction  is  generally  drawn  between  these  two  kinds  of  change 
by  calling  the  permanent  kind  a  chemical  change,  and  the  temporary 
kind  a  physical  change. 

An  instrument  indispensable   for   the   study   of   chemistry   is    the 


Fig.  i. 

balance  (Fig.   i) — a  pair  of   scales  sufficiently  sensitive  to  show  small 
differences  of  weight. 


2  INTRODUCTION. 

If  a  portion  of  iron  be  weighed  before  and  after  it  has  rusted,  the 
iron,  together  with  its  coat  of  rust,  will  be  found  to  be  heavier  than  the 
original  iron. 

Since  matte);  in  a  chemical  sense,  is  anything  which  possesses  weight, 
the  quantity  of  matter  in  the  rust  is  greater  than  that  in  the  iron.  It 
must  not  be  supposed  that  any  matter  has  been  created  during  the  rust- 
ing. The  matter  which  has  now  become  attached  to  the  iron  has  been 
acquired  from  the  atmosphere,  where  it  previously  existed  in  the  in- 
visible, but  none  the  less  weighable,  form  of  matter,  the  gaseous  state. 

Another  common  example  of  a  chemical  change  is  furnished  by  heat- 
ing a  lump  of  marble  at  a  red  heat.  There  is  here  no  very  conspicuous 
alteration  in  the  appearance  of  the  marble,  although  the  structure  of 
the  piece  ia  seen  to  have  been  somewhat  modified.  It  can  easily  be 
shown,  however,  that  there  has  been  a  permanent;  change  wrought  in 
the  marble,  for  when  the  lump  has  cooled  it  is  found  to  become  hot 
again,  and  to  crumble  to  powder  when  water  is  poured  upon  it ;  neither 
of  these  manifestations  occurs  when  the  original  marble  is  wetted  with 
water. 

By  weighing  the  marble  before  and  after  it  has  been  heated,  a  loss  of 
weight  may  be  proved  to  have  occurred  during  this  chemical  change — 
a  quantity  of  matter  has  left  the  marble. 

Here,  however,  there  has  been  no  destruction  of  matter  ;  that  which 
has  left  the  marble  has  disappeared  because  it  has  been  converted  into 
the  invisible  or  gaseous  form,  and  has  spread  itself  through  the  sur- 
rounding atmosphere. 

By  allowing  iron  to  rust  in  a  tightly  corked  bottle  (containing  air), 
and  by  heating  marble  in  an  apparatus  designed  to  prevent  the  gas 
which  is  evolved  from  passing  into  the  surrounding  atmosphere,  it  can 
easily  be  demonstrated  that  neither  the  bottle  nor  the  apparatus  alters 
in  weight  during  the  rusting  or  heating. 

A  little  reflection  will  show  the  reason  for  this.  When  an  "  empty  " 
bottle  is  tightly  corked  there  is  enclosed  in  it  a  portion  of  the  atmos- 
phere, which  is  weighed  with  the  bottle  and  remains  unchanged  until 
the  cork  is  removed.  If  iron  is  also  in  the  bottle,  it  rusts  by  attaching 
to  itself  a  portion  of  the  atmosphere  present,  and  the  atmosphere  loses 
just  as  much  matter  as  the  iron  gains  during  the  process,  so  that  the 
total  amount  of  matter,  and  therefore  of  weight,  in  the  bottle  remains 
unaltered. 

So,  also,  when  the  apparatus  containing  the  marble  is  heated,  the  gas 
which  leaves  the  marble  is  restrained  from  disseminating  itself  through 
the  surrounding  atmosphere  and  from  no  longer  affecting  the  balance. 
When  kept,  as  it  were,  on  the  balance-pan  by  being  suitably  caught,  it 
is  weighed  with  the  rest  of  the  marble,  so  that  there  is  the  same  quan- 
tity of  matter  on  the  pan  as  there  was  before,  and  the  total  weight 
remains  unaltered. 

The  above  observations  are  concisely  expressed  in  the  definition  of 
the  principle  of  the  conservation  of  matter :— In  any  space  the  total 
quantity  of  matter  remains  the  same,  although  the  matter  may  move 
from  one  part  of  the  space  to  another  or  be  transformed  from  one  kind  of 
matter  into  another.  The  special  enclosure  of  the  iron  and  the  marble 
vyould  be  unnecessary  for  the  above  proof  of  the  principle,  were  it  pos- 
sible to  weigh  the  whole  room  in  which  the  experiments  are  performed. 


INTRODUCTION. 


The  two  chemical  changes  which  have  been  so  far  discussed  are  essen- 
tially different,  in  that  the  iron  has  had  another  kind  of  matter  (the 
oxygen  gas  of  the  atmosphere)  added  to  it,  whilst  the  marble  has  had 
another  kind  of  matter  (the  gas  carbon  dioxide)  separated  from  it. 

The  first  kind  of  change,  the  addition  of  two  or  more  kinds  of  matter 
to  each  other,  producing  a  third  kind,  is  known  as  chemical  combination. 
The  latter,  the  separation  of  one  kind  of  matter  into  two  or  more 
different  kinds,  is  known  as  chemical  decomposition. 

It  has  been  found  that  iron  can  undergo  only  the  first  kind  of 
chemical  change — it  can  only  be  converted  into  another  kind  of  matter 
by  chemical  combination ;  iron  cannot  be  decomposed.  Much  investi- 
gation has  shown  that  this  peculiarity  of  iron  is  shared  by  76  other 
kinds  of  matter,  so  that  all  substances  fall  into  two  classes,  namely  : 

Elements,  or  those  substances  which  cannot  be  decomposed. 

Compounds,  or  those  substances  which  can  be  decomposed. 

The  .substances  in  the  latter  class  are,  of  course,  much  more  numerous 
than  the  elements.  They  may  be  decomposed  into  other,  simpler 
compounds,  or  into  the  elements  of  which  they  consist. 

Thus,  the  first  products  of  the  decomposition  of  marble  are  lime  (the 
solid  referred  to  above  as  becoming  hot  when  water  is  poured  upon  it), 
and  carbon  dioxide  gas.  Each  of  these,  however,  is  itself  a  compound, 
and  can  be  further  decomposed  (not  easily  by  heat),  the  first  into 
calcium  and  oxygen,  the  second  into  carbon  and  oxygen.  These  three 
substances — calcium,  carbon,  and  oxygen — are  not  capable  of  decom- 
position, so  far  as  we  know. 

The  following  list  includes  the  various  kinds  of  matter  at  present 
believed  to  be  elements.  It  will  be  understood  that  the  category. is 
liable  to  both  extension  and  contraction;  for  the  discovery  of  new 
elements,  the  existence  of  which  has  been  unsuspected,  or  the  demon- 
stration that  what  has  heretofore  been  called  an  element  is  in  reality  a 
compound,  may  at  any  time  necessitate  an  alteration  of  the  list.  The 
reason  for  the  division  of  the  elements  into  non-metals  and  metals  will 
be  given  hereafter. 

The  Non-Metallic  Elements  are  (20). 


*0xygen. 
*Hydrogen. 
*Nitrogen. 

Sulphur. 
Selenium. 
Telluriura.f 

*Fluorine. 
•Chlorine. 

Bromine. 

*Argon. 
"Helium. 
*Krypton. 

Carbon. 

Iodine. 

*Neon. 

Phosphorus. 

*Xenon. 

Boron. 

Arsenic.f 

Silicon. 

*  Gases  at  the  ordinary  temperature. 

+  Arsenic  and  tellurium  are  frequently  classed  among  the  metals,  which  they  resemble  in 
some  of  their  properties. 


INTRODUCTION. 
The  Metals  are  (56). 


Caesium. 

Aluminium. 

Zinc. 

Copper. 

Mercury. 

Rubidium. 

Gallium. 

Nickel. 

Bismuth. 

Silver. 

Potassium. 

Germanium,  f 

Cobalt. 

Lead. 

Gold. 

Sodium. 

Zirconium. 

Iron. 

Thallium. 

Platinum. 

Lithium. 

Thorium. 

Manganese. 

Tin 

Palladium. 

Barium. 
Strontium. 
Calcium. 
Magnesium. 
Beryllium. 

*Yttrium. 
*Erbium. 
*Samarium. 
Scandium. 
Cerium. 
Lanthanum. 
Neodymium. 

Chromium. 
Cadmium. 
Uranium. 
Indium. 

-i  in. 
Titanium. 
Tantalum. 
Molybdenum. 
Tungsten. 
Vanadium. 
Antimony,  f 

Rhodium. 
Ruthenium. 
Osmium. 
Iridium. 

Praseodymium. 

Niobium. 

*  Terbium. 

*  Ytterbium. 

Thulium. 

Many  of  these  elements  are  so  rarely  met  with,  that  they  have  not 
received  any  useful  application,  and  are  interesting  only  to  the  pro- 
fessional chemist.  This  is  the  case  with  the  elements  in  the  last 
column  of  the  Table,  p.  3,  among  the  non-metallic  elements,  and  with 
a  large  number  of  the  metals. 

The  following  list  includes  those  elements  with  which  it  is  important 
that  the  general  student  should  become  familiar,  together  with  the 
symbolic  letters  by  which  it  is  customary  to  represent  them,  for  the 
sake  of  brevity,  in  chemical  writings  : — 

Non-Metallic,  Elements  of  practical  importance  (13). 


Oxygen, 

0 

Sulphur, 

S 

Fluorine, 

F 

Hydrogen, 

H 

Chlorine, 

Cl 

Nitrogen, 

N 

Phosphorus, 

P 

Bromine, 

Br 

Carbon, 

C 

Arsenic, 

As 

Iodine, 

I 

Boron, 

B 

Silicon, 

Si 

Metallic  Elements  of  pi'actical  importance  (28). 


Potassium,        K    (JKaliwn) 

Cadmium. 

Cd 

Sodium,             Na  (Natrium) 

Uranium, 

U 

Barium,             Ba 
Strontium,         Sr 

Copper, 
Bismuth, 

Cu  (Cuprum) 
Bi 

Calcium,           Ca 
Magnesium,       Mg 

Lead, 

Pb  (Plumbum) 

Aluminium,       Al 

Tin, 
Titanium, 

Sn  (Stannum) 
Ti 

Zinc,                   Zn 

Tungsten, 
Thorium, 

W  (  Wolframium) 
Th 

Nickel,              Ni 

Cerium, 

Ce 

Cobalt,              Co 
Iron,                  Fe  (Ferrum) 

Antimony, 

Sb  (Stibium) 

Manganese,      Mn 
Chromium,       Cr 

Mercury, 
Silver, 

Hg  (Hydrargyrum) 
Ag  (Argentum) 

Gold, 

Au  (Aurum) 

Platinum, 

Pt 

*  -mere  is  some  doubt  as  to  the  elementary  nature  of  these  substances 
f  Sometimes  classed  among  the  non-metals. 

INTRODUCTION.  5 

Although  the  41  elements  here  enumerated  are  of  practical  import- 
ance, many  of  them  derive  their  importance  solely  from  their  having 
met  with  useful  applications  in  the  arts.  The  number  of  elements 
known  to  play  an  important  part  in  the  chemical  changes  concerned  in 
the  maintenance  of  animal  and  vegetable  life  is  very  limited. 

Elements  concerned  in  the  Chemical  Changes  occurring  in  Life. 


Non-Metallic. 

Metallic. 

Oxygen. 

Sulphur 

Potassium. 

Aluminium. 

Hydrogen. 

Sodium. 

Nitrogen. 
Carbon. 

Silicon. 

Chlorine. 
Iodine. 

Calcium. 
Magnesium. 

Manganese. 

These  elements  will,  of  course,  possess  the  greatest  importance  for 
those  who  study  Chemistry  as  a  branch  of  general  education,  since  a 
knowledge  of  their  properties  is  essential  for  the  explanation  of  the 
simple  chemical  changes  which  are  daily  witnessed. 

The  student  who  takes  an  interest  in  the  useful  arts  will  also 
acquaint  himself  with  the  remainder  of  the  41  elements  of  practical 
importance,  whilst  the  mineralogist  and  professional  chemist  must 
extend  his  studies  to  every  known  element. 

By  far  the  greater  proportion  of  the  various  materials  supplied  to  us 
by  animals  and  vegetables  consists  of  the  four  elements — oxygen, 
hydrogen,  nitrogen,  and  carbon ;  and  if  we  add  to  these  the  two  most 
abundant  elements  in  the  mineral  world,  silicon  and  aluminium,  we 
have  the  six  elements  composing  the  bulk  of  all  matter. 

It  is  computed  that  of  the  mineral  matter  of  the  earth's  crust  oxygen 
constitutes  50  per  cent.,  silicon  2 5. 3,  aluminium  7. 3,  iron  5,  calcium  3.5, 
magnesium  2.5,  sodium  2.3,  potassium  2.2,  and  hydrogen  i.  No  other 
element  is  present  to  a  greater  extent  than  0.3  per  cent. 

The  formation  of  a  chemical  compound  consists  in  the  combination 
of  two  or  more  elements,  brought  about  by  the  inherent  attraction  of 
the  elements  for  each  other.  This  attraction  varies  between  different 
elements.  Whilst  some  combine  with  each  other  immediately  they  are 
brought  in  contact,  others  show  no  such  tendency.  In  the  sequel,  the 
nature  of  chemical  attraction  will  receive  attention.  It  must  here  be 
stated  that  the  phenomenon  of  combination  has  long  been  attributed 
to  a  force  termed  chemical  affinity :  thus  the  rusting  of  iron  is  said  to 
consist  in  the  formation  of  a  compound  of  iron  with  oxygen,  determined 
by  the  chemical  affinity  of  these  elements  for  each  other.* 

A  characteristic  of  a  chemical  compound  is  homogeneity  of  struc- 
ture. Pure  compounds  seldom  exist  in  nature.  The  rock  called  granite, 
for  example,  is  not  a  single  chemical  compound,  but  a  mixture  of 
chemical  compounds,  as,  indeed,  is  rendered  apparent  by  a  merely 
superficial  examination,  when  it  is  seen  that  there  are  three  distinctly 
different  substances  in  the  granite.  This  at  once  stigmatises  the  rock 

*  For  the  sake  of  simplicity,  no  reference  has  been  made  to  the  necessity  for  the  presence 
of  other  substances  besides  oxygen  and  iron  for  the  formation  of  rust.  It  will  be  familiar  to 
most  readers  that  water  is  one  of  these  essentials. 


6  INTRODUCTION. 

as  a  mixture,  for  it  is  never  possible  to  see  the  elements  in  a  compound. 
When  the  granite  is  powdered,  a  microscope  is  requisite  to  make  its 
heterogeneous  character  visible,  but  by  taking  advantage  of  some  essen- 
tial difference  between  the  properties  of  the  three  constituent  sub- 
stances—as,  for  instance,  the  different  rates  at  which  they  sink  in  water 
— a  separation,  more  or  less  perfect,  may  be  effected. 

No  such  differentiation  of  the  parts  of  a  lump  of  sugar  can  be  detected. 
This  is  a  pure  compound,  and  is  homogeneous,  so  that  when  it  is 
powdered,  every  granule  of  it  possesses  the  same  properties  as  those 
of  the  whole  mass — each  will  dissolve  in  water,  will  taste  sweet,  &c. 

Thus,  a  mixture  of  elements  or  compounds  is  readily  distinguished 
from  a  pure  compound  by  the  fact  that  each  constituent  of  the  mixture 
retains  its  individual  properties,  whereas  in  a  pure  compound  the 
properties  of  its  constituents  (elements)  are  entirely  obliterated. 

Most  natural  substances  consist  of  mixtures  of  compounds.  .  The 
classification  of  the  science  of  chemistry  into  organic  chemistry,  dealing 
with  animal  and  vegetable  substances,  and  inorganic  chemistry,  dealing 
with  mineral  substances,  is  based  on  the  supposition,  formerly  held, 
that  compounds  produced  through  the  operation  of  animal  and  vegetable 
life  (such  as  sugar,  starch,  &c.)  are  essentially  different  from  those 
which  are,  or  have  been,  formed  without  the  intervention  of  life. 
This  classification  is  still  adopted  as  convenient  for  the  purposes  of  study. 

It  is  the  object  of  the  chemist  both  to  determine  the  constituents  of 
every  substance — a  process  termed  analysis — and  to  build  up  every 
substance  from  its  constituents — a  process  termed  synthesis. 

When  these  processes  are  directed  merely  to  the  determination  of 
the  nature  or  quality  of  the  constituents,  they  are  said  to  be  qualitative, 
while  when  they  take  cognisance  of  the  proportion  which  the  con- 
stituents bear  to  each  other,  they  are  quantitative — gravimetric  if  the 
proportion  by  weight  is  considered,  volumetric  if  the  proportion  is  by 
volume. 

In  the  early  history  of  Chemistry,  investigations  were  purely  quali- 
tative, and  had  they  remained  so  the  whole  of  chemical  knowledge 
might  be  told  in  a  dozen  pages  of  this  book.  It  was  the  use  of  the 
balance  that  revealed  the  very  essence  of  the  science— the  fact  that 
every  compound  is  of  constant  quantitative  composition. 

Marble,  chalk,  and  coral  were  early  recognised  by  qualitative  analysis 
to  consist  of  the  same  compound  mixed  with  small  amounts  of  other 
substances.  Afterwards,  quantitative  analysis  showed  that  in  each 
case  the  compound  in  question  contains,  by  weight,  56  per  cent,  of  lime 
and  44  per  cent,  of  carbon  dioxide. 

Moreover,  the  same  compound,  now  called  calcium  carbonate,  was 
soon  synthesised  by  bringing  together  lime  and  carbon  dioxide  made 
from  other  sources  than  any  of  the  three  minerals  named ;  it  was  found 
that,  whatever  proportions  of  lime  and  carbon  dioxide  were  used,  the 
compound  produced  always  contained  no  more  and  no  less  than  56  per 
cent,  of  the  one  and  44  per  cent,  of  the  other. 

Thus,  if  28  parts  of  lime  were  brought  into  contact  with  72  parts  of 
carbon  dioxide,  not  100  but  50  parts  of  calcium  carbonate  were  formed ; 
the  28  parts  of  lime  combined  with  only  22  parts  of  carbon  dioxide 
(the  same  ratio  as  56  : 44)  and  50  of  carbon  dioxide  were  left  over 
uncombined. 


INTRODUCTION.  7 

It  is  sufficiently  remarkable  that  calcium  carbonate  from  marble 
formed  ages  ago  by  solidification  of  a  fused  mass  under  great  pressure, 
from  chalk  deposited  during  ages  as  mud  from  suspension  in  water, 
from  coral  built  up  by  marine  animals  in  our  own  day,  and  from 
material  made  in  a  few  minutes  in  a  laboratory,  should  have  the  same 
quantitative  composition. 

When  a  number  of  facts  of  this  kind  had  been  accumulated  it  became 
possible  to  assert  that  constancy  of  quantitative  composition  is  the 
criterion  by  which  a  compound  may  be  known.  Any  form  of  matter 
showing  variation  of  composition  cannot  be  a  single  compound. 

For  instance,  a  mass  of  chalk  which  has  been  wetted  with  water 
contains  a  considerable  proportion  of  the  latter,  but  one  which  varies 
with  the  source  of  the  chalk ;  hence  there  is  here  no  compound  of  chalk 
with  water.  On  the  other  hand,  lime  from  any  source  absorbs  always 
32  per  cent,  of  its  weight  of  water — the  product  is  a  compound. 

Lime  and  carbon  dioxide  which  have  been  spoken  of  as  the  con- 
stituents of  calcium  carbonate  are  only  the  proximate,  not  the  ultimate 
constituents  thereof.  For  each  is  capable  of  decomposition,  though  not 
easily  by  heat,  into  elements,  the  lime  into  calcium  and  oxygen  and 
the  carbon  dioxide  into  carbon  and  oxygen.  What  is  true  of  the 
combination  of  lime  with  carbon  dioxide  is  true  of  that  of  calcium  or 
carbon  with  oxygen;  wherever  or  however  these  compounds  are  ob- 
tained, they  contain  their  constituent  elements  always  in  the  same 
proportion. 

A  collection  of  observed  facts  in  agreement  with  each  other  enables 
the  investigator  to  formulate  a  law  of  Nature  which  remains  valid  so 
long  as  newly  discovered  facts  do  not  contradict  it.  In  this  case  the 
law,  which  may  be  regarded  as  the  sheet-anchor  of  Chemical  science,  is 
known  as — 

The  Law  of  Constant  Proportions. — Every  compound  contains  its 
constituent  elements  always  in  the  same  proportion,  from  whatever 
source  the  compound  may  be  obtained. 

An  attempt  to  explain  this  and  other  similar  laws  which  the  student 
will  learn  presently,  led  Dalton,  a  century  ago,  to  the  hypothesis  as  to 
the  structure  of  matter,  called  the  atomic  theory.  The  facts  and  argu- 
ments which  justify  this  hypothesis  will  be  referred  to  hereafter.  It  is, 
however,  essential  that  the  student  should  attempt  to  grasp  the  funda- 
mental conception  on  which  the  theory  is  based  before  embarking  on  a 
study  of  the  relationships  between  the  elements. 

The  fundamental  conception  is  this : — When  matter  is  submitted  to 
a  process  of  subdivision,  a  certain  fineness  will  ultimately  be  attained 
beyond  which  disintegration  will  be  impossible ;  in  other  words,  any 
given  mass  of  matter  consists  of  a  number  of  particles,  each  of  which  cannot 
'be  divided.  Thus,  when  a  piece  of  marble  has  been  ground  to  powder, 
the  single  particle  has  become  a  large  number  of  particles.  Now,  by 
the  hypothesis  stated  above,  could  the  process  of  grinding  be  perfected, 
a  stage  would  be  reached  when  it  would  be  impossible  to  further  in- 
crease the  number  of  these  particles,  for  each  would  be  indivisible. 
The  ultimate  particle  of  marble  would  then  have  been  attained.  These 
ultimate  particles  of  matter  are  called  molecules. 

But  it  has  been  already  stated  that  when  marble  is  heated,  it  is 
decomposed  into  lime  and  carbon  dioxide,  so  that  it  is  possible  to  sub- 


INTRODUCTION. 

divide  marble  by  a  process  other  than  mechanical  grinding;  but  the 
product  is  no  longer  marble.  What  is  true  of  the  lump  of  marble 
should  be  true  also  of  its  mechanically  indivisible  particle,  or  molecule. 
The  molecules  of  marble  can  still  be  divided  by  decomposing  them. 

It  is  highly  probable  that  the  molecules  of  marble,  were  they 
separated,  would  be  found  to  be  invisible.  The  smallest  visible  particle 
of  marble  is  probably  an  aggregate  of  many  molecules.  It  is  not 
possible  to  render  marble  invisible,  because  we  have  no  means  for 
moving  the  molecules  which  make  up  these  aggregates  appreciably 
further  from  each  other.  This  is  because  the  method  usually  adopted 
for  the  purpose  of  separating  molecules  from  each  other — namely,  the 
application  of  heat — decomposes  the  molecules  of  marble. 

There  are  many  substances,  however,  the  molecules  of  which  are  not 
decomposed  by  a  moderately  intense  heat,  and  are  moved  so  far  apart 
from  each  other  by  the  application  of  this  agency,  that  the  whole  mass 
becomes  invisible.  Water  is  a  familiar  example,  steam  being  invisible 
until  it  is  so  far  chilled  that  the  separated  molecules  have  come 
together  again  to  form  visible  particles.  Gases  which  remain  such  at 
the  ordinary  temperature  require  to  be  very  much  chilled  in  order  to 
bring  their  molecules  sufficiently  close  to  each  other  to  form  visible 
particles — in  other  words,  to  convert  the  gas  into  a  liquid. 

There  are  several  methods  for  subdividing  a  substance  without 
decomposing  it,  of  which  two  (mechanical  grinding  and  the  application 
of  a  moderate  heat)  have  been  quoted.  Such  methods  may  be  called 
physical  methods  of  subdivision,  inasmuch  as  they  do  not  produce  a 
chemical  change. 

A  MOLECULE  may  now  be  denned  as  the  ultimate  particle  of  a  com- 
pound or  element,  divisible  only  by  chemical  change. 

Inasmuch  as  an  element  cannot  be  decomposed,  its  molecules  must 
be  incapable  of  any  further  division  such  as  that  possible  for  the 
molecule  of  a  compound  like  marble.  This  is  true  when  the  molecules 
of  the  element  exist  by  themselves ;  there  is  no  evidence  to  show  that 
the  molecules  of  oxygen,  for  instance,  can  be  divided  so  long  as  the 
oxygen  exists  by  itself  in  an  uncombined  condition. 

There  is  excellent  evidence,  however,  that  the  molecules  of  many 
compounds  contain  half  the  quantity  of  oxygen  that  the  molecule  of 
this  element  contains.  It  must  be  admitted,  therefore,  that  the  oxygen 
molecule  consists  of  two  parts,  which  can  only  be  separated  from  each 
other  when  the  molecule  enters  into  combination.  The  same  argument 
applies  to  other  elements,  the  molecules  of  the  majority  of  which 
consist  of  parts,  although  several  have  no  parts. 

These  parts  of  elementary  molecules  are  indivisible  either  by  physical 
or  chemical  methods  ;  they  are  therefore  the  true  indivisibles  or  atoms. 

An  ATOM  may  be  denned  as  the  smallest  particle  of  an  element 
existing  in  a  molecule,  indivisible  by  any  means. 

A  consideration  of  the  above  definition,  together  with  that  given  for 
a  compound,  will  show  that  to  speak  of  the  atom  of  a  compound  would 
be  a  contradiction  of  terms. 

What  has  been  said  above  as  to  the  fundamental  conception  of  the 
atomic  theory  may  be  thus  summarised.  Matter  is  not  capable  of  in- 
finite subdivision,  but  consists  of  particles  which  are  indivisible  and  are 
called  atoms  ;  these  have  no  separate  existence,  but  occur  in  combination 


INTRODUCTION  9 

with  each  other  to  form  molecules,  which  are  the  smallest  particles 
capable  of  separate  existence.  When  the  atoms  thus  united  are  of  the 
same  kind,  the  molecule  is  that  of  an  element ;  when  they  are  of  dif- 
ferent kinds  the  molecule  is  that  of  a  compound.  When  compound 
molecules  are  decomposed  the  atoms  of  the  constituent  elements  are 
momentarily  liberated,  but  immediately  recombine  to  form  new  mole- 
cules. Each  atom  of  the  same  element  has  the  same  weight ;  but  the 
atoms  of  different  elements  have  different  weights. 

How  Dalton  applied  this  conception  to  explain  the  laws  of  chemical 
combination  is  fully  set  forth  in  the  chapter  on  General  Principles. 

It  is  agreed  among  chemists  that  the  symbol  for  an  element  shall 
represent  one  atom,  and  a  certain  number  of  parts  by  weight,  of  the 
element.  This  figure  is  termed  the  atomic  weight  of  the  element,  and 
is  believed  to  be  the  number  of  times  that  an  atom  of  the  element  is 
heavier  than  an  atom  of  the  gaseous  element  hydrogen,  which  is  said  to 
weigh  i.  It  is  an  abstract  number,  and  may  represent  any  units  of 
weight.  Thus,  the  symbol  O  means  one  atom  of  oxygen  and  16  unit 
weights  of  oxygen — it  may  be  16  grains,  16  Ibs.,  16  grams,  &c. 

Since  the  atomic  theory  does  not  admit  the  existence  of  the  atom  of 
a  compound,  a  compound  cannot  have  an  atomic  weight. 

The  molecular  weight  of  either  an  element  or  a  compound  is  the 
number  of  times  that  the  molecule  is  heavier  than  that  of  hydrogen, 
the  molecule  of  which  is  said  to  weigh  2. 

The  molecular  weight  of  a  substance  is  ascertained  by  doubling  the 
number  of  times  that  a  volume  of  the  substance  in  the  form  of  vapour 
or  gas  is  heavier  than  an  equal  volume  of  hydrogen,  weighed  at  the 
same  temperature  arid  pressure.*  This  value  is  known  as  the  vapour 
density^  of  the  gas,  and  is  determined  by  weighing  a  stoppered  globe 
(such  as  that  shown  in  fig.  50)  of  known  weight,  first  when  it  is  full 
of  hydrogen,  and  then  when  it  is  full  of  the  vapour  or  gas  whose  vapour 
density  is  to  be  determined  ;  obviously,  the  vapour  density  will  be  the 
quotient, 

weight  of  (globe  +  gas)  -  weight  of  globe 
weight  of  (globe  +  hydrogen)  —  weight  of  globe. 

Hence  the  MOLECULAR  WEIGHT  of  an  element  or  compound  is  twice 
the  number  of  times  that  a  volume  of  it  in  the  state  of  gas  is  heavier 
than  an  equal  volume  of  hydrogen  weighed  at  the  same  temperature 
and  pressure. 

As  the  molecule  of  an  element  contains  only  atoms  of  the  same  kind, 
each  having  the  same  atomic  weight,  the  molecular  weight  of  the 
element  must  be  a  multiple  of  the  atomic  weight  by  i,  2,  3,  &c.,  accord- 
ingly as  the  molecule  contains  i,  2,  3,  &c.,  atoms. 

Now  the  molecule  of  a  compound  can  never  contain  less  than  one 
atom  of  any  of  its  constituent  elements  because  an  atom  cannot  be 
divided.  Hence  the  molecular  weight  of  a  compound  can  never  contain 

*  It  will  be  remembered  that  gases  expand  in  volume  when  heated  or  when  submitted  to  a 
reduced  pressure ;  hence  a  given  volume  of  gas  never  has  the  same  weight  unless  its  tem- 
perature and  pressure  are  the  same  each  time  it  is  weighed  (except  in  the  rare  event  of  a 
diminished  temperature  compensating  for  a  diminished  pressure). 

f  This  term  is  used  because  the  majority  of  substances  must,  like  water,  be  vaporised  by 
heat  before  they  are  in  the  gaseous  state. 


10  INTRODUCTION. 

less  than  one  atomic  weight  of  each  of  the  constituent  elements,  though 
it  may  contain  more, 

It  is  possible,  therefore,  to  define  the  ATOMIC  WEIGHT  of  an  element 
as  the  smallest  weight  of  it  found  in  one  molecular  weight  of  any  of  its 
compounds. 

For  example,  by  the  method  described  above  carbon  dioxide  is  found 
to  have  the  vapour  density  22,  consequently  its  molecular  weight  is  44. 
Now  analysis  shows  that  44  parts  by  weight  of  carbon  dioxide  contain 
1 2  parts  by  weight  of  carbon,  and  as  this  is  the  smallest  weight  of  this 
element  that  occurs  in  one  molecular  weight  of  any  of  its  compounds, 
it  is  the  atomic  weight. 

When  the  molecule  of  an  element  contains  only  one  atom  the  symbol 
for  the  element  represents  both  the  atom  and  the  molecule  ;  thus  Hg 
means  both  a  molecule  and  an  atom  of  mercury  because  the  molecules 
of  this  element  are  monatomic.  On  the  other  hand,  the  molecules  of 
hydrogen  and  oxygen  are  H2  and  02  respectively,  these  elements  having 
diatomic  molecules.  Phosphorus  is  an  element  having  tetratomic  mole- 
cules, expressed  by  the  symbol  P4.  Such  molecular  symbols  represent 
twice  or  four  times  the  atomic  weight ;  thus  02=i6x2  =  32  parts  by 
weight.  P4  =  3i  X4=i24  parts  by  weight. 

It  follows  from  what  was  said  above  as  to  the  method  of  ascertaining 
the  molecular  weight,  that  if  the  volume  of  one  unit  weight  of  hydrogen 
be  called  unit  volume,  the  molecular  weight  of  any  gas,  expressed  in  the 
same  units,  must  be  called  two  volumes.  For  example,  if  the  volume 
occupied  by  one  gram  of  hydrogen  be  called  one  volume,  32  grams  of 
oxygen  will  occupy  two  volumes.  The  symbol  for  any  molecule,  there- 
fore, represents  two  volumes  of  the  substance  in  the  state  of  gas. 

The  symbol  for  a  compound  is  called  a  formula,  and  represents  the 
molecule  of  the  compound,  which  consists  of  atoms  of  its  constituent 
elements  united  together,  so  that  the  formula  is  the  symbols  for  these 
atoms  written  side  by  side ;  thus,  HC1  represents  a  molecule  of  a  com- 
pound of  hydrogen  with  chlorine ;  HCN,  the  molecule  of  a  compound 
of  hydrogen,  carbon,  and  nitrogen  ;  and  each  represents  two  volumes  of 
the  compound  in  the  state  of  gas.  When  analysis  shows  that  there  are 
2,  3.  or  4  atomic  weights,  and  therefore  atoms,  of  the  same  element 
present  in  one  molecule  of  the  compound,  this  is  expressed  by  writing 
2,  3,  or  4  after  the  symbol  for  the  element.  Thus,  H2S04  represents  a 
compound  whose  molecule  contains  two  atomic  weights  or  atoms  of 
hydrogen,  one  atomic  weight  or  atom  of  sulphur,  and  four  atomic 
weights  or  atoms  of  oxygen. 

Thus  the  number  of  parts  by  weight  expressed  by  the  formula  for  a 
compound  is  the  sum  of  the  atomic  weights  of  the  elements  present ; 
HC1  means  1  +  35.5  =  36.5  parts  by  weight  of  hydrogen  chloride; 
HCN  means  1  +  12  +  14  =  27  parts  by  weight  of  hydrogen  cyanide; 
H2S04  means  (i  x  2)4-32  f  (16x4)  =  98  parts  by  weight  of  sulphuric 
acid. 

The  mere  contact  or  mixture  of  substances  is  expressed  by  the  sign 
+  ;  thus  H,  +  C12  implies  that  a  molecule  of  hydrogen  has  been  brought 
into  contact  with  a  molecule  of  chlorine. 

From  the  point  of  view  of  the  atomic  theory,  chemical  combination  is 
regarded  as  consisting  in  the  exchange  of  atoms  in  one  molecule  for 
those  in  another,  when  the  molecules  are  brought  in  contact. 


INTRODUCTION.  1 1 

For  example,  chemical  combination  occurs  between  hydrogen  and 
chlorine,  to  form  hydrochloric  acid,  the  change  being  represented  by 
the  chemical  equation  H2  +  C12=  2HC1,  which  implies  that  the  molecules 
of  hydrogen  and  chlorine  exchange  atoms. 

It  will  be  seen  from  the  statements  made  above,  that  this  equation 
also  implies  that  2  parts  by  weight  or  2  vols.  of  hydrogen  and  35.5  x  2 
parts  by  weight  or  2  vols.  of  chlorine,  yield  36.5  x  2  parts  by  weight 
or  4  vols.  of  hydrochloric  acid. 

It  must  be  remembered  that  a  chemical  equation  is  only  a  short 
mode  of  expressing  the  result  of  an  experiment,  and  cannot  be  used,  like 
a  mathematical  equation,  to  effect  the  solution  of  a  problem. 

A  chemical  equation  may  be  written  to  express  what  is  likely  to  be 
the  result  of  the  action  of  different  molecules  upon  each  other,  but  it 
has  no  value  until  verified  by  experiment. 

Chemical  decomposition  is  the  separation  of  the  atoms  composing  a 
molecule,  which  must  precede  the  formation  of  a  new  molecule.  Thus, 
the  decomposition  of  steam  by  a  very  high  temperature  is  expressed  by 
the  equation  2H20  =  2H2  +  02,  which  conveys  the  information  that  two 
molecules  or  36  parts  by  weight  or  4  vols.  of  steam  have  suffered 
chemical  decomposition,  and  have  formed  two  molecules  or  4  vols.,  or 
4  parts  by  weight  of  hydrogen,  and  one  molecule  or  2  vols.,  or  32  parts 
by  weight  of  oxygen. 

Chemical  changes  are  always  attended  by  evolution  or  absorption  of 
heat.  As  a  general  rule,  the  formation  of  compound  molecules  from 
elementary  molecules  evolves  heat,  whilst  the  formation  of  elementary 
molecules  from  compound  molecules  absorbs  heat.  Hence  it  will  be 
found  that  the  application  of  heat  is  generally  required  for  the  com- 
mencement of  chemical  change,  in  order  to  effect  that  separation  of 
atoms  from  their  molecules  which  must  precede  every  chemical  trans- 
formation of  matter.  When  any  chemical  change  appears  to  occur 
without  any  change  of  temperature  being  observed,  it  is  because  the 
total  heat  absorbed  in  the  destruction  of  the  original  molecules  is  equal 
to  the  total  heat  evolved  in  the  construction  of  the  new  molecules. 

The  formation  of  water  by  the  chemical  combination  of  hydrogen 
and  oxygen  consists  in  the  separation  of  the  atoms  which  compose  the 
oxygen  molecule,  and  of  those  composing  two  hydrogen  molecules,  an 
atom  of  hydrogen  from  each  hydrogen  molecule  uniting  with  an  atom 
of  oxygen  from  the  oxygen  molecule,  as  expressed  in  the  equation, 
00  +  HH+TLH=IttIO  +  IfHO.  Here,  it  is  evident  that  the  conver- 
sion of  a  molecule  of  oxygen  into  water  is  effected  by  the  exchange  of 
each  of  its  oxygen  atoms  for  two  hydrogen  atoms. 

Since  hydrogen  is  taken  as  the  chemical  standard  or  unit,  and  one 
atom  of  oxygen  is  exchangeable  for,  or  combines  with,  two  atoms  of 
hydrogen,  oxygen  is  said  to  be  divalent  or  diad,  often  expressed  by 
writing  it  thus,  0".  The  atoms  of  some  elements  are  exchangeable  for, 
or  combine  with,  three  atoms  of  hydrogen,  and  are  said  to  be  trivalent 
or  triad"' ;  others  for  four,  quadrivalent  or  tetrad™,  or  for  five,  quinqui- 
valent or  pentad* ,  and  so  on. 

A  convenient  classification,  according  to  valency,  is  thus  arrived  at, 
which  is  liable,  however,  to  a  great  number  of  exceptions. 


12  INTRODUCTION. 

Monads— Br,  01,  F,  I,  K,  Ag,  Na. 

Diads— Ba,  Cd,  Ca,  Co,  Cu,  Fe,  Pb,  Mg,  Mn,  Hg,  Ni,  0,  Sr,  S,  Zn. 

Triads— Al,  Sb,  As,  Bi,  B,  Or,  Au,  N,  P. 

Tetrads— C,  Pt,  Si,  Sn. 

In  studying  the  properties  of  bodies,  a  distinction  must  be  drawn 
between  physical  and  chemical  properties.  The  physical  properties  are 
those  in  which  either  the  mass  or  the  molecules  are  alone  concerned, 
whilst  the  chemical  properties  concern  the  atoms.  Thus,  the  condition 
whether  solid,  liquid,  or  gas,  the  colour,  odour,  taste,  hardness,  relative 
weight  (or  specific  gravity),  would  come  under  the  head  of  physical  pro- 
perties. For  a  solid,  the  geometrical  form  of  its  crystal  and  the  tem- 
perature at  which  it  melts  are  important  for  identification ;  and  for  a 
liquid,  the  temperature  at  which  it  boils. 

Chemists  use  the  metric  system  of  weights  and  measures.  It  will  be 
remembered  that  the  unit  of  weight  in  this  system  is  one  gram,  and 
that  the  unit  of  capacity  is  that  volume  which  one  gram  of  water  occu- 
pies at  4°  C.  (at  which  temperature  a  given  weight  of  water  has  a 
smaller  volume  than  at  any  other  temperature)  ;  this  unit  of  volume  is 
called  a  cubic  centimetre.  One  thousand  cubic  centimetres  make  i  litre. 
One  gram  is  equivalent  to  15.43  grains,  and  one  litre  is  equivalent  to 
1.76  pint.  One  metre  or  100  centimetres  or  1000  millimetres  =  39. 37 
inches. 


INORGANIC    CHEMISTRY. 


CHEMISTRY  OF  THE  NON-METALLIC  ELEMENTS 
AND  THEIR  COMPOUNDS. 


THE   ELEMENTS   OF  WATER. 

i.  Until  the  latter  half  of  the  eighteenth  century,  water  was  regarded 
as  an  elementary  form  of  matter.  It  was  first  resolved  into  its  con- 
stituent elements,  hydrogen  and  oxygen,  by  subjecting  it  to  the  in- 
fluence of  the  voltaic  current,  which  decomposes  or  analyses  the  water 
by  overcoming  the  chemical  attraction  by  which  its  elements  are  held 
together. 

An  arrangement  for  this  purpose  is  represented  in  Fig.  2. 


Fig-.  2. — Electrolysis  of  water. 

The  glass  vessel  A  contains  water,  to  which  a  little  sulphuric  acid  has  been  added 
to  increase  its  power  of  conducting  electricity,  for  pure  water  conducts  so  imper- 
fectly that  it  is  decomposed  with  great  difficulty.  B  and  C  are  platinum  plates 
bent  into  a  cylindrical  form,  and  attached  to  the  stout  platinum  wires,  which  are 
passed  through  corks  in  the  lateral  necks  of  the  vessel  A,  and  are  connected  by 
binding  screws  with  the  copper  wires  D  and  E,  which  proceed  from  the  galvanic 
battery  G.  H  and  0  are  glass  tubes  with  brass  (or  glass)  caps  and  stop-cocks,  and 
are  enlarged  into  a  bell-shape  at  their  lower  ends  for  the  collection  of  a  consider- 
able volume  of  gas.  These  tubes  are  filled  with  the  acidified  water  by  sucking  out 


14  ELECTROLYSIS   OF  WATER. 

the  air  through  the  opened  stop-cocks;  on  closing  these,  the  pressure  of  the 
atmosphere  will,  of  course,  sustain  the  column  of  water  in  the  tubes i.  (*  is  a 
Grovefs  battery,  consisting  of  five  cells  or  earthenware  vessels  (A,  Fig.  3)  filled  witi 


Fig-  3- 


Fig.  4. 


diluted  sulphuric  acid  (one  measure  of  oil  of  vitriol  to  four  of  water).  In  each  of 
these  cells  is  placed  a  bent  plate  of  zinc  (B),  which  has  been  amalgamated  or 
rubbed  with  mercury  (and  diluted  sulphuric  acid)  to  protect  it  from  corrosion  by 
the  acid  when  the  battery  is  not  in  use.  Within  the  curved  portion  of  this  plate 
rests  a  small  flat  vessel  of  unglazed  earthenware  (C),  filled  with  strong  nitric  acid, 
in  which  is  immersed  a  sheet  of  platinum-foil  (D).  The  platinum  (D)  of  each  cell 
is  clamped,  at  its  upper  edge,  to  the  zinc  (B)  in  the  adjoining  cell  (Fig.  4),  so  that 

at  one  end  (P,  Fig.  2)  of  the  battery  there  is  a  free 
platinum  plate,  and  at  the  other  (Z)  a  free  zinc 
plate.  These  plates  are  connected  with  wires  D 
and  E  by  means  of  the  copper  plates  L  and  K, 
attached  to  the  ends  of  the  wooden  trough  in 
which  the  cells  are  arranged.  The  wire  D  (Fig.  2), 
which  is  connected  with  the  last  zinc  plate  of  the 
battery,  is  often  called  the  "  negative  pole,"  whilst 
E,  in  connection  with  the  last  platinum  plate,  is 
called  the  "  positive  pole." 

When  the  connection  is  established  by  means  of 
the  wires  D  and  E  with  the  "  electrolytic  cell  "  (A), 
the  "  galvanic  current "  is  commonly  said  to  pass 
along  the  \vire  E  to  the  platinum  plate  C,  through 
the  acidified  water  in  the  electrolytic  cell,  to  the 
platinum  plate  B,  and  thence  along  the  wire  D 
back  to  the  battery. 

Since  the  electricity  travels  into  and  out  of  the 
electrolytic  cell  by  the  plates  B  and  C,  these  are 
called  the  electrodes  (r]\eKTpov,  amber — root  of  elec- 
tricity ;  66os,  a  way).  The  plate  C,  or  way  into  the 
cell,  is  called  the  anode  (cwa,  towards  :  65os)  ;  the 
plate  B,  or  way  out  of  the  cell,  is  the  cathode  (/cara, 
away  from  :  65os). 

Another  form  of  apparatus  for  this  experiment 
is  shown  in  fig.  5.  The  water  displaced  by  the 
gases  accumulating  in  the  tubes  A,  o,  collects  in 
the  bulb  1)  upon  the  longer  branch,  and  exerts  the 
pressure  necessary  to  force  the  gases  out  when  the 
stop-cocks  are  opened.  The  stop-cocks,  being 
made  of  glass,  are  not  corroded  by  the  acid. 

2.  During  this  "passage  of  the  current"  (which  is  only  a  figurative 
mode  of  expressing  the  transfer  of  the  electric  influence),  the  water 
intervening  between  the  plates  B  and  C  is  decomposed,  its  hydrogen 
being  attracted  to  the  plate  B  (negative  pole  or  cathode),  and  the 
oxygen  to  the  plate  C  (positive  pole  or  anode).  The  gases  can  be  seen 
adhering  in  minute  bubbles  to  the  surface  of  each  plate,  and  as  they 


Fig.  5. — Electrolysis  of  water. 


ELECTROLYSIS   OF  WATER.  15 

increase  in  size  they  detach  themselves,  rising  through  the  acidified 
water  in  the  tubes  H  and  O,  in  which  the  two  gases  are  collected. 

Since  no  transmission  of  gas  is  observed  between  the  two  plates,  it 
is  evident  that  the  H  and  O  separated  at  any  given  moment  from  each 
plate  do  not  result  from  the  decomposition  of  one  particle  of  water,  but 
'from  two  particles,  as  represented  in  Fig.  5,  where  A  represents  the 
particles  of  water  lying  between  the  plates  P  and  Z  before  the 
"  current"  is  passed,  and  B  the  state  of  the  particles  when  the  current 
has  been  established.  P  is  (the  anode)  in  connection  with  the  last 
platinum  plate  of  the  battery,  and  Z  is  (the  cathode)  in  connection 
with  the  last  zinc  plate. 


0 

0 

0 

0 

0 

0 

O 

0 

0 

oooooooo 


HHHt/Ht/HH 


1-  +  -f 


Fig.  6. 


The  signs  +  and  -  made  use  of  in  B  refer  to  a  common  mode  of 
accounting  for  the  decomposition  of  water  by  the  battery,  on  the  sup- 
position that  the  oxygen  is  in  a  negatively  electric  condition,  and 
therefore  attracted  by  the  positive  pole  P ;  whilst  the  hydrogen  is  in  a 
positively  electric  condition,  and  is  attracted  by  the  negative  pole  Z. 

In  the  foregoing  explanation,  the  part  played  by  the  sulphuric  acid  has  been 
omitted  for  the  sake  of  simplicity.  Pure  water  could  not  be  decomposed  unless  by 
a  very  much  stronger  battery.  For  a  discussion  of  the  part  played  by  the  sulphuric 
acid  the  reader  must  refer  to  the  chapter  011  General  Principles. 

The  decomposition  of  compounds  by  galvanic  electricity  is  termed 
electrolysis.*  When  a  compound  of  a  metal  with  a  non-metal  is  decom- 
posed in  this  manner,  the  metal  is  usually  attracted  to  the  (negative) 
pole  in  connection  with  the  zinc  plate  of  the  battery,  whilst  the  non- 
metal  is  attracted  to  the  (positive)  pole  connected  with  the  platinum 
plate  of  the  battery. 

Hence  the  metals  are  frequently  spoken  of  as  electro-positive  elements, 
and  the  non-metals  as  electro-negative. 

3.  If  the  passage  of  the  "current"  be  interrupted  when  the  tube  H 
has  become  full  of  gas,  the  tube  0  will  be  only  half  full,  since  water  is 
a  compound  of  hydrogen  and  oxygen  in  the  proportion  of  two  volumes  of 
hydrogen  to  one  volume  of  oxygen."1?  When  the  wider  portions  of  the 
tubes  (fig.  2)  are  also  filled,  the  two  gases  may  be  distinguished  by 
opening  the  stop-cocks  in  succession  and  presenting  a  burning  match. 
The  hydrogen  will  be  known  by  its  kindling  with  a  slight  detonation 
and  burning  with  a  very  pale  flame  at  the  jet ;  whilst  the  oxygen  will 
very  much  increase  the  brilliancy  of  the  burning  match,  and  if  a  spark 

*  "HXerpov,  amber — root  of  electricity ;  Avw,  to  loosen. 

t  The  volume  of  the  oxygen  is  always  found  to  be  slightly  less  than  one-half  the  volume 
of  the  hydrogen  in  this  experiment,  both  because  the  solubility  of  oxygen  in  water  is  rather 
greater  than  that  of  hydrogen,  and  because  a  small  proportion  of  the  oxygen  is  evolved  in 
the  condition  of  ozone,  which  occupies  only  two-thirds  of  the  volume  occupied  by  an  equal 
weight  of  oxygen  (see  Ozone). 


!6  ELECTKOLYSIS   OF  HYDROCHLORIC  ACID. 

left  at  the  extremity  of  the  match   be  presented  to  the  oxygen,  the 
spark  will  be  kindled  into  a  flame. 

A  volume  of  oxygen  weighs  16  times  as  much  as  an  equal  volume 
of  hydrogen,  so  that  if  one  volume  of  hydrogen  be  said  to  weigh  one 
part  by  weight,  one  volume  of  oxygen  will  weigh  16  parts  by  weight. 
But  in  water  the  proportion  of  hydrogen  to  oxygen  is  2  volumes  :  i 
volume.  Therefore  the  proportion  by  weight  of  these  two  element* 
in  the  water  must  be  2  :  16,  or  water  is  a  compound  of  hydrogen  and 
oxygen  in  the  proportion  of  2  parts  by  weight  of  hydrogen  to  16  parts  by 
weight  of  oxygen.  Since  the  atom  of  oxygen  is  believed  to  weigh  16 
times  as  much  as  the  atom  of  hydrogen,  the  simplest  view  of  the  com- 
position of  the  molecule  of  water  is  that  it  contains  2  atoms  of  hydrogen 
and  i  atom  of  oxygen;  its  formula  may  therefore  be  represented 

asH20. 

4.  The  decomposition  of  water  by  electrolysis  must  be  compared 
with  a  like  experiment  in  which  the  compound 
decomposed  is  one  of  hydrogen  with  the  ele- 
ment chlorine,  a  gas  called  hydrogen  chloride. 
A  solution  of  this  gas  in  water,  commonly 
known  as  hydrochloric  acid,  yields  equal 
volumes  of  hydrogen  and  chlorine  when  elec- 
trolysed. 

The  apparatus  represented  in  Fig.  5  requires  a  little 
alteration  when  it  is  to  be  used  for  the  electrolysis  of 
hydrochloric  acid,  and  generally  takes  the  form  shown 
in  Fig.  7.  As  chlorine  attacks  platinum,  the  electrodes 
are  of  carbon,  which  cannot  be  sealed  in  glass  but 
must  pass  through  corks.  Strong  hydrochloric  acid  is 
poured  into  the  bulb  until  both  limbs  are  filled  with 
the  acid  :  the  stop-cocks  are  left  open  and  the  wires 
from  the  electrodes  are  connected  with  the  poles  of  a 
battery  of  five  or  six  Grove's  cells.  The  gases  are 
allowed  to  escape  until  the  liquid  is  saturated  with 
chlorine  and  cannot  dissolve  any  more,  this  gas  being 
sufficiently  soluble  in  water  to  vitiate  the  experiment, 
•^o-  7-  The  stop-cocks  are  then  closed  and  the  gases  allowed 

to  collect.     The  proportion  of  chlorine  is  always  too 

small,  owing  to  the  difficulty  of  saturating  the  liquid  with  it.  By  dissolving  as 
much  common  salt  in  the  hydrochloric  acid  as  it  will  take  up,  a  better  result  is 
obtained. 

The  chlorine  is  evolved  at  the  electrode  connected  with  the  platinum 
of  the  battery  (the  anode).  It  will  be  recognised  by  its  greenish-yellow 
colour  and  pungent  odour. 

A  volume  of  chlorine  weighs  35.5  times  as  much  as  an  equal  volume 
of  hydrogen,  so  that  hydrogen  chloride  is  a  compound  of  hydrogen  and 
chlorine  in  the  proportion  of  i  part  by  weight  of  hydrogen  to  35.5  parts 
by  weight  of  chlorine.  The  atom  of  chlorine  is  believed  to  weigh  35.5 
times  as  much  as  that  of  hydrogen,  hence  a  molecule  of  hydrogen 
chloride  may  be  regarded  as  a  compound  of  i  atom  of  hydrogen  with 
i  atom  of  chlorine,  represented  by  the  formula  HC1. 

It  will  be  noticed  that — 

i  vol.  chlorine  unites  with  i  vol.  hydrogen, 
i  vol.  oxygen        „         „      2  vols.       „ 
Later  it  will  be  seen  that  i  vol.  of  the  element  nitrogen  unites  with 


DECOMPOSITION   OF   STEAM.  I/ 

3  vols.  of  hydrogen,  and  there  is  excellent  evidence  that  if  carbon, 
which  is  a  solid  very  difficult  to  vaporise,  could  be  obtained  as  a  gasr 
i  vol.  of  it  would  combine  with  4  vols.  of  hydrogen.  No  element  is 
known,  i  vol.  of  which  combines  with  more  than  4  vols.  of  hydrogen. 

Here  is  an  important  basis  for  classification  of  the  elements,  for  all  those 
that  combine  with  hydrogen  belong  to  one  of  the  above  four  classes, 
while  the  rest  may  be  referred  to  the  same  classes  as  will  be  explained 
presently  and  as  has  been  indicated  at  p.  n. 

5.  Another  method  of  effecting  the  decomposition  of  water  by  electri- 
city consists  in  passing  a  succession  of  electric  sparks  through  steam. 
It  is  probable  that  in  this  case  the  decomposition  is  produced  rather 
by  the  intense  heat  of  the  spark  than  by  its  electric  influence. 

For  this  purpose,  however,  the  galvanic  battery  does  not  suffice, 
since  no  spark  can  be  passed  through  any  appreciable  interval  between 
the  wires  of  the  battery — a  fact  which  electricians  refer  to  in  the 
statement  that,  although  the  quantity  of  electricity  developed  by  the 
galvanic  battery  is  large,  its  tension  or  pressure  is  too  low  to  allow  it  to 


Fig.  8. — Decomposition  of  steam  by  electric  sparks. 

discharge  itself  in  sparks  like  the  electricity  from  the  machine  or  from 
the  induction  coil,  which  possesses  a  very  high  tension,  though  its 
quantity  is  small. 

The  most  convenient  instrument  for  producing  a  succession  of 
electric  sparks  is  the  induction-coil,  in  which  a  current  of  low  tension, 
sent  from  a  weak  battery  through  a  coil  of  stout  wire  and  back  to  the 
battery,  induces  or  excites  a  current  of  high  tension  in  a  coil  of  thin 
wire  of  great  length,  wound  outside  the  thick  coil.  This  current  is 
capable  of  discharging  itself  in  sparks,  such  as  are  obtained  from  the 
electrical  machine. 

Fig.  8  represents  the  arrangements  for  exhibiting  this  experiment. 

A  is  a  half-pint  flask  furnished  with  a  cork  in  which  three  holes  are  bored  ;  in 
one  of  these  is  inserted  the  bent  glass  tube  B,  which  dips  beneath  the  surface  of 
the  water  in  the  trough  C. 

D  and  E  are  glass  tubes,  in  each  of  which  a  platinum  wire  has  been  sealed  so  as 
to  project  about  an  inch  at  both  ends  of  the  tube.  These  tubes  are  thrust  through 
the  holes  in  the  cork,  and  the  wires  projecting  inside  the  flask  are  made  to 
approach  to  within  about  ^  of  an  inch,  so  that  the  spark  may  easily  pass  between 
them. 

The  flask  is  somewhat  more  than  half  filled  with  water,  the  cork  inserted,  and 
the  tube  B  allowed  to  dip  beneath  the  water  in  the  trough,  the  wires  in  D  and  E 
being  connected  with  the  thin  copper  wires  passing  from  the  induction-coil  F, 
which  is  connected  by  stout  copper  wires  with  the  small  battery  G. 

B 


1 8  DECOMPOSITION  OF   STEAM. 

The  water  in  the  flask  is  boiled  for  about  fifteen  minutes,  until  all  the  air  con- 
tained in  the  flask  has  been  displaced  by  steam.  When  this  is  the  case  it  will  be 
found  that  if  a  glass  test-tube  (H)  filled  with  water  be  inverted*  over  the  oiifu 
of  the  tube  B,  the  bubbles  of  steam  will  entirely  condense,  with  the  usual  shaip 
rattling  sound,  and  only  insignificant  bubbles  of  air  will  rise  to  the  top  ot  the s  test 
tube.  If  now.  whilst  the  boiling  is  still  continued,  the  handle  of  the  coil  (F)  be 
turned  so  as  to  cause  a  succession  of  sparks  to  pass  through  the  steam  in  the  flask, 
large  bubbles  of  incondensable  gas  will  accumulate  in  the  tube  H.  This  gas  con- 
sists of  the  hydrogen  and  oxygen  gases  in  a  mixed  state,  having  been  released  from 
their  combined  condition  in  water  by  the  action  of  the  electric  sparks.  I  he  gas 
may  be  tested  by  closing  the  mouth  of  the  tube  H  with  the  thumb,  raising  it  to  an 
upright  position,  and  applying  a  lighted  match,  when  a  sharp  detonation  will 
indicate  the  re-combination  of  the  gases.f 

It  has  long  been  known  that  a  very  intense  heat  is  capable  of  decomposing  water. 
The  temperature  required  for  the  purpose  is  below  the  melting-point  of  platinum, 
.as  may  be  shown  by  the  apparatus  represented  in  fig.  9. 


Fig.  9. — Decomposition  of  steam  by  heat. 

A  platinum  tube  (t)  is  heated  by  the  burner  &,  the  construction  of  which  is 
shown  at  the  bottom  of  the  cut.  It  consists  of  a  wide  brass  tube,  from  which  the 
coal-gas  issues  through  two  rows  of  holes,  between  which  oxygen  is  supplied 
through  the  holes  in  the  narrow  tube,  brazed  into  a  longitudinal  slit  between  the 
two  rows  of  holes  in  the  gas  tube.  The  oxygen  is  supplied  from  a  gas  bag  or  gas- 
holder, with  which  the  pipe  (V)  is  connected. 

The  flask  (/)  containing  boiling  water  is  furnished  with  a  perforated  cork, 
Carrying  a  brass  tube  (a),  which  slips  into  one  end  of  the  platinum  tube,  into  the 
other  end  of  which  another  brass  tube  (0)  is  slipped  ;  this  is  prolonged  by  a  glass 
tube  attached  by  india-rubber  so  as  to  deliver  the  gas  under  a  small  jar  standing 
upon  a  bee-hive  shelf  in  a  trough. 

The  platinum  tube  is  not  heated  until  the  whole  apparatus  is  full  of  steam ,  and 
no  more  bubbles  of  air  are  seen  to  rise  through  the  water  in  the  trough  ;  the  gas 
burner  is  then  lighted,  and  the  oxygen  turned  on  until  the  platinum  tube  is 
heated  to  a  very  bright  red  heat ;  bubbles  of  the  mixture  of  hydrogen  and  oxygen 
produced  by  the  decomposition  of  the  water  may  then  be  collected  in  the  small  jar, 
and  afterwards  exploded  by  applying  a  flame. 

In  these  experiments,  the  high  temperature  to  which  the  s£eam  is  exposed  causes 
its  molecules  to  vibrate  with  such  high  velocities  that  the  equilibrium  of  chemical 
attraction  between  their  component  atoms  is  disturbed,  and  new  molecules  of 
hydrogen  and  oxygen  are  produced.  These  are  immediately  carried  out  of  the 
heated  region  by  the  current  of  steam. 

*  The  end  of  the  tube  B  should  be  bent  upwards  and  thrust  into  a  perforated  cork  with 
notches  cut  down  the  sides.  By  slipping  this  cork  into  the  neck  of  the  test-tube,  the  latter 
will  be  held  firmly. 

t  With  a  powerful  coil,  a  cubic  inch  of  explosive  gas  may  be  collected  in  about  fifteen 
minutes. 


ACTION   OF   METALS   ON  WATER.  19 

6.  In  this  case,  the  force  of  chemical  attraction  holding  the  atoms 
of  oxygen  and  hydrogen  together  in  the  form  of  water,  has  been  over- 
come by  the  physical  force   of  heat.     But  water  may  be  more  easily 
decomposed  by  acting  upon  it  with  some  element  which  has  sufficient 
chemical  energy  to  enable  it  to  displace  the  hydrogen. 

No  non-metallic  element  is  capable  of  effecting  this  at  the  ordinary 
temperature.  Among  the  practically  important  metals,  there  are  five 
which  have  so  powerful  an  attraction  for  oxygen  that  it  is  necessary  to 
preserve  them  in  bottles  filled  with  some  liquid  free  from  that  element, 
such  as  petroleum  (composed  of  carbon  and  hydrogen),  to  prevent  them 
from  combining  with  the  oxygen  of  the  atmosphere.  These  metals  are 
capable  of  decomposing  water  with  great  facility. 

Metals  which  decompose  water  at  the  ordinary  temperature. — Potas- 
sium, Sodium,  Barium,  Strontium,  Calcium. 

7 .  When  a  piece  of  potassium  is  thrown  upon  water,  it  takes  fire  and 
burns  with  a  fine  violet  flame,  floating  about  as  a  melted  globule  upon 
the  surface  of  the  water,  and  producing  in   the  act  of  combination 
enough  heat  to  kindle  the  hydrogen  as  it  escapes.     The  violet  colour  of 
the  flame  is  due  to  the  presence  of  a  little  potassium  in  the  form  of 
vapour.     The  same  results  ensue  if  the  potassium  be  placed  on  ice.    The 
water  in  which  the  potassium  has  been  dissolved  is  soapy  to  the  touch 
and  taste,  and  has  a  remarkable  action  upon  certain  colouring  matters. 
Paper  coloured  with  the  yellow  dye   turmeric  becomes  brown   when 
dipped  in  it,  and  paper  coloured  with  red  litmus  becomes  blue.     Sub- 
stances possessing  these  properties  have  been  known  from  a  very  remote 
period   as    alkaline    substances,   apparently   because    they   were    first 
observed  by  the  alchemists  in  the  ashes  of   plants  called  kali.     The 
alkalies  are  amongst  the  most  useful  of  chemical  agents. 

8.  Definition  of  an  alkali. — A  compound  substance,  very  soluble  in 
water,  turning  red  litmus  blue  and  turmeric  brown. 

These  alkaline  properties  are  directly  opposed  to  the  characters  of 
sour  or  acid*  substances,  such  as  vinegar  or  vitriol,  which  change  the 
blue  litmus  to  red.  When  an  acid  liquid,  such  as  vinegar  (acetic  acid) 
or  vitriol  (sulphuric  acid)  is  added  to  an  alkaline  liquid,  the  charac- 
teristic properties  of  the  latter  are  destroyed,  the  alkali  being  neu- 
tralised. 

An  acid  substance  may  be  known  by  its  property  of  neutralising  an 
alkali  (either  entirely  or  partly). 

The  minute  investigation  into  the  action  of  potassium  upon  the 
water  would  require  considerable  manipulative  skill.  It  would  be 
necessary  to  weigh  accurately  the  potassium  employed,  to  evaporate  the 
resulting  solution  in  a  silver  basin  (most  other  materials  being  corroded 
by  the  alkali),  and  after  all  the  water  had  been  expelled  by  heat,  to 
ascertain  the  composition  of  the  residue  by  a  chemical  analysis. 

It  would  be  found  to  contain  by  weight  i  part  of  hydrogen,  16  parts 
of  oxygen,  and  39  parts  of  potassium. 

Since  water  contains  2  parts  by  weight  of  hydrogen,  combined  with 
1 6  parts  by  weight  of  oxygen,  it  is  evident  that  the  product  of  the 
a,ction  of  potassium  on  water  is  formed  by  the  substitution  of  39  parts 
of  potassium  for  i  part  of  hydrogen. 

It  is  found  that  whenever  potassium  takes  the  place  of  hydrogen  in  a 

*  From  a**?,  a  point,  referring  to  the  pungency  or  sharpness  of  the  acid  taste. 


20 


ALKALIES  AND  ACIDS. 


compound,  39  parts  of  the  former  are  exchanged  for  one  of  the  latter, 
and  this  is  generally  expressed  by  stating  that  39  is  the  chemical  equi- 
valent of  potassium. 

The  chemical  equivalent  of  a  metal  expresses  the  weight  of  it  which 
is  required  to  be  substituted  for  one  part  by  weight  of  hydrogen  in 
compounds  of  hydrogen. 

9.  The  action  of  potassium  upon  water  is  an  example  of  the  produc- 
tion of  compounds  by  substitution  of  one  element  for  another,  a  mode 
of  formation  which  is  far  more  common  than  the  production  of  com- 
pounds by  direct  combination  of  their  elements. 

If  the  symbol  K  represent  39  parts  by  weight  of  potassium,  its  action 
upon  water  would  be  represented  by  the  chemical  equation. 

H20   +  K  =  KOH  +  H. 
Water.         Caustic  potash.* 

But  since  the  atoms  cannot  exist,  except  in  combination  as  mole- 
cules, it  would  be  strictly  correct  to  write  the  equation  thus : 

2H20  +  K2  =  2KOH  +  H2. 

Since  the  molecular  equation  can  always  be  obtained  by  doubling  the 
atomic  equation,  the  latter  will  be  most  commonly  given  in  this  work, 
as  involving  fewer  numbers. 

Sodium  has  a  less  powerful  attraction,  or  affinity,  for  oxygen  than 
potassium  has ;  it  does  not,  therefore,  evolve  so  much  heat  when  it 
combines  with  oxygen,  for  it  is  generally  noticed  that  the  greater  the 

affinity  between  two  elements  the 
greater  is  the  quantity  of  heat 
evolved  when  they  combine.  Thus 
sodium  does  not  usually  take  fire 
when  thrown  upon  cold  water, 
although  sufficient  heat  is  evolved 
to  fuse  at  once  the  metal.  By 
holding  a  lighted  match  over  the 
globule  as  it  swims  upon  the 
water,  the  hydrogen  may  be 
kindled,  when  its  flame  is  bright 
yellow,  from  the  presence  of  the 

Fio.  I0  sodium.     The  solution  is  strongly 

alkaline  from  the  soda  produced. 

By  placing  the  sodium  on  a  piece  of  blotting-paper  laid  on  the  water,  it 
may  be  made  to  ignite  the  hydrogen  spontaneously,  because  the  paper 
keeps  the  sodium  stationary,  and  prevents  it  from  being  so  rapidly 
cooled  by  the  water.  Several  cubic  inches  of  hydrogen  may  easily  be 
collected  by  placing  a  piece  of  sodium  as  large  as  a  pea  in  a  small  wire- 
gauze  box  (A,  Fig.  10),  and  holding  it  under  an  inverted  cylinder  (B) 
failed  with  water  and  standing  on  a  bee-hive  shelf.f 

The  product  of  the  action  of  sodium  upon  water  contains  i  part  by 
weight  of  hydrogen,  16  of  oxygen,  and  23  of  sodium,  so  that  the  2* 
parts  of  sodium  have  been  exchanged  for,  or  been  found  chemically 
equivalent  to,  i  part  of  hydrogen. 

i,  in  allusion  to  its  corrosive  properties  ;  and  potash,  from  its 
cl  from  the  washings  of  wood  ashes  *— M-J  J •     • 

t  This  experiment  sometimes  ends  in  an  explosion. 


ACTION   OF   METALS  ON  WATER.  21 

Taking  the  symbol  Na  to  represent  23  parts  by  weight  of  sodium,  its 
action  would  be  expressed  thus  :  H20  4-  Na  =  NaOH  +  H. 

Barium,  strontium,  and  calcium  decompose  water  less  rapidly  than 
potassium  and  sodium  do. 

10.  The  increase  in  molecular  motion  caused  by  heat  disturbs  the 
equilibrium  of  chemical  attraction,  so  that  metals  which  refuse  to  de- 
compose water  at  the  ordinary  temperature  will  do  so  if  the  tempera- 
ture be  raised,  and  accordingly  magnesium  and  manganese,  which  are 
without  action  upon  cold  water,  decompose  it  at  the  boiling-point,  disen- 
gaging  hydrogen,    and  producing   magnesia  (MgO,   a  feebly  alkaline 
earth)  and  oxide  of  manganese  (MnO). 

But  the  greater  number  of  the  common  metals  must  be  raised  to  a 
much  higher  temperature  than  this  before  they  will  decompose  water. 
The  following  metals  abstract  the  oxygen  from  water  at  high  tempera- 
tures, those  at  the  commencement  of  the  list  requiring  to  be  heated  to 
redness  (about  600°  C.),  and  the  temperature  required  progressively 
increasing  until  it  attains  whiteness  for  those  at  the  end  of  the  list. 

Metals  which  decompose  water  at  a  temperature  above  a  red  heat. — 
Zinc,  Iron,  Chromium,  Cobalt,  Nickel,  Tin,  Antimony,  Aluminium, 
Lead,  Bismuth,  Copper. 

The  noble  metals,  as  they  are  called,  which  exhibit  no  tendency  to 
oxidise  in  air,  are  incapable  of  removing  the  oxygen  from  water,  even 
at  high  temperatures. 

Metals  which  are  incapable  of  decomposing  water. — Mercury,  Silver, 
Gold,  Platinum. 

Metals  decompose  water  more  readily  when  in  a  very  fine  state  of  division  or 
placed  in  a  state  of  electrical  polarisation  by  contact  with  other  metals  more 
electro-negative  than  themselves.  Thus  zinc,  in  contact  with  precipitated  copper, 
decomposes  water  slowly  at  the  ordinary  temperature,  hydrogen  being  evolved, 
and  zinc  hydrate  separated  in  white  flakes. 

The  copper-zinc  couple  made  by  precipitating  copper  sulphate  with  zinc-foil  in 
excess,  and  washing,  is  very  useful  in  many  operations  where  a  slow  production  of 
hydrogen  is  required. 

HYDROGEN. 

H  =  i  part  by  weight  =  I  volume. 

1 1 .  Preparation  of  hydrogen. — The  simplest  process,  chemically  speak- 
ing, for  preparing  hydrogen  in  quantity,  consists  in  passing  steam  over 
red-hot  iron.     An  iron  tube  (A,  Fig.   1 1 )  is  filled  with  iron  nails  and 

B 


Fig.  it. — Preparation  of  hydrogen  from  steam. 


22  PREPARATION  OF  HYDROGEN. 

placed  in  a  furnace  (B),  where  it  is  heated  to  redness  by  gas  burners. 
A  current  of  steam  is  then  passed  through  it  by  boiling  the  water •  m 
the  flask  (C),  which  is  connected  with  the  iron  tube  by  a  glass  tube  (D) 
and  perforated  corks.  The  hydrogen  is  collected  from  the  glass  tube 
(G)  in  cylinders  (E)  filled  with  water,  and  inverted  in  the  trough  (£ ) 
upon  the  bee-hive  shelf  (H),  the  first  portions  being  allowed  to  escape, 
as  containing  the  air  in  the  apparatus. 

The  iron  combines  with  the  oxygen  of  the  water  to  form  the  black 
oxide  of  iron  (Fe3O4)  which  will  be  found  in  a  crystalline  state  upon  the 
surface  of  the  metal.  The  decomposition  is  represented  by  the  equa- 
tion 4H90  +  Fe3  =  Fe3O4  +  H8. 

The  atomic  weight  of  iron  being  56,  the  Fe3  in  the  above  equation 
represent  56  x  3,  or  168  parts  by  weight  of  iron. 

Other  methods  for  depriving  steam  of  its  oxygen,  and  therefore  tor 
preparing  hydrogen,  will  be  noticed  in  the  sequel. 

The  process  by  which  hydrogen  is  most  commonly  prepared  con- 
sists in  dissolving  iron  or  zinc  in  a  mixture  of  sulphuric  acid  and 
water. 

Zinc  is  the  most  convenient  metal  for  this  purpose.  It  is  used  either 
in  small  fragments  or  cuttings,  or  as  granulated  zinc,  prepared  by 

melting  it  in  a  ladle  and 
pouring  it  from  a  height  of 
three  or  four  feet  into  a 
pailful  of  water ;  when 
thus  granulated  it  exposes 
a  larger  surface  to  tho 
action  of  the  acid.  The 
zinc  is  placed  in  the  bottle 
(A,  Fig.  12),  covered  with 
water  to  the  depth  of  two 
or  three  inches,  and  diluted 
sulphuric  acid  slowly 
poured  in  through  the 
funnel  tube  (B)  until  a 
pretty  brisk  effervescence 
Fig.  12.— Preparation  of  hydrogen.  js  observed.  The  hydrogen 

is  unable  to  escape  through 

the  funnel  tube,  since  the  end  of  this  is  beneath  the  surface  of 
the  water,  but  it  passes  off  through  the  bent  tube  (C),  and  is  col- 
lected over  water  as  usual,  the  first  portion  being  rejected  as  con- 
taining air. 

By  allowing  the  solution  left  in  the  bottle  to  cool  in  another  vessel, 
crystals  of  zinc  sulphate  (white  vitriol)  may  be  obtained. 

It  will  be  noticed  that  the  liquid  becomes  very  hot  during  the  action 
of  the  acid  upon  the  zinc,  the  heat  being  produced  by  the  chemical  com- 
bination. The  black  flakes  which  separate  during  the  dissolution  of  the 
zinc  are  metallic  lead,  which  is  always  present  in  the  zinc  of  commerce, 
and  much  accelerates  the  evolution  of  hydrogen  by  causing  galvanic 
action.  Pure  zinc  placed  in  contact  with  diluted  sulphuric  acid  evolves 
hydrogen  very  slowly.  By  attaching  a  piece  of  platinum  to  the  pure 
zinc,  so  as  to  form  a  galvanic  couple,  the  reaction  may  be  considerably 
hastened. 


PROPEKTIES   OF   HYDROGEN.  23 

The  preparation  of  hydrogen  by  dissolving  zinc  in  diluted  sulphuric 
acid  may  be  represented  by  the  equation* 

H2S04  +  Zn  =  ZnS04  +  H2. 
Sulphuric  acid.       Zinc  sulphate. 

The  symbol  Zn  here  represents  an  atom  of  zinc,  which  is  65  times  as 
heavy  as  the  atom  of  hydrogen.  An  atom  of  zinc  has  here  displaced 
2  atoms  of  hydrogen,  whereas  it  was  found  that  an  atom  of  potassium 
displaced  only  i  atom  of  hydrogen  ;  this  is  often  expressed  by  saying 
that  potassium  is  a  monovalent  element — i.e.  is  exchangeable  for  i  atom 
of  hydrogen.  But  since  65  parts  of  zinc  displace  2  parts  of  hydrogen, 
zinc  is  a  divalent  element — i.e.  is  exchangeable  for  2  atoms  of  hydrogen. 
This  is  commonly  expressed  by  writing  the  symbol  of  zinc  Zn". 

It  may  be  supposed  that  the  atom  of  a  monovalent  element,  such  as 
hydrogen  or  potassium,  exerts  its  chemical  attraction  in  one  direction 
only,  as  represented  by  a  single  line  or  bond  attached  to  the  symbol, 
thus  H-,  K-  ;  whilst  a  divalent  element,  such  as  zinc,  exerts  chemical 
attraction  in  two  directions,  represented  by  attaching  two  lines  to  the 
symbol,  thus  -Zn-,  or  Zn<.  Since  an  atom  of  oxygen  combines  with 
two  atoms  of  hydrogen,  it  must  also  exert  chemical  attraction  in  two 
directions,  so  that  a  molecule  of  water  may  be  represented  as  H — 0 — H. 
The  displacement  of  half  the  hydrogen  by  potassium  (p.  17)  then  pro- 
duces K — O — H,  caustic  potash,  and  the  displacement  of  both  atoms 
of  hydrogen  by  zinc  produces  Zn<  >O,  or  zinc  and  oxygen  united  by 
both  their  bonds  of  chemical  attraction,  forming  zinc  oxide.  . 

Iron  might  be  used  instead  of  zinc,  and  the  solution,  when  evaporated, 
would  then  deposit  crystals  of  green  vitriol  or  copperas  (sulphate  of  iron, 
or  ferrous  sulphate,  FeS04),  the  action  of  iron  upon  the  sulphuric  acid 
being  represented  by  the  equation  H2S04  +  Fe  =  FeS04  +  H2,  which 
shows  that  i  atom  (56)  of  iron  has  taken  the  place  of  2  atoms  of 
hydrogen,  and  that  the  iron  is  divalent,  like  zinc. 

12.  Physical  properties  of  hydrogen. — This  gas  is  invisible,  and  in- 
odorous when  pure.  The  hydrogen  obtained  by  the  ordinary  methods 
has  a  very  disagreeable  smell,  caused  by  the  presence  of  minute  quan- 
tities of  compounds  of  hydrogen  with  sulphur,  arsenic,  and  carbon  ;  but 
the  gas  prepared  with  pure  zinc  and  sulphuric  acid  is  quite  free  from 
smell.  The  most  remarkable  physical  property  of  hydrogen  is  its 
lightness.  It  is  the  lightest  of  all  kinds  of  matter,  being  about  TV  as 
heavy  as  air,  and  -^^-^Q  as  heavy  as  water. 

The  lightness  of  hydrogen  may  be  demonstrated  by  many  interesting  experi- 
ments. Soap  bubbles  or  small  balloons  (of  collodion,  for  example)  will  ascend  very 
rapidly  if  inflated  with  hydrogen.  A  light  beaker  glass  maybe  accurately  weighed 
in  a  pair  of  scales  ;  it  may  then  be  held  with  its  mouth  downwards,  and  the 
hydrogen  poured  up  into  it  from  another  vessel.  If  it  be  then  replaced  upon  the 
scale-pan  with  its  mouth  downwards,  it  will  be  found  very  much  lighter  than  before. 
Another  form  of  the  experiment  is  represented  in  Fig.  13,  where  a  light  glass  shade 
has  been  suspended  from  the  balance  and  counterpoised,  the  equilibrium  being,  of 
course,  at  once  disturbed  when  hydrogen  is  poured  up  into  the  shade.  If  a 
stoppered  gas  jar  full  of  hydrogen  be  held  with  its  mouth  downwards,  and  a  piece 
of  smouldering  brown  paper  held  under  it,  the  smoke,  which  would  rise  freely  in 
the  air,  is  quite  unable  to  rise  through  the  hydrogen,  and  remains  at  the  mouth  of 
the  jar  until  the  stopper  is  removed,  when  the  hydrogen  quickly  rises  and  the 
smoke  follows  it. 

*  Iu  this  equation  the  excess  of  water  which  must  be  added  to  dissolve  the  zinc  sulphate 
is  not  set  down.  Hydrogen  could  not  be  prepared  according  to  the  equation  as  it  stands, 
because  the  zinc  sulphate  would  collect  round  the  metal  and  prevent  further  action. 


24  PROPERTIES  OF  HYDROGEN. 

ii  The  employment  of  hydrogen  for  filling  balloons  renders  a  know- 
ledge of  the  relation  between  the  weights  of  equal  volumes  of  hydrogen 
and  atmospheric  air  of  great  importance.  The  number  expressing  this 
relation  is  termed  the  Specific  Gravity  of  hydrogen. 

(DEFINITION.— The  specific  gravity  of  a  gas  or  vapour  is  the  weight 
of  a  volume  of  it  compared  with  that  of  an  equal  volume  of  some  other 
gas,  selected  as  a  standard,  at  the  same  temperature  and  pressure.) 
'  If  the  weight  of  a  given  volume  of  purified  and  dried  air  be  repre- 
sented as  unitv,  an  equal  volume  of  hydrogen,  at  the  same  temperature 
and  pressure, "would  weigh  0.0695,  which  is  expressed  by  saying  that 
the  specific  gravity  of  hydrogen  (air  =  i)  is  0.0695. 


Fig.  13- 

In  ascertaining  the  weights  of  different  volumes  of  gases,  it  is  of  the 
greatest  importance  that  they  should  have  some  definite  temperature 
and  pressure,  since  the  volume  of  a  given  weight  of  gas  is  augmented 
by  increase  of  temperature  and  by  decrease  in  pressure.  It  is  usual 
to  state  the  weights  of  gases,  either  at  60°  Fahrenheit  and  30  inches 
barometer,  or  at  o°  Centigrade  and  760  millimetres  barometer. 

One  litre  of  hydrogen  at  o°  C.  and  760  mm.  Bar.  weighs  0.09  gram, 
so  that  one  gram  (15.43  grains)  of  hydrogen,  at  o°  0.  and  760  mm.  Bar., 
measures  n.ii  litres  (one  litre  =  61.024  cubic  inches  =  1.76  pint). 

One  grain  of  hydrogen,  at  60°  F.  and  30  inches  Bar.,  measures  46.45 
cubic  inches. 

It  is  now  easy  to  calculate  how  much  zinc  it  would  be  necessary  to  dissolve  in 
sulphuric  acid  in  order  to  obtain  any  desired  volume,  say  100  litres,  of  hydrogen. 
Referring  to  the  equation  for  the  preparation  of  hydrogen,  Zn  +  H2S04  =  H2  +  ZnS04, 
and  remembering  that  Zn  represents  65  parts  by  weight  of  zinc,  and  H2  represent 
2  parts  by  weight  of  hydrogen,  such  a  problem  can  be  solved  by  ordinary  propor- 
tion ;  thus — 

(2  grams  H)  22.22  litres  :  100  litres  :  165  grams  zinc  :  x. 

37  =  292  grams  zinc  give  100  litres  of  hydrogen  at  o°  C.  and  760  mm.  Bar, 


DIFFUSION.  25 

14.  It  will  be  observed,  in  the  experiment  with  the  balance  (Fig.  13), 
that  the  gas  gradually  falls  out  of  the  jar,  notwithstanding  its  lightness, 
and  is  displaced  by  air ;  so  that,  after  a  time,  the  equilibrium  is  restored, 
proving  that  the  molecules  of  hydrogen  possess  motion  which  is  inde- 
pendent of  gravitation.  This  motion  of  the  molecule  gives  rise  to  the 
phenomenon  known  as  diffusion. 

Diffusion  is  the  intermixture  of  molecules  brought  about  by  their 
power  of  moving  amongst  each  other.  This  power  is  possessed  in  the 
highest  degree  by  gaseous  molecules,  all  gases  being  capable  of  perfect 
and  comparatively  rapid  intermixture.  Some  liquids,  such  as  alcohol 
and  water,  also  intermix  perfectly,  although  comparatively  slowty, 
whilst  other  liquids,  such  as  oil  and  water,  diffuse  into  each  other  only 
to  a  very  limited  extent.  "When  alcohol  is  poured  on  to  water,  it 
forms  a  separate  layer  on  the  surface  of  the  water,  because  it  is  the 
specifically  lighter  of  the  two  ;  after  a  time,  however,  the  two  layers 
.are  no  longer  discernible,  and  the  liquid  is  a  homogeneous  mixture  of 
alcohol  and  water.  In  the  same  way  hydrogen  will  float  on  air,  but 
only  for  a  very  short  time,  since  the  rate  of  diffusion  of  this  gas  is  very 
rapid.  A  homogeneous  mixture  of  hydrogen  and  air  is  speedily 
formed. 

Even  among  solids  the  phenomenon  of  diffusion  is  not  unknown  ; 
thus  a  piece  of  gold  lying  on  a  piece  of  lead  will  gradually  diffuse 
through  the  lead,  but  the  process  occupies  years. 

The  molecules  of  all  gases  do  not  move  with  the  same  velocity,  so 
that  some  gases  diffuse  more  rapidly  than  others.  This  has  been 
discovered  by  confining  a  gas  in  a  vessel  closed  by  some  material  having 
very  minute  pores,  and  immersing  the  vessel  in  an  atmosphere  of  some 
other  gas.  The  passage  of  the  molecules  through  the  pores  of  the 
material  closing  the  vessel  is  sufficiently  slow  to  allow  of  a  comparison 
between  the  velocities  of  passage  or  rates  of  diffusion  of  the  two  gases. 

The  diffusion  tube  (Fig.  14)  employed  for  this  purpose  is  a  glass  tube 
(A)  closed  at  one  end  by  a  plate  of  plaster  of  Paris  (B).  If  this  tube 
be  filled  with  hydrogen,*  and  its  open  end  immersed  in  coloured 
water,  the  water  will  be  observed  to  rise  rapidly  in  the  tube,  on 
account  of  the  rapid  escape  of  the  hydrogen  through  the  pores  of  the 
plaster.  The  external  air,  of  course,  passes  into  the  tube  through 
the  pores  at  the  same  time,  but  much  less  rapidly  than  the  hydrogen 
passes  out,  so  that  the  ascent  of  the  column  of  water  (C)  marks  the 
difference  between  the  volume  of  hydrogen  which  passes  out,  and  that 
of  air  which  passes  into  the  tube  in  a  given  time,  and  allows  a  measure- 
ment to  be  made  of  the  rate  of  diffusion  ;  that  is,  of  the  velocity  with 
which  the  gas  issues  as  compared  with  the  velocity  with  which  the  air 
enters,  this  velocity  being  always  taken  as  unity,  t  To  determine  the 
rate  of  diffusion,  it  is  of  course  necessary  to  maintain  the  water  at  the 
same  level  within  and  without  the  diffusion  tube,  so  as  to  exclude  the 
influence  of  pressure. 

This  method  has  disclosed  the  law  of  diffusion  of  gases,  namely,  that 

*  This  tube  must  be  filled  by  displacement  (see  Fig.  20),  in  order  not  to  wet  the  plaster.  A 
piece  of  sheet  caoutchouc  may  be  tied  over  the  plaster  of  Paris,  so  that  diffusion  may  not 
commence  until  the  sheet  is  removed. 

f  Air  being  a  mixture  of  nitrogen  and  oxygen,  its  rate  of  diffusion  is  intermediate 
between  the  rates  of  those  gases  ;  however,  since  the  proportions  of  the  gases  are  very 
nearly  constant,  no  error  of  any  magnitude  arises. 


26  DIFFUSION  OF  GASES. 

the  rates  of  diffusion  of  gases  vary  inversely  as  the  square  roots  of  their 
relative  weights.  Thus,  oxygen  is  16  times  as  heavy  as  hydrogen,  so 
that  the  rate  of  diffusion  of  hydrogen  :  the  rate  of  diffusion  of  oxygen 
:  :  J\6  :  ,Ji  ;  in  other  words,  hydrogen  will  mix  with  another  gas  four 
times  as  fast  as  oxygen  will  mix  with  that  gas. 

To  prove  that  the  ascent  of  the  hydrogen  due  to  its  lightness  is  not  instrumental 
in  drawing  up  the  water  in  the  diffusion  tube,  the  experiment  may  be  made  as  in 


Fig.  14.— Diffusion  tube.  Fig.  15. 

Fig.  15,  where  the  plate  of  plaster  (o)  is  turned  downwards,  so  that  the  diffusion  is 
made  to  take  place  in  opposition  to  the  action  of  gravity.  This  tube  is  filled  by 
passing  hydrogen  in  through  the  tube  (s),  and  allowing  the  air  to  escape  through  (t), 
which  is  afterwards  closed  by  a  cork.  The  plaster  of  Paris  (o)  is  tied  over  with 
caoutchouc  whilst  the  tube  is  filled. 

Since  the  relation  between  the  weights  of  equal  volumes  of  hydrogen  and  air  is 
that  of  0.069  :  i,  the  rates  of  diffusion  are  as  I  :  \/o  069 — that  is,  hydrogen 
diffuses  about  3.8  times  as  rapidly  as  atmospheric  air,  or  3.8  measures  of  hydrogen 
will  pass  out  of  the  diffusion  tube  whilst  one  measure  of  air  is  passing  in.  In  a 
similar  manner  hydrogen  would  escape  through  minute  openings  with  four  times 
the  velocity  of  oxygen  ;  and  laboratory  experience  shows  that  a  cracked  jar,  or  a 
bottle  with  a  badly  fitting  stopper,  may  often  be  used  to  retain  oxygen  but  not 
hydrogen. 

A  very  striking  illustration  of  the  high  rate  of  diffusion  of  hydrogen  is  arranged 
as  represented  in  Fig.  16.  A  is  a  cylinder  of  porous  earthenware  (such  as  are 
employed  in  galvanic  batteries)  closed  at  one  end,  and  furnished  at  the  other  with 
a  perforated  caoutchouc  stopper  or  a  cork  bung,  through  which  passes  a  glass  tube 
B,  about  six  feet  long  and  half  an  inch  in  diameter.  The  bung  is  made  air-tight 
by  coating  it  with  sealing-wax  dissolved  in  spirit  of  wine.  This  tube  being  sup- 
ported so  that  its  lower  end  dips  about  an  inch  below  the  surface  of  water,  a  jar  of 
coal-gas  is  held  over  the  porous  cylinder,  when  the  velocity  of  the  particles  of  the 
gas  is  manifested  by  their  being  forced  (not  only  out  of  the  mouth  of  the  jar  C, 
which  is  open  at  the  bottom,  but  also)  through  the  pores  of  the  earthenware  jar, 
the  air  from  which  is  violently  driven  out,  as  if  by  blowing,  through  the  tube,  and 
is  seen  bubbling  up  rapidly  through  the  water.  When  the  air  has  ceased  to  bubble 
out,  and  a  large  volume  of  gas  has  entered  the  porous  jar,  the  bell- jar  C  is  removed, 
when  the  gas  escapes  so  rapidly  through  the  pores,  that  a  column  of  twenty  to 
thirty  inches  of  water  is  drawn  rapidly  up  the  tube  B.  If  the  greatest  height  to 
which  the  water  ascends  be  marked,  and  when  it  has  returned  to  its  former  level,  a 
jar  of  hydrogen  be  held  over  the  porous  cylinder,  it  will  be  found  that  the  above 
phenomena  are  manifested  in  a  much  higher  degree,  showing  that  coal-gas,  being 
heavier  than  hydrogen,  does  not  pass  nearly  so  rapidly  through  the  pores  of  the 
earthenware  as  hydrogen  does. 

By  connecting  the  porous  cylinder  A,  by  means  of  a  short  piece  of  tube,  with  a 
two-necked  bottle,  like  that  represented  in  Fig.  20,  and  passing  through  a  cork  in 
the  other  neck,  a  piece  of  tube  extending  to  the  bottom  of  the  bottle  and  drawn  out 


CONSTITUTION   OF   GASES. 


to  an  open  point  at  its  upper  extremity,  water  may  be  forced  out  in  a  stream 
of  two  or  three  feet  in  height  by  holding  the  jar  of  hydrogen  over  the  porous 
cylinder. 

The  great  difference  in  the  rates  of  diffusion  of  hydrogen  and  oxygen  may  be 
easily  shown  by  the  arrangement  represented  in  Fig.  17.  A  is  a  jar  filled  with  a 
mixture  of  two  volumes  of  oxygen  with  one  volume  of  hydrogen,  communicating 
through  the  stop-cock  and  flexible  tube  with  the 
glass  tube  j5,  which  is  fitted  through  a  perforated 
cork  in  the  bowl  of  the  common  tobacco-pipe  6", 
the  sealing-waxed  end  of  which  dips  under  water 
in  the  trough  D.  By  opening  the  stop-cock  and 
pressing  the  jar  down  in  the  water,  the  mixed 
gases  may  be  forced  rapidly  through  the  pipe, 
and  if  a  small  cylinder  (.Z?)  be  filled  with  them, 
the  mixture  will  be  found  to  detonate  violently 
on  the  approach  of  a  flame.  But  if  the  gas  be 
made  to  pass  very  slowly  through  the  pipe  (at  the 
rate  of  about  a  cubic  inch  per  minute),  the  hydro- 
gen will  diffuse  through  the  pores  of  the  pipe  so 
much  faster  than  the  oxygen,  that  the  gas  col- 
lected in  the  cylinder  will  contain  so  little  hydro- 
gen as  to  be  no  longer  explosive,  and  to  exhibit 
the  property  of  oxygen  to  rekindle  a  partly  ex- 
tinguished match. 

The  fact  that  the  phenomenon  of  diffu- 
sion is  shown  by  solids  and  liquids  as  well 
as  by  gases  has  led  to  the  conclusion  that 
in  all  three  states  of  matter  the  molecules 
are  in  constant  motion.  In  a  solid  the 
distance  through  which  each  molecule 
moves  is  very  small  because  the  molecules 
are  so  close  together  that  they  attract  and 
hinder  each  other.  It  is  supposed  that 
heat  increases  the  motion  until  presently 
the  molecules  are  moving  rapidly  enough 
partly  to  counteract  their  attraction  for 
each  other,  whereupon  the  solid  melts  to 
a  liquid.  In  the  liquid  the  molecules  are 
still  under  the  influence  of  each  other  so 
that  they  cannot  move  freely  through 
space,  which  is  the  characteristic  of  gaseous 
molecules.  By  heating  the  liquid  it 
eventually  boils  and  becomes  a  vapour, 
which,  when  its  temperature  is  consider- 
ably above  that  at  which  the  liquid  boils, 
has  the  properties  of  a  gas. 

In  a  true  gas  the  molecules  would  move  without  influencing  each 
other  in  any  regard,  except  in  so  far  as  they  might  collide  and  rebound 
like  billiard-balls.  They  would  never  stick  together,  so  to  speak. 

Now  it  has  been  shown  by  experiment  that  the  volume  of  a  gas  varies 
inversely  as  the  pressure  to  which  it  is  subjected  (Boyle's  Law).  Thus, 
if  1000  c.c.  of  hydrogen  be  measured  when  the  barometer  stands  at 
760  min.,  this  volume  will  become  500  c.c.  when  the  pressure  is  in- 
creased to  760x2  =  1520  mui.,  or  2000  c.c.  when  the  pressure  is 
diminished  to  380  mm. 

It  has   further   been    shown  that    the   volume  of  a  gas  is  directly 


28 


CONSTITUTION  OF  GASES. 


proportional  to  its  absolute  temperature,  that  is,  the  temperature  shown 
by  the  Centigrade  thermometer  +  273  (Charles'  Law).  For  example, 
1000  c.c.  of  hydrogen  at  273°  abs.  become  2000  c.c.  at  546  abs.  or 
coo  c.c.  at  136.5°  abs.  . 

But  although  these  laws  have  been  experimentally  discovered,  it 
acknowledged  that  no  known  gas  conforms  with  them  absolutely,  and 
particularly  do  gases  deviate  from  them  when  under  high  pressure  or 
at  low  temperature.  This  is  because  under  these  conditions  the  gases 
are  nearer  the  liquid  condition  than  they  are  under  low  pressure  or 
at  high  temperature  ;  the  molecules  are  nearer  together  and  more  under 
the  influence  of  each  other. 

It  has  been  proved  by  mathematics  that  the  ideal  gas  would  obey  the 


Fig.  17. — Separation  of  hydrogen  and  oxygen  by  atmolysis.* 

laws  of  Boyle  and  Charles  accurately,  and  different  gases  certainly  differ 
in  the  degree  to  which  they  deviate  from  the  laws,  so  that  degrees  of 
gaseous  state,  or  good  and  bad  gases,  may  be  recognised.  Those  gases 
deviate  least  which  are  the  most  difficult  to  liquefy,  for  they  are  farthest 
removed  from  the  liquid  state.  Hydrogen  is  the  best  gas,  in  this 
sense,  that  is  known,  hence  on  this  account,  as  well  as  on  account  of  its 
lightness,  it  is  the  best  standard  for  comparison  of  weights  and  volumes 
of  gases.  Carbon  dioxide,  on  the  other  hand,  is  a  poor  gas  at  the 
ordinary  temperature  and  pressure,  for  it  is  then  not  far  above  its 
liquefying  point ;  but  it  improves  if  its  temperature  is  raised  or  its 
pressure  reduced. 

The  diminution  which  occurs  in  the  volume  of  a  gas  when  the 
pressure  upon  it  is  increased,  or  when  the  temperature  of  it  is  de- 
creased, can  only  be  ascribed  to  the  approachment  of  the  molecules 
nearer  to  each  other.  When  the  distance  between  the  molecules  is 

*  This  term  has  been  applied  to  the  separation  of  gases  by  diffusion;  dr/nos,  vapour;  A.VW, 
to  loosen. 


PROPERTIES   OF  HYDROGEN. 


sufficiently  diminished  the  gas  becomes  a  liquid.  Thus  it  is  that  all 
gases  can  be  liquefied  by  great  pressure  or  extreme  cold,  or  a  com- 
bination of  the  two.  Hydrogen  has  been  proved  to  be  the  most 
difficult  of  common  gases  to  liquefy,  but  this  object  has  at  length  been 
achieved,  and  liquid  hydrogen  is  found  to  be  transparent,  colourless, 
and  mobile;  it  boils  at  -  252°  C.  and  freezes  to  colourless  crystals  at 

-  257°  o. 

There  is  a  temperature  for  every  gas  above  which  no  amount  of 
pressure  can  liquefy  the  gas ;  this  is  called  the  critical  temperature  of 
that  gas,  or  the  absolute  boiling-point  of  the  corresponding  liquid. 

This  value  for  hydrogen  appears  to  be  —  242°  C.,  but  for  some  gases, 
such  as  carbon  dioxide,  it  is  above  the  ordinary  temperature,  so  that 
they  can  be  liquefied  by  pressure  alone.  The  pressure  required  to 
liquefy  a  gas  at  its  critical  temperature  is  called  the  critical  pressure  of 
the  gas,  that  of  hydrogen  being  15  atmospheres.  The  liquefaction  of 
gases  is  further  treated  of  under  Air. 


Fig.  18. 


Fig.  19. 


Fig.  20. 


Hydrogen  is  one  of  the  least  soluble  of  gases ;  100  volumes  of  water 
dissolve  only  1.83  vols.  of  the  gas  at  15°  C.  This  is  only  to  be  ex- 
pected from  the  difficulty  with  which  it  is  liquefied,  it  being  generally 
the  case  that  the  more  easily  liquefied  gases  are  the  more  soluble. 

15.  Chemical  properties  of  hydrogen. — The  most  conspicuous  chemical 
property  of  hydrogen  is  its  disposition  to  burn  in  air  when  raised  to  a 
moderately  high  temperature,  entering  into  combination  with  the 
oxygen  of  the  air  to  form  water.  The  formation  of  water  during  the 
combustion  of  hydrogen  gave  rise  to  its  name  (vSwp,  water). 

Since  an  atom  of  oxygen  combines  with  two  atoms  of  hydrogen  to  form  water, 
the  gases  will  not  combine  unless  under  the  influence  of  some  force,  such  as  heat  or 
electricity,  to  assist  in  resolving  their  molecules  into  the  constituent  atoms. 

On  introducing  a  taper  into  an  inverted  jar  of  hydrogen  (Fig.  18),  the  flame  of 
the  taper  is  extinguished,  but  the  hydrogen  burns  with  a  pale  flame  at  the 
mouth  of  the  jar,  and  the  taper  may  be  rekindled  at  this  flame  by  slowly  with- 
drawing it. 

The  lightness  and  combustibility  of  hydrogen  may  be  illustrated  simultaneously 
by  some  interesting  experiments.  If  two  equal  gas  cylinders  be  filled  with 
hydrogen,  and  held  with  their  mouths  respectively  upwards  and  downwards,  it 
will  be  found  on  testing  each  with  a  taper  after  the  same  interval,  that  the 


3o  COMBUSTION  OF  HYDROGEN. 

hydrogen  has  entirely  escaped  from  the  cylinder  held  with  its  mouth  upwards, 
whilst  the  other  still  remains  nearly  filled  with  the  gas. 

The  hydrogen  maybe  scooped  out  of  the  jar  A  (Fig.  19)  with  the  small  cylinder 
B  attached  to  a  handle.  On  removing  B,  and  applying  a  taper  to  it,  the  gas  will 

V cylinder  may  be  filled  with  hydrogen  by  displacement  of  air  (Fig.  20),  if  the 
tube  from  the  hydrogen  bottle  be  passed  up  into  it. 

If  such  a  dry  cylinder  of  hydrogen  be  kindled  whilst  held  with  its  mouth  down- 
wards, the  formation  of  water  during  the  combustion  of  the  hydrogen  will  be 
indicated  by  the  deposition  of  dew  upon  the  sides  of  the  cylinder. 

Bv  softening  a  piece  of  glass  tube  in  the  flame  of  a  spirit-lamp,  drawing  it  out 
and  filing  it  across  in  the  narrowest  part  (Fig.  21),  a  jet  can  be  made  from  which 
the  hydrogen  may  be  burnt.  This  jet  may  be  fitted 
by  a  perforated  cork  to  any  common  bottle  for  con- 
taining the  zinc  and  sulphuric  acid  (Fig.  22). 

The  hydrogen  must  be  allowed  to  escape  for  some 
minutes  before  applying  a  light,  because  it  forms  an 
explosive  mixture  with  the  air  contained  in  the  bottle. 


Fig.  21. 


Fig-.  22. 


This  may  be  proved,  without  risk,  by  placing  a  little  granulated  zinc  in  a  soda- 
water  bottle  (old  form),  pouring  upon  it  some  diluted  sulphuric  acid,  and  quickly 
inserting  a  perforated  cork,  carrying  a  piece  of  glass  tube  about  three  inches  long, 
and  one-eighth  of  an  inch  wide.  If  this  tube  be  immediately  applied  to  a  flame, 
the  mixture  of  air  and  hydrogen  will  explode,  and  the  cork  and  tube  will  be  pro- 
jected to  a  considerable  distance. 

By  inverting  a  small  test-tube  over  the  jet  in  Fig.  22,  a  specimen  of  the  hydrogen 
may  be  collected,  and  may  be  kindled,  to  see  if  it  burns  quietly,  before  lighting  the 
jet. 

A  dry  glass,  held  over  the  flame,  will  collect  a  considerable  quantity  of  water, 
formed  by  the  combustion  of  the  hydrogen. 

The  combustion  of  hydrogen  produces  a  greater  heating  effect  than 
that  of  an  equal  weight  of  any  other  combustible  body.  It  has  been 
determined  that  i  gram  of  hydrogen,  in  the  act  of  combining  with 
8  grams  of  oxygen,  produces  enough  heat  to  raise  34,462  grams  of  water 
from  o°  C.  to  i°  0.  The  temperature  of  the  hydrogen  name  is  pro- 
bably about  2000°  C.  Notwithstanding  its  high  temperature,  the  flame 
of  hydrogen  is  almost  devoid  of  illuminating  power,  on  account  of  the 
absence  of  solid  particles. 

1 6.  If  a  taper  be  held  several  inches  above  a  cylinder  of  hydrogen, 
standing  with  its  mouth  upwards,  the  gas  will  be  kindled  with  a  loud 
explosion,  because  an  explosive  mixture  of  hydrogen  and  air  is  formed 
in  and  around  the  mouth  of  the  cylinder. 

A  stoppered  glass  jar  (Fig.  23)  is  filled  with  hydrogen  and  supported  upon  three 
blocks  ;  if  the  hydrogen  be  kindled  at  the  neck  of  the  jar,  it  will  burn  quietly  until 
air  has  entered  from  below  in  sufficient  proportion  to  form  an  explosive  mixture, 
which  will  then  explode  with  a  loud  report. 

The  same  experiment  may  be  tried  on  a  smaller  scale,  with  the  two-necked 
copper  vessel  (Fig.  24),  the  lower  aperture  being  opened  some  few  seconds  after  the 
hydrogen  has  been  kindled  at  the  upper  one. 

The  explosion  of  the  mixture  of  hydrogen  and  air  is  due  to  the  sudden 
expansion  caused  by  the  heat  generated  in  the  combination  of  the 


OXYGEN.  3 1 

hydrogen  with  the  oxygen  throughout  the  mixture.  After  the  explo- 
sion of  the  mixture  of  hydrogen  and  air  (oxygen  and  nitrogen),  the 
substances  present  are  steam  (from  the  combination  of  the  hydrogen 
and  oxygen)  and  nitrogen,  which  are  expanded  by  the  heat  developed 
in  the  combination,  to  a  volume  far  greater  than  the  vessel  can  contain, 


Fig.  24. 


so  that  a  portion  of  the  gas  and  vapour  issues  very  suddenly  into  the 
surrounding  air,  the  collision  with  which  produces  the  report. 

If  pure  oxygen  be  substituted  for  air,  the  explosion  will  be  more 
violent,  because  the  mixture  is  not  diluted  with  the  inactive  nitrogen. 
The  further  study  of  this  subject  must  be  preceded  by  that  of  oxygen. 


OXYGEN. 

0  =  1 6  parts  by  weight  =  I  volume. 

17.  Oxygen  is  the  most  abundant  of  the  elementary  substances.     It 
constitutes  about  one-fifth  (by  volume)  of  atmospheric  air,  where  it  is 
merely  mixed,  not  combined,  with  the  nitrogen,  which  composes  the 
bulk  of  the  remainder.     Water  contains  eight-ninths  (by  weight)  of 
oxygen ;  whilst  silica  and  alumina,  which  compose  the  greater  part  of 
the  solid  earth  (as  far  as  we  know  it),  contain  about  half  their  weight 
of  oxygen. 

Before  inquiring  which  of  these  sources  will  most  conveniently  furnish 
pure  oxygen,  it  will  be  desirable  for  the  student  to  acquire  some  know- 
ledge of  the  properties  of  this  element,  and  of  the  chemical  relations 
which  it  bears  to  other  elementary  bodies,  for  without  such  knowledge 
it  will  be  found  very  difficult  to  understand  the  processes  by  wThich 
oxygen  is  procured. 

1 8.  Physical  properties  of  oxygen. — From  the  fact  that  it  occurs  in 
an  uncombined  state  in  the  atmosphere,  it  will  be  inferred  that  oxygen 
is  perfectly  invisible,  and  without  odour.     It  is  a  little  more  than  one- 
tenth  heavier  than  air,  which  is  expressed  in  the  statement  that  its 
specific  gravity  is  1.105. 

In  the  study  of  theoretical  chemistry,  it  is  expedient  to  select  hydro- 
gen instead  of  air  as  the  standard  with  which  the  specific  gravities  of 


32  PROPERTIES   OF  OXYGEN. 

gases  are  compared  ;  for  the  atomic  weights  are  also  referred  to  hydrogen 
as  the  unit,  and  in  the  case  of  the  common  elementary  gases  the  atomic 
weights  are  identical  with  their  specific  gravities  (H=i).  Thus  the 
specific  gravity  of  oxygen  (H=i)  is  16,  or,  more  exactly,  15.88.  It 
will  be  found  convenient  to  remember  that  the  specific  gravity  of  a  gas 
or  vapour  is  the  weight  in  grams  of  ii.n  litres  of  it. 

Oxygen  boils  at  -  182°  C.  under  atmospheric  pressure,  so  that  it  is 
liquid  at  temperatures  below  this. 

The  liquid  has  a  steel-blue  colour  ;  its  sp.  gr.  at  - 182°  C.  is  1.135  (water=i)  ; 
its  critical  temperature  (p.  25)  is  -119°  C.,  and  its  critical  pressure  is  51  atmo- 
spheres. The  liquid  is  attracted  by  a  magnet.  Owing  to  its  low  temperature 
liquid  oxygen  is  chemically  very  inactive,  and  has  no  action  on  such  readily 
oxidisable  substances  as  phosphorus,  sodium  or  potassium.  A  mixture  of  powdered 
charcoal  and  liquid  oxygen  can,  however,  be  detonated  by  exploding  a  small  charge 
of  mercuric  fulminate  in  it. 

Oxygen  is  slightly  soluble  in  water;  100  volumes  of  water  absorb 
4  volumes  of  oxygen  at  o°  C.  and  3  volumes  at  15°  C. 

19.  Chemical  properties  of  oxygen. — This  element  is  remarkable  for 
the  wide  range  of  its  chemical  attraction  for  other  elementary  bodies, 
with  all  of  which,  except  two,  it  is  capable  of  entering  into  combination. 
Fluorine  and  bromine  are  the  only  elements  which  are  not  known  to  unite 
with  oxygen* 

With  nearly  all  the  elements  oxygen  combines  in  a  direct  manner  ; 
that  is,  without  the  apparent  intervention  of  any  third  substance, 
although,  since  it  has  been  proved  that  perfectly  dry  oxygen  will  not 
combine  with  other  elements,  it  must  be  admitted  that  moisture  (or 
some  other  third  substance)  is  essential  to  the  chemical  combination. t 

There  are  only  seven  elements  (among  those  of  practical  importance) 
which  do  not  unite  in  a  direct  manner  with  oxygen — viz.  chlorine,  bromine, 
iodine,  fluorine,  gold,  silver,  platinum. 

(DEFINITION. — The  compounds  of  oxygen  with  other  elements  are 
called  Oxides.) 

The  act  of  combination  with  oxygen,  or  oxidation,  is  generally  a  slow 
process,  and  its  effects  are  not  immediately  perceived.  Some  familiar 
examples  of  oxidation  are — the  tarnishing  or  rusting  of  metals  by  air, 
the  gradual  decay  of  wood,  the  drying  of  oils  in  paint,  the  formation  of 
vinegar  from  alcoholic  liquids,  the  respiration  of  animals  and  com- 
bustion. 

In  all  these  processes  heat  is  generated  ;  but  it  is  not  usually  noticed 
unless  it  is  sufficient  to  render  the  particles  of  matter  luminous,  which 
is  the  case  only  with  combustion. 

(DEFINITION. — Combustion  is  chemical  combination  attended  with 
heat  and  light.) 

20.  Phosphorus,  the  only  non-metal  which  combines  with  oxygen  at  the. 
ordinary  temperature,  affords  a  good  illustration  of   oxidation.     This 
element,  a  solid  at  the  ordinary  temperature,  is  preserved  in  bottles 
filled  with  water,  on  account  of  the  readiness  with  which  the  oxygen  of 
the  air  combines  with  it.     If  a  small  piece  of  phosphorus  be  dried  bv 

*  The  newly  discovered  elements  argon,  helium,  krypton,  neon  and  xenon,  do  not  combine 
with  oxygen. 

f  Charcoal  may  be  heated  to  redness  in  dry  oxygen  without  visible  combustion.  Sulphur 
and  phosphorus,  which  inflame  in  moist  oxygen  at  260°  C.  and  60°  C.  respectively,  may  be 
distilled  in  the  dry  gas  at  440°  C.  and  290°  C.  respectively. 


COMBUSTION  IN  OXYGEN. 


33 


Fig.  25. 


gentle  pressure  between  blotting-paper,  and  exposed  to  the  air,  its 
particles  begin  to  combine  at  once  with  oxygen,  and  the  heat  thus 
developed  slightly  raises  the  temperature  of  the  mass. 

Now,  heat  generally  encourages  chemical  union,  so  that  the  effect  of 
this  rise  of  temperature  is  to  induce  a  more  extensive  combination  of 
the  phosphorus  with  the  oxygen,  causing  a  greater  development  of  heat 
in  a  given  time,  until  the  temperature  is  sufficient  to  render  the  particles 
brilliantly  luminous,  and  a  true  case  of  combustion  results — the  com- 
bination of  the  phosphorus  with  oxygen,  attended  with  production  of 
heat  and  light.  In  cold  weather,  the  phosphorus  seldom  takes  fire  until 
rubbed,  or  touched  with  a  hot  wire. 

(DEFINITION. — Combustion  in  air  is  the  chemical  combination  of  the 
elements  of  the  combustible  with  the  oxygen  of  the  air,  attended  with 
development  of  heat  and  light.) 

If  a  dry  glass  (Fig.  25)  be  placed  over  the  burning  phosphorus,  the 
thick  white  smoke  which  proceeds 
from  it  may  be  collected  in  the  form 
of  snowy  flakes.  These  flakes  are 
commonly  termed  phosphoric  oxide  or 
phosphoric  anhydride,*  and  are  com- 
posed of  80  parts  by  weight  of  oxygen, 
and  62  parts  of  phosphorus  (P205). 

If  the  white  flakes  are  exposed  to 
the  air  for  a  short  time,  they  attract 
moisture  and  become  little  drops, 
which  have  a  very  sour  or  acid  taste. 
It  was  mentioned  at  page  19  that  all 
substances  which  have  such  a  taste  have  been  found  also  to  be  capable 
of  changing  the  blue  colour  of  litmus  t  to  red  ;  whence  the  chemist  is 
in  the  habit  of  employing  paper  dyed  with  blue  litmus  for  the  recogni- 
tion of  an  acid. 

(DEFINITION. — Anhydride,  a  compound  which  produces  an  acid  when 
brought  into  contact  with  water.) 

For  the  exact  definition  of  an  acid,  see  page  35. 

During  the  slow  combination  of  phosphorus  with  the  oxygen  of  the 
air,  before  actual  combustion  commences,  only  48  parts  of  oxygen  unite 
with  62  parts  of  phosphorus,  forming  the  substance  called  phosphorous 
oxide  or  phosphorous  anhydride  (P203). 

(DEFINITION. — The  endings  -ous  and  -ic  distinguish  between  two  com- 
pounds formed  by  oxygen  with  the  same  element ;  -ous  implying  the 
smaller  proportion  of  oxygen.) 

Unless  the  temperature  of  the  air  be  rather  high,  the  fragment  of 
phosphorus  will  not  take  fire  spontaneously,  but  its  combustion  may 
always  be  ensured  by  exposing  a  larger  surface  to  the  action  of  the 
air.  As  a  general  rule,  a  fine  state  of  division  favours  chemical  combi- 
nation, because  the  attractive  force-inducing  combination  operates  only 
between  substances  in  actual  contact ;  and  the  smaller  the  size  of  the 
particles,  the  more  completely  will  this  condition  be  fulfilled. 

Thus  if  a   small  fragment  of   dry  phosphorus  be  placed  in  a  test-tube,   and 

*  Anhydride,  or  without  water,  from  av,  negative,  and  vSoup,  water. 

f  A  colouring-  matter  prepared  from  a  lichen,  Rocella  tinctoria ;  the  cause  of  the  change 
of  colour  will  be  more  easily  understood  hereafter. 

C 


34 


COMBUSTION  IN  OXYGEN. 


dissolved  in  a  little  car bon  bisulphide,  the  solution  when  poured  upon  blotting-paper 
(Fig.  26),  will  part  with  the  solvent  by  evaporation,  leaving  the  phosphorus  ma 
very  finely  divided  state  upon  the  surface  of  the  paper,  where  it  is  so  rapidly 
attacked  by  the  oxygen  of  the  air  that  it  bursts  spontaneously  into  a  blaze. 

Though  the  light  emitted  by  phosphorus  burning  in  air  is  very 
TDrilliant,  it  is  greatly  increased  when  pure  oxygen  is  employed  ;  for 
since  the  nitrogen  with  which  the  oxygen  in  air  is  mixed  takes  no  part 
in  the  act  of  combustion,  it  impedes  and  moderates  the  action  of  the 


Fig.  26. 


Fig.  27. — Phosphorus  burning-  in  oxygen. 


oxygen.  Each  volume  of  the  latter  gas  is  mixed,  in  air,  with  four 
volumes  of  nitrogen,  so  that  we  may  suppose  five  times  as  many 
particles  of  oxygen  to  come  into  contact,  in  a  given  time,  with  the 
particles  of  the  phosphorus  immersed  in  the  pure  gas,  which  will 
account  for  the  great  augmentation  of  the  temperature  and  light  of  the 
burning  mass. 

To  demonstrate  the  brilliant  combustion  of  phosphorus  in  oxygen,  a  piece  not 
larger  than  a  good-sized  pea  is  placed  in  a  little  copper  or  iron  cup  upon  an  iron 
stand  (Fig.  27),  and  kindled  by  being  touched  with  a  hot  wire.  The  globe  (of  thin 
well-annealed  glass),  having  been  previously  filled  with  oxygen,  and  kept  in  a  plate 
containing  a  little  water,  is  placed  over  the  burning  phosphorus. 

It  will  be  observed  that  the  same  white  clouds  of  phosphoric  an- 
hydride are  formed,  whether  phosphorus  is  burnt  in  oxygen  or  in  air, 
exemplifying  the  fact  that  a  substance  will  combine  with  the  same  pro- 
portion of  oxygen  whether  its  combustion  be  effected  in  pure  oxygen  or  in 

atmospheric  air.  The  apparent  increase 
of  heat  is  due  to  the  combustion  of  a 
greater  weight  of  phosphorus  in  a  given 
time  and  space.  The  total  heating  effect 
produced  by  the  combustion  of  a  given 
weight  of  phosphorus  is  the  same  whether 
air  or  pure  oxygen  be  employed. 

21.  Sulphur  (brimstone)  affords  an 
example  of  a  non-metallic  element  which 
will  not  enter  into  combination  with 
oxygen  until  its  temperature  has  been 
raised  very  considerably.  When  sulphur 
is  heated  in  air,  it  soon  melts  ;  and  when 
its  temperature  reaches  500°  F.  (260°  0.), 
it  takes  fire,  burning  with  a  pale  blue 
flame.  If  the  burning  sulphur  be  plunged  into  a  jar  of  oxygen,  the  blue 
light  will  bocome  very  brilliant,  but  the  same  act  of  combination  occurs 
—32  parts  by  weight  of  oxygen  uniting  with  32  parts  of  sulphur  to  form 


Fig.  2i 


Sulphur  burning  in 
oxygen. 


NATUKE   OF  ACIDS.  35 

sulphurous  acid  gas  or  sulphurous  anhydride  (S02),  which  may  be  recog- 
nised in  the  jar  by  the  well-known  suffocating  smell  of  brimstone  matches. 
The  experiment  is  most  conveniently  performed  by  heating  the  sulphur 
in  a  deflagrating  spoon  (A,  Fig.  28),  which  is  then  plunged  into  the  jar 
of  oxygen,  its  collar  (B)  resting  upon  the  neck  of  the  jar,  which  stands 
in  a  plate  containing  a  little  water.  The  water  absorbs  a  part  of  the 
sulphurous  acid  gas,  and  will  be  found  capable  of  strongly  reddening 
litmus-paper.  It  is  possible  to  produce,  though  not  by  simple  combus- 
tion, a  compound  of  sulphur  with  half  as  much  more  oxygen  (S03, 
sulphuric  anhydride),  showing  that  a  substance  does  not  always  take  up 
its  fidl  share  of  oxygen  when  burnt. 

The  luminosity  of  the  flame  of  sulphur  is  far  inferior  to  that  of 
phosphorus,  because,  in  the  former  case,  there  are  no  extremely  dense 
particles  in  the  flame  corresponding  with  those  of  the  phosphoric  oxide 
produced  in  the  combustion  of  phosphorus. 

22.  Carbon,  also  a  non-metallic  element,  requires  the  application  of  a 
higher  temperature  than  sulphur  does  to  induce  it  to  enter  into  direct 
uni6n  with  oxygen ;  indeed,  perfectly  pure  carbon  appears  to  require 
a  heat  approaching    whiteness  to  produce    this  effect.     But  charcoal 
(the  carbon  in  which  is  associated  with  not  inconsiderable  proportions 
of  hydrogen  and  oxygen)  begins  to  burn  in  air  at  a  much  lower  tempera- 
ture;   and  if  a  piece  of  wood  charcoal,  with  a  single  spot  heated  to 
redness,  be  lowered  into  a  jar  of  oxygen,  the  adjacent  particles  will 
soon  be  raised  to  the  combining  temperature,  and  the  whole  mass  will 
glow  intensely,  32  parts  by  weight  of  oxygen  uniting  with   12  parts 
of  carbon  to  form  carbonic  acid  gas  (C02)  or  carbonic  anhydride,  which 
will  redden  a  piece  of  moistened  blue  litmus-paper  suspended  in  the 
jar.     It  should  be  remembered  that  carbon  is  an  essential  constituent 
of  all  ordinary  fuel,  and  carbonic  acid  gas  is  always  produced  by  its 
combustion. 

It  will  be  noticed  that  the  combustion  of  the  charcoal  is  scarcely 
attended  with  flame ;  and  when  pure  carbon  (diamond,  for  example)  is 
employed,  no  flame  whatever  is  produced  in  its  combustion,  because 
carbon  is  not  convertible  into  vapour,  and  all  flame  is  vapour  or  gas  in 
the  act  of  combustion  ;  hence,  only  those  substances  burn  with  flame  which 
are  capable  of  yielding  combustible  gases  or  vapours. 

23.  The  three  examples  of   sulphur,  phosphorus  and  carbon    suffi- 
ciently illustrate  the  tendency  of  non-metals  to  form  acids  by  union  with 
oxygen  and  water,  which  originally  led  to  the  adoption  of  its  name, 
derived  from  6£vs,  acid,  and  yewda),  I  produce.     All  the  common  non- 
metallic  elements,  except  hydrogen,  bromine  and  fluorine,  are  capable  of 
forming  anhydrides,  by  their  union  with  oxygen. 

Definition  of  an  acid. — A    compound  containing   hydrogen,  which, 

when  in    contact    with    alkali  (p.  19)  exchanges    its    hydrogen,  or  a 
portion  of  it,  for  the  alkali  metal. 
For  example — 

HC1           +           NaOH  =             NaCl             -f         H20 

Hydrochloric  acid.               Soda.  Sodium  chloride.                Water. 

H2S04        +           2KOH  =           K2S04             +        2H20 

Sulphuric  acid.                 Potash.  Potassium  sulphate.              Water. 

H3P04        +          2NaOH  =        Na<jHP04          +        2H20 

Phosphoric  acid.                 Soda.  Sodium  phosphate.              Water. 

24.  The  metals,  as    a  class,  exhibit  a  greater    disposition  to  unite 


36  NATURE  OF  BASES. 

directly  with  oxygen,  though  few  of  them  will  do  so  in  their  ordinary 
condition,  and  at  the  ordinary  temperature.  Several  metals,  such  as 
iron  and  lead,  are  superficially  oxidised  when  exposed  to  air  under 
ordinary  conditions,  but  this  would  not  be  the  case  unless  the  air  con- 
tained water  and  carbonic  acid  gas,  which  favour  the  oxidation  in  a 
very  decided  manner.  Among  the  metals  which  are  of  importance  in 
practice,  five  only  are  oxidised  by  exposure  to  dry  air  at  the  ordinary 
temperature,  viz.,  potassium,  sodium,  barium,  strontium,  and  calcium, 
the  attraction  of  these  metals  for  oxygen  being  so  powerful  that  they 
must  be  kept  under  petroleum,  or  some  similar  liquid  free  from  oxygen. 
On  the  other  hand,  three  of  the  common  metals,  silver,  gold,  and 
platinum,  have  so  little  attraction  for  oxygen  that  they  cannot  be 
induced  to  unite  with  it  directly,  even  at  high  temperatures. 

If  a  lump  of  sodium  be  cut  across  with  a  knife,  the  fresh  surfaces 
will  exhibit  a  splendid  lustre,  but  will  very  speedily  tarnish  by  combin- 
ing with  oxygen  from  the  air,  which  gives  rise  to  a  coating  of  sodium 
oxide,  and  this  to  some  extent  protects  the  metal  beneath  from  oxidation. 
The  freshly  cut  sodium  shines  in  the  dark  like  phosphorus.  Even  when 
the  attraction  of  the  sodium  for  oxygen  is  increased  by  the  application 
of  heat,  it  is  long  before  the  mass  of  sodium  is  oxidised  throughout, 
unless  the  temperature  be  sufficiently  high  to  convert  a  portion  of  the 
sodium  into  vapour,  which  bursts  through  the  crust  of  oxide,  and  burns 
with  a  yellow  flame ;  if,  when  this  has  occurred,  the  spoon  in  which  the 
sodium  is  heated  (see  Fig.  28)  be  plunged  into  a  jar  of  oxygen,  the 
yellow  flame  will  be  more  brilliant. 

Sixteen  parts  by  weight  of  oxygen  (i  atom)  here  combine  with  46 
parts  of  sodium  (2  atoms)  to  form  sodium  oxide  (Na2O),  which  remains 
in  the  spoon  in  a  fused  state.  When  the  spoon  is  cool,  it  may  be  placed 
in  water,  which  will  dissolve  the  oxide,  converting  it  into  the  alkali  soda, 

Na^O   +  H20  =  2NaHO 
Water.          Soda, 

25.  Zinc  serves  as  an  example  of  a  metal  which  has  no  disposition 
to  enter  into  combination  with  oxygen  at  the  ordinary  temperature,* 
but  is  induced  to  unite  with  it  by  a  very  moderate  heat.  If  a  little 
zinc  (spelter)  be  melted  in  a  ladle  or  crucible,  and  stirred  about  with 
an  iron  rod,  it  burns  with  a  beautiful  greenish  flame,  produced  by  the 
union  of  the  vapour  of  zinc  with  the  oxygen  of  the  air.  But  the 
combustion  is  far  more  brilliant  if  a  piece  of  zinc  foil  be  made  into  a 
tassel,  gently  warmed  at  the  end,  dipped  into  a  little  flowers  of  sulphur, 
kindled,  and  let  down  into  a  jar  of  oxygen,  when  the  flame  of  the 
burning  sulphur  will  ignite  the  zinc,  which  burns  with  great  brilliancy. 
On  withdrawing  what  remains  of  the  tassel  after  the  combustion  is 
over,  it  will  be  found  to  consist  of  a  brittle  mass,  which  has  a  fine 
yellow  colour  while  hot,  and  becomes  white  as  it  cools.  This  is  the 
zinc  oxide  (ZnO),  formed  by  the  union  of  16  parts  by  weight  of  oxygen 
with  65  parts  of  zinc. 

The  zinc  oxide  does  not  possess  the  properties  of  an  acid  or  an  alkali 
and  belongs  to  another  class  of  compounds  termed  bases,  which  are  not 
soluble  in  water  as  the  alkalies  are,  but,  like  them,  are  capable  of 
neutralising  the  acids  either  partly  or  entirely.  Thus,  if  the  zinc  oxide 
were  added  to  diluted  sulphuric  acid  as  long  as  the  acid  would  dissolve 
*  Unless  water  and  carbonic  acid  gas  be  present,  as  in  common  air. 


METALS  AND   OXYGEN.  37 

it,  the  well-known  corrosive  properties  of  the  acid  would  be  destroyed, 
although  it  would  still  retain  the  power  of  reddening  blue  litmus,  and 
the  solution  would  now  contain  a  new  substance,  or  salt,  called  zinc 
sulphate  (ZnS04). 

(DEFINITION. — A  base  is  a  compound  body  which  is  capable  of  neu- 
tralising an  acid,  either  partly  or  entirely.)  t 

It  will  be  observed  that  an  alkali  is  only  a  particular  species  of  base, 
and  might  be  defined  as  a  base  which  is  very  soluble  in  water. 

(DEFINITION. — A  salt  is  a  compound  formed  when  the  hydrogen  in 
an  acid  is  exchanged,  either  entirely  or  partly,  for  a  metal ;  thus  sodium 
chloride,  NaCl,  is  formed  by  the  exchange  of  the  H  in  HC1,  hydro- 
chloric acid,  for  sodium  ;  sodium  phosphate,  Na2HP04,  is  formed  from 
phosphoric  acid,  H3P04,  by  the  substitution  of  sodium  for  two-thirds  of 
the  hydrogen.) 

26.  Iron,  in  its  ordinary  form,  like  zinc,  is  not  oxidised  by  dry  air  or 
oxygen  at  the  ordinary  temperature  ;  but  if  it  be  heated  even  to  only 
500°  F.  a  film  of  oxide  of  iron  forms  upon  its  surface,  and  as  the 
temperature  is  raised,  the  thickness  of  the  film  increases,  until  eventually 
it  becomes  so  thick  that  it  can  be  detached  by  hammering  the  surface, 
as  may  be  seen  in  a  smith's  forge.  If  an  iron  rod  as  thick  as  the  little 
finger  be  heated  to  whiteness  at  the  extremity,  and  held  before  the 
nozzle  of  a  powerful  bellows,  it  will  burn 
brilliantly  throwing  off  sparks  and  drop- 
ping melted  oxide  of  iron.  If  a  stream 
of  oxygen  be  substituted  for  air,  the  com- 
bustion is  of  the  most  brilliant  descrip- 
tion A  watch-spring  (iron  combined  with 
about  i  per  cent,  of  carbon)  may  be  easily 
made  to  burn  in  oxygen  by  heating  it  in 
a  flame  till  its  elasticity  is  destroyed,  and 
coiling  it  into  a  spiral  (A,  Fig.  29),  one  end 
of  which  is  fixed,  by  means  of  a  cork,  in 
the  deflagrating  collar  B  ;  if  the  other  FiS'-  ^—Watch-spring  burning 
end  be  filed  thin  and  clean,  clipped  into  a 

little  sulphur,  kindled  and  immersed  in  a  jar  of  oxygen  (C)  standing 
in  a  plate  of  water,  the  burning  sulphur  will  raise  the  temperature  of 
the  iron  to  the  point  of  combustion,  and  the  spring  will  be  converted 
into  molten  drops  of  oxide. 

The  black  oxide  of  iron  formed  in  all  these  cases  is  really  a  combina- 
tion of  two  distinct  oxides  of  iron,  one  of  which  contains  16  parts  by 
weight  of  oxygen  and  56  parts  of  iron,  and  would  be  written  FeO, 
whilst  the  other  contains  48  parts  of  oxygen  and  112  parts  of  iron, 
expressed  by  the  formula  Fe003.  To  distinguish  them,  the  former  is 
usually  called  ferrous  oxide,  and  the  latter  ferric  oxide,  which,  combined 
with  water,  constitutes  ordinary  rust. 

The  black  oxide  usually  contains  one  molecule  of  each  oxide,  so  that 
it  would  be  written  FeO.Fe203,  or  Fe304.  It  is  powerfully  attracted 
by  the  magnet,  and  is  often  called  magnetic  oxide  of  iron.  The 
abundant  magnetic  ore  of  iron,  of  which  the  loadstone  is  a  variety,  has 
a  similar  composition. 

Iron  in  a  very  fine  state  of  division  takes  fire  spontaneously  in  air 
as  certainly  as  phosphorus  does.  Pyrophoric  iron  can  be  obtained  (by 


38  PKEPARATION  OF  OXYGEN. 

a  process  to  be  described  hereafter)  as  a  black  powder,  which  must  be 
preserved  in  sealed  tubes.  When  the  tube  is  opened,  and  its  contents 
thrown  into  the  air,  oxidation  occurs,  and  is  attended  with  a  vivid 
glow.  In  this  case  the  red  oxide  of  iron  is  produced  instead  ot  the 
black  oxide.  . 

Both  these  oxides  of  iron  are  capable  of  neutralising,  or  partly  net 
tralising,  acids,  and  are  therefore  basic  oxides  or  bases,  like  the  oxides 
of  zinc  and  sodium  obtained  in  previous  experiments.  So  general  is 
the  disposition  of  metals  to  form  oxides  of  this  class,  that  it  may  be 
regarded  as  one  of  the  distinguishing  features  of  a  metal,  for  no  non- 
metal  ever  forms  a  base  with  oxygen. 

(DEFINITION.— A  metal  is  an  element  capable  of  forming  a  base  by 
combining  with  oxygen.) 

Many  metals  are  capable  also  of  forming  anhydrides  with  oxygen  ; 
thus,  tin  forms  stannic  anhydride  (Sn02),  antimony  forms  antimonic 
anhydride  (Sb205),  and  it  is  always  found  that  a  metallic  anhydride 
contains  a  larger  proportion  of  oxygen  than  any  of  the  other  oxides 
which  the  metal  may  happen  to  form. 

27.  There  is  a  third  class  of  oxides,  termed  the  indifferent  oxides, 
because  they  are  neither  anhydrides  nor  bases ;  such  oxides  may  be  formed 
either  by  non-metals  or  metals  ;  thus  water  (H20),  the  oxide  of  hydrogen, 
is  an  indifferent  oxide,  and  the  black  oxide  of  manganese  (Mn02)  is  an 
example  of  an  indifferent  metallic  oxide. 

As  the  most  stable  compound  of  oxygen  with  hydrogen,  namely,  water, 
has  the  formula  OH2,  oxygen  is  the  type  of  the  divalent  elements  (p.  23). 

28.  Preparation  of  oxygen. — For  almost  all  the  useful  arts  in  which 
uncombined  oxygen  is  required,  the  diluted  gas  contained  in  atmospheric 
air  is  sufficient,  since  the  nitrogen  mixed  with  it  does  not  interfere  with 
its  action. 

From  atmospheric  air  pure  oxygen  was  first  obtained  by  Lavoisier 
towards  the  end  of  the  last  century.  His  process  is  far  too  tedious  to 
be  employed  as  a  general  method  of  preparing  oxygen,  but  it  affords  a 
very  good  example  of  the  relation  of  heat  to  chemical  action.  Some 
mercury  was  poured  into  a  glass  flask  with  a  long  narrow  neck,  which 
was  placed  on  a  furnace,  so  that  its  temperature  might  be  constantly 
maintained  at  about  349°  C.  (660°  F.)  for  twelve  days.  The  mercury 
boiled,  and  a  portion  of  it  was  converted  into  vapour,  which  condensed 
in  the  neck  of  the  flask  and  ran  back  again.  Eventually  part  of  the 
mercury  was  converted  into  a  dark  powder,  which  became  red  on 
cooling,  having  combined  with  the  oxygen  of  the  air  (or  undergone 
oxidation)  to  form  the  red  oxide  of  mercury. 

By  heating  this  oxide  of  mercury  to  a  temperature  approaching,  a  red 
heat  (about  500°  C.  or  1000°  F.)  it  is  decomposed  into  mercury  and 
oxygen  gas  (HgO  =  Hg  +  O). 

It  is  very  generally  found,  as  in  this  instance,  that  heat  of  moderate 
intensity  favours  the  operation  of  chemical  attraction,  whilst  a  more 
intense  heat  annuls  it. 

For  the  purpose  of  experimental  demonstration,  the  decomposition  of  the  oxide 
of  mercury  may  be  conveniently  effected  in  the  apparatus  represented  by  Fig.  30, 
where  the  oxide  is  placed  in  the  hard  glass  tube  A,  and  heated  by  the  gas-burner 
B,  the  metallic  mercury  being  condensed  in  the  bend  C  and  the  oxygen  collected 
in  the  gas  cylinder  D,  filled  with  water,  and  standing  upon  the  bee-hive  shelf  of 


PEEPAEATION  OF  OXYGEN.  39 

the  pneumatic  trough  E.  It  may  be  identified  by  its  property  of  kindling  into 
flame  the  spark  left  at  the  end  of  a  wooden  match.  If  the  heat  be  continued  for  a 
sufficient  length  of  time,  the  whole  of  the  oxide  of  mercury  will  disappear,  being 
resolved  into  its  elements.  In  technical  language,  the  mercury  is  said  to  be  reduced. 
Upon  the  first  application  of  heat  the  red  oxide  suffers  a  physical  change,  in  conse- 
quence of  which  it  becomes  black  ;  but  its  red  colour  returns  again  if  it  be  allowed 
to  cool. 


Fig.  30. — Preparation  of  oxygen  from  oxide  of  mercury. 

This  method  of  obtaining  unmixed  oxygen  from  the  air  is  much  too  costly  to 
be  employed  on  a  large  scale. 

Brings  process  for  preparing  oxygen  from  the  air  depends  upon  the  facts  that 
when  barium  oxide  (BaO)  is  heated  in  air  it  combines  with  oxygen,  forming 
barium  dioxide  (Ba02),  and  that  when  this  latter  is  heated  more  strongly,  or 
under  diminished  pressure,  it  gives  up  oxygen,  again  becoming  BaO,  thus  : — 
(i)  BaO  +  0  =  Ba02;  (2)  Ba02  =  BaO  +  0.  The  original  barium  oxide  is  used 
again. 

Air  (purified  from  carbon  dioxide)  is  pumped  under  pressure  (10  Ibs.  per  square 
inch)  through  retorts  containing  the  barium  oxide,  heated  at  700°  C.  ;  when  the 
issuing  gas  is  no  longer  approximately  pure  nitrogen,  the  air  current  is  stopped 
and  the  residual  nitrogen  in  the  retorts  is  pumped  out  until  the  pressure  has 
fallen  to  about  2  Ibs.  per  square  inch.  The  barium  dioxide  then  gives  off  much 
of  its  oxygen,  which  is  collected  in  a  gasholder.  The  cycle  of  operations  is 
repeated. 

Another  process  which  has  been  used  depends  upon  the  principle  that  the  oxides 
of  manganese,  when  heated  in  contact  with  alkalies  and  air,  are  capable  of  absorb- 
ing the  oxygen  from  the  air,  and  of  subsequently  giving  it  up  again  if  heated  in  a 
current  of  steam. 

To  illustrate  this  process,  about  four  ounces  of  dry  sodium  manganate  (which 
may  be  purchased  cheaply  in  a  crude  state)  are  introduced  into  a  porcelain  tube  * 
(£,  Fig.  31)  fixed  in  a  furnace.  One  end  of  the  tube  is  connected  with  a  two-branched 
glass  tube,  so  that  either  a  current  of  air  may  be  passed  through  it  by  the  tube  #, 
or  a  current  of  steam  from  the  flask  w.  On  heating  the  manganate  in  the  tube  to 
dull  redness,  and  passing  the  steam  over  it,  oxygen  is  evolved,  and  may  be  collected 
in  the  jar  o.  2Na2Mn04  +  2H20  =  4NaHO  +  Mn203  +  03. 

Sodium  Manganese 

mauganate.  CaustlC  soda'      sesquioxide. 

If  the  current  of  steam  be  discontinued  and  the  air  be  slowly  passed  through 
the  tube  «,  the  oxygen  of  the  air  will  be  absorbed,  and  its  nitrogen  may  be 
collected  in  the  jar  n.  4NaHO  +  Mn203  +  3(0  +  N4)  =  2Na2Mn04  +  2H20  +  N12. 

Air. 

If  the  proper  temperature  be  employed,  the  stream  of  gas  issuing  from  the  tube 
may  be  constantly  kept  up,  and  may  be  made  to  consist  of  oxygen  or  nitrogen 
accordingly  as  steam  or  air  is  passed  through  the  tube.  The  current  of  air  is 
regulated  by  the  nipper-tap  <?. 

The  gas-furnace  represented  in  Fig.  31  consists  of  a  row  of  twelve  Bunsen  burners 
each  having  a  stop-cock  by  which  the  flame  is  regulated.  The  horizontal  pipe  &, 

*  A  copper  tube  with  screw-caps,  into  which  narrow  brass  or  copper  tubes  are  brazed  may 
be  advantageously  substituted  for  the  porcelain  tube.  The  process  is  much  facilitated  by 
mixing  the  manganate  of  soda  with  an  equal  weight  of  oxide  of  copper. 


40  PREPARATION  OF  OXYGEN. 

from  which  they  spring,  is  capable  of  being  raised  or  lowered  at  pleasure  The 
porcelain  tube  t  is  laid  in  a  semi-cylindrical  trough  made  of  stout  iron  rods,  and 
filled  with  pieces  of  pumice-stone  or  fire-brick.  Above  this  is  placed  a  correspond- 
ing trough,  so  that  the  tube  is  entirely  surrounded  by  glowing  material.  The  heat 
must  be  applied  gradually  to  avoid  splitting  the  tube. 


Fig.  31. — Extraction  of  oxygen  from  air. 

Oxygen  is  now  obtained  approximately  free  from  nitrogen  by  a 
physical  method  which  takes  advantage  of  the  fact  that  nitrogen  has  a 
lower  boiling-point  than  oxygen,  so  that  when  the  temperature  of  liquid 
air  (p.  74)  is  slowly  raised  the  nitrogen  boils  away  before  the  oxygen. 

29.  The  only  other  natural  source  from  which  it  has  been  found  con- 
venient to  prepare  pure  oxygen,  is  a  black  mineral  composed  of  manga- 
nese and  oxygen.  It  is  found  in  some  parts  of  England,  but  much 
more  abundantly  in  Germany  and  Spain,  whence  it  is  imported  for  the 
use  of  the  bleacher  and  glassmaker.  Its  commercial  name  is  manga- 
nese, but  it  is  known  to  chemists  as  binoxide  of  manganese  or  manganese 
dioxide  (Mn02),  and  to  mineralogists  by  several  names  designating 
different  varieties.  The  most  significant  of  these  names  is  pyrolusite, 
referring  to  the  facility  with  which  it  may  be  decomposed  by  heat 
(TTUJO,  fire,  and  Xvw,  to  loosen). 

One  of  the  cheapest  methods  of  preparing  oxygen  consists  in  heating 
small  fragments  of  this  black  oxide  of  manganese  in  an  iron  retort, 
placed  in  a  good  fire,  the  gas  being  collected  in  jars  filled  with  water, 
and  standing  upon  the  shelf  of  the  pneumatic  trough,  or  in  a  gas- 
holder *r  gas-bag,  if  large  quantities  are  required. 

The  attraction  existing  between  manganese  and  oxygen  is  too  power- 
ful to  allow  the  metal  to  part  with  the  whole  of  its  oxygen  when  heated, 
so  that  only  one-third  of  the  oxygen  is  given  off  in  the  form  of  gas,  a 
brown  oxide  of  manganese  being  left  in  the  retort :  tMnO9  = 
Mn304  +  02. 

30.  By  far  the  most  convenient  source  of  oxygen,  for  general  use  in 
the  laboratory,  is  the  artificial  salt  called  chlorate  of  potash,  or  potassium 
chlorate,  which  is  largely  manufactured  for  fireworks,  percussion-cap 
composition,  &c.  If  a  few  crystals  of  this  salt  be  heated  in  a  test- 
tube  over  a  spirit  lamp  (Fig.  32)  they  soon  melt  (360°  C.)  to  a  clear  liquid, 


PREPARATION   OF   OXYGEN.  41 

which  presently  begins  (400°   C.)  to  boil  from  the  disengagement  of 

bubbles  of  oxygen,  easily  recognised  by  introducing  a  match  with  a 

spark  at  the  end  into  the  upper  part 

of  the  tube.      If   the   action   of    heat 

is   continued   until    no    more    oxygen 

is   given  off,   the  residue    in  the  tube 

is  the  salt  termed  potassium  chloride ; 


KCKX 


KC1 


Potassium     Potassium 
chlorate.       chloride. 


or 


To  ascertain  what  quantity  of  oxygen  would 
be  furnished  by  a  given  weight  of  the  chlorate, 
the  atomic  weights  must  be  brought  into  use. 
Referring  to  the  table  of  atomic  weights,  it  is 
found  that  K  =  39,  0  =  16  and  Cl  =  35.5  ;  hence 
the  molecular  weight  of  potassium  chlorate  is 
•easily  calculated. 

One  atomic  weight  of  potassium 

„  „  chlorine 

Three  atomic  weights  of  oxygen 


Fig'.  32. 


39 

35-5 
48 


KC103=  122.5 
So  that  122.5  grams  of  chlorate  would  yield  48  grams  of  oxygen. 

Since  16  grams  of  oxygen  (more  accurately  15.88)  measure  ii.n  litre?  (p.  32), 
the  48  grams  will  measure  33.33  litres. 

Hence  it  is  found  that  122.5  grams  of  potassium  chlorate  would  give  33.33 
litres  of  oxygen  measured  at  o°  C.  and  760  mm.  Bar. 

Since  the  complete  decomposition  of  the  potassium  chlorate  requires 
a  more  intense  heat  than  a  glass  vessel  will  usually  endure,  it  is  cus- 
tomary to  mix  the  chlorate  with  about  one-fifth  of  its  weight  of 
powdered  black  oxide  of  manganese,  when  the  whole  of  the  oxygen  is 
given  off  at  a  comparatively  low  temperature  (about  360°  C.),  though 
the  oxide  of  manganese  itself  suffers  no  change,  and  its  action  has  not 
yet  received  any  explanation  which  is  quite  satisfactory. 

Fig.  33  shows  a  very  convenient  arrangement  for  preparing  and  collecting 
oxygen  for  the  purpose  of  demonstrating  its  relations  to  combustion.  A  is  a 


Fig.  33. — Preparation  of  oxygen, 

Florence  flask  in  which  the  glass  tube  B  is  fixed  by  a  perforated  cork.  C  is  a 
tube  of  vulcanised  india-rubber.  The  gas-jar  is  filled  with  water,  and  supported 
upon  a  bee-hive  shelf.  If  pint  gas-jars  be  employed,  20  grams  of  potassium 


42  SYNTHESIS   OF  WATER. 

chlorate,  mixed  with  4  grams  of  binoxide  of  manganese,  will  furnish  a  sufficient 
supply  of  gas  for  the  ordinary  experiments.  The  binoxide  of  manganese  should  be 
thoroughly  dried  by  moderately  heating  it  in  a  crucible  before  being  mixed  with 
the  chlorate.  It  is  also  advisable  to  test  it  by  heating  a  little  of  it  with  the 
chlorate,  since  charcoal  and  sulphuret  of  antimony,  which  form  very  explosive 
mixtures  with  chlorate  of  potash,  have  sometimes  been  sold  by  mistake  for  bin- 
oxide  of  manganese.  The  heat  must  be  moderated  according  to  the  rate  at  which 
the  gas  is  evolved,  and  the  tube  C  must  be  taken  out  of  the  water  before  the  lamp 
is  removed,  or  the  contraction  of  the  gas  in  cooling  will  suck  the  water  back  into 
the  flask.  The  first  jar  of  gas  will  contain  the  air  with  which  the  flask  was  filled 
at  the  commencement  of  the  experiment.  The  oxygen  obtained  will  have  a  slight 
smell  of  chlorine. 

WATER. 

H20  — 18  grams  —  z  volumes  (vapour). 

31.  Synthesis  of  water  from  its  elements. — It  has  been  seen  already 
(p.  30)  that  the  combination  of  hydrogen  with  oxygen  to  form  water 
is  attended  with  great  evolution  of  heat  and  consequent  expansion,  and 
hence  the  mixture  of  these  gases  is  found  to  explode  violently  on  con- 
tact with  flame. 

The  experiment  may  be  made  safely  in  a  soda-water  bottle  (old  form).  The 
bottle  is  filled  with  water,  and  inverted  with  its  mouth  beneath  the  surface  of  the 
water  ;  enough  oxygen  is  then  passed  up  into  it  to  one-third  of  its  volume  ;  if  the 
remainder  of  the  water  is  then  displaced  by  hydrogen,  and  the  mouth  of  the  bottle 
presented  to  the  flame  of  a  spirit-lamp,  a  very  violent  explosion  occurs,  attended 
with  a  vivid  blue  flash  in  the  bottle.  If  the  mouth  of  the  bottle  be  presented 
towards  a  screen  of  paper,  at  a  distance  of  20  or  30  inches,  the  paper  will  be 
violently  torn  to  pieces,  bearing  witness  to  the  concussion  between  the  expanded 
steam  issuing  from  the  bottle  and  the  external  air. 

If  some  of  the  mixture  of  oxygen  with  twice  its  volume  of  hydrogen  be  intro- 
duced into  a  jar  provided  with  a  stop-cock  to  which  is  attached  a  piece  of 
caoutchouc  tubing  and  a  small  glass  tube,  and  if  the  jar  be  pressed  down  in  a 


34- 


35- 


trough  of  water,  soap-bubbles  may  be  inflated  with  the  gas,  and  these  will  ascend 
rapidly  in  the  air,  and  explode  violently  when  touched  with  a  flame,  which  must 
not,  of  course,  be  applied  to  the  bubble  until  it  is  at  some  distance  away,  from  the 
tube,  for  fear  of  exploding  the  mixture  in  the  jar. 

The  mixture  of  2  volumes  H  and  I  volume  0  explodes  when  heated  to  600°  C 
but  it  may  be  exposed  to  a  temperature  of  over  1000°  C.  without  the  occurrence  of 


CAVENDISH  EUDIOMETER. 


43 


any  combination  if  it  be  carefully  dried,  by  freshly  distilled  phosphoric  anhy- 
dride, in  the  dark.  The  precaution  to  exclude  light  is  essential  because  the  moist 
gases  combine  even  at  the  ordinary  temperature  when  exposed  to  light,  and 
although  the  combination  is  extremely  slow,  the  amount  of  water  produced  thereby 
is  sufficient  to  ensure  explosion  at  600°  C.* 

Contact  with  finely  divided  platinum  starts  the  combination  of  H  and  0  at  the 
ordinary  temperature,  and  a  red  hot  platinum  wire  causes  even  the  dried  gases  to 
explode.  Electric  sparks  also  explode  the  dried  gases. 

32.  In  order  to  demonstrate  the  production  of  water  in  the  explosion,  the 
Cavendish  eudiometer -\  (Fig.  34)  is  employed.  This  is  a  strong  glass  vessel,  with  a 
stopper  firmly  secured  by  a  clamp  (A),  and  provided  with  two  platinum  wires  (P), 
which  pass  through  the  stopper,  and  approach  very  near  to  each  other  within  the 
eudiometer,  so  that  the  electric  spark  may  easily  be  passed  between  them.  By 
screwing  the  stop-cock  B  into  the  plate  of  an  air-pump,  the  eudiometer  may  be 
exhausted.  It  is  then  screwed  on  to  the  jar  represented  in  Fig.  35,  which  contains 
a  mixture  of  two  measures  of  hydrogen  with  one  measure  of  oxygen,  standing  over 
water.  On  opening  the  stop-cocks  between  the  two  vessels,  the  eudiometer 
becomes  filled  with  the  mixture,  and  the  quantity  which  has  entered  is  indicated 
by  the  rise  of  water  in  the  jar.  The  glass  stop-cock  C  having  been  closed  to 
prevent  the  brass  cap  from  being  forced  off  by  the  explosion,  the  eudiometer  is 
again  screwed  on  to  its  foot,  and  an  electric  spark  passed  between  the  platinum 
wires,  either  from  a  Ley  den  jar  or  an  induction  coil,  when  the  two  gases  will 
combine  with  a  vivid  flash  of  light,*  attended  with  a  very  slight  concussion,  but 
no  noise,  since  there  is  no  collision  with  the  external  air.  For  an  instant  a  mist 
is  perceived  within  the  eudiometer,  which  condenses  into  fine  drops  of  dew,  con- 
sisting of  the  water  formed  by  the  combination  of  the  gases,  which  was  here 
induced  by  the  high  temperature  of  the  electric  spark,  as  it  was  in  the  former 
experiment  by  the  high  temperature  of  the  flame.  If  the  gases  have  been  mixed 
in  the  exact  proportion  of 
two  measures  of  hydrogen 
to  one  measure  of  oxygen, 
the  eudiometer  will  now  be 
again  vacuous,  and  if  it  be 
screwed  on  to  the  capped 
jar,  may  be  filled  a  second 
time  with  the  mixture, 
which  may  be  exploded  in 
the  same  manner. 

The  entire  disappearance 
of  the  gases  may  be  rendered 
obvious  to  the  eye  by  ex- 
ploding the  mixture  over 
mercury.  For  this  purpose 
the  mixed  gases  should  be 


-.  36. — Detonating  gas  collected  from  voltameter. 


collected  from  water  itself,  which  is  strongly  acidified  with  sulphuric  acid,  and 
decomposed  in  the  voltameter  (A,  Fig.  36)  by  the  aid  of  five  or  six  cells  of  Grove  s 
battery.  The  voltameter  contains  two  platinum  plates  (B),  attached  to  the 
platinum  wires  C  and  D.  which  are  connected  with  the  opposite  poles  of  the 
battery.  The  first  few  bubbles  of  the  mixture  of  hydrogen  and  oxygen  evolved 
having  been  allowed  to  escape,  in  order  to  displace  the  air,  the  gas  may  be  collected 
in  the  small  eudiometer  (E),  which  has  been  previously  filled  with  water.  This 
eudiometer  is  a  cylinder  of  very  thick  glass,§  closed  at  one  end,  and  having  two 
stout  platinum  wires  cemented  into  holes  drilled  near  the  closed  end,  the  wires 
approaching  sufficiently  near  to  each  other  to  allow  the  passage  of  the  electric 
spark.  Having  been  filled  with  the  mixture  of  hydrogen  and  oxygen  from  tl 

*  In  these  experiments  very  pure  electrolytic  gas  made  by  electrolysing  a  solution  of 
purified  barium  hydroxide  was  used. 

•f  So  named  from  evSios,  fine  or  clear,  and  ^rpov,  a  measure,  because  an  instrument  upon 
the  same  principle  has  been  used  to  determine  the  degree  of  purity  of  the  atmosphere.     . 
eudiometer  was  employed  by  Cavendish  about  the  year  1770,  for  the  synthesis  of  water. 

t  Since  the  steam  produced  at  the  moment  of  combination  is  here  prevented  from  expana- 
ing,  the  heat  which  would  have  expanded  it  is  saved,  so  that  the  temperature  is  higher  and 
the  flash  of  light  brighter  than  when  the  combination  is  effected  in  an  open  vessel. 

§  The  bore  of  the  eudiometer  should  be  about  half  an  inch  in  diameter,  and  the  thicknes 
of  its  sides  about  gths  of  an  inch  ;  its  length  is  7  inches. 


44 


EUDIOMETRIC  ANALYSIS   OF  AIE, 


voltameter,  the  eudiometer  is  closed  with  the  finger,  and  transferred  to  a  basin 
containing  mercury,  where  it  is  pressed  firmly  down  upon  a  stout  cushion  of  india- 
rubber,  and  the  spark  passed  through  the  mixed  gases,  either  from  the  coil  or  the 
Leyden  jar.  The  combustion  occurs  with  violent  concussion,  but  without 
noise  ;  and  since  the  eudiometer  is  vacuous  after  the  gases  have  combined,  the 
cushion  will  be  found  to  be  very  firmly  pressed  against  its  open  end.  On  loosening 
the  cushion,  the  mercury  will  be  violently  forced  up  into  the  eudiometer,  which 
will  be  completely  filled  with  it,  proving  that  when  an  electric  spark  is  passed 
through  the  mixture  of  2  volumes  of  hydrogen  and  I  volume  of  oxygen,  no  residue 
of  gas  remains. 

This  may  also  be  demonstrated  with  the  siphon  eudiometer,  shown  in  Fig.  37,  by 
confining  about  a  cubic  inch  of  the  explosive  mixture  in  the  closed  limb,  over 
water,  and  stopping  the  open  limb  securely  with  a  cork,  so  as  to  leave  a  space  filled 
with  air  between  the  cork  and  the  water.  The  eudiometer  must  be  very  firmly 
fixed  on  a  stand,  or  it  will  be  broken  by  the  concussion.  After  it  has  been  proved, 
it  may  be  held  in  the  hand,  as  in  the  figure.  By  firing  mixtures  of  hydrogen  and 
oxygen,  in  different  proportions,  in  the  same  manner,  it  may  be  shown  that  any 
excess  of  either  gas  above  the  ratio  of  2H  :  0  will  remain  uncombined  after 
the  explosion.  Care  is  required  in  these  experiments,  since  eudiometers  are  often 
burst  by  the  explosion  of  the  mixture  of  2  volumes  of  hydrogen  with  i  volume  of 
oxygen. 

The  explosion  and  the  flash  of  light  in  the  foregoing  experiments  are  both  the 
results  of  the  heat  generated  in  the  act  of  combination  ;  so  that  the  water  produced 
represents  so  much  less  energy  as  corresponds  with  the  heat  given  off  in  the  com- 
bination. This  heat  has  been  measured  by  means  of  a  calorimeter,  and  it  has  been 
found  that  2  grams  of  H  and  16  grams  of  0,  in  combining  to  form  liquid  water, 
generate  enough  heat  to  raise  68,924  grams  of  water  from  o°  C.  to  i°  C.  Of  this 
quantity,  9666  represent  the  heat  generated  by  the  change  of  state  from  the  gas  to 
the  liquid,  so  that  the  difference,  59.258,  represents  the  heat  generated  by  the 
chemical  action  occurring  between  2  grains  of  hydrogen  and  16  grains  of  oxygen 
in  forming  18  grams  of  water  in  the  state  of  gas.  This  may  be  expressed  by 
H2  +  0  =  H20  +  59,258  heat-units,  the  heat-unit  being  the  quantity  of  heat  required 
to  raise  the  temperature  of  I  gram,  of  water  from  o°  C.  to  i°  C. 

The  quantity  of  heat  produced  in  any  chemical  action  is  a  measure  of  the  amount 
of  chemical  energy  which  is  exerted.  To  decompose  18  grams  of  steam  we  must 
employ  an  amount  of  energy,  in  the  form,  for  example,  of  electricity,  corresponding 
with  59,258  heat-units.  (See  chapter  on  General  Principles.) 

33.  The  knowledge  of  the  volumes  in  which  hydrogen  and  oxygen 
combine,  is  turned  to  account  in  the  analysis  of  gases,  to  ascertain  the 
proportion  of  hydrogen  or  oxygen  contained  in  them.  Suppose,  for 
example,  it  be  required  to  determine  the  amount  of  oxygen  in  a 
sample  of  atmospheric  air ;  the  latter  is  mixed  with  hydrogen,  in 
more  than  sufficient  quantity  to  combine  with  the  largest  proportion 
of  oxygen  which  could  be  present,  and  when  the 
combination  has  been  induced  by  the  electric  spark, 
the  volume  of  gas  which  has  disappeared  (2 
volumes  H  + 1  volume  0)  has  only  to  be  divided 
by  three  to  give  the  volume  of  the  oxygen. 

A  bent  eudiometer  (Fig.  37)  may  be  used.    Having  been 
completely  filled  with  water  (previously  boiled  to  expel 
dissolved  air),  it  is  inverted  in  the  trough,  and  the  specimen 
of  air  is  introduced  (say  10  c.c.).     The  open  limb  is  then 
closed  by  the  thumb,  and  the  eudiometer  turned  so  as  to 
transfer  the  air  to  the  closed  limb.     A  stout  glass  rod  is 
thrust  down  the  open  limb,  so  as  to  displace  enough  water 
to  equalise  the  level  in  both   limbs,   in  order  that  the 
volume  of  the  air  may  not  be  diminished  by  the  pressure 
™in         *  +1,    •     i  A  A  °-f  ?   ^igher  column  of  water  in  the  open   limb.      The 
volume  of  the  included  air  having  been  accurately  noted,  the  open  limb  of  the  tube 
again  filled  up  with  water,  inverted  in  the  trough,  and  a  quantity  of  hydrogen 
introduced,  equal  to  about  half  the  volume  of  the  air.     This  having  been  trans- 


Fig-  37-— Siphon 
eudiometer. 


SYNTHESIS  OF  STEAM. 


45 


ferred,  as  before,  to  the  closed  limb,  the  columns  of  water  are  again  equalised,  and 
the  volume  of  the  mixture  of  air  and  hydrogen  ascertained.  The  open  limb  is  now 
firmly  closed  with  the  thumb,  and  the  electric  spark  passed  through  the  mixture, 
either  from  the  Leyden  jar  or  the  induction-coil.  On  removing  the  thumb,  after 
the  explosion,  the  volume  of  gas  in  the  closed  limb  will  be  found  to  have  diminished 
very  considerably.  Enough  water  is  poured  into  the  open  limb  to  equalise  the 
level,  and  the  volume  of  gas  is  observed.  If  this  volume  be  subtracted  from  the 
volume  before  explosion,  the  volume  of  gas  which  has  disappeared  will  be  ascer- 
tained, and  one-third  of  this  will  represent  the  oxygen,  which  has  condensed  with 
twice  its  volume  of  hydrogen  into  the  form  of  water.  Thus  the  numbers  recorded 
will  be— 

Volume  of  air  analysed 10  c.c. 


Volume  of  air  mixed  with  hydrogen 
After  explosion 


Difference 


\ 

/  ...     6.0,, 

6  divided  by  3  =  2  c.c.  of  oxygen. 

In  exact  experiments,  a  correction  would  be  required  for  any  variation  of  the 
temperature  or  barometric  pressure  during  the  progress  of  the  analysis. 

34.  It  will  have  been  observed,  in  the  experiment  upon  the  synthesis 
of  water  in  the  Cavendish  eudiometer,  that  the  volume  of  water  obtained 
is  very  small  in  comparison  with  that  of  the  gases  before  combination, 
about  1870  volumes  of  the  mixed  gases  being  required  to  form  one 
volume  of  liquid  water,  because  after  the  chemical  attraction  has  caused 
the  molecules  of  H  and  O  to  form  steam,  the  cohesive  attraction  has 
caused  the  molecules  of  steam  to  unite  and  form  liquid  water.  In  order 
to  watch  the  effect  of  the  chemical  attraction  only,  we  must  prevent  the 
steam  from  changing  its  state  after  it  is  produced. 

If  the  mixture  of  hydrogen  and  oxygen  be  measured  and  exploded  at 
or  above  the  boiling-point  of  water,  it  is 
found  that  the  steam  produced  occupies 
two-thirds  of  the  volume  of  the  mixed 
gases,  measured  at  the  same  temperature 
and  atmospheric  pressure.  Hence,  two 
volumes  of  hydrogen  combine  with  one 
volume  of  oxygen  to  form  two  volumes  of 
aqueous  vapour,  at  the  same  temperature  and 
pressure* 

The  combination  of  hydrogen  and  oxygen  in 
a  vessel  heated  to  the  boiling-point  of  water  is 
effected  in  the  apparatus  shown  in  Fig.  38,  where 
the  closed  limb  of  the  eudiometer  is  surrounded 
by  a  tube  into  which  steam  is  passed  from  a  flask 
connected  with  the  wide  tube  by  a  cork  and  a 
short  wide  piece  of  bent  glass  tubing,  jacketed 
with  caoutchouc  to  prevent  loss  of  heat.  The 
steam  escapes  through  the  tube  (£)  which  enters 
the  cork  at  the  bottom.  The  closed  limb  of  the 
eudiometer  having  been  filled  with  mercury,  a 
small  quantity  of  the  mixture  of  hydrogen  and 
oxygen  obtained  from  the  voltameter  (Fig.  36)  is  introduced  into  it  through  a  tube 
passed  down  the  open  limb,  the  displaced  mercury  being  run  out  through  the  tube  <?, 
which  is  closed  by  a  nipper-tap.  The  closed  limb  is  then  heated  by  the  steam,  and 
the  mercury  in  the  two  limbs  levelled  from  time  to  time  by  running  a  little  out 
through  c,  until  the  gas  in  the  closed  limb  no  longer  expands.  Its  volume  is  then 
*  The  latest  researches  show  that  the  exact  volume  ratio  is  2.0024  H  :  i  0. 


Fig-.  38. — Synthesis  of  water 
at  100°  C. 


46 


SYNTHESIS   OF  WATER  BY  WEIGHT. 


observed,  an  inch  more  mercury  poured  into  the  open  limb,  which  is  then  tightly 
closed  by  a  cork,  and  the  spark  from  the  induction-coil  (Fig.  8)  is  passed  by  the 
wires  -  and  +.  After  the  explosion,  the  cork  is  removed,  and  the  mercury 
levelled  in  the  two  limbs,  when  the  volume  of  the  steam  will  be  found  to  be 
just  two-thirds  of  the  volume  of  the  gas  before  the  explosion.  On  cooling  down, 
the  steam  condenses,  and  the  mercury  entirely  fills  the  closed  limb  of  the 
eudiometer. 

That  2  volumes  of  steam  should  contain  2  volumes  of  hydrogen  and 
i  volume  of  oxygen  would  appear,  on  physical  grounds,  impossible,  since 
two  bodies  cannot  occupy  the  same  space  at  the  same  time ;  but  it  must 
be  remembered  that  the  two  bodies  in  question  have  lost  their  individu- 
ality in  consequence  of  their  chemical  combination  by  which  they  have 
become  one  body — water. 

35.  The  synthesis  of  water  by  weight  is  difficultly  effected  with 
accuracy  by  weighing  the  gases  themselves,  on  account  of  their  large 
volume.  It  is  therefore  accomplished  by  passing  an  indefinite  quantity 
of  hydrogen  over  a  known  weight  of  pure  hot  oxide  of  copper,  when 
the  hydrogen  combines  with  the  oxygen  of  the  oxide  to  form  water. 
The  loss  of  weight  suffered  by  the  oxide  of  copper  gives  the  amount  of 
oxygen ;  and  if  this  be  deducted  from  the  weight  of  the  water,  that  of 
the  hydrogen  will  be  ascertained.  In  this  way  it  is  shown  that  water 
contains  8  parts  of  oxygen  to  every  i  part  of  hydrogen.* 

The  apparatus  employed  for  this  purpose  is  represented  in  Fig.  39.  li  is  the 
bottle  in  which  hydrogen  is  generated  from  diluted  sulphuric  acid  and  zinc  ;  the 
gas  passes,  in  p,  through  solution  of  potash,  which  absorbs  any  sulphuretted 
hydrogen  ;  then  through  s,  containing  pumice-stone  (used  on  account  of  its  porous 
character),  saturated  with  a  strong  solution  of  silver  nitrate,  which1  removes 


Fig.  39.— Synthesis  of  water  by  weight. 

arsenic  and  antimony  from  the  hydrogen  ;  the  gas  then  passes  through  vv,  contain- 
ing pumice  saturated  with  oil  of  vitriol  to  absorb  moisture.  The  bulb  c,  with  the 
oxide  of  copper,  is  weighed  before  and  after  the  experiment,  as  are  the  globe  a,  for 
condensing  the  water,  and  the  tube  t,  containing  pumice  and  oil  of  vitriol,  to 
absorb  the  aqueous  vapour.  Of  course  the  bulb  o  must  not  be  heated  until  the 
hydrogen  has  displaced  all  the  air  from  the  apparatus. 

As  an  example,  10  grams  of  CuO  were  employed,  and  7.98  grams  Cu  were 
left,  2.2725  grams  water  being  collected.  10-7.98  =  2.02  grams  0-  2272;- 
2.02  =  0.2525  grams  H  ;  2.2725  :  2.02  :  :  100  :  88.88  ;  2.2725  :  0.2525  :  :  100  :  ii.ii. 
100  parts  by  weight  of  water,  therefore,  contain  88.88  0  and  ii.n  H.  This  is 
the  usual  method  of  stating  the  composition  of  a  substance.  To  deduce  the 
chemical  formula,  we  must  divide  each  constituent  by  its  atomic  weight  • 
88.88  -r  16  =  5.5  atomic  weights  of  0;  II.II-M  =  II.II  atomic  weights  of  H.  Then 
5.55  :  1 1. ii  :  :  i  atom  0  :  2  atoms  H. 

I  The  above  experiment  would  also  serve  for  fixing  the  atomic  weight  of  copper 

for  it  shows  that  100  parts  by  weight  of  cupric  oxide  contains  79.8  parts  of  copper 

and  20.2  parts  of  oxygen.    Then  20.2  :  79.8  :  :  16  :  63.2  ;  so  that  if  cupric  oxide 

*  The  latest  value  for  this  ratio  is  7.94  O  :  i  H. 


FORMULA  FOE  WATER.  47 

contains  one  atom  of  copper  to  one  atom  of  oxygen,  the  atomic  weight  of  copper 
would  be  63.2. 

35«.  A  volume  of  steam  is  found  to  weigh  9  times  as  much  as  an 
equal  volume  of  hydrogen  weighs  at  the  same  temperature  and  pres- 
sure. Now,  evidence  (the  value  of  which  will  be  better  appreciated 
after  more  experimental  facts  have  been  described)  has  been  gathered, 
from  both  the  chemical  and  physical  study  of  gases,  that  equal  volumes 
of  gases  measured  at  the  same  temperature  and  pressure  contain  the  same 
number  of  molecules  (Avogadro's  Law).  It  follows  that  the  number  of 
times  that  a  volume  of  one  gas,  A,  is  heavier  than  a  volume  of  another 
gas,  B,  is  also  the  number  of  times  that  each  molecule  in  A  is  heavier 
than  each  molecule  in  B.*  Consequently  the  molecule  of  steam  weighs 
9  times  as  much  as  the  molecule  of  hydrogen ;  but  the  molecule  of 
hydrogen  contains  2  atoms,  and  therefore  weighs  two  units,  so  the 
molecule  of  steam  must  weigh  1 8  units.  It  is  by  similar  reasoning  that 
that  the  molecular  weights  of  all  gases  are  decided.  (See  Introduction.) 

It  will  now  be  understood  that  the  formula  for  a  compound  is  deter- 
mined both  by  a  quantitative  analysis  or  quantitative  synthesis  of  the 
compound,  and  by  ascertaining  its  specific  gravity  when  H  =  i  (its 
vapour  density). 

A  quantitative  synthesis  of  water  shows  that  it  contains  H  and  0  in 
the  proportion  of  i  :  8 ;  a  determination  of  its  vapour  density  shows 
that  its  molecular  weight  is  18  ;  hence  its  formula  must  be  H20,  which 
is  in  agreement  with  the  proportion  i  :  8  (2  :  16),  and  with  the  molecular 
weight  1 8  (2  -r  1 6). 

It  has  been  seen  (p.  24)  that  one  gram  of  hydrogen  occupies  (at 
standard  temperature  and  pressure)  1 1 . 1 1  litres,  so  that  2  grams  occupy 
22.22  litres.  As  the  molecular  weight  of  a  gas  is  the  number  of 
times  that  it  is  heavier  than  2  unit  weights  of  hydrogen,  it  follows  that  the 
molecular  weight  of  any  gas  expressed  in  grams  occupies  22.22  litres  at 
standard  temperature  and  pressure. 

36.  It  is  evident  that,  although  hydrogen  is  generally  designated  the 
combustible  gas,  and  oxygen  the  supporter  of  combustion,  the  applica- 
tion of  these  terms  depends  entirely  upon  circumstances,  since  the 
phenomenon  of  combustion  is  a  reciprocal  operation  in  which  both  ele- 
ments have  an  equal  share. 

This  may  be  illustrated  by  a  simple  experiment.  The  hydrogen  and  oxygen 
reservoirs,  H  and  O,  Fig.  40,  are  connected  with  two  bent  glass  tubes  passing 
through  a  cork  into  an  ordinary  lamp  glass  <?,  upon  the  upper  opening  of  which  a 
plate  of  talc  is  laid.  In  order  to  prevent  the  ends  of  the  glass  tubes  from  being 
fused  by  the  burning  gases,  little  platinum  tubes,  made  by  rolling  up  pieces  of 
platinum  foil,  are  placed  in  the  orifices,  and  the  glass  is  melted  round  them 
by  the  blowpipe  flame.  The  hydrogen  being  lighted,  and  the  oxygen  turned  on  to 
about  the  same  extent,  the  lamp-glass  is  placed  over  the  cork,  when  the  hydrogen 
burns  steadily.  If  the  oxygen  be  slowly  turned  off,  the  flame  will  gradually  leave 
the  hydrogen  tube  and  come  over  to  the  oxygen,  which  will  continue  burning  in  the 
atmosphere  of  hydrogen.  By  again  turning  on  the  oxygen,  the  flame  may  be  sent 
over  to  the  hydrogen  tube.  With  a  little  care  the  flame  may  be  made  to  occupy 
an  intermediate  position  between  the  two  burners,  and  to  leap  from  one  to  the  other 
at  pleasure.  The  experiment  may  also  be  performed  with  coal  gas  and  oxygen. 

*  This  is,  of  course,  only  true  if  all  the  molecules  in  a  gas  have  each  the  same  weight. 
There  is  no  reason  to  suppose  that  the  molecules  of  any  one  gas  differ  appreciably  from  each 
other  in  weight,  but  even  if  they  did  the  ai-gument  would  be  true  of  the  mean  weight  of  each 
molecule,  i.e.,  the  weight  of  the  gas  divided  by  the  number  of  molecules  in  it. 


48  THE  OXYHYDROGEN  BLOWPIPE. 

37  The  great  energy  with  which  hydrogen  combines  with  oxygen  is 
turned  to  account  for  the  purpose  of  producing  very  high  temperatures 
(about  2500°  C.) 

The  ox'uJiydrogen  blowpipe  (Fig.  41)  is  an  apparatus  for  burning  a  jet  of  hydro- 
gen mixed  with  half  its  volume  of  oxygen.  The  gases  are  supplied  from  separate 
gas-holders  (or  bags  with  pressure-boards  and  weights)  through  the  tubes  Hand 
0,  which  conduct  them  into  the  brass  sphere  B.  Each  of  these  tubes  is  provided 
with  a  valve  of  oiled  silk  opening  outwards,  so  as  to  prevent  the  passage  of  either 
gas  into  the  receptacle  containing  the  other.  The  tube  A  is  stuffed  with  thin 
copper  wires,  which  would  rapidly  conduct  away  the  heat  and  extinguish  the 


Fig.  41. — Oxyhydrog-en  blowpipe. 


Fig.  40. — Reciprocal  combustion. 

flame  of  the  mixed  gases  burning  at  the  jet,  should  it  tend  to  pass  back  and 
ignite  the  mixture  in  B.  The  stop-cocks  D  and  E  allow  the  flow  of  the  gases  to 
be  regulated  so  that  they  may  mix  in  the  right  proportions.  If  the  hydrogen  be 
kindled  first,  it  will  be  found  that,  as  soon  as  the  oxygen  is  turned  on,  the  flame  is 
reduced  to  a  very  much  smaller  volume,  because  the  undiluted  oxygen  required  to 
maintain  it  occupies  only  one-fifth  of  the  volume  of  the  atmospheric  air,  from 
which  the  hydrogen  was  at  first  supplied  with  oxygen.  The  heat  developed  by 
the  combustion  being  therefore  distributed  over  a  much  smaller  area,  the  tem- 
perature at  any  given  point  of  the  flame  must  be  much  higher,  and  very  few  sub- 
stances are  capable  of  enduring  it  without  fusion.*  Lime  is  one  of  these  ;  and  if  a 
cylinder  of  lime  be  supported,  as  at  L  (Fig.  41),  in  the  focus  of  the  flame,  its  particles 
become  heated  to  incandescence,  and  a  light  is  obtained  which  is  visible  at  night 
from  very  great  distances,  so  as  to  be  well  adapted  for  signalling  and  lighthouses. 
For  such  purposes  coal-gas  is  often  used  instead  of  hydrogen  (oxycalcium  or 
Dritmmond  light). 

If  a  shallow  cavity  be  scooped  in  a  lump  of  quicklime,  a  few  scraps  of  platinum 
placed  in  it,  and  exposed  to  the  oxyhydrogen  flame  (Fig.  42),  a  fused  globule  of 
platinum  of  very  considerable  size  may  be  obtained  in  a  few  seconds.  By  em- 
ploying a  furnace  made  of  lime,  platinum  is  fused  in  quantities  sufficient  to,  cast 
large  ingots,  a  result  unattainable  by  any  other  furnace  heated  by  combustion. 
Pipeclay,  which  resists  the  action  of  all  ordinary  furnace-heats,  may  be  fused  into 
a  glass  in  this  flame,  whilst  gold  and  silver  are  instantaneously  melted,  and  vaporised 
into  a  dense  smoke. 

*  The  temperature  of  the  hydrogen  flame  in  air  is  about  2000°  C.,  while  in  oxygen  it  is 
over  2500°.  The  last  temperature  could  not  be  surpassed,  because  it  is  that  at  which  steam 
is  dissociated  or  resolved  into  its  elements,  which  re-combine  as  soon  as  the  temperature  falls 
below  that  point. 


OCCLUSION  OF  HYDROGEN.  49 

38.  In  its  chemical  relations  to  other  elements,  hydrogen  is  diametri- 
cally opposed  to  oxygen.  Whereas  the  latter  combines  directly  with  the 
greater  number  of  the  elements,  hydrogen  will  enter  into  direct  com- 
bination with  very  few ;  all  the  metals  form  compounds  with  oxygen,, 
but  very  few  combinations  of  metals  with  hydrogen  have  been  obtained.. 
Indeed,  in  its  relations  to  other  elements,  hydrogen  closely  resembles 
the  metals,  though  it  does  not  fall  within  the  definition  of  a  metal  given 
above,  since  it  does  not  form  a  base  with  oxygen,  and  its  combinations, 
with  the  salt  radicles  (chlorine,  &c.)  are  acids,  and  not  salts,  as  is  the 
case  with  metals. 

Hydrogen  is  absorbed,  or  occluded,  by  many  metals  to  a  greater  extent  than  are 
most  other  gases,  and  by  palladium  more  than  by  any  other  metal.  This  pheno- 
menon of  occlusion,  which  may  be  compared  with  that  of  solution,  generally  occurs 
more  readily  when  the  metal  is  heated,  and  allowed  to  cool,  in  the  gas  ;  when 
treated  in  this  way  hammered  palladium  absorbs  some  600  times  its  volume  of 
hydrogen,  though  fused  palladium  does  not  absorb  so  much.  When  a  metal 
containing  occluded  gas  is  strongly  heated  (particularly  in  a  vacuum  or  in  an 
atmosphere  of  another  gas),  the  occluded  gas  is  given  off,  just  as  a  gas  dissolved  in 
water  is  expelled  when  the  solution  is  heated.  Palladium  absorbs  most  hydrogen 
when  it  is  used  as  the  cathode  in  an  electrolytic  cell  containing  dilute  acid  (p.  14). 
In  this  case  the  metal  may  take  up  about  900  times  its  volume,  and  in  doing  so  it 
increases  about  1.5  per  cent,  in  length.  This  expansion  forms  the  basis  of  experi- 
mental methods  for  demonstrating  the  occlusion.  A  palladium  wire  (24  inches)  is 
passed  through  the  bottom  cork  of  a  vertical  glass  tube,  containing  dilute  sulphuric 
acid,  and  is  there  made  fast ;  the  other  end  of  the  wire  is  attached  to  a  long  rod, 
pivoted  horizontally  to  serve  as  an  index.  The  wire  is  attached  to  the  zinc  of  a 
Grove's  battery,  the  platinum  of  the  battery  being  attached  to  a  platinum  wire 
which  also  passes  through  the  glass  tube.  During  the  electrolysis  of  the  dilute 
sulphuric  acid,  the  index  descends,  showing  that  the  wire  is  increasing  in  length  ; 
the  non-recovery  of  the  index  when  the  electrolysis  is  stopped  shows  that  the 
expansion  was  not  a  mere  thermal  effect. 

It  has  been  supposed  that  the  palladium  saturated  with  hydrogen  is  a  compound 
of  the  formula  Pd3H2.*  The  hydrogenised  palladium  is  a  far  more  active  reducing 
agent  than  is  free  hydrogen,  for  it  reduces  chlorates  to  chlorides  and  nitrates  to 
nitrites.  If  the  whole  of  the  hydrogen  be  regarded  as  being  occluded,  its  specific 
gravity  in  this  condition  would  be  0.62,  and  its  atomic  heat  5.88.  The  absorption 
of  i  gram  of  hydrogen  by  palladium  black  evolves  4370  gram  units  of  heat.  At 
atmospheric  pressure  no  absorption  of  hydrogen  by  palladium  occurs  above  145°  C., 
but  at  higher  pressures  the  absorption  occurs  at  much  higher  temperatures. 

39.  Chemical  relations  of  water  to  other  substances. — In  its  chemical 
relations  water  presents  this  very  remarkable  feature,  that,  although  it 
is  an  indifferent  oxide,  its  combining  tendencies  extend  over  a  wider 
range  than  those  of  any  other  compound.  Its  combinations  with  other 
substances  are  generally  called  hydrates.  Water  combines  with  two  of 
the  elementary  substances,  viz.,  chlorine  and  bromine,  but  no  other 
element  is  even  dissolved  by  water  in  any  considerable  quantity.  Oxygen, 
hydrogen,  and  nitrogen  are  dissolved  by  water,  in  very  small  quantity, 
but  become  only  mechanically  diffused  through  it,  and  do  not  enter 
into  chemical  combination. 

When  water  attacks  a  compound  body,  it  may  do  so  in  one  of  two 
ways  :  (i)  A  simple  solution  may  be  effected.  In  this  case  any  chemi- 
cal combination  which  may  occur  between  the  compound  and  the  water 
is  of  so  loose  a  nature  that  it  is  possible  to  recover  the  compound  un- 
changed by  merely  evaporating  the  water.  (2)  The  water  may  combine 

*  The  term  hydrogenium,  applied  by  Graham  to  the  hydrogen  occluded  by  palladium,  on 
the  supposition  that  it  existed  merely  in  a  state  of  condensation  in  the  metal,  must  be  aban- 
doned if  the  existence  of  this  compotind  be  admitted. 

D 


50  DISSOLUTION  IN  WATER. 

with  the  compound  to  produce  a  new  compound  of  such  stability  that 
the  original  substance  cannot  be  recovered  by  mere  evaporation.  The 
new  compound  may  then  pass  into  simple  solution. 

It  might  at  first  be  thought  that  simple  solution  was  only  a  physical 
phenomenon,  since  there  is  no  permanent  alteration  in  the  properties  of 
the  dissolved  substance.  This  view  would  be  supported  by  the  obser- 
vation that  when  a  solid  is  dissolved,  there  is  a  reduction  of  tempera- 
ture, such  as  is  always  noticed  in  the  merely  physical  change  from  the 
solid  to  the  liquid  form  ;  and  that  when  a  gas  is  dissolved  there  is  a  rise 
of  temperature  such  as  is  noticed  when  a  gas  passes  to  the  liquid  form. 
When  careful  measurements  are  made,  however,  it  is  found  that  the 
thermal  change  involved  in  the  dissolution  cannot  be  entirely  accounted 
for  by  the  physical  change  of  state.  Consequently  it  must  be  allowed 
that  chemical  combination  is  concerned  in  the  process  of  dissolution 
although  the  most  obvious  relations  produced  are  of  a  physical  nature. 
At  this  juncture  attention  will  be  called  to  the  principal  facts  concern- 
ing solution,  a  discussion  of  the  deductions  to  be  drawn  from  them 
being  for  the  present  postponed. 

When  common  saltpetre  (nitre  or  nitrate  of  potash)  is  shaken  with 
water,  it  is  rapidly  dissolved,  the  water  becoming  sensibly  colder.  If 
fresh  portions  of  saltpetre  are  added  till  the  water  is  unable  to  dissolve 
any  more,  it  is  found  that  100  grams  of  water  (at  60°  F.)  have  dissolved 
about  30  grams  of  saltpetre.  Such  a  solution  is  a  cold  saturated  solution 
of  saltpetre.  If  the  solution  be  set  aside  in  an  open  vessel,  the  water 
will  slowly  pass  off  in  vapour,  and  the  saltpetre  will  be  gradually 
deposited,  its  particles  arranging  themselves  in  the  regular  geometrical 
shape  of  the  six-sided  prism,  which  is  its  common  crystalline  form. 
The  crystals  of  saltpetre  do  not  contain  any  water  ;  they  are  anhydrous. 

If  saltpetre  is  added  to  boiling  water,  and  stirred  (with  a  glass  rod) 
until  the  water  refuses  to  dissolve  any  more,  100  grams  of  water  is  found 
to  have  dissolved  about  200  grams ;  this  is  a  hot  saturated  solution. 

As  a  general  rule,  solids  are  dissolved  more  quickly  and  in  larger 
quantity  by  hot  water  than  cold. 

One  of  the  commonest  methods  of  crystallising  a  solid  substance 
consists  in  dissolving  it  in  hot  water  and  allowing  the  solution  to 
cool  slowly.  The  more  slowly  it  cools,  the  larger  and  more  symmetrical 
are  the  crystals. 

A  hot  saturated  solution  is  not  generally  the  best  for  crystallising, 
because  it  deposits  the  dissolved  body  too  rapidly.  Thus  the  hot 
solution  of  saltpetre  prepared  as  above  would  solidify  to  a  mass  of 
minute  crystals  on  cooling;  but  if  100  grams  of  saltpetre  be  dissolved 
in  120  c.c.  of  boiling  water,  it  will  form  crystals  of  2  or  3  inches  long 
when  slowly  cooled  (in  a  covered  vessel).  If  the  solution  be  stirred 
while  cooling,  the  crystals  will  be  very  minute,  having  the  appearance 
of  a  white  powder. 

Some  solids,  however,  refuse  to  crystallise,  even  from  a  hot  saturated 
solution,  if  it  be  kept  absolutely  undisturbed. 

Sodium  sulphate  affords  a  good  example  of  this.  If  the  crystallised  sulphate  be 
added  to  boiling  water  in  a  flask,  as  long  as  it  is  dissolved,  the  water  will  take  into 
solution  more  than  twice  its  weight  of  the  salt,  yielding  a  solution  which  boils  at 
220°  F.  (104. 5°  C.).  If  this  solution  be  allowed  to  cool  in  the  open  flask,  an  abundant 
crystallisation  will  occur,  for  cold  water  dissolves  only  about  one-third  of  its  weight 
of  crystallised  sulphate.  But  if  the -flask  (which  should  be  globular)  be  tightly 


SUPERS ATUEATED   SOLUTIONS.  51 

corked  whilst  the  solution  is  boiling,  it  may  be  kept  for  several  days  without 
crystallising,  although  moved  about  from  one  place  to  another.  In  this  condition 
the  solution  is  said  to  be  super-saturated.  On  withdrawing  the  cork,  the  air  enter- 
ing the  partly  vacuous  space  above  the  liquid  will  be  seen  to  disturb  the  surface 
slightly,  and  from  that  point  beautiful  prismatic  crystals  will  shoot  through  the 
liquid  until  the  whole  has  become  a  nearly  solid  mass.  A  considerable  elevation 
of  temperature  is  observed,  consequent  upon  the  passage  from  the  liquid  to  the 
solid  form.  If  the  solution  of  sodium  sulphate  be  somewhat  weaker,  containing 
exactly  two-thirds  of  its  weight  of  the  crystals,  it  may  be  cooled  without  crystallis- 
ing, even  in  vessels  covered  with  glass  plates,  but  a  touch  with  a  glass  rod  will  start 
the  crystallisation  immediately. 

The  crystallisation  of  a  supersaturated  solution  is  provoked  by  contact  with  a 
crystal  of  the  salt  itself.  Minute  crystals  of  sodium  sulphate  are  present  in  th  e 
floating  dust  of  the  air,  and  cause  the  crystallisation  when  they  fall  into  the 
supersaturated  solution.  A  perfectly  clean  glass  rod  may  be  dipped  into  the 
liquid  without  causing  crystallisation,  but  a  rod  which  has  been  exposed  to  air 
will  have  some  particles  of  sodium  sulphate  on  it,  and  will  start  crystallisation  ;  if 
the  rod  be  heated  so  as  to  render  the  sodium  sulphate  from  the  dust  anhydrous,  it 
will  no  longer  cause  crystallisation  unless  it  be  drawn  through  the  hand.  Air 
filtered  through  cotton-wool  does  not  cause  supersaturated  solutions  to  crystallise. 
If  the  solution  of  sodium  sulphate  containing  two-thirds  of  its  weight  of  the  crystals 
be  allowed  to  cool  in  a  flask  closed  by  a  cork  furnished  with  two  tubes  plugged  with 
cotton-wool,  it  will  be  found  that,  on  withdrawing  the  plugs  and  blowing  through 
one  of  the  tubes  dipping  into  the  solution,  no  crystallisation  occurs  ;  but  if  air  be 
blown  by  a  pair  of  bellows  into  the  same  solution,  it  will  crystallise  at  once. 

Sodium  hyposulphite  (thiosulphate)  and  sodium  acetate  yield  supersaturated 
solutions  which  are  less  likely  to  be  crystallised  by  dust  than  the  sodium  sul- 
phate. If  a  warm  supersaturated  solution  of  sodium  acetate  be  very  carefully 
poured  upon  a  cold  supersaturated  solution  of  sodium  hyposulphite,  in  a  narrow 
cylinder,  which  is  then  covered  and  allowed  to  cool,  a  crystal  of  the  hyposulphite 
may  be  dropped  in  without  causing  crystallisation  till  it  reaches  the  lower  layer 
of  hyposulphite  solution  ;  a  crystal  of  sodium  acetate  may  then  be  dropped  in  to 
start  the  crystallisation  of  the  upper  layer. 

Supersaturated  solution  of  sodium  acetate  is  used  in  railway  foot-warmers, 
where  the  heat  evolved  in  the  crystallisation  renders  it  four  times  as  efficacious 
as  the  same  volume  of  hot  water. 

A  most  beautiful  illustration  of  the  power  of  unfiltered  air  to  start  crystallisation 
is  afforded  by  a  solution  of  alum  which  has  been  dissolved  in  half  its  weight  of 
water  at  194°  F.  (90°  C.)  and  allowed  to  cool  in  a  flask,  the  mouth  of  which  is  closed 
by  a  plug  of  cotton-wool.  In  this  state  it  may  be  kept  for  weeks  without  crystal- 
lising, but.  on  withdrawing  the  plug,  crystallisation  will  be  seen  to  start  at  a  few 
points  on  the  surface  immediately  under  the  opening  of  the  neck,  and  will  spread 
slowly  from  these,  octahedral  crystals  of  alum  of  half  an  inch  or  more  in  diameter 
being  built  up  in  a  few  seconds,  the  temperature,  at  the  same  time,  rising  very 
considerably. 

In  the  laboratory,  stirring  is  always  resorted  to  in  order  to  induce  crystallisa- 
tion, if  it  does  not  occur  spontaneously.  Thus  it  is  usual  to  test  for  potassium  in 
a  solution  by  adding  tartaric  acid,  which  should  cause  the  formation  of  minute 
crystals  of  hydro-potassium  tartrate  (cream  of  tartar),  but  the  test  seldom  succeeds 
unless  the  solutions  are  briskly  stirred  together  with  a  glass  rod.  An  amusing 
illustration  of  this  is  afforded  by  pouring  a  solution  of  tartaric  acid  into  a  solution 
of  saltpetre,  and  allowing  the  clear  mixture  to  run  over  a  large  plate  of  glass. 
Letters  traced  on  the  glass  with  the  finger  will  now  be  rendered  visible  by  the 
deposition  of  the  crystals  of  the  tartrate  upon  the  glass. 

39A.  Every  crystal  may  be  referred  to  one  of  comparatively  few  types,  although 
the  identification  of  the  parent  form  of  a  crystal  is  not  always  easy,  and  is  an  art 
in  itself,  known  as  crystallography. 

The  classification  of  crystals  is  based  on  the  symmetry  of  their  faces  around  a 
plane  or  an  axis  drawn  through  the  crystal.  A  plane  of  symmetry  in  a  geometrical 
form  is  a  plane  dividing  the  form  in  such  a  manner  that  the  two  parts  have  the 
relationship  of  object  and  image  to  each  other.  When  a  crystal  is  turned  round  on 
a  certain  axis,  it  must  be  rotated  through  a  certain  angle  before  it  appears  again 
of  the  same  form  to  the  observer  ;  accordingly  as  the  rotation  is  through  £,  £,  £  or 
£  of  360°,  the  crystal  is  said  to  have  a  2-,  3-,  4-,  or  6-fold  axis  of  symmetry. 


cj  2  CRYSTALS. 

The  following  are  the  principal  fundamental  forms,  and 
figures  are  indicated  in  Fig.  43  by  corresponding  numbers  : 
from  an  acute-angled  parallelopipedon  and  devoid  of  symmetry. 
having  one  plane  of  symmetry  and  derived  from  a  parallelopipedon  witl 
singular  and  two  acute-angled  faces.     (3)  Rkomtic,  derived  from 
parallelopipedon.  and  having  two  planes  of  symmetry  at  right  angles  to  et 
(4)  Quadratic,  having  a  four-fold  axis  of  symmetry,  and  derived  from  a  lect 
angular  parallelopipedon  with  a  square  base.     (5)  Trigonal,  having  a  1 three-fo Id 
axis  of  symmetry,  and  derived  from  a  right  triangular  prism,     (b)  MexaV"^ 
having  a  six-fold  axis  of  symmetry,  and  derived  from  a  right  hexagonal  pi  ism 
(7)  Regular,  derived  from  the  cube,  and  having  three  two-fold  axes  of  symmetry 
at  right  angles  to  each  other. 


Fig'.  43. — Forms  of  crystals. 

40.  Crystals  of  sodium  sulphate  contain,  in  a  state  of  combination 
with  the  salt,  more  than  half  their  weight  of  water.  Their  composi- 
tion is — 

Anhydrous  sodium  sulphate  (Na2S04)  142  parts,  or  one  molecule  ; 
Water 180     „      or  ten  molecules, 

as  expressed  by  the  formula  Na2S04.  ioH20.  If  the  crystals  are  left 
exposed  to  the  air,  they  gradually  effloresce,  or  become  covered  with  a 
white  opaque  powder.  This  powder  is  the  anhydrous  sodium  sulphate 
into  which  the  entire  crystals  would  ultimately  become  converted  by 
exposure  to  air.  Since  most  crystals  containing  water  have  their 
crystalline  form  destroyed  or  modified  by  the  loss  of  the  water,  it  is 
commonly  spoken  of  as  water  of  crystallisation. 

Coloured  salts,  containing  water  of  crystallisation,  generally  change 
colour  when  the  water  is  removed.  The  sulphate  of  copper  (blue  stone] 
affords  an  excellent  example  of  this.  The  beautiful  blue  prismatic 
crystals  of  this  salt  contain — 

Anhydrous  sulphate  of  copper  (CuS04)  159.5  parts,  or  one  molecule  : 
Water 90         „       or  five  molecules, 

as  expressed  by  the  formula  CuS04-5H20. 


WATER   OF   CRYSTALLISATION   AND   CONSTITUTION.  53 

When  these  are  exposed  to  the  air  at  the  ordinary  temperature  they 
remain  unchanged  •  but  if  heated  to  the  boiling-point  of  water  they 
become  opaque,  a^  may  be  easily  crumbled  down  to  a  nearly  white 
powder.  This  powder  contains — 

Anhydrous  sulphate  of  copper  (CuS04)  159.5  parts,  or  one  molecule  ; 
Water        .     % 18        .,      or  one  molecule, 

and  would  therefore  be  represented  by  CuS04.H.,O.  The  four  molecules 
of  water,  which  have  been  expelled,  constituted  the  water  of  crystallisa- 
tion, upon  which  the  form  and  colour  of  the  sulphate  of  copper  depend. 
When  the  white  powder  is  moistened  with  water,  combination  occurs 
with  great  evolution  of  heat, 'and  the  blue  colour  is  reproduced.  The 
one  molecule  of  water  which  still  remains  is  not  expelled  until  the  salt 
is  heated  to  390°  F.  (199°  0.),  proving  that  it  is  held  to  the  sulphato 
of  copper  by  a  more  powerful  chemical  attraction.  On  this  account  it 
is  spoken  of  as  water  of  constitution,  and,  in  order  that  the  formula  of 
the  salt  may  exhibit  the  difference  between  the  water  of  constitution 
and  of  crystallisation,  it  is  usually  written  CuS04.H,0.4Aq.  (Aqua, 
water.) 

(DEFINITION. — Water  of  crystallisation  of  salts  is  that  which  is  gene- 
rally expelled  at  212°  F.  (100°  C.),  and  is  connected  with  the  form  and 
colour  of  the  crystals.  Water  of  constitution  is  not  generally  expelled  at 
212°  F.,  and  is  in  more  intimate  connection  with  the  chemical  properties 
of  the  salt.) 

Several  of  the  so-called  sympathetic  inks  employed  for  writings  which  are 
invisible  until  heated,  depend  upon  the  change  of  colour  produced  by  loss  of 
water  of  crystallisation.  Characters  written  with  a  weak  solution  of  cobalt 
chloride  and  allowed  to  dry,  are  very  nearly  invisible,  since  the  pink  colour  of  so 
small  a  quantity  of  the  salt  is  scarcely  noticed  :  but  on  warming  the  paper,  the 
pink  hydrated  chloride  of  cobalt  (CoCl2.6Aq)  loses  water  of  crystallisation,  and  the 
blue  chloride  with  one  molecule  of  water  is  produced.  On  exposure  to  air  this 
again  absorbs  water,  and  the  writing  fades  away. 

Some  salts  have  so  great  a  tendency  to  combine  with  water  that  they 
become  moist  or  deliquesce  when  exposed  to  air.  This  deliquescence  is 
exhibited  in  a  marked  degree  by  calcium  chloride  and  its  great  attrac- 
tion for  water  is  turned  to  advantage  in  drying  air  and  other  gases  by 
passing  them  through  tubes  filled  with  the  salt. 

Nearly  all  salts  appear  to  combine  with  water  at  very  low  temperatures  :  such 
compounds,  which  are  decomposed  at  temperatures  above  o°  C.,  have  been  termed 
cryo-liydrates  (/c/>yos,  frost).  Common  salt  combines  with  ice  to  form  the  cryo- 
hydrate  NaCl.ioAq,  which  remains  liquid  down  to  -  20°  C.  Hence  arises  the  use 
of  crushed  ice  and  salt  as  a  freezing  mixture,  for  just  as  ice  alone,  in  melting, 
lowers  the  temperature  to  o°  C.,  the  melting-point  of  ice,  so  the  compound  of  ice 
and  NaCl,  in  melting  lowers  the  temperature  to  about  -  20°  C.,  the  melting-point 
of  the  cryo-hydrate. 

41.  Most  bases  are  capable  of  combining  with  water  to  form  hydrates, 
as  exemplified  in  the  slaking  of  lime.  Anhydrous  lime  or  quick-lime 
(CaO),  when  wretted  with  water,  combines  with  it,  evolving  much  heat, 
and  crumbling  to  a  loose  bulky  powder,  which  is  hydrate  of  lime  or  slake  " 
lime  (CaO.H20).  This  affords  an  example  of  the  second  mode  of  att 
referred  to  above ;  for  some  of  the  lime  passes  into  solution  when  muc 
water  is  used,  but  the  original  quick-lime  cannot  be  recovered  by  me: 
evaporating  the  water.  At  a  red  heat,  however,  the  water  is  expell 
and  anhydrous  lime  remains. 


54 


WELL,   SPRING  AND  RIVER  WATERS. 


CO 

I- 

du 
•th 


42.  Since  several  hydrates  do  not  yield  water   when    heated,    the 
hydrate  of  a  metal  is  defined  as  a  compound  formed^by  the  exchange  of 
a  part  of  the  hydrogen  in  water  for  a  metal  :  thut^gpota^sium  hydrate 
KOH  is  formed  from  water  HOH  by  the  exchange  of  H  for  K  :  calcium 
hydrate  Ca(OH),  is  formed  from  two  molecules  of  water  (HOH)2  by 
the  exchange   of  H2   for  (^iad)   calcium.     The  imaginary  group  OH, 
hydroxyl,  would  then  be  the  radicle  of  ike  hydrate^,  which  are  often 
termed  hydroxides. 

43.  Water  from  natural  sources.  —  Pure  water  is  not  found  in  nature. 
Rain  is  the  purest  form  of  natural  water,  but  contains  certain  gases  which 
it  collects  from  the  atmosphere  during  $s  fall.     As  soon  as  it  reaches 
the  earth  it  begins  to   dissolve  small  portions   of   the  various  solid 
materials  with  which  it  comes  in  contact,  and  thus  becomes  charged 
with  salts  and  other  substances  to  an  extent  varying,  of  course,  with 
the  nature  of  the  soils  and  rocks  which  it  has  touched,  and  attaining 
its  highest  point  in  sea  water,  which  contains  a  larger  proportion  of 
saline  matters  than  water  from  any  other  natural  source. 

If  a  quantity  of  rain,  spring,  river,  or  sea  water  be  boiled  in  a  flask 
furnished  with  a  tube  also  filled  with  the  water,  and  passing  under  a 
gas  cylinder  standing  in  a  trough  of  the  same  water  (Fig.  44),  it  will  be 
found  to  give  off  a  quantity  of  gas  which  was  previously  held  in  solution 
by  the  water,  and  is  now  set  free  because  gases  are  less  soluble  in  hot 

than  in  cold  water.  Tne 
quantity  of  this  gas  varies 
according  to  the  source  of  the 
water,  but  always  contains 
the  gases  existing  in  atmo- 
spheric air,  viz.,  nitrogen, 
oxygen,  and  carbonic  acid 
gas.  One  gallon  of  rain 
water  will  generally  furnish 
about  4  cubic  inches  of  nitro- 
gen, 2  cubic  inches  of  oxygen, 
and  i  cubic  inch  of  carbonic 
acid  gas.  It  is  worthy  of 
remark,  that  the  nitrogen 
and  oxygen  have  been  dis- 
solved by  the  water,  not  in 
the  proportions  in  which  they  exist  in  the  atmosphere,  but  in  the  pro- 
portions in  which  they  ought  to  be  dissolved,  if  it  be  true  that  they 
exist  in  the  air  in  the  condition  of  mere  mechanical  admixture.  The 
oxygen  thus  carried  down  from  the  air  by  rain  appears  to  be  service- 
able in  maintaining  the  respiration  of  aquatic  animals,  and  in  confer- 
ring upon  river  waters  a  self-purifying  power,  by  acting  upon  certain 
organic  matters  which  would  probably  prove  hurtful  to  animals,  and 
converting  them  into  harmless  products  of  oxidation.  In  the  cases 
t  rivers  contaminated  with  the  sewage  of  towns,  this  action  of  the 
laso  ved  oxygen  is  probably  of  great  importance.  The  carbonic  acid 
issolved  in  ram  water  also  probably  serves  some  useful  purposes  in 
he  chemical  economy  of  nature.  (See  Carbonic  Acid.) 


Fig.  44- 


Tk!  a  gaS  exPresses  the  volume  of  gas  absorbed  by  one 

I  water.     The  numbers  0.02989  and  0.01478  respectively  represent  the 


HARD  AND   SOFT  WATERS.  55 

volumes  of  oxygen  and  nitrogen  absorbed  by  one  volume  of  water,  when  exposed 
to  the  action  of  either  gas,  in  a  pure  state,  at  59°  F.  (15°  C.).  When  a  mixture  of 
gases  is  brought  into  contact  with  water,  the  proportions  in  which  the  gases  are 
absorbed  can  be  ascertained  by  multiplying  the  co-efficient  of  solubility  of  each 
gas  by  its  proportion  by  volume  in  the  mixture.  Thus,  when  water  is  exposed  to 
air,  containing  i  volume  of  oxygen  and  -f  volume  of  nitrogen,  the  quantities  dis- 
solved by  one  volume  of  water  are — 

Oxygen i  x  0.02989  —  0.00597, 

Nitrogen •     .    i  x  0.01478  =-  0.01182; 

or  almost  exactly  two  volumes  of  N  to  one  volume  of  0. 

44.  The  waters  of  wells,  springs,  and  rivers,  and  especially  those  of 
the  two  first-named  sources,  differ  very  much  from  each  other,  according 
to  the  nature  of  the  layers  of  rock  or  earth  over  or  through  which  they 
have  passed,  and  from  which  they  dissolve  a  great  variety  of  substances, 
some  familiar  to  us  in  daily  life,  others  only  met  with  in  chemical 
collections.  Under  the  former  head  may  be  enumerated  Glauber's  salt 
(sodium  sulphate),  common  salt  (sodium  chloride),  Epsom  salt  (mag- 
nesium sulphate),  gypsum  (calcium  sulphate),  chalk  (calcium  carbonate), 
common  magnesia  (magnesium  carbonate),  carbonic  acid,  and  silica. 

Among  the  substances  known  only  to  the  chemist  may  be  mentioned 
sulphuretted  hydrogen,  potassium  sulphate,  potassium  chloride,  calcium 
chloride,  magnesium  chloride,  phosphates,  bromides  and  iodides  of 
calcium  and  magnesium  (rarely),  aluminium  sulphate,  carbonate  of  iron 
(ferrous  carbonate),  and  certain  vegetable  substances.* 

The  well  waters  of  certain  localities  (as,  for  example,  those  of  large 
towns)  also  frequently  contain  salts  of  nitric  and  nitrous  acids,  and  of 
ammonia. 

The  waters  of  springs  and  rivers  do  not  differ  very  materially  from 
well  waters  as  to  the  nature  of  the  substances  which  they  contain, 
though,  in  the  case  of  river  waters  more  particularly,  the  quantity  of 
these  substances  is  materially  influenced  by  the  conditions  of  rapid 
motion  and  exposure  to  air  under  which  such  waters  are  placed. 

The  palatable  quality  of  a  water  is  largely  dependent  upon  the 
quantity  of  dissolved  gas  which  it  contains.  Thus,  a  water  which  is 
agreeable  for  drinking  will  become  insipid  after  it  has  been  boiled  and 
the  dissolved  air  in  this  way  expelled.  The  presence  of  dissolved  solid 
matter  in  the  water  also  influences  its  taste,  preference  being  generally 
expressed  for  those  waters  which  are  not  exceedingly  poor  in  such 
solids;  it  is  undesirable,  however,  that  the  quantity  should  exceed  35 
grains  per  gallon  (Thames  water,  as  supplied  to  the  metropolis,  contains 
about  22  grains  per  gallon).  A  decision  as  to  the  wholesomeness  of  a 
water,  or  as  to  its  fitness  for  feeding  boilers,  &c.,  can  be  given  by  the 
analyst  alone ;  the  considerations  which  influence  his  dictum  are  indi- 
cated in  the  following  statements. 

Household  experience  has  established  a  classification  of  the  waters 
from  natural  sources  into  soft  and  hard  waters — a  division  which  depends 
chiefly  upon  the  manner  in  which  they  act  upon  soap.  If  a  piece  of 
soap  be  gently  rubbed  in  soft  water  (rain  water,  for  example)  it  speedily 
furnishes  a  froth  or  lather,  and  its  cleansing  powers  can  be  readily 
brought  into  action  ;  but  if  a  hard  water  (spring  water)  be  substituted 
for  rain  water,  the  soap  must  be  rubbed  for  a  much  longer  time  before 

*  Although  it  is  certainly  known  that  the  acids  and  bases  capable  of  forming-  the  salts 
here  enumerated  may  be  detected  in  spring-  and  river  waters,  their  exact  distribution  amongst 
each  other  is  still  It  matter  of  uncertainty. 


56  CAUSE  OF  HARDNESS. 

a  lather  can  be  produced,  or  its  effect  in  cleansing  rendered  evident ;  a 
number  of  white  curdy  flakes  also  make  their  appearance  in  the  hard 
water,  which  were  not  seen  when  soft  water  was  used.  The  explanation 
of  this  difference  is  a  purely  chemical  one. 

Soap  is  formed  by  the  combination  of  a  fatty  acid  with  an  alkali ;  it  is 
manufactured  by  boiling  oil  or  fat  with  potash  or  soda,  the  former  for 
soft,  the  latter  for  hard  soaps.  In  the  preparation  of  ordinary  hard 
soap,  the  soda  takes  from  the  oil  or  fat  two  acids — stearic  and  oleic 
acid — which  exist  in  abundance  in  most  varieties  of  fat,  and  unites 
with  them  to  form  soap,  which  in  chemical  language  would  be  spoken 
of  as  a  mixture  of  stearate  and  oleate  of  sodium. 

If  soap  be  rubbed  in  soft  water  until  a  little  of  it  has  dissolved,  and 
some  Epsom  salts  (magnesium  sulphate)  be  dissolved  in  water,  and 
poured  into  the  soap  water,  curdy  flakes  will  be  produced,  as  when  soap 
is  rubbed  in  hard  water,  and  the  soap  water  will  lose  its  property  of 
frothing  when  stirred ;  the  magnesium  sulphate  has  decomposed  the 
soap,  forming  sodium  sulphate,  which  remains  dissolved  in  the  water, 
and  insoluble  curdy  flakes,  which  consist  of  stearate  and  oleate  of 
magnesium. 

Similar  to  the  effect  of  the  magnesium  sulphate  is  that  of  hard  waters  ; 
their  hardness  is  attributable  to  the  presence  of  the  different  salts  of 
calcium  and  magnesium,  all  of  which  decompose  the  soap  in  the  manner 
exemplified  above ;  the  peculiar  properties  of  the  soap  in  forming  a 
lather  and  dissolving  grease  can  therefore  be  manifested  only  when  a 
sufficient  quantity  has  been  employed  to  decompose  the  whole  of  the 
salts  of  calcium  and  magnesium  contained  in  the  quantity  of  water 
operated  on,  and  thus  a  considerable  amount  of  soap  must  be  rendered 
useless  when  hard  water  is  employed. 

On  examining  the  interior  of  a  kettle  in  which  spring,  well,  or  river 
water  has  been  boiled,  it  will  be  found  to  be  coated  more  or  less  thickly 
with  -a,  fur  or  incrustation,  generally  of  a  brown  colour,  and  the  harder 
the  water  the  more  speedily  will  this  incrustation  be  deposited.  A 
chemical  examination  shows  this  deposit  to  consist  chiefly  of  calcium  car- 
bonate (chalk)  in  the  form  of  minute  crystals,  which  may  be  discovered 
by  the  microscope ;  it  usually  contains,  in  addition,  some  magnesium  car- 
bonate, calcium  sulphate,  and  small  quantities  of  oxide  of  iron  (rust) 
and  vegetable  matter,  the  last  two  substances  imparting  its  brown 
colour.  In  order  to  explain  the  formation  of  this  deposit,  it  is  neces- 
sary to  become  acquainted  with  the  particular  condition  in  which  the 
calcium  carbonate  exists  in  natural  waters  ;  it  is  hardly  dissolved  to  any 
perceptible  extent  by  pure  water,  though  it  may  be  dissolved  in  con- 
siderable quantity  by  water  containing  carbonic  acid.  This  statement, 
which  is  of  great  importance  in  connection  with  natural  waters,  may 
be  verified  in  the  following  manner  :  A  little  slaked  lime  is  well  shaken 
up  in  a  bottle  of  distilled  or  rain  water,  which  is  afterwards  set  aside 
for  an  hour  or  two ;  as  soon  as  that  portion  of  the  lime  which  has  not 
been  dissolved  has  subsided,  the  clear  portion  is  carefully  poured  into  a 
glass,  and  a  little  soda  water  (a  solution  of  carbonic  acid  in  water)  is 
added  to  it ;  the  first  addition  of  the  carbonic  acid  to  the  lime  water 
causes  a  milkiness,  due  to  the  formation  of  minute  particles  of  calcium 
carbonate;  this  being  insoluble  in  the  water,  separates  from  it,  or 
precipitates,  and  impairs  the  transparency  of  the  liquid  ;  a  further 


BOILER  INCRUSTATIONS.  57 

addition  of  carbonic  acid  water  renders  the  liquid  again  transparent, 
for  the  carbonic  acid  dissolves  the  calcium  carbonate  which  has 
separated. 

If  this  clear  solution  be  introduced  into  a  flask,  and  boiled  over  the 
.spirit-lamp  or  gas-flame,  it  will  again  become  turbid,  for  the  free  car- 
bonic acid  will  be  expelled  by  the  heat,  and  the  calcium  carbonate  will 
be  deposited,  not  now,  however,  in  so  fine  a  powder  as  befere,  but  in 
small,  hard  grains,  which  have  a  tendency  to  fix  themselves  firmly  upon 
the  sides  of  the  flask,  and,  when  examined  by  the  microscope,  are  seen 
to  consist  of  small  crystals. 

In  a  similar  manner,  when  natural  waters  are  boiled,  the  carbonic 
.acid  gas  which  they  contain  is  expelled,  and  the  carbonates  of  calcium, 
magnesium,  and  iron  are  precipitated,  since  they  are  insoluble  in  water 
which  does  not  contain  carbonic  acid.  But,  by  the  ebullition  of  the 
water,  a  portion  of  it  has  been  dissipated  in  vapour,  and  if  there  be 
much  calcium  sulphate  present,  the  quantity  of  water  left  may  not  be 
sufficient  to  retain  the  whole  of  the  salt  in  solution  ;  calcium  sulphate 
requires  about  500  parts  of  cold  water  to  dissolve  it,  and  is  nearly 
insoluble  in  water  having  a  higher  temperature  than  212°  F.,  as  would 
be  the  case  in  boilers  worked  under  pressure,  so  that  it  would  readily 
be  deposited.  It  contributes  much  to  the  formation  of  compact  incrus- 
tations. Should  the  water  contain  much  vegetable  matter,  this  is  often 
deposited  in  an  insoluble  condition,  the  whole  eventually  forming  to- 
gether a  hard  compact  mass,  composed  of  successive  thin  layers,  on  the 
bottom  and  sides  of  the  vessel  in  which  the  water  has  been  boiled.  The 
^'furring"  of  a  kettle  is  objectionable,  chiefly  in  consequence  of  its 
retarding  the  ebullition  of  the  water,  since  the  deposit  is  a  very  bad 
conductor  of  heat,  and  therefore  impedes  the  transmission  of  heat  from 
the  fire  to  the  water ;  hence  the  common  practice  of  introducing  a 
round  stone  or  marble  into  the  kettle,  in  order,  by  its  perpetual  rolling, 
to  prevent  the  particles  of  calcium  carbonate  from  forming  a  compact 
layer.  In  steam  boilers,  however,  even  more  serious  inconvenience 
than  loss  of  time  sometimes  arises  if  this  deposit  be  allowed  to  accumu- 
late, and  to  form  a  thick  layer  of  badly  conducting  material  on  the 
bottom  of  the  boiler,  since  the  latter  is  then  liable  to  become  red  hot, 
and  to  collapse.  But  even  though  this  calamity  be  escaped,  the  wear 
and  tear  of  the  boiler  is  very  much  increased  in  consequence  of  the  for- 
mation of  this  deposit,  since  its  hardness  often  renders  it  necessary  to 
detach  it  with  the  hammer,  much  to  the  injury  of  the  iron  boiler-plates, 
which  are  also  subject  to  increased  oxidation  and  corrosion  in  con- 
sequence of  the  high  temperature  which  the  incrustation  permits  them 
to  attain  by  preventing  their  contact  with  the  water.  Moreover,  it  is 
obvious  that  a  greater  expenditure  of  fuel  is  requisite  in  order  to  heat 
the  water  through  such  a  non-conducting  "  boiler  scale."  Many  pro- 
positions have  been  brought  forward  for  the  prevention  of  these  in- 
crustations ;  some  substances  have  been  used,  of  which  the  action 
appears  to  be  purely  mechanical,  in  preventing  the  aggregation  of  the 
deposited  particles.  Clay,  sawdust,  and  other  matters  have  been 
employed  with  this  view  ;  but  the  action  of  sal  ammoniac  (ammonium 
chloride),  which  has  also  been  found  efficacious,  must  be  explained  upon 
purely  chemical  principles.  When  this  salt  is  boiled  with  calcium  car- 
bonate, mutual  decomposition  ensues,  producing  calcium  chloride  and 


58  TEMPORARY  AND  PERMANENT  HARDNESS. 

ammonium  carbonate,  of  which  salts  the  former  is  very  soluble  in  water, 
while  the  latter  passes  off  in  vapour  with  the  steam.  The  ammonium 
chloride,  however,  corrodes  the  metal  of  the  boiler.  Solutions  of  the 
caustic  alkalies,  of  alkaline  carbonates,  arsenites,  tannates,  &c.,  are  also 
occasionally  employed  to  prevent  the  formation  of  incrustations  in 
boilers,  and  probably  act  by  precipitating  calcium  carbonate  and  other 
calcium  compounds  which  act  as  nuclei,  around  which  the/wr  collects 
as  a  loose  deposit  or  mud. 

The  deposit  formed  in  boilers  fed  with  sea  water  consists  chiefly  of  calcium 
sulphate  and  magnesium  hydrate,  the  latter  produced  by  the  decomposition  of  the 
magnesium  chloride  present  in  sea  water.  As  hydrochloric  acid  is  another  product 
of  the  decomposition  of  magnesium  chloride  solution,  water  containing  any  con- 
siderable quantity  of  this  salt  is  liable  to  corrode  the  plates  of  a  boiler. 

The  incrustations  formed  in  cisterns  and  pipes  by  hard  water  are  also  produced 
by  the  carbonates  of  calcium  and  magnesium  deposited  in  consequence  of  the 
escape  of  the  free  carbonic  acid  which  held  them  in  solution.  Many  interesting 
natural  phenomena  may  be  explained  upon  the  same  principle.  The  so-called 
petrify  ing  springs,  in  many  cases,  owe  their  remarkable  properties  to  the  consider- 
able quantity  of  calcium  carbonate  dissolved  in  carbonic  acid  which  they  contain  ; 
when  any  object,  a  basket,  for  example,  is  repeatedly  exposed  to  the  action  of  these 
waters,  it  becomes  coated  with  a  compact  layer  of  the  carbonate,  and  thus  appears 
to  have  suffered  conversion  into  limestone.  The  celebrated  waters  of  the  Sprudel 
at  Carlsbad,  of  San-Filippo  in  Tuscany,  and  of  Saint  Allyre  in  Auvergne  are  the 
best  instances  of  this  kind. 

The  stalactites  and  stalagmites.*  which  are  formed  in  many  caverns  or  natural 
grottoes,  afford  beautiful  examples  of  the  gradual  separation  of  calcium  carbonate 
from  water  charged  with  carbonic  acid.  Each  drop  of  water,  as  it  trickles  through 
the  roof  of  the  cavern,  becomes  surrounded  with  a  shell  of  calcium  carbonate,  the 
length  of  which  is  prolonged  by  each  drop,  as  it  falls,  till  a  stalactite  is  formed, 
varying  in  colour  according  to  the  nature  of  the  substances  which  are  separated 
from  the  water  together  with  the  carbonate  (such  as  the  oxides  of  iron  and  vege- 
table matter)  ;  and  as  each  drop  falls  from  the  point  of  the  stalactite  upon  the 
floor  of  the  cavern,  it  deposits  there  another  shell,  which  grows,  like  the  upper  one, 
but  in  the  opposite  direction,  and  forms  a  stalagmite,  thus  adorning  the  grotto 
with  conical  pillars  of  calcium  carbonate,  sometimes,  as  in  the  case  of  the  oriental 
alabaster,  variegated  with  red  and  yellow,  and  applicable  to  ornamental  purposes. 

When  water  which  has  been  boiled  for  some  time  is  compared  with 
unboiled  water  from  the  same  source,  it  is  found  to  have  become  much 
softer,  and  this  can  now  be  easily  explained,  for,  a  considerable  portion 
of  the  salts  of  calcium  and  magnesium  having  separated  from  the  water, 
the  latter  is  not  capable  of  decomposing  so  large  a  quantity  of  soap. 
The  amount  of  hardness  which  is  thus  destroyed  by  boiling  is  generally 
spoken  of  as  temporary  hardness,  to  distinguish  it  from  the  permanent 
hardness  due  to  the  soluble  salts  of  calcium  and  magnesium  which  still, 
remain  in  the  boiled  water.  It  is  customary  with  analytical  chemists, 
in  reporting  upon  the  quality  of  natural  waters,  to  express  the  hardness 
by  a  certain  number  of  degrees  which  indicate  the  number  of  grains  of 
chalk  or  calcium  carbonate  which  would  be  dissolved  in  a  gallon  of 
water  containing  carbonic  acid,  in  order  to  render  its  hardness  equal 
to  that  of  the  water  examined  ;  that  is,  to  render  it  capable  of  decom- 
posing an  equal  quantity  of  soap.  Thus,  when  a  water  is  spoken  of  as 
having  16  degrees  of  hardness,  it  is  implied  that  16  grains  of  calcium 
carbonate  dissolved  in  a  gallon  of  water  containing  carbonic  acid,  would 
render  that  gallon  of  water  capable  of  decomposing  as  much  soap  as  a 
gallon  of  the  water  under  consideration. 

,  I  drop ;  trTaAa-yjua,  a  drop. 


CLAEK'S   PROCESS.  59 

The  utility  of  a  water  for  household  purposes  must  be  estimated 
therefore,  not  merely  according  to  the  total  number  of  degrees  of 
hardness  which  it  exhibits,  but  also  by  the  proportion  of  that  hardness 
which  may  be  regarded  as  temporary ;  that  is,  which  disappears  when 
the  water  is  boiled.  Thus,  the  total  hardness  of  the  New  River  water 
amounts  to  nearly  1 5  degrees,  that  of  the  Grand  Junction  Company  to 
14  degrees,  and  yet  these  waters  are  quite  applicable  to  household  uses, 
since  their  hardness  is  reduced  by  boiling  to  about  5  degrees.  It  has 
been  ascertained  that  every  degree  of  hardness  in  water  gives  rise  to  a 
waste  of  about  10  grains  of  soap  for  every  gallon  of  water  employed,  and 
hence  the  use  of  100  gallons  of  Thames  or  New  River  water  in  washing 
will  be  attended  with  the  loss  of  about  2  Ibs.  of  soap;  this  loss  is 
reduced,  however,  to  about  one-third  when  the  temporary  hardness  has 
been  destroyed  by  boiling.  The  addition  of  washing  soda  (sodium 
carbonate)  removes  the  permanent  hardness  due  to  the  presence  of  the 
sulphates  of  calcium  and  magnesium  in  the  water,  for  both  these  salts 
are  decomposed  by  the  sodium  carbonate  which  separates  the  calcium 
and  magnesium  as  insoluble  carbonates,  whilst  sodium  sulphate  remains 
dissolved  in  the  water.*  The  household  practice  of  boiling  the  water, 
and  adding  a  little  washing  soda,  is  therefore  very  efficacious  in  re- 
moving the  hardness.  Clark's  process  for  softening  waters  depends 
upon  the  neutralisation  of  the  free  carbonic  acid  contained  in  the  water 
by  the  addition  of  a  certain  quantity  of  lime ;  the  calcium  carbonate 
so  produced  separates  together  with  the  carbonates  of  calcium  and 
magnesium,  which  were  previously  retained  in  solution  by  the  free 
carbonic  acid ;  this  process,  therefore,  affects  chiefly  the  temporary 
hardness ;  moreover,  the  earthy  carbonates  which  are  separated  appear 
to  remove  from  the  water  a  portion  of  the  organic  matter  which  it 
contains,  and  thus  effect  a  very  important  purification.  The  water 
under  treatment  is  mixed,  in  large  tanks,  with  a  due  proportion  of 
lime  or  lime-water  (the  quantity  necessary  having  been  determined  by 
preliminary  experiment),  and  the  mixture  allowed  to  settle  until  per- 
fectly clear,  when  it  is  drawn  off  into  reservoirs.t  A  modern  improve- 
ment in  the  process  (Porter-Clark  process)  consists  in  separating  the 
deposit  by  a  remarkably  expeditious  filtration,  which  dispenses  with 
much  of  the  tank-space  required  by  the  original  process. 

Waters  which  are  turbid  from  the  presence  of  clay  in  a  state  of 
suspension,  are  sometimes  purified  by  the  addition  of  a  small  quantity 
of  alum  or  of  aluminium  sulphate,  when  the  alumina  is  precipitated  by 
the  calcium  carbonate  present  in  the  water,  and  carries  down  with  it 
mechanically  the  suspended  clay,  leaving  the  water  clear. 

The  organic  matter  contained  in  water  may  be  vegetable  matter  dis- 
solved from  the  earth  with  which  it  has  come  in  contact,  or  resulting 
from  the  decomposition  of  plants,  or  it  may  be  animal  matter  derived 
either  from  the  animalcules  and  fish  naturally  existing  in  it,  or  from 
the  sewage  of  towns,  and,  in  the  case  of  well  waters,  from  surface 
drainage. 

It  is  believed  upon  good  medical  authority,  that  cholera,  diarrhoea, 
and  typhoid  fever  are  propagated  by  certain  micro-organisms  called 

*  CaSO4          +          Na2CO3         =  Na2SO4  +  CaCO3 

Calcium  sulphate      Sodium  carbonate.     Sodium  sulphate.     Calcium  carbonate. 
f  Thames  and  New  River  water  are  softened,  in  this  way,  to  3.5°,  or  to  a  lower  point  than 
by  an  hour's  boiling". 


60  ACTION  OF  WATER  ON  LEAD. 

bacilli,  which  are  present  in  the  evacuations  of  persons  suffering  from 
those  maladios,  and  are  conveyed  into  water  which  is  allowed  to  become 
contaminated  by  sewage. 

On  this  account,  much  attention  is  paid,  in  the  analysis  of  water 
intended  for  drinking,  to  the  detection  of  organic  matters  containing 
nitrogen  (so-called  albuminoid  matters)  which  would  be  conveyed  into 
the  water  in  sewage.  The  analytical  operations  necessary  for  this  pur- 
pose require  great  care  and  skill,  and  the  conclusions  to  be  drawn  from 
their  results  are  by  no  means  finally  agreed  upon  among  scientific 
chemists.  Attempts  are  also  made  to  determine  the  number  of  bacteria 
(including  bacilli)  present  in  the  water,  which  is  rejected  if  these  are 
very  numerous. 

There  are,  however,  certain  simple  tests,  which  may  often  determine  whether  it 
is  worth  while  to  undertake  a  more  elaborate  examination  of  the  water. 

1.  Pour  half  a  pint  of  the  water  into  a  wide-mouthed  bottle  or  decanter,  close  it 
with  the  stopper  or  with  the  palm  of  the  hand,  and  shake  it  violently  up  and  down. 
If  an  offensive  odour  is  then  perceived,  the  water  is  probably  contaminated  by 
sewage  gas,  and  possibly  with  other  constituents  from  the  same  source. 

2.  Add  to  a  little  of  the  water  a  drop   or  two  of  dilute  sulphuric  acid,    and 
enough  potassium  permanganate  (^Condy's  red  fluid  or  ozonised  water}  to  tinge  it 
of  a  faint  rose  colour  ;  cover  the  vessel  with  a  glass  plate  or  a  saucer.     If  the  pink 
tinge  be  still  visible  after  the  lapse  of  a  quarter  of  an  hour,  the  water  is  probably 
wholesome. 

3.  Pour  a  little  solution  of  silver  nitrate  (lunar  caustic)  into  a  carefully  cleaned 
glass,  and  see  that  it  remains  transparent ;  then  pour  in  some  of  the  water  ;  should 
a  strong  milkiness  appear,  which  is  not  cleared  up  on  adding  a  little  diluted  nitric 
acid,  the  water  probably  contains  much  sodium  chloride,  which  is  always  found  in 
sewage-water,  but  seldom  in  wholesome  waters  in  any  large  quantity,  unless  near 
the  sea  coast. 

To  render  an  impure  water  fit  to  drink,  a  chemist  would  naturally  recommend 
distillation,  but  in  many  cases  this  is  impracticable,  and  the  consumer  may  protect 
himself  to  a  great  extent  by  boiling  the  water  (a  high  temperature  being  inimical 
to  micro-organisms),  or  by  filtering  it  through  charcoal  or  spongy  iron,  or  by 
applying  Clark's  process,  or  treating  it  with  alum  (p.  59). 

45.  One  of  the  most  important  points  to  be  taken  into  account  in 
estimating  the  qualities  of  a  water  is  its  action  upon  lead,  since  this 
metal  is  unfortunately  so  generally  employed  for  the  storage  and  trans- 
mission of  water,  and  cases  frequently  occur  in  which  the  health  has 
been  seriously  injured  by  repeated  small  doses  of  compounds  of  lead 
taken  in  water  which  has  been  kept  in  a  leaden  cistern.  If  a  piece  of 
bright,  freshly-scraped  lead  be  exposed  to  the  air,  it  speedily  becomes 
tarnished  from  the  formation  of  a  thin  film  of  the  oxide  of  lead,  pro- 
duced by  the  action  of  the  atmospheric  oxygen  ;  this  oxide  of  lead  is 
soluble  in  water  to  some  extent,  and  hence,  when  lead  is  kept  in 
contact  with  water,  the  oxygen  which  is  dissolved  in  the  latter  acts  upon 
the  metal,  and  the  oxide  so  produced  is  dissolved  by  the  water  ;  but 
fortunately,  different  waters  act  with  very  different  degrees  of  rapidity 
upon  the  metal,  according  to  the  nature  of  the  substances  which  they 
contain. 

The  film  of  oxide  which  forms  upon  the  surface  of  the  lead  is  in- 
soluble, or  nearly  so,  in  water  containing  much  sulphate  or  carbonate 
pt  calcium,  so  that  hard  waters  may  generally  be  kept  without  danger 
in  leaden  cisterns,  but  soft  waters,  and  those  which  contain  nitrites  or 
nitrates,  should  not  be  drunk  after  contact  with  lead. 

Nearly  all  waters  which  have  been  stored  in  leaden  cisterns  contain  a  trace  of 
the  metal,  and  since  the  action  of  this  poison,  in  minute  doses,  upon  the  system  I 


SEA  WATER.  6 1 

so  gradual  that  the  mischief  is  often  referred  to  other  causes,  it  is  much  to  be 
desired  that  lead  should  be  discarded  altogether  for  the  construction  of  cisterns 
(See  Lead.} 

To  detect  lead  in  a  water,  fill  a  glass  tumbler  with  it,  place  this  on  white  paper, 
add  a  drop  or  two  of  diluted  nitric  acid,  and  some  hydrosulphuric  acid  ;  a  dark 
brown  tinge  will  be  seen  on  looking  through  the  water  from  above. 

Mineral  waters,  as  they  are  popularly  called,  are  simply  spring  waters 
containing  so  large  a  quantity  of  some  ingredient  as  to  have  a  decided 
medicinal  action.  They  are  differently  named  according  to  the  nature 
of  their  predominating  constituent.  Thus,  a  chalybeate  water  contains 
a  considerable  quantity  of  a  salt  of  iron  (usually  ferrous  carbonate  dis- 
solved by  free  carbonic  acid)  ;  an  acidulous  water  is  distinguished  by  a 
large  proportion  of  carbonic  acid,  and  is  well  exemplified  in  the  cele- 
brated Seltzer  water ;  a  sulphureous  or  hepatic  water  has  the  nauseous 
odour  due  to  the  presence  of  sulphuretted  hydrogen.  The  Harrogate 
water  is  eminently  sulphureous.  Saline  waters  are  such  as  contain  a 
large  quantity  of  some  salt ;  thus  the  saline  springs  of  Cheltenham  are 
rich  in  common  salt  and  sodium  sulphate. 

The  chalybeate  waters,  which  are  by  no  means  uncommon,  become 
brown  when  exposed  to  the  air,  and  deposit  a  rusty  sediment  which 
consists  of  the  ferric  hydrate,  formed  by  the  action  of  the  oxygen  of  the 
air  on  the  carbonate.  (See  Iron.) 

46.  Sea  water  contains  the  same  salts  as  are  found  in  waters  from 
other  natural  sources,  but  is  distinguished  by  the  very  large  proportion 
of  sodium  chloride  (common  salt).     A  gallon  of  sea   water  contains 
usually  about  2 500  grains  of  saline  matter,  of  which  1890  grains  consist 
of  common  salt.     The  circumstance  that  clothes  wetted  with  sea  water 
never  become  perfectly  dry  is  to  be  ascribed  chiefly  to  the  magnesium 
chloride  present  in  the  water,  which  is  distinguished  by  its  tendency  to 
deliquesce  or  become   damp   in    moist   air.     There  are  two  elements, 
bromine  and  iodine,  which  are  found  combined  with  metals  in  appreciable 
quantity  in  sea  water,  though  they  are  of  somewhat  rare  occurrence  in 
other  waters  derived  from  natural  sources. 

47.  By  distillation  pure  water  may  be  obtained  from  most  spring  and 
river  waters. 

(DEFINITION. — -Distillation  is  the  conversion  of  a  liquid  into  a  vapour 
and  its  re-condensation  into  the  liquid  form  in  another  vessel.) 

Fig.  45  represents  the  ordinary  form  of  still  in  common  use,  in  which  A  is  a 
copper  boiler  containing  the  water  to  be  distilled  ;  B  the  head  of  the  still,  which 
lifts  out  at  b,  and  is  connected  by  the  neck  C  with  the  worm  D,  a  tin  pipe  coiled 
round  in  the  tub  E  and  issuing  at  F.  The  steam  from  the  boiler,  passing  into  the 
worm,  is  condensed  to  the  liquid  state,  being  cooled  by  the  water  in  contact  with 
the  worm  ;  this  water,  becoming  heated,  passes  off  through  the  pipe  G,  being 
displaced  by  cold  water,  which  is  allowed  to  enter  through  H.  If  10  gallons  of 
river  water  be  taken,  8£  may  be  distilled  over,  but  the  first  half-gallon  should  be 
collected  separately,  as  it  contains  ammonia  and  carbonic  acid. 

A  form  of  apparatus  for  distillation  of  water  and  other  liquids  is  shown  in 
Fig.  46.  A  is  a  stoppered  retort,  the  neck  of  which  fits  into  the  tube  of  a  Liebig's 
condenser  (B),  which  consists  of  a  glass  tube  (C)  fitted  by  means  of  corks  into  a 
glass,  copper,  or  tinned  iron  tube  D,  into  which  a  stream  of  cold  water  is  passed 
by  the  funnel  E,  the  heated  water  running  out  through  the  upper  tube  F.  The 
water  furnished  by  the  condensation  of  the  steam  passes  through  the  quilled 
receiver  Gr,  into  the  flask  H.  Heat  is  gradually  applied  to  the  retort  by  a  ring  gas- 
burner. 

Many  special  precautions  are  requisite  in  order  to  obtain  absolutely 


62 


DISTILLATION. 


pure  distilled  water  for  refined  experiments,  but  for  ordinary  purposes 
the  common  methods  of  distillation  yield  it  in  a  sufficient  pure  con- 
dition. 

The  saline  matters  present  in  the  water  are  of  course  left  behind  in 
the  still  or  retort.     Sea  water  is  now  frequently  distilled  on  board  ship 


45- 


when  fresh  water  is  scarce.  The  vapid  and  disagreeable  taste  of  distilled 
water,  which  is  due  to  its  having  been  deprived  of  the  dissolved  air 
during  the  distillation,  is  remedied  by  the  use  of  Normandy's  still,  which 
provides  for  the  restoration  of  the  expelled  air. 


Fig.  46.— Distillation  :  Liebig-'s  condenser. 


48    The  physical  properties  of  water  are  too  well  known  to  r 
any  detailed  description.     Its  specific  gravity  in  the  liquid  state 


PEROXIDE   OF   HYDROGEN.  63 

being  taken  as  the  standard  to  which  the  specific  gravities  of  liquid  and 
solid  bodies  are  referred. 

(DEFINITION. — The  specific  gravity  of  a  liquid  or  solid  body  is  its 
weight  as  compared  with  that  of  an  equal  volume  of  pure  water  at 
60°  F.— 15.5°  C.) 

Water  assumes  the  solid  form,  under  ordinary  circumstances,  at  32°  F. 
(o°  C.),  and  may  be  obtained  in  six-sided  prismatic  crystals.  Snow  con- 
sists of  beautiful  stellate  groupings  of  these  crystals.  Ice  has  the 
specific  gravity  0.9184.  In  the  act  of  freezing,  water  expands  very 
considerably,  so  that  174  volumes  of  water  at  60°  F.  become  184  volumes 
of  ice.  The  breakage  of  vessels,  splitting  of  rocks,  &c.,  by  the  con- 
gelation of  water  are  due  to  this  expansion.  Water  passes  off  in  vapour 
at  all  temperatures,  the  amount  of  water  evolved  in  a  given  time  of 
course  increasing  with  the  temperature.  The  boiling-point  of  water  is 
212°  F.  (100°  C.).  Its  absolute  boiling-point  (p.  29)  is  365°  C. 

(DEFINITION. — The  boiling-point  of  a  liquid  is  the  constant  tempera- 
ture indicated  by  a  thermometer,  immersed  in  the  vapour  of  the  boiling 
liquid,  in  the  presence  of  a  coil  of  platinum  wire,  to  facilitate  disengage- 
ment of  vapour,  and  at  a  pressure  of  760  mm.  Bar.) 

At  and  above  212°  F.  at  the  ordinary  atmospheric  pressure  (30  in. 
Bar.),  water  is  an  invisible  vapour  of  specific  gravity  0.625  (air=i). 
One  cubic  inch  of  water  at  60°  F.  becomes  1696  cubic  inches  of  vapour 
at  212°  F. 

From  the  definition  of  molecular  weight  given  on  p.  47  it  will  be  seen 
that  if  the  specific  gravity  of  a  gas  in  relation  to  air  be  required,  it 
may  be  obtained  by  multiplying  half  the  molecular  weight  by  0.0695, 
which  represents  the  specific  gravity  of  hydrogen  referred  to  air  as  the 
unit.  Thus  the  specific  gravity  of  steam  (air=i)  is  9x0.0695  = 
0.625. 

49.  Peroxide  of  Hydrogen  or  Hydrogen  Dioxide,  H2O2  (oxygenated 
water).  Minute  quantities  of  this  compound  are  found  in  snow  and  rain,  but 
no  other  natural  occurrence  of  it  has  been  proved  with  certainty.* 

To  prepare  hydrogen  dioxide  the  barium  dioxide  referred  to  on  p.  39  is  powdered, 
suspended  in  water,  and  added  gradually  to  water  through  which  carbon  dioxide  is 
passing  ;  the  water  is  thus  charged  with  hydrogen  dioxide  : 

Ba02  +  H?0  +  C02  =  BaC03  f  H202. 

The  barium  carbonate  (BaC03)  is  allowed  to  settle,  and  the  clear  solution  of  H202 
poured  off. 

Pure  hydrogen  dioxide  is  made  by  first  dissolving  Ba02  in  the  least  possible 
quantity  of  dilute  nitric  acid  and  adding  to  the  solution  one  of  barium  hydroxide 
(baryta  water).  The  precipitate  is  Ba02.8H20  ;  it  is  washed  by  decantation  and 
gradually  added  to  dilute  H2S04,  care  being  taken  to  leave  the  liquid  very  slightly 
acid  f  :  Ba02  +  H2S04  =  H202+BaS04.  The  precipitate  is  allowed  to  settle,  and 
the  clear  liquid  is  evaporated  either  in  a  vacuum  over  oil  of  vitriol,  or  on  the 
water-bath  at  a  temperature  below  75°  C.,  until  it  contains  about  50  per  cent,  of 
H202,  when  it  is  finally  distilled  under  a  pressure  of  10-70  mm.  ;  the  water  passes 
over  first  and  then  the  pure  dioxide.  The  operations  of  concentration  and  distil- 
lation require  great  care,  and  the  solution  first  made  should  be  free  from  salts  of 
the  heavy  metals  ;  for  incautious  heating  of,  the  access  of  dust  to,  or  the  presence 
of  such  salts  in,  the  concentrated  dioxide  renders  it  liable  to  explode  by  sudden 
decomposition  into  water  and  oxygen:  H202  =  H20  +  0.  Even  when  preserved 

*  H2O2  is  frequently  produced  when  substances  are  oxidised  by  free  oxygen  in  presence 
of  water  ;  thus  it  is  invariably  to  be  detected  in  water  in  which  lead  has  been  exposed  to  the 
air. 

t  If  the  H2SO4  were  added  to  the  BaO2.8H2O,  instead  of  as  recommended,  the  H2O2  would 
be  decomposed  by  the  remaining  BaO2  as  fast  as  it  was  formed. 


64  TESTS   FOR   HYDROGEN   DIOXIDE. 

from  adventitious  matter  the  pure  dioxide  slowly  decomposes,  so  that  dangerous. 
pressure  due  to  accumulated  oxygen  may  arise  in  any  closed  vessel  containing  it. 

Pure  hydrogen  dioxide  is  a  syrupy,  colourless  liquid  of  sp.  gr.  1.5  and  boiling  at 
69°  C.  under  26  mm.  pressure.  '  It  is  more  soluble  in  ether  than  in  water,  so  that 
the  former  extracts  it  from  its  solution  in  the  latter.  It  oxidises  many  organic 
matters  so  rapidly  that  it  sometimes  ignites  them.  Its  tendency  to  explode  has- 
been  already  mentioned. 

When  diluted  with  water,  hydrogen  dioxide  is  in  no  sense  dangerous,  although 
far  from  a  stable  substance.  The  commercial  "  10  volume "  hydrogen  peroxide 
contains  about  3  per  cent,  of  H202,  and  yields,  from  I  volume  of  the  solution, 
10  volumes  of  oxygen  when  decomposed.  It  may  be  preserved  for  a  considerable 
time  if  it  contain  a  small  proportion  of  acid  ;  alkali  has  the  opposite  effect,  and 
if  the  solution  is  neutral,  it  takes  up  alkali  from  the  glass  bottle  and  is  decomposed 
thereby. 

A  remarkable  feature  of  hydrogen  dioxide  is  the  ease  with  which  it  decomposes 
into  water  and  oxygen,  with  evolution  of  heat,  by  mere  contact  with  many  sub- 
stances which  are  themselves  unchanged  by  the  dioxide.*  Thus,  finely  divided 
gold,  platinum,  and  silver,  which  have  no  direct  attraction  for  oxygen,  cause  this 
evolution  of  oxygen,  Manganese  dioxide  also  decomposes  the  H202  in  a  solution 
without  undergoing  any  apparent  change  ;  but  if  an  acid  be  present  the  MnOa  will 
be  reduced  to  MnO  and  will  dissolve  as  a  manganous  salt,  a  fact  which  is  some- 
what surprising,  seeing  that  the  H202  is  so  ready  to  part  with  its  oxygen.  There 
are,  however,  a  number  of  reactions  in  which  hydrogen  dioxide  acts  as  a  reducing 
agent.  If  some  of  the  3  per  cent,  solution  be  added  to  some  silver  oxide  suspended 
in  water,  the  brown  colour  of  the  oxide  will  pass  into  the  black  of  finely  divided 
silver  and  minute  bubbles  of  oxygen  will  escape  :  Ag20  +  H202  -  Ag2  +  H20  +  O.  By 
adding  ammonia  very  carefully  to  silver  nitrate  solution  until  the  precipitate  formed 
at  first  is  only  just  re-dissolved,  and  then  adding  some  H202  and  heating,  the  silver 
will  be  deposited  in  its  lustrous  form,  convincing  the  experimenter  that  it  is  indeed 
in  the  metallic  state. 

Another  reducing  action  of  H202  is  its  effect  on  an  acid  solution  of  potassium 
permanganate  (K9Mn208),  the  pink  colour  of  which  it  rapidly  discharges,  with 
evolution  of  oxygen  :  K2Mn208  +  3H2S04  +  5H202  =  K2S04  +  2MnS04  +  8H20  + 502. 
Here  05  from  the  dioxide  have  united  with  05  from  the  permanganate. 

Notwithstanding  its  behaviour  in  the  foregoing  changes  as  a  reducing  agent,  a 
compound  so  ready  to  part  with  its  oxygen,  as  is  hydrogen  dioxide,  will,  of  course, 
act  as  an  oxidising  agent.  If  some  black  lead  sulphide  is  treated  with  hydrogen 
dioxide  it  is  rapidly  oxidised  to  the  white  lead  sulphate,  PbS  +  4.H202  =  PbS04=;4H20. 
It  is  to  be  noted  that  in  many  cases  the  oxidising  effect  of  the  dioxide  is  much 
accelerated  by  the  presence  of  a  small  quantity  of  a  reducing  agent ;  thus  a  mixture 
of  indigo  solution  and  the  dioxide  is  at  once  decolourised  (by  oxidation  of  the 
indigo)  on  addition  of  a  drop  of  ferrous  sulphate  solution. 

A  very  striking  reaction  of  hydrogen  dioxide  is  that  with  chromic  acid.  If  a 
solution  of  H202  be  added  to  a  weak  solution  of  potatsium  dichromate  acidified 
with  sulphuric  acid,  the  beautiful  blue  colour  of  perchromic  acid  appears ; 
K2Cr.207  +  H2S04  +  H202  =  K2S04  +  H20  +  H2Cr208.t  Af ter  a  few  minutes,  the  blue 
colour  changes  to  a  very  pale  green,  the  perchromic  acid  being  decomposed  by  the 
sulphuric  acid,  yielding  the  green  chromium  sulphate,  and  free  oxygen,  which 
adheres  in  bubbles  to  the  side  of  the  vessel,  H2Cra08  +  3H2S04  =  Cr2(S04)3  +  4H2O  +  04. 
If  the  blue  solution  be  shaken  with  a  little  ether,  which  dissolves  the  perchromic 
acid  and  rises  with  it  to  the  surface  where  it  forms  a  blue  layer,  the  colour  is  much 
more  lasting,  and  very  minute  quantities  of  hydrogen  dioxide  may  thus  be  detected. 
Still  more  delicate  tests  for  hydrogen  dioxide  are  the  production  of  a  yellow  colour 
with  titam'c  acid,  and  a  yellowish  precipitate  with  uranium  salts. 

The  decomposition  of  H202  into  H20  and  0  is  attended  by  evolution  of  heat, 
amounting  to  23,000  gram-units  of  heat  for  each  gram-molecule  of  H202.  When 
H2  and  0  combine  to  form  H20,  69,000  units  of  heat  are  evolved  ;  hence,  when 
H20  is  decomposed,  69,000  units  must  be  absorbed,  so  that  we  have,  in  the  forma- 
tion of  water.  H2+0  =  H20 +  69,000  heat-units.  But  since  the  decomposition  of 
H.202  into  H20  and  0  evolves  23,000  units,  its  formation  from  H20  and  0  would 

*  Such  inexplicable  changes  as  this  are  sometimes  included  under  the  general  denomina- 
tion of  catalysis,  or  decomposition  by  contact  or  by  catalytic  action. 

f  It  is  by  no  means  certain  that  this  formula  represents  the  composition  of  the  blue  com  - 
pound. 


OZONE. 


absorb  the  same  quantity,  and  we  should  have  H20  +  0  =  H202  -  23,000  units. 
From  the  two  equations  we  get  H2  +  02  —  H202  +  69,000  -  23,000  or  H2-f02  = 
H202  + 46,000  heat-units.  Now,  by  the  laws  of  thermo-cheinistry,  every  chemical 
change  tends  to  produce  that  body  in  the  formation  of  which  most  heat  is  liberated  ; 
hence  water,  and  not  hydrogen  dioxide,  is  the  general  result  of  chemical  changes 
in  which  H  and  0  are  concerned. 

The  uses  of  hydrogen  peroxide  are  chiefly  as  an  oxidising  agent. 
Thus  it  is  applied  for  bleaching  materials  which  are  too  tender  to  be 
subjected  to  the  drastic  action  of  bleaching  powder.  A  like  effect  is 
produced  on  dark  hair,  which  becomes  yellow  on  treatment  with  hair- 
wash  containing  this  reagent.  Photography,  ivory-bleaching,  and  clean- 
ing old  pictures  afford  other  outlets  for  hydrogen  peroxide. 

50.  Ozone. — This  is  the  name  given  to  a 
modified  form  of  oxygen,  of  the  true  nature  of 
which  there  is  still  some  doubt,  as  it  has  never 
been  obtained  unmixed  with  ordinary  oxygen, 
but  it  appears  to  be  formed  by  the  union  of  3 
atoms  of  oxygen  (occupying  3  volumes),  to  pro- 
duce a  molecule  of  ozone  (occupying  2  volumes). 
Just  as  hydrogen  dioxide  (H202)  may  be  regarded 
as  formed  by  the  combination  of  a  molecule  of 
water  (H20)  with  an  atom  of  oxygen,  so  ozone 
may  be  viewed  as  a  combination  of  a  molecule  of 
oxygen  (02)  with  an  atom  of  oxygen.  It  would 
then  be  half  as  heavy  again  as  ordinary  oxygen, 
and  experiment  has  shown  that  its  rate  of  diffu- 
sion is  in  accordance  with  this  view. 

It  derives  its  name  from  its  peculiar  odour 
(6fcii',  to  smell),  which  is  often  perceived  in  the 
air  of  the  sea  or  of  the  open  country,  and  in 
linen  which  has  been  dried  in  country  air. 
According  to  Hartley,  I  volume  of  ozone  in  2\ 
million  volumes  of  air  may  be  perceived  by  the 
smell.  Oxygen  appears  to  be  capable  of  assum- 
ing this  ozonised  condition  under  various  circum- 
stances, the  principal  of  which  are,  the  passage 
of  silent  electric  discharges,*  and  the  contact 
with  substances  (such  as  phosphorus)  undergoing 
slow  oxidation  in  the  presence  of  water.  A 
portion  f  of  the  oxygen  obtained  in  the  decom- 
position of  water  by  the  galvanic  current  also 
exists  in  the  ozonised  condition,  as  may  be  per- 
ceived by  its  odour. 

The  use  of  an  induction-tube  (Fig.  47)  affords 
the  readiest  method  of  demonstrating  the  cha- 
racteristic properties  of  ozone. 


Fig.  47. — Ozonising  apparatus. 


The  construction  of  the  apparatus  will  be  readily  understood  from  the  figure. 
The  outside  cylinder  and  the  innermost  tube  are  filled  with  dilute  sulphuric  acid, 
which  serves  the  double  purpose  of  conducting  the  electricity  and  keeping  down 
the  temperature  of  the  oxygen  or  air.  When  the  wires  are  connected  with  the 
poles  of  an  induction-coil  the  two  portions  of  dilute  sulphuric  acid  are  oppositely 
electrified,  so  that  the  space  between  the  two  liquids  is  submitted  to  the  high 
pressure  electrical  discharge  necessary  for  the  resolution  of  the  oxygen  molecules 
into  their  atoms,  and  the  recombination  of  these  to  form  molecules  of  ozone. 
Through  this  space  the  air  or  oxygen  (dried  by  passing  through  oil  of  vitriol)  is 
passed  in  the  direction  of  the  arrows.  The  induction-tube  must  be  made  of  thin 
glass,  and  the  space  between  the  inner  and  the  outer  tube  must  be  as  narrow  as 
possible. 

The  ordinary  chemical  test  for  ozone  is  a  damp  mixture  of  starch  paste  with 
potassium  iodide.  If  this  mixture  be  brushed  over  strips  of  white  cartridge  paper 

*  It  is  the  odour  of  ozone  which  is  perceived  in  working  an  ordinary  electrical  machine. 
•}•  Varying  from  a  trace  to  17  per  cent.,  according  to  the  electrical  conditions. 

E 


66  OZONE. 

these  will  remain  unchanged  in  ordinary  air  ;  but  when  they  are  exposed  to 
ozonised  air  (such  as  that  which  has  passed  through  the  induction-tube),  they  wjll 
immediately  assume  a  blue  colour.  The  ozone  sets  free  the  iodine  from  the  KI, 
which  has  the  specific  property  of  imparting  a  blue  colour  to  starch.  Papers 
impregnated  with  manganese  sulphate,  lead  acetate,  or  thallous  oxide,  become 
brown,  in  the  first  two  cases  from  the  formation  of  the  peroxide  of.  the  metal 
and  in  the  last  case  from  the  formation  of  thallic  oxide,  under  the  influence  of 
ozone. 

.  If  the  ozonised  air  be  passed  into  a  solution  of  indigo  (sulphlndigotic  acid  largely 
diluted)  the  blue  colour  will  soon  disappear,  since  the  ozone  oxidises  the  indigo, 
and  gives  rise  to  products  which,  in  a  diluted  state,  are  nearly  colourless.  Ordinary 
oxygen  is  incapable  of  bleaching  indigo  in  this  manner.  If  the  ozone  is  passed 
through  a  tube  of  vulcanised  caoutchouc,  this  will  soon  be  perforated  by  the 
corrosive  effect  of  the  ozone,  whilst  ordinary  oxygen  would  be  without  effect  upon 
it.  If  ozonised  air  be  passed  into  a  flask  with  a  little  mercury  at  the  bottom,  the 
surface  of  the  mercury  will  soon  become  tarnished  by  the  formation  of  oxide, 
and  when  the  mercury  is  shaken  round  the  flask  it  will  adhere  to  the  sides,  which 
is  not  the  case  with  pure  mercury.  It  is  stated  that  if  both  the  mercury  and  the 
ozone  be  dry,  the  gas  will  be  converted  into  oxygen,  but  the  mercury  will  not  be 
oxidised. 

When  ozone  is  passed  slowly  through  a  glass  tube  heated  in  the  centre  by  a 
spirit-lamp,  it  loses  its  power  of  affecting  the  iodised  starch-paper,  the  ozone 
having  been  re-converted  into  ordinary  oxygen  under  the  influence  of  heat  ; 
2(OO2)  =  3(02).  A  temperature  of  250°  C.  is  sufficient  to  effect  this  change.  A 
given  volume  of  oxygen  diminishes  when  a  portion  of  it  is  converted  into  ozone 
by  the  silent  electric  discharge,  and  it  regains  its  original  volume  when  the  ozone 
is  re-converted  by  heat.  The  conversion  of  oxygen  into  ozone  is  attended  by 
absorption  of  heat  ;  302  =203  —  59,200  units. 

When  a  given  quantity  of  oxygen  is  electrised,  or  subjected  to  the  action  of 
surfaces  charged  with  opposite  electricities,  as  in  the  induction  tube,  only  one-fifth, 
at  most,  is  converted  into  ozone  ;  but  if  the  ozone  be  now  removed  by  some  sub- 
stance which  absorbs  it,  a  fresh  quantity  of  the  oxygen  may  be  ozonised.* 

The  facts  that  ozone  can  be  produced  in  pure  oxygen  and  that  its  formation  is 
accompanied  by  a  contraction  in  volume,  lead  to  the  conclusion  that  ozone  is  a 
condensed  form  of  oxygen.  When  the  ozonised  oxygen  has  been  heated  it  is 
found  to  have  expanded  to  exactly  the  same  volume  which  the  pure  oxygen 
occupied,  and  to  no  longer  contain  any  ozone.  By  introducing  turpentine  into  the 
ozonised  gas  all  the  ozone  is  absorbed,  and  a  measurement  of  the  contraction 
caused  by  this  absorption  reveals  the  fact  that  the  volume  which  has  disappeared 
is  twice  the  volume  of  the  contraction  effected  by  ozonising  the  oxygen.  Thus, 
if  n  c.c.  of  gas  disappeared  when  the  oxygen  was  ozonised,  2n  c.c.  will  be  absorbed 
by  the  turpentine.  Therefore  3  vols.  of  the  original  oxygen  must  have  become 
2  vols.  of  ozone,  and  if  the  gas  had  been  heated,  instead  of  having  been  treated 
with  turpentine,  these  2  vols.  of  ozone  would  have  expanded  again  to  3  vols.  of 
oxygen.  If  one  atom  of  oxygen  be  regarded  as  occupying  one  volume,  then  one 
molecule  (2  atoms)  must  occupy  2  vols.  ;  so  that  in  producing  ozone  one  molecule 
of  oxygen  has  been  combined  with  one  atom  of  oxygen,  forming  a  molecule  of 
ozone,  020. 

When  a  neutral  solution  of  potassium  iodide  is  introduced  into  ozonised  oxygen 
there  is  no  contraction  in  volume,  and  yet  all  the  ozone  is  destroyed  ;  at  the  same 
time  iodine  is  liberated  from  the  potassium  iodide.  If  the  quantity  of  this  iodine 
be  determined,  it  is  found  to  be  as  much  as  would  (under  other  circumstances)  be 
liberated  by  a  volume  of  oxygen  identical  with  the  volume  which  disappeared 
when  the  oxygen  was  ozonised.  The  explanation  of  these  observations  is  easy  if 
the  above  view  of  the  constitution  of  ozone  be  adopted;  for  the  facts  maybe 
expressed  by  the  equation  —  y 

002(2  vols.)  +  2KI  +  HOH  =  2KOH  +  12  +  02  (2  vols.), 
showing  that  it  is  the  third  atom  of  oxygen  in  the  molecule  of  ozone  which  has 


electric  ediSr?i0?h°f  °Z°ne  f°rmed  dependS  Up°n  the  intensity  a°d  frequency  of  the 

ratert      ArcoS?       t  ^T^S  "^  the  temPerature-      Th«  last-named    influence   is  the 

Seat      2?C    T!  n?r     %     ?  re0S«arches  <l88o>  2O  Per   ce"t.  of  the  oxygen  becomes 

-25   C,  12  per  cent,  at  20°  C.,  and  2  per  cent,  at  100°  C.  ;  more  lately  (i8oO  it 

SUEZ.  5'2  Per  Cent<  at  2°°  C"  and  °nly  I0'4  Per  cent"  ^en  at  -£?c.  cSbe 


ATMOSPHERIC   OZONE.  67 

liberated  the  iodine.     If  the  solution  of  potassium  iodide  be  acidified  (and  thus- 
converted  virtually  into  a  solution  of  hydriodic  acid),  twice  as  much  iodine  will  be< 
liberated  and  the  volume  of  the  ozone  will  be  reduced  to  one-half  • 
OO2(2  vols.)  +  4HI  =  2H20  +  I4  +  0  (i  vol.). 

By  placing  a  freshly  scraped  stick  of  phosphorus  (scraped  under  water  to  avoid 
inflammation)  at  the  bottom  of  a  quart  bottle,  with  enough  water  to  cover  half 
of  it,  and  loosely  covering  the  bottle  with  a  glass  plate,  enough  ozone  may  be 
accumulated  in  a  few  minutes  to  be  readily  recognised  by  the  odour  and  the 
iodised  starch.  The  water  at  the  bottom  of  the  bottle  is  found  to  contain,  besides 
the  phosphorus  and  phosphoric  acids,  formed  by  the  slow  oxidation  of  the  phos- 
phorus, some  hydrogen  dioxide,  whence  it  has  been  supposed  that  the  formation 
of  ozone  is  due  to  the  decomposition  of  a  molecule  of  oxygen  into  electro -negative 
oxygen,  which  combines  with  another  molecule  of  oxygen  to  form  ozone,  and 
electro-positive  oxygen,  which  combines  with  a  molecule  of  water  to  form  hydrogen 
dioxide.  Thus. 

—  +  +         - 

02  +  00  +  H20  =  H200  +  020. 

This  view  is  supported  by  the  circumstance  that  hydrogen  dioxide  appears  to  be 
produced  in  every  case  where  ozone  is  formed  in  the  presence  of  water. 

When  ozonised  oxygen  is  shaken  with  hydrogen  dioxide,  the  above  equation  is 
reversed,  water  and  ordinary  oxygen  being  formed.* 

Impure  ether  and  essential  oils,  such  as  turpentine,  slowly  absorb  oxygen  (and 
perhaps  ozone)  from  the  air.  There  are  thus  produced  organic  peroxides  which 
yield  hydrogen  dioxide  in  contact  with  water,  so  that  old  samples  of  these  com- 
pounds exhibit  the  reactions  of  hydrogen  dioxide.  A  solution  of  hydrogen  dioxide 
in  ether  (ozonic  ether)  has  been  used  as  a  test  for  blood  stains. 

Contact  with  blood  decomposes  hydrogen  dioxide,  and  the  oxygen  which  is 
liberated  is  capable  of  blueing  guaiacum  resin.  Accordingly,  if  a  blood-stain  be 
moistened  with  tincture  of  guaiacum  (a  solution  of  the  resin  in  spirit  of  wine),  and 
afterwards  with  the  ozonic  ether,  it  acquires  an  intense  blue  colour,  which  may 
be  detected,  even  on  a  coloured  fabric,  by  pressing  a  piece  of  white  blotting-paper 
upon  it. 

Ozone  has  attracted  much  notice,  because  a  minute  proportion  of  the  oxygen 
in  the  atmosphere  appears  sometimes  to  be  present  in  this  form,  and  its  active 
properties  have  naturally  led  to  the  belief  that  it  must  exercise  some  influence 
upon  the  sanitary  condition  of  the  air.  This  idea  is  encouraged  by  the  circum- 
stance that  no  indications  of  ozone  can  be  perceived  in  crowded  cities,  where  there 
are  so  many  oxidisable  substances  to  consume  the  active  oxygen,  whilst  the  air  in 
the  open  country  and  at  the  seaside  does  give  evidence  of  its  presence.  Some 
chemists  assert  that  their  experiments  have  demonstrated  the  very  important  fact 
that  a  portion  of  the  oxygen  developed  by  growing  plants  is  in  the  ozonised  form, 
but  the  evidence  on  the  subject  is  conflicting.  Houzean  fixes  the  maximum  pro- 
portion of  ozone  at  T^fHJTRrth  of  the  volume  of  air.  The  proportion  is  highest  in 
May  and  June,  lowest  in  December  and  January. 

Ozonised  oxygen  exhibits  a  sky-blue  colour  when  viewed  along  a  column  of  one 
metre  in  length.  The  blue  colour  becomes  very  deep  under  a  pressure  of  several 
atmospheres.  It  has  been  suggested  that  the  blue  colour  of  the  sky  is  due  to  our 
regarding  it  through  the  ozonised  atmosphere.  By  passing  ozonised  oxygen 
through  a  tube  immersed  in  liquid  oxygen  which  is  evaporating,  the  ozone  is  con- 
densed to  a  blue  liquid  boiling  at-  106°  C.  and  yielding  a  violently  explosive  blue 
gas.  Ozone  is  slightly  soluble  in  water  ;  100  vols.  water  dissolve  0.83  vols.  ozone 
(at  i°  C.). 

In  want  of  stability  ozone  resembles  hydrogen  dioxide  ;  contact  with  manga- 
nese dioxide  converts  it  into  ordinary  oxygen.  Even  shaking  with  powdered  glass 
will  de-ozonise  the  ozonised  oxygen.  When  kept  for  some  days,  all  the  ozone  is 
gradually  re-converted  into  oxygen. 

ATMOSPHERIC  AIR 

51.  Atmospheric  air  consists  chiefly  of  a  mixture  of  nitrogen  and 
oxygen,  roughly  in  the  proportion  of  4  vols.  N  :  i  vol.  0.  There  are 

*  The  oxygen  obtained  by  the  action  of  warm  sulphuric  acid  on  barium  dioxide,  or  on 
crystallised  potassium  permanganate,  resembles  ozone  in  its  odour  and  action  on  the  iodised 
starch  paper. 


68 


COMPOSITION   OF  AIE. 


also  present  a  small  proportion  of  argon,  and  very  small  proportions 
of  carbonic  acid  gas  (carbon  dioxide)  and  ammonia.  Vapour  of  water 
is,  of  course,  always  present  in  the  atmosphere  in  varying  proportions. 
Since  the  atmosphere  is  the  receptacle  for  all  gaseous  emanations,  other 
substances  may  be  discovered  in  it  by  very  minute  analysis,  but  in  pro- 
portions too  small  to  have  any  perceptible  influence  upon  its  properties. 
Thus  marsh-gas  or  light  carburetted  hydrogen,  sulphuretted  hydrogen, 
and  sulphurous  acid  gas,  can  often  be  traced  in  it,  the  last  especially  in 
or  near  towns. 

Although  the  proportion  of  oxygen  in  the  air  at  a  given  spot  may  be 
much  diminished,  and  that  of  carbonic  acid  gas  increased,  by  processes 
of  oxidation  (such  as  respiration  and  combustion)  at  that  place,  the 
operation  of  wind  and  of  diffusion  so  rapidly  mixes  the  altered  air  with 
the  immensely  greater  general  mass  of  the  atmosphere,  that  the  varia- 
tions in  the  composition  of  air  in  different  places  are  very  slight. 
Thus  it  has  been  found  that  the  proportion  of  oxygen  in  the  air  in 
the  centre  of  Manchester  was,  at  most,  only  0.2  per  cent,  below  the 
average. 

Composition  of  dry  air  by  volume  and  by  weight. 


Volume. 
Nitrogen 
Oxygen  . 
Argon 
Carbon  dioxide 


Weight. 

.     78.40  per  cent,  75.95  per  cent. 

•  20.94  „  .  23.10  „ 

0.63  „  .  0.90  „ 

0.03  „  .  0.05  „ 

The  proportion  of  aqueous  vapour  may  be  stated,  on  the  average,  as 
1.4  per  cent,  by  volume,  or  0.87  per  cent,  by  weight  of  the  air.  The 
total  weight  of  atmospheric  air  surrounding  the  globe  exceedes  300,000 
million  tons.  A  litre  of  dry  air  at  o°  C.  and  760  mm.  weighs  1.293 
grams. 

The  exact  volumetric  analysis  of  air  has  been  already  given  (p.  44). 

The  proportion  of  oxygen  to  nitrogen  in  air  may  be  exhibited  by  suspending 
a  stick  of  phosphorus  upon  a  wire  stand  (A,  Fig.  48)  in  a  measured  volume  of 
air  confined  over  water.  The  cylinder  (B)  should  have  been  previously  divided 
into  five  equal  spaces,  by  measuring  water  into  it,  and  marking  each  space  by  a 


Fig.  49- 

-  a  few  hours,  the  phosphorus  will  have  corn- 
oxygen  to  form  phosphorous  and  phosphoric  acids. 
by  the   water,    leaving  four   of  the   spaces    occupied   by 


ANALYSIS   OF  AIR.  69 

The  same  result  may  be  arrived  at  in  a  much  shorter  time  by  burning  the 
phosphorus  in  the  confined  portion  of  air. 

A  fragment  of  phosphorus  dried  by  careful  pressure  between  blotting-paper,  is 
placed  upon  a  convenient  stand  (A,  Fig.  49)  and  covered  with  a  tall  jar,  having  an 
opening  at  the  top  for  the  insertion  of  a  well-fitting  stopper  (which  should  be 
greased  with  a  little  lard),  and  divided  into  seven  parts  of  equal  capacity.  The 
jar  should  be  placed  over  the  stand  in  such  a  manner  that  the  water  may  occupy 
the  two  lowest  spaces  into  which  the  jar  is  divided.  The  stopper  of  the  jar  is 
furnished  with  a  hook,  to  which  a  piece  of  brass  chain  (B)  is  attached,  long  enough 
to  touch  the  phosphorus  when  the  stopper  is  inserted.  The  end  of  this  chain  is 
heated,  and  the  stopper  tightly  fixed  in  its  place.  On  allowing  the  hot  chain  to 
touch  the  phosphorus,  the  latter  bursts  into  vivid  combustion,  filling  the  jar  with 
thick  white  fumes,  and  covering  its  sides  for  a  few  moments  with  white  flakes  of 
phosphoric  anhydride.  At  the  commencement  of  the  experiment,  the  water  in  the 
jar  will  be  depressed,  in  consequence  of  the  expansion  of  the  air  due  to  the  heat 
produced  in  the  burning  of  phosphorus,  but  presently,  when  the  combustion  begins 
to  decline,  the  water  rises,  and  continues  to  do  so  until  it  has  ascended  to  the  line 
(C),  so  as  to  occupy  the  place  of  one-fifth  of  the  air  employed  in  the  experiment. 
The  phosphorus  will  then  have  ceased  to  burn,  the  white  flakes  upon  the  sides  of 
the  jar  will  have  acquired  the  appearance  of  drops  of  moisture,  and  the  fumes  will 
have  gradually  disappeared,  until,  in  the  course  of  half  an  hour,  the  air  remaining 
in  the  jar  will  be  as  clear  and  transparent  as  before,  the  whole  of  the  phosphoric 
anhydride  having  been  absorbed  by  the  water.  The  jar  should  now  be  sunk  in 
water,  so  that  the  latter  may  attain  to  the  same  level  without  as  within  the  jar. 
On  removing  the  stopper,  it  will  be  found  that  the  nitrogen  in  the  jar  will  no 
longer  support  the  combustion  of  a  taper. 

In  the  rigidly  accurate  determination  of  the  proportion  of  oxygen  to  nitrogen 
and  argon  in  the  air,  it  is  of  course  necessary  to  guard  against  any  error  arising 
from  the  presence  of  the  water,  carbonic  acid  gas,  and  ammonia.  *  With  this  view, 


Fig.  50. — Exact  analysis  of  air. 

Dumas  and  Boussingault,  to  whom  we  are  originally  indebted  for  our  exact  know- 
ledge of  the  composition  of  the  air,  caused  it  to  pass  through  a  series  of  tubes 
(A,  Fig.  50)  containing  potash,  in  order  to  remove  the  carbonic  acid  gas,  then 
through  a  second  series  (B)  containing  sulphuric  acid,  to  absorb  the  ammonia  and 
water  ;  the  purified  air  then  passed  through  a  glass  tube  (C)  filled  with  bright 
copper  heated  to  redness  in  a  charcoal  furnace,  which  removed  the  whole  of  the 
oxygen,  whilst  the  nitrogen  passed  into  the  large  globe  (N). 

Both  the  tube  (containing  the  copper)  and  the  globe  were  carefully  exhausted 
of  air  and  accurately  weighed  before  the  experiment ;  on  connecting  the  globe  and 
the  tube  with  the  purifying  apparatus,  and  slowly  opening  the  stop-cocks,  the 
pressure  of  the  external  air  caused  it  to  flow  through  the  series  of  tubes  into  Hie 
globe  destined  to  receive  the  nitrogen.  When  a  considerable  quantity  of  air  had 
passed  in,  the  stop-cocks  were  again  closed,  and  after  cooling,  the  weight  of  the 
globe  was  accurately  determined.  The  difference  between  this  weight  and  that 
of  the  empty  globe,  before  the  experiment,  gave  the  weight  of  the  nitrogen  which 
had  entered"  the  globe  ;  but  this  did  not  represent  the  whole  of  the  nitrogen  con- 
tained in  the  analysed  air,  for  the  tube  containing  the  copper  had,  of  course, 
remained  full  of  nitrogen  at  the  close  of  the  experiment.  This  tube,  having  been 
weighed,  was  attached  to  the  air-pump,  the  nitrogen  exhausted  from  it,  and  the 
tube  again  weighed  ;  the  difference  between  the  two  weighings  furnished  the 

*  It  would  be  satisfactory,  of  course,  to  deprive  the  air  of  its  argon  also,  in  making-  this 
experiment,  and  thus  arrive  at  the  true  proportion  of  nitrogen  to  oxygen ;  no  method  is 
known,  however,  for  removing  argon  from  a  gas.  It  muht  be  remembered  that  this  gas  has 
only  recently  been  discovered,  and  Dumas  and  Boussingault  estimated  it  with  the  nitrogen, 
thus  making  the  proportion  of  this  constituent  too  high. 


70  SPRENGEL'S   AIR-PUMP. 

weight  of  the  nitrogen  remaining  in  the  tube,  and  was  added  to  the  weight  of  that 
received  in  the  globe.  The  oxygen  was  represented  by  the  increase  of  the  weight 
of  the  exhausted  tube  containing  the  copper,  which  was  partially  converted  into 
CuO  by  combining  with  the  oxygen  of  the  air  passed  through  it. 

52.  The  nitrogen  remaining  (together  with  the  argon)  after  the  re- 
moval of  the  oxygen  from  air  in  the  above  experiments  was  so  called  on 
account  of  its  presence  in  nitre  (saltpetre,  KN03).  In  physical  pro- 
perties it  resembles  oxygen,  but  is  somewhat  lighter  than  that  gas,  its 
specific  gravity  being  0.967. 

This  difference  in  the  specific  gravities  of  the  two  gases  is  well  exhibited  by  the 
arrangement  shown  in  Fig.  51.  A  jar  of  oxygen  (0)  is  closed  with  a  glass  plate, 
and  placed  upon  the  table.  A  jar  of  nitrogen 
(TV'),  also  closed  with  a  glass  plate,  is  placed 
over  it,  so  that  the  two  gases  may  come  in  con- 
tact when  the  glass  plates  are  removed.  The 
nitrogen  floats  for  some  seconds  above  the  oxy- 
gen, and  if  a  lighted  taper  be  quickly  intro- 
duced through  the  neck  of  the  upper  jar,  it 
will  be  extinguished  in  passing  through  the 
nitrogen,  and  will  be  rekindled  brilliantly  when 
it  reaches  the  oxygen  in  the  lower  jar. 


Fig.  51. 


Fig.  52. — Sprengel's  pump.     Dialysis  of  air. 


It  might  at  first  sight  appear  surprising  that  oxygen  and  nitrogen, 
though  of  different  specific  gravities,  should  exist  in  uniform  proportions 
in  all  parts  of  the  atmosphere,  unless  in  a  state  of  chemical  combina- 
tion ;  but  an  acquaintance  with  the  property  of  diffusion  (p.  25) 
possessed  by  gases,  teaches  us  that  gases  mix  with  each  other  in  opposition 
to  gravitation,  and  when  mixed  always  remain  so. 

It  was  shown  by  Graham  that  a  partial  separation  of  the  nitrogen  and  oxygen 
in  air  may  be  effected,  on  the  same  principle  as  that  of  hydrogen  and  oxygen  at 
page  28,  by  taking  advantage  of  the  difference  in  their  rates  of  diffusion.  He 
devised,  however,  a  more  convenient  process,  founded  upon  the  dialytlc  (osmotic) 
passage  of  the  gases  through  caoutchouc,  which  he  ascribed  to  the  absorption  of 
the  gas  by  the  solid  material  upon  one  side,  and  its  escape  on  the  other. 

A  bag  («,  Fig.  52)  is  made  of  a  fabric  composed  of  a  layer  of  caoutchouc  between 
two  layers  of  silk,  such  as  that  employed  for  waterproof  garments  ;  a  piece  of 
carpet  is  placed  inside  the  bag  to  keep  the  sides  apart,  and  the  edges  of  the  bag 


DUST  IN  THE  AIR.  71 

are  made  perfectly  air-tight  with  solution  of  caoutchouc.  To  maintain  a  vacuum 
within  the  bag,  it  is  supported  by  a  rod  v,  and  attached  to  SprengeVs  air-pump,  in 
which  a  stream  of  mercury,  allowed  to  flow  from  a  funnel  (/)  down  a  tube  (<?)  six 
feet  long,  draws  the  air  out  of  the  bag,  through  a  lateral  tube  (A),  until  all  the  air 
is  exhausted,  which  is  indicated  by  the  barometer  tube  &,  the  lower  end  of  which 
dips  into  a  cistern  of  mercury.  When  the  mercury  in  this  tube  stands  at  almost 
exactly  the  same  height  as  the  standard  barometer,  the  exhaustion  is  complete. 
If  a  test-tube  (cT)  filled  with  mercury  be  now  inverted  over  the  end  of  the  long 
tube  c,  which  is  bent  upwards  for  that  purpose,  the  bubbles  of  air  which  are  drawn 
through  the  sides  of  the  vacuous  bag,  and  carried  down  the  long  tube  by  the  little 
pistons  of  liquid  mercury  as  they  fall,  will  pass  up  into  the  test-tube  ;  when  the 
latter  is  filled  with  the  gas,  its  mouth  is  closed  with  the  thumb,  withdrawn  from 
the  mercury,  and  a  match  with  a  spark  at  the  end  inserted,  when  the  spark  will 
burst  out  into  flame,  showing  that  the  specimen  of  air  collected  is  much  richer  in 
oxygen  than  ordinary  atmospheric  air.  The  overflow  tube  g  delivers  the  mercury 
which  is  to  be  returned  to  the  funnel/. 

The  dialytic  passage  of  oxygen  through  caoutchouc  into  a  vacuum  is  twice  as 
rapid  as  that  of  nitrogen,  so  that  the  air  collected  in  the  tube  contains  twice  as 
much  oxygen  as  the  external  air. 

This  osmotic  passage  of  gases  through  solids  is  quite  unconnected  with  diffusibility 
of  the  gases,  and  appears  to  depend  rather  upon  the  chemical  nature  of  the  gas 
and  of  the  solid.  It  is  thus  connected  with  the  occlusion  of  gases  by  solids.  In 
consequence  of  this  osmotic  passage,  tubes  of  iron  or  platinum,  which  are  quite 
impermeable  by  hydrogen  at  the  ordinary  temperature,  allow  it  to  pass  rapidly 
through  their  walls  at  high  temperatures. 

That  air  is  simply  a  mechanical  mixture  of  its  component  gases  is 
amply  proved  by  the  circumstance  that  it  possesses  all  the  properties 
which  would  be  predicted  for  a  mixture  of  these  gases  in  such  propor- 
tions ;  whilst  the  essential  feature  of  a  chemical  compound  is,  that  its 
properties  cannot  be  foreseen  from  those  of  its  constituents.  (See  p.  6.) 

The  absence  of  active  chemical  properties  is  a  very  striking  feature 
of  nitrogen,  and  admirably  adapts  it  for  its  function  of  diluting  the 
oxygen  in  the  atmosphere.  This  is  even  more  true  of  the  small  pro- 
portion of  argon  in  the  air,  for  this  gas  appears  to  be  devoid  of  all 
chemical  properties. 

The  chemical  relations  of  air  to  animals  and  plants  will  be  more 
appropriately  discussed  hereafter.  (See  Carbonic  Acid,  Ammonia.) 

In  considering  the  composition  of  air,  much  attention  has  been 
directed  of  late  years  to  the  dust  or  minute  particles  of  solid  matter 
which,  although  much  heavier  than  air,  are  suspended  in  it  by  the  action 
of  currents,  and  may  always  be  detected  by  a  beam  from  the  sun  or  the 
electric  lamp  or  the  lime -light,  which  would  be  invisible  along  its  track 
through  optically  pure  air.  Such  dust  has  been  found  to  contain  iron, 
lime,  silica,  and  other  inorganic  substances,  besides  organic  matter. 

The  fine  particles  of  mineral  substances  present  in  the  dust  are  the 
probable  cause  of  the  crystallisation  of  supersaturated  solutions  of  salts 
(p.  51)  when  exposed  to  air.  The  vegetable  particles  appear  to  contain 
minute  seeds  which  germinate  when  deposited  in  certain  liquid  or  moist 
solid  substances,  and  give  rise  to  mould,  mildew,  and  fermentation.  The 
animal  particles  are  believed  to  contain  the  germs  by  the  agency  of 
which  certain  forms  of  disease  are  spread. 

The  dust  of  the  air  has  also  a  considerable  influence  on  the  produc- 
tion of  fogs.  Air  at  the  ordinary  temperature  (16°  0.)  is  said  to  be 
"  dry"  when  it  contains  less  than  5  grams  of  water  vapour  per  cubic 
metre  (35.37  cubic  feet),  and  "damp  "  when  it  contains  more  than  10 
grams  of  water  vapour  in  this  volume,  the  sensation  of  dryness  or 


72  LIQUEFACTION  OF  GASES. 

dampness  having  relation  to  the  degree  of  rapidity  with  which  the 
water  excreted  by  the  skin  is  able  to  evaporate.  When  damp  air  is 
chilled  the  water  vapour  is  deposited  from  it  in  the  form  of  fog, 
unless  the  air  be  optically  pure,  when  no  condensation  of  the  water 
occurs.  It  would  appear  from  this  that  the  dust  particles  in  the  air 
form  nuclei  around  which  the  aqueous  vapour  can  precipitate,  much  as 
the  crystals  form  around  a  particle  in  a  super-saturated  solution.  The 
aggravation  of  a  fog  by  smoke  may  perhaps  be  partly  due  to  such  a  cause. 

It  has  been  shown  that  dust  particles  are  not  alone  in  causing  precipitation  of 
aqueous  vapour,  many  gases  which  are  free  from  suspended  particles  having  a 
similar  effect.  Sulphur  dioxide  is  an  example  ;  this  gas  is  always  present  in 
London  air,  being  a  product  of  the  combustion  of  coal  containing  iron  pyrites  ;  it 
is  more  abundant  in  foggy  weather,  but  whether  it  is  a  cause  of  the  fog  or  is 
merely  retained  thereby  remains  uncertain. 

Liquid  Air. — The  simplest  method  of  liquefying  a  gas  is  to  cool  it 
at  atmospheric  pressure  to  a  temperature  below  that  at  which  the 
liquid  to  be  formed  boils.  Liquefaction  then  ensues  just  as  steam 
condenses  to  water  when  cooled  below  100°  C.  By  increasing  the 
pressure  on  a  liquid,  its  boiling-point  is  raised,  hence  if  a  gas  be  com- 
pressed it  requires  less  cooling  to  liquefy  it,  for  the  boiling-point  of  the 
liquid  to  be  formed  is  higher.  Thus  it  is  generally  economical  to 
compress  the  gas,  as  well  as  cool  it,  and  this  was  the  method  by  which 
the  majority  of  the  gases  were  originally  liquefied ;  it  is  illustrated  in 
the  chapter  on  Ammonia. 

Oxygen,  having  a  low  critical  temperature  (p.  29),  was  not  liquefied 
until  a  suitable  means  for  obtaining  such  low  temperature  had  been 
found.  Advantage  was  taken  of  the  latent  heat  of  evaporation,  that 
is,  the  heat  absorbed  when  a  liquid  becomes  a  gas.  An  easily  liquefied 
gas  was  evaporated  around  a  vessel  containing  one  more  difficulty 
liquefied,  which  in  its  turn  was  evaporated  around  a  still  more  difficulty 
liquefied  gas,  and  so  on.  The  liquids  had  successively  lower  boiling- 
points,  so  that  the  temperature  descended  by  steps  until  at  last  the 
critical  temperature  of  oxygen  was  attained,  whereupon  this  gas  could 
be  liquefied  by  pressure. 

The  modern  method  of  making  liquid  air  depends  on  a  disappearance 
of  heat  quite  analogous  to  the  latent  heat  of  evaporation.  If  the  ideal 
gas  (p.  28)  were  allowed  to  expand  without  doing  any  work,*  its 
temperature  would  remain  unchanged.  But  when  an  imperfect  gas 
expands  it  becomes  a  better  gas,  and  in  so  doing  absorbs  heat  for 
precisely  the  same  reason  that  a  liquid  absorbs  heat  when  it  becomes 
a  gas,  but  in  much  smaller  degree.  Now  the  higher  the  pressure  or 

B  lower  the  temperature  of  a  gas.  the  higher  is  its  degree  of  imperfec- 
tion (p.  28),  so  that  expansion  from  a  higher  pressure  or  at  a  low 
temperature  absorbs  more  heat  than  when  it  occurs  at  a  low  pressure 
or  at  a  high  temperature. 

The  actual  quantity  of  heat  absorbed  by  expansion  is  much  too  small 

to  lower  the  temperature  of  air  to  the  liquefying-point,  were  it  not  for 

an  ingenious  method  of  storing  up  the  cold  produced  by  the  expansion. 

In  the  Linde  machine,  for  liquefying  air,  for  example,  the  air  which  has 

een  slightly  cooled  by  expansion  is  used  to  cool  that  about  to  be 

of  theUaCtmosp^ered  **  ^  °Me  *  "  expanded  into  a  vacuum> instead  of  against  the  pressure 


LIQUEFACTION  OF  AIR. 


73 


expanded,  and  when  this  second  quantity  has  expanded  it  cools  a  third 
quantity,  and  so  on.  The  cumulative  eft'ect  of  this  regenerative  cooling 
is  to  lower  the  temperature  of  the  air  until  it  liquefies.  Of  course,  to 
economise  the  cold,  the  same  air  is  expanded  and  compressed  alternately. 
From  what  was  said  above  it  will  be  seen  that  as  the  temperature  of 
the  air  gets  lower,  each  expansion  entails  a  larger  absorption  of  heat. 

Fig.  53  represents  an  apparatus  for  applying  the  foregoing  principles.  Air  com- 
pressed at  some  200  atmospheres  is  admitted  at  A  into  a  lengthy  coil  B  of  metal 
pipe,  passing  concentrically  through  a  similarly  coiled  pipe  C.  The  other  end  of 
the  inner  coil  opens  into  a  box  D  and  is  provided  with  a  valve  E.  One  end  of  the 
outer  coil  also  opens  into  the  box  D,  whilst  the  other  end  is  connected  with  a  com- 
pressing pump  T.  The  coils  and  box  are  embedded  in  a  packing  of  wool,  not 
shown  in  the  figure,  contained  in  the  casing  H.  To  operate  the  apparatus  the 
valve  E  is  opened  until  the  air  issues  into  the  box  D  at  a  reduced  pressure  of  some 
20  atmospheres.  The  expanded  and  consequently  cooled  air  passes  up  the  outer 
coil  to  pump  2,  which  compresses  it  again  to  200  atmospheres  and  forces  it  through 


Fig.  53. — Liquefaction  of  air. 

a  coil  of  pipe  round  which  water  circulates  in  the  cooler  /.  Here  it  is  deprived  of 
the  heat  imparted  to  it  by  the  work  of  the  pump,  and  is  passed  back  to  the  inner 
coil  to  undergo  the  same  cycle  once  more.  It  will  be  seen  that  as  the  air  cooled 
by  expansion  passes  around  the  inner  coil,  it  cools  the  air  about  to  be  expanded, 
and  that  each  portion  of  air  issuing  from  the  inner  coil  must  be  colder  than  that 
which  preceded  it.  After  a  time  this  accumulated  cold  becomes  sufficient  to  lower 
the  temperature  to  -  193°  C.,  whereupon  liquid  air  collects  in  box  D  and  may  be 
drawn  off  through  tap  K.  It  is  found  more  economical  not  to  let  the  gas  expand 
to  atmospheric  pressure,  as  the  smaller  amount  of  work  necessary  to  pump  air  at 
20  atmospheres  pressure,  and  the  increased  cooling  due  to  the  work  which  the 
expanding  gas  has  to  do  in  moving  the  expanded  gas  at  this  pressure,  more  than 
balance  the  extra  cooling  which  might  be  obtained  by  expansion  to  a  lower 
pressure. 

To  preserve  liquid  air  for  more  than  a  few  moments  it  must  be 
drawn  off  into  a  vacuum  vessel,  that  is,  a  vessel  surrounded  by  a  shell 
enclosing  a  vacuous  space  around  the  walls  of  the  vessel.  The  vacuum 
prevents  passage  of  heat,  and  the  effect  is  enhanced  by  silvering  the 
surface  of  the  shell  so  as  to  reflect  heat  rays  falling  upon  it. 

Since  oxygen  boils  at  a  temperature  some  ioc  0  higher  than  that 
at  which  nitrogen  boils,  freshly  made  liquid  air  contains  nearly  50  per 


74  SEPAKATION  OF  OXYGEN  AND  NITKOGEN. 

cent,  by  volume  of  oxygen.     It  is  turbid  from  the  presence  of  crystals 


JUKI    Ul    »U.    411.    VC1  V    ilociiiT     A.  j.  .  n  , 

of  oxygen  which  is  obtained  by  fractionally  distilling  the  liquid,  so  that 

the  nitrogen  boils  away  first. 

Fractional  distillation  is  the  operation  of  separating  mixed  liquids  by 

carefully  raising  their  temperature  so  as  to  distil  first  that  which  has 

the  lowest  boiling-point. 

The  apparatus  employed  for  separating  oxygen  and  nitrogen  in  this  manner  is  of 

the  type  shown  in  Fig.  54.  Here  the  compressed  air  admitted  at  A  passes  through 
the  inner  pipes  of  two  concentric  coils  B  and  <7,  the 
two  currents  uniting  again  at  D  to  pass  through  a  coil 
E  situated  in  the  receiver  F.  The  valve  G  being 
opened,  the  air  expands  into  the  receiver  and  passes 
away  through  the  outer  pipe  of  the  coil  C.  Presently, 
liquid  air  begins  to  collect  in  F,  as  in  the  apparatus 
already  described,  but  its  temperature  is  somewhat 
higher  than  in  that  case  because  of  the  air  passing 
through  the  coil  E.  As  a  result  nitrogen  boils  away 
from  the  liquid,  and  passing  up  the  outer  pipe  of  coil 
B,  issues  at  H.  By  opening  valve  I  the  liquid  oxygen 
in  the  receiver  may  be  allowed  to  evaporate  through 
the  outer  pipe  of  coil  B,  so  as  to  be  collected  for  use 
at  the  extremity  K.  The  valves  L  are  adjusted  so 
that  the  proportion  of  hot  gas  passing  through  each 
coil  may  be  in  relation  to  the  larger  proportion  of 
nitrogen  than  of  oxygen  passing  away. 

Attempts  to  liquefy  hydrogen  on  the  prin- 
ciple employed  in  liquefying  air  fail  unless  the 
hydrogen  is  first  cooled  to  -  205°  C.  by  passing 
through  a  coil  of  metal  pipe  surrounded  by 
liquid  air  boiling  at  reduced  pressure.  This 
may  be  ascribed  to  the  fact  that  hydrogen  is 
a  much  better  gas  than  air,  so  that  it  is  less 
cooled  by  expansion.* 

One  of  the  most  remarkable  of  the  many 
interesting  experiments  that  can  be  performed 
with  liquid  air  consists  in  absorbing  it  by  a 
wad  of  cotton  wool  which  has  been  mixed  with 
finely  divided  charcoal  and  igniting  the  cotton ;  it  burns  like  gun- 
cotton,  and  if  fired  by  a  small  primer  of  mercuric  fulminate  it  detonates 
with  violence.  It  is  said  that  this  form  of  explosive  has  been  used  in 
blasting  operations  in  excavating  the  Simplon  tunnel. 


Fig.  54.— Separation  of  O 
and  N  by  liquefaction. 


NITROGEN. 

N  =  14  parts  by  weight  =  i  vol. 

53.  Besides  its  presence  in  air,  nitrogen  is  elsewhere  found  in  nature 
as  a  constituent  of  saltpetre  or  potassium  nitrate  (KNO3),  and  Chili 
saltpetre  or  sodium  nitrate  (NaN03).  It  also  occurs  as  ammonia  (NH3) 
in  the  atmosphere  and  in  the  gaseous  emanations  from  volcanoes.  It 
is  contained  in  the  greater  number  of  animal,  and  in  many  vegetable, 

*  Indeed,  it  appears  that  the  cooling  of  the  hydrogen  by  expansion  is  negligible  until  the 
temperature  has  fallen  considerably,  probably  to  about  -  80°  C. 


PROPERTIES   OF  NITROGEN. 


75 


substances,  and  therefore  has  a  most  important  share  in  the  chemical 
phenomena  of  life. 

Nitrogen  is  generally  obtained  by  burning  phosphorus  in  a  portion 
of  air  confined  over  water  (Fig.  55).  The  phosphorus  is  floated  on  the 
water  in  a  small  porcelain  dish,  kindled,  and  covered  with  a  bell-jar. 
The  nitrogen  remains  mixed  with  clouds  of  phosphoric  anhydride 
(P205),  which  may  be  removed  by  allowing  the  gas  to  stand  over  water, 
100  vols.  of  which  dissolve  only  1.4  vols.  of 
nitrogen  at  the  ordinary  temperature. 

When  nitrogen  is  required  in  larger 
quantity,  it  is  more  conveniently  prepared 
by  passing  air  from  a  gas-holder,  over 
metallic  copper  heated  to  redness  in  a  tube. 
If  the  air  be  passed  through  solution 
of  ammonia  before  passing  over  the 
heated  copper,  a  short  length  of  copper 
will  suffice,  since  the  oxide  formed 
will  be  reduced  by  the  ammonia  ; 
3CuO  +  2NH3  =  Cu3  +  3H2O  +  N2. 

The  nitrogen  separated  from  air, 
however,  always  contains  nearly  i  per 
cent,  by  volume  of  argon.  To  prepare  pure  nitrogen  some  com- 
pound of  the  element  must  be  decomposed  ;  thus  an  oxide  of  nitrogen 
may  be  passed  over  red  hot  copper.  Or  a  solution  of  ammonium  nitrite 
(or  mixed  solutions  of  potassium  nitrite  and  ammonium  chloride) 
may  be  boiled  in  a  flask  provided  with  a  delivery  tube;  NH4N02  = 


Fig.  55. — Preparation  of  nitrogeu. 


The  remarkable  chemical  inactivity  of  free  nitrogen  has  already  been 
alluded  to  (p.  71).  It  has  been  seen,  however,  to  be  capable  of  com- 
bining directly  with  boron  and  silicon,  and  magnesium  and  titanium 
unite  with  it  even  more  readily  at  a  high  temperature.  Although  it  is 
so  indifferent  to  oxygen  at  ordinary  temperatures  it  unites  with  that 
element  when  a  mixture  of  the  two  is  subjected  to  the  high  tem- 
perature of  electric  sparks,  forming  oxides  of  nitrogen.  Nitrogen 
is  conspicuous  among  the  elements  for  forming,  with  hydrogen,  a 
powerful  alkali  (ammonia,  NH3),  whilst  the  feeble  chemical  ties 
which  hold  it  in  combination  with  other  elements,  joined  to  its 
character  of  a  permanent  gas,  render  many  of  its  compounds  very 
unstable  and  explosive,  as  is  the  case  with  the  so-called  chloride  and 
iodide  of  nitrogen,  gun-cotton,  the  fulminates  of  silver  and  mercury, 
nitro-glycerine,  &c. 

The  discovery  of  nitrogen  was  made  in  1772  by  Rutherford  (Pro- 
fessor of  Botany  in  the  University  of  Edinburgh),  who  was  led  to  it  by 
the  observation  that  respired  air  was  still  unfit  to  support  life  when  all 
the  carbonic  acid  had  been  absorbed  from  it  by  a  caustic  alkali.  Hence 
the  name  azote  (a,  priv.,  and  faij,  life),  formally  bestowed  upon  this 
gas. 

Nitrogen  becomes  a  colourless  liquid  at  -  194°  C.,  the  temperature  at 
which  it  boils  under  atmospheric  pressure.  Its  critical  temperature  is 
—  146°  C.,  and  its  critical  pressure  is  35  atmospheres.  When  rapidly 
evaporated  a  portion  of  the  liquid  nitrogen  freezes  to  a  colourless  solid, 
melting  at  -  214°  C. 


76  ARGON. 

Nitrogen  is  the  type  of  the  trivalent  elements  (p.  u),  its  most 
stable  compound  with  hydrogen  being  NH3,  ammonia. 

ARGON. 
A  =  39.6  parts  by  weight  =  2  vols. 

Rayleigh  (1894)  found  that  whereas  i  litre  of  nitrogen  prepared 
from  compounds  of  the  element,  such  as  from  an  oxide  of  nitrogen  by 
passing  it  over  red-hot  copper,  weighs  1.2505  gram,  i  litre  of  nitrogen 
prepared  by  depriving  purified  air  of  its  oxygen  weighs  1.2572  gram. 
Cavendish  had  long  before  recorded  that  when  oxygen  is  added  in  small 
doses  to  atmospheric  nitrogen  through  which  electric  sparks  are  passed 
and  which  is  contained  in  a  vessel  also  containing  alkali  to  absorb  the 
oxides  of  nitrogen  produced,  a  small  residue  of  gas  is  left  which  cannot 
be  caused  to  combine  with  oxygen  under  the  influence  of  the  sparks. 
It  has  now  been  proved  that  Cavendish's  residue  is  not  obtainable  when 
nitrogen  other  than  that  from  the  atmosphere  is  used,  and  that  it  is 
this  residue  which  makes  atmospheric  nitrogen  about  \  per  cent. 
heavier  than  other  nitrogen,  as  observed  by  Rayleigh.  The  latter,  in 
conjunction  with  Ramsay,  examined  the  gas  and  concluded  that  it  was 
an  element  so  devoid  of  any  tendency  to  combine  with  other  elements, 
and  therefore  of  chemical  energy,  that  it  might  aptly  be  termed  argon 
(a,  without,  epyov,  work). 

Argon  is  prepared  by  passing  air  first  over  caustic  potash  to  absorb 
carbon  dioxide,  then  through  strong  sulphuric  acid  to  absorb  aqueous 
vapour,  and  finally  over  red-hot  magnesium  or  lithium  which  combines 
with  the  oxygen  of  the  air  to  form  magnesium  or  lithium  oxide  and 
with  the  nitrogen  to  form  magnesium  or  lithium  nitride. 

As  the  combination  of  nitrogen  with  either  metal  does  not  occur  rapidly,  the 
passage  of  the  gas  through  the  red-hot  tube  containing  the  metal  must  be  repeated 
several  times  before  the  argon  is  pure. 

A  modification  of  Cavendish's  experiment  also  serves  for  obtaining  argon.  A 
large  inverted  flask  (50  litres)  is  closed  with  a  rubber  cork  through  which  pass  five 
glass  tubes.  Through  two  of  these  are  passed  conducting  wires  terminating  within 
the  flask  in  platinum  electrodes,  and  connected  at  their  other  ends  with  the  poles 
of  an  apparatus  (an  electrical  transformer  supplied  with  40  amperes  at  30  volts), 
yielding  electric  current  at  very  high  pressure  (6000  volts).  A  third  tube  serves 
for  the  introduction  of  a  jet  of  caustic  soda  solution  which  plays  against  the  side 
of  the  flask  ;  a  fourth  tube  serves  to  remove  this  solution  as  it  runs  down  into  the 
neck.  Through  the  fifth  tube,  a  mixture  of  1 1  vols.  oxygen  and  9  vols.  air  is 
introduced  continuously  into  the  flask.  When  the  transformer  is  set  to  work,  an 
"electric  flame  "  plays  between  the  electrodes,  and  is  probably  an  actual  flame  of 
burning  nitrogen,  for  the  latter  rapidly  disappears,  being  dissolved  as  oxides  of 
nitrogen  in  the  alkali.*  About  20  litres  of  the  gases  maybe  combined  per  hour, 
and  finally  a  mixture  of  argon  and  oxygen  is  obtained  from  which  the  latter  may 
be  absorbed  by  admitting  pyrogallic  acid. 

The  argon  thus  obtained  amounts  to  0.6  per  cent,  of  the  air.  It  is  a 
colourless  gas,  without  odour  ;  it  is  19.8  times  as  heavy  as  hydrogen  so 
that  its  molecular  weight  is  39.6.  It  boils  at  -  186°  C.  and  melts  at 
-  189.5°  *>  its  critical  temperature  is  -  117.4°  and  its  critical  pressure 
53  atmospheres ;  hence,  at  the  ordinary  temperature,  it  is  far  removed 
from  the  liquid  state  and  obeys  the  gas  laws  well.  100  vols.  of  water 
dissolve  4.1  vols.  of  argon  at  15°  C.,  and  the  gas  is  found  in  the  water 
from  several  mineral  springs. 

»  Crookes  has  suggested  the  manufacture  of  nitrates  in  this  manner  from  the  atmosphere. 


EARE   GASES.  77 

The  most  remarkable  feature  of  argon  is  the  fact  that  it  has  resisted 
all  attempts  to  combine  it  with  other  elements  ;  no  compound  of  it  is 
known.  Hence  its  atomic  weight  has  not  been  ascertained  by  the 
method  outlined  at  p.  10;  but  it  behaves  physically  as  though  its 
molecules  were  monatomic  in  which  case  its  atomic  weight  is  identical 
with  its  molecular  weight. 

Helium.  He  =  4  parts  by  weight  =  2  vols. — When  argon  was  discovered, 
search  was  made  for  it  in  other  places  than  the  atmosphere,  and  while 
submitting  to  spectrum  analysis  0?.i\)  some  gas  obtained  by  heating  the 
rare  mineral  clecelte,  Eamsay  (1895)  detected  a  bright  yellow  line  coin- 
ciding with  that  first  detected  (1868)  in  the  spectrum  of  the  luminous  atmo- 
sphere which'is  seen  surrounding  the  sun  when  he  is  eclipsed.  The  line  had  been 
ascribed  to  an  element,  provisionally  named  helium,  but  as  no  terrestrial  matter 
had  shown  the  same  spectrum,  it  was  concluded  that  the  element  was  non-existent 
on  the  earth. 

Ramsay's  gas  is  no  doubt  the  same  matter  as  had  been  termed  helium.  It  is 
obtainable  from  several  other  minerals,  besides  cleveite,  by  heating  them,  particu- 
larly such  as  contain  uranium  ;  the  mineral  is  placed  in  a  glass  tube,  which  is  then 
exhausted  by  a  mercury  pump  (Fig.  70)  and  heated,  the  gas  being  collected  by 
pumping  it  out  of  the  tube.  The  helium  is  generally  only  a  fraction  of  the  total 
gas  evolved,  and  must  be  separated  from  the  other  gases  as  argon  is. 

Helium  is  colourless,  odourless,  and  exceedingly  light,  being  only  twice  as 
heavy  as  hydrogen;  its  sp.  gr.  (air  =  i)  is  0.14.  It  is  very  slightly  soluble  in 
water,  100  vols.  of  water  dissolving  about  1.4  vols.  at  15°  c!,  and  has  resisted  all 
attempts  to  liquefy  it.  It  has  been  identified  as  accompanying  argon  in  the  water 
from  the  King's  Well  at  Bath. 

It  is  supposed  that  helium  exists  in  minerals  in  a  state  of  combination,  but  the 
gas  not  yet  been  caused  to  combine  with  any  other  element ;  hence  its  atomic 
weight  is  not  chemically  known.  It  behaves  physically,  however,  like  a  mona- 
tomic gas,  so  that  its  atomic  weight  should  be  identical  with  its  molecular  weight, 
namely  4. 

Krypton,  Xenon,  and  Neon. — When  a  vessel  containing  argon,  as  it  is 
prepared  from  the  atmosphere,  is  cooled  by  immersion  in  liquid  air,  the  gas  liquefies, 
and  on  allowing  the  temperature  to  rise  the  first  portion  which  boils  off  is  a  mixture 
of  helium  and  another  gas,  neon,  the  vapour  density  of  which  is  20.3.  The  next  gas 
to  distil  is  argon,  and  the  residue  is  a  mixture  of  yet  two  other  gases,  krypton,  of 
vapour  density  40.5,  and  xenon,  of  vapour  density  63.5.  By  several  such  fractional 
distillations  the  argon,  krypton,  and  xenon  are  completely  separated,  and  are 
recognised  by  their  characteristic  spectra.  Helium  and  neon  are  separated  by 
cooling  them  by  liquid  hydrogen,  when  the  neon  freezes.  All  these  gases  are 
supposed  to  have  monatomic  molecules.  The  amount  of  helium,  krypton,  neon, 
and  xenon  in  the  air  is  exceedingly  small,  about  0.0025  per  cent,  of  the  argon 
present. 

AMMONIA. 

NH3  =17  parts  by  weight  =  2  volumes. 

54.  Ammonia  belongs  to  organic  rather  than  to  inorganic  nature. 
It  is  generally  a  product  of  the  decomposition  of  nitrogenous  matter. 
Dead  animal  and  vegetable  matters  yield  it  in  putrefaction.  Bones 
furnish  it  by  destructive  distillation  ;  so  does  coal,  the  fossilised  plant. 
Its  compounds  are  found  in  beds  of  guano  (the  excrement  of  sea-fowl), 
and  the  most  important  of  them,  sal  ammoniac,  was  first  made  in  Egypt 
from  the  dung  of  camels.  Its  mineral  sources  are  chiefly  volcanic  ; 
ammonium  sulphate  is  found  in  Tuscan  boric  acid,  and  occurs  as 
mascagnine  in  the  form  of  an  efflorescence  on  recent  lavas.  It  may 
be  produced  by  the  combination  of  nitrogen  and  hydrogen,  induced  by 
electric  discharge,  but  its  formation  soon  stops  unless  it  is  absorbed 
by  an  acid  as  fast  as  it  is  produced,  because  when  6  per  cent,  of  the 


78  AMMONIA. 

mixed  gases  has  become  converted  into  ammonia  the  compound  begins 
to  be  decomposed  by  the  electric  sparks.* 

The  proportion  of  ammonia  existing  in  atmospheric  air  is  so  small 
that  it  is  difficult  to  determine  it  with  precision ;  it  appears,  however, 
not  to  exceed  5  milligrams  in  a  cubic  metre,  for  although  ammonia  is. 
constantly  sent  forth  into  the  air  by  the  putrefaction  of  animal  and 
vegetable  substances  containing  nitrogen,  it  is  soon  absorbed  by  water, 
and  even  by  earth  and  other  porous  solids.  Rain  water  contains  from 
i  to  2  parts  per  million  of  ammonia.  With  the  aid  of  certain  micro- 
organisms in  the  soil,  certain  families  of  plants  can  utilise  the  uncom- 
bined  nitrogen  of  the  atmosphere  as  food  for  their  growth,  but  for  a, 
large  number  of  plants  the  chief  supply  of  nitrogen  is  that  contained 
in  the  ammonia,  nitrates  and  nitrites  contained  in  the  air,  the  soil,  and 
the  water.  During  the  life  of  an  animal,  it  restores  to  the  air  the 
nitrogen  which  formed  part  of  its  wasted  organs,  mainly  as  urea  and 
uric  acid  in  the  urine,  the  nitrogen  of  these  being  eventually  converted 
into  ammonia  when  the  excretion  undergoes  putrefaction.  Dead 
animal  and  vegetable  matter,  when  putrefying,  restores  its  nitrogen  to 
the  air,  chiefly  in  the  forms  of  ammonia  and  substances  closely  allied  to 
it,  but  partly  also,  it  is  said,  in  the  free  state  ;  when  such  matter  is 
burnt  all  the  nitrogen  is  liberated  in  an  uncombined  condition.  Am- 
monia appears  to  be  formed  from  atmospheric  nitrogen  by  the  growth 
of  fungi  (which  evolve  hydrogen)  and  by  the  decay  of  wood.  Nitrogen 
is  also  slowly  absorbed  from  air  by  sawdust  mixed  with  lime  and  by 
glucose  mixed  with  soda  ;  the  nitrogen  being  evolved  as  ammonia  when 
these  materials  are  afterwards  heated  with  soda-lime. 

The  liquor  ammonice,  or  solution  of  ammonia  in  water,  which  is  so 
largely  used  in  medicine  and  the  arts,  is  obtained  chiefly  from  the 
ammoniacal  liquor  resulting  from  the  destructive  distillation  of  coal  for 
the  manufacture  of  gas.t  The  ammoniacal  liquor  of  the  gasworks  con- 
tains ammonia  in  combination  with  carbonic  and  hydrosulphuric  acids. 
To  recover  the  ammonia  the  liquor  is  heated  with  lime  in  a  still ;  the 
ammonia  and  hydrosulphuric  acid  are  thus  expelled  and  are  conducted 
into  a  covered  tank  containing  sulphuric  acid  or  hydrochloric  acid, 
which  absorbs  the  ammonia  and  allows  the  hydrosulphuric  acid  to 
escape  through  a  pipe  in  the  cover  of  the  tank,  to  be  burnt,  or  other- 
wise disposed  of,  in  order  that  it  may  not  cause  a  nuisance  by  its  evil 
odour  and  poisonous  properties.  Ammonium  sulphate  or  chloride 
(according  to  which  acid  has  been  used)  crystallises  from  the  acid  in 
the  tank.  The  former  is  sold  as  a  manure  ;  the  latter  is  generally  used 
for  making  pure  ammonia.  The  crystals  of  ammonium  chloride  are 
moderately  heated  in  an  iron  pan  to  deprive  them  of  tar,  and  are  finally 
purified  by  sublimation,  that  is,  by  converting  them  into  vapour  and 
allowing  this  vapour  to  condense  again  into  the  solid  form.  For  this 
purpose  the  crystals  are  heated  in  a  cylindrical  iron  vessel  covered  with 
an  iron  dome  lined  with  fireclay.  The  ammonium  chloride  rises  in 
vapour  below  a  red  heat,  and  condenses  upon  the  dome  in  the  form  of 
the  fibrous  cake  known  in  commerce  as  sal  ammoniac. 

*  The  heat  evolved  in  the  combination  N  +  H3=NH3  is  only  1195  gram  units  ;  hence  it  is 
not  surprising1  that  the  reaction  is  difficult  to  realise. 

f  Considerable  quantities  of  ammonia  are  now  being-  recovered  from  the  products  of  com- 
bustion obtained  from  blastfurnaces  (q.v.),  in  which,  of  course,  it  originates  from  the  distilla- 
tion of  coal.  The  ovens  in  which  coke  is  manufactured  are  also  furnishing  ammonia. 


PEEPAEATION  OF  AMMONIA. 


79 


To  obtain  ammonia  from  this  salt,  an  ounce  of  it  is  reduced  to  coarse 
powder,  and  rapidly  mixed  with  2  ounces  of  powdered  quicklime.  The 
mixture  is  gently  heated  in  a  dry  Florence  flask  (Fig.  56),  and  the  gas 
being  little  more  than  half  as  heavy  as  air  (sp.  gr.  0.59)  may  be  collected 
in  dry  bottles  by  displacement  of  air,  the  bottles  being  allowed  to  rest 
upon  a  piece  of  tin  plate  which  is  perforated  for  the  passage  of  the 
tube.  To  ascertain  when  the  bottles  are  filled,  a  piece  of  red  litmus- 
paper  may  be  held  at  some  little  distance  above  the  mouth,  when  it 
will  at  once  acquire  a  blue  colour  if  the  ammonia  escapes.  The  bottles 
should  be  closed  with  greased  stoppers. 

The  action  is  explained  by  the  following  equation : 


2NH4C1 

Ammonium 

chloride. 


CaO     =    CaCl2 
Lime.  Calcium 

chloride. 


H90 


2NH3. 
Ammonia. 


The  readiest  method  of  obtaining  gaseous  ammonia  for  the  study  of  its  pro- 
perties consists  in  gently  heating  the  strongest  liquor  ammonice  in  a  retort  or  flask 


0** 


Fig.  56. — Preparation 
of  ammonia. 


Fig.  57- 


provided  with  a  bent  tube  for  collecting  the  gas  by  displacement  (Fig.  57).  The 
gas  is  evolved  from  the  solution  at  a  very  low  temperature,  and  may  be  collected 
unaccompanied  by  steam. 

Ammonia  is  readily  distinguished  by  its  very  characteristic  smell, 
and  its  powerful  alkaline  action  upon  red  litmus  and  turmeric  papers. 
It  is  absorbed  by  water  in  greater  proportion  by  volume  than  any  other 
common  gas,  one  volume  of  water  absorbing  more  than  700  volumes  of 
ammonia  at  the  ordinary  temperature,  and  becoming  ij  volume  of 
solution  of  ammonia.  During  the  dissolution  of  the  gas  much  more  heat 
is  evolved  than  corresponds  with  the  heat  of  liquefaction  of  the  gas  ;  * 
this  excess  of  heat  can  only  be  attributed  to  chemical  combination ;  but 
no  definite  compound  of  ammonia  with  water  has  been  obtained,  and 
the  gas  gradually  escapes  on  exposing  the  solution  to  the  air.  As  is 
the  case  with  all  solutions  of  gases,  the  quantity  of  ammonia  retained 
by  the  water  is  dependent  upon  the  temperature  and  pressure  ;  the 
escape  of  the  gas  from  the  solution  is  attended  with  great  production  of 
cold,  much  heat  becoming  latent  in  the  conversion  of  the  ammonia  from 
the  liquid  to  the  gaseous  state. 

*  Seventeen  grams  of  ammonia  evolve  20,300  gram-units  of  heat  when  dissolved  in  excess 
of  water. 


So 


SOLUTION   OF  AMMONIA. 


The  rapid  absorption  of  ammonia  by  water  is  well  shown  by  filling  a  globular 
flask  (Fig.  58)  with  the  gas,  keeping  it  with  its  mouth  downwards  in  a  small 
capsule  of  mercury  which  is  placed  in  a  large  basin.  If  this  basin  be  filled  with 
water,  it  cannot  come  into  contact  with  the  ammonia  until  the  mouth  of  the  flask 
is  raised  out  of  the  mercury,  when  the  water  will  quickly  enter  and  fill  the  flask. 
The  water  should  be  coloured  with  reddened  litmus  to  exhibit  the  alkaline  reaction 
of  the  ammonia. 

That  the  amount  of  ammonia  in  solution  varies  with  the  pressure  may  be  proved 
by  filling  a  barometer  tube,  over  30  inches  long,  with  mercury  to  within  an  inch 
of  the  top,  filling  it  up  with  strong  ammonia,  closing  the  mouth  of  the  tube,  and 
inverting  it  with  its  mouth  under  mercury  ;  on  removing  the  finger  the  diminished 
pressure  caused  by  the  gravitation  of  the  column  of  mercury  in  the  tube  will  cause 


Fig.  59- 


Fig-.  60. 


the  solution  of  ammonia  to  boil,  from  the  escape  of  a  large  quantity  of  the  gas, 
which  will  rapidly  depress  the  mercury.  If  the  pressure  be  now  increased  by 
gradually  depressing  the  tube  in  a  tall  cylinder  of  mercury  (Fig.  59).  the  water  will 
again  absorb  the  ammoniacal  gas. 

To  exhibit  the  easy  expulsion  of  the  ammoniacal  gas  from  water  by  heat,  a 
moderately  thick  glass  tube,  about  12  inches  long  and  £  inch  in  diameter,  may  be 
nearly  filled  with  mercury,  and  then  filled  up  with  strong  solution  of  ammonia  ;  on 
closing  it  with  the  thumb,  and  inverting  it  into  a  vessel  of  mercury  (Fig.  60),  the 
solution  will,  of  course,  rise  above  the  mercury  to  the  closed  end  of  the  tube.  By 
grasping  this  end  of  the  tube  in  the  hand,  a  considerable  quantity  of  gas  maybe 
expelled,  and  the  mercury  will  be  depressed.  If  a  little  hot  water  be  poured  over 
the  top  of  the  tube,  the  latter  will  become  filled  with  ammoniacal  gas,  which  will 
be  absorbed  again  by  the  water  when  the  tube  is  allowed  to  cool,  the  mercury 
returning  to  fill  the  tube. 


AMMONIA  FREEZING-MACHINES.  8 1 

The  solution  of  ammonia,  which  is  an  article  of  commerce,  may  be 
prepared  by  conducting  the  gas  into  water  contained  in  a  two-necked 
bottle,  the  second  neck  being  connected  with  a  tube  passing  into  another 
bottle  containing  water,  in  which  any  escaping  ammonia  may  be  con- 
densed. The  strength  of  the  solution  is  inferred  from  its  specific 
gravity,  which  is  lower  in  proportion  as  the  quantity  of  ammonia  in  the 
solution  is  greater. 

Thus,  at  57°  F.  (14°  C.),  a  solution  of  sp.  gr.  0.8844  contains  36  parts  by  weight 
of  ammonia  in  100  parts  of  solution  (liquor  ammonice  fortissimus)  ;  0.9251,  20  per 
cent.  ;  0.9593,  10  per  cent.  (British  Pharmacopoeia).  The  specific  gravity  is  ascer- 
tained by  comparing  the  weights  of  equal  volumes  of  water  and  of  the  solution  at 
the  same  temperature.  For  this  purpose  a  light  stoppered  bottle,  or  picnometer,  is 
provided,  capable  of  containing  about  two  fluid  ounces.  This  is  thoroughly  dried, 
and  counterpoised  in  a  balance  by  placing  in  the  opposite  pan  a  piece  of  lead,  which 
may  be  cut  down  to  the  proper  weight.  The  bottle  is  then  filled  with  solution  of 
ammonia,  the  temperature  observed  with  a  thermometer  and  recorded,  the  stopper 
inserted,  and  the  bottle  weighed.  It  is  then  well  rinsed  out,  filled  with  distilled 
water,  the  temperature  equalised  with  that  of  the  ammonia  by  placing  the  bottle 
either  in  warm  or  cold  water,  and  the  weight  ascertained  as  before.  The  specific 
gravity  is  obtained  by  dividing  the  weight  of  the  solution  of  ammonia  by  that  of 
the  water.  The  ammonia  meter,  a  form  of  hydrometer  (Fig.  61),  is  a  convenient 
instrument  for  rapidly  ascertaining  the  specific  gravity  of  liquids  lighter  than 
water.  It  consists  of  a  hollow  glass  float  with  a  long  stem,  weighted  with  a  bulb 
containing  shot  or  mercury,  so  that  when  placed  in  distilled  water  it  may  sink  to 
1000°  of  the  scale  marked  on  the  stem,  this  number  representing  the  specific 
gravity  of  water.  When  placed  in  a  liquid  lighter  than  water,  it  must,  of  course, 
sink  lower  in  order  to  displace  more  liquid  (since  solids  sink  until  they  have  dis- 
placed their  own  weight  of  liquid).  By  trying  it  in  liquids  of  known  specific 
gravities,  the  mark  upon  the  scale  to  which  it  sinks  may  be  made  to  indicate  the 
specific  gravity  of  the  liquid.  The  ammonia  meter  generally  has  a  scale  so  divided 
that  it  indicates  at  once  the  precentage  weight  of  ammonia.  In  this  country  the 
specific  gravity  of  a  liquid  is  always  supposed  to  be  taken  at  62°  F.  (16°  C.). 

The  common  name  for  solution  of  ammonia,  spirit  of  hart's  horn,  is 
derived  from  the  circumstance  that  it  was  originally  obtained  for 
medicinal  purposes  by  distilling  shavings  of  that  material. 

Ammonia  is  far  removed  from  the  ideal  gas  (p.  27);  its  critical 
temperature  is  about  130°  C.,  so  that  it  can  be  liquefied  at  the  ordinary 
temperature,  6J  atmospheres  sufficing 
at  10°  C.  The  liquid  is  colourless,  has 
sp.  gr.  at  o°  C.  =  0.63  and  boils  at 
-  33.5°  C.,  so  that  the  gas  liquefies  at 
this  temperature  under  atmospheric 
pressure.  It  freezes  to  a  white  crystal- 
line mass  which  melts  at  —  78°  C. 
The  comparative  ease  with  which  the 
gas  may  be  liquefied  has  led  to  its 
application  in  Carre's  freezing  ap- 
paratus (Fig.  61),  in  which  the  gas 
generated  by  heating  a  concentrated 
solution  of  ammonia  in  a  strong 
iron  boiler  (A)  is  liquefied  by  its  ^_^^_^^^^^^^ 
own  pressure  in  an  iron  receiver  (B)  ^ 

placed     in     cold     water.        When      the      Fig..  62.— Carry's  freezing  apparatus. 

boiler     is    taken    off    the     fire     and 

cooled    in    water,    the    liquefied   ammonia    evaporates    very    rapidly 
from  the  receiver  back   into  the  boiler,  thereby  producing  so  much 

F 


82 


LIQUEFACTION   OF  AMMONIA. 


AID! 


cold  *  that  a  vessel  of  water  (C)  placed  in  spirit  of  wine  contained  in 
a  cavity  in  the  receiver,  is  at  once  congealed  into  ice. 

To  refrigerate  large  spaces  by  means  of  liquid  NH3,  the  gas  is  compressed  by  a 
pump  into  a  coil  immersed  in  a  tank,  and  the  liquid  formed  is  allowed  to  evaporate 
through  another  coil  also  immersed  in  a  tank,  the  gas  returning  to  the  suction 
side  of  the  compression  pump.  Brine  (which  can  be  cooled  considerably  below 

o°  C.  without  freezing)  is  passed 
through  the  second  tank  where  it  is 
cooled  by  the  evaporating  NH3,  and 
then  through  pipes  in  the  space  to  be 
cooled,  then  through  the  first  tank, 
where  it  cools  the  compressed  NH3, 

tank. 

The  liquefaction  of  ammonia  is  very 
easily  effected  by  heating  the  ammo- 
niated  silver  chloride  (AgC1.3NH3)  in 
one  limb  of  a  sealed  tube,  the  other 
limb  of  which  is  cooled  in  a  freezing- 
mixture.  A  piece  of  stout  glass  tube 
(A,  Fig.  137),  about  12  inches  long  and 
|  inch  in  diameter,  is  drawn  out,  at 
about  an  inch  from  one  end,  to  a 
narrow  neck.  About  20  grams  of  silver 
chloride  (dried  at  400°  F.)  are  intro- 
duced into  the  tube,  so  as  to  lie  loosely  in  it.  For  this  purpose  a  gutter  of  stiff 
uaper  (B)  should  be  cut  so  as  to  slide  loosely  in  the  tube,  the  silver  chloride 
placed  upon  it,  and  when  it  has  been  thrust  into  the  tube  (held  horizontally)  the 
latter  should  be  turned  upon  its  axis,  so  that  the  silver  chloride  may  fall  out  of 
the  paper,  which  may  be  then  withdrawn.  The  tube  is  now  drawn  out  to  a  narrow 
neck  at  about  an  inch  from  the  other  end,  as  in  C,  and  afterwards  carefully  bent, 
as  in  D,  care  being  taken  that  none  of  the  chloride  falls  into  the  short  limb  of  the 
tube,  which  should  be  about  4  inches  long.  The  tube  is  then  supported  by 
a  holder,  so  that  the  long  limb  may  be  horizontal,  and  is  connected  by  a  tube  and 


Fig.  64. 

cork  with  an  apparatus  delivering  dry  NH3,  prepared  by  heating  80  grams  of  N"H4C1 
with  an  equal  weight  of  CaO  in  a  flask,  and  passing  the  gas,  first  into  an  empty 
bottle  (A,  Fig.  64)  standing  in  cold  water,  and  afterwards  through  a  bottle  (B) 
filled  with  lumps  of  quicklime,  to  absorb  all  aqueous  vapour.  The  long  limb  of  the 
tube  must  be  surrounded  with  filtering  paper,  which  is  kept  wet  with  cold  water. 
The  current  of  ammonia  should  be  continued  at  a  moderate  rate,  until  the  tube  and 
its  contents  no  longer  increase  in  weight,  which  will  occupy  about  three  hours — 

*  Seventeen  grams  of  ammonia  absorb  5661  gram  units  of  heat  in  vaporising-  at  -40°  C. 
The  specific  heat  of  liquid  ammonia  between  o°  and  20°  C.  is  1.02,  being  higher  than  that  of 
water,  a  rare  occurrence. 


COMBUSTION  OF  AMMONIA. 


about  2.2  grams  of  NH3  being  absorbed.  The  longer  limb  is  sealed  by  the  blow- 
pipe flame  whilst  the  gas  is  still  passing,  and  then,  as  quickly  as  possible,  the 
shorter  limb,  keeping  that  part  of  the  tube  which  is  occupied  by  the  arnmoniated 
silver  chloride  still  surrounded  by  wet  paper. 

When  the  shorter  limb  of  this  tube  is  cooled  (Fig.  65),  in  a  mixture  of  ice  and 
salt  (or  of  8  ounces  of  sodium  sulphate  and  4  measured  ounces  of  common  hydro- 
chloric acid),  whilst  the  longer  limb  is  gently  heated  from  end  to  end  by  waving  a 
spirit-lamp  beneath  it,  the  NH3  evolved  by  the  heat  from  the  ammoniated  silver 
chloride,  which  partly  fuses,  condenses  to  a  beautifully  clear  liquid  in  the  cold 
limb.  When  this  is  withdrawn  from  the  freezing- 
mixture,  and  the  tube  allowed  to  cool,  the  liquid 
ammonia  boils  and  gradually  disappears  entirely, 
the  gas  being  again  absorbed  by  the  silver  chloride, 
so  that  the  tube  is  ready  to  be  used  again. 

A  small  quantity  of  liquefied  ammonia  may  be 
more  conveniently  obtained  by  means  of  a  tube 
prepared  as  above,  but  containing  about  twelve 
inches  of  fragments  of  well-dried  wood  charcoal 
saturated  with  dry  NH3.  The  shorter  limb  of  the 
tube  should  be  drawn  out  to  a  long  narrow  point  Fig.  65.— Liquefaction  of  ammonia, 
before  sealing.  This  limb  being  immersed  in  the 

freezing-mixture,  the  other  is  placed  in  a  long  test-tube  containing  water,  which  is 
heated  to  boiling.  The  ammonia  soon  returns  to  the  charcoal  when  the  tube  cools. 

Liquefied  ammonia  dissolves  potassium  and  sodium  to  a  blue  solution  containing 
the  compounds  KH3N-NH3K  and  NaH3N'NH3Na  ;  iodine,  sulphur,  and  phosphorus 
are  also  dissolved  by  it. 

Ammonia  is  feebly  combustible  in  atmospheric  air,  as  may  be  seen  by 
holding  a  taper  just  within  the  mouth  of  an  inverted  bottle  of  the  gas, 
which  burns  with  a  peculiar  livid  flickering  light  around  the  flame,  but 
will  not  continue  to  burn  when  the  flame  is  removed,  because  the  tem- 
perature produced  by  such  a  feeble  combustion  of  the  hydrogen  in  air 
is  not  high  enough  to  continue  the  decomposition  of  the  ammonia. 
During  its  combustion  the  hydrogen  is  converted  into  water,  and  the 
nitrogen  set  free.  In  oxygen,  however,  ammonia  burns  with  a  con- 
tinuous flame. 

This  is  very  well  shown  by  surrounding  a  tube  delivering  a  stream  of  ammonia 
(obtained  by  heating  strong  solution  of  ammonia  in  a  retort)  with  a  much  wider 
tube  open  at  both  ends  (Fig.  66)  through  which  oxygen  is  passed  by  holding  a 
flexible  tube  from  a  gas-bag  or  gas- 
holder underneath  it.  On  kindling 
the  stream  of  ammonia  it  will  give  a 
steady  flame  of  10  to  12  inches  long. 

The  elements  of  ammonia  are 
easily  separated  from  each  other 
by  passing  the  gas  through  a  red- 
hot  tube,  or  still  more  readily 
by  exposing  it  to  the  action  of 
the  high  temperature  of  the  elec- 
tric spark,  when  the  volume  of 
the  gas  rapidly  increases  until 
it  is  doubled,  2  volumes  of 
ammonia  being  decomposed  into 
i  volume  of  nitrogen  and  3 
volumes  of  hydrogen,  showing 


Fig.  66. 


that  the  molecule  of  ammonia  probably  contains  atoms  of  N  and  H  in 
the  proportion  of  i  :  3. 

For  this   experiment  a  measured   volume   of   NH3    is  confined  over  mercury 


84  COMPOSITION  OF  AMMONIA. 

(Fig.  67),  in  a  tube  through  which  platinum  wires  are  sealed  for  the  passage  of 
the  spark  from  an  induction-coil.  The  volume  of  the  gas  is  doubled  in  a  few 
minutes,  and  if  the  tube  be  furnished  with  a  stop-cock  (A),  the  presence  of  free 
hydrogen  may  be  shown  by  filling  the  open  limb  with  mercury  and  kindling  the 
gas  as  it  issues  from  the  jet.  The  decomposition  ceases  when  only  3  per  cent,  of 
ammonia  remains  (p.  77). 

Another  method  of  demonstrating  that  ammonia  is  formed  from  I  volume  N  and 
3  volumes  H  takes  advantage  of  the  fact  that  when  chlorine  reacts  with  ammonia,  the 
hydrogen  of  the  latter  combines  with  the  former 
to  make  hydrogen  chloride,   HC1,   which  may 
readily  be  absorbed  by  water,  leaving  the  nitro-  „  , 

gen.     The  tube  A  (Fig.  68),  graduated  into  three 
equal  parts,  is  filled  with  chlorine.  A  strong  solu- 


Fig.  67. 


Fig.  68. — Decomposition  of  ammonia  by  chlorine. 


tion  of  ammonia  having  been  poured  into  the  funnel  B,  the  stop-cock  is  opened  so 
that  some  of  the  NH3  may  enter  the  tube.  A  violent  reaction  ensues,  and  white 
fumes  of  ammonium  chloride,  NH4C1,  are  formed,  due  to  the  combination  of  the 
HC1  produced  with  excess  of  NH3.  More  ammonia  is  now  admitted,  and  the  tube 
is  shaken.  Owing  to  the  fact  that  the  NH4C1  produced  is  a  solid  and  dissolves 
in  the  water,  the  pressure  in  the  tube  is  now  below  that  of  the  atmosphere,  so 
that  when  the  bent  tube  C,  dipping  into  water,  is  attached  to  the  funnel  and  the 
stop-cock  is  opened,  water  rushes  in  to  fill  two-thirds  of  the 
tube.  The  remaining  gas  is  found  to  be  nitrogen. 

As  might  be  expected  from  its  powerfully  alkaline 
character,  ammonia  exhibits  a  strong  attraction  for 
acids,  which  it  neutralises  perfectly.  If  a  bottle  of 
ammonia  gas,  closed  with  a  glass  plate,  be  inverted 
over  a  similar  bottle  of  hydrochloric  acid  gas,  and 
the  glass  plates  withdrawn  (Fig.  69),  the  gases  will 
combine,  unless  they  be  perfectly  dry,  (cf.  p.  32), 
with  disengagement  of  much  heat,  forming  a  white 
solid,  ammonium  chloride  (NH4C1),  in  which  the 
acid  and  alkali  have  neutralised  each  other.  Again, 
if  ammonia  be  added  to  diluted  sulphuric  acid,  the  latter  will  be 
entirely  neutralised,  and  by  evaporating  the  solution,  crystals  of 
ammonium  sulphate,  (NH4)2S04,  may  be  obtained. 


Fig.  69. 


AMMONIUM  AMALGAM.  85 

The  substances  thus  produced  by  neutralising  the  acids  with  solution 
of  ammonia  bear  a  strong  resemblance  to  the  salts  formed  by  neutralis- 
ing the  same  acids  with  solutions  of  potash  and  soda,  a  circumstance 
which  would  encourage  the  idea  that  the  solution  of  ammonia  must 
contain  an  alkaline  hydroxide  (NH4OH),  similar  to  KOH  or  NaOH. 

Berzelius  was  the  first  to  make  an  experiment  which  appeared  strongly  to  favour 
this  view.  The  negative  pole  of  a  galvanic  battery  was  placed  in  contact  with 
mercury  at  the  bottom  of  a  vessel  containing  a  strong  solution  of  ammonia,  in 
which  the  positive  pole  of  the  battery  was  immersed.  Oxygen  was  disengaged  at 
this  pole,  whilst  the  mercury  in  contact  with  the  negative  pole  swelled  to  four  or 
five  times  its  original  bulk,  and  became  a  soft  solid  mass,  still  preserving,  however, 
its  metallic  appearance.  *  At  a  very  low  temperature  the  mass  becomes  dark  grey 
and  crystalline.  So  far,  the  result  of  the  experiment  resembles  that  obtained  when 
potassium  hydroxide  is  decomposed  under  similar  circumstances,  the  oxygen  sepa- 
rating at  the  positive  pole,  and  the  potassium  at  the  negative,  where  it  combines 
with  the  mercury.  Beyond  this,  however,  the  analogy  does  not  hold ;  for  in  the 
latter  case  the  metallic  potassium  can  be  readily  separated  from  the  mercury,  whilst 
in  the  former,  all  attempts  to  isolate  the  ammonium  have  failed,  for  the  soft  solid 
mass  resolves  itself,  almost  immediately  after  its  preparation,  into  mercury,  am- 
monia (NH3),  and  hydrogen,  one  volume  of  the  latter  being  separated  for  two 
volumes  of  ammonia.  This  would  also  tend  to  support  the  conclusion  that  a  sub- 
stance having  the  composition  NH3  +  H  or  NH4  had  united  with  the  mercury  ;  and 
since  the  latter  is  not  known  to  unite  with  any  non-metallic  substance  without 
losing  its  metallic  appearance,  it  would  be  fair  to  conclude  that  the  soft  solid  was 
really  an  amalgam  of  ammonium.  However,  the  increase  in  the  weight  of  the 
mercury  is  so  slight,  and  the  "  amalgam,"  whether  obtained  by  this  or  by  other 
methods,  is  so  unstable,  that  it  would  appear  safer  to  attribute  the  swelling  of  the 
mercury  to  a  physical  change  caused  by  the  presence  of  the  ammonia  and  hydrogen 
gases.  This  view  is  supported  by  the  observation  that  when  the  amalgam  is  sub- 
jected to  pressure  its  volume  varies  nearly  in  the  inverse  ratio  of  the  pressure.  It 
is  difficult  to  believe  that  the  solution  of  ammonia  does  really  contain  ammonium 
hydroxide  (NH3  +  H20  =  NH4OH),  when  we  find  it  evolving  ammonia  so  easily, 
although  at  o°  C.  the  amount  of  ammonia  dissolved  approaches  that  required  for 
this  formula  ;  but  it  is  equally  difficult,  upon  any  other  hypothesis,  to  explain  the 
close  resemblance  between  the  salts  obtained  by  neutralising  acids  with  this  solu- 
tion and  those  furnished  by  potash  and  soda. 

The  ordinary  mode  of  exhibiting  the  production  of  the  so-called  amalgam  of 
ammonium  consists  in  acting  upon  the  ammonium  chloride  (NH4C1)  with  sodium 
amalgam.  A  little  pure  mercury  is  heated  in  a  test-tube,  and  a  pellet  of  sodium 
thrown  into  it,  when  combination  occurs  with  great  energy.  When  the  amalgam 
is  nearly  cool  it  may  be  poured  into  a  larger  tube  containing  a  moderately  strong 
solution  of  ammonium  chloride  ;  the  amalgam  at  once  swells  to  many  times 
its  bulk,  forming  a  soft  solid  lighter  than  the  water,  which  may  be  shaken  out  of 
the  tube  as  a  cylindrical  mass,  rapidly  effervescing  with  evolution  of  NH3  +  H, 
and  soon  recovering  its  original  volume  and  liquid  condition. 

55.  Ammonia  is  easily  expelled  from  its  salts  by  an  alkali,  so  that 
an  ammonium  salt  is  easily  detected  by  boiling  the  suspected  substance 
with  caustic  soda,  when  the  odour  of  ammonia  will  be  perceived : 
NH4C1  +  NaOH  =  NaCl  +  NH3  +  H20. 

When  an  ammonium  salt  is  heated  it  is  split  up  into  ammonia  and 
the  acid  from  which  it  is  formed,  ammonium  chloride,  for  example, 
becoming  ammonia  and  hydrogen  chloride,  NH401  =  NH3  +  HC1 1 ;  but 
if  these  products  be  allowed  to  cool  together,  they  combine  again  to 
produce  the  original  salts.  This  behaviour  furnishes  an  example  of  the 

*  This  experiment  is  more  conveniently  made  with  a  strong  solution  of  ammonium  sul- 
phate in  a  common  plate.  A  sheet  of  platinum  connected  with  the  positive  pole  of  the 
battery  (five  or  six  Grove's  cells)  is  immersed  in  the  solution,  and  a  piece  of  filter-paper  is 
laid  upon  it,  on  which  is  a  globule  of  mercury  ;  the  negative  pole  is  plunged  into  the  latter. 

f  Ammonium  chloride  does  not  dissociate  if  perfectly  dry. 


86  DISSOCIATION. 

phenomenon  called  dissociation,  which  differs  from  decomposition  in 
that  the  constituents  into  which  a  compound  is  dissociated  by  heat  re- 
combine  if  they  are  allowed  to  cool  together  ;  the  products  of  the 
decomposition  of  a  compound,  on  the  other  hand,  do  not  so  recombine. 

The  dissociation  of  ammonium  chloride  may  be  demonstrated  by  taking  ad- 
vantage of  the  low  specific  gravity  of  NH3  as  compared  with  that  of  HC1  (NH3  is 
17  2  =  8.5,  and  HC1  36.5/2=18.25  times  heavier  than  H).  On  this  account  NH3 
diffuses  more  rapidly  than  HC1.  A  fragment  of  ammonium  chloride  is  placed  in  a 
narrow  test-tube  with  a  plug  of  asbestos  at  a  little  distance  above  it,  a  piece  of  red 
litmus-paper  is  placed  in  the  tube,  and  the  ammonium  chloride  and  the  asbestos 
are  heated  ;  the  NH3,  being  lighter,  diffuses  through  the  asbestos  before  the  HC1 
does,  and  blues  the  red  litmus-paper,  but  soon  after  the  HC1  diffuses  through,  and 
the  litmus  is  again  reddened. 

The  volatility  of  ammonia  and  of  the  ammonium  salts  renders  a 
solution  of  the  gas  useful  as  an  alkali  in  cases,  such  as  in  analysis, 
where  the  fixed  alkalies,  potash,  and  soda,  would  be  objectionable  on 
account  of  their  fixity.  Ammonia  finds  application  in  making  sodium 
carbonate  (q.v.)  and,  as  already  explained,  in  freezing-machines. 

Ammonia  has  a  tendency  to  combine  as  a  whole  with  many  metallic 
salts,  much  as  water  does  ;  a  typical  compound  of  this  sort  is 
CuS04.5NH3.  It  readily  loses  ammonia  when  heated. 

Although  free  nitrogen  and  hydrogen  can  only  with  difficulty  be  made  to  form 
ammonia  by  direct  combination,  this  compound  is  produced  when  the  nitrogen 
meets  with  hydrogen  in  the  nascent  state  ;  that  is,  at  the  instant  of  its  liberation 
from  a  combined  form.  Thus,  if  a  few  iron-filings  be  shaken  with  a  little  water 
in  a  bottle  of  air,  so  that  they  may  cling  round  the  sides  of  the  bottle,  and  a  piece 
of  red  litmus-paper  be  suspended  between  the  stopper  and  the  neck,  it  will  be  found 
to  have  assumed  a  blue  colour  in  the  course  of  a  few  hours,  and  ammonia  may  be 
distinctly  detected  in  the  rust  which  is  produced.  It  appears  that  the  water  is 
decomposed  by  the  iron  in  the  presence  of  the  carbonic  acid  of  the  air  and  water, 
and  that  the  hydrogen  liberated  enters  at  once  into  combination  with  the  nitrogen, 
held  in  solution  by  the  water,  to  form  ammonia. 

56.  For  many  years  ammonia  was  the  only  compound  of  nitrogen 
with  hydrogen  which  was  known.     Lately,  two  others  have  been  dis- 
covered— namely,  hydrazine,  N2H4,  a  colourless  gas,  and  hydrogen  nitride 
(hydrazoic  acid),  N3H,  a  volatile  liquid,  possessed,  as  its  alternative  name 
implies,  of  the  properties  proper  to  an  acid.     The  importance  of  these 
compounds  resides  in  the  light  which  they  throw  upon  the  theory  of 
organic  nitrogen  compounds,  and  can  only  be  appreciated  when  these 
are  being  discussed.     They  have  as  yet  received  no  practical  application, 
and  since  they  are  prepared  by  the  action  of  reducing  agents  on  nitric 
acid  or  its  derivatives,  a  further  consideration  of  them  will  be  found 
after  the  treatment  of  this  subject. 

57.  Production  of  nitrous  and  nitric  acids  from  ammonia. — If  a  few 
drops  of  a  strong  solution  of  ammonia  are  poured  into  a  pint  bottle,  and 
ozonised  air  (from  the  tube  for  ozonising  by  induction,   Fig.  47)   is 
passed  into  the  bottle,  thick  white   clouds  speedily  form,  consisting  of 
ammonium  nitrite  (NH4N02),  the  nitrous  acid  having  been  produced  by 
the  oxidation  of  the  ammonia  at  the  expense  of  the  ozonised  oxygen — 

2NH3  +  03  =  H20  +  NH4N02. 

If  copper  filings  be  shaken  with  solution  of  ammonia  in  a  bottle  of 
air,  white  fumes  will  also  be  produced,  together  with  a  deep  blue  solu- 
tion containing  copper  oxide  and  ammonium  nitrite  ;  the  act  of  oxida- 


OXIDATION   OF  AMMONIA.  87 

tion  of  the  copper  appearing  to  have  induced  a  simultaneous  oxidation 
of  the  ammonia. 

A  coil  of  thin  platinum  wire  made  round  a  pencil,  if  heated  to  redness 
at  the  lower  end   and    suspended   in   a   flask  (Fig.  70)    with  a  little 
strong  ammonia  at  the  bottom,  will  continue  to  glow 
for  a  great  length  of  time,   in  consequence  of  the 
combination  of  the  ammonia  with  the  oxygen  of  the 
air  at  its  surface,  attended  with  great  evolution  of 
heat.     Thick  white  clouds  of   NH4N02  are  formed, 
and   frequently   red    vapour    of    nitrous    anhydride 
(N203)  itself.     A  coil  of  thin  copper  wire  acts  in  a 
similar  manner. 

When  a  tube  delivering  oxygen  is  passed  down  to  the 
bottom  of  the  flask,  the  action  is  far  more  energetic,  the  heat 
of  the  platinum  rising  to  whiteness,  whereupon  an  explosion 
of  the  mixture  of  ammonia  and  oxygen  ensues.  After  the 
explosion  the  action  recommences,  so  that  the  explosion  repeats  itself  as  often 
as  may  be  wished.  It  is  unattended  with  danger  if  the  mouth  of  the  flask  be 
pretty  large,  but  it  is  advisable  to  surround  the  flask  with  a  cylinder  of  coarse 
wire  gauze.  By  regulating  the  stream  of  oxygen,  the  bubbles  of  that  gas  may  be 
made  to  burn  as  they  pass  through  the  ammonia  at  the  bottom  of  the  flask. 

The  oxidation  of  ammonia  may  also  be  shown  by  the  arrangement  represented 
in  Fig.  71.     Air  is  slowly  passed  from  the  glass  gas-holder  B,  through  very  weak 
ammonia  in  the  bottle  «,  into  a  hard  glass  tube 
having  a  piece  of  red  litmus-paper  at  b  and  a 
plug  of  platinised  asbestos  in  the  centre,  heated 
by  a  gas-burner  ;  a  piece  of  blue  litmus-paper  is 
placed  at  ^ ,  and  the  tube  is  connected  with  a 
large  globe  (d~).    The  red  litmus  at  b  is  changed 
to  blue  by  the  ammonia,  whilst  the  blue  litmus 
at  c  is  reddened  by  the  nitrous  acid  produced 


Fig-.  71. — Oxidation  of  ammouia. 

in  its  oxidation,  and  clouds  of  ammonium  nitrite,  accompanied  by  red  nitrous 
fume*,  appear  in  d.  To  obtain  all  the  results  in  perfection,  small  quantities  of 
ammonia  must  be  successively  introduced  into  a. 

When  hydrogen  or  coal  gas  burns  in  air,  small  quantities  of  nitrous  and  nitric 
acids  are  produced,  apparently  by  the  oxidation  of  atmospheric  nitrogen. 

58.  In  the  presence  of  strong  bases,  and  of  porous  materials  to  favour 
the  change,  ammonia  may  suffer  further  oxidation  to  nitric  acid,  which 
acts  on  the  base  to  form  a  nitrate;  thus,  2NH3  +  CaO  +  O8  =  Ca(N03)., 
(calcium  nitrate)  +  3HqO. 

It  has  already  been  seen  that  the  rapid  oxidation  (combustion)  of 
ammonia  produces  nitrogen  and  water. 

This  formation  of  nitrates  from  ammonia  is  commonly  referred  to  as 
nitrification,  and  appears  to  be  concerned  in  the  formation  of  the 


88 


COMBINATION  OF  NITROGEN  WITH  OXYGEN. 


natural  supplies  of  saltpetre  which  are  of  so  great  importance  to  the 
arts,* 

It  is  brought  about  by  a  micro-organism  (the  nitrifying  organism) 
which  accelerates  the  oxidation  of  the  ammonia  produced  by  the  decay 
of  nitrogenous  organic  matter  in  the  soil. 

It  would  appear  that  at  least  two  micro-organisms  are  concerned  in  the  produc- 
tion of  nitrates.  The  one  induces  the  formation  of  nitrites  from  the  ammonia, 
whilst  the  other  induces  oxididation  of  these  to  nitrates.  Nitrification  can  only 
occur  when  some  basic  substance,  like  calcium  carbonate,  is  present  to  neutralise 
the  acids  produced  ;  being  dependent  on  a  micro-organism,  it  can  only  proceed  at 
temperatures  which  are  not  inhibitory  to  the  life  of  the  organism  (between  o°  and 
55°  C.).  Darkness  favours  the  process. 


COMPOUNDS  OF  NITROGEN  AND  OXYGEN. 

59.  Though  these  elements  under  ordinary  conditions  exhibit  no 
attraction  for  each  other,  six  compounds,  which  contain  them  in 
different  proportions,  have  been  obtained  by  different  processes,  viz. 
N20,  NO,  N203,  N02,  N205. 

When  a  succession  of  strong  electric  sparks  from  the  induction-coil 
is  passed  through  atmospheric  air  in  a  dry  flask  (especially  if  the  air  be 
mixed  with  oxygen),  a  red  gas,  nitric  peroxide  (N0?),  is  formed ;  if 
water  be  present  this  is  absorbed  and  converted  into  nitrous  and  nitric 
acids;  2N02  +  H20  =  HN02  +  HN03. 

If  the  experiment  be  made  in  a  U-tube  having  one  limb  surmounted  by  a 
stoppered  globe  into  which  platinum  wires  are  sealed  (fig.  72)  filled  Math  water 
coloured  with  blue  litmus,  the  latter  will  very  soon  be  reddened  by  the  acid 
formed,  and  the  air  will  be  found  to  diminish  very 
considerably  in  volume,  eventually  losing  its  power  of 
supporting  combustion,  in  consequence  of  the  removal 
of  oxygen. 

When  a  few  inches  of  magnesium  tape  are  burnt  in  a 
gas-jar  of  air,  red  fumes  may  be  perceived  on  looking 
down  the  jar  at  the  close  of  the  combustion,  and  the 
presence  of  N203  or  N02  may  be  shown  by  drawing  the 
residual  air  through  a  mixture  of  potassium  iodide  with 
a  little  starch  and  acetic  acid,  when  the  iodine  is  set  free 
and  blues  the  starch.  This  renders  it  probable  that  the 
electric  spark  causes  the  combination  of  nitrogen  and 
oxygen  on  account  of  its  high  temperature. 

When  ozonised  air  (p.  65)  is  passed  into  water,  nitric 
acid  is  found  in  solution.  Kain  water  contains  about 
one  part  per  million  of  nitric  acid,  in  the  form  of 
nitrates. 

When  hydrogen  gas,  mixed  with  a  small 
quantity  of  nitrogen,  is  burnt,  the  water  collected 
from  it  is  found  to  have  an  acid  taste  and  re- 
action, due  to  the  presence  of  a  little  nitric  acid, 
resulting  from  the  combination  of  the  nitrogen 
with  the  oxygen  of  the  air  under  the  influence  of 
the  intense  heat  of  the  hydrogen  flame. 
Since  all  the  compounds  of  nitrogen  and  oxygen  are  obtained,  in 

practice,  from  nitric  acid,  the  chemical  history  of  that  substance  may 

conveniently  that  of  the  oxides  of  nitrogen. 

*  The  charcoal  which  has  been  used  in  the  sewer  ventilators  has  been  found  to  contain 
abundance  of  nitrates. 


Fig.  72. 


PREPARATION   OF   NITRIC   ACID.  89 

NITRIC  ACID,  OR  HYDROGEN  NITRATE. 
HNO3  =  63  parts  by  weight  =  2  volumes. 

60.  This  most  important  acid  is  obtained  from  saltpetre,  which  is 
found  as  an  incrustation  upon  the  surface  of  the  soil  in  hot  and  dry 
climates,  as  in  some  parts  of  India  and  Peru.  The  salt  imported  into 
this  country  from  Bengal  and  Oude  consists  of  potassium  nitrate 
(KN03),  whilst  t/he  Peruvian  or  Chilian  saltpetre  is  sodium  nitrate,  or 
"  nitrate  "  (NaN03).  Either  of  these  will  serve  for  the  preparation  of 
nitric  acid. 

On  the  small  scale,  in  the  laboratory,  nitric  acid  is  prepared  by  dis- 
tilling potassium  nitrate  with  an  equal  weight  of  concentrated  sulphuric 
acid. 

As  an  experiment,  4  ounces  of  powdered  nitre,  thoroughly  dried,  are  introduced 
into  a  stoppered  retort  (Fig.  73)  and  2  J  measured  ounces  of  concentrated  sulphuric 
acid  poured  upon  it.  As  soon  as  the 
acid  has  soaked  into  the  nitre,  a 
gradually  increasing  heat  is  applied 
by  an  Argand  burner,  when  the  acid 
distils.  It  must  be  preserved  in  a 
stoppered  bottle. 

When  the  acid  has  ceased  distil- 
ling, the  retort  should  be  allowed 
to  cool,  and  filled  with  water.  On 
heating  for  some  time  the  saline 
residue  will  dissolve.  The  solution 
may  then  be  poured  into  an  evapora- 
ting dish,  and  evaporated  to  a 
small  bulk.  On  allowing  the  con-  Fig.  73. — Preparation  of  nitric  acid, 

centrated  solution  to  cool,  crystals 

of  bisulphate  of  potash  or  potassium  hydrogen  sulphate  (KHS04)  are  deposited,  a 
salt  which  is  very  useful  in  many  metallurgical  and  analytical  operations. 

The  decomposition  of  potassium  nitrate  by  an  equal  weight  of  sul- 
phuric acid  is  explained  by  the  equation — 

KN03  +  H2S04  =  HN03  +  KHS04. 

It  would  appear  at  first  sight  that  one-half  of  the  sulphuric  acid 
might  be  dispensed  with,  inasmuch  as  one  molecule  could  be  made  to 
decompose  two  molecules  of  potassium  nitrate,  2KN03H-H2S04  = 
2HNO3  +  K2SO4,  but  it  is  found  that  when  a  smaller  quantity  of 
sulphuric  acid  is  used,  so  high  a  temperature  is  required  to  effect  the 
complete  decomposition  of  the  saltpetre  (the  above  equation  then  repre- 
senting only  the  first  stage  of  the  action),  that  much  of  the  nitric  acid 
is  decomposed ;  and  the  normal  potassium  sulphate  (K2S04),  which 
would  be  the  final  result,  is  not  nearly  so  easily  dissolved  out  of  the 
retort  by  water  as  is  the  bisulphate. 

For  the  preparation  of  large  quantities  of  nitric  acid,  sodium  nitrate 
is  substituted  for  potassium  nitrate,  being  much  cheaper,  and  furnish- 
ing a  larger  proportion  of  nitric  acid. 

For  the  decomposition  of  the  sodium  nitrate  can  be  represented  by  the  above 
equation,  if  Na  be  substituted  for  K,  and  on  comparing  the  equations  it  will  be 
seen  that  85  parts  by  weight  of  NaN03  yield  the  same  quantity  of  HN03  as  that 
yielded  by  101  parts  by  weight  of  KN03. 

The  sodium  nitrate  is  introduced  into  an  iron  cylinder  (A,  Fig.  74)  and  about 
five-sixths  of  its  weight  of  sulphuric  acid  is  poured  upon  it  through  a  stoppered 


9o 


PEOPEETIES   OF  NITRIC   ACID. 


opening  at  the  back.*  Heat  is  then  applied  by  a  furnace,  into  which  the  cylinders 
are  built  in  pairs,  when  the  nitric  acid  passes  off  in  vapour,  and  is  condensed  in  a 
series  of  stoneware  bottles  (B),  surrounded  with  cold  water.  The  commercial  acid 
is  liable  to  contain  chlorine,  hydrochloric  acid,  and  iodic  acid  (from  sodium 
chloride  and  iodate  in  the  nitrate),  sulphuric  acid,  sodium  sulphate,  nitrogen 

oxides,  and  iron.  It  is  purified 
by  redistillation,  the  middle 
portion  of  the  distillate  being 
pure. 

In  the  preparation  of 
nitric  acid,  it  will  be  ob- 
served at  the  beginning 
and  towards  the  end  of  the 
operation  that  the  retort 
becomes  filled  with  a  red 
vapour.  This  is  due  to  the 
decomposition  by  heat  of  a 
portion  of  the  colourless 
vapour  of  nitric  acid,  into 
water,  oxygen,  and  nitric 
peroxide,  2HNO,  =  H90  + 

Fig.  74  —Preparation  of  nitric  acid.  X   ,      XT/-\      AT.  •      »8    A    * 

O  +  2N02,  this  last  form- 
ing the  red  vapour,  a  portion  of  which  is  absorbed  by  the  nitric  acid, 
and  gives  it  a  yellow  colour  (red  fuming  nitric  acid).  The  pure  nitric 
acid  is  colourless,  but  if  exposed  to  sunlight  it  becomes  yellow,  a 
portion  suffering  this  decomposition.  In  consequence  of  the  accumula- 
tion of  the  oxygen  in  the  upper  part  of  the  bottle,  the  stopper  is  often 
forced  out  suddenly  when  the  bottle  is  opened,  and  care  must  be  taken 
that  drops  of  this  very  corrosive  acid  be  not  spirted  into  the  face. 

The  strongest  nitric  acid  (obtained  by  distilling  perfectly  dry  nitre 
with  an  equal  weight  of  pure  oil  of  vitriol,  and  collecting  the  middle 
portion  of  the  acid  separately  from  the  first  and  last  portions,  which 
are  somewhat  weaker)  emits  very  thick  grey  fumes  when  exposed  to 
damp  air,  because  its  vapour,  though  itself  transparent,  absorbs  water 
very  readily  from  the  air,  and  condenses  into  very  minute  drops  of 
dilute  nitric  acid  which  compose  the  fumes.  The  weaker  acids  com- 
monly sold  in  the  shops  do  not  fume  so  strongly.  A  criterion  of  the 
strength  of  any  sample  of  the  acid  is  afforded  by  the  specific  gravity, 
which  may  be  ascertained  by  the  methods  described  for  ammonia, 
using  a  hydrometer  adapted  for  liquids  heavier  than  water.  Thus 
the  strongest  acid  (HN03)  has  the  specific  gravity  1.52  ;t  whilst  the 
ordinary  aquafortis  or  dilute  nitric  acid  has  the  sp.  gr.  1.29,  and 
contains  only  46  per  cent,  of  HN03.  The  concentrated  nitric  acid 
usually  sold  by  the  operative  chemist  (double  aquafortis)  has  the  sp.  gr. 
1.41,  arid  contains  67.5  per  cent,  of  HN03. 

A  very  characteristic  property  of  nitric  acid  is  that  of  staining  the 
skin  yellow.  It  produces  the  same  effect  upon  most  animal  and  vege- 
table matters,  especially  if  they  contain  nitrogen.  The  application  of 

*  To  avoid  difficiilties  due  to  frothing  when  strong  H2SO4  is  used,  it  is  now  customary  to 
use  a  somewhat  weaker  acid  (chamber  acid,  q.v.)  and  to  redistil  the  Itss  concentrated  nitric 
acid  obtained,  with  strong  stilphuric  acid. 

f  It  is  extremely  difficult  to  obtain  the  HNO3  free  iroin  any  extraneous  wafer,  as  it  under- 
goes decomposition  not  only  when  vaporised  at  the  boiling-point,  but  even  at  ordinary  tem- 
peratures. Distillation  in  a  vacuum  is  more  successful. 


OXIDATION   BY   NITRIC   ACID.  91 

this  in  dyeing  silk  a  fast  yellow  colour  may  be  seen  by  dipping  a  skein 
of  white  silk  in  warm  dilute  nitric  acid,  and  afterwards  immersing  it  in 
dilute  ammonia,  which  converts  the  yellow  colour  into  brilliant  orange. 
When  sulphuric  or  hydrochloric  acid  is  spilt  upon  the  clothes,  a  red 
stain  is  produced,  and  a  little  ammonia  restores  the  original  colour ; 
but  nitric  acid  stains  are  yellow,  and  ammonia  intensifies  instead  of 
removing  them,  though  it  prevents  the  cloth  from  being  eaten  into 
holes. 

Nitric  acid  changes  most  organic  colouring  matters  to  yellow,  but, 
unless  very  concentrated,  it  merely  reddens  litmus.  If  solutions  of 
indigo  and  litmus  are  warmed  in  separate  flasks,  and  a  little  nitric  acid 
added  to  each,  the  indigo  will  become  yellow  and  the  litmus  red.  Here 
the  indigo  (C8H5NO)  acquires  oxygen  from  the  nitric  acid,  and  is  con- 
verted into  isatine  (C8H5N02). 

When  nitric  acid  is  heated,  it  begins  to  boil  at  86°  C.,  but  it  cannot 
be  distilled  unchanged,  for  a  considerable  quantity  is  decomposed  into 
nitric  peroxide,  oxygen,  and  water,  the  two  first  passing  off  in  the 
gaseous  form,  whilst  the  water  remains  in  the  retort  with  the  nitric 
acid,  which  thus  becomes  gradually  more  and  more  dilute,  until  it  con- 
tains 68  per  cent,  of  HN03,  when  it  passes  over  unchanged,  at  the 
temperature  of  248°  F.  (120°  C.).  The  specific  gravity  of  this  acid  is 
1.42  ;  its  composition  corresponds  approximately  with  the  hydrate 
2HN03.3H,0.  If  an  acid  weaker  than  this  be  submitted  to  distillation, 
water  will  pass  off  until  acid  of  this  strength  is  obtained,  when  it  distils 
unchanged.  A  similar  result  is  obtained  when  dry  air  is  passed 
through  strong  or  weak  nitric  acid  at  15°  C. ;  an  acid  of  64  per  cent, 
strength  (corresponding  with  HN03.2H20)  is  produced  in  either 
case. 

The  specific  gravity  of  the  vapour  of  nitric  acid,  at  86°  C.,  has  been 
determined  as  29.6  (H=  i),  which  is  sufficiently  near  to  half  of  63  to 
warrant  the  formula  HN03,  for  the  molecule  of  nitric  acid  (p.  47). 

The  facility  with  which  nitric  acid  parts  with  a  portion  of  its  oxygen 
renders  it  very  valuable  as  an  oxidising  agent.  Comparatively  few 
substances  which  are  capable  of  forming  compounds  with  oxygen  can 
escape  oxidation  when  treated  with  nitric  acid. 

A  small  piece  of  phosphorus  dropped  into  a  porcelain  dish  containing 
the  strongest  nitric  acid  (and  placed  at  some  distance  to  avoid  danger), 
is  soon  attacked  by  the  acid,  generally  with  such  violence  as  to  burst 
into  flame,  and  sometimes  to  shatter  the  dish  ;  the  product  is  phosphoric 
acid,  the  highest  state  of  oxidation  of  phosphorus. 

When  sulphur  is  heated  with  nitric  acid,  it  is  actually  oxidised  to  a 
greater  extent  than  when  burnt  in  pure  oxygen,  for  in  this  case  it  is- 
converted  into  sulphurous  anhydride  (S02),  whilst  nitric  acid  converts 
it  into  sulphuric  acid,  H,SO4. 

Charcoal,  which  is  so  unalterable  by  most  chemical  agents  at  the 
ordinary  temperature,  is  oxidised  by  nitric  acid.  If  the  strongest  nitric 
acid  be  poured  upon  finely  powdered  charcoal,  the  latter  takes  fire  at 
once.  Even  iodine,  which  is  not  oxidised  by  free  oxygen,  is  converted! 
into  iodic  acid  (HIO3)  by  nitric  acid. 

But  it  is  especially  in  the  case  of  metals  that  the  oxidising  powers  of 
nitric  acid  are  called  into  useful  application. 

If  a  little  black  oxide  of  copper  be   heated  in  a  test-tube  with  nitric 


92  ACTION  OF  NITRIC  ACID   ON  METALS. 

acid,  it  dissolves,  without  evolution  of  gas,  yielding  a  blue  solution, 
which  contains  copper  nitrate,  2HNO3  +  CuO  =  H20  +  Cu(NO3),. 

But  when  nitric  acid  is  poured  upon  metallic  copper  (copper  turn- 
ings), very  violent  action  ensues,  red  fumes  are  abundantly  evolved, 
and  the  metal  dissolves  in  the  form  of  copper  nitrate,  nitric  oxide  being 
formed,  8HNO3  +  Cu3  =  3Cu(NO3)2  +  4H20  +  2NO.  The  nitric  oxide 
itself  is  colourless,  but  as  soon  as  it  comes  into  contact  with  the  oxygen 
of  the  air,  it  is  converted  into  the  red  nitric  peroxide,  NO  +  O  =  NO2. 

A  certain  amount  of  nitric  peroxide  is  always  produced  directly  by  the  action 
of  copper  on  nitric  acid,  the  proportion  depending  upon  the  concentration  of  the 
acid  and  the  ratio  of  acid  to  copper.  When  excess  of  concentrated  nitric  acid  is 
used  the  gas  consists  of  N02  (with  about  10  per  cent,  of  N203)  and  contains  no 
NO  ;  on  the  other  hand,  when  the  acid  is  diluted  with  twice  its  volume  of  water 
nearly  pure  NO  is  evolved.  The  following  view,  although  it  may  not  represent 
the  actual  course  of  the  chemical  change,  is  useful  in  expounding  the  nature  of 
the  action.  Since  nitric  acid  tends  to  decompose  into  H20,2N02  and  0,  two 
molecules  of  the  acid  might  be  expected  to  oxidise  one  atom  of  copper, 
Cu  +  2HN03  =  CuO  +  H20  +  2NO2  ;  the  copper  oxide  would  immediately  react  with 
another  portion  of  the  nitric  acid  to  give  copper  nitrate,  CuO  +  2HN03  =  Cu(N03)2  + 
H20.  When  more  copper  is  present  the  N02  might  be  expected  to  be  reduced  to 
NO,  Cu  +  N02  =  CuO  +  NO,  the  copper  oxide  dissolving  as  before.  Since  NO2  re- 
acts with  water  to  form  nitrous  (and  nitric)  acid,  little  would  be  expected  in  the 
gas  from  a  dilute  nitric  acid,  but  the  proportion  of  NO  would  be  expected  to  be 
increased  because  the  reduction  of  the  N02  would  be  more  possible  when  it  could 
not  escape  from  the  solution  as  gas. 

It  has  been  shown  that  nitric  acid  which  is  free  from  nitrous  acid  (always 
present  in  commercial  samples)  has  a  very  tardy,  if  any,  action  on  many  metals, 
so  that  it  would  seem  as  if  the  oxidation  were  really  effected  by  the  nitrous  acid. 
A  very  small  quantity  of  this  suffices  to  start  the  action,  because  the  nitric  oxide 
produced  reduces  another  portion  of  the  nitric  acid  to  nitrous  acid,  thus  serving  as 
a  carrier  of  oxygen  from  the  nitric  acid  to  the  metal. 

By  the  action  of  metals  on  nitric  acid  of  various  strengths  all  the  reduction 
products  of  nitric  acid  —  namely,  the  oxides  of  nitrogen,  nitrogen,  hydroxylamine, 
hyponitious  acid,  and  ammonia  —  can  be  obtained.  Those  metals  whose  attraction 
for  oxygen  is  feeble  (those  which  do  not  decompose  water,  or  only  do  so  at  a  very 
high  temperature,  p.  21)  do  not  reduce  HN03  to  a  lower  state  of  oxidation  than 
NO  ;  those  metals  which  decompose  water  at  a  red  heat  yield  all  the  reduction 
products  ;  whilst  those  which  decompose  water  either  at  the  ordinary  temperature 
or  below  a  red  heat  yield  even  hydrogen.  The  nature  of  the  products  varies  with 
the  state  of  dilution,  and  with  the  temperature.  Silver  behaves  like  copper  with 
nitric  acid.  Iron  evolves  nearly  pure  NO  when  dissolved  in  nitric  acid  diluted 
with  either  one  part  or  12  parts  of  water.  Zinc,  with  i  :  2  strength  of  acid  (hot  or 
cold)  evolves  nearly  equal  volumes  of  NO  and  N20,  but  with  the  strong  acid  it 
evolves  scarcely  any  NO,  but  a  mixture  of  about  2  volumes  N20  and  I  volume  N  ; 
with  dilute  nitric  acid  zinc  yields  ammonia  (which  of  course  remains  combined  with 
the  nitric  acid  in  the  form  of  ammonium  nitrate),  possibly  produced  by  the 
action  of  hydrogen,  liberated  by  the  dissolution  of  the  metal  in  the  acid 
(just  as  when  zinc  is  dissolved  in  dilute  sulphuric  acid),  on  the  nitric  acid, 


Though  all  the  metals  in  common  use,  except  gold  and  platinum,  are  oxidised 
by  nitric  acid,  they  are  not  all  dissolved  ;  aluminium  is  superficially  oxidised  but 
not  further  attacked  ;  tin  and  antimony  are  left  by  the  acid  in  the  state  of  insoluble 
oxides,  which  possess  acid  properties  and  do  not  unite  with  nitric  acid.  When 
concentrated  nitric  acid  is  poured  upon  tin,  no  action  is  observed  ;  *  but  on  adding 
a  little  water,  N02  is  evolved  in  abundance,  and  the  tin  is  converted  into  a  white 
powder,  metastannic  acid.  On  stirring  this  white  mixture  with  slaked  lime  the 
smell  of  ammonia  is  perceived,  this  gas  having  been  liberated  from  ammonium 

*  This  is  often  noticed  in  the  case  of  strong  nitric  acid,  and  is  possibly  to  be  explained  by 
supposing  that  the  nitrous  acid  present  is  rapidly  used  up  and  cannot  be  re-formed  in  such  a 
concentrated  acid  (see  above).  The  strongest  nitric  acid  which  has  been  obtained  is  without 
action  on  chalk,  even  when  boiled  therewith. 


THE   ANALYSIS   OF  NITRATES. 


93 


nitrate  by  the  lime.      Thus  tin  reduces  even  moderately  strong   nitric  acid  to 
ammonia. 

"When  a  solution  of  potassium  nitrate  is  mixed  with  a  strong  solution  of  caustic 
potash,  and  heated  with  granulated  zinc,  ammonia  is  abundantly  disengaged,  being 
produced  by  the  nascent  hydrogen  from  the  action  of  the  zinc  upon  the  caustic 
potash.  Aluminium  acts  thus  even  in  dilute  solutions. 

Nitric  acid  is  completely  reduced,  yielding  only  nitric  oxide,  when  shaken  with 
strong  sulphuric  acid  and  mercury.  On  this  fact  is  based  the  application  of  the 
nitrometer  (Fig.  75)  for  estimating  the  quantity  of  a  nitrate  present  in  a  substance. 
The  apparatus  is  filled  with  mercury  by  opening  the  stop-cock  and  pouring  the 
metal  into  the  open  limb.  The  stop-cock  having  been  closed,  the  right-hand  limb 
is  lowered  so  that  the  mercury  in  it  may  be  at  a  lower  level  than  that  in  the  other 
limb.  The  solution  to  be  tested  is  poured  into  the  cup  and  sucked  into  the 
graduated  limb  by  opening  the  stop-cock  until  all  liquid  has  passed  through,  care 
being  taken  not  to  admit  air.  Oil  of  vitriol  is  next  sucked  in,  in  a  similar  manner, 
and  the  closed  limb  is  thoroughly  shaken 
to  mix  the  mercury  with  the  solution  and 
acid.  Nitric  oxide  is  rapidly  evolved, 
and  when  no  more  is  seen  to  collect  in 
the  graduated  tube,  the  mercury  is 
brought  to  the  same  level  in  each  limb, 
as  shown  in  the  cut,  and  the  volume  of 
nitric  oxide  is  read  by  means  of  the 
graduations  on  the  tube.  The  stop-cock 
has  two  holes  bored  in  it,  so  that  the 
apparatus  may  be  washed  out  through 
the  small  tube  beside  the  cup.  The 
weight  of  nitric  acid  present  may  be 
calculated  from  the  volume  of  nitric 
oxide  measured,  for  63  grams  of  nitric 
acid  (HN03)  yield  22.22  litres  of  nitric 
oxide  (NO)  at  760  mm.  pressure  and  o°  C. 

All  the  metals  in  common  use 
are  attacked  by  nitric  acid,  except 
gold,  platinum,  and,  in  less  degree, 
aluminium,  so  that  this  acid  is  used 
to  distinguish  and  separate  these 
metals  from  others  of  less  value. 
The  ordinary  ready  method  of  as- 
certaining whether  a  trinket  is 
made  of  gold  consists  in  touching 
it  with  a  glass  stopper  wetted  with 
nitric  acid,  which  leaves  gold  un- 
touched, but  colours  base  alloys 
blue,  from  the  formation  of  copper 
nitrate.  The  touch-stone  allows  this 
mode  of  testing  to  be  applied  with  great  accuracy.  It  consists  of  a 
species  of  black  basalt,  obtained  chiefly  from  Silesia.  If  a  piece  of  gold 
be  drawn  across  its  surface,  a  golden  streak  is  left,  which  is  not 
affected  by  moistening  with  nitric  acid  ;  whilst  the  streak  left  by  brass, 
or  any  similar  base  alloy  is  rapidly  dissolved  by  the  acid.  Experience 
enables  an  operator  to  determine,  by  means  of  the  touch-stone,  pretty 
nearly  the  amount  of  gold  present  in  the  alloy,  comparison  being  made 
with  the  streaks  left  by  alloys  of  known  composition. 

Action  of  nitric  acid  on  organic  substances. — The  oxidising  action  of 
nitric  acid  on  some  organic  substances  is  so  powerful  as  to  be  attended 
with  inflammation ;  if  a  little  of  the  strongest  acid  be  placed  in  a 
porcelain  capsule,  and  a  few  drops  of  oil  of  turpentine  be  poured  into  it 


1.  75. — Nitrometer. 


94  RADICLES   AND   SUBSTITUTION. 

from  a  test-tube  fixed  to  the  end  of  a  long  stick,  the  turpentine  takes 
fire  with  a  sort  of  explosion.  By  boiling  some  of  the  strongest  acid  in 
a  test-tube  (Fig.  76),  the  mouth  of  which  is  loosely  stopped  with  a 
plug  of  raw  silk  or  of  horse-hair,  the  latter  may  be  made  to  take  fire 
and  burn  brilliantly  in  the  vapour  of  nitric  acid. 

In  many  cases  the  products  of  the  action  of  nitric  acid  exhibit  a  most 
interesting  relation  to  the  substances  from  which  they  have  been  pro- 
duced, one  or  more  atoms  of  the  hydrogen  of 
the  original  compound  having  been  removed  in 
the  form  of  water  by  the  oxygen  of  the  nitric 
acid,  whilst  the  spaces  thus  left  vacant  have 
been  filled  up  by  the  nitric  peroxide  resulting 
from  the  de-oxidation  of  the  nitric  acid,  pro- 
ducing what  is  termed  a  nitro-substitution  com- 
pound. A  very  simple  example  of  this  displace- 
ment of  H  by  NO2,  is  afforded  by  the  action  of 
_  nitric  acid  upon  benzene.  A  little  concentrated 

Fio.    6  nitric   acid    is    placed  in  a  flask,  and   benzene 

cautiously  dropped  into  it ;  a  violent  action 
ensues,  and  the  acid  becomes  of  a  deep  red  colour  ;  if  the  contents  of 
the  flask  be  now  poured  into  a  large  vessel  of  water,  a  heavy  yellow  oily 
liquid  is  separated,  having  a  powerful  odour,  like  that  of  bitter  almond 
oil.  This  substance,  which  is  used  to  a  considerable  extent  in  perfumery 
under  the  name  of  essence  of  Mirbane,  is  called  nitro-benzene,  and  its 
formula,  C6H3(N02),  at  once  exhibits  its  relation  to  benzene,  C6H6. 

To  understand  the  nature  of  this  reaction  the  theory  of  radicles  and 
of  substitution  must  be  realised.  Just  as  the  molecules  of  most  elements 
may  be  regarded  as  consisting  of  two  parts,  neither  of  which  is  capable 
of  a  separate  existence,  so  the  molecules  of  most  compounds  may  be 
looked  upon  as  composed  of  two  or  more  parts  or  radicles,  none  of 
which  can  exist  alone.  Water,  for  example,  consists  of  the  radicles 
H-  and  -OH,  united  by  one  "  bond  "  from  each,  which  bond  causes 
the  radicle  to  enter  into  a  new  combination  immediately  it  is  liberated. 
The  acids  which  contain  oxygen,  or  oxy -acids,  consist  of  one  or  more 
hydroxyl  (-  OH)  radicles  and  an  acid  radicle.  Thus  nitric  acid  is 
N02*OH,  containing  the  acid-radicle  nitroxyl  (N02)  and  one  hydroxyl 
radicle. 

Such  radicles  take  part  in  chemical  reactions,  and  may  be  substituted 
for  elements,  as  though  they  were  themselves  elements.  Thus  when 
the  hydroxyl  radicle  exists  in  one  of  the  reacting  substances  it  may  be 
expected  to  occur  in  one  of  the  products,  unless  the  reaction  be  of  so 
drastic  a  character  as  to  break  up  the  radicles  of  the  reacting  sub- 
stances. It  follows  that  a  large  number  of  chemical  changes  (par- 
ticularly in  organic  chemistry)  are  to  be  explained  as  exchanges  between 
the  radicles  of  compounds,  in  the  same  way  that  many  are  to  be 
explained  as  exchanges  between  the  elementary  atoms  constituting  the 
reacting  compounds — e.g.,  KI  +  HC1  =  KOI  +  HI. 

Benzene  contains  the  radicle  C6H5,  so  that  the  reaction  between 
benzene  and  nitric  acid  may  be  represented  as  an  exchange  of  the 
O^Hg  radicle  of  the  benzene  for  the  OH  radicle  of  the  nitric  acid,  the 
nitroxyl  radicle  having  been  substituted  for  hydrogen  in  the  benzene, 
H-C6H5  +  N02OH  =  N02-C6H5  +  H-OH. 


COMPOSITION  OF  NITRIC  ACID.  95 

It  is  by  an  action  of  this  description  that  nitric  acid  gives  rise  to 
gun-cotton,  and  other  explosive  substances  of  the  same  class,  when 
acting  upon  the  different  varieties  of  woody  fibre,  as  cotton,  paper,  saw- 
dust, tfcc.  For  making  these,  nitric  acid  finds  extended  application.* 

61.  Nitrates. — Its  powerful  action  on  bases  places  nitric  acid  among 
the  strongest  of  the  acids,  though  the  disposition  of  its  elements  to 
assume  the  gaseous  state  at  high  temperatures,  conjoined  with  the 
feeble  attraction  existing  between  nitrogen  and  oxygen,  causes  its  salts 
to  be  decomposed,  without  exception,  by  heat. 

The  nature  of  the  decomposition  varies  with  the  metal  contained  in  the  nitrate. 
The  nitrates  of  alkali  metals  are  first  converted  into  nitrites  by  the  action  of  heat ; 
thus  KN03  gives  KN02  and  O  ;  the  nitrites  themselves  being  eventually  decom- 
posed, evolving  nitrogen  and  oxygen,  and  leaving  the  oxide  of  the  metal.  The 
nitrates  of  copper  and  lead  evolve  nitric  peroxide  (N02)  and  oxygen,  the  oxides 
being  left.  The  nitrate  of  mercury  leaves  red  oxide  of  mercury,  which  is  decom- 
posed at  a  higher  temperature  into  mercury  and  oxygen. 

Nitric  acid  is  a  monobasic  acid,  because  it  contains  only  one  atom  oi 
hydrogen  which  can  be  exchanged  for  a  metal.  It  will  be  found  that 
it  is  only  the  H  of  the  OH  radicles  in  an  oxy-acid  which  can  be  exchanged 
for  metals  ;  the  OH  groups  may  thus  be  said  to  impart  an  acid  character 
to  a  compound.  Comparatively  few  of  the  nitrates  are  in  common  use ; 
they  will  be  mentioned  under  the  metals  of  which  they  are  the  salts. 

The  oxidising  effects  of  nitric  acid  are  shared  to  some  extent  by  the 
nitrates.  A  mixture  of  nitrate  of  lead  with  charcoal  explodes  when 
sharply  struck,  from  the  sudden  evolution  of  carbonic  acid  gas,  produced 
by  the  oxidation  of  the  carbon.  If  a  few  crystals  of  copper  nitrate  be 
sprinkled  with  water  and  quickly  wrapped  up  in  tinfoil,  the  latter  will, 
after  a  time,  be  so  violently  oxidised  as  to  emit  brilliant  sparks. 

But  in  the  case  of  the  nitrates  of  alkali  metals,  the  oxidation  takes  place  only  at 
a  high  temperature.  If  a  little  nitre  be  fused  in  an  earthen  crucible  or  an  iron 
ladle,  and,  when  it  is  at  a  red  heat,  some  powdered  charcoal,  and  afterwards  some 
flowers  of  sulphur,  be  thrown  into  it,  the  energy  of  the  combustion  will  testify  to 
the  violence  of  the  oxidation.  In  this  manner  the  carbon  is  converted  into  potas- 
sium carbonate  (K2C03),  and  the  sulphur  into  potassium  sulphate  (K2S04).  (See 
Ounpoicder.) 

Determination  of  the  composition  of  nitric  acid. — A  definite  weight,  say  10  grams, 
of  pure  lead  oxide  is  mixed  with  5  grams  of  nitric  acid,  and  the  mixture  is  gently 
heated  as  long  as  vapour  of  water  escapes  ;  PbO  +  2HN03  =  H20  +  Pb(N03)2.  Say 
that  the  residue  weighs  14.27  grams  ;  then 

From  the  weight  of  lead  oxide  and  nitric  acid       .         .     15.00  grams 
Deduct  weight  of  lead  oxide  and  lead  nitrate        .        .     14.27       „ 

Water  which  has  been  expelled  .        .        .      0.73 

corresponding  with   .3  or  o<og  gram  H. 

The  mixture  of  lead  nitrate  and  excess  of  lead  oxide  is  then  strongly  heated  in 
a  tube  containing  copper,  when  Pb(N03)2+Cu5  — PbO +5CuO-fN2  ;  the  nitrogen 
is  collected  and  measured.  Say  that  884.7  c-c-  of  N  are  obtaine"d  ;  these  weigh 
884.7  x  Tr¥nr  gram=  1. 19  gram,  since  I II 10  c.c.  of  N  weigh  14  grams. 

Hence  we  find,  in  5  grams  of  nitric  acid,  i.n  gram  N,  0.08  gram  H,  and,  by 
difference,  3,73  grams  0.  Dividing  these  numbers  by  the  atomic  weights,  14,  I, 
and  1 6,  we  obtain  0.08  atom  of  N,  0.08  atom  of  H,  and  0.24  atom  of  0,  or  i  atom 
of  H  to  i  atom  of  N  and  3  atoms  of  O.  This  would  give,  for  the  molecule  of 
nitric  acid,  HN03,  1  +  14  +  48=  =63,  a  result  agreeing  from  that  obtained  from 
the  sp.  gr.  of  its  vapour  (see  page  91). 

*  It  is  stated  that  nitrous  acid  in  the  nitric  acid  exerts  the  same  kind  of  influence  in  sub- 
stitution reactions  of  nitric  acid  as  it  exerts  in  the  action  of  the  acid  on  metals  (p.  92). 


96  NITEOUS   OXIDE. 

62.  Anhydrous  nitric  acid  or  nitric  anhydride  (N205)  is  obtained  by 
gently  heating  silver  nitrate  in  a  slow  current  of  chlorine,  great  care  being  taken 
to  exclude  every  trace  of  water ;  2AgN03  +  Cl2  =  2AgCl  +  6  +  N205. 

It  may  also  be  obtained  by  adding  anhydrous  phosphoric  acid  to  the  strongest 
nitric  acid  cooled  in  snow  and  salt,  and  carefully  distilling  at  as  low  a  temperature 
as  possible.  The  distillate  separates  into  two  layers,  the  lower  of  which  is  a 
compound  2N205.H2O,  called  dinitric  acid;  the  upper  layer  is  separated  and 
cooled. 

The  anhydride  is  condensed  as  a  crystalline  solid.  It  forms  transparent 
colourless  prisms  which  melt  at  30°  C.,  and  boil  at  47°  C.  By  a  slightly  higher 
temperature  it  is  readily  decomposed  ;  and  it  has  been  said  to  decompose  even 
at  the  ordinary  temperature,  in  sealed  tubes  which  were  shattered  by  the  evolved 
gas.  It  is  more  stable  in  the  dark.  When  the  anhydride  is  brought  in  contact 
with  water,  much  heat  is  evolved,  and  nitric  acid.  H2O.N205,  is  produced. 

The  specific  gravity  of  the  vapour  of  nitric  anhydride  being  unknown,  it  is  only 
a  surmise  that  its  molecule  is  represented  by  N2O5. 

63.  Nitrous  oxide  or  laughing  gas  (N20  =  44  parts  by  weight  =  2 
volumes)  is  prepared  by  heating  ammonium  nitrate,  when  it  is  resolved 
with   evolution   of   heat,  into  water   and   nitrous   oxide ;  NH4N03  = 
2H20  +  N20. 

To  obtain  nitrous  oxide,  an  ounce  of  ammonium  nitrate  may  be  gently  heated 
in  a  small  retort,  when  it  melts,  boils,  and  gradually  disappears  entirely  in  the 
forms  of  steam  and  nitrous  oxide.  The  latter  may  be  collected  with  slight  loss 
over  water. 

In  the  preparation  of  nitrous  oxide,  if  the  temperature  be  too  high,  the  gas  may 
contain  nitric  oxide  and  nitrogen;  NH4N03  =  NO  +  N  +  2H20.  Moreover,  since 
80  grams  (i  gram-molecule)  of  NH4N03  evolve  some  31,000  gram-units  of  heat  when 
decomposed  into  H20  and  N20,  explosion  is  liable  to  occur.  To  purify  the  gas,  it 
should  be  passed  through  a  strong  solution  of  ferrous  sulphate,  to  absorb  the  nitric 
oxide,  and  afterwards  through  potash  to  absorb  acid  vapours. 

Nitrous  oxide  is  colourless,  but  has  a  slight  odour  and  a  sweetish 
taste.  Its  characteristic  anaesthetic  property  is  well  known.  It  accele- 
rates the  combustion  of  a  taper  like  oxygen  itself,  and  will  even  kindle 
into  flame  a  spark  at  the  end  of  a  match,  for  it  is  readily  decomposed 
into  N2  and  0  by  the  temperature  of  burning  wood.  When  C  is  burnt 
into  C02  by  2N20,  it  evolves  36,000  more  units  of  heat  than  when 
burnt  in  O2,  showing  that,  contrary  to  the  usual  law,  heat  is  evolved  in 
the  decomposition  of  the  N20,  amounting  to  18,000  units  per  molecule. 
Such  a  compound  is  said  to  be  endothermic,  whilst  a  compound  like 
water,  which  is  formed  with  evolution  of  heat  is  called  exothermic. 
Nitrous  oxide  can  readily  be  distinguished  from  oxygen  by  shaking  it 
with  water,  which  absorbs,  at  the  ordinary  temperature,  about  three- 
fourths  of  its  volume  of  the  nitrous  oxide.  It  is  absorbed  in  larger 
quantity  by  alcohol.  It  is  also  much  heavier  than  oxygen,  its  specific 
gravity  being  1.53,  and  is  liquefied  by  a  pressure  of  40  atmospheres  at 
7°  C,  and  solidified  at  -  115°  C.  The  liquid  is  now  sold  in  wrought- 
iron  vessels  for  use  as  an  anaesthetic  in  dental  surgery.  In  small  doses 
it  has  an  intoxicating  effect,  whence  its  title  of  "  laughing  gas." 

The  liquid  nitrous  oxide  has  a  very  low  refractive  index  ;  its  sp.  gr.  is  o.  94  at 
O°  C.,  and  it  boils  at  -  90°  C.  A  lighted  match  thrown  into  the  liquid  burns  with 
great  brilliancy.  When  it  is  mixed  with  carbon  bisulphide  and  evaporated  in 
vacuo,  the  temperature  falls  to  —  140°  C.  The  critical  temperature  of  N20  is  39°  C., 
and  the  critical  pressure  is  73  atmos. 

64.  Nitric  oxide  (NO  =  30  parts  by  weight  =  2  volumes)  is  usually 
obtained  by  the  action  of  copper  upon  diluted  nitric  acid  (see  page  146). 

Twenty  grams  of  copper  turnings  or  clippings  are  introduced  into  a  retort, 


NITRIC   OXIDE. 


97 


and  85  c.c.  of  a  mixture  of  concentrated  nitric  acid  with  an  equal  volume 
of  water  are  poured  upon  them.  A  very  gentle  heat  may  be  applied  to  assist 
the  action,  and  the  gas  may  be  collected  over  water  (see  Fig.  109),  which  absorbs 
the  red  fumes  (N02)  formed  by  the  union  of  the  NO  with  the  oxygen  of  the  air 
contained  in  the  retort. 

The  nitric  oxide  prepared  by  the  action  of  copper  on  nitric  acid  generally  con- 
tains nitrous  oxide.  Pure  nitric  oxide  may  be  obtained  by  heating  in  a  retort 
6.5  grams  potassium  nitrate,  65  grams  of  ferrous  sulphate,  and  85  c.c.  of  dilute 
sulphuric  acid  (containing  one  measure  of  acid  to  three  measures  of  water),  which 
will  yield  about  1133  c.c.  of  gas;  2KN03  +  6FeS04  +  4ELSO,  =  K«SO,+ 


Nitric  oxide  is  distinguished  from  all  other  gases  by  the  production 
of  a  red  gas,  when  the  colourless  nitric  oxide  is  allowed  to  come  in 
contact  with  uncombined  oxygen,  the  presence  of  which,  in  mixtures  of 
gases,  may  be  readily  detected  by  adding  a  little  nitric  oxide.  The  red 
gas  consists  chiefly  of  nitric  peroxide  (N02)  when  the  oxygen  is  in 
excess,  otherwise  it  contains  also  some  nitrous  anhydride  (N9O  ). 

The  combination  of  nitric  oxide  with  oxygen  may  be  exhibited  by  decanting  a 
pint  bottle  of  oxygen,  under  water,  into  a  tall  jar  filled  with  water  coloured  with 
blue  litmus,  and  adding  to  it  a  pint 
bottle  of  nitric  oxide  (Fig.  77).  Strong 
red  fumes  are  immediately  produced, 
and  on  gently  agitating  the  cylinder, 
the  fumes  are  absorbed  by  the  water, 
reddening  the  litmus.  The  oxygen 
will  now  have  been  reduced  to  half  its 
volume,  and  if  another  pint  of  nitric 
oxide  be  added,  the  remainder  of  the 
oxygen  will  be  absorbed,  showing  that 
two  volumes  of  nitric  oxide  combine 
with  one  volume  of  oxygen,  forming 
nitric  peroxide  which  is  absorbed  by 
the  water.  In  presence  of  water  and 
excess  of  oxygen,  NO  is  entirely  con- 
verted into  nitric  acid  ;  2NO  +  H20  +  03 
=  2HN03. 

The  addition  of  nitric  oxide  to 
atmospheric  air  was  one  of  the 
earliest  methods  employed  for  removing  the  oxygen  in  order  to  deter- 
mine the  composition  of  air  ;  but  important  variations  were  observed 
in  the  results,  in  consequence  of  the  occasional  formation  of  N203  in 
addition  to  the  N02. 

In  all  its  properties  nitric  oxide  is  very  different  from  nitrous  oxide. 
It  is  much  lighter,  having  almost  exactly  the  same  specific  gravity  as 
air,  viz.,  1.04,  and  is  not  dissolved  to  an  important  extent  by  water.  It 
is  more  difficult  to  liquefy,  for  its  critical  temperature  is  -  93°  C.  ;  its 
boiling  point  is  -  153°  0.  When  a  lighted  taper  is  immersed  in  nitric 
oxide  it  is  extinguished,  although  this  gas  contains  twice  as  much  oxy- 
gen as  nitrous  oxide,  which  so  much  accelerates  the  combustion  of  a 
taper,  for  the  elements  are  held  together  by  a  stronger  attraction  in 
the  nitric  oxide,  so  that  its  oxygen  is  not  so  readily  available  for  the 
support  of  combustion.  (The  nitric  oxide  prepared  from  copper  and 
nitric  acid  sometimes  contains  so  much  nitrous  oxide  that  a  taper 
burns  in  it  brilliantly.)  Even  phosphorus,  when  just  kindled,  is  ex- 
tinguished in  nitric  oxide,  but  when  allowed  to  attain  to  full  combus- 
tion in  air,  and,  therefore,  to  a  temperature  high  enough  to  decompose 
the  nitric  oxide  into  N  and  0,  it  burns  with  extreme  brilliancy  in  the 


98 


REDUCTION  OF  NITRIC   OXIDE. 


gas.  Indeed,  nitric  oxide  appears  to  be  the  least  easy  of  decomposition 
of  the  whole  series  of  oxides  of  nitrogen,  which  accounts  for  its  being 
the  most  common  result  of  the  decomposition  of  the  other  oxides. 
Nitrous  oxide  itself,  when  passed  through  a  red-hot  tube,  is  partly  con- 
verted into  nitric  oxide  ;  and  when  a  taper  burns  in  a  bottle  of  nitrous 
oxide,  the  upper  part  of  the  bottle  is  often  filled  with  a  red  gas,  indica- 
ting the  formation  of  nitric  oxide,  and  its  oxidation  by  the  air  entering 
the  bottle. 

The  difference  in  the  stability  of  the  two  gases  is  also  shown  by  their 
behaviour  with  hydrogen.  A  mixture  of  nitrous  oxide  with  an  equal 
volume  of  hydrogen  explodes  when  in  contact  with  flame,  yielding  steam 
and  nitrogen,  but  a  mixture  of  equal  volumes  of  nitric  oxide  and  hydra- 
gen  burns  quietly  in  air,  the  hydrogen  not  decomposing  the  nitric 
oxide  except  at  the  temperature  of  a  strong  electric  spark.  An  excess 
of  hydrogen,  however,  is  capable  of  decomposing  nitric  oxide,  ammonia 
and  water  being  formed. 

If  two  volumes  of  nitric  oxide  are  mixed  with  five  volumes  of  hydrogen  and  the 
gas  passed  through  a  tube  having  a  bulb  filled  with  platinised  asbestos  (Fig.  78).* 
the  mixture  issuing  from  the  orifice  of  the  tube  produces  the  red  gas  by  contact 

with  the  air,  which  will  strongly  redden 
blue  litmus  ;  but  if  the  platinised 
asbestos  is  heated  with  a  spirit-lamp, 
the  hydrogen,  encouraged  by  the  action 
of  the  platinum  (p.  87).  decomposes 
the  nitric  oxide,  and  strongly  alkaline 
vapours  of  ammonia  are  produced,  re- 
storing the  blue  colour  to  the  reddened 
litmus;  NO +  H5  =  NH3  + H20.  It  will 
be  remembered  that  when  oxygen  is  in 
excess,  ammonia  is  converted,  under 
the  influence  of  platinum,  into  water 
and  nitrous  acid  (p.  87). 

Nitric  oxide  is  readily  absorbed 
by  ferrous  salts,  with  which  it 

Fjg  78  forms  dark  brown  solutions.  If 

a  little  solution  of  ferrous  sulphate 

(FeS04)  be  shaken  in  a  cylinder  of  nitric  oxide  closed  with  a  glass 
plate,  the  gas  will  be  immediately  absorbed  and  the  solution  will 
become  dark  brown.  On  applying  heat,  the  brown  compound  is 
decomposed. 

When  shaken  with  moist  ferrous  hydroxide,  NO  is  reduced  to  N2O 
and  N.  In  the  presence  of  caustic  soda,  sodium  hyponitrite  (Na2N2O2) 
and  ammonia  are  also  produced.  By  employing  a  large  excess  of  soda, 
one-fifth  of  the  nitric  oxide  may  be  converted  into  the  hyponitrite. 

65.  Nitrous  anhydride  (N203  or  NO.N02=  76  parts  by  weight). — 
Ammonium  nitrite  is  said  to  exist  in  minute  quantity  in  rain  water, 
and  nitrites  are  occasionally  found  in  well-waters,  where  they  have 
probably  been  formed  by  the  oxidation  of  ammonia  (p.  87).  Small 
quantities  of  ammonium  nitrite  appear  to  be  formed  by  the  combustion 
in  air  of  gases  containing  hydrogen,  this  element  uniting  with  the 
atmospheric  oxygen  and  nitrogen. 

Nitrous  anhydride  may  be  obtained  by  heating    starch  with  nitric 


*  Asbestos  which  has  been  wetted  with  solution  of  platinic  chloride,  dried,  and  heated  to 
redness,  to  reduce  the  platinum  to  the  metallic  state. 


NITROUS   ANHYDRIDE. 


99 


acid,  but  the  most  convenient  process  consists  in  gently  heating  nitric 
acid  (sp.  gr.  1.35)  with  an  equal  weight  of  white  arsenic,  and  passing 
the  gas,  first  through  a  U-tube  (Fig.  79)  surrounded  with  cold  water, 
to  condense  undecomposed  nitric  acid,  then  through  a  similar  tube 
containing  calcium  chloride  to  absorb  aqueous  vapour,  and  afterwards 
into  a  U-tube  surrounded  with  ice.  Through  a  small  tube  opening 
into  the  bend  of  this 
U-tube,  the  condensed 
nitrous  anhydride  drops 
into  a  tube  drawn  out  to 
a  narrow  neck,  so  that 
it  may  be  drawn  off  and 
seale  I  by  the  blow- 
pipe— 


White  arsenic. 


Fig\  79. — Preparation  of  nitrous  anhydride. 


Arsenic  acid. 

The  white  arsenic  is  here 
used  merely  as  a  reducing 
agent  to  remove  oxygen  from 
the  nitric  acid.  N203  is  the 
anhydride  of  nitrous  acid, 
HN02  (H2O.N203)  ;  this  acid 

is  so  unstable  that  it  immediately  breaks  up  into  H20  and  N203  ;  2HN02  = 
H20  +  N203.  The  object  of  the  above  reaction,  therefore,  is  to  remove  two  atoms 
of  oxygen  from  two  molecules  of  nitric  acid  —  2HN03  =  H20  +  N203  +  02.  \  White 
arsenic,  As406,  is  arseniow*  anhydride  and  readily  oxidises  to  arsem'c  anhydride, 
As4010,  which  then  combines  with  water  to  form  arsenic  acid6H2O.As4010(  =  4H3As04). 
Hence  one  molecule  of  white  arsenic  combines  with  four  atoms  of  oxygen  and  will 
therefore  reduce  four  molecules  of  nitric  acid.  The  student  should  endeavour  to 
sift  in  this  manner  all  chemical  equations  which  appear  to  him  complex. 

Nitrous  anhydride  is  also  prepared  by  decomposing  the  acid  nitrosyl 
sulphate  (see  Aqua  regia)  with  a  small  quantity  of  water  — 
2NOHS04  +  H20  =  2H2S04  +  N203. 

If  the  gas  liberated  in  these  reactions  be  cooled  to  -  20°  C.,  a  pure 
indigo-blue  liquid,  supposed  to  be  N203,  is  formed  ;  but  if  the  tempera- 
ture be  allowed  to  rise  the  colour  becomes  dirty  and  the  liquid  is  a 
mixture  of  nitrogen  tetroxide  (nitric  peroxide),  N2O4,  and  nitrous 
anhydride.  It  boils  below  the  ordinary  temperature  giving  a  red  gas 
which  consists  of  equal  volumes  of  nitric  oxide  and  nitric  peroxide, 
the  proportion  of  the  latter  gradually  increasing  until  the  remaining 
liquid  has  the  green  colour  and  the  composition  of  N204.  It  thus  seems 
that  N203  can  only  exist  at  low  temperatures  and  in  the  liquid  condi- 
tion. The  liquid  is  readily  obtained,  although  not  quite  pure,  by 
passing  nitric  oxide  into  cooled  liquid  nitrogen  tetroxide.  But  when 
equal  volumes  of  NO  and  N02  gases  are  mixed,  no  contraction  occurs, 
as  would  be  the  case  if  they  combined  to  N203  ;  NO  (2  volumes)  +  N02 
(2  volumes)  =  N203  (2  volumes). 

Water  at  about  o°  C.  dissolves  nitrous  anhydride,  yielding  a  blue 
solution,  which,  as  the  temperature  rises,  becomes  a  solution  of  nitric 
acid,  nitric  oxide  escaping  with  effervescence  ; 

3N203  +  H20  =  2HN03  +  4  NO. 

The    blue   solution   is  believed   to   contain    nitrous  acid,  HN02  or 


100  NITRIC   PEROXIDE. 

NO.OH;  N203  +  H20  =  2HNO2;  but  this  compound  has  not  been  ob- 
tained in  a  pure  state.  A  very  dilute  solution  of  the  acid  may  be 
preserved  for  some  time,  and  even  distilled,  without  decomposition. 

The  salts  of  nitrous  acid,  or  nitrites,  are  interesting  on  account  of 
their  production  from  the  nitrates  by  the  action  of  heat  (p.  95). 

When  potassium  nitrate  is  fused  in  a  fire-clay  crucible  and  heated  to  redness,  it 
evolves  bubbles  of  oxygen,  and  slowly  becomes  potassium  nitrite  (KNOg).  The 
heat  may  be  continued  until  a  portion  removed  on  the  end  of  an  iron  rod,  and  dis- 
solved in  water,  gives  a  strongly  alkaline  solution.  The  fused  mass  may  then  be 
poured  upon  a  dry  stone,  and,  when  cool,  broken  into  fragments  and  preserved  in 
a  stoppered  bottle.  On  heating  a  fragment  of  the  nitrite  with  dilute  H2S04,  red 
vapours  are  disengaged,  but  these  contain  little  nitrous  acid,  the  greater  part  of 
this  being  decomposed  by  the  water  into  HNO3  and  NO.  When  nitrous  acid  acts 
on  ammonia,  both  compounds  are  decomposed,  water  and  nitrogen  being  produced  ; 
NH3  +  HN02= N2  +  2H20. 

When  solutions  of  nitrites  are  heated  in  contact  with  air,  they  gradually  absorb 
oxygen,  becoming  converted  into  solutions  of  nitrates. 

Nitrous  acid  may  be  regarded  as  a  solution  of  NO  and  N02  in  water 
(H2O.N203  or  H2O.NO.N02).  The  former  tends  to  combine  with 
oxygen  to  form  N03,  and  the  latter  tends  to  part  with  oxygen  to  form 
NO,  so  that  nitrous  acid  can  behave,  according  to  circumstances,  either 
as  a  reducing  agent  or  an  oxidising  agent.  Obviously  any  compound 
capable  of  parting  with  oxygen  to  NO  cannot  obtain  oxygen  under  the 
same  circumstances  from  N02. 

Nitrous  acid  reduces  potassium  permanganate,  but  oxidises  ferrous  sulphate.  It 
will  also  oxidise  the  hydrogen  of  hydriodic  acid  (HI),  thereby  liberating  the  iodine  ; 
since  a  very  small  quantity  of  the  latter  can  be  detected  by  taking  advantage  of  its 
property  of  bluing  starch,  the  addition  of  hydriodic  acid  (KI  and  H2S04)  to  nitrous 
acid  (KN02  +  H2S04)  forms  a  very  delicate  test  for  the  latter:  -HI  +  NO-OH  = 
H-OH  +  I  +  NO. 

66.  Nitric  peroxide  (N02  =  46  parts  by  weight,  or  N204  =  92  parts  = 
2  volumes). — By  passing  a  mixture  of  nitric  oxide  with  half  its  volume 
of  oxygen,  free  from  every  trace  of  moisture,  into  a  perfectly  dry  tube 
cooled  in  a  mixture  of  ice  and  salt,  the  dark  red 
gas  is  condensed  into  colourless  prismatic  crystals 
which  melt  at  -  12°  C.  into  a  nearly  colourless 
liquid.  This  gradually  becomes  yellow  as  the  tem- 
perature rises,  and  at  15°  C.  has  a  deep  orange 
colour.  It  is  very  volatile,  boiling  at  71°  F. 
(22°  C.),  to  a  red-brown  vapour,  which  was  long 
mistaken  for  a  permanent  gas,  on  account  of  the 
great  difficulty  of  condensing  it  when  once  mixed 

with  air  OT  oxygen-     Nitric   Peroxide  is  also  ob- 
tained, mixed   with  one-fourth  of   its   volume  of 
oxygen,  by  heating  lead  nitrate  (Fig.  80) ;  Pb(N03)2  =  PbO  +  2NO2  +  O. 
The  vapour  of  nitric  peroxide  is  much  heavier  than  atmospheric  air. 

Its  vapour  density  diminishes  as  the  temperature  rises.  At  140°  C.  the  gas  is 
23  times  as  heavy  as  hydrogen,  showing  its  molecular  weight  to  be  46.  This 
variation  in  density,  in  conjunction  with  the  other  changes  with  increase  of  tem- 
perature, leads  to  the  belief  that  the  molecule  of  nitric  peroxide  at  low  temperatures 
(in  its  liquid  state)  is  N204,  and  becomes  dissociated  into  2N02  at  high  tempera- 
tures. At  500°  C.  the  gas  becomes  nearly  colourless,  being  almost  entirely  dis- 
sociated into  NO  and  O. 

N02  is  absorbed  by  many  finely  divided  metals,  forming  compounds  called 
nitro -metals.  These  are  very  unstable,  and  yield  most  of  the  reactions  of  NO2. 


STRUCTURAL  FORMULAE.  IOI 

Nitro-copper,  Cu2N02,  is  obtained  when  N02  is  passed  over  freshly  reduced  Cu  at 
30°  C. 

By  mixing  N205  with  the  green  liquid  obtained  by  condensing  the  vapours  from 
the  action  of  HN03  on  As406  the  N203  contained  in  the  liquid  is  converted  into 
N204;  N205  +  N203  =  2N204. 

Its  colour  varies  with  the  temperature,  becoming  very  dark  at  100°  F. 
(30°  C.).  The  smell  of  the  vapour  is  very  characteristic.  The  vapour 
supports  the  combustion  of  strongly  burning  charcoal  or  phosphorus,  and 
oxidises  most  of  the  metals,  potassium  taking  fire  in  it  spontaneously. 
Nitric  peroxide  must,  therefore,  rank  as  a  powerful  oxidising  agent, 
and  it  is  the  presence  of  this  substance  in  considerable  proportion  in 
the  red  fuming  nitric  acid  that  imparts  to  it  higher  oxidising  powers 
than  those  of  the  colourless  nitric  acid.  This  red  acid,  the  so-called 
nitrous  acid  of  commerce,  is  prepared  by  introducing  sulphur  into  the 
retorts  containing  the  mixture  of  sodium  nitrate  and  sulphuric  acid 
employed  in  the  preparation  of  the  nitric  acid,  a  portion  of  which  is 
de-oxidised  by  the  sulphur  and  converted  into  nitric  peroxide. 

Water  in  excess  immediately  decomposes  nitric  peroxide  into  nitrous 
acid  and  nitric  acid,  2NO2  +  H20  =  HN03  +  HNO2,  so  that  the  peroxide 
is  not  an  independent  anhydride. 

When  water  is  gradually  added  to  liquid  nitric  peroxide,  the  liquid  effervesces 
from  escape  of  nitric  oxide,  and  becomes  green,  blue,  and  ultimately  colourless  ; 
3NO2  +  H20  =  NO  +  2HN03.  If  the  red  nitric  acid  of  commerce  be  gradually  diluted 
with  water,  it  will  be  found  to  undergo  similar  changes,  always  becoming  colourless- 
at  last.  The  nitric  acid  which  has  been  used  in  a  Grove's  battery  has  a  green- 
colour,  from  the  large  amount  of  nitric  peroxide  which  has  accumulated  in  it,  in- 
consequence of  the  decomposition  of  the  acid  by  the  hydrogen  disengaged  during 
the  action  of  the  battery;  H  +  HN03  =  H20  +  N02.  If  this  green  acid  be  diluted 
with  a  little  water  it  becomes  blue,  and  a  larger  quantity  of  water  renders  it  colour- 
less, causing  the  evolution  of  nitric  oxide.  Similar  colours  are  obtained  by  passing 
nitric  oxide  into  nitric  acid  of  different  degrees  of  concentration,  apparently  because 
nitric  peroxide  is  formed  and  dissolved  by  the  acid. 

When  silver,  mercury,  and  some  other  metals  are  dissolved  in  cold  nitric  acid,  a 
green  or  blue  colour  is  often  produced,  leading  a  novice  to  suspect  the  presence  of 
copper,  the  colour  being  really  caused  by  the  dissolution,  in  the  unaltered  nitric 
acid,  of  the  nitric  peroxide,  produced  by  the  de-oxidation  of  another  portion. 

The  facility  with  which  nitrous  anhydride  and  nitric  peroxide  can 
be  decomposed  with  formation  of  nitric  oxide  renders  it  probable  that 
they  really  contain  this  group  of  elements  as  a  radicle  nitroxyl,  NO. 
To  express  this  they  may  plausibly  be  represented  as  formed  on  the 
same  plan  as  that  on  which  a  molecule  of  water  is  formed.  Just  as 
in  H  -  0  -  H,  the  two  atoms  of  hydrogen  are  linked  together  by  the 
diatomic  oxygen,  so  in  nitrous  anhydride,  0  =  N-0-N  =  0,  two  mole- 
cules of  nitric  oxide  are  linked  together  by  the  atom  of  oxygen,  whilst 
in  nitric  peroxide  (N204)  a  molecule  of  NO  is  bound  up  with  a  molecule 

of  N02,  thus,  0  =  N  -  O  -  N^f    .    If  nitric  anhydride  be  represented  by 


\N-O-  N^f    ,  it   is   easy  to  understand   the   behaviour  of  these 
O^  ^0 


three  oxides  with  the  alkalies.  Thus,  by  the  action  of  nitrous  anhy- 
dride on  caustic  potash,  potassium  nitrite  K  -  0  -  N  =  0,  in  which  K 
is  substituted  f  or  0  :  N  -  ,  is  formed,  whilst  nitric  anhydride  gives 
potassium  nitrate  K  -  O  -  NO2,  and  nitric  peroxide  gives  a  mixture  of 


102  ANALYSIS   OF   OXIDES   OF  NITROGEN. 

both  salts.     The  remaining  oxide  of  nitrogen  N2O  may  be  represented 
as  N.O.N 


Such  formulae  as  the  above  are  termed  structural  formula,  since  they 
essay  to  represent  the  way  in  which  the  molecule  is  built  up,  so  far 
as  it  is  possible  to  represent  a  three-dimensional  structure  on  one 
plane.  They  must  be  written  with  due  regard  to  the  valency  of  the 
elements  ;  thus  nitrogen  should  always  appear  either  as  trivalent  or 
pentavalent,  for  its  atom-linking  power  has  always  one  or  other  of  these 
values.  They  must  also  be  written  with  regard  to  the  constitution  of 
the  compound,  that  is,  the  relationships  which  the  various  atoms  show 
towards  each  other  ;  thus,  since  there  is  evidence  that  the  nitrogen 
atom  and  two  of  the  oxygen  atoms  in  nitric  acid  behave  as  the  radicle 
N02,  no  structural  formula  failing  to  represent  the  N  as  directly 
attached  to  two  oxygen  atoms  could  be  accepted. 

All  the  oxides  of  nitrogen  are  endothermic  compounds  (p.  96),  which 
accounts  for  the  indisposition  of  N  and  0  to  combine  directly.  The 
following  equations  represent  the  number  of  calories  or  gram-units  of 
heat  (p.  44)  evolved  by  the  decomposition  of  one  gram-molecule  (the 
molecular  weight  expressed  in  grams)  of  N20,  NO  and  N02  : 

N20   =  N2+  0    +  18,000  cal. 
ISO    =  N   +  O    +  21,500  „ 
N02  =  N    +  02  +      7650  „ 

The  general  principle  upon  which  the  determination  of  the  composi- 
tion of  these  oxides  has  been  determined  is  the  decomposition  of  a 
measured  volume  of  the  gaseous  oxide  either  by  heat  alone,  or  by 
burning  some  oxidisable  substance  in  it,  and  measuring  and  analysing 
the  volume  of  the  gases  or  gas  obtained. 

Thus,  when  nitrous  oxide  is  passed  through  a  red-hot  tube,  its  volume  is  increased 
by  one-half,  the  gas  becoming  a  mixture  of  I  volume  of  oxygen  and  2  volumes  of 
nitrogen.  This  shows  that  the  ratio  of  atoms  of  nitrogen  to  oxygen  in  the  gas  is 
2:1.  That  the  formula  is  N20.  not  N402,  is  decided  by  the  specific  gravity  of 
the  gas. 

When  a  known  volume  of  nitric  oxide  is  passed  over  a  weighed  quantity  of  red- 
hot  copper  and  the  nitrogen  which  passes  on  is  collected  and  measured,  it  is  found 
that  for  every  16  parts  by  weight  of  oxygen  absorbed  by  the  copper  (judged  from 
its  gain  of  weight)  I  i.i  I  litres  of  nitrogen  are  collected  ;  but  this  volume  of  nitrogen 
weighs  14  grams  (p.  47),  so  that  the  nitric  oxide  must  contain  0  :  N  =  16  :  14,  or 
one  atom  of  oxygen  to  one  atom  of  nitrogen.  That  the  formula  is  NO,  not  N2O2, 
follows  from  the  specific  gravity  of  the  gas. 

The  other  oxides  of  nitrogen  are  similarly  analysed. 

67.  Reduction  products  of  citric  acid.  —  By  the  action  of  nascent 
hydrogen,  that  is,  hydrogen  at  the  moment  of  its  liberation,*  nitric 
acid,  the  most  highly  oxidised  nitrogen  compound,  may  be  made  to 
yield  successive  reduction  products  until  the  most  highly  hydrogenised 
nitrogen  compound,  ammonia,  is  formed.  The  reduction  may  be  re- 
garded as  occurring  in  the  following  stages,  although  to  realise  such 
progressive  steps  is  difficult,  if  not  impossible,  in  practice.  The  first 
stage  of  the  reduction  will  be  nitrous  acid,  N02-OH-f-H2  =  NO'OH  + 
H20.  In  the  second  stage,  N'OH  would  be  expected  to  be  produced, 
but  in  a  compound  of  this  formula  only  one  of  the  atom-linking  powers 

*  When  it  might  be  supposed  to  be  still  in  the  condition  of  free  atoms,  and  therefore 
more  active.  The  usual  method  of  applying  nascent  hydrogen  is  to  liberate  it  in  the  liquid 
on  which  it  i-s  to  act  by  placing  zinc  and  sulphuric  acid,  or  merely  sodium  amalgam,  therein. 


HYPONITEOUS  ACID.  103 

of  the  nitrogen  would  be  satisfied ;  hence  this  group  of  atoms  is  in- 
capable of  a  separate  existence,  but,  if  produced,  immediately  combines 
with  a  like  group,  forming  hyponitrous  acid,  HON  :  N'OH.  The  third 
stage  of  the  reduction  consists  in  the  introduction  of  hydrogen  into  the 
hyponitrous  acid,  whereby  the  molecule  is  made  to  yield  either  two 
molecules  of  a  compound  called  hydroxylamine,  HON  :  N'OH  +  H4  = 

H     H\ 

+       \N"-OH,  or  one  molecule  of  a  compound  called  hydra- 

H     W 

zine,  HON  :  N-OH  +  H6  =  H2N  :  NH2  +  2HOH.  The  final  stage  of  the 
reduction  transforms  the  hydroxylamine  into  ammonia. 

Hyponitrous  acid,  H2N.20.2.  Nitrous  oxide  might  be  expected  to  be  the  anhy- 
dride of  this  acid,  N20  +  H20  =  H2N202,  but  an  aqueous  solution  of  this  gas  does 
not  contain  hyponitrous  acid.  The  hyponitrites  are  obtained  by  reducing  solutions 
of  the  nitrates  or  nitrites  by  the  nascent  hydrogen  generated  when  sodium  amalgam 
is  introduced  into  the  solution.  Thus,  a  solution  of  sodium  hyponitrite  is  obtained 
when  sodium  amalgam  is  added,  little  by  little,  to  a  strong  solution  of  sodium 
nitrate,  or  nitrite,  kept  cool.  The  hyponitrite  most  easily  obtained  in  a  pure 
condition  is  the  silver  salt,  Ag2N202,  which  is  thrown  down  as  a  yellow  precipitate 
when  silver  nitrate  is  added  to  the  solution  of  sodium  hyponitrite.  The  yellow 
precipitate  dissolves  in  ammonia  and  in  dilute  nitric  acid,  but  is  precipitated 
unchanged  by  neutralising  the  solvent  ;  it  is  insoluble  in  acetic  acid.  By  adding 
hydrochloric  acid  to  the  silver  salt,  hyponitrous  acid  passes  into  the  solution  and 
silver  chloride  remains  undissolved  ;  the  solution  is  colourless  and  acid  to  litmus, 
but  it  will  not  liberate  carbon  dioxide  from  the  alkali  carbonates  ;  when  kept  it 
decomposes  with  formation  of  N20  and  H20.  By  adding  the  silver  salt  to  a 
solution  of  HC1  in  ether,  filtering  and  evaporating  the  ethereal  solution,  crystals 
of  H2N202  are  obtained  ;  they  are  very  explosive,  like  other  compounds  containing 
the  group  'N  ;  N\  In  acid  solution  potassium  permanganate  oxidises  hyponitrous 
acid  to  nitric  acid,  but  in  alkaline  solution  a  nitrite  is  formed.  The  formation  of 
hyponitrous  acid  by  the  reduction  of  nitric  oxide  in  presence  of  water  has  been 
mentioned  at  p.  98  ;  another  reaction  by  which  it  is  produced  will  be  mentioned 
below. 

Hydroxylamine,  NH./OH,  may  be  obtained  by  the  reduction  of  nitric  acid,  but  is 
better  prepared  by  passing  nitric  oxide  through  a  series  of  flasks  containing  tin  and 
strong  hydrochloric  acid.  The  hydrogen  evolved  from  the  metal  and  acid  (the 
evolution  is  generally  hastened  by  the  addition  of  a  few  drops  of  platinic  chloride, 
the  platinum  of  which  deposits  on  the  tin  and  forms  a  galvanic  couple)  may  be 
regarded  as  converting  the  NO  into  NH2OH.  The  hydroxylamine,  being  possessed 
of  basic  properties,  combines  with  the  hydrochloric  acid  and  remains  in  the  solution 
as  hydroxylamine  hydrochloride,  NH2OH.HC1,  together  with  stannous  chloride. 
The  tin  is  precipitated  by  the  addition  of  H2S  ;  the  SnS  is  filtered  off  and  the  filtrate 
evaporated,  when  the  hydroxylamine  hydrochloride  crystallises. 

To  obtain  free  hydroxylamine,  the  hydrochloride  is  dissolved  in  methyl  alcohol 
and  a  solution  of  sodium  in  the  same  solvent  is  added  ;  sodium  chloride  is  precipi- 
tated and  is  filtered  off  ;  the  filtrate  is  then  distilled  under  reduced  pressure,  Avhen 
methyl  alcohol  passes  over,  followed  by  hydroxylamine.  In  this  process  the  sodium 
methoxide,  CH3ONa,  contained  in  the  solution  of  sodium  in  methyl  alcohol,  reacts 
with  the  hydroxylamine  hydrochloride,  forming  sodium  chloride,  hydroxylamine 
and  methyl  alcohol  :  NH2.OH.HCl  +  CH3ONa  =  NH2OH  +  CH3OH  +  NaCl.  Sodium 
hydroxide  cannot  be  substituted  for  the  methoxide  because  water  would  be  one  of 
the  products,  and  this  decomposes  the  hydroxylamine. 

Hydroxylamine  crystallises  in  white  needles,  jnelts  at  33°  C.,  and  boils  at  58°  C. 
under  22  mm.  pressure,  but  explodes  when  heated  to  90°  C.  under  ordinary  pres- 
sure. It  is  odourless  and  has  an  alkaline  reaction  ;  when  exposed  to  air  it 
deliquesces  and  ultimately  evaporates  ;  even  in  sealed  tubes  it  slowly  undergoes 
decomposition. 

Hydroxylamine  and  its  salts  are  very  easily  oxidised  to  nitrous  oxide  and  water 
so  that  they  reduce  cupric  oxide  in  alkaline  solutions  to  cuprous  oxide,  4CuO  + 
2NH2.OH  =  2Cu20  +  N20  +  3H2O.  Ferrous  hydroxide,  however,  is  oxidised  by  hy- 
droxylamine, which  is  thereby  reduced  to  ammonia ;  on  the  other  hand,  an  acid 


104  CLASSIFICATION  OF  ACIDS. 

ferric  solution  is  reduced  by  hydroxylamine.  An  aqueous  solution  of  the  hydro- 
chloride  is  used  as  a  photographic  developer. 

The  f  rue  base  combines  with  many  metallic  salts  in  the  same  way  that  water  and 
ammonia  do. 

If  hydroxylamine  be  regarded  as  formed  on  the  type  of  water,  it  will 
be  seen  to  contain  the  radicle  NH2  in  place  of  H  in  H.OH.  Equally 
well  it  may  be  said  to  be  ammonia  in  which  one  hydrogen  atom  has 
been  exchanged  for  OH.  Before  hydroxylamine  was  known,  it  could  be 
prophesied  that  such  a  compound  would  be  more  basic  than  is  water, 
and  less  basic  than  is  ammonia.  For  it  is  found  that  the  presence  of 
an  NH2  group  in  a  compound  tends  to  make  that  compound  basic, 
whilst  the  presence  of  an  OH  group  tends  to  make  it  acid.  Thus  the 
basic  properties  of  NH2H  are  enfeebled  by  the  substitution  of  an  OH 
group  for  H. 

The  acid  properties  of  N02.OH  are  stronger  than  those  of  NO.OH, 
which  in  their  turn  are  stronger  than  those  of  HO.N  :  N.OH.  It 
would  thus  seem  that  N02  is  a  stronger  acid  radicle  than  NO,  and 
that  the  two  hydroxyl  groups  in  hyponitrous  acid  do  not  compensate  in 
acid-producing  power  for  the  absence  of  an  oxy  -nitrogen  group. 

Since  there  are  two  OH  groups  in  hyponitrous  acid,  this  is  a  dibasic 
acid,  that  is  to  say,  it  contains  two  hydrogen  atoms  which  can  be  dis- 
placed by  metals. 

Classification  of  acids.  —  Acids  are  classified  into  monobasic,  dibasic,  tribasic, 
and  tetrabasic  according  as  they  have  one,  two,  three,  or  four  hydroxyl  groups. 
Nitric  acid  is  monobasic  ;  N02.OH.  Sulphuric  acid  is  dibasic  ;  S02(OH)9.  Phos- 
phoric acid  is  tribasic  ;  PO(OH)3.  Silicic  acid  is  tetrabasic  ;  Si(OH)4. 

On  considering  these  formulas  it  will  be  apparent  that  since  -  OH  is  a  monovalent 
radicle  (NOg)1  is  a  monovalent  radicle,  for  it  combines  with  only  one  OH. 
Similarly,  (SOg)11  is  a  divalent  radicle,  (PO)"1  a  trivalent,  and  (Si)iv  a  tretravalent 
radicle. 

Normal  salts  are  those  in  which  all  the  H  of  the  hydroxyl  groups  is  exchanged  for 
metal,  as,  for  instance,  in  normal  potassium  sulphate  S02(OK)2,  normal  sodium 
phosphate  P(ONa)3.  Acid  salts  are  those  in  which  only  part  of  the  hydrogen  has 
been  exchanged  for  the  metal,  as,  for  instance,  acid  potassium  sulphate,  S02OH.OK, 
diacid  sodium  phosphate,  PO(OH)2(ONa). 

In  forming  a  normal  salt  from  a  divalent  metal,  like  calcium,  and  a  monobasic 
acid,  like  nitric  acid,  it  is  necessary  to  have  two  molecules  of  the  acid  in  order  to 
obtain  sufficient  hydrogen  for  the  metal  to  displace  ;  thus  Ca  will  displace  the  H 

from  2(N02OH)  forming  -$Q2.fy>  Ca-     Tne   trivalent  aluminium  would  require 

2     N02.0x 
three  molecules  of  nitric  acid  :   N02.0-^A1.    A  similar  process  of  counterbalanc- 

N02.0/ 

ing  occurs  when  a  dibasic  acid  forms  a  normal  salt  with  a  trivalent  element  ;  thus, 
aluminium  sulphate  can  only  be  formed  from  2  atoms  of  Al1"  and  three  molecules 
of  H2S04  : 

s°a<0^Al  or  Al2i"(S04)3. 


Basic  salts  are  generally  composed  of  a  normal  salt  and  a  hydroxide  of  the 
metal,  as  in  basic  bismuth  nitrate  Bi  (N03)3.2Bi(OH)3. 

Double  salts   are  those  in  which    the    hydrogen   of   the   hydroxyl   has   been 

exchanged  for  different  metals,  as  in  potassium-sodium   carbonate    CO 
potassium-aluminium  sulphate 


AMIDES.  105 


Equivalents  Of  acids  and  bases.—  When  a  metal  is  substituted  for  half 
the  hydrogen  in  water  the  compound  is  a  hydroxide,  e.g.,  sodium  hydroxide  NaJOH  ; 

OH  /OH 

calcium    hydroxide  Ca"  <  nTT    aluminium  hydroxide  Alm  <r—  OH.      When  both 

\OH 
atoms  of  hydrogen  in  water  are  exchanged  for  metal  an  oxide  of  the  metal  is  pro- 

o  /°\ 

duced  NaONa,  or  Na20,  Ca  <Q>Ca,  or  CaO,  A1^-0~)A1,  or  A1203. 

When  a  base  neutralises  an  acid,  a  salt  is  formed,  a  base  being  either  the  oxide 
or  the  hydroxide  of  a  metal.  Thus  the  three  bases,  potash  (KOH),  soda  (NaOH), 
and  lime  (CaO),  neutralise  nitric  acid  in  accordance  with  the  equations  : 

KOH  +  HN03  =  KN03  +  H20  ;  NaOH  +  HN03  =  NaN03  +  H20  : 
56  63  40  63 

CaO  +  2HN03  =  Ca(N03)2  +  H20. 
56  126 

From  these  equations  it  is  seen  that  56  parts  of  KOH,  40  parts  of  NaOH,  and 
28  parts  of  CaO  are  required,  respectively,  to  neutralise  63  parts  of  nitric  acid. 
Consequently  these  proportions  of  these  bases  are  equivalent  to  each  other  in 
neutralising  power,  and  this  will  hold  good  towards  other  acids  than  nitric  acid, 
thus  it  will  be  found  that  112  parts  of  KOH  are  required  to  neutralise  98  parts  of 
H2S04,  and  that  80  parts  of  NaOH  and  56  parts  of  CaO  will  suffice  for  the  same 
purpose,  the  ratio  being  56  :  40  :  28,  as  before. 

^  The  equivalent  of  a  base  is  the  number  of  grams  of  it  which  will  neutralise  one 
/gram-molecule  of  a  monobasic  acid. 

Again,  if  the  quantity  of  different  acids  required  to  neutralise  a  given  weight  of 
a  base  be  compared,  the  ratio  between  the  quantities  will  be  found  to  be  constant 
for  every  base.  Thus  63  parts  of  nitric  acid,  49  parts  of  sulphuric  acid,  and  32§ 
parts  of  phosphoric  acid  are  required  respectively  to  neutralise  56  parts  by  weight 
of  potash.  These  quantities  of  these  acids  are  therefore  equivalent  to  each  other 
in  neutralising  power  ;  and  moreover  the  same  ratio  will  be  found  to  hold  when 
the  acids  are  used  to  neutralise  40  parts  of  NaOH  or  56  parts  of  CaO. 

The  equivalent  of  an  acid  is  the  number  of  grams  of  it  which  will  neutralise  one 
gram-molecule  of  potash  or  soda. 

It  will  be  obvious  that  when  a  table  of  equivalents  is  constructed  the  quantity 
of  any  acid  which  must  be  added  to  any  base  to  form  a  neutral  salt  can  be  seen 
at  a  glance,  for  this  quantity  is  the  equivalent  of  the  acid  and  of  the  base 
respectively. 

For  the  hydrogen  of  ammonia  there  may  be  substituted  potassium, 
sodium,  and  a  few  other  metals  having  a  high  affinity  for  oxygen. 
Thus  by  passing  dry  ammonia  over  gently  heated  sodium,  sodamide, 
NaNH2,  is  formed  ;  potassamide,  KN"H2,  is  similarly  prepared.  These 
are  white  waxy  substances  which  melt  (at  155°  and  270°  C.  respectively) 
to  greenish  liquids  and  partly  sublime  ;  at  a  red  heat  they  are  converted 
into  their  elements.  Water  immediately  decomposes  them,  yielding 
NaOH,  or  KOH  and  NH3. 

Compounds  containing  the  amidogen  group  (NH2)  are  called  amides. 
When  nitrous  acid  is  brought  in  contact  with  an  amide  at  the  ordinary 
temperature  (in  aqueous  solution),  the  amidogen  group  is  exchanged 
for  the  hydroxyl  of  the  nitrous  acid,  and  the  NH2  thus  removed  reacts 
with  the  NO  of  the  acid  to  form  N2  and  H2O.  Thus  the  simplest 
amide,  hydrogen  amide  or  ammonia  NH2'H,  reacts  with  nitrous  acid  to 
form  hydrogen  hydroxyl  or  water:  NH2'H  +  NO'OH  =  HO'H  +  N2  + 
H'OH.  This  reaction  is  typical  of  one  which  is  very  commonly 
employed  in  organic  chemistry  for  substituting  OH  for  NH2.  When 


'  106  DIAZO-COMPOUNDS. 

it  is  applied  to  hydroxylamine,  or  hydroxyl-amide,  NH2'OH,  it  does  not 
occur  on  exactly  the  same  lines,  possibly  because  hydroxyl-hydroxyl,  or 
hydrogen  dioxide,  HOOH,  which  would  be  the  product,  is  too  unstable 
to  be  formed  under  the  circumstances.  The  actual  reaction  between 
nitrous  acid  and  hydroxylamine  at  ordinary  temperatures  may  be 
represented  by  the  equation  NH2OH  +  NOOH  =  HOH  +  N20  +  HOH. 
Since  nitrous  acid  cannot  be  preserved  in  aqueous  solution  its  applica- 
tion for  such  reactions  is  effected  by  generating  it  at  the  moment  when 
it  is  required  by  dissolving  sodium  nitrite  in  the  solution  to  be  treated, 
and  adding  an  acid  to  liberate  nitrous  acid  from  the  nitrite. 

In  the  case  of  a  large  number  of  amides,  particularly  those  derived 
from  organic  compounds,  when  the  aqueous  solution  of  the  amide  is 
kept  cool  by  ice,  no  nitrogen  is  evolved  on  the  addition  of  nitrous  acid. 
This  is  because  the  nitrogen  of  the  amidogen  and  of  the  nitrous  acid 
remain  combined  together  to  form  a  group,  -N  :  N*.  in  which  each 
nitrogen  atom  is  able  to  attach  to  itself  a  monovalent  element  or 
radicle.  Such  a  nitrogen  group  is  called  a  diazo-group,  and  compounds 
containing  it  are  called  diazo-compouuds.  To  exemplify  the  diazo- 
reaction  the  following  hypothetical  equation  for  the  reaction  of  ammonia 
on  nitrous  acid  at  a  low  temperature  may  be  written  :  HvNH2  +  NOOH 
=  HN  :  N'OH  +  HOH.  The  diazo  compound  represented  by  the  for- 
mula HN  :  N'OH  has  not  been  obtained,  but  it  will  be  seen  that  hypo- 
nitrous  acid  may  be  regarded  as  formed  on  this  type,  HO  being  exchanged 
for  the  left-hand  hydrogen  atom.  A  comparison  of  the  formula  for 
hydroxylamine  with  that  for  ammonia  will  at  once  lead  to  the  con- 
clusion that  the  reaction  between  nitrous  acid  and  hydroxylamine  at  a 
low  temperature  should  produce  hyponitrous  acid  ;  this  is  the  case,  for  by 
mixing  cold  dilute  solutions  of  hydroxylamine  hydrochloride  and  sodium 
nitrite,  sodium  chloride  and  hydroxylamine  nitrite  are  formed,  the 
latter  immediately  passing  into  hyponitrous  acid  ;  by  adding  acetic 
acid  and  silver  nitrate  the  yellow  silver  hyponitrite  is  precipitated  : 
(i)  HO-NH9,HCl  +  NaO-NO  =  NaCl  +  HO-NH2,HO-NO;  (2)HONH9  + 
HONO  =  HO-N  :  N'OH  +  HOH.  The  diazo-compounds  which  contain 
hydroxyl  readily  decompose  when  the  temperature  is  raised,  the  products 
of  the  decomposition  being  the  same  as  those  which  result  from  the 
interaction  of  the  original  amide  with  nitrous  acid  at  a  high  tempera- 
ture. Thus,  if  the  above  experiment  be  conducted  at  a  high  tempera- 
ture (above  50°  C.)  nitrous  oxide  is  rapidly  evolved,  and  no  hypo- 
nitrous  acid  can  be  detected  in  the  solution. 

Hydrazine,  N2H4. — It  has  already  been  pointed  out  that  radicles  are 
incapable  of  a  separate  existence  ;  they  can,  however,  unite  with  them- 
selves to  form  compounds.  From  this  point  of  view  hydrogen  dioxide 
is  dihydroxyl  HO'OH.  Diamidogen  or  hydrazine,  H2N'NH2  is  another 
case  of  this  kind  ;  as  noticed  at  p.  103,  it  is  produced  by  the  reduction 
of  hyponitrous  acid  (sulphurous  acid  being  the  reducing  agent),  but  this 
is  not  a  convenient  method  for  preparing  it. 

To  prepare  hydrazine,  30  grams  of  potassium  diazomethanedisulphonate  (<?.  r.)  is 
added  in  fine  powder  to  a  solution  made  by  first  saturating  a  20  per  cent,  solution  of 
KOH  with  S02  and  then  adding  10  grams  of  KOH.  The  mixture  is  warmed  until 
colourless,  healed  to  boiling  with  150  c.c.  of  dil.  H2S04  (i  15),  filtered  and  cooled, 
whereupon  hydrazine  sulphate,  N2H4,H2S04  crystallises.  The  sulphate  is  dissolved 
in  a  very  little  water  and  mixed  with  the  exact  quantity  of  KOH  to  convert  the 
H2S04  into  K2S04,  and  with  sufficient  absolute  alcohol  to  precipitate  all  the  K2S04. 


HYDKOGEN   NITRIDE.  1 07 

After  filtration  the  alcohol  is  distilled  and  the  temperature  is  raised  to  115°  C., 
whereupon  hydrazine  hydrate,  jST2H4,H20,  distils.  This  is  added  to  a  retort  con- 
taining BaO,  heated  for  some  hours  at  1 10°  C.,  and  finally  distilled  under  diminished 
pressure  in  a  current  of  hydrogen.  A  large  quantity  of  hydrazine  sulphate  must 
be  used  for  a  successful  result. 

Hydrazine  is  a  colourless  liquid  of  sp.  gr.  1.013  '•>  ^  boils  at  113.5°  @. 
and  melts  at  1.4°  C.  It  dis^lves  in  water  evolving  much  heat 
(37,800  cals.  per  gram-molecule),  forming  a  hydrate  N2H4,2H2O  which 
passes  into  N2H4,H2O  if  the  water  is  evaporated.  The  latter  hydrate  is 
remarkably  stable,  resembling  the  caustic  alkalies  in  many  respects 
but  of  even  more  caustic  properties  ;  it  is  a  colourless  fuming  liquid  of 
sp.  gr.  ro3,  melts  at  -40°  C.  and  boils  at  120°  C.  It  is  powerfully 
alkaline  and  corrodes  cork,  rubber,  and  even  glass  when  heated,  so  that 
these  materials  must  be  avoided  in  its  manufacture  ;  hydrazine  itself, 
however,  does  not  attack  glass.  With  acids  hydrazine  hydrate  yields 
two  classes  of  salts,  e.g.,  N2H4,  HCland  N2H4,2HC1 ;  those  with  one  mole- 
cular proportion  of  acid  are  the  more  stable. 

Hydrazine  and  its  compounds  are  powerful  reducing  agents. 

Hydrogen  nitride,  azoimlde,  hydra-zoic  acid,  or  hydronitrous  acid. — When  hydra- 
zine hydrate  is  treated  with  nitrous  acid  in  a  cooled  dilute  solution  it  is  converted 

into  hydrogen  nitride,  ?>  NFL  ;  H2N'NH2  +  NO'OH  =  ?>NH-i  2HOH. 

This  compound  is  a  colourless  liquid  (b.p.  37°  C.),  characterised  by  its  explosive- 
ness  and  its  foul  odour.  It  is  distinguished  from  the  other  compounds  of  nitrogen 
with  hydrogen  by  its  acid  properties.  It  dissolves  many  metals  with  evolution  of 
hydrogen  and  production  of  metallic  nitrides,  such  as  Zn11  (N3)2.  It  has  been 
sought  to  explain  these  acid  properties  by  regarding  hydrogen  nitride  as  a  nitric 
acid  derivative,  the  nitrogen  of  which  might  be  supposed  to  retain  an  acid  bias. 
It  is  noticeable  that  most  nitrogen  compounds  in  which  the  nitrogen  is  not  present 
as  NH2,  or  an  equivalent  group,  have  an  acid  character. 

Hydrogen  nitride  is  only  obtained  in  small  quantity  by  the  above  reaction.  It 
is  most  conveniently  prepared  by  the  interaction  between  sodamide  and  nitrous 
oxide,  sodium  nitride,  from  which  the  free  acid  can  be  obtained,  being  produced  ; 
NH2Na  +  N20=:N3Na  +  H20.  Sodium  is  gently  heated  in  a  porcelain  boat  con- 
tained in  a  combustion  tube  through  which  dry  ammonia  is  passed  ;  when  the 
metal  has  been  completely  converted  into  sodamide.  a  current  of  dry  N20  is  sub- 
stituted for  the  NH3,  the  temperature  being  raised  to  about  200°  C.  The  sodium 
nitride  is  transferred  to  a  flask  and  distilled  with  dilute  sulphuric  acid.  To  the 
dilute  solution  of  N3H  which  distils  over  silver  nitrate  is  added,  whereby  silver 
nitride  N3Ag  is  precipitated  in  a  white  crystalline  form.  This  is  washed  and  dis- 
tilled with  dilute  H2S04.  A  solution  containing  27  per  cent,  of  N3H  is  thus 
obtained  ;  it  is  fractionally  distilled,  and  the  first  fraction  is  dried  over  calcium 
chloride  and  redistilled.  The  27  per  cent,  solution  is  a  slightly  viscid  liquid, 
specifically  heavier  than  water  ;  it  evolves  N3H  at  the  ordinary  temperature,  and 
the  vapour  gives  thick  clouds  when  in  contact  with  ammonia.  The  acid  corrodes 
the  skin  and  produces  giddiness  and  headache  when  inhaled.  Most  of  the  salts 
crystallise  well,  those  of  silver  and  mercurous  mercury  being  insoluble  ;  they  are 
all  explosive,  except  those  of  the  alkali  metals. 

There  is  a  remarkable  similarity  between  hydrazoic  acid  and  hydrochloric  acid, 
extending  even  to  their  salts  which  resemble  each  other  in  solubility  and  crystal- 
line form  ;  indeed,  in  the  case  of  sodium  nitride  the  resemblance  extends  to  the 
salt  taste. 

Silver  nitride  may  conveniently  be  obtained  by  cautiously  warming  1.5  gram  of 
hydrazine  sulphate  with  4  c.c.  of  nitric  acid  of  sp.  gr.  I  3  and  passing  the  N2H 
which  is  evolved  into  a  solution  of  AgN03. 


IO8  FORMS  OF  CARBON. 

CARBON. 

C=  12  parts  by  weight.* 

68.  This  element  is  especially  remarkable  for  its  uniform  presence  in 
organic  substances.  The  ordinary  laboratory  test  by  which  the  chemist 
decides  whether  a  substance  under  examination  is  of  organic  origin, 
consists  in  heating  it  with  limited  access  of  air,  and  observing  whether 
any  blackening  from  separation  of  carbon  (carbonisation)  ensues. 

Few  elements  are  capable  of  assuming  so  many  different  aspects  as 
is  carbon.  It  is  met  with  transparent  and  colourless  in  the  diamond, 
opaque,  black,  and  quasi-metallic  in  graphite  or  black  lead,  dull  and 
porous  in  wood  charcoal,  and  under  new  conditions  in  anthracite,  coke, 
and  gas-carbon. 

In  nature,  free  carbon  may  be  said  to  occur  in  the  forms  of  diamond, 
graphite,  and  anthracite  (the  other  varieties  of  coal  containing  con- 
siderable proportions  of  other  elements). 

Apart  from  its  great  beauty  and  rarity,  the  diamond  possesses  a 
special  interest  in  chemical  eyes,  from  its  having  perplexed  philosophers 
up  to  the  middle  of  the  last  century,  notwithstanding  the  simplicity  of 
the  experiments  required  to  demonstrate  its  true  nature.  The  first  idea 
of  it  appears  to  have  been  obtained  by  Newton,  when  he  perceived  its 
great  power  of  refracting  light,  and  thence  inferred  that,  like  other 
bodies  possessing  that  property  in  a  high  degree,  it  would  prove  to  be 
combustible  (" an  unctuous  substance  coagulated").  When  the  pre- 
diction was  verified,  the  burning  of  diamonds  was  exhibited  as  a 
marvellous  experiment,  but  no  accurate  observations  appear  to  have 
been  made  till  1772,  when  Lavoisier  ascertained,  by  burning  diamonds 
suspended  in  the  focus  of  a  burning-glass  in  a  confined  portion  of 
oxygen,  that  they  were  entirely  converted  into  carbonic  acid  gas.  In 
more  recent  times  this  experiment  has  been  repeated  with  the  utmost 
precaution,  and  the  diamond  has  been  clearly  demonstrated  to  consist 
of  carbon  in  a  crystallised  state. 

A  still  more  important  result  of  this  experiment  was  the  exact  determination  of 
the  composition  of  carbon  dioxide,  without  which  it  would  not  be  possible  to 
ascertain  exactly  the  proportion  of  carbon  in  any  of  its  numerous  compounds,  since 
it  is  always  weighed  in  that  form. 

The  classical  experiments  upon  the  synthesis  of  carbon  dioxide  were  conducted 
with  the  arrangement  represented  in  Fig.  81. 

Within  a  porcelain  tube  A,  which  is  heated  to  redness  in  a  charcoal  fire,  was 
placed  a  little  platinum  tray,  accurately  weighed,  and  containing  a  weighed  quantity 
of  fragments  of  diamond.  One  end  of  the  tube  was  connected  with  a  gas-holder  B, 
containing  oxygen,  which  was  thoroughly  purified  by  passing  through  the  tube  C, 
containing  potash  (to  absorb  any  carbonic  acid  gas  and  chlorine  which  it  might 
contain),  and  dried  by  passing  over  pumice  soaked  with  concentrated  sulphuric 
acid  in  I)  and  E.  To  the  other  end  of  the  porcelain  tube  A,  there  was  attached  a 
glass  tube  F,  also  heated  in  a  furnace,  and  containing  oxide  of  copper  to  convert 
into  carbon  dioxide  (CO^  gas  any  carbon  monoxide  (CO)  which  might  have  been 
formed  in  the  combustion  of  the  diamond.  The  C02  was  then  passed  over  pumice 
soaked  with  sulphuric  acid  in  G,  to  remove  any  traces  of  moisture,  and  afterwards 
into  a  weighed  bulb-apparatus  H,  containing  solution  of  potash,  and  two  weighed 
tubes  I,  K,  containing,  respectively,  solid  potash  and  sulphuric  acid  on  pumice,  to 
guard  against  the  escape  of  aqueous  vapour  taken  up  by  the  excess  of  oxygen  in  its 
passage  through  the  bulbs  H.  The  increase  of  weight  in  H,  I,  K,  represented  the 

*  Inasmuch  as  carbon  is  non-volatile,  the  volume  occupied  by  one  atomic  weight  of  it  is 
not  known. 


COMBUSTION   OF   DIAMOND. 


109 


C0.2  formed  in  the  combustion  of  an  amount  of  diamond  indicated  by  the  loss  of 
weight  suffered  by  the  platinum  tray,  and  the  difference  between  the  diamond  con- 
sumed and  the  C02  formed  would  express  the  amount  of  oxygen  which  had  com- 
bined with  the  carbon.  A  large  number  of  experiments  conducted  in  this  manner, 


Fig-.  81. — Exact  synthesis  of  carbonic  acid  gas. 

both  with  diamond  and  graphite,  showed  that  12  parts  of  carbon  furnished  44  parts 
of  C02,  and  consumed,  therefore,  32  parts  of  oxygen. 

A  convenient  arrangement  for  burning  a  diamond  in  oxygen  is  shown  in  Fig.  82. 
The  diamond  is  supported  in  a  short  helix  of  platinum  wire  A,  which  is  attached  to 
the  copper  wires  B  B,  passing  through  the  cork  C,  and  connected  with  the  terminal 
wires  of  a  Grove's  battery  of  five  or  six  cells.  The  globe  having  been  filled  with 
oxygen  by  passing  the  gas  down  into  it  till  a  match  indicates  that  the  excess  of 
oxygen  is  streaming  out  of  the  globe,  the  cork  is  inserted,  and  the  wires  connected 
with  the  battery.  When  the  heat  developed  in  the  platinum  coil 
by  the  passage  of  the  current,  has  raised  the  diamond  to  a  full  ~~i£<i 

red  heat,  the  connection  with  the  battery  may  be  interrupted,  and  **' 

the  diamond  will  continue  to  burn  with  steady  and  intense 
brilliancy. 

To  an  observer  unacquainted  with  the  satisfactory- 
nature  of  this  demonstration,  it  would  appear  incredible 
that  the  transparent  diamond,  so  resplendent  as  to 
have  been  reputed  to  emit  light,  should  be  identical 
in  its  chemical  composition  with  graphite  (plumbago  or  black  lead),  from 
which,  in  external  appearance,  it  differs  so  widely.  For  this  difference 
is  not  confined  to  their  colour  ;  in  crystalline  form  they  are  not  in  the 
least  alike,  the  diamond  occurring  generally  in  octahedral  crystals, 
whilst  graphite  is  found  either  in  amorphous  masses  (that  is,  having  no 
definite  crystalline  form),  or  in  six-sided  plates  which  are  not  geo- 
metrically allied  with  the  form  assumed  by  the  diamond.  Carbon, 
therefore,  is  dimorphous,  or  occurs  in  two  distinct  crystalline  forms. 
Even  in  weight,  diamond  and  graphite  are  very  dissimilar,  the  former 
having  an  average  specific  gravity  of  3.5  and  the  latter  of  2.3.  Again, 


110  DIAMOND  AND   GRAPHITE. 

a  crystal  of  diamond  is  the  hardest  of  all  substances,  whence  it  is  used 
for  cutting  and  for  writing  upon  glass,  but  a  mass  of  graphite  is  soft 
and  easily  cut  with  a  knife.  The  diamond  is  a  non-conductor  of  elec- 
tricity, but  the  conducting  power  of  graphite  renders  it  useful  in  the 
electrotype  process. 

Diamonds  are  chiefly  obtained  from  Golconda,  Borneo,  Kimberley  in 
South  Africa,  and  the  Brazils.  They  usually  occur  in  sandstone  rock 
or  in  mica  slate.  The  hardness  of  the  diamond  renders  it  necessary 
to  employ  diamond-dust  for  the  purpose  of  cutting  and  polishing  it, 
which  is  effected  with  the  aid  of  a  revolving  disc  of  steel,  to  the  surface 
of  which  the  diamond-dust  is  applied  in  the  form  of  a  paste  made  with 
oil.  The  crystal  in  its  natural  state  is  best  fitted  for  the  purpose  of 
the  glazier,  for  its  edges  are  usually  somewhat  curved,  and  the  angle 
formed  by  these  cuts  the  glass  deeply,  while  the  angle  formed  by 
straight  edges,  like  those  of  an  ordinary  jeweller's  diamond,  is  only 
adapted  for  scratching  or  writing  upon  glass.  Drills  with  diamond 
points  have  been  employed  in  tunnelling  through  hard  rocks.  The 
diamond-dust  used  for  polishing,  &c.,  is  obtained  from  a  dark  amorphous 
diamond  (Carbonado)  found  at  Bahia  in  the  Brazils;  1000  ounces 
annually  are  said  to  have  been  occasionally  obtained  from  this  source. 
When  burnt,  the  diamond  always  leaves  a  minute  proportion  of  ash  of 
a  yellowish  colour  in  which  silica  and  oxide  of  iron  have  been  detected. 
A  genuine  diamond  may  be  known  by  its  combining  the  three  qualities 
of  extreme  hardness,  enabling  it  to  scratch  hardened  steel,  high  specific 
gravity  (3.52),  and  insolubility  in  hydrofluoric  acid.*  Sapphire  (A1203) 
is  nearly  as  hard  as  diamond,  but  its  specific  gravity  is  about  4. 

Although  the  diamond,  when  preserved  from  contact  with  the  air, 
may  be  heated  very  strongly  in  a  furnace,  without  suffering  any  change, 
it  is  not  proof  against  the  intense  heat  of  the  discharge  taking  place 
between  two  carbon  points  attached  to  the  terminal  wires  of  a  powerful 
galvanic  battery.  If  the  experiment  be  performed  in  a  vessel  exhausted 
of  air,  the  diamond  becomes  converted  into  a  black  coke-like  mass  which 
closely  resembles  graphite  in  its  properties. 

Graphite  always  leaves  more  ash  than  the  diamond,  consisting  chiefly 
of  the  oxides  of  iron  and  manganese,  with  particles  of  quartz,  and  some- 
times titanic  oxide.  The  purest  specimens  are  those  of  compact  amor- 
phous graphite  from  Borrowdale  in  Cumberland ;  an  inferior  variety, 
imported  from  Ceylon,  is  crystalline,  being  composed  of  hexagonal 
plates.  Graphite  is  obtained  artificially  in  the  manufacture  of  cast 
iron :  in  some  cases,  a  portion  of  the  carbon  of  the  cast  iron  separates 
in  cooling,  in  the  form  of  crystalline  scales  of  graphite,  technically 
called  kish.  In  the  grey  variety  of  cast  iron  these  scales  of  graphite 
are  diffused  through  the  mass  of  the  metal,  and  are  left  undissolved 
when  the  iron  is  dissolved  by  an  acid. 

Graphite  is  far  more  useful  than  the  diamond,  for,  in  addition  to  its 
application  in  black-lead  pencils,  and  for  covering  the  surface  of  iron  in 
order  to  protect  it  from  rust,  it  is  largely  employed,  in  admixture  with 

*  Artificial  diamonds  have  been  made  by  dissolving  amorphous  carbon  in  molten  iron 
heated  to  nearly  3000°  C.  in  the  electric  furnace,  and  suddenly  cooling  the  metal  by  pouring- 
it  into  molten  lead.  In  this  way  only  the  surface  of  the  globules  of  iron  is  immediately 
solidified.  The  interior  expands  as  it  cools  and  creates  that  pressure  on  the  carbon  it  contains, 
which  appears  to  be  essential  to  the  formation  of  diamond.  By  dissolving  the  iron  in.  adds 
the  diamonds  are  left.  They  are  never  comparable  with  the  natural  product. 


CHARCOAL.  Ill 

clay,  for  the  fabrication  of  the  plumbago  crucibles  (blue  pots),  which  are 
so  valuable  to  the  metallurgist  for  their  power  of  resisting  high  tem- 
peratures and  sudden  change  of  temperature.  Graphite  is  also  some- 
times employed  for  lubricating,  to  diminish  friction  in  machinery,  and 
hr  facing  or  imparting  a  glazed  surface  to  gunpowder. 

Inferior  kinds  of  graphite  are  treated  by  Profile's  process.  The  graphite  is 
heated  with  2  parts  of  sulphuric  acid  and  iV^h  or  -jVtii  of  potassium  chlorate.  A 
part  of  the  graphite  is  thus  oxidised  and  converted  into  graphitic  acid,  C11H405. 
When  the  graphite  so  treated  is  washed,  dried,  and  heated  to  redness,  the  graphitic 
acid  is  decomposed,  evolving  steam  and  carbonic  oxide  gas,  which  swells  up  the 
graphite  to  a  light  voluminous  powder  which  can  be  separated  from  the  heavy 
earthy  impurities  by  floating  it  in  water.  When  much  silica  is  present  in  the 
graphite,  a  little  sodium  fluoride  is  added  after  the  potassium  chlorate  has  been 
decomposed. 

(Anthracite  and  the  other  varieties  of  coal  will  be  described  in  a 
separate  section.) 

69.  Several  varieties  of  carbon  ("  pseudo-carbons "),  obtained  by 
artificial  processes,  are  employed  in  the  arts.  The  most  important  of 
these  are  lamp  black,  wood  charcoal,  and  animal  charcoal. 

Lamp  black  approaches  more  nearly  in  composition  to  pure  carbon 
than  either  of  the  others,  and  is  the  soot  obtained  from  the  imperfect 
combustion  of  resinous  and  tarry  matters  (or  of  highly  bituminous 
coal),  from  which  source  it  derives  the  small  quantities  of  resin,  nitro- 
gen, and  sulphur  which  it  contains.  The  uses  of  this  substance,  as  an 
ingredient  of  pigments,  of  printing-ink,  and  of  blacking,  depend  evi- 
dently more  upon  its  black  colour  than  upon  its  chemical  properties. 
Diamond  black  is  a  very  pure  variety  of  lamp  black  obtained  by  the 
imperfect  combustion  of  the  natural  hydrocarbon  gas  of  the  Ohio- 
petroleum  region.  Spanish  black  is  charcoal  made  from  waste  cork. 

Wood  charcoal  presents  more  features  which  arrest  the  attention  of 
the  chemist,  as  well  on  account  of  its  specific  properties  as  of  the 
influence  exercised  by  the  method  adopted  for  obtaining  it,  upon 
its  fitness  for  the  particular  purpose  which  it  may  be  destined  to 
serve. 

If  a  piece  of  wood  be  heated  in  an  ordinary  fire,  it  is  speedily  con- 
sumed, with  the  exception  of  a  grey  ash  consisting  of  the  incombustible 
mineral  substances  which  it  contained  ;  if  the  experiment  were  per- 
formed in  such  a  manner  that  the  products  of  combustion  of  the  wood 
could  be  collected,  these  would  be  found  to  consist  of  carbonic  acid  gas- 
and  water  ;  woody  fibre  is  composed  of  carbon,  hydrogen,  and  oxygen 
in  the  proportion  represented  by  the  formula  C6H1005,  and  when  it  is 
burnt,  the  oxygen,  in  conjunction  with  more  oxygen  derived  from  the 
air,  converts  the  carbon  and  hydrogen  into  carbon  dioxide  and  water. 
But  if  the  wood  be  heated  in  a  glass  tube,  closed  at  one  end,  it  will  be 
found  impossible  to  reduce  it,  as  before,  to  an  ash,  for  a  mass  of  char- 
coal will  remain,  having  the  same  form  as  that  of  the  piece  of  wood  ;  in 
this  case,  the  oxygen  of  the  air  not  having  been  allowed  free  access  to> 
the  wood,  no  true  combustion  has  occurred,  but  the  wood  has  under- 
gone destructive  distillation,  that  is,  its  elements  have  arranged  them- 
selves, under  the  influence  of  the  high  temperature,  into  different  forms 
of  combination,  for  the  most  part  simpler  in  their  chemical  composition 
than  the  wood  itself,  and  capable,  unlike  the  wood,  of  enduring  that 
temperature  without  decomposition  ;  thus,  it  is  merely  an  exchange  of 


112 


DESTRUCTIVE   DISTILLATION   OF   WOOD. 


an  unstable  for  a  stable  equilibrium  of  the  particles  of  matter  com- 
posing the  wood. 

(DEFINITION. — Destructive  distillation  is  the  resolution  of  a  complex 
substance  into  simpler  vapours  and  gases  under  the  influence  of  heat, 
out  of  contact  with  air.) 

The  vapours  issuing  from  the  mouth  of  the  tube  will  be  found  acid 
to  blue  litmus-paper  ;  they  have  a  peculiar  odour,  and  readily  take  fire 
on  contact  with  flame.  These  will  be  more  particularly  noticed  here-- 
after, as  they  contain  some  very  useful  substances.  The  charcoal  which 
is  left  is  not  pure  carbon,  but  contains  considerable  quantities  of  oxygen 
and  hydrogen  with  a  little  nitrogen,  and  the  mineral  matter  or  ash  of 
the  wood. 

When  the  charcoal  is  to  be  used  for  fuel,  it  is  generally  prepared  by 
a  process  in  which  the  heat  developed  by  the  combustion  of  a  portion 

of  the  wood  is  made  to  effect 
the  charring  of  the  rest.  With 
this  view  the  billets  of  wood 
are  built  up  into  a  heap 
(Fig.  83)  around  stakes  driven 
into  the  ground,  a  passage 
being  left  so  that  the  heap 
may  be  kindled  in  the  centre. 
This  mound  of  wood,  which 
is  generally  from  ^o  to  qo 

Fig.  83-Charcoal  heap.  feet&  in    diameter,     £     closely 

covered  with  turf  and  sand,  except  for  a  few  inches  around  the  base, 
where  it  is  left  uncovered  to  give  vent  to  the  vapour  of  water  expelled 
from  the  wood  in  the  first  stage  of  the  process.  When  the  heap  has 
been  kindled  in  the  centre,  the  passage  left  for  this  purpose  is  carefully 
closed  up.  After  the  combustion  has  proceeded  for  some  time,  and  it 
is  judged  that  the  wood  is  perfectly  dried,  the  open  space  at  the  base 

is  also  closed,  and  the  heap 
left  to  smoulder  for  three  or 
four  weeks,  when  the  wood  is 
perfectly  carbonised. 

Upon  an  average,  2  2  parts 
of  charcoal  are  obtained  by 
this  process  from  100  of 
wood. 

On  the  small  scale,  the 
operation  may  be  conducted 

Fig.  ^-Distillation  of  wood.  in  a  SlaSS  retort>  as  shown  in 

Fig.  84,  where  the  water,  tar, 

and  naphtha  are  deposited  in  the  globular  receiver,  and  the  inflammable 
gases  are  collected  over  water. 

During  the  destructive  distillation  the  hydrogen  and  oxygen  of  the 
wood  are  for  the  most  part  expelled  in  the  forms  of  wood  naphtha 
(CH40),  pyroligneous  acid  (C2H402),  carbon  dioxide,  carbon  monoxide, 
water,  &c.,  leaving  a  residue  containing  a  much  larger  proportion  of 
carbon  than  that  contained  by  the  original  wood. 

Much  attention  has  been  paid  to  the  manufacture  of  charcoal  for  gunpowder  (a 
mixture  of  charcoal,  sulphur,  and  saltpetre),  and  it  has  been  found  that  the  higher 


CHARCOAL   FOR   GUNPOWDER.  113 

the  temperature  to  which  the  charcoal  is  exposed  in  its  preparation,  the  larger  the 
proportion  of  hydrogen  and  oxygen  expelled,  and  the  more  nearly  does  the  charcoal 
approach  in  composition  to  pure  carbon  ;  but  it  is  not  found  advantageous  in 
practice  to  employ  so  high  a  temperature,  since  it  yields  a  dense  charcoal  of  difficult 
combustibility,  and  therefore  less  fitted  for  the  manufacture  of  powder.  The 
average  composition  of  wood,  exclusive  of  ash,  is,  in  100  parts — 50  parts  carbon, 
6  parts  hydrogen,  and  44  parts  oxygen. 

The  composition  of  the  charcoal  prepared  at  different  temperatures  is  given  in 
the  following  table  : 


Temperature 
of  Cli  irring. 

C.irbou. 

Hydrogen. 

Oxygen. 

Ash. 

270°  C. 

71.0 

4.60 

23.00 

1.40 

363° 

80.  1 

3-71 

14-55 

1.64 

476° 

85.8 

3-13 

9-47 

i.  60 

519° 

86.2 

3-" 

9.11 

i..<8 

The  charcoal  employed  for  black  gunpowder  in  this  country  is  prepared  at  tem- 
peratures between  360°  C.  and  520°  C.  It  will  be  seen  that  the  proportion  of 
carbon,  upon  which  the  heating  value  of  the  charcoal  depends,  increases  with  the 
final  temperature  of  carbonisation  ;  but  it  has  been  found  that  the  rapidity  with 
which  the  temperature  is  raised  has  also  a  great  effect  in  increasing  the  proportion 
of  carbon,  as  shown  in  the  following  table  : 


Final 
Temperature. 

Time  of 
Heating-. 

Percentage 
of  Carliou. 

Final 
Temperature. 

Time  of 
Heating. 

Percentage 
of  Carbon. 

410°  C. 
414° 
490° 

5    hours 

2f         „ 

3i     .. 

81.65 

83.14 
84.19 

490°  C. 

Sf 

2f  hours 

3f    „ 
3      » 

86.34 
83-32 
86.52 

The  charcoal  prepared  between  260°  and  320°  C.  has  a  brown  colour  (char'bon 
roux),  and  since  it  is  more  easily  inflamed  than  the  black  charcoal  obtained  at 
higher  temperatures,  it  is  used  in  powders  where  the  proportion  of  sulphur  is 
reduced.  It  is  prepared  by  exposing  the  wood,  in  an  iron  cylinder,  to  the  action  of 
high  pressure  steam  heated  to  about  280°  C.  Charcoal  prepared  at  low  tempera- 
tures gives  somewhat  higher  velocities  to  gunpowder  in  which  it  is  used,  but 
absorbs  much  more  moisture  than  that  prepared  at  high  temperatures. 

Light  woods,  such  as  alder,  willow,  and  dogwood,*  are  selected  for  the  preparation 
of  charcoal  for  gunpowder,  because  they  yield  a  lighter  and  more  easily  combus- 
tible charcoal,  dogwood  being  employed  for  the  best  quality  of  powder  for  small 
arms.  This  wood  is  chiefly  imported,  since  it  has  not  been  successfully  grown  in 
this  country.  It  is  stripped  of  its  bark,  and  either  exposed  for  a  length  of  time  to 
the  air  or  dried  in  a  hot  chamber.  Considerable  loss  of  charcoal  occurs  if  damp 
wood  be  charred,  a  portion  of  the  carbon  being  oxidised  by  the  steam  at  a  high 
temperature. 

In  order  to  convert  the  wood  into  charcoal,  i^  cwt.  of  wood  is  packed  into  a 
sheet-iron  cylinder  or  sl'q)  (Fig.  85),  one  end  of  which  is  closed  by  a  tightly-fitting 
cover,  and  the  other  by  a  perforated  plate,  to  allow  of  the  escape  of  the  gases  and 
vapours  expelled  during  the  carbonisation.  This  cylinder  is  then  introduced  into  a 
cylindrical  cast-iron  retort,  built  into  a  brick  furnace,  and  provided  with  a  pipe  (L) 
for  the  escape  of  the  products,  which  are  usually  carried  back  into  the  furnace  (B) 
to  be  consumed.  The  process  of  charring  occupies  from  2\  to  3^  hours,  and  as  soon 
as  it  is  completed,  which  is  known  by  the  violet  tint  of  the  (carbonic  oxide)  flame 

*  Dogwood  charcoal  is  not  made  from  the  true  dogwood  (cornus),  but  from  the  alder 
buckthorn  (Ithamnus  frangula),  commonly  called  black  dogwood. 


DEODORISING  BY  CHARCOAL. 


from  the  pipe  leading  into  the  fire,  the  slip  is  transferred  to  an  iron  box  or  ex- 
tinguisher, where  the  charcoal  is  allowed  to  cool.  About  40  Ibs.  of  charcoal 
are  obtained  from  the  above  quantity  of  wood.  Charcoal  prepared  by  this  process 
is  spoken  of  as  cylinder  charcoal,  to  distinguish  it  from  pit  charcoal,  prepared  by 

the  ordinary  process  of  charcoal  burning 
(Fig.  83),  and  used  for  fuse  composi- 
tions, &c.,  but  not  for  the  best  gun- 
powder. The  fitness  of  the  charcoal 
for  the  manufacture  of  powder  is  gener- 
ally judged  of  by  its  physical  characters. 
It  is  of  course  desirable  that  the  charcoal 
should  be  as  free  from  incombustible 
matter  as  possible.  The  proportion  of 
the  ash  left  by  different  charcoals  varies 
considerably,  but  it  seldom  exceeds  2 
per  cent.  This  ash  consists  chiefty  of 
the  carbonates  of  potassium  and  cal- 
cium ;  it  also  contains  calcium  phos- 
phate, magnesium  carbonate,  silicate 
and  sulphate  of  potassium,  chloride  of 
sodium,  and  the  oxides  of  iron  and 
manganese. 

The  charcoal  is  kept  for  about  a,  fort- 
night before  being  ground  for  making 


Fig.  85. — Charcoal  retort. 


gunpowder,  for  if  ground  when  fresh,  before  it  has  absorbed  moisture  and  oxygen 
from  the  air,  it  is  liable  to  spontaneous  combustion. 

The  infusibility  of  the  charcoal  left  by  wood  accounts  for  its  very 
great  porosity,  upon  which  some  of  its  most  remarkable  and  useful 
properties  depend.  The  application  of  charcoal  for  the  purpose  of 
"  sweetening "  fish  and  other  food  in  a  state  of  incipient  putrefaction 
has  long  been  practised,  and  more  recently  charcoal  has  been  employed 
for  deodorising  all  kinds  of  putrefying  and  offensive  animal  or  vegetable 
matter.  This  property  of  charcoal  depends  upon  its  power  of  absorbing 
into  its  pores  very  considerable  quantities  of  the  gases,  especially  of 
those  which  are  easily  absorbed  by  water.  Thus,  i  cubic  inch  of 
charcoal  is  capable  of  absorbing  about  100  cubic  inches  of  ammonia  gas 
and  50  cubic  inches  of  sulphuretted  hydrogen,  both  which  are  con- 
spicuous among  the  offensive  results  of  putrefaction.  This  condensation 
of  gases  by  charcoal  is  a  mechanical  effect,  and  does  not  involve  a 
chemical  combination  of  the  charcoal  with  the  gas ;  it  is  exhibited  most 
powerfully  by  charcoal  which  has  been  recently  heated  to  redness  in  a 
closed  vessel,  and  cooled  out  of  contact  with  air  by  plunging  it  under 
mercury.  Eventually,  the  offensive  gases  absorbed  by  the  charcoal  are 
chemically  acted  on  by  the  oxygen  of  the  air  in  its  pores.  A  cubic  inch 
of  wood  charcoal  absorbs  nearly  10  cubic  inches  of  oxygen,  and  when 
the  charcoal  containing  the  gas  thus  condensed  is  presented  to  another 
gas  which  is  capable  of  undergoing  oxidation,  this  latter  gas  is  oxidised 
and  converted  into  inodorous  products.  Thus,  if  charcoal  be  exposed 
to  the  action  of  air  containing  sulphuretted  hydrogen  gas  (H2S),  it 
condenses  within  its  pores  both  this  gas  and  the  atmospheric  oxygen, 
which  slowly  converts  the  H2S  into  sulphuric  acid  (HjSOJ.  The  pre- 
sence of  so  much  air  in  charcoal  renders  it,  like  wood,  apparently  lighter 
than  water  ;  when  powdered  it  sinks  in  water,  its  true  specific  gravity 
varying  from  1.4  to  1.9. 

The  great  porosity  of  wood  charcoal  is  strikingly  exhibited  by  attaching  a  piece 
of  lead  to  a  stick  of  charcoal  (Fig.  86),  so  as  to  sink  it  in  a  cylinder  of  water,  which 
is  then  placed  under  the  receiver  of  the  air. pump.  On  exhausting  the  air,  innumer- 


ABSOEPTION   OF  GASES  BY  CHARCOAL.  115 

able  bubbles  will  start  from  the  pores  of  the  charcoal,  causing  brisk  effervescence. 
If  a  glass  tube  16  or  18  inches  long  be  thoroughly  tilled  with  ammonia  gas  (Fig.  87), 
supported  in  a  trough  containing  mercury,  and 'a  small  stick  of  recently  calcined 
charcoal  introduced  through  the  mercury  into  the  tube,  the  charcoal  will  absorb  the 
ammonia  so  rapidly  that  the  mercury  will  soon  be  forced  up  and  fill  the  tube, 
carrying  the  charcoal  up  with  it,  On  removing  the  charcoal  and  placing  it  upon 
the  hand,  a  sensation  of  cold  will  be  perceived  from  the  rapid  escape  of  ammonia 
perceptible  by  its  odour. 

By  exposing  a  fragment  of  recently  calcined  wood  charcoal  under  a  jar  filled  with 
hydrosulphuric  acid  gas  for  a  few  minutes,  so  that  it  may  become  saturated  with 
the  gas,  and  then  covering  it  with  a  jar  of  oxygen,  the  latter  gas  will  act  upon 
the  former  with  such  energy  that  the  charcoal  will  burst  into  vivid  combustion. 
The  jar  must  not  be  closed  air-tight  at  the  bottom,  or  the  sudden  expansion 
may  burst  it.  Charcoal  in  powder  exposed  in  a  porcelain  crucible  mav  also  be 


86. 


Fig.  87. 


employed  in  the  same  way.  It  should  be  pretty  strongly  heated  in  the  covered 
crucible,  and  allowed  to  become  nearly  cool  before  being  exposed  to  the  hydro- 
sulphuric  acid. 

Charcoal  prepared  from  hard  woods  absorbs  the  largest  volume  of  gas.  Thus 
charcoal  made  from  the  shell  of  the  cocoa-nut  will  absorb  170  times  its  volume  of 
ammonia  gas  and  18  times  its  volume  of  oxygen,  although  its  pores  are  quite 
invisible,  and  its  fracture  exhibits  a  semi-metallic  lustre. 

As  the  gases  which  are  evolved  in  putrefaction  are  of  a  poisonous 
character,  the  power  of  wood  charcoal  to  remove  them  acquires  great 
practical  importance,  and  is  applied  in  very  many  cases ;  the  charcoal  in 
coarse  powder  is  thickly  strewn  over  matters  from  which  the  effluvium 
proceeds,  or  is  exposed  in  shallow  trays  to  the  air  to  be  sweetened,  as  in 
the  wards  of  hospitals,  &c.  It  has  even  been  placed  in  a  flat  box  of 
wire  gauze  to  be  fixed  as  a  ventilator  before  a  window  through  which 
the  contaminated  air  might  have  access,  and  respirators  constructed  on 
the  same  principle  have  been  found  to  afford  protection  against 
poisonous  gases  and  vapours.  The  ventilating  openings  of  sewers  in 
the  streets  may  also  be  fitted  with  cases  containing  charcoal  for  the 
same  purpose.  Water  is  often  filtered  through  charcoal  in  order  to 
free  it  from  the  noxious  and  putrescent  organic  matters  which  it  some- 
times contains.  For  all  such  uses  the  charcoal  should  have  been  re- 
cently heated  to  redness  in  a  covered  vessel,  in  order  to  expel  the 
moisture  which  it  attracts  when  exposed  to  the  air ;  and  the  charcoal 
which  has  lost  its  power  of  absorption  will  be  found  to  regain  it  in 
great  measure  when  heated  to  redness. 

This  power  of  absorption  which  charcoal  possesses  is  not  confined  to 


Il6  ANIMAL   CHAKCOAL. 

gases,  for  many  liquid  and  solid  substances  are  capable  of  being  removed 
by  that  agent  from  their  solution  in  water.  This  is  most  readily  traced 
in  the  case  of  substances  which  impart  a  colour  to  the  solution,  such 
colour  being  often  removed  by  the  charcoal ;  if  port  wine  or  infusion  of 
logwood  be  shaken  with  powdered  charcoal  (especially  if  the  latter  has 
been  recently  heated  to  redness  in  a  closed  crucible),  the  liquid,  when 
filtered  through  blotting-paper,  will  be  found  to  have  lost  its  colour ; 
the  colouring-matter,  however,  seems  merely  to  have  adhered  to  the 
charcoal,  for  it  may  be  extracted  from  the  latter  by  treatment  with  a 
weak  alkaline  liquid. 

The  decolorising  power  of  wood  charcoal  is  very  feeble  in  comparison 
with  that  possessed  by  bone-black  or  animal  charcoal,  which  is  obtained 
by  heating  bones  in  vessels  from  which  the  air  is  excluded.  Bones  are 
composed  of  about  one-third  of  animal  and  two-thirds  of  mineral  sub- 
stances, the  latter  including  calcium  phosphate,  which  amounts  to 
more  than  half  the  weight  of  the  bone,  and  a  little  calcium  carbonate. 
When  bone  is  heated,  as  in  a  retort,  so  that  air  is  not  allowed  to  have 
free  access  to  it,  the  animal  matter  undergoes  destructive  distillation, 
its  elements — carbon,  hydrogen,  nitrogen,  and  oxygen — assuming  other 
forms,  the  greater  part  of  the  last  three  elements,  together  with  a 
portion  of  the  carbon,  escaping  in  different  gaseous  and  vaporous 
products,  while  a  considerable  proportion  of  the  carbon  remains  behind, 
intimately  mixed  with  the  earthly  ingredients  of  the  bone,  and  con- 
stituting the  substance  known  as  animal  charcoal.  The  great  differ- 
ence between  the  products  of  the  destructive  distillation  of  bone  and 
of  wood  deserves  a  passing  notice.  If  a  fragment  of  bone  or  a  shaving 
•of  horn  be  heated  in  a  glass  tube  closed  at  one  end,  the  vapours  which 
are  evolved  will  be  found  strongly  alkaline  to  test-papers,  while  those 
furnished  by  the  wood  were  acid ;  this  difference  is  to  be  ascribed 
mainly  to  the  presence  of  nitrogen  in  the  bone,  wood  beirg  nearly  free 
from  that  element;  it  will  be  found  to  hold  good,  as  a  general  rule, 
that  the  results  of  the  destructive  distillation  of  animal  and  vegetable 
matters  containing  much  nitrogen  are  alkaline,  frcm  the  presence  of 
ammonia  (NH3)  and  similar  compounds,  while  those  furnished  by  non- 
nitrogenised  substances  possess  acid  characters;  the  peculiar  odour 
which  is  emitted  by  the  heated  bone  is  characteristic,  and  affords  us  a 
test  by  which  to  distinguish  roughly  between  nitrogenised  and  non- 
nitrogenised  bodies. 

An  examination  of  the  charred  mass  remaining  as  the  ultimate  result 
of  the  action  of  heat  upon  bone,  shows  it  to  contain  much  less  carbon 
than  that  furnished  by  wood,  for  the  bone  charcoal  contains  nearly 
nine- tenths  of  its  weight  of  phosphate  (with  a  little  carbonate)  of 
calcium ;  the  consequence  of  the  presence  of  so  large  an  amount  of 
•earthy  matter  must  be  to  extend  the  particles  of  carbon  over  a  larger 
area,  and  thus  to  expose  a  greater  surface  for  the  adhesion  of  colouring- 
matters,  &c.  This  may  partly  help  to  explain  the  very  great  superiority 
of  bone-black  to  wood  charcoal  as  a  decolorising  agent,  and  the  explana- 
tion derives  support  from  the  circumstance,  that  when  animal  charcoal 
is  deprived  of  its  earthy  matter,  for  chemical  uses,  by  washing  with 
hydrochloric  acid,  its  decolorising  power  is  very  considerably  reduced. 
The  application  of  this  variety  of  charcoal  is  not  confined  to  the  chemical 
laboratory,  but  extends  to  manufacturing  processes.  The  sugar  refiner 


STABILITY   OF   CHARCOAL.  Ii; 

decolorises  his  syrup  by  filtering  it  through  a  layer  of  animal  charcoal, 
and  the  distiller  employs  charcoal  to  remove  the  fusel  oil  with  which 
distilled  spirits  are  frequently  contaminated. 

Carbon  is  remarkable,  among  elementary  bodies,  for  its  indisposition 
to  enter  directly  into  combination  with  the  other  elements,  whence  it 
follows  that  most  of  the  compounds  of  carbon  have  to  be  obtained  by 
indirect  processes.  This  element  appears,  indeed,  to  be  incapable  of 
uniting  with  any  other  at  the  ordinary  temperature,  and  this  circum- 
stance is  occasionally  turned  to  useful  account,  as  when  the  ends  of 
wooden  stakes  are  charred  before  being  plunged  into  the  earth,  when 
the  action  of  the  atmospheric  oxygen,  which,  in  the  presence  of  moisture, 
would  be  very  active  in  effecting  the  decay  of  the  wood,  is  resisted  by 
the  charcoal  into  which  the  external  layer  has  been  converted.  Tlie 
employment  of  black-lead  to  protect  metallic  surfaces  from  rust  i* 
another  application  of  the  same  principle.  At  a  high  temperature, 
however,  carbon  combines  readily  with  oxygen,  sulphur,  and  with  some 
of  the  metals,  and,  at  a  very  high  temperature,  even  with  hydrogen  and 
nitrogen.  The  tendency  of  carbon  to  combine  with  oxygen  under  the 
influence  of  heat,  is  shown  when  a  piece  of  charcoal  is  strongly  heated 
at  one  point,  when  the  carbon  at  this  point  at  once  combines  with  the 
oxygen  of  the  surrounding  air  (forming  carbonic  acid  gas),  and  the  heat 
developed  by  this  combustion  raises  the  neighbouring  particles  of  carbon 
to  the  temperature  at  which  the  element  unites  with  oxygen,  and  thus 
the  combustion  is  gradually  propagated  throughout  the  mass,  which  is 
ultimately  converted  entirely  into  carbonic  acid  gas,  nothing  remaining 
but  the  white  ash,  composed  of  the  mineral  substances  derived  from  the 
wood  employed  for  preparing  the  charcoal.  It  is  worthy  of  remark,  that 
if  charcoal  had  been  a  better  conductor  of  heat,  it  would  not  have  been 
so  easily  kindled,  since  the  heat  applied  to  any  point  of  the  mass  would 
have  been  rapidly  diffused  over  its  whole  bulk,  and  this  point  could 
not  have  attained  the  high  temperature  requisite  for  its  ignition,  until 
the  whole  mass  had  been  heated  nearly  to  the  same  degree ;  this  is 
actually  found  to  be  the  case  in  charcoal  which  has  been  very  strongly 
heated  (out  of  contact  with  air),  when  its  conducting  power  is  greatly 
improved  and  it  kindles  with  very  great  difficulty.  The  ignition 
temperature  of  carbon  (charcoal  or  coke)  appears  to  be  about  400°  C. 
The  calorific  value  of  carbon  in  the  form  of  wood  charcoal  is  represented 
by  the  number  8080 — that  is,  i  gram  of  carbon,  when  burnt  so  as  to 
form  carbonic  acid  gas,  is  capable  of  raising  8080  grams  of  water  from 
o°  C.  to  i°  0. 

A  given  weight  of  charcoal  will  produce  twice  as  much  available  heat 
as  an  equal  weight  of  wood,  since  the  former  contains  more  actual  fuel 
and  less  oxygen,  and  much  of  the  heat  evolved  by  the  wood  is  absorbed 
or  rendered  latent  in  the  steam  and  other  vapours  which  are  produced 
by  the  action  of  heat  upon  it.  The  attraction  possessed  by  carbon  for 
oxygen  at  a  high  temperature  is  turned  to  account  in  metallurgic 
operations,  when  coal  and  charcoal  are  employed  for  extracting  the 
metals  from  their  compounds  with  oxygen.* 

The  unchangeable  solidity  of  carbon  is  another  remarkable  feature. 

*  Easily  reducible  oxides,  such  as  oxide  of  lead,  give  carbon  dioxide  when  heated  with 
charcoal  :  2PbO  +  C  =  Pb2  +  CO2,  but  oxides  which  are  not  easily  reducible,  such  as  oxide 
of  zinc,  give  carbonic  oxide  :  ZnO  +  C  — CO  +  Zn. 


Il8  ALLOTROPIC   MODIFICATIONS. 

Only  at  the  temperature  (3000°  0.)  attainable  in  the  electric  furnace 
can  carbon  be  vaporised ;  even  then  it  does  not  appear  to  pass  through 
the  liquid  condition.  Melted  iron  and  some  other  fused  metals  dissolve 
carbon,  but  beyond  these  there  is  no  solvent  by  the  aid  of  which 
carbon  may  be  brought  into  the  liquid  form  by  the  process  of  solution ; 
for  although  charcoal  gradually  disappears  when  boiled  with  sulphuric 
and  nitric  acids,  it  does  not  enter  into  simple  solution,  but  is  converted, 
as  will  be  seen  hereafter,  into  carbon  dioxide. 

The  very  striking  difference  in  properties  exhibited  by  diamond, 
graphite,  and  charcoal,  lead  to  the  belief  that  they  consist  of  dissimilar 
carbon  molecules.  The  investigation  of  the  specific  heats  and  other 
physical  constants  of  these  three  varieties  indicates  that  the  diamond 
molecule  contains  more  atoms  than  the  graphite  molecule  contains,  and 
that  the  charcoal  molecule  is  still  less  complex. 

When  an  element  is  capable  of  appearing  in  two  or  more  forms,  having 
different  physical  properties,  these  forms  are  said  to  be  allotropic. 

(DEFINITION. — Allotropy  is  the  assumption  of  different  properties 
without  loss  of  chemical  identity.) 

Such  cases,  like  those  of  isomerism  among  the  compounds  of  carbon 
(see  Organic  Chemistry),  will  probably  be  explained  by  differences  in 
the  position  and  arrangement  of  the  atoms  in  the  molecule. 

The  specific  heat  of  diamond  increases  with  rise  of  temperature  more  rapidly  than 
that  of  any  other  substance,  ranging  from  0.113  at  ll°  c-  to  0.459  at  985°  C.  The 
specific  heat  of  graphite  at  ordinary  temperature  is  about  0.2.  It  is  worthy  of  note 
that  graphite  is  the  final  form  of  any  kind  of  carbon  which  is  submitted  to  a  high 
temperature.  Thus  it  is  common  to  heat  carbon  rods  or  plates  which  are  to  be 
used  as  electrodes  and  must  therefore  have  the  best  possible  electrical  conductivity 
and  power  of  resisting  chemical  attack,  to  the  highest  attainable  temperatures  in 
order  to  "  graphitise  "  them. 

Pure  carbon  is  prepared  with  some  difficulty  ;  the  charcoal  obtained  by  heating 
some  pure  organic  substance  containing  C,  H.  and  O,  such  as  white  sugar-candy, 
in  a  closed  crucible,  is  heated  in  a  porcelain  tube,  as  strongly  as  possible,  in  a 
current  of  dry  chlorine  gas  until  no  more  HC1  is  produced.  The  residue  in  the 
tube  is  nearly  pure  carbon.  The  carbon  deposited  when  acetylene  is  passed  through 
a  red  hot  tube  is  a  very  pure  form. 

70.  Carbon  is  capable  of  combining  with  oxygen  in  two  proportioijs, 
forming  the  compounds  known  as  carbonic  oxide  or  carbon  monoxide 
(CO)  and  carbon  dioxide  (C02). 

CARBON  DIOXIDE  OR  CARBONIC  ACID  GAS. 
C02  =  44  parts  by  weight  — 2  volumes. 

71.  It  has  been  already  mentioned  that  carbonic  acid  gas  is  a  com- 
ponent of  the  atmosphere,  which  usually  contains  about  3  volumes  of 
carbonic  acid  gas  in   10,000  volumes  of  air.     The  proportion  is  smaller 
at  high  altitudes.     It  is  greater  during  the  night  than  in  the  day,  since 
plants  only  decompose  carbon  dioxide  in  daylight.     The  oleander  leaf 
was  found  to  decompose,  on  an  average,  in  sunlight,  1108  cubic  centi- 
metres (67.6  cubic  inches)  of  C02  per  square  metre  (about  n  square 
feet)  of  leaf -surface,  per  hour. 

The  proportion  of  CO2  does  not  vary  materially  in  the  neighbourhood 
of  a  town. 

Carbonic  acid  gas  is  chiefly  formed  by  the  operation  of  the  atmo- 
spheric oxygen  in  supporting  combustion  and  respiration.  All  sub- 


SOURCES   OF   CARBON  DIOXIDE.  119 

stances  used  as  fuel  contain  a  large  proportion  of  carbon,  which,  in  the 
act  of  combustion,  combines  with  the  oxygen,  and  escapes  into  the 
atmosphere  in  the  form  of  carbonic  acid  gas.  In  the  process  of  respira- 
tion, the  carbonic  acid  gas  is  formed  from  the  carbon  contained  in  the 
blood  and  in  the  different  portion>  of  the  animal  frame  to  which  oxygen 
is  conveyed  by  the  blood ;  the  latter,  in  passing  through  the  lungs, 
gives  out,  in  exchange  for  the  oxygen,  a  quantity  of  carbonic  acid  gas 
produced  by  the  union  of  a  former  supply  of  oxygen  with  the  carbon  of 
the  digested  food,  which  has  passed  into  the  blood  and  has  not  been 
required  for  the  repair  of  wasted  tissue.  This  conversion  of  the  carbon 
of  the  food  into  carbonic  acid  gas  will  be  again  referred  to  ;  it  will  be 
at  once  evident  that  it  must  be  concerned  in  the  maintenance  of  the 
animal  heat. 

The  leaves  of  plants,  under  the  influence  of  light,  have  the  power 
of  decomposing  the  carbon  dioxide  of  the  atmosphere,  the  carbon  of 
which  is  applied  to  the  production  of  vegetable  compounds  forming 
portions  of  the  organism  of  the  plant,  and  when  this  dies,  the  carbon 
is  restored,  after  a  lapse  of  time  more  or  less  considerable,  to  the 
atmosphere,  in  the  same  form,  namely,  that  of  carbon  dioxide,  in  which 
it  originally  existed  there.  If  a  plant  should  have  been  consumed  as 
food  by  animals,  its  carbon  will  have  been  eventually  converted  into 
carbonic  acid  gas  by  respiration  ;  the  use  of  the  plant  as  fuel,  either 
soon  after  its  death  (wood),  or  after  the  lapse  of  time  has  converted 
it  into  coal,  will  also  consign  its  carbon  to  the  air  in  the  form  of 
carbon  dioxide.  Even  if  the  plant  be  left  to  decay,  this  process  in- 
volves a  slow  conversion  of  its  carbon  into  carbon  dioxide  by  the 
oxygen  of  the  air. 

Putrefaction  and  fermentation  are  also  very  important  processes 
concerned  in  restoring  to  the  air,  in  the  form  of  carbonic  acid  gas,  the 
carbon  contained  in  dead  vegetable  and  animal  matter.  Although,  in 
a  popular  sense,  these  two  processes  are  distinct,  yet  their  chemical 
operation  is  of  the  same  kind,  consisting  in  the  resolution  of  a  complex 
substance  into  simpler  forms,  produced  by  contact  with  some  minute 
living  plant  or  animal.  The  discussion  of  the  true  nature  of  the  pro- 
cess (which  is  even  now  somewhat  obscure)  would 
be  premature  at  this  stage,  and  it  will  suffice  for  the 
present  to  state  that  carbonic  acid  gas  is  one  of  the 
simpler  forms  into  which  the  carbon  is  converted 
by  the  metamorphosis  which  ensues  so  quickly 
upon  the  death  of  animals  and  vegetables. 

The  production  of  carbon  dioxide  in  combustion,  respira- 
tion, and  fermentation,  may  be  very  easily  proved  by 
experiment.  If  a  dry  bottle  be  placed  over  a  burning  wax 
taper  standing  on  the  table,  the  sides  of  the  bottle  will  be 
covered  with  dew  from  the  combustion  of  the  hydrogen  in 
the  wax  ;  and  if  a  little  clear  lime-water  be  shaken  in  the 
bottle,  the  milky  deposit  of  calcium  carbonate  will  in- 
dicate the  formation  of  carbon  dioxide. 

By  arranging  two  bottles,  as  represented  in  Fig.  88,  and 
inspiring  through  the  tube  A,  air  will  bubble  through  the 
lime-water  in  B,  before  entering  the  lungs,  and  will  then 
be  found  to  contain  too  little  carbon  dioxide  to  produce  a 
milkiness,  but  on  expiring  the  air,  it  will  bubble  through  C,  and  will  render  the 
lime-water  in  this  bottle  very  distinctly  turbid. 


120  PREPARATION  OF  CAEBON  DIOXIDE. 

If  a  little  sugar  be  dissolved  in  eight  or  ten  times  its  weight  of  warm  (not  hot) 
water,  in  a  flask  provided  with  a  cork  and  delivery  tube  and  a  little  dried  yeast, 
previously  rubbed  down  with  water,  added,  fermentation  will  begin  in  the  course  of 
an  hour  or  less,  and  carbonic  acid  gas  may  be  collected  in  a  jar  standing  in  a 
pneumatic  trough. 

72.  In  the  mineral  kingdom,  carbon  dioxide  is  pretty  abundant. 
The  gas  issues  from  the  earth  in  some  places  in  considerable  quantity, 
as  at  Nauheim,  where  there  is  said  to  be  a  spring  exhaling  about 
1,000,000  Ibs.  of  the  gas  annually.  Many  spring  waters,  those  of 
Seltzer  and  Pyrmont,  for  example,  are  very  highly  charged  with  the 
gas. 

Carbon  dioxide  is  found  in  the  air  of  soils  in  larger  proportion  than 
in  the  atmosphere,  amounting  to  20  or  30,  and  occasionally  even  to 
600,  vols.  in  10,000.  It  increases  with  the  temperature,  and  originates 
from  the  decay  of  vegetable  matter. 

But  it  occurs  in  far  larger  quantity  in  the  immense  deposits  of  lime- 
stone, marble,  and  chalk,  which  compose  so  large  a  portion  of  the  crust 
of  the  globe.  Calcium  carbonate  is  also  met  with  in  the  animal  king- 
dom. Oyster-shells  contain  98  per  cent,  and  egg-shells  97  per  cent,  of 
it,  and  pearls  contain  about  two- thirds  of  their  weight. 

The  expulsion  of  the  carbonic  acid  gas  from  limestone  (CaC03)  forms 
the  object  of  the  process  of  lime  burning,  by  which  the  large  supply  of 
lime  (CaO)  is  obtained  for  building  and  other  purposes.  But  if  it  be 
required  to  obtain  the  carbonic  acid  gas  without  regard  to  the  lime,  it 
is  better  to  decompose  the  carbonate  with  an  acid. 

Preparation  of  carbonic  acid  gas. — The  form  of  the  calcium  car- 
bonate, and  the  nature  of  the  acid  employed,  are  by  no  means  matters 
of  indifference.  If  dilute  sulphuric  acid  be  poured  upon  fragments 
of  marble,  the  effervescence  which  occurs  at  first  soon  ceases,  for  the 
surface  of  the  marble  becomes  coated  with  the  nearly  insoluble  calcium 
sulphate,  by  which  it  is  protected  from  the  further  action  of  the  acid — 

CaC03  +  H.2S04  =  CaS04  +  H20  +  C02  ; 
Marble.     Sulphuric     Calcium 
acid.         sulphate. 

if  the  marble  be  finely  powdered,  or  if  powdered  chalk  be  employed, 
each  particle  of  the  carbonate  will  be  attacked.  When  lumps  of 
calcium  carbonate  are  acted  upon  by  hydrochloric  acid,  there  is  no 
danger  that  any  will  escape  the  action  of  the  acid,  for  the  calcium 
chloride  produced  is  one  of  the  most  soluble  salts — 

CaC03   +   2HC1  =    CaCl2  +  H20  +  C02. 
Marble.  Hydrochloric  Calcium 
acid.         chloride. 

For  the  ordinary  purposes  of  experiment,  carbonic  acid  gas  is  most 
easily  obtained  by  the  action  of  hydrochloric  acid  upon  small  fragments 
of  marble  contained  either  in  a  two-necked  bottle  (Fig.  n)  or  in  the 
centre  bulb  of  a  Kipp's  apparatus  (Fig.  89).  The  gas  should  be  washed 
by  passing  it  through  a  little  water  in  a  wash-bottle  and  may  be  collected 
by  downward  displacement. 

When  carbon  dioxide  is  required  on  a  large  scale  it  is  used  in  the 
form  of  furnace  gases,  which  contain  nitrogen  from  the  air  and  C02 
from  the  combustion  of  the  fuel ;  or  of  lime-kiln  gases,  the  C02  in 
which  is  derived  from  the  limestone ;  or  of  fermenting  tun  gases,  con- 
sisting of  nearly  pure  C02  due  to  the  fermentation  of  sugar. 


EXPERIMENTS  WITH   CARBON  DIOXIDE. 


121 


73.  Properties  of  carbon  dioxide. — Carbonic  acid  gas  is  invisible,  like 
the  gases  already  examined,  but  is  distinguished  by  a  peculiar  pungent 
odour,  as  is  perceived  in  soda-water.  It  is  more  than  half  as  heavy 


Fi£  8c. — Preparation  of  carbonic  acid  gas. 

again  as  atmospheric  air,  its  specific  gjavity  being  1.529,  which  causes 
its  accumulation  near  the  floor  of  such  confined  spaces  as  the  Grotto  del 
Cane,  where  it  issues,  from  fissures  in  the  rock. 

The  high  specific  gravity  of  C02  may  be  shown  by  pouring  it  into  a  light  jar 
attached  to  a  balance,  and  counterpoised  by  a  weight  in  the  opposite  scale  (Fig.  90). 


Fig-.  90. 

Another  favourite  illustration  consists  in  floating  a  soap-bubble  on  the  surface  of 
a  layer  of  the  gas  generated  in  the  large  jar  (Fig.  91),  by  pouring  diluted  sulphuric 
acid  upon  a  few  ounces  of  chalk  made  into  a  thin  cream. with  water. 

If  a  small  balloon,  made  of  collodion,  be  placed  in  the  jar  A  (Fig.  92)  it  will 
ascend  on  the  admission  of  carbonic  acid  gas  through  the  tube  B. 


122 


EXPERIMENTS   WITH   CARBON   DIOXIDE. 


If  smouldering  brown  paper  be  held  at  the  mouth  of  a  jar,  like  that  in  Fig.  93. 
the  smoke  will  float  upon  the  surface  of  the  carbonic  acid  gas,  and  will  sink  with  it 
on  removing  the  stopper. 

The  power  which  carbonic  acid  gas  possesses  of  extinguishing  flame 
is  very  important,  and  has  received  practical  application  in  the  case  of 


Fig.  92. 


-  93- 


Fig.  94. 


burning  mines  which  must  otherwise  have  been  flooded  with  water.* 
Many  attempts  have  also  been  made  from  time  to  time  to  employ  this 
gas  for  subduing  ordinary  conflagrations,  but  their  success  has  hitherto 
been  very  partial.  It  will  be  remembered  that  pure  nitrogen  is  also 
capable  of  extinguishing  the  flame  of  a  taper,  but  a  large  proportion  of 
this  gas  may  be  present  in  air  without  affecting  the  flame,  whereas  a 

*  All  gases  which  take  no  pirt  in  combustion  may  extinguish  flame,  even  in  the  presence 
of  air,  by  absorbing  heat  and  reducing  the  temperature  below  the  burning -point. 


EFFECTS   OF   CARBON   DIOXIDE   ON   COMBUSTION.       ,       123 

taper  is  extinguished  in  air  containing  one-eighth  of  its  volume  of  car- 
bonic acid  gas,  and  is  sensibly  diminished  in  brilliancy  by  a  much 
smaller  proportion  of  the  gas. 

A  candle  is  extinguished  in  air  to  which  14  per  cent,  of  its  volume  of  CO.,  has 
been  added  ;  22  per  cent,  of  nitrogen  must  be  added  to  produce  the  same  effect. 
The  corresponding  figures  for  a  coal-gas  flame  are  33  %  and  46  %  ;  and  for  a 
hydrogen  flame  58  %  and  70  %. 

The  power  of  extinguishing  flame,  conjoined  with  the  high  density  of  carbonic 
acid  gas,  admits  of  some  very  interesting  illustrations. 

Carbon  dioxide  may  be  poured  from  some  distance  upon  a  candle,  and  will 
extinguish  it  at  once.'  By  using  a  gutter,  made  of  thin  wood  or  stiff  paper,  to 
conduct  the  gas  to  the  flame,  it  may  be  extinguished  from  a  distance  of  several 
feet. 

A  large  torch  of  blazing  tow  may  be  plunged  beneath  the  surface  of  the  carbonic 
acid  gas  in  the  jar  (Fig.  91). 

Carbon  dioxide  may  be  raised  in  a  glass  bucket  (Fig.  93)  from  a  large  jar, 
and  poured  into  another  jar,  the  air  in  which  has  been  previously  tested  with  a 
taper. 

A  wire  stand  with  several  tapers  fixed  at  different  levels  may  be  placed  in  the 
jar  A  (Fig.  94),  and  carbon  dioxide  gradually  admitted  through  a  flexible  tube  con- 
nected with  the  neck  of  the  jar,  from  the  cistern  B,  a  hole  in  the  cover  of  which 
allows  air  to  enter  it  as  the  gas  flows  out  ;  the  flame  of  each  taper  will  gradually 
expire  as  the  surface  of  the  gas  rises  in  the  jar. 

A  jar  of  oxygen  may  be  placed  over  a  jar  of  C02,  as  shown  in  Fig.  51,  and  a 
taper  let  down  through  the  oxygen,  in  which  it  will  burn  brilliantly,  into  the  C02, 
which  extinguishes  it,  and  if  it  be  quickly  raised  again  into  the  oxygen,  it  will 
rekindle  with  a  slight  detonation.  This  alternate  extinction  and  rekindling  may 
be  repeated  several  times. 

On  account  of  this  extinguishing  power  of  carbonic  acid  gas,  a  taper 
cannot  continue  to  burn  in  a  confined  portion  of  air  until  it  has 
exhausted  the  oxygen,  but  only  until  its  combustion  has  produced  a 
sufficient  quantity  of  carbon  dioxide  to  extinguish  the  flame.* 

To  demonstrate  this,  advantage  may  be  taken  of  the  circumstance  that  phos- 
phorus will  continue  to  burn  in  spite  of  the  presence  of  carbonic  acid  gas.  Upon 
the  stand  A  (Fig.  95)  a  small  piece  of  phosphorus  is  placed,  and  a  taper  attached  to 
the  stand  by  a  wire.  The  cork  B  fits  air-tight  into  the  jar,  and  carries  a  piece  of 
copper  wire  bent  so  that  it  may  be  heated  by  the  flame  of 
the  taper.  A  little  water  is  poured  into  the  plate  to  pre- 
vent the  entrance  of  any  fresh  air.  If  the  taper  be  kindled, 
and  the  jar  placed  over  it,  the  flame  will  soon  die  out  ; 
and  on  moving  the  jar  so  that  the  hot  wire  may  touch  the 
phosphorus,  its  combustion  will  show  that  a  considerable 
amount  of  oxygen  still  remains. 

In  the  same  manner,  an  animal  can  breathe  a 
confined  portion  of  air  only  until  he  has  charged 
it  with  so  much  carbonic  acid  gas  that  the  hurtful 
effect  of  this  gas  begins  to  be  felt,  a  considerable  quantity  of  oxygen 
still  remaining. 

If  the  air  contained  in  the  jar  A  (Fig.  96),  standing  over  water,  be  breathed  two 
or  three  times  through  the  tube  B,  a  painful  sense  of  oppression  will  soon  be  felt 
in  consequence  of  the  accumulation  of  carbonic  acid  gas.  The  air  may  thus  be 
•charged  with  10  volumes  of  carbonic  acid  gas  in  100  volumes,  the  oxygen  becom- 
ing reduced  to  about  one-half  its  original  quantity.  By  immersing  a  deflagrating 
spoon  C,  containing  a  piece  of  burning  phosphorus,  and  having  a  lighted  taper 
attached,  it  may  be  shown  that,  although  there  is  enough  carbonic  acid  gas  to 

*  When  the  taper  is  extinguished,  the  air  contains  in  100  volumes  18^  volumes  of  oxygen 
And  2  volumes  of  carbonic  acid  ya«. 


124 


RESPIRATION. 


Fig.  96. 


extinguish  the  taper,  the  oxygen  is  not  exhausted,  for  the  phosphorus  continues  to 
burn  rapidly. 

Carbonic  acid  gas  is  not  poisonous  when  taken  into  the  stomach,  but 
acts  most  injuriously  when  breathed,  by  offering  an  obstacle  to  the 

escape  of  carbonic  acid  gas,  by  diffu- 
sion^  from  the  blood  of  the  venous 
circulation  in  the  lungs,  and  its  con- 
sequent exchange  for  the  oxygen 
necessary  to  arterial  blood.  Any 
hindrance  to  this  interchange  must 
impede  respiration,  and  such  hind- 
rance would  of  course  be  afforded  by 
carbonic  acid  gas  present  in  the  air 
inhaled,  in  proportion  to  its  quantity. 
There  is  evidently  a  distinction  be- 
tween air  which  has  had  carbon 
dioxide  added  to  it  and  air  in  which 
there  is  a  like  amount  of  carbon 
dioxide  produced  by  respiration.  Thus 
air  which  has  had  its  content  of  carbon 
dioxide  raised  to  i  per  cent,  by  addi- 
tion of  the  gas  may  be  breathed  with 
impunity,  but  if  there  be  this  propor- 
tion present  as  a  result  of  respiration  the  effect  on  most  persons  would 
be  very  deleterious. 

Notwithstanding  the  many  attempts  which  have  been  made  to  trace  some  other 
product  of  respiration  which  might  account  for  the  harmful  character  of  expired 
air,  there  is  still  no  satisfactory  explanation  of  the  observation  that  the  air  of  a 
room  becomes  progressively  more  unwholesome  as  the  carbon  dioxide  in  it  is 
increased  by  respiration.  It  has  often  been  stated,  and  the  statement  has  as  often 
been  controverted,  that  a  specific  poison  accompanies  the  products  of  respiration.  It 
is  more  probable  that  the  oppressive  character  of  a  close  room  is  due  to  other  exhala- 
tions from  the  body,  and  is  not  really  an  effect  of  the  carbon  dioxide  of  the  breath. 

It  is  agreed  amongst  those  who  concern  themselves  with  ventilation 
that  the  percentage  of  carbon  dioxide  in  the  air  of  a  room  or  building 
is  an  index  of  the  wholesomeness  of  the  air.  Thus  it  is  considered 
inadvisable  to  breathe  for  any  length  of  time  in  air  containing  more 
than  TO  volumes  of  CO2  in  10,000  volumes  (o.i  per  cent.).  The  air  of 
a  room  contains  too  much  C02  if  half  a  measured  ounce  of  lime-water 
becomes  turbid  when  shaken  in  a  half -pint  bottle  of  the  air. 

When  the  carbon  dioxide  amounts  to  50  volumes  per  10,000  volumes 
of  air  (0.5  per  cent.)  most  persons  are  attacked  by  the  languor  and 
headache  attending  bad  ventilation.  A  large  proportion  of  carbonic 
acid  gas  produces  insensibility,  and  air  containing  20  per  cent,  of  its 
volume  causes  suffocation.  The  danger  in  entering  old  wells,  cellars, 
and  other  confined  places,  is  due  to  the  accumulation  of  this  gas,  either 
exhaled  from  the  earth  or  produced  by  decay  of  organic  matter.  The 
ordinary  test  applied  to  such  confined  air  by  introducing  a  candle  is 
only  to  be  depended  upon  if  the  candle  burns  as  brightly  in  the  con- 
fined space  as  in  the  external  air  ;  should  the  flame  become  at  all  dim, 
it  would  be  unsafe  to  enter,  for  experience  has  shown  that  combustion 
may  continue  for  some  time  in  an  atmosphere  dangerously  charged 
with  carbonic  acid  gas. 


VENTILATION. 


125 


The  accidents  from  choke  damp  and  after  damp  in  coal  mines,  and 
from  the  accumulation,  in  brewers'  and  distillers'  vats,  of  the  carbonic 
acid  gas  resulting  from  fermentation,  are  also  examples  of  its  fatal  effect. 

The  air  issuing  from  the  lungs  of  a  man  at  each  expiration  contains 
from  4  to  4.5  volumes  of  carbonic  acid  gas  in  100  volumes  of  air,  and 
could  not,  therefore,  be  breathed  again  without  danger.  The  total 
amount  of  carbonic  acid  gas  evolved  by  the  lungs  and  skin  amounts  to 
about  0.7  cubic  foot  per  hour.  Adding  this  to  the  carbonic  acid  gas 
already  present  in  the  air  (say  0.04  per  cent.),  the  total  should  be  dis- 
tributed through  at  least  3500  cubic  feet,  in  order  that  it  may  be 
breathed  again  with  perfect  safety,  that  is,  in  order  that  the  CO.,, 
which  is  regarded  as  the  indicator,  should  not  exceed  0.06  per  cent, 
by  volume.  Hence  the  necessity  for  a  constant  supply  of  fresh 
air  by  ventilation,  to  dilute  the  expired  air  to  such  an  extent  that 
it  may  cease  to  impede  respiration.  This  becomes  the  more  neces- 
sary where  a  demand  is  made  on  the  atmospheric  oxygen  by  candles 
or  gas-lights.  An  ordinary  gas-burner  consumes  at  least  3  cubic 
feet  of  gas  per  hour,  which  requires  rather  more  than  its  own 


Fig.  97. 


Fig. 


Fig.  99. 


volume  of  oxygen  for  combustion,  and  produces  about  1.7  cubic  foot  of 
carbonic  acid  gas.  Fortunately,  a  natural  provision  for  ventilation 
exists  in  the  circumstance  that  the  processes  of  respiration  and  com- 
bustion, which  contaminate  the  air,  also  raise  its  temperature,  thus 
diminishing  its  specific  gravity  by  expansion,  and  causing  it  to  ascend 
and  give  place  to  fresh  air.  Hence  the  vitiated  air  always  accumulates 
near  the  ceiling  of  an  apartment,  and  it  becomes  necessary  to  afford  it 
an  outlet  by  opening  the  upper  sash  of  the  window,  since  the  chimney 
ventilates  immediately  only  the  lower  part  of  the  room. 

These  principles  may  be  illustrated  by  some  very  simple  experiments. 

Two  quart  jars  (Fig.  97)  are  rilled  with  carbonic  acid  gas,  and  after  being  tested 
with  a  taper,  a  4-02.  flask  is  lowered  into  each,  one  flask  containing  cold  and  the 
other  hot  water.  After  a  few  minutes  the  jar  with  the  cold  flask  will  still  contain 
enough  carbonic  acid  gas  to  extinguish  the  taper,  whilst  the  air  in  the  other  jar  will 
support  combustion  brilliantly. 

A  tall  stoppered  glass  jar  (Fig.  98)  is  placed  over  a  stand,  upon  which  three 
lighted  tapers  are  fixed  at  different  heights.  The  vitiated  air,  rising  to  the  top  of 
the  jar,  will  extinguish  the  uppermost  taper  first,  and  the  others  in  succession.  By 
quickly  removing  the  stopper  and  raising  the  jar  a  little  before  the  lowest  taper  has 
expired,  the  jar  will  be  ventilated  and  the  taper  revived. 

A  similar  jar  (Fig.  99),  with  a  glass  chimney  fixed  into  the  neck  through  a  cork 


126 


VENTILATION   OF   MINES. 


or  piece  of  vulcanised  tubing,  is  placed  over  a  stand  with  two  tapers,  one  of  which 
is  near  the  top  of  the  jar,  and  the  other  beneath  the  aperture  of  the  chimney  ;  if  a 
crevice  for  the  entrance  of  air  be  left  between  the  jar  and  the  table,  the  lower  taper 
will  continue  to  burn  indefinitely,  whilst  the  upper  one  will  soon  be  extinguished 
by  the  carbonic  acid  gas  accumulating  around  it. 

In  ordinary  apartments,  the  incidental  crevices  of  the  doors  arid 
windows  are  depended  upon  for  the  entrance  of  fresh  air,  whilst  the 
contaminated  air  passes  out  by  the  chimney;  but  in  large  buildings 
special  provision  must  be  made  for  the  two  air  currents.  In  mines 
this  becomes  the  more  necessary,  since  the  air  receives  much  additional 
contamination  by  the  gases  (marsh-g^s  and  carbon  dioxide)  evolved 
from  the  workings,  and  by  the  smoke  occasioned  in  blasting  with 
gunpowder.  Mines  are  generally  provided  with  two  shafts  for  venti- 
lation, under  one  of  which  (the  upcast  shaft)  a  fire  is  maintained  to 
produce  the  upward  current,  which  carries  off  the  foul  air,  whilst  the 
fresh  air  descends  by  the  other  (downcast  shaft).  The  current  of  fresh 


Fig.  100. 


air  is  forced  by  wooden  partitions  to  divide  itself,  and  to  pass  through 
every  portion  of  the  workings. 

The  operation  of  such  provisions  for  ventilation  is  easily  exhibited. 

A  tall  jar  (Fig.  100)  is  fitted  with  a  ring  of  cork,  carrying  a  wide  glass  chimney 
(A).  If  this  be  placed  over  a  taper  standing  in  a  plate  of  water,  the  accumulation 
of  vitiated  air  will  soon  extinguish  the  taper  ;  but  if  a  second  chimney  (B),  sup- 
ported in  a  wire  ring,  be  placed  within  the  wide  chimney,  fresh  air  will  enter 
through  the  interval  between  the  two,  and  the  smoke  from  a  piece  of  brown 
paper  will  demonstrate  the  existence  of  the  two  currents,  as  shown  by  the 
arrows. 

A  small  box  (Fig.  101)  is  provided  with  a  glass  chimney  at  each  end.  In  one  of 
these  (B)  representing  the  upcast  shaft,  a  lighted  taper  is  suspended.  A  piece  of 
smoking  brown  paper  may  be  held  in  each  chimney  to  show  the  direction  of  the 
current.  On  closing  A  with  a  glass  plate,  the  taper  in  B  will  be  extinguished,  the 
entrance  of  fresh  air  being  prevented.  By  breathing  gently  into  A  the  taper  will 
also  be  extinguished.  The  experiment  may  be  varied  by  pouring  carbon  dioxide 
and  oxygen  alternately  into  A,  when  the  taper  will  be  extinguished  and  rekindled 
by  turns. 

A  pint  bell- jar  (Fig.  102)  is  placed  over  a  taper  standing  in  a  tray  of  water.  If  a 
chimney  (a  common  lamp-glass)  be  placed  on  the  top  of  the  jar,  the  flame  of  the 
taper  will  gradually  die  out,  because  no  provision  exists  for  the  establishment  of  the 
two  currents,  but  on  dropping  a  piece  of  tinplate  or  cardboard  into  the  chimney  so 


SODA  WATER. 


127 


as  to  divide  it,  the  taper  will  be  revived,  and  the  smoke  from  the  brown  paper  will 
distinguish  the  upcast  from  the  downcast  shaft. 

If  a  little  water  be  poured  into  a  wide-mouthed  bottle  of  carbon 
dioxide,  and  the  bottle  be  then  firmly  closed  by  the  palm  of  the  hand, 
it  will  be  found,  on  shaking  the  bottle  violently,  that  the  gas  is 
absorbed,  and  the  palm  of  the  hand  is  sucked  into  the  bottle.  The 
presence  of  carbonic  acid  in  the  solution  may  be  proved  by  pouring  it 
into  lime-water,  in  which  it  will  produce  a  precipitate  of  calcium  car- 
bonate, redissolved  by  a  further  addition  of  the  solution  of  carbonic 
acid. 

One  pint  of  water  shaken  in  a  vessel  containing  carbonic  acid  gas,  at 
the  ordinary  pressure  of  the  atmosphere,  and  at  the  ordinary  tempera- 
ture, will  dissolve  about  one  pint  of  the  gas,  equal  in  weight  to  nearly 
1 6  grains.  If  the  gas  be  confined  in  the  vessel  under  a  pressure  equal 
to  twice  or  thrice  that  of  the  atmosphere — that  is,  if  twice  or  thrice 
the  quantity  of  gas  be  compressed  into  the  same  space — the  water  will 
still  dissolve  one  pint  of  the  gas,  but  the  weight  of  this  pint  will  now 
be  twice  or  thrice  that  of  the  pint  of  uncompressed  gas,  so  that  the 
water  will  have  dissolved  32  or  48  grains  of  the  gas,  accordingly  as  the 
pressure  had  been  doubled  or  trebled.  As  soon,  however,  as  the  pres- 
sure is  removed,  the  compressed  carbonic  acid  gas  will  resume  its 
former  state,  with  the  exception  of  that  portion  which  the  water  is- 
capable  of  retaining  in  solution  under  the  ordinary  pressure  of  the- 
atmosphere.  Thus,  if  the  water  had  been  charged  with  carbonic  acid 
gas  under  a  pressure  equal  to  thrice  that  of  the  atmosphere,  and  had 
therefore  absorbed  48  grains  of  the  gas,  it  would  only  retain  16  grains 
when  the  pressure  was  taken  off,  allowing  32  grains  to  escape  in 
minute  bubbles,  producing  the  appearance  known  as  effervescence.  This 
affords  an  explanation  of  the  properties  of  soda-water,  which  is  prepared 
by  charging  water  with  carbonic  acid  gas  under  considerable  pressure,, 
and  rapidly  confining  it  in  strong  bottles.  As  soon  as  the  resistance 
offered  by  the  cork  to  the  expansion  of  the  gas  is  removed,  the  excess 
above  that  which  the  water  can  hold  in  solution  at  the  ordinary  pressure 
of  the  air,  escapes  with  effervescence.  In.  a  similar  manner  the  waters- 
of  certain  springs  become  charged  with  carbonic  acid  gas,  under  high 
pressure,  beneath  the  surface  of  the  earth,  and  when,  upon  their  rising 
to  the  surface,  this  pressure  is  removed,  the  excess  escapes  with 
effervescence,  giving  rise  to  the  sparkling  appearance  and  sharp  flavour 
which  render  spring  water  so  agreeable.  On  the  other  hand,  the 
waters  of  lakes  and  rivers  are  usually  flat  and  insipid,  because  they  hold 
in  solution  so  small  a  quantity  of  carbonic  acid  gas. 

The  solution  of  CO.,  in  water  is  believed  to  contain  the  true  carbonic 
acid  or  hydrogen  carbonate,  H2C03,  or  CO(OH)2,  for  C02  +  H20  =  H2C03, 
but  there  is  no  direct  evidence  in  support  of  this  view. 

The  sparkling  character  of  champagne,  bottled  beer,  <fec.,  is  due  to  the 
presence  in  these  liquids  of  a  quantity  of  carbonic  acid  gas  which  has 
been  generated  by  fermentation  subsequent  to  bottling,  and  has  there- 
fore been  retained  in  the  liquid  under  pressure.  In  the  case  of  Seidlitz 
powders  and  soda-water  powders,  the  effervescence  caused  by  dissolving 
them  in  water  is  due  to  the  disengagement  of  carbonic  acid  gas,  by  the 
action  of  the  tartaric  acid,  which  composes  one  of  the  powders,  upon 
the  bicarbonate  of  soda  composing  the  other  powder,  producing  tartrate- 


128 


LIQUEFACTION  OF   CAEBON  DIOXIDE. 


of  soda  and  carbonic  acid  gas.  In  the  dry  state  these  powders  may  be 
mixed  without  any  chemical  change,  but  the  addition  of  water  imme- 
diately causes  the  effervescence.  Many  baking  powders  are  mixtures 
of  this  kind,  being  used  for  imparting  lightness  and  porosity  to  bread 
and  cakes,  by  distending  the  dough  with  bubbles  of  carbonic  acid  gas. 

The  solubility  of  carbonic  acid  in  water  is  of  great  importance  in  the 
chemistry  of  nature ;  for  this  acid,  brought  down  from  the  atmosphere 
dissolved  in  rain,  is  able  to  act  chemically  upon  rocks,  such  as  granite, 
which  contain  alkalies — the  carbonic  acid  attacking  these,  and  thus 
slowly  disintegrating  or  crumbling  down  the  rock,  an  effect  much 
assisted  by  the  mechanical  action  of  the  expansion  of  freezing  water  in 
the  interstices  of  the  rock.  It  appears  that  soils  are  thus  formed  by 
the  slow  degradation  of  rocks,  and  when  these  soils  are  capable  of 
supporting  plants,  the  solution  of  carbonic  acid  is  again  of  service,  not 
only  as  possibly  providing  the  plant  with  carbon  through  its  roots,  but 
as  a  solvent  for  certain  portions  of  the  mineral  food  of  the  plant  (such 
as  calcium  phosphate),  which  pure  water  could  not  dissolve,  and  which 
the  plant  cannot  take  up  except  in  the  dissolved  state. 

74.  Liquefaction  of  carbon  dioxide. — It  is  generally  found  that  the 
greater  the  solubility  of  a  gas  in  water  the  more  easily  the  gas  can  be 
liquefied  ;  thus  C02  is  much  more  easily  liquefied  than  is  either  hydrogen 
or  oxygen.  At  about  the  ordinary  temperature  (63°  F.,  17°  0.),  a 
pressure  of  54  atmospheres  (800  Ibs.  per  square  inch)  condenses  the 
gas  to  a  colourless  liquid  of  sp.  gr.  0.83  (water  =  i),  and  boiling-point 
—  80°  C.  If  the  temperature  of  the  gas  is  reduced  to  o°  C.,  a  pressure 
of  35  atmospheres  suffices  to  liquefy  it. 

Liquid  carbon  dioxide  dissolves  in  alcohol  and  in  ether,  but  not  in 
water.  When  allowed  to  evaporate  rapidly  so  much  heat  is  absorbed 
by  its  passage  into  the  gaseous  state  that  a  part  of  the  liquid  becomes 

solid    carbon    dioxide,   a 

( L—       ...  0    snow-like   substance,    of 

specific  gravity  1.4. 

Q^^><^;  =3        The  critical    tempera- 

ture (p.    29)    of    carbon 

dioxide  is  31°  C.     It  is 

c  C~ ' ilJ    worthy     of     note      that 

nitrous  oxide,  which 
has  the  same  molecular 
weight  as  carbon  dioxide, 
has  nearly  the  same 
critical  temperature  and 
boiling-point. 

A  small  specimen  of  liquid 
carbon  dioxide  is  easily  pre- 
pared. A  strong  glass  tube 
(A,  Fig.  103)  is  selected, 
about  12  inches  long,  T\  inch 
diameter  in  the  bore,  and 
rV  inch  thick  in  the  walls. 
Fi»-  T°3-  With  the  aid  of  the  blow- 

pipe    flame     this     tube     is 

softened  and  drawn  off  at  about  an  inch  from  one  end.  as  at  B,  which  is  thus  closed 
(C).  This  operation  should  be  performed  slowly,  in  order  that  the  closed  end  may 
not  be  much  thinner  than  the  walls  of  the  tube.  When  the  tube  has  cooled, 


EXPERIMENTS   WITH   SOLID   CARBON  DIOXIDE. 


129 


between  30  and  40  grs.  of  powdered  bicarbonate  of  ammonia  (ordinary  sesqui- 
carbonate  which  lias  crumbled  down)  are  tightly  rammed  into  it  with  a  glass  rod. 
This  part  of  the  tube  is  then  surrounded  with  a  few  folds  of  wet  blotting-paper  to 
keep  it  cool,  and  the  tube  is  bent,  just  beyond  the  carbonate  of  ammonia  to  a  some- 
what obtuse  angle  (D).  The  tube  is  then  softened  at  about  an  inch  from  the  open 
end,  and  drawn  out  to  a  narrow  neck  (E),  through  which  a  measured  drachm  of  oil 
of  vitriol  is  poured  down  a  funnel-tube,  so  as  not  to  soil  the  neck,  which  is  then 
carefully  drawn  out  and  sealed  by  the  blowpipe  flame,  as  at  F.  The  empty  space  in 
the  tube  should  not  exceed  £  cubic  inch. 

When  the  tube  is  thoroughly  cold,  it  is  suspended  by  strings  in  such  a  position 
that  the  operator,  having  retired  behind  a  screen  at  some  distance,  may  reverse  the 
tube,  allowing  the  acid  to  flow  into  the  limb  containing  the  carbonate  of  ammonia  ; 
or  the  tube  may  be  fixed  in  a  box  which  is  shut  up,  and  reversed  so  as  to  bring  the 
tube  into  the  required  position. 

If  the  tube  be  strong  enough  to  resist  the  pressure,  it  will  be  found,  after  a  few 
hours,  that  a  layer  of  liquid  C02  has  been  formed  upon  the  surface  of  the  solution 
of  ammonium  sulphate.  By  cooling  the  empty  limb  in  a  mixture  of  pounded  ice 
and  salt,  or  of  hydrochloric  acid  and  sodium  sulphate,  the  liquid  can  be  made  to 
distil  itself  over  into  this  limb,  leaving  the  ammonium  sulphate  in  the  other. 

Liquid  C02  is  now  sold  in  steel  cylinders  provided  with  screw  valves,  like  those 
containing  compressed  oxygen  (Fig.  40).  When  the  cylinder  is  turned  on  its  head 
and  the  valve  is  opened,  the  liquid  is  ejected,  and  at  once  solidifies  to  carbonic 
acid  "snow,"  which  may  be  collected  by  surrounding  the  nozzle  with  sacking. 
The  solid  should  be  quickly  shaken  on  to  a  sheet  of  paper,  and  emptied  into  a 
beaker  placed  within  a  larger  beaker,  the  interval  being  filled  up  by  flannel.  By 
covering  the  beaker  with  a  dial  glass,  the  solid  may  be  kept  for  some  time. 

The  solid  carbon  dioxide  evaporates  without  melting,  for  its  own  evaporation 
keeps  it  at  a  temperature  below  its  melting-point.  It  produces  a  sharp  sensation  of 
cold  when  placed  upon  the  hand,  and  if  pressed  into  actual 
contact  with  the  skin  causes  a  painful  frost-bite.  Its  rapid 
evaporation  may  be  shown  by  placing  a  few  fragments  on  the 
surface  of  water  in  the  globe  (Fig.  104),  which  has  a  tube  pass- 
ing down  to  the  bottom,  through  which  the  pressure  of  the 
carbonic  acid  gas  forces  the  water  to  a  considerable  height. 

The  solid  carbon  dioxide  is  soluble  in  ether,  and  it  evapo- 
rates from  this  solution  far  more  rapidly,  because  the  liquid  is 
a  better  conductor  of  heat  than  the  highly  porous  solid,  and 
abstracts  heat  more  rapidly  from  surrounding  objects. 

It  thus  lowers  the  temperature  to  the  boiling-point  of  C02. 

If  a  layer  of  ether  be  poured  upon  water,  and  some  solid 
carbon  dioxide  be  thrown  into  it,  the  water  is  covered  with  a 
layer  of  ice. 

'On  immersing  the  bulb  of  a  thermometer  into  the  solution 
of  solid  carbon  dioxide  in  ether,  the  mercury  becomes  solid,  and 
the  bulb  may  be  hammered  out  into  a  disk. 

By  placing  a  piece  of  filter-paper  in  an  evaporating  dish, 
pouring  a  pound  or  so  of  mercury  into  it,  immersing  a  wire 
turned  into  a  flat  spiral  at  the  end,  covering  the  mercury  with 
ether,  and  throwing  in  some  solid  carbon  dioxide,  the  mercury, 
may  soon  be  frozen  into  a  cake.  If  this  be  suspended  by  the 
wire  in  a  vessel  of  water,  the  mercury  melts,  descending  in 
silvery  streams  to  the  bottom  of  the  vessel,  leaving  a  cake  of 
ice  on  the  wire,  with  icicles  formed  during  the  descent  of  the 
mercury.  This  experiment  is  rendered  more  effective  by  using  an  inverted 
gas-jar,' to  the  neck  of  which  is  attached,  by  a  perforated  cork,  a  test-tube  to 
catch  the  mercury.  The  round  lid  of  a  cardboard  box  gives  a  nice  disk  of  frozen 
mercury. 

Even  in  a  red-hot  vessel,  with  prompt  manipulation,  the  mercury  may  be  solidi- 
fied by  the  solution  of  solid  carbon  dioxide  in  ether.  For  this  purpose  a  platinum 
dish  is  heated  to  redness  over  a  large  Bunsen  burner,  a  few  lumps  of  carbon  dioxide 
are  thrown  into  it,  upon  these  is  held  a  copper  or  platinum  dish  containing  the 
mercury,  in  which  is  also  held  a  wire  to  serve  as  a  handle  for  withdrawing  the 
mercury.  Some  more  carbon  dioxide  is  thrown  upon  the  mercury,  and  ether  is 
spirted  on  to  it  from  a  small  washing-bottle.  One  or  two  additions  of  the  carbon 


Fig-.  104. 


130  CARBONATES. 

dioxide  and  ether  alternately  will  freeze  the  mercury,  which  may  be  withdrawn 
from  the  flames  by  the  wire  handle. 

Carbon  dioxide  is  advantageously  used  in  freezing-machines  on  the  principle 
described  for  ammonia  (p.  82)  ;  for  although  it  absorbs  much  less  heat  in  passing 
from  the  liquid  to  the  gaseous  state  (about  60  cals.  per  gram,  at  10°  C.'  as  against 
320  cals.  for  ammonia),  the  volume  to  be  pumped  per  unit  weight  is  much  less. 

75.  Carbonic  acid  gas  maybe  separated  from  most  other  gases  by  the 
action  of  potash,  which  absorbs  it,  forming  potassium  carbonate.     The 
proportion  of  carbonic  acid  gas  is  inferred,  either  from  the  diminution 
in  volume  suffered  by  the  gas  when  treated  with  potash,  or  from  the 
increase  of  weight  of  the  latter. 

In  the  former  case  the  gas  is  carefully  measured  over  mercury  (Fig-  105),  with 
due  attention  to  temperature  and  barometric  pressure,  and  a  little  concentrated 

solution  of  potash  is  thrown  up  through 
a  curved  pipette  or  syringe,  introduced 
into  the  orifice  of  the  tube  beneath  the 
surface  of  the  mercury.  The  tube  is 
gently  shaken  for  a  few  seconds  to  pro- 
mote the  absorption  of  the  gas,  and, 
after  a  few  minutes'  rest,  the  diminu- 
tion of  volume  is  read  off.  Instead  of 
solution  of  potash,  damp  potassium 
hydroxide  in  the  solid  state  is  some- 
times introduced,  in  the  form  of  small 
sticks  or  balls  attached  to  a  wire.  To 
determine  the  weight  of  carbonic  acid 
gas  in  a  gaseous  mixture,  the  latter  is 
passed  through  a  bulb-apparatus  (H,  Fig. 
81),  containing  a  strong  solution  of 
potash,  and  weighed  before  and  after 
the  passage  of  the  gas.  A  little  tube, 
containing  solid  potash,  or  calcium 
chloride,  or  pumice-stone  moistened 
Fip.  105.  with  sulphuric  acid,  must  be  attached 

to  the  bulb-apparatus,  for  the  purpose 

of  retaining  any  vapour  of  water  which  the  large  volume  of  unabsorbed  gas  might 
carry  away  in  passing  through  the  solution  of  potash. 

The  method  for  proving  the  composition  of  carbon  dioxide  by  weight 
has  been  given  at  p.  109.  Its  composition  by  volume  is  dealt  with 
on  p.  136. 

76.  Salts  formed  by  carbonic  acid. — Although  so  ready  to  combine 
with  the  alkalies  and  alkaline  eirths  (as  shown  in  its  absorption  by 
solution  of  potash  and  by  lime-water),  carbonic  acid  must  be  classed 
among  the  weaker  acids.     It  does  not  neutralise  the  alkalies  completely, 
and  it  may  be  displaced  from  its  salts  by  most  other  acids.     Its  action 
upon  the  colouring  matter  of  litmus  is  feeble  and   transient.     Tf  a 
solution  of  carbonic  acid  be  added  to  blue  infusion  of  litmus,  a  wine-red 
liquid  is  produced,  which  becomes  blue  again  when  boiled,  losing  its 
carbonic  acid;  whilst  litmus  reddened  by  sulphuric,  hydrochloric,  or 
nitric   acid,  acquires  a  brighter   red  colour,  which   is   permanent  on 
boiling.     On  forcing  CO.,  into  solution  of  litmus  at  several  atmospheres 
pressure  a  bright  red  colour  is  produced ;  but  this  is  not  permanent. 

With  each  of  the  alkalies  carbonic  acid  forms  two  well-defined  salts, 
the  carbonate  and  bicarbonate.  Thus,  the  carbonates  of  potassium  and 
sodium  are  represented  by  the  formulae,  K3CO3  and  Na2CO3,  whilst  the 
bicarbonates  are  KHC03  and  NaHC03.  The  existence  of  the  latter 


COMPOSITION   OF   CARBON   DIOXIDE.  131 

salts  would  favour  the  belief  in  the  existence  of  the  compound  H3CO3, 
although  this  has  not  yet  been  obtained  in  the  separate  state. 

The  formula  H2C03  represents  carbonic  acid  as  a  dibasic  acid,  that  is, 
an  acid  containing  two  atoms  of  H  for  which  metals  may  be  substituted. 

Carbonates  may  be  normal,  acid,  or  basic.  A  normal  carbonate  is 
one  in  which  all  the  hydrogen  in  H2C03  is  exchanged  for  a  metal  or 
metals,  as  in  sodium  carbonate,  Na2CO3,  and  calcium  carbonate,  CaC03. 

An  acid  carbonate  is  one  in  which  only  half  of  the  hydrog:n  is 
exchanged  for  a  metal,  as  in  hydrosodium  carbonate,  JSTaHCOr  A 
basic  carbonate  is  a  norm-al  carbonate  in  combination  with  a  hydrate  of 
the  metal,  as  in  white  lead,  basic  lead  carbonate,  2PbC03.Pb(OH)2. 

Perfectly  dry  carbonic  acid  gas  is  not  absorbed  by  pure  quicklime  (CaO),  until  it 
is  heated  to  35o°-4OO°  C. 

Two  hard  glass  tubes  closed  at  one  end,  and  bent  as  in  Fig.  106,  are  perfectly 
dried,  and  filled,  over  mercury,  with  well-dried  carbonic  acid  gas.  Fragments  of 
lime  are  taken,  whilst  red  hut,  out  of  a  crucible,  cooled  under  the  mercury,  inserted 


Fig.  106. 


Fig-.  107. 


into  the  tubes,  and  transferred  to  the  upper  end.  No  absorption  of  the  gas  occurs, 
though  the  tubes  be  left  for  some  days  ;  but  if  one  of  them  be  heated  by  a  Bunsen 
burner,  the  CO.,  is  rapidly  absorbed,  and  the  mercury  is  forced  up  into  the  tube. 

77.  To  demonstrate  the  presence  of  carbon  in  carbon  dioxide,  a  pellet  of 
potassium  is  introduced  into  a  bull)  tube,  through  which  a  current  of  the  gas 
(dried  by  passing  through  oil  of  vitriol,  or  over  chloride  of  calcium)  is  flowing,  and 
the  heat  of  a  spirit-lamp  is  applied  to  the  bulb.  The  metal  soon  burns  in  the  gas, 
which  it  robs  of  its  oxygen,  leaving  the  carbon  as  a  black  mass  in  the  bulb 
(Fig.  107).  The  potassium  remains  in  the  form  of  potassium  carbonate,  3C02  +  K4  = 
2K0CO3  +  C.  If  slices  of  sodium  be  arranged  in  a  test-tube  in  alternate  layers 
with  dried  chalk  (calcium  carbonate),  and  strongly  heated  with  a  spirit-lamp, 
vivid  combustion  will  ensue,  and  much  carbon  will  be  separated  (CaCO3  +  Na4  = 
€aO  +  2Na,20  +  C). 

When  C0.2  is  submitted  to  the  action  of  electric  sparks  in  an  apparatus  such  as 
that  shown  in  Fig.  72,  it  expands  slightly,  having  been  partially  converted  into 
CO  +  0,  but  if  the  sparking  is  continued,  the  mixture  explodes  to  form  LO2, 
restoring  the  original  volume  of  the  gas.  In  a  partial  vacuum  in  which  the  pressure 
ihe  CO2  is  only  5  millimetres  nearly  70  per  cent,  of  the  C02  may  be  decomposed 
this  way. 

CARBON  MONOXIDE  OR  CARBONIC  OXIDE. 

CO  =  28  parts  by  weight  =  2  volumes. 

78.  The   combustion   of    potassium    or    sodium    in    carbon    dioxide 
deprives  the  gas  of  all  its  oxygen,  but  other  metals,  which  are  not 


132 


CARBON  MONOXIDE. 


endowed  with  so  powerful  an  attraction  for  oxygen,  do  not  carry  the 
decomposition  of  carbon  dioxide  to  its  final  limit ;  thus,  iron,  zinc  and 
magnesium  at  a  high  temperature  only  deprive  the  gas  of  one-half  of 
its  oxygen,  a  result  which  may  also  be  brought  about  at  a  red  heat  by 
carbon  itself.  If  an  iron  tube  filled  with  fragments  of  charcoal  be 
heated  to  redness  in  a  furnace  (Fig.  n),  and  carbon  dioxide  be  trans- 
mitted through  it,  it  will  be  found,  on  collecting  the  gas  which  issues 
from  the  other  extremity  of  the  tube,  that  on  the  approach  of  a  taper 
the  gas  takes  fire,  and  burns  with  a  beautiful  blue  lambent  flame,  similar 
to  that  which  is  often  observed  to  play  over  the  surface  of  a  clear  fire. 
Both  flames,  in  fact,  are  due  to  the  same  gas,  and  in  both  cases  this 
gas  is  produced  by  the  same  chemical  change,  for,  in  the  tube,  the 
carbon  dioxide  yields  half  of  its  oxygen  to  the  charcoal,  both  becoming 
converted  into  carbonic  oxide  ;  CO2  +  C=  aCO.  In  the  fire,  the  carbon 
dioxide  is  formed  by  the  combustion  of  the  carbon  of  the  fuel  in  the 
oxygen  of  the  air  entering  at  the  bottom  of  the  grate ;  and  this  CO2,  in 
passing  over  the  layer  of  heated  carbon  in  the  upper  part  of  the  fire,  is 
partly  converted  into  carbonic  oxide,  which  inflames  when  it  meets 


Fig.  108. — Reverberatory  furnace  for  copper-smelting-. 

with  the  oxygen  in  the  air  above  the  surface  of  the  fuel,  and  burns 
with  its  characteristic  blue  flame,  reproducing  carbon  dioxide.*  The 
carbon  monoxide  occupies  twice  the  volume  of  the  carbon  dioxide  from 
which  it  was  produced. 

This  conversion  of  carbon  dioxide  into  carbon  monoxide  is  of  great 
importance,  on  account  of  its  extensive  application  hi  metallurgic 
operations.  It  is  often  desirable,  for  instance,  that  a  flame  should  be 
made  to  play  over  the  surface  of  an  ore  placed  on  the  bed  or  hearth  of  a 
reverberatory  furnace  (Fig.  108).  This  object  is  easily  attained  when  the 
coal  affords  a  large  quantity  of  inflammable  gas  :  but  with  anthracite 
coal,  which  burns  with  very  little  flame,  and  is  frequently  employed  in 
such  furnaces,  it  is  necessary  to  pile  a  high  column  of  coal  upon  the 
grate,  so  that  the  carbon  dioxide  formed  beneath  may  be  convert? d  into 
carbonic  oxide  in  passing  over  the  heated  coal  above,  and  when  this  gas 
reaches  the  hearth  of  the  furnace,  into  which  air  is  admitted,  it  burns 

*  It  is  stated  that  when  the  temperature  of  a  fuel  in  a  furnace  has  attained  1000°  C.,  the 
carbon  burns  directly  to  carbon  monoxide.  When  cai'bon  is  heated  in  partially  dried  oxygen, 
carbon  monoxide  alone  is  produced,  showing  that  this  is  the  first  product  of  the  combustion  ; 
it  remains  carbon  monoxide  because  the  oxygen  is  too  dry  to  burn  it  to  the  dioxide  (p.  133). 
The  carbon  of  gaseous  carbon  compounds  burns  tirst  to  carbon  monoxide,  which  is  further 
oxidi-cd  to  the  dioxide. 


PROPERTIES   OF   CARBONIC   OXIDE.  133 

with  a  flume  which  spreads  over  the  surface  of  the  ore.  It  is  frequently 
advantageous  to  make  carbon  monoxide  in  this  way  in  a  grate  (producer) 
at  some  distance  from  the  furnace  and  to  conduct  it  thither  through 
pipes.  (See  Chemistry  of  Fuel.}  The  temperature  of  the  flame  of 
carbonic  oxide  burning  in  air  is  estimated  at  about  1400°  C. 

The  attraction  of  carbonic  oxide  for  oxygen  is  turned  to  account  in 
removing  that  element  from  combination  with  iron  in  its  ores,  as  will 
be  seen  hereafter. 

Dry  carbon  monoxide  will  not  combine  with  dry  oxygen  unless  the 
mixture  of  gases  be  very  strongly  heated.  This  fact  is  an  instance  of 
the  influence  which  water  vapour  exercises  in  chemical  combination 
(compare  p.  32). 

It  follows  that  dry  carbon  monoxide  will  not  burn  in  dry  air  or  dry  oxygen.  To 
demonstrate  this  fact,  carbon  monoxide  is  passed  through  strong  sulphuric  acid  and 
kindled  at  a  jet  ;  the  flame  is  introduced  into  an  inverted  gas  jar  containing 
ordinary  air  to  show  that  the  combustion  will  continue  in  such  a  vessel ;  the  air  in 
a  similar  jar  is  now  dried  by  shaking  strong  sulphuric  acid  in  it,  the  acid  is  quickly 
poured  out,  and  the  flame  introduced  into  the  inverted  jar,  whereupon  combustion 
immediately  ceases. 

Judging  by  analogy  with  other  elements,  whose  combination  with  two  atoms  of 
oxygen  produces  twice  as  much  heat  as  their  combination  with  one  atom,  the 
conversion  of  C  into  C0.2  should  produce  twice  as  much  heat  as  its  conversion  into 
CO.  When  C,  in  the  form  of  charcoal,  burns  to  form  G02,  each  gram  of  C  produces 
8080  gram  units  of  heat;  or  C,  12  grams,  +  02,  32  grams,  =  C0.2  +  96,960  units 
of  heat.  Now  carbon  cannot  be  burned  directly  to  form  CO,  but  when  CO  burns 
to  form  CO.,,  I  gram  of  CO  produces  2403  units  of  heat ;  or  CO,  28  grams,  +  0, 
1 6  grams.  =  C0.2  +  67.284  units  of  heat.  In  the  first  equation,  16  grams  of  0 
produce  48,480  units,  and  in  the  second  67,284  units  of  heat.  But  in  the  first  case, 
solid  carbon  is  converted  into  gas,  a  change  of  state  which  must  absorb  much  of 
the  heat  produced.  If  the  C  were  in  the  state  of  gas  to  begin  with,  in  both  cases, 
it  is  probable  that  we  should  have  O,  16  grams,  +  C,  12  grams.  =  CO  +  67,284 
units  of  heat,  and  02,  32  grams,  +  C,  12  grams,  =  C02  +  134,568  units  of  heat,  so 
that  i  gram  of  C  would  give  11,2 14  units  of  heat  when  burned  to  C02.  But  when 
i  gram  of  solid  C  burns  to  C02  it  gives  only  8080  units  of  heat :  hence  11,214- 
8080,  or  3134  units,  represent  the  heat  required  to  convert  i  gram  of  solid  carbon 
into  gas. 

79.  Carbonic  oxide  is  very  poisonous ;  and  it  appears  that  the  acci- 
dents which  too  frequently   occur  from    burning  charcoal  or  coke  in 
braziers  and  chafing-dishes  in  close  rooms,  result  from  the  poisonous 
effects  of  the  small  quantity  of  carbonic  oxide  which  is  produced  and 
escapes  combustion,  since  the  amount  of  carbonic  acid  gas  thus  diffused 
through  the  air  is  not  sufficient,  in  mo.vt  cases,  to  account  for  the  fatal 
result.     The  carbonic  oxide  formed  in  cast-iron  stoves  diffuses  through 
the  hot  metal  into  the  air  of  a  room.     It  is  certainly  fatal  to  breathe 
air  |  con  taming  i  per  cent,  of  CO,  and  it  is  said  that  so  little  as  0.05  per 
cent,  may  prove  fatal. 

80.  The  poisonous   character   of  carbon  monoxide   is  raised  as  an 
objection  to  the  proposed  use  of  this  gas  for  purposes  of  illumination. 
The  character  of  the  flame  of  carbonic  oxide  would  appear  to  afford 
little  promise  of  its  utility  as  an  illuminating  agent ;  but  that  it  is 
possible  so  to  employ  it  is  easily  demonstrated  by  kindling  a  jet  of  the 
gas  which  has  been  passed  through  a   wide  tube  containing  a  little 
cotton    moistened    with    rectified    coal   naphtha   (benzene),  when   the 
carbon  monoxide  will  be  found  to  burn  with  a  very  luminous  flame. 
The  carbonic  oxide  destined  to  be  employed  for  illuminating  purposes  is 
prepared  by  passing  steam  over  white  hot  coke,  a  mixture  of  carbon 


134 


PREPARATION   OF   CARBONIC   OXIDE. 


monoxide  and  hydrogen  being  thus  produced  ;  C  +  H20  =  CO  +  H2. 
The  water-gas  always  contains  some  carbon  dioxide,  the  quantity  being 
greater  the  lower  the  temperature  of  the  coke.  This  is  because  at 
lower  temperatures  the  coke  burns  in  steam  to  carbon  dioxide,  not  to 
carbon  monoxide;  C+  2H2O  =  CO2-f  2H2.  Water-gas  usually  consists 
of  about  50  per  cent,  of  H,  40  per  cent,  of  CO,  5  per  cent,  of  CO2,  and 
5  per  cent,  of  N  (from  air  and  the  coke).  Since  neither  hydrogen  nor 
carbon  monoxide  is  possessed  of  any  odour,  this  mixture  would  not  be 
detected  in  the  atmosphere  of  a  room  where  there  was  a  leaky  gas- 
pipe,  and  the  presence  of  the  poisonous  carbon  monoxide  would  remain 
unsuspected.  Thus,  it  becomes  incumbent  upon  those  supplying  such 
gas  to  dwelling-houses  to  render  it,  by  mixing  some  gas  or  vapour  with 
it,  at  least. as  odorous  as  is  ordinary  coal-gas,  an  escape  of  which  is  so 
easily  detected. 

The  application  of  water-gas  in  this  country,  for  illuminating  purposes,  is  at 
present  limited  to  its  admixture  with  coal-gasj  for  which  purpose  it  is  rendered 
luminous  by  hydrocarbons  obtained  from  the  destructive  distillation  of  petroleum. 

The  decomposition  of  steam  by  red-hot  carbon  "is  also  taken  advantage  of  in 
order  to  procure  a  flame  from  anthracite  coal  when  employed  for  heating  boilers. 
The  coal  being  burnt  on  fish-bellied  bars,  beneath  which  a  quantity  of  water  is 
placed,  the  radiated  heat  converts  the  water  into  steam,  which  is  carried  by  the 
draught  into  the  fire,  where  it  furnishes  carbonic  oxide  and  hydrogen,  both  capable 
of  burning  with  flame  under  the  bottom  of  the  boiler.  The  temperature  of  the 
bars  is  also  thus  reduced,  so  that  they  are  not  so  much  injured  by  the  intense  heat 
of  the  glowing  fuel. 

81.  Carbonic  oxide,  unlike  carbon  dioxide,  is  nearly  insoluble  in 
water.  It  is  even  lighter  than  air,  its  specific  gravity  being  0.967. 
In  its  chemical  relations  it  is  an  indifferent  oxide,  that  is,  it  has  neither 
acid  nor  basic  properties.  It  is  liquid  below  -  190°  C.  (its  boiling- 
point),  and  solid  at  -  211°  C.  (its  melting-point).  Its  critical  tempera- 
ture is  —  140°  C.  These  con- 
stants approximate  to  tile 
corresponding  constants  for 
nitrogen. 

82.  A  very  instructive  process 
for  obtaining  carbonic  oxide,  con- 
sists in  heating  crystallised  oxalic 
acid  with  three  times  its  weight  of 
oil  of  vitriol.  If  the  gas  be  col- 
lected over  water  (Fig.  109),  and 
one  of  the  jars  be  shaken  with  a 
little  lime-water,  the  milkiness 
imparted  to  the  latter  will  indicate 
abundance  oi  carbon  dioxide  ; 
whilst,  on  removing  the  glass  plate, 
and  applying  a  light,  the  carbonic 
oxide  will  burn  with  its  character- 
istic blue  flame.  The  gas  thus  obtained  is  a  mixture  of  equal  volumes  of  carbonic 
oxide  and  carbonic  acid  gases.  Crystallised  oxalic  acid  is  represented  by  the  formula 
C2H204.2Aq,  and  if  the  water  of  crystallisation  be  left  out  of  consideration,  its 
decomposition  maybe  represented  by  the  equation  C2H204=H2O  +  CO  + C02,  the 
change  being  determined  by  the  attraction  of  the  oil  of  vitriol  for  water.  To  obtain 
pure  CO,  the  mixture  of  gases  must  be  passed  through  a  bottle  containg  solution 
of  potash,  to  absorb  the  CO2  (Fig.  no). 

But  pure  CO  is  much  more  easily  obtained  by  the  action  of  sulphuric  acid  upon 
crystallised  potassium  ferrocyanide  (yellow  prussiate  of  potash)  at  a  moderate  heat. 
Since  the  gas  contains  small  quantities  of  sulphurous  and  carbonic  ucid  gases,  it 


109. 


DECOMPOSITION   OF   CARBON   MONOXIDE. 


135 


must  be  passed  through  solution  of  potash  if  it  be  required  perfectly  pure.     The 
chemical  change  which  occurs  in  this  process  is  expressed  thus  : 

K4C6N6Fe  +  6H.20  +  6H.2S04  =  6CO    +    2K.2S04    +    3<NH4)2SO4  +  FeS04 
Pota.-sium  Potassium         Ammonium         Ferrous 

ferrocyanide.  sulphate.  sulphate.  sulphate. 

Ten  grams  of  crystallised  ferrocyanide,  Avith  135  grams  (73  c.c.)  of  sulphuric  acid 
(sp.  gr.  1.84)  and  13  grams  of  water,  give  about  3^  litres  of  CO. 

If  the  boiling  is  continued  after  the  evolution  of  CO  has  ceased',  much  sulphurous 
acid  gas  is  disengaged  (2FeS04  +  2H.2S04=:Fe.2(SO4) 


Fig-,  no. — Preparation  of  carbonic  oxide. 

83.  To  demonstrate  the  production  of  C0.2  during  the  combustion  of  CO,  a  jar  of 
the  gas  is  closed  with  a  glass  plate,  and  after  placing  it  upon  the  table,  the  plate  is 
slipped  aside  and  a  little  lime-water  quickly  poured  into  the  jar.  On  shaking,  no 
milkiness  indicative  of  carbonic  acid  gas  should  be  perceived.  The  plate  is  then 
removed  and  the  gas  kindled.  On  replacing  the  plate  and  shaking  the  jar,  an 
abundant  precipitation  of  calcium  carbonate  will  occur. 

Carbonic  oxide  forms  an  explosive  mixture  with  half  its  volume  of  oxygen  ;  if 
the  mixture  be  absolutely  free  from  vapour  of  water,  it  does  not  explode  on  passing 
an  electric  spark  through  it. 

When  carbonic  oxide  is  passed  through  a  red-hot  porcelain  tube,  a  portion  of  it  is 
decomposed  into  carbonic  acid  gas  and  carbon  ;  and  when  the  experiment  is  con- 
ducted without  special  arrangements,  the  carbonic  oxide  is  reproduced  as  the 
temperature  of  the  gas  falls.*  But  by  passing  through  the  centre  of  the  porcelain 
tube  a  brass  tube,  through  which  cold  water  is  kept  running,  the  decomposition 
has  been  demonstrated  by  the  deposition  of  carbon  upon  the  cooled  tube,  and  by 
collecting  the  carbonic  acid  gas  formed.  Carbonic  acid  gas  is  also  decomposed  by 
intense  heat  into  carbonic  oxide  and  oxygen  ;  but  if  these  gases  be  allowed  to  cool 
down  slowly  in  contact,  they  recombine.  The  gas  drawn  from  the  hottest  region 
of  a  blast-furnace  (see  Iron),  and  rapidly  cooled,  so  as  to  prevent  rcombination,  was 
found  to  contain  both  carbonic  oxide  and  oxygen. 

When  electric  sparks  are  passed  through  carbon  dioxide,  about  one-third  of  it 
becomes  CO  +  0,  but  this  reaction  does  not  go  any  further  because  the  CO  +  0  begin 
to  recombine.  By  passing  a  pellet  of  phosphorus  into  the  gas  and  continuing  the 
sparks,  all  the  C0,2  may  be  decomposed  into  CO  +  0,  for  the  phosphorus  will  com- 
bine with  the  oxygen,  and  C0.2  cannot  be  reformed. 

The  reducing  action  of  carbonic  oxide  upon  metallic  oxides,  at  high  temperatures, 
may  be  illustrated  by  passing  the  pure  gas  from  a  bag  or  gas-holder,  first  through  a 
bottle  of  lime-water  (B,  Fig.  ill),  to  prove  the  absence  of  carbonic  acid  gas,  then 

*  It  is  stated  that  CO  heated  at  500°  C.  alwa>s  contains  a  little  CO2,  but  no  carbon  is 
deposited.  If  tins  be  true  a  lower  oxi.te  of  carbon  must  be  supposed  to  be  fonne-i. 


136  COMPOSITION   OF   THE   OXIDES   OF   CARBON. 

over  oxide  of  copper,  contained  in  the  tube  C,  arid  afterwards  again  through  liine- 
water  in  D.  When  enough  gas  has  been  passed  to  expel  the  air,  heat  may  be  applied 
to  the  tube  by  the  gauze-burner  E.  when  the  formation  of  carbonic  acid  gas  will  be 
immediately  shown  by  the  second  portion  of  lime-water,  and  the  black  oxide  of 
copper  will  be  reduced  to  red  metallic  copper. 


Fig.  in. — Reduction  of  oxide  of  copper  by  carbonic  oxide. 

If  precipitated  peroxide  of  iron  be  substituted  for  oxide  of  copper,  iron  in  the 
state  of  black  powder  will  be  left,  and  if  allowed  to  cool  in  the  stream  of  gas,  will 
take  tire  when  it  is  shaken  out  into  the  air.  becoming  reconverted  into  the  peroxide 
(Iron  pyroplioi'iis). 

Carbonic  oxide  is  absorbed  by  potassium  hydrate  at  100°  C.,  potassium  formate 
being  produced:  CO  +  KOH  =  HCOOK.  If  carbonic  oxide  be  passed  over  soda- 
lime  in  a  glass  tube  heated  by  a  gas  furnace,  sodium  carbonate  is  formed,  and 
hydrogen  liberated  ;  CO  +  2XaOH  =  Xa.2CO3  +  H2. 

84.  Composition  by  volume  of  carbon  monoxide  and  carbon  dioxide.— 
When  carbon  burns  in  oxygen,  the  volume  of  the  carbon  dioxide  pro- 
duced is  exactly  equal  to  that  of  the  oxygen,  so  that  one  volume  of 
oxygen  furnishes  one  volume  of  carbon  dioxide,  or,  since  equal  volumes 
of  gases  contain  the  same  number  of  molecules  (p.  47),  a  molecule  of 
carbon  dioxide  contains  a  molecule  of  oxygen. 

When  one  volume  of  carbon  dioxide  (containing  one  volume  of  oxygen) 
is  passed  over  heated  carbon,  it  yields  two  volumes  of  carbonic  oxide  ; 
hence  two  volumes,  or  one  molecule,  of  this  gas  contain  one  volume,  or 
half  a  molecule,  of  oxygen. 

85.  It  will  be  seen  in  the  next  few  pages  that  carbon  can  combine 
with  hydrogen  and  with  chlorine  in  the  sense  that  one  atom  of  carbon 
can  fix  four  atoms  of  hydrogen  or  of  chlorine,  but  no  more.     Carbon  is 
therefore  the  type  of  the  tetravalent  elements  (p.  1 1  ),  and  may  be  con- 
sidered as  exerting  its  affinity  in  four  directions,  >C<.     When  all  of 
these  affinities  are  satisfied  by  the  affinities  of  other  elements,  the  carbon 
will  be  unable  to  combine  with  any  other  element.     Thus,  the  carbon 

H\    ,/H 

in  the  compound       y®\       will  be  unable  to  combine  with  any  more 

^       XH 

hydrogen  or  with  any  chlorine ;  this  compound,  CH4,  is  therefore  said 
to  be  a  saturated  compound.  It  has  already  been  seen  that  oxygen 
exerts  affinity  in  two  directions,  -0—  ;  consequently  one  atom  of  oxygen 
is  equivalent  to  two  atoms  of  hydrogen  in  saturating  power,  and  carbon 
dioxide  is  a  saturated  compound,  O<  >0<  >O.  On  the  other  hand, 
carbon  monoxide  should  be  an  unsaturated  compound,  >C<  >0,  and 
should  be  capable  of  combining  with  other  elements  in  a  manner  not 
possible  for  carbon  dioxide.  Thus  it  will  be  found  in  the  sequel 
that  carbon  monoxide  is  much  more  chemically  active  than  the 


ACETYLENE.  137 

dioxide  ;  it  will  combine  directly  with  chlorine  to  form  the  compound 

C1\ 

^>C  <  >  O,  and  with  many  of    the  metals.      The  fact   that  carbon 

CK 

monoxide  combines  with  oxygen  with  liberation  of  heat  is  in  itself  an 

indication  of  the  residual  affinity  of  the  carbon  in  carbon  monoxide. 

COMPOUNDS  OF  CARBON  WITH  HYDROGEN. 

86.  No  two  other  elements  are  capable   of  occurring  in  so   many 
different  forms  of  combination  as  are  carbon  and  hydrogen.     The  hydro- 
carbons, as  these  compounds  are  generally  designated,  include  most  of 
the  inflammable   gases   which  are  commonly  met  with,  and  a  great 
number  of  the  essential  oils,  naphthas,  and  other  useful  substances. 
There  is  reason  to  believe  that  all  these  bodies,  even  such  as  are  found 
in  the  mineral  kingdom,  have  been  originally  derived  from  vegetable 
sources,  and  their  history   belongs,  therefore,    to  the   department  of 
organic  chemistry.     The  three  simplest   examples  of  such  compounds 
will,  however,  be  brought  forward  in  this  place  to  afford  a  general 
insight  into  the  mutual  relations  of  these  two  important  elements. 

87.  Acetylene  (C2H2=26  parts  by  weight).  —  When  very  intensely 
heated,  carbon  can  combine  with  hydrogen   to  form  acetylene.      The 
necessary  temperature  is   produced  by  the   electric  arc,    that    is,    the 
electrical  discharge  between  two  pieces  of  dense  carbon    (electrodes) 
connected  with  the  opposite  terminals  of  a  source  of  electric  current, 
such  as  a  dynamo  or  a  powerful  galvanic  battery.     When  this  arc  is 
surrounded  by  an  atmosphere  of  hydrogen  some  acetylene  is  formed. 
The    experiment    has    no    practical    importance,    because    but    little 
acetylene  is  obtained  in  proportion  to  the  energy  employed,  but  its 
theoretical  interest  is  very  great,  since  it  is  the  first  step  in  the  pro- 
duction   of  organic    substances    by   the   direct   synthesis   of    mineral 
elements  ;  acetylene  (C.,H9)  being  convertible  into  olefiant  gas  (C2H4), 
this  last  into  alcohol  (C2H6O)  and  alcohol  into  a  very  large  number  of 
organic  products. 

The  electric  arc  is,  however,  used  indirectly  for  the  production  of 
acetylene.  For  this  purpose  a  mixture  of  lime  and  carbon,  in  the  form 
of  coke  or  charcoal,  is  heated  by  the  arc  in  order  to  make  calcium  car- 
bide, CaC2,  an  evil  smelling,  grey,  crystalline  substance  which  yields 
acetylene  and  slaked  lirne  when  treated  with  water,  CaC.,  +  2H.,0  = 


In  places  remote  from  gas-works,  acetylene,  made  from  calcium  car- 
bide and  water,  is  burnt  as  an  illummant  instead  of  coal  gas,  which  it 
exceeds  in  illuminating  value  nearly  1  5-fold.  Thus  the  manufacture  of 
calcium  carbide  has  become  an  industry  and  will  receive  attention  in 
the  section  devoted  to  calcium  compounds,  but  a  word  may  be  said  here 
about  the  electric  furnace  to  the  development  of  which  in  recent  years 
we  owe  several  useful  substances  beside  calcium  carbide. 

This  furnace  is  varied  in  form  to  suit  the  particular  requirement, 
but  consists  in  principle  of  an  electric  arc,  radiation  from  which  is  pre- 
vented by  a  fire-brick  casing.  The  material  to  be  heated  is  introduced, 
.as  far  as  possible,  between  the  electrodes  where  the  temperature  may 
rise  as  high  as  3500°  C.  This  is  a  much  higher  temperature  than 


138 


THE   ELECTRIC   FURNACE. 


that  attainable  (about  1500°  C.)  in  any  furnace  heated  with  ordinary 
fuel,  and  chemical  changes  occur  in  the  electric  furnace  which  cannot 
ba  otherwise  produced.  Such  a  furnace  is  shown  in  perspective  in 
Fig.  112.  The  shell  of  the  furnace  A  is  here  cut  away  to  show  the 
position  of  the  carbon  electrodes  B,  which  are  mounted  in  metal  clamp 


Fi.41.  112. — Electric  Fnruace. 

carried  on  slides  and  connected  by  leads  with  the  current  supply  terminals. 
In  series  with  the  electrodes  is  an  electromagmnt  E,  by  means  of  which 
the  arc  may  be  deflected  in  any  required  direction,  for  example,  down 
into  the  crucible  C  containing  the  body  to  be  heated.  The  crucible  is 

carried  on  a  suitable  platform 
which  is  raised  or  lowered  by  a 
lever,  the  handle  D  of  the  lever 
being  held  by  a  catch  F,  when  the 
platform  which  also  forms  the 
bottom  of  the  furnace,  is  in  position. 
When  lowered,  platform  and  cruci- 
ble can  be  withdrawn  from  below 
the  furnace  by  means  of  the  slide 
shown  in  the  figure.  Fig.  113 
shows  another  form  of  mounting 
for  the  carbon  electrode,  adapted 
for  inserting  the  carbon  through 
a  hole  in  the  lid  of  the  furnace 
and  turning,  raising,  or  lowering  it,  so  as  to  make  any  required  angle 
with  the  other  carbon  or  the  crucible. 

Unless  calcium  carbide  is  preserved  in  hermetically  sealed  vessels  it 
is  speedily  decomposed  by  the  moisture  of  the  air,  and  it  is  to  the  impure 
acetylene  evolved  by  this  action  that  the  carbide  owes  its  evil  odour. 


Fig.  113. 


PREPARATION  OF  ACETYLENE.  139 

This  chemical  change  evolves  a  considerable  amount  of  heat  (28, 500 gram- 
units  of  heat  per  64  grams  of  CaC2),  a  fact  which  must  not  be  neglected 
in  making  acetylene  from  the  carbide ;  for  the  gas  is  not  only  explosive 
when  mixed  with  air  or  oxygen,  as  is  hydrogen,  but  explodes  by  itself 
when  suddenly  heated  under  a  pressure  of  two  atmospheres,  a  pressure 
which  may  easily  obtain  in  a  carelessly  constructed  generator.  This 
explosion  of  the  unmixed  gas  is  due  to  the  separation  of  its  elements, 
C.H9  =  C2  +  H2. 

To  prepare  acetylene  in  the  laboratory  10  grams  of  calcium  carbide 
are  introduced  into  a  flask  which  is  then  fitted  with  a  dropping  funnel 
and  a  delivery  tube  (Fig.  114).  Water*  is  allowed  to  drop  slowly  from 
the  funnel  on  to  the  carbide  and  the  gas  is  collected  over  water,  care 
being  taken  that  all  air  is  first  expelled  from  the  flask  by  the  issuing 
gas  (see  above).  It  will  bs  noted  that  the  carbide  becomes  hot  and 
swells,  behaving  like  quicklime  when  it  is  slaked  to  calcium  hydroxide, 
which  indeed  is  the  residue  left  in  the  flask  when  all  the  gas  has  been 
evolved. 

On  a  large  scale  it  is  not  considered  safe  to  drop  water  on  to  the  carbide,  because 
the  temperature  is  liable  to  rise  unduly.  Instead,  the  carbide  is  dropped  into  water 
so  that  there  may  always  he  an  excess  of  the  latter  to  absorb  the  heat  and  keep  the 
generator  cool.  Moreover,  the  excess  of  water  dissolves  some  of  the  impurities, 
ammonia  and  sulphuretted  hydrogen,  from  the  gas. 

The  amount  of  acetylene  obtainable  from  a  given  weight  of  pure  calcium  carbide 
lias  been  ascertained  by  careful  analysis,  and  the  result  is  expressed  by  the  equation 
CaC2+2H20  =  C2H2  +  Ca(OH)2,  that  is  to  say,  40+12x2  =  64  parts 'by  weight  of 
CaC2  yield  12x2+1x2  =  26  parts  by  weight  of  C.2H2.  If  the  parts  by  weight  be 
grams  the  acetylene  will  measure  22.22  litres  at  6°  C.  and  760  mm.  (see  p.  47). 
Thus  the  10  grains  of  the  carbide  used  above  would  yield  about  3.5  litres  of  acetylene. 
But  the  commercial  carbide  is  far  from  pure,  and  seldom  yields  more  than  80  per 
cent,  of  the  theoretical  volume  of  acetylene.  The  impurities  in  the  carbide  also 
evolve  gases,  the  chief  of  which  are  the  evil  smelling  phosphoretted  hydrogen  and 
sulphuretted  hydrogen.  To  rid  the  acetylene  of  the  latter  it  must  be  passed 
through  a  wash-bottle  containing  caustic  soda,  and  the  former  is  then  removed  by 
a  second  bottle  containing  nitric  acid  and  cupric  nitrate. 

Acetylene  is  constantly  found  among  the  products  of  the  incomplete 
combustion  and  destructive  distillation  of  sub.-tances  rich  in  carbon; 
hence  it  is  always  present  in  small  quantity  in  coal  gas.  anel  may  be 
produced  in  abundance  by  passing  the  vapour  of  ether  through  a  red- 
hot  tube.  Ths  character  by  which  acetylene  is  most  easily  recognised 
is  that  of  producing  a  fine  led  precipitate  (cuprous  acetylide)  in  an 
ammoniacal  solution  of  cuprous  chloride. 

The  original  process  for  preparing  this  precipitate,  is  that  in  which  the  acetylene 
is  produced  by  the  imperfect  combustion  occurring  when  a  jet  of  atmospheric  air  i& 
allowed  to  burn  in  coal  gas. 

An  adapter  (A,  Fig.  114)  is  connected  at  its  narrow  end  with  a  pipe  supplying: 
coal  gas.  The  wider  opening  is  closed  by  a  bung  with  two  holes,  one  of  which 
receives  a  piece  of  brass  tube  (B)  about  three-quarters  of  an  inch  wide  and  7  inches 
long,  Avhile  in  the  other  is  inserted  a  glass  tube  (C)  which  conducts  the  gas  to  the 
bottom  of  a  separating  funnel  (D).  The  lower  opening  of  the  brass  tube  B  is 
closed  with  a  cork,  through  which  passes  the  glass  tube  E  connected  with  a  gas- 
holder or  bag  containing  atmospheric  air.  To  commence  the  operation,  the  gas 
is  turned  on  through  the  tube  F,  and  when  all  air  is  supposed  to  be  expelled,  the 
tube  E  is  withdrawn,  together  with  its  cork,  and  a  light  is  applied  to  the  lower 
opening  of  the  brass  tube,  the  supply  of  coal  gas  being  so  regulated  that  it  shall 
burn  with  a  small  flame  at  the  end"  of  the  tube.  A  feeble  current  of  air  is  then 

*  A  saturated  solution  of  salt  has  been  recommended  as  preferable  to  pure  water  ;  it  has 
a  less  euerg-etic  action  on  the  carbide,  ?o  that  the  temperature  does  not  rise  so  high. 


140 


ACETYLENE  FROM   IMPERFECT   COMBUSTION. 


allowed  to  issue  from  the  tube  E.  which  is  passed  up  through  the  flame  into  the 
adapter,  where  the  jet  of  air  continues  to  burn  in  the  coal  gas.*  and  may  be  kept 
burning  for  hours  with  a  little  attention  to  the  proportions  in  which  the  gas  and 
air  are  supplied.  A  solution  of  cuprous  chloride  in  ammonia  is  poured  into  the 

separating  funnel  through  the  lateral  open- 
ing G,  so  that  the  imperfectly  burnt  gas  may 
pass  through  it,  when  the  cuprous  acetylide 
is  precipitated  in  abundance.  When  a 
sufficient  quantity  of  precipitate  has  been 
formed,  or  the  copper  solution  is  exhausted, 
the  liquid  is  run  out  through  the  stopcock 
(H)  on  to  a  filter,  and  a  fresh  portion  in- 
troduced. By  heating  the  precipitate  with 
HC1  acetylene  is  evolved. 

A  solution  of  cuprous  chloride  suitable 
for  this  experiment  is  conveniently  prepared 
in  the  following  manner  :  500  grains  of 
black  oxide  of  copper  are  dissolved  in  7 
measured  ounces  of  common  hydrochloric 
acid,  in  a  flask,  and  boiled  for  about  twenty 
minutes  with  400  grains  of  copper  in  filings 
or  fine  turnings.  The  brown  solution  of 
cuprous  chloride  in  hydrochloric  acid,  thus 
obtained,  is  poured  into  about  3  pints  of 
water  contained  in  a  bottle  ;  the  white 
precipitate  (cuprous  chloride)  is  allowed  to 
subside,  the  water  drawn  off  with  a  siphon, 
and  the  precipitate  rinsed  into  a  2O-ounce 
bottle,  which  is  then  quite  filled  with  water 
and  closed  with  a  stopper.  When  the  pre- 
cipitate has  again  subsided,  the  water  is 
drawn  off,  and  4  ounces  of  powdered  chloride 
of  ammonium  are  introduced,  the  bottle 
being  again  filled  up  with  water,  closed  and 
shaken.  The  cuprous  chloride  is  entirely 
dissolved  by  the  chloride  of  ammonium, 
but  would  be  precipitated  if  more  water  were  added.  When  required  for  the  pre- 
cipitation of  acetylene,  the  solution  may  be  mixed  with  about  one-tenth  of  its  bulk 
of  strong  ammonia  (0.880),  which  may  be  poured  into  the  separating  funnel  (D) 
before  the  copper  solution  is  introduced.  Four  measured  ounces  of  the  solution 
are  sufficient  for  one  charge,  and  yield,  in  three  hours,  about  3  measured  ounces  of 
the  moist  precipitate.  The  blue  solution  of  ammoniacal  cupric  chloride,  filtered 
from  the  red  precipitate,  may  be  rendered  serviceable  again  by  being  shaken,  in  a 
stoppered  bottle,  with  precipitated  copper,  prepared  by  reducing  a  solution  of  sul- 
phate of  copper,  acidified  Avith  hydrochloric  acid,  with  a  plate  of  zinc. 

If  the  acetylene  copper  precipitate  be  collected  on  a  filter,  washed,  and 
dried,  either  by  mere  exposure  to  the  air,  or  over  oil  of  vitriol,  it  will  be 
found  to  explode  with  some  violence  when  gently  heated,  and  it  is  said 
that  the  accidental  formation  of  this  compound  in  copper  or  bra:?s  pipes, 
through  which  coal  gas  passes,  has  occasionally  given  rise  to  explosions. 

When  acetylene  purified  from  phosphoretted  and  sulphuretted  hydrogen  is  passed 
through  solution  of  nitrate  of  silver,  a  white  curdy  precipitate  is  formed,  resembling 
chloride  of  silver  in  appearance,  but  insoluble  in  ammonia  (which  turns  it  yellow) 
as  well  as  in  nitric  acid. 

It  may  be  more  easily  prepared  by  suspending  a  funnel  over  a  Bunsen  burner 
which  has  caught  fire  inside  the  tube,  and  drawing  the  products  of  imperfect 
combustion,  by  means  of  an  aspirator,  through  a  solution  of  silver  nitrate.  This 
precipitate  may  also  be  used  for  the  preparation  of  acetylene,  by  heating  it  with 
hvdrochloric  acid. 


Fig.  1 14. 
Preparation  of  cuprous  acetylide. 


*  It  is  advisable  to  attach  a  piece  of  thin  platinum  wire  to  the  mouth  of  the  glass  tube  to 
reiider  the  flame  of  the  air  more  visible. 


PROPERTIES   OF  ACETYLENE.  141 

When  this  precipitate  is  washed  and  allowed  to  dry,  it  is  violently  explosive  if 
heated  or  struck,  particularly  when  it  has  been  prepared  from  a  slightly  ammoniacal 
solution  of  nitrate  of  silver.  A  minute  fragment  of  it  placed  on  a  glass  plate, 
and  touched  with  a  red-hot  wire,  detonates  loudly  and  shatters  the  glass  like  ful- 
minate of  silver.  In  a  solution  of  hyposulphite  of  gold  and  sodium,  acetylene  gives 
a  yellowish,  very  explosive  precipitate. 

The  copious  formation  of  acetylene  during  the  imperfect  combustion  of  ether,  is 
very  readily  shown  by  introducing  a  few  drops  of  ether  into  a  test-tube,  adding  a 
little  ammoniacal  solution  of  cuprous  chloride,  kindling  the  ether  vapour  at  the 
mouth  of  the  tube,  and  inclining  the  latter  so  as  to  expose  a  large  surface  of  the 
copper  solution,  when  a  large  quantity  of  the  red  cuprous  acetylide  is  pi-oduced.  If 
nitrate  of  silver  be  substituted  for  the  copper  solution,  the  white  precipitate  of 
silver  acetylide  is  formed  abundantly. 

Acetylene  is  a  colourless  gas  having  a  peculiar  odour,  which  is  always 
perceived  where  co  >1  gas  is  undergoing  imperfect  combustion.  It  burns 
with  an  extraordinarily  bright  smoky  flame,  best  seen  by  dropping  a 
piece  of  calcium  carbide  into  a  test-tube  containing  some  water  and 
inserting  a  cork  carrying  a  jet  at  which  the  gas  may  be  ignited  when 
all  the  air  has  been  expelled.  Its  most  remarkable  property  is  that  of 
inflaming  spontaneously  when  brought  in  contact  with  chlorine.  If  a 
jet  of  the  gas  be  allowed  to  pass  into  a  bottle  of  chlorine,  it  will  take 
fire  and  burn  with  a  red  flame,  depositing  much  carbon.  When 
chlorine  is  decanted  up  into  a  cylinder  containing  acetylene  standing 
over  water,  a  violent  explosion  immediately  takes  place,  attended 
with  a  vivid  flash,  and  separation  of  a  large  amount  of  carbon ; 


> 

Water  absorbs  about  its  own  volume  of  the  gas.  The  solution  smells 
strongly  of  the  gas,  and  yields  a  decided  precipitate  with  ammoniacal 
cuprous  chloride  and  with  silver  nitrate.  Alcohol  is  a  better  solvent 
for  acetylene,  while  acetone  dissolves  about  25  times  its  volume  at 
15°  C.  Acetylene  is  liquid  at  o°  C.  under  38  atmospheres  pressure 
and  at  —85°  C.,  at  760  mm. ;  hence  the  latter  temperature  is  its  boiling- 
point.  The  critical  temperature  is  37°  C.,  and  the  critical  pressure  67 
atmospheres.  Liquid  acetylene  is  colourless  and  its  sp.  gr.  is  0.45  at  o°  C. 

If  the  acetylene  copper  precipitate  be  suspended  in  solution  of 
ammonia,  and  heated  with  a  little  granulated  zinc,  the  acetylene  com- 
bines with  the  (nascent)  hydrogen  to  form  olefiant  gas  (C2H4).  Further 
particulars  respecting  acetylene  are  given  under  Organic  Chemistry. 

The  heat  evolved  by  the  combustion  of  a  given  weight  of  acetylene  is 
more  than  that  produced  when  the  same  weight  of  a  mixture  containing 
the  same  proportion  of  carbon  and  hydrogen,  such  as  would  be  obtained 
by  suspending  carbon  dust  in  hydrogen,  is  burnt.  This  shows  that 
acetylene  is  an  endothermic  compound  (p.  96). 

When  2.6  grams  of  CgHg,  containing  24  grains  of  C  and  2  grams  of  H,  are  burnt, 
315,000  gram  units  of  heat  are  evolved  ;  but  when  these  weights  of  C  and  H  are 
burnt  separately,  or  merely  mixed  together,  only  257,000  units  are  evolved.  The 
difference,  +  58,000  units,  must  be  due  to  the  disruption  of  the  combination 
between  the  C  and  H  in  the  acetylene  ;  that  is,  the  heat  of  formation  of  acetylene 
must  be  -  58,000. 

When  16  grams  of  methane,  CH4.  containing  12  grams  of  C  and  4  grams  of  H, 
are  burnt,  213,000  gram  units  of  heat  are  evolved.  The  same  weights  of  C  and  H, 
burnt  in  mixture  give  231,000  units.  In  this  case,  therefore,  18,000  units  of  heat 
must  have  been  absorbed  in  disuniting  the  C  and  H  in  the  methane,  so  that  this 
compound  is  exothermic,  its  heat  of  formation  being  +  18,000. 

*  It  is  sav.l  that  a  trace  of  air  is  essential  for  the  explosion. 


142  OLEFIANT   GAS. 

Endothermic  compounds  are  liable  to  decompose  suddenly,  or  detonate,  when 
subjected  to  a  shock.  Thus  when  a  small  quantity  (o.  i  gram)  of  the  explosive 
compound  mercuric  fulminate  is  fired  in  acetylene,  the  gas  explodes,  although  no 
oxygen  is  present  other  than  the  small  quantity  in  the  fulminate.  A  similar 
result  follows  if  a  wire  heated  to  about  750°  C.  is  introduced  into  the  gas.  These 
effects  are  much  more  marked  when  the  gas  is  under  pressure  and  extend  even  to 
liquid  acetylene. 

The  explosion  of  a  mixture  of  acetylene  and  air  or  oxygen  is  all  the  more  violent 
owing  to  the  endothermic  character  of  acetylene.  As  the  equation  for  the  com- 
bustion is  C2H2  +  05  =  2C02-*-H20,  the  most  explosive  mixture  is  one  of  2.  volumes 
of  acetylene  and  5  volumes  of  oxygen,  or  25  volumes  of  air. 

88.  defiant  gas  or  ethylene  (C2H4  =  28  parts  by  weight). — This  gas 
is  found  in  larger  quantity  than  is  acetylene,  among  the  products  of  the 
action  of  heat  upon  coal  and  other  substances  rich  in  carbon,  and  it  is 

an  important  constituent  of  the 
illuminating  gases  obtained  from 
such  materials. 

Olefiant  gas  may  readily  be 
prepared  by  the  action  of  strong 
sulphuric  acid  (oil  of  vitriol, 
H.,SO4)  upon  alcohol  (spirit  of 
wine,  C2H60). 

Two  measures  of  oil  of  vitriol  are 
introduced  into  a  flask  (Fig.  115),  and 
one  measure  of  alcohol  is  gradually 
poured  in,  the  flask  being  agitated 
after  each  addition  ;  much  heat  is 
evolved,  and  there  would  be  danger 
in  mixing  large  volumes  suddenly.* 
Fig-.  115. — Preparation  of  olefiant  gas.  On  applying  a  moderate  heat,  the 

liquid  darkens   and   effervesces   and 

the  gas  may  be  collected  in  jars  filled  with  water.  When  the  mixture  has  become 
thick,  and  the  evolution  of  the  gas  is  slow,  the  end  of  the  tube  must  be  removed 
from  the  water  and  the  lamp  extinguished.  Eighty-five  c.c.  of  spirit  of  wine 
generally  give  about  8  litres  of  olefiant  gas. 

The  gas  will  be  found  to  have  a  very  peculiar  odour,  in  which  that  of  ether  and 
of  sulphurous  acid  gas  are  perceptible.  One  of  the  jars  may  be  closed  with  a  glass 
plate,  and  placed  upon  the  table  with  its  mouth  upwards  :  on  the  approach  of  a 
flame,  the  gas  will  take  fire,  burning  with  a  bright  white  flame  characteristic  of 
olefiant  gas,  and  seen  to  best  advantage  when,  after  kindling  the  gas,  a  stream  of 
water  is  poured  down  into  the  jar  in  order  to  displace  the  gas. 

Another  jar  of  the  gas  may  be  well  washed  by  transferring  it  repeatedly  from  one 
jar  to  another  under  water,  a  little  solution  of  potash  may  then  be  poured  into  it, 
and  the  jar  violently  shaken,  its  mouth  being  covered  'with  a  glass  plate  ;  the 
potash  will  remove  all  the  sulphurous  acid  gas,  and  the  gas  will  now  exhibit 
the  peculiar  faint  odour  which  belongs  to  olefiant  gas. 

The  purified  gas  may  be  transferred,  under  water,  to  another  jar,  kindled,  and 
allowed  to  burn  out ;  if  a  little  lime-water  be  then  shaken  in  the  jar,  its  turbidity 
will  indicate  the  presence  of  carbonic  acid  gas,  which  is  produced  together  with 
water,  when  olefiant  gas  burns  in  air,  C2H4  +  04  =  2C02  +  2H2O. 

A  somewhat  better  yield  of  gas  is  obtained  by  boiling  syrupy  phosphoric  acid 
(sp.  gr.  1.75)  in  a  flask  and  dropping  in  alcohol  slowly,  the  temperature  of  the 
mixture  being  kept  at  about  200°  C. 

On  comparing  the  composition  of  olefiant  gas  (C.,H4)  with  that  of 
alcohol  (C2H6O),  it  is  evident  that  the  former  may  be  supposed  to  be 
produced  from  the  latter  by  the  abstraction  of  a  molecule  of  water 
(H20)  which  is  removed  by  the  sulphuric  acid,  though  other  secondary 
changes  occur,  resulting  in  the  separation  of  carbonaceous  matter  and 

*  If  methylated  spirit  be  employed,  the  mixture  will  have  a  dark,  red-brown  colour. 


EXPERIMENTS   WITH   ETHYLENE. 


143 


the  production  of  sulphurous  acid  gas.  A  more  complete  explanation 
of  the  action  of  sulphuric  acid  upon  alcohol  must  be  reserved  for  the 
chemical  history  of  this  compound. 

Olefiant  gas  derives  its  name  from  its  property  of  uniting  with 
chlorine  and  bromine  to  form  oily  liquids,  a  circumstance  which  is 
applied  for  the  determination  of  the  proportion  of  this  gas  present  in 
coal  gas,  upon  which  part  of  the  illuminating  value  of  coal  gas  depends. 
The  compound  with  chlorine  (C3H4C13)  is  known  as  Dutch  liquid,  having 
been  discovered  by  Dutch  chemists,  and  is  remarkable  for  its  resem- 
blance to  chloroform  in  odour. 

To  exhibit  the  formation  of  Dutch  liquid,  a  quart  cylinder  (Fig.  116)  is  half  filled 
with  olefiant  gas,  and  half  with  chlorine,  which  is  rapidly  passed  up  into  it,  from  a 
bottle  of  the  gas,  under  water.  The 
cylinder  is  then  closed  with  a  glass 
plate,  and  supported  with  its  mouth 
downwards  under  water  in  a  xepa- 
nitlng  funnel,  furnished  with  a 
glass  stop-cock.  The  volume  of 
the  mixed  gases  begins  to  diminish 
immediately,  drop-;  of  oil  being 
formed  upon  the  side  of  the  cylin- 
der and  the  surface  of  the  water. 
As  the  drops  increase,  they  fall  to 
the  bottom  of  the  funnel.  Water 
must  be  poured  into  the  funnel  to 
make  good  that  which  rises  into 
the  cylinder,  and  when  the  whole 
of  the  gas  has  disappeared,  the  oil 
may  be  drawn  out  of  the  funnel 
through  the  stop-cock  into  a  test- 
tube,  in  which  it  is  shaken  with  a 
little  potash  to  absorb  any  excess  of 
chlorine.  The  fragrant  odour  of 
the  Dutch  liquid  will  then  be  per- 
ceived, especially  on  pouring  it  out 
into  a  shallow  dish. 

In  applying  this  principle  to  the 
measurement  of  the  illuminating 
hydrocarbons  in  coal  gas,  daylight 
must  be  excluded,  or  an  error  would 
be  caused  by  the  union  of  the  free 
hydrogen  with  the  chlorine  or  bro- 
mine. The  bromine  test  may  be 
applied  in  the  tube  represented  in  Fig.  117.  The  gas  to  be  examined  is  measured 
over  water  in  the  divided  limb  «,  with  due  attention  to  temperature  and  pressure  ; 
the  tube  being  held  perpendicularly,  the  limb  b  will  remain  filled  with  water,  so 
that  gas  cannot  escape  nor  air  enter.  A  drop  or  two  of  bromine  is  poured  into 
this  limb,  which  is  then  depressed  beneath  the  water  in  the  pneumatic  trough,  and 
closed  by  the  stopper  c.  On  shaking  the  gas  with  the  water  and  bromine,  the 
latter  will  absorb  the  illuminating  hydrocarbons  ;  and  if  the  tube  be  again  opened 
under  water,  the  volume  of  the  gas  in  a  will  be  found  to  have  diminished,  and  the 
diminution  gives  an  approximate  estimate  of  the  olefiant  gas  and  other  illuminating 
hydrocarbons. 

A  very  instructive  experiment  consists  in  filling  a  three-pint  cylinder  one-third 
full  of  olefiant  gas,  then  rapidly  filling  it  up,  under  water,  with  two  pints  of 
chlorine,  closing  its  mouth  with  a  glass  plate,  shaking  it  to  mix  the  gases,  slipping 
the  plate  aside  and  applying  a  light,  when  the  mixture  burns  with  a  red  flame 
which  passes  gradually  down  the  cylinder,  and  is  due  to  the  combination  of  the 
hydrogen  with  the  chlorine,  the  whole  of  the  carbon  being  separated  in  the  solid 
state— C2H4  +  C14  =  4HC1  +  C.2. 

When  olefiant  gas  is  subjected  to  the  action  of  high  temperatures,  as 


Fig.  116. 


Fig.  n7. 


I44 


MARSH   GAS. 


by  passing  through  heated  tubes,  one  portion  is  decomposed  into  marsh 
gas  (CH4)  with  separation  of  carbon,  acetylene  (C2H9)  and  hydrogen 
being  also  produced ;  this  decomposition  will  be  found"  to  be  of  great 
importance  in  the  manufacture  of  coal  gas. 

The  action  of  heat  upon  olefiant  gas  is  most  conveniently  shown  by  exposing  it 
to  the  spark  from  an  induction-coil  in  the  apparatus  shown  in  Fig.  67. 

The  carbon  separated  during  the  sparking  sometimes  forms  a  conducting  com- 
munication, and  allows  the  current  to  pass  without  a  spark.  This  may  be  obviated 
by  reversing  the  current,  or  by  gently  shaking  the  tube. 

The  olefiant  gas  wTill  expand  to  nearly  twice  its  former  volume. 
To  show  the  production  of  acetylene,  another  arrangement  may  be  found  con- 
venient (Fig.  118).     A  globe  with  four  necks  is  employed;  through  two  of  these 
necks  are  passed,  airtight  with  perforated  corks,  the  copper  wires  connected  with 
the  induction-coil.     A  third  neck  receives  a  tube,  conveying  olefiant  gas  from  a 
gas-holder,  whilst  from  the  fourth  proceeds  a  tube  dipping 
to  the  bottom  of  a  small  cylinder.   When  the  whole  of  the 
air  has  been  displaced  by  olefiant  gas,  a  solution  of  cuprous 
chloride  in  ammonia  is  poured  into  the  cylinder,  and  the 
gas  allowed  to  bubble  through  it,  when  the  absence  of 
acetylene  will  be  shown  by  there  being  no  red  compound 
formed.    As  soon,  however,  as  the  spark  is  passed,  the  red 
precipitate  will  appear,  and  in  a  very  few  minutes  a  large 
quantity  will  be  deposited.     Coal  'gas  may  be  employed 
instead  of  olefiant  gas,  but  of  course  a  smaller  quantity  of 
the  copper  compound  will  be  obtained. 


89.  Marsh,  gas,  methane,  or  light  carburetted 
hydrogen  (CH4=i6  parts  by  weight).  Thi-<  hy- 
drocarbon is  found  in  nature,  being  produced 
wherever  vegetable  matter  is  undergoing  decom- 
position in  the  presence  of  moisture.  The 
bubbles  rising  from  stagnant  pools,  when  col- 
lected and  examined,  are  found  to  contain  marsh 
gas  mixed  with  carbonic  acid  gas,  and  there  is 
reason  to  believe  that  these  two  gllses  represent 

olefl:int  gas.  the  principal  forms  in  which  the  hydrogen  and 

oxygen  respectively  were   separated  from    wood 

during  the  process  of  irs  conversion  into  coal.  This  would  account  for 
the  constant  presence  of  marsh  gas  in  the  coal  formations,  where  it  is 
usually  termed  fire-damp.  It  is  occasionally  found  pent  up  under- 
pressure between  the  layers  of  coal,  and  the  pores  of  the  latter  are 
sometimes  so  full  of  it  that  it  may  be  seen  rising  in  bubbles  when  the 
freshly  hewn  coal  is  thrown  into  water.  Perhaps  a  similar  origin  is  to 
be  ascribed  to  the  liquid  hydrocarbons  chemically  similar  to  marsh  gas, 
which  are  found  so  abundantly  in  Pennsylvania  and  Canada,  and  are 
known  by  the  general  name  of  petroleum.  From  certain  gas-springs 
in  Pennsylvania,  marsh  gas.  olefiant  gas,  and  ethane,  C2H6,  are  dis- 
charged at  very  high  pressure,  and  are  employed  for  heating  and  lighting. 

Marsh  gas  is  obtained  artificially  by  the  folloAring  process  : 

35  grams  of  dried  sodium  acetate  are  finely  powdered  and  mixed,  in  a  mortar, 
with  35  grams  of  the  mixture  of  calcium  hydroxide  and  sodium  hydroxide,  which 
is  sold  as  soda-lime.     The  mixture  is  heated  in  a  Florence  flask  (or  better  a  copper 
tube,  for  the  alkali  corrodes  the  glass)  and  the  gas  collected  over  water. 
The  decomposition  will  be  evident  from  the  following  equation  : — 

NaC2H302         +         NaOH         =         Na.2C03         +         CH4. 
Sodium  acetate.  Caustic  sodi.  Sodium  carbonate. 

The  marsh  gas  will  be  easily  recognised  by  its  burning  with  a  pale  illuminating 


EXPLOSIONS   OF  FIRE-DAMP.  145; 

flame,  far  inferior  in  brilliancy  to  those  of  olefiant  gas  and  acetylene,  but  unattended 
with  smoke.* 

By  heating  a  mixture  of  alumina  and  carbon  in  the  electric  furnace,  aluminium 
carbide,  A14C3,  is  obtained.  This  is  decomposed  by  water  yielding  methane  just  as 
calcium  carbide  yields  acetylene-- -A14C3  +  I2H20  =  3CH4  +  4A1(OH)3  (aluminium 
hydroxide). 

The  properties  of  this  gas  deserve  a  careful  study,  on  account  of  the 
frequent  fatal  explosions  to  which  it  gives  rise  in  coal-mines,  where  it  is 
often  found  accumulated  under  pressure,  and  discharging  itself  with 
considerable  force  from  the  fissures  or  blowers  made  in  hewing  the  coal. 
March  gas  has  no  characteristic  smell  like  that  of  coal  gas,  and  the  miner 
thence  receives  no  timely  warning  of  its  presence ;  it  is  much  lighter 
than  air  (sp.  gr.  0.5596),  and  therefore  very  readily  diffuses  itself 
(page  25)  through  the  air  of  the  mine,  with  which  it  forms  an  explosive 
mixture  as  soon  as  it  amounts  to  one-fourteenth  of  the  volume  of  the 
air.  The  gas  issuing  from  the  blower  would  burn  quietly  on  the 
application  of  a  light,  since  the  marsh  gas  is  not  explosive  unless  mixed 
with  the  air,  when  a  large  volume  ot  the  gas  is  burnt  in  an  instant, 
causing  a  sudden  evolution  of  a  great  deal  of  heat,  and  a  consequent 
sudden  expansion  or  explosion  exerting  great  mechanical  force.  The 
most  violent  explosion  occurs  when  i  volume  of  marsh  gas  is  mixed 
with  2  volumes  of  oxygen,  since  this  quantity  is  exactly  sufficient  to 
effect  the  complete  combustion  of  the  carbon  and  hydrogen  of  the 
gas,  and  therefore  to  evolve  the  greatest  amount  of  heat :  CH4  +  04  = 
CO2  +  2H20.  The  calculated  pressure  exerted  by  the  exploding  mixture 
of  marsh  gas  and  oxygen  amounts  to  37  atmospheres,  or  555  Ibs.  upon 
the  square  inch.  Since  air  contains  one-fifth  of  its  volume  of  oxygen f 
it  would  be  necessary  to  employ  10  volumes  of  air  to  i  volume  of  marsh 
gas  in  order  to  obtain  perfect  combustion,  but  the  explosion  will  be 
much  less  violent  on  account  of  the  presence  of  the  8  volumes  of  inert 
nitrogen,  the  calculated  pressure  exerted  by  the  explosion  being  only 
14  atmospheres,  or  210  Ibs.  on  the  square  inch.  Of  course,  if  more  air 
be  employed,  the  explosion  will  be  proportionally  weaker,  until,  when 
there  are  more  than  14  volumes  of  air  to  each  volume  of  marsh  gas,  the 
mixture  will  be  no  longer  explosive,  but  will  burn  with  a  pale  flame 
around  a  taper  immersed  in  it.  The  severity  of  the  explosion  of  a 
gaseous  mixture  depends  on  the  rate  at  which  the  chemical  combination 
proceeds  throughout  the  mixture.  If,  on  a  certain  number  of  particles- 
combining,  the  heat  evolved  has  to  be  shared  between  the  neighbouring 
combustible  particles  and  a  number  of  inert  particles  the  temperature 
of  the  former  may  not  rise  to  the  ignition  point,  whereupon  propagation 
of  the  combination  ceases.  It  must  be  remembered  that  an  excess  of 
either  of  the  reacting  gases  also  serves  as  an  inert  gas.  Hence  in  every 
explosive  mixture  there  is  an  upper  limit  and  a  lower  limit  to  the  propor- 
tion of  the  constituents,  and  it  is  only  between  these  limits  that  explosion 
occurs.  In  the  case  of  methane  and  air  the  explosion  only  occurs  if 
the  methane  is  mixed  with  between  6  and  14  times  its  volume  of  air. 
The  carbonic  acid  gas  resulting  from  the  explosion  is  called  by  miners 
the  after-damp,  and  its  effects  are  generally  fatal  to  those  who  may  have 
escaped  death  from  the  explosion  itself. 

Coal  gas,  which  contains  much  hydrogen,  requires  a  smaller  volume 

*  The  gas  prepared  by  the  above  process  contains  acetone,  which  increases  its  luminosity. 
For  the  preparation  of  pure  marsh  gas,  see  Organic  Chemistry. 

K 


146 


DAVY'S   SAFETY  LAMP. 


of  air  than  does  marsh  gas  to  render  it  explosive.  With  i6-candle  gas, 
such  as  is  used  in  London,  6  volumes  of  air  to  i  volume  of  gas  would 
give  the  most  powerful  explosion,  and  the  limits  are  about  3.5  and 
14  volumes  of  air. 

Fortunately,  marsh  gas  requires  a  much  higher  temperature  to  in- 
flame it  than  most  other  inflammable  gases  ;  a  solid  body  at  an  ordinary 
red  heat  does  not  kindle  the  gas  unless  kept  in  contact  with  it  for  a 
•considerable  period ;  contact  with  flame,  or  with  a  body  heated  to  white- 
ness, being  required  to  ignite  it  instantaneously. 

If  two  strong  gas  cylinders  be  filled,  respectively,  with  mixtures  of  2  volumes 
hydrogen  and  I  volume  oxygen,  and  of  I  volume  marsh  gas  and  2  volumes  oxygen, 
it  will  be  found,  on  holding  them  with  their  mouths  downwards,  and  inserting  a 
red-hot  iron  bar  that  the  marsh  gas  mixture  will  not  explode,  but  if  the  bar  be 
transferred  at  once  to  the  hydrogen  mixture  there  will  be  an  explosion.  A  lighted 
taper  may  then  be  used  to  explode  the  marsh  gas  and  oxygen. 

In  consequence  of  the  high  temperature  required  to  inflame  the  mixture  of  marsh 
gas  and  air,  it  is  necessary  that  the  mixture  be  allowed  to  remain  for  an  appreciable 
time  in  contact  with  the  flame  before  its  particles  are  raised  to  the  igniting-point. 
It  was  on  this  principle  that  Stephenson's  original  safety-lamp  was  constructed,  the 
flame  being  surrounded  with  a  tall  glass  chimney,  the  rapid  draught  through  which 
caused  the  explosive  mixture  to  be  hurried  past  the  flame  without  igniting. 

To  illustrate  this,  a  copper  funnel  holding  about  two  quarts  is  employed,  the 
neck  of  which  has  an  opening  of  about  ^  inch  in  diameter.  The  funnel  being 

placed   mouth    downwards 

\  in  the    pneumatic    trough, 

the  orifice  is  closed  with  the 
finger,  and  a  half-pint  of 
coal  gas  passed  up  into  the 
funnel.  The  latter  is  now 
raised  from  the  water,  so 
that  it  may  become  entirely 
filled  with  air.  By  depress- 
ing the  funnel  to  a  consider- 
able depth  in  the  water,  the 
aperture  being  still  closed 
by  the  finger,  the  mixture 
will  be  confined  under  con- 
siderable pressure,  and  if  a 
lighted  taper  be  held  to  the 
aperture,  and  the  finger 
Fig.  119.  removed,  it  will  be  found 

that    the    mixture    sweeps 

past  the  flame  without  exploding,  until  the  water  has  reached  the  same  level  in 
the  funnel  as  in  the  trough,  when  the  gas  comes  to  rest  and  explodes  with  great 
violence. 

Davy's  safety  lamp  (Fig.  120)  is  an  application  of  the  principle  that 
ignited  gas  (flame)  is  extinguished  by  contact  with  a  large  surface  of 
a  good  conductor  of  heat,  such  as  copper  or  iron. 

If  a  thin  copper  wire  be  coiled  round  into  a  helix,  and  carefully  placed  over  the 
wick  of  a  burning  taper  (Fig.  121),  the  flame  will  be  at  once  extinguished,  its  heat 
being  so  rapidly  transmitted  along  the  wire  that  the  temperature  falls  below  the 
point  at  which  the  combustible  gases  enter  into  combination  with  oxygen,  and 
therefore  the  combustion  ceases.  If  the  coil  be  heated  to  redness  in  a  spirit-lamp 
flame  before  being  placed  over  the  wick,  it  will  not  abstract  the  heat  so  readily, 
and  will  not  extinguish  the  flame.  If  a  copper  tube  were  substituted  for  the  coiled 
wire,  the  same  result  would  be  obtained,  and  by  employing  a  number  of  tubes  of 
very  small  diameter,  so  that  the  metallic  surface  may  be  very  large  in  proportion  to 
the  volume  of  ignited  gas,  the  most  energetic  combustion  may  be  arrested,  a  fact  of 
which  advantage  is  taken  in  the  oxy-hydrogen  blow-pipe  (p.  48).  It  is  evident  that 
the  exposure  of  a  large  extent  of  cooling  surface  to  the  action  of  the  flame  may  be 


DAVY'S   SAFETY  LAMP. 


effected  either  by  increasing  the  length  or  by  diminishing  the  width  of  the  metallic 
tubes,  so  that  wire  gauze,  which  may  be  regarded  as  a  collection  of  very  short  tubes, 
will  form  an  effectual  barrier  to  flame,  provided  that  it  has  a  sufficient  number  of 
meshes  to  the  inch. 

If  a  piece  of  iron  wire  gauze,  containing  about  400  meshes  to  the  square  inch, 
be  depressed  upon  a  flame,  it  will  extinguish  that  portion  with  which  it  is  in 
contact,  and  the  combustible  gas  which  escapes  through  the  gauze  may  be  kindled 
by  a  lighted  match  held  on  the  upper  side.  By  holding  the  gauze  2  or  3  inches 


Fig.  120. 


Fig.  121. 


Fig.  122. 


above  a  gas  jet,  the  gas  may  be  lighted  above  it  without  communicating  the  flame 
to  the  burner  itself. 

When  blazing  spirit  is  poured  upon  a  piece  of  wire  gauze  (Fig.  122),  the  flame 
will  remain  upon  the  gauze,  and  the  extinguished  spirit  will  pass  through.  A  little 
benzene  or  turpentine  may  be  added  to  the  spirit,  so  that  its  flame  may  be  more 
visible  at  a  distance. 

The  safety  lamp  (Fig.  120)  is  an  oil  lamp,  the  flame  of  which  is  sur- 
rounded by  a  cage  of  iron  wire  gauze,  having  700  or  800  meshes  in  the 
square  inch,  and  made  double  at  the  top,  where  the  heat  of  the  flame 
chiefly  plays.  This  cage  is  protected  by  stout  iron  wires  attached  to  a 
ring  for  suspending  the  lamp.  A  brass  tube  passes  up  through  the  oil 
reservoir,  and  in  this  there  slides,  with  con- 
siderable friction,  a  wire  bent  at  the  top,  so  that 
the  wick  may  be  trimmed  without  taking  off  the 
cage.  The  lower  part  of  the  cage  is  now  made 
of  glass,  to  afford  more  light. 

If  this  lamp  be  suspended  in  a  large  jar,  closed  at  the 
top  with  a  perforated  wooden  cover  A  (Fig.  123),  and 
having  an  aperture  (B)  below,  through  which  coal  gas  is 
allowed  to  pass  slowly  into  the  jar,  the  flame  will  be  seen 
to  waver,  to  elongate  very  considerably,  and  to  be  ulti- 
mately extinguished,  when  the  wire  cage  will  be  filled 
with  a  mixture  of  coal  gas  and  air  burning  tranquilly 
within  the  gauze,  which  prevents  the  flame  from  passing 
to  ignite  the  explosive  atmosphere  surrounding  the 
lamp  ;  that  an  explosive  mixture  really  fills  the  jar  may 
be  readily  ascertained  by  introducing  through  an  aper- 
ture (C)  in  the  cover,  the  unprotected  flame  of  a  taper,  when  an  explosion  will 
occur. 

This  experiment  illustrates  the  action  of  the  Davy  lamp  in  a  mine  which  contains 
fire-damp.  It  would  obviously  be  unsafe  to  allow  the  lamp  to  remain  in  the 
explosive  mixture  when  the  cage  is  filled  with  flame,  for  the  gauze  would  either 
become  sufficiently  heated  to  kindle  the  surrounding  gas,  or  would  be  oxidised  and 
eaten  into  holes,  which  would  allow  the  passage  of  the  flame.  Nor  should  the 
lamp  be  exposed  to  a  very  strong  draught,  which  might  possibly  be  able  to  carry 
the  flame  through  the  meshes. 

When  the  Davy  lamp  is  brought  into  an  atmosphere  containing  fire-damp,  a 
"  cap  "  of  blue  flame  is  observed  to  play  above  the  tip  of  the  illuminating  flame. 


148  COAL-MINE  EXPLOSIONS. 

This  incipient  combustion  is  more  marked  when  a  hydrogen  flame  is  substituted 
for  an  oil  flame,  and  the  height  of  the  cap  furnishes  an  indication  of  the  quantity 
of  fire-damp  present.  Such  a  modified  Davy  lamp  becomes  a  fire-damp  indicator, 
showing  as  little  as  0.25  per  cent. 

All  coal  contains  a  considerable  quantity  of  gas  occluded  or  condensed  in  its 
pores,  part  of  which  issues  when  the  surface  of  the  coal  is  exposed,  and  part 
is  retained,  and  can  be  extracted  by  exposure  in  vacuo  and  moderately  heating. 
Bituminous  coals  evolve  more  C02  and  N,  and  less  CH4,  than  anthracite  does, 
hence  these  coals  may  often  be  worked  with  naked  lights,  while  seams  of  steam 
coal  and  anthracite  are  dangerous.  Cannel  coal  has  occluded,  beside  the  above 
gases,  some  ethane,  C2H6,  and  Whitby  jet  has  been  found  to  contain  butane,  C4H10. 
The  gas  from  blowers  sometimes  contains  97  per  cent,  by  volume  of  marsh  gas,  with 
a  little  C02  and  N. 

"Whenever  naked  flames  are  used  in  the  mine,  there  must  always  be 
great  risk ;  in  most  seams  of  coal  there  are  considerable  accumulations 
of  fire-damp  ;  when  a  fissure  is  made,  the  gas  escapes  very  rapidly  from 
the  llower,  and  the  air  in  its  vicinity  may  soon  become  converted  into 
an  explosive  mixture.  In  mines  where  small  quantities  of  fire-damp 
are  known  to  be  continually  escaping  from  the  coal,  ventilation  is 
depended  upon  in  order  to  dilute  the  gas  with  so  large  a  volume  of  air 
that  it  is  no  longer  explosive,  and  finally  to  sweep  it  out  of  the  mine  ; 
but  it  has  occasionally  happened  that  the  ventilation  has  been  interfered 
with  by  a  door  having  been  left  open  in  one  of  the  galleries,  or  by  a 
passage  having  been  obstructed  through  the  accidental  falling  in  of  a 
portion  of  the  coal,  and  an  explosive  mixture  has  then  been  formed. 

The  presence  of  fine  dust  of  coal  in  the  air  of  the  mine  greatly 
increases  the  liability  to  explosion ;  indeed,  there  is  no  doubt  that  in 
some  cases  the  dust  has  been  the  sole  cause  of  the  explosion.  Most 
combustible  substances  mixed  in  a  finely  divided  state  with  air,  burn 
so  rapidly  as  to  produce  effects  of  explosion.  Flour  mills  have  been 
destroyed  from  this  cause  in  very  dry  weather. 

If  some  lycopodlum,  the  seed  of  the  club-moss,  sometimes  called  vegetable  brimstone, 
be  placed  in  a  glass  funnel,  the  stem  of  which  has  been  lightly  stopped  with  wool, 
and  has  two  or  three  feet  of  wide  vulcanised  tubing  attached  to  it,  the  lycopodium 
may  be  blown  out  in  a  cloud  by  a  sudden  puff  of  air,  and  if  a  lighted  taper  be  held 
in  the  cloud,  an  immense  volume  of  flame  may  be  formed. 

Explosions  in  dusty  mines  are  more  common  when  gunpowder  is  used  for  blasting 
than  when  the  modern  nitro-powders  are  used.  This  has  been  attributed  to  the 
considerable  quantity  of  CO  which  occurs  among  the  products  of  explosion  of 
blasting  gunpowder.  This,  or  any  other  inflammable  gas,  serves  to  start  the 
explosion  of  the  dusty  air. 

An  ingenious  fire-damp  indicator  has  been  constructed  of  two  platinum  wires, 
which  are  heated  by  a  magneto-electric  current.  One  wire! is  sheltered  from  the 
fire-damp,  and  the  other,  being  exposed  to  it,  glows  more  strongly  on  account  of 
the  slow  combustion  of  the  fire-damp  at  the  surface  of  the  platinum  (see  Platinum*). 
By  a  careful  comparison  of  the  two  wires,  it  is  said  that  0.25  per  cent,  of  marsh 
gas  in  air  may  be  detected,  whilst  the  Davy  lamp  will  not  indicate  less  than 
2  per  cent. 

STRUCTURE  OF  FLAME. 

90.  The  consideration  of  the  structure  and  properties  of  ordinary 
flames  is  necessarily  connected  with  the  history  of  olefiant  gas  and 
marsh  gas.  Flame  may  be  defined  as  gaseous  matter  heated  to  the 
temperature  at  which  it  becomes  visible,  or  emits  light.  Solid  particles 
begin,  for  the  most  part,  to  emit  light  when  heated  to  about  500°  C.  ; 
but  gases,  on  account  of  their  lower  radiating  power,  must  be  raised  to 
a  far  higher  temperature,  and  hence  the  point  of  visibility  is  seldom 


NATURE   OF  FLAME.  149 

attained,  except  by  gases  which  are  themselves  combustible,  and  there- 
fore capable  of  producing,  by  their  own  combination  with  atmospheric 
oxygen,  the  requisite  degree  of  heat.  The  presence  of  a  combustible  gas 
(or  vapour),  therefore,  is  one  of  the  conditions  of  the  existence  of  flame  ; 
a  diamond,  or  a  piece  of  thoroughly  carbonised  charcoal,  will  burn  in 
oxygen  with  a  steady  glow,  but  without  flame,  since  the  carbon  is  not 
capable  of  conversion  into  vapour,  while  sulphur  burns  with  a  voluminous 
flame,  in  consequence  of  the  facility  with  which  it  assumes  the  vaporous 
condition.  It  will  be  observed,  moreover,  that  in  the  case  of  a  non- 
volatile combustible,  the  combination  with  oxygen  is  confined  to  the 
surface  of  contact,  whilst  in  the  flame  of  a  gas  or  vapour  the  combustion 
extends  to  a  considerable  depth,  the  oxygen  intermingling  with  the 
gaseous  fuel. 

Flames  ma}''  be  conveniently  spoken  of  as  simple  or  compound,  accord- 
ingly as  they  involve  one  or  more  phenomena  of  combustion ;  thus,  for 
example,  the  flames  of  hydrogen  and  carbonic  oxide  are  simple,  whilst 
those  of  marsh  gas,  olefiant  gas,  and  hydrocarbons  generally,  are  com- 
pound, since  they  involve  both  the  conversion  of  hydrogen  into  water 
and  of  carbon  into  carbon  dioxide. 

It  is  obvious  that  simple  flames  must  be  hollow  in  ordinary  cases, 
such  as  that  of  a  gas  issuing  from  a  tube  into  the  air,  the  hollow  being 
occupied  by  the  combustible  gas  to  which  the  oxygen  does  not  pene- 
trate. 

All  the  flames  which  are  ordinarily  turned  to  useful  account  are  com- 
pound flames,  and  involve  several  distinct  phenomena.  Before  examin- 
ing these  more  particularly,  it  will  be  advantageous  to  point  out  the 
conditions  which  regulate  the  luminosity  of  flames. 

In  order  that  a  flame  may  emit  a  brilliant  light,  it  is  essential  that  it 
should  containi  particles  which,  either  from  their  own  nature  or  from 
the  conditions  Wilder  which  they  are  placed,  do  not  admit  of  very  much 
expansion  by  the  heat  of  the  flame,  but  are  capable  of  being  heated  to 
incandescence.  Thus  the  flame  of  the  oxyhydrogen  blowpipe  (p.  48) 
emits  a  very  pale  light,  but  if  the  mixture  of  oxygen  and  hydrogen  be 
restrained  from  expanding  when  fired,  as  in  the  Cavendish  eudiometer, 
it  gives  a  bright  flash  ;  or  if  the  flame  be  directed  upon  some  solid  body 
little  affected  by  the  heat,  such  as  lime,  the  light  is  very  intense. 

Phosphorus  and  arsenic  burn  with  very  luminous  flames,  in  con- 
sequence of  the  formation  of  very  dense  vapours  of  phosphoric  and 
arsenious  oxides  during  the  combustion  ;  the  density  of  the  vapours 
being  here  attended  with  the  same  result  as  that  produced  by  the 
restrained  expansion  of  the  steam  formed  in  the  Cavendish  eudiometer. 

It  is  not  necessary  that  the  incandescent  matter  should  be  a  product 
of  the  combustion  ;  any  extraneous  solid  in  a  finely  divided  state  will 
confer  illuminating  power  upon  a  flame.  Thus,  the  flame  of  hydrogen 
may  be  rendered  highly  luminous  by  blowing  a  little  very  fine  charcoal 
powder  into  it. 

The  luminosity  of  all  ordinary  flames  is  due  to  the  presence  of  highly 
heated  carbon  in  a  state  of  very  minute  division,  and  it  remains  to  con- 
sider the  changes  by  which  this  finely  divided  carbon  is  separated  in  the 
flame. 

A  candle,  a  lamp,  and  a  gas-burner  exhibit  contrivances  for  procuring 
light  artificially  in  different  degrees  of  complexity,  the  candle  being  the 


150  ILLUMINATING  FLAMES. 

most  complex  of  the  three.  When  a  new  candle  is  lighted,  the  first 
portion  of  the  wick  is  burnt  away  until  the  heat  reaches  that  part 
which  is  saturated  with  the  wax  or  tallow  of  which  the  candle  is  com- 
posed ;  this  wax  or  tallow  then  undergoes  destructive  distillation,  yield- 
ing a  variety  of  products,  among  which  olefiant  gas  is  found  in  abund- 
ance. The  flame  furnished  by  the  combustion  of  these  products  melts 
the  fuel  around  the  base  of  the  wick,  through  which  it  then  mounts  by 
capillary  attraction,  to  be  decomposed  in  its  turn,  and  to  furnish  fresh 
gases  for  the  maintenance  of  the  flame.  In  a  lamp,  the  fuel  being 
liquid  at  the  commencement,  the  process  of  fusion  is  dispensed  with ; 
and  in  a  gas-burner,  where  the  fuel  is  supplied  in  a  gaseous  form,  the 
process  of  destructive  distillation  has  been  already  effected  at  a  distance. 
It  will  be  seen,  however,  that  the  final  result  is  similar  in  all  three 
cases,  the  flame  being  maintained  by  such  gases  as  hydrogen,  acetylene, 
marsh  gas,  and  olefiant  gas  arising  from  the  destructive  distillation  of 
wax,  tallow,  oil,  coal,  &c. 

The  shape  of  the  candle  flame  is  common  to  all  flames  which  consist 
of  gas  issuing  from  a  small  circular  jet,  like  the  wick  of  the  candle. 
The  gas  issues  from  the  jet  in  the  form  of  a  cylinder,  which,  however, 
immediately  becomes  a  diverging  cone  by  diffusing  into  the  surrounding 
air.  When  this  cone  is  kindled,  the  margin  of  it,  where  intermixture 
with  the  surrounding  air  is  most  complete,  will  be  perfectly  burnt,  but 
the  gases  in  the  interior  of  the  diverging  cone  cannot  burn  until  they 
have  ascended  sufficiently  to  meet  with  fresh  air  ;  since  these  unburnt 
gases  are  continually  diminishing  in  quantity,  the  successive  circles  of 

combustion  must  diminish  in  diameter 
and  the  conical  shape  is  the  only  possible 
form. 

On  examining  an  ordinary  flame — 
that  of  a  candle,  for  instance — it  is 
seen  to  consist  of  three  concentric 


Fig.  124.  Fig.  125. 

cones  (Fig.  124),  the  innermost,  around  the  wick,  appearing  almost  black, 
the  next  emitting  a  bright  white  light,  and  the  outermost  being  so  pale 
as  to  be  scarcely  visible  in  broad  daylight.  There  is  also  apparent  a 
bright  blue  cup  surrounding  the  base  of  the  flame. 

The  dark  innermost  cone  consists  merely  of  the  gaseous  combustible 
to  which  the  air  does  not  penetrate,  and  which  therefore  is  not  in  a 
state  of  combustion. 


STRUCTURE   OF  A  CANDLE  FLAME.  151 

The  nature  of  this  cone  is  easily  shown  .by  experiment :  a  strip  of  cardboard  held 
across  the  flame  near  its  base  will  not  burn  in  the  centre  where  it  traverses  the 
innermost  cone  ;  a  piece  of  wire  gauze  depressed  upon  the  flame  near  the  wick 
(Fig.  125)  will  allow  the  passage  of  the  combustible  gas,  which  may  be  kindled 
above  it.  The  gas  may  be  conveyed  out  of  the  flame  by  means  of  a  glass  tube, 
inserted  into  the  innermost  cone,  and  may  be  kindled  at  the  other  extremity  of  the 
tube,  which  should  be  inclined  downwards  (Fig.  126). 

A  piece  of  phosphorus  in  a  small  spoon  held  in  the  interior  of  the  flame  of  a 
spirit-lamp  will  melt  and  boil,  but  will  not  burn  unless  it  be  removed  from  the 
flame,  and  may  then  be  extinguished  by  replacing  it  in  the  flame. 


Fig.  126. 


Fig.  127. 


The  combustible  gas  from  the  interior  of  a  flame  may  be  collected  in  a  flask 
(Fig.  1 27)  furnished  with  two  tubes,  one  of  which  (A)  is  drawn  out  to  a  point  for 
insertion  into  the  flame,  whilst  the  other  (B),  which  passes  to  the  bottom  of  the 
flask,  is  bent  over  and  prolonged  by  a  piece  of  vulcanised  tubing  so  that  it  may 
act  as  a  siphon.  The  flask  is  filled  up  with  water,  the  jet  inserted  into  the  interior 
of  a  flame,  and  the  siphon  set  running  by  exhausting  it  with  the  mouth.  As  the 
water  flows  out  through  the  siphon,  the  gas  is  drawn  into  the  flask,  and  after 
removing  the  tube  from  the  flame,  the  gas  may  be  expelled  by  blowing  down  the 
siphon  tube,  and  may  be  burnt  at  the  jet.  When  a  candle  is  used  for  this  experi- 
ment, some  solid  products  of  destructive  distillation  will  be  found  condensed  in 
the  flask. 

In  the  second  or  luminous  cone,  combustion  is  proceeding,  but  it 
is  by  no  means  perfect,  being  attended  by  the  separation  of  a  quantity 
of  carbon,  which  confers  luminosity  upon  this  part  of  the  flame.  The 
presence  of  free  carbon  is  shown  by  depressing  a  piece  of  porcelain 
upon  this  cone,  when  a  black  film  of  soot  is  deposited.  The  liberation 
of  the  carbon  is  due  to  the  decomposition  of  the  hydrocarbons  by  the 
heat,  which  separates  the  carbon  from  the  hydrogen,*  and  this  latter 
undergoing  combustion  evolves  sufficient  heat  to  raise  the  separated 
carbon  to  a  white  heat,  the  supply  of  air  which  penetrates  into  this 
portion  of  the  flame  being  insufficient  to  effect  the  combustion  of  the 
whole  of  the  carbon. 

According  to  Lewes  the  temperature  of  the  innermost  cone  of  a  hydrocarbon 
flame  rises  to  about  1000°  C.  near  the  apex  of  the  cone.  This  temperature  is 
sufficiently  high  to  decompose  the  heavier  hydrocarbons  into  acetylene.  This 
acetylene  is  decomposed,  with  liberation  of  carbon,  in  the  luminous  cone  where 
the  temperature  rises  to  1300°  C.,  owing  to  the  combustion  of  the  carbon  monoxide 
and  hydrogen,  the  former  produced  by  the  imperfect  oxidation,  and  the  latter  by 
the  decomposition,  of  the  hydrocarbons  in  the  innermost  cone. 

Some  very  simple  experiments  will  illustrate  the  nature  of  the  luminous  portion 
of  flame. 

*  The  action  of  heat  011  hydrocarbons  is  to  break  them  down,  or  "crack"  them,  into  such 
as  contain  a  higher  percentage  of  carbon;  these,  in  their  turn,  are  decomposed  with  liberation 
of  carbon  at  very  high  temperatures. 


EXPERIMENTS   ON  FLAME. 


Over  an  ordinary  candle  flame  (Fig.  128)  a  tube  may  be  adjusted  so  as  to  convey 
the  finely  divided  carbon  from  the  luminous  part  of  the  flame  into  the  flame  of 
hydrogen,  which  will  thus  be  rendered  as  luminous  as  the  candle  flame,  the  dark 
colour  of  the  carbon  being  apparent  in  its  passage  through  the  tube. 

One  of  the  limbs  of  the  U  tube  (Fig.  129)  contains  a  tuft  of  cotton  wool  b.  On 
kindling  the  hydrogen  supplied  through  c  at  the  orifice  of  each  tube,  no  difference 
will  be  seen  in  the  flames  until  a  drop  of  benzene  (C6H6)  is  placed  upon  the 
cotton,  when  its  vapour,  mingling  with  the  hydrogen,  will  furnish  enough  carbon 
to  render  the  flame  brilliantly  luminous. 

The  pale  outermost  cone,  or  mantle,  of  the  flame,  in  which  the 
separated  carbon  is  finally  consumed,  may  be  termed  the  cone  of  perfect 
combustion,  and  is  much  thinner  than  the  luminous  cone,  the  supply  of 
air  to  this  external  shell  of  flame  being  unlimited,  and  the  combustion 
therefore  speedily  effected. 

The  bright  blue  cup  surrounding  the  base  of  the  flame  is  formed  by 
the  perfect  combustion  (without  any  separation  of  carbon)  of  a  small 


128. 


Fig.  129. 


Fig,  130. — Air  burning  in 
coal  gas. 


portion  of  the  hydrocarbons  owing  to  the  complete  admixture  of  air  at 
this  point. 

The  mantle  of  the  flame  may  be  rendered  more  visible  by  burning  a  little  sodium 
near  the  flame,  when  the  mantle  is  tinged  strongly  yellow. 

According  to  another  view,  based  on  the  observation  that  acetylene — a  constant 
product  of  checked  combustion — can  be  discovered  in  the  products  of  the  combus- 
tion of  a  hydrocarbon  flame  burning  under  ordinary  conditions,  the  mantle  is  a  thin 
layer  of  the  flame  rendered  non-luminous  by  admixture  with  the  surrounding  air, 
the  cooling  effect  of  which  gradually  quenches  the  combustion. 

By  means  of  a  siphon  about  one-third  of  an  inch  in  diameter,  the  nature  of  the 
different  portions  of  an  ordinary  candle  flame  may  be  very  elegantly  shown.  If  the 
orifice  of  the  siphon  be  brought  just  over  the  extremity  of  the  wick,  the  combus- 
tible gases  and  vapours  will  pass  through  it,  and  may  be  collected  in  a  small  flask, 
where  they  can  be  kindled  by  a  taper.  On  raising  the  orifice  into  the  luminous 
portion  of  the  flame,  voluminous  clouds  of  black  smoke  will  pour  over  into  the 
flask,  and  if  the  siphon  be  now  raised  a  little  above  the  point  of  the  flame,  carbonic 
acid  gas  can  be  collected  in  the  flask,  and  may  be  recognised  by  shaking  with  lime- 
water. 

The  reciprocal  nature  of  the  relation  between  the  combustible  gas  and  the  air 


GAS  BUENEES.  153 

which  supports  its  combustion  may  be  illustrated  in  a  striking  manner  by  burning  a 
jet  of  air  in  an  atmosphere  of  coal  gas. 

A  quart  glass  globe  with  three  necks  is  connected  at  A  (Fig.  130)  with  thegaspipe 
by  a  vulcanised  tube.  The  second  neck  (B),  at  the  upper  part  of  the  globe,  is  con- 
nected by  a  short  piece  of  vulcanised  tube  with  a  piece  of  glass  tube  about  \  inch 
wide,  from  which  the  gas  may  be  burnt.  Into  the  third  and  lowermost  neck  is 
inserted,  by  means  of  a  cork,  a  thin  brass  tube  C  (an  old  cork-borer),  about  \  inch 
in  diameter.  When  the  gas  is  turned  on,  it  may  be  lighted  at  the  upper  neck  ;  and 
if  a  lighted  match  be  then  quickly  thrust  up  the  tube  C,  the  air  which  enters  it  will 
take  tire,  and  burn  inside  the  globe. 

A  simple  experiment  to  show  the  burning  of  gas  in  air  may  be  made  with  an 
Argand  burner  (Fig.  131).  The  flame  having  been  turned  low,  a  dish  (or  dial-glass 
containing  water  to  prevent  cracking)  is  placed  so  as  to  close  the  top  of  the  chimney, 
when  the  gas  flame  will  be  extinguished,  and  the  air  which  enters  the  inner  circle 
will  burn  with  a  pale  flame,  which  may  be  made  more  visible  by  thrusting  up  a 
copper  wire  dipped  in  hydrochloric  acid.  A  bottomless  beaker  makes  a  good 
chimney  for  this  purpose. 

An  interesting  confirmation  of  the  above  views  as  to  the  structure  of  an  illumi- 
nating flame  is  furnished  by  observing  what  occurs  when  the  rate  at  which  the 
gaseous  combustible  is  supplied  to  the  flame  is  very  gradually  increased,  either  by 
kindling  a  candle  the  wick  of  which  has  been  cut  short,  or  by  slowly  increasing  the 
gas  supply  to  an  ordinary  burner.  When  the  flame  is  very  small  it  is  seen  to  consist 
of  a  bright  blue  inner  cone  surrounded  by  a  pale  lilac  mantle.  The  bright  blue 
cone  is  an  area  of  combustion  where  there  is  sufficient  air  to  burn  the  hydrocarbons 
to  gaseous  products,  without  separation  of  carbon,  but  not  sufficient  to  burn  them 
completely  to  C02  and  H20.  It  has  been  shown  that  under  these  conditions  much 
of  the  carbon  in  the  hydrocarbons  burns  to  carbon  monoxide,  and  only  a  part  of  the 
hydrogen  is  burnt.  The  CO  and  H  escape  from  the  inner  cone  and  burn  when  they 
come  in  contact  with  more  air,  forming  the  mantle.  As  the  supply  of  gas  is  in- 
creased a  luminous  spot  becomes  visible,  and  gradually  increases  in  area  until  it 
becomes  the  luminous  cone,  at  the  same  time  the  core  of  unburnt  gas  makes  its 
appearance.  What  was  at  first  the  inner  blue  cone  now  becomes  the  bright  blue 
cup  at  the  base  of  the  flame,  and  the  mantle  remains.  The  advent  of  the  luminous 
spot  indicates  that  the  quantity  of  gas  has  so  far  increased  that  there  is  now 
insufficient  air  to  burn  the  carbon  separated  from  the  hydrocarbons  by  the  heat  of 
the  flame. 

The  luminosity  of  a  flame  is  materially  affected  by  the  pressure  of  the  atmosphere 
in  which  it  burns,  a  diminution  of  pressure  causing  a  loss  of  illuminating  power.  If 
the  light  of  a  given  flame  burning  in  the  air  when  the  barometer  stands  at  30  inches 
be  represented  by  100,  each  diminution  of  i  inch  in  the  height  of  the  barometer 
will  reduce  the  luminosity  by  5  ;  and,  conversely,  when  the  barometer  rises  I  inch, 
the  luminosity  will  be  increased  by  5.  This  is  not  due  to  any  difference  in  the  rate 
of  burning,  which  remains  prettj*-  constant,  but  to  the 
more  complete  impenetration  of  the  rarefied  air  and  the 
gases  composing  the  flame  ;  this  gives  rise  to  the  sepa- 
ration of  a  smaller  quantity  of  incandescent  carbon.  In 
air  at  a  pressure  of  120  inches  of  mercury,  the  flame  of 
alcohol  is  highly  luminous. 

From  this  review  of  the  structure  of  flame, 
it  is  evident  that,  in  order  to  secure  a  flame 
which  shall  be  useful  for  illumination,  atten- 
tion must  be  paid  to  the  supply  of  oxygen  (or 
air),  and  to  the  composition  of  the  fuel  em- 
ployed. Much  attention  has  been  paid  to  the 
construction  of  burners  which,  by  causing  the 
illuminant  to  issue  into  the  air  at  a  rate  and 
in  a  shape  best  suited  to  the  production  of  Fig-.  i3i._Argand  Burner, 
lighting  effect,  shall  give  the  most  economical 

result,  that  is,  the  highest  illuminating  value  (candle  power)  per  unit  of 
combustible.  The  use  of  the  chimney  of  an  Argand  burner  (Fig.  132) 
affords  an  instance  of  the  necessity  for  attention  to  the  proper  supply 


154  SMOKELESS  GAS  BURNER. 

of  air.  Without  the  chimney,  the  flame  is  red  at  the  edges  and  smoky, 
for  the  supply  of  air  is  not  sufficient  to  consume  the  whole  of  the  car- 
bon which  is  separated,  and  the  temperature  is  not  competent  to  raise 
it  to  a  bright  white  heat,  defects  which  are  remedied  as  soon  as  the 
chimney  is  placed  over  it  and  the  rapidly  ascending  heated  column  of 
air  draws  in  a  liberal  supply  beneath  the  burner,  as  indicated  by  the 
arrows. 

By  using  two  chimneys,  and  causing  the  air  to  pass  down  between 
them,  so  as  to  be  heated  before  reaching  the  flame,  and  to  be  less 
capable  of  chilling  the  flame,  an  equal  amount  of  light  may  be  obtained 
from  a  much  smaller  supply  of  gas ;  this  is  the  principle  underlying  the 
regenerative  burner. 

The  importance  of  the  chemistry  of  illuminating  flames  has,  however, 
much  diminished  during  the  past  few  years  owing  to  the  perfection  to 
which  the  system  of  illumination  first  put -on  a  practical  basis  by 
Welsbach,  has  been  brought.  Whereas  in  an  illuminating  flame  the 
combustible  supplies,  not  only  the  heat  required  to  raise  a  dense  sub- 
stance to  the  temperature  at  which  it  can  emit  light,  but  also  the 
dense  substance  (carbon)  itself,  under  the  Welsbach  or  Auer  system 
the  sole  function  of  the  combustible  is  to  supply  heat,  the  dense  sub- 
stance being  an  incombustible  material  suspended  in  the  flame.  Hence 
the  principle  of  the  system  is  the  same  as  that  of  the  Drummond  light 
(p.  48)  known  many  years  before  Welsbach. 

Since  a  luminous  flame  contains  carbon  in  a  condition  in  which  it  is 
very  readily  deposited  on  any  surface  held  in  the  flame,  it  is  desirable 
that  a  gas  burner  which  is  to  be  used  for  heating,  whether  for  pro- 
ducing light  or  for  any  other  purpose,  should  supply  a  non-luminous 
flame.  A  deposit  of  soot  forms  a  non-conducting  layer  through  which 
the  heat  travels  slowly;  moreover,  every  particle  of  soot  which  escapes 
combustion  signifies  a  loss  in  the  calorific  power  of  the  gas.  The 
smokeless  gas  burners  employed  in  laboratories  and  kitchens  exhibit 
the  result  of  mixing  the  gas  with  a  considerable  proportion  of  air 
before  burning  it,  the  luminous  part  of  the  flame  then  entirely  dis- 
appearing, because  there  is  sufficient  oxygen  in  the  flame  to  burn  the 
hydrocarbons  before  they  can  be  decomposed  with  separation  of  carbon. 
By  careful  adjustment  of  the  supply  of  air  the  combustion  can  be  made 
to  take  place  in  a  smaller  space  than  when  the  gas  has  to  seek  its  air 
supply  from  the  surrounding  atmosphere.  For  the  same  amount  of  gas 
consumed,  that  flame  which  is  the  smaller  will  have  the  higher  tempera- 
ture, although  it  must  be  understood  that  the 
same  amount  of  heat  is  produced  from  a  given 
volume  of  gas,  however  it  is  burnt,  provided 
that  the  combustion  is  complete,  i.e.,  that 
the  products  are  only  C02  and  H20. 

The    principle    upon    which    all   air-gas 
burners   are  constructed   is   illustrated    by 
Bunseris  burner   (Fig.  132),  in   which    the 
Fig.  i32.-Bunsen's  burner.       gas  is  conveyed  through  a  narrow  jet  into  a 
wide  tube,   at  the  base  of  which   are   two 

large  holes  for  the  admission  of  air.  When  a  good  supply  of  gas  is 
turned  on,  a  quantity  of  air,  about  2^  times  the  volume  of  the  gas,  is 
drawn  in  through  the  lower  apertures,  and  the  mixture  of  air  and  gas 


THE  WELSBACH  BURNER. 


I55 


may  be  kindled  at  the  orifice  of  the  wide  tube,  its  rapid  motion  pre- 
venting the  flame  from  passing  down  the  tube.  By  closing  the  air-holes 
with  the  fingers,  a  luminous  flame  is  at  once  produced. 

The  luminosity  of  the  flame  may  also  be  destroyed  by  supplying  nitrogen  instead 
of  air  to  the  Bunsen  burner,  when  the  diminution  of  the  light  is  partly  due  to  the 
increased  area  of  the  flame  and  partly  to  the  cooling  effect  of  the  nitrogen,  by  which 
the  temperature  is  lowered  below  that  at  which  the  hydrocarbons  are  decomposed 
with  separation  of  carbon.  This  cooling  effect  occurs  to  some  extent  when  air  is 
supplied  to  the  burner  ;  the  nitrogen  in  this  air  lowers  the  temperature  of  the  flame 
just  at  that  point  where,  in  a  luminous  flame,  the  hydrocarbons  are  decomposed, 
although  the  more  perfect  combustion  makes  the  temperature  in  other  portions  of 
the  non-luminous  flame  higher  than  at  corresponding  points  of  the  luminous  flame. 
When  the  air  and  coal  gas  are  heated  before  being  supplied  to  the  burner  the  cooling 
effect  of  the  nitrogen  is  counteracted,  and  the  flame  becomes  luminous.  The 
ordinary  Bunsen  flame  consists  of  only  two  cones  ;  the  inner  one  is  a  core  of 
mixture  of  air  and  gas  which  cannot  be  kindled  because  its  rate  of  passage  is  more 
rapid  than  the  rate  at  which  a  flame  can  travel  in  it  ;  the  combustion  occurs  in  the 
outer  cone,  where  the  speed  has  diminished. 

When  the  gas  supply  to  a  Bunsen  burner  is  checked,  the  velocity  of  issue  of  the 
mixture  of  air  and  gas  becomes  so  far  diminished  that  it  i?  no  longer  greater  than 
the  rate  at  which  the  flame  can  travel  in  the  mixture,  consequently  the  flame  passes 
down  the  tube  of  the  burner  and  burns  at  the  jet  from  which  the  coal-gas  issues  ;  here 
the  checked  combustion  will  give  rise  to  much  acetylene,  detected  by  its  odour. 
By  slipping  a  glass  tube,  some  three  or  four  feet  long,  over  the  tube  of  the  burner, 
taking  care  not  to  cover  the  air  inlet,  and  kindling  the 
gas  at  the  orifice  of  this  tube,  the  flashing  back  of  the 
flame  may  be  observed.  If  the  glass  tube  be  constricted 
at  a  point  some  foot  or  so  away  from  the  orifice,  the 
descending  flame  will  be  stopped  at  this  constriction, 
for  here  the  velocity  of  issue  will  be  again  sufficiently 
great  to  prevent  further  flashing  back.  Inasmuch  as  the 
flame  at  the  constriction  is  burning  out  of  contact  with 
surrounding  air,  only  such  products  are  formed  by  its 
combustion  as  can  be  produced  by  the  action  of  the 
oxygen  supplied  in  the  air  from  the  burner  ;  these  in- 
clude much  CO  and  H,  so  that  a  second  flame  composed 
of  these  gases  burning  in  the  air  will  generally  be  seen 
at  the  orifice  of  the  tube.  A  more  elaborate  apparatus 
for  showing  this  experiment  is  seen  in  Fig.  133  ;  in 
this  the  height  of  the  constriction  can  be  varied  by 
sliding  the  outer  tube  on  the  rubber  rings  A  A.  Air 
and  gas  are  supplied  through  the  T-piece.  Fis?<  I33 

The  Welsbach    mantle  is  a  skeleton  of   the 

highly  infusible  oxide  of  thorium  containing  about  i  per  cent,  of  oxide 
of  cerium.  This  mixture  has  a  remarkable  power  of  converting  the  heat 
energy  of  the  burning  gas  into  light  energy,*  and  when  the  mantle  is 
suspended  in  a  suitable  air-gas  flame  it  produces  light  at  about  one- 
fifth  the  cost  for  gas  that  is  involved  if  the  same  gas  is  burnt  as  a 
luminous  flame. 

The  Welsbach  mantle  is  made  by  soaking  in  a  solution  containing  the  nitrates  of 
thorium  and  cerium,  and  generally  ammonium  nitrate,  a  knitted  cylinder  of  cotton 
thread,  drawn  together  by  an  asbestos  thread  at  one  end.     After  drying,  the  cotton 
is  ignited  and  allowed  to  burn  away,  leaving  the  mineral  matter  in  the  exact  form  01 
the  original  cotton  thread.     The  mantle  lis  then  heated  very  strongly  to  "harden 
it,  and  dipped  in  a  solution  of  collodion  to  stiffen  it  for  the  market ;  when  it 
placed  on  the  burner  and  the  gas  is  kindled  the  film  of  collodion  rapidly  b 

The  air-gas  burner  for  the  Welsbach  light  is  constructed  in  such  a  manner  that 
the  mixture  of  air  and  gas  issuing  from  the  burner  is  nearly  in  the  proper  propor 
*  It  is  claimed  that  as  much  as  25  percent,  is  converted. 


156  THE  BLOWPIPE  FLAME. 

tion  for  complete  combustion  ;  that  is  to  say,  the  mixture  should  be  "  self -burning," 
requiring  little  or  none  of  the  surrounding  air.  In  this  manner  the  hottest  attain- 
able flame  is  produced.  The  burner  generally  has  the  form  of  the  frusta  of  two 
cones,  the  upper  inverted  on  the  lower  ;  the  gas  issues  as  a  jet  into  the  lower  cone 
and  draws  in  some  four  or  five  times  its  volume  of  air.  The  orifice  of  the  burner 
tube  must  be  covered  with  wire  gauze  to  prevent  the  flame  from  flashing  back.  The 
flame  of  a  burner  of  this  kind  is  characterised  by  the  inner  cone  having  a  much 
greener  appearance  than  has  that  of  the  ordinary  Bunsen  flame.  The  temperature 
of  the  hottest  portion  of  the  ordinary  Bunsen  flame,  the  centre  of  the  outer  cone,  is 
stated  to  be  about  1500°  C.,  whilst  at  the  same  point  in  this  "solid  "  flame  the  tem- 
perature is  said  to  be  about  1600°  C.  Fig.  134  shows  an  Argand  burner  converted 
into  such  a  gauze  burtier  by  a  covering  of  wire  gauze.  When  this  is  placed  over  the  gas 
burner,  a  supply  of  air  is  drawn  in  at  the  bottom  by  the  ascending  stream  of  gas, 
and  the  mixture  burns  above  the  gauze  with  a  very  hot  smokeless  flame,  the  metallic 
meshes  preventing  the  flame  from  passing  down  to  the  gas  below. 

The  candle  power  of  the  Welsbach  light  is  about  18  per  cubic  foot  of  gas  per  hour, 
whilst  that  of  a  flat  flame  is  between  2  and  3  on  the  same  basis. 


Fig1.  134. — Gauze  burner.  Fig.  135. — Blowpipe  flame. 

91.  The  blowpipe  flame. — The  principles  already  laid  down  will  render 
the  structure  of  the  blowpipe  flame  easily  intelligible.  It  must  be 
remembered  that  in  using  the  blowpipe,  the  stream  of  air  is  not  pro- 
pelled from  the  lungs  of  the  operator  (where  a  great  part  of  its  oxygen 
would  have  been  consumed),  but  simply  from  the  mouth,  by  the  action 
of  the  muscles  of  the  cheeks.  The  first  apparent  effect  upon  the  flame 
is  entirely  to  destroy  its  luminosity,  the  free  supply  of  air  effecting  the 
immediate  combustion  of  the  carbon.  The  size  of  the  flame,  moreover, 
is  much  diminished,  and  the  combustion  being  concentrated  into  a 
smaller  space,  the  temperature  must  be  much  higher  at  any  given  point 
of  the  flame.  In  structure,  the  blowpipe  flame  is  similar  to  the  ordinary 
flame,  consisting  of  three  distinct  cones,  the  innermost  of  which  (A, 
Fig.  135)  is  filled  with  the  cool  mixture  of  air  and  combustible  gas. 
The  second  cone,  especially  at  its  point  (R),  is  termed  the  reducing 
flame,  for  the  supply  of  oxygen  at  that  part  is  not  sufficient  to  convert 
the  carbon  into  carbon  dioxide,  but  leaves  it  as  carbonic  oxide,  which 
speedily  reduces  almost  all  metallic  oxides  placed  in  that  part  of  the 
flame  to  the  metallic  state.  The  outermost  cone  (0)  is  called  the 
oxidising  flame,  for  there  the  supply  of  oxygen  from  the  surrounding 
air  is  unlimited,  and  any  substance  prone  to  combine  with  oxygen  at  a 
high  temperature  is  oxidised  when  exposed  to  the  action  of  that  portion 
of  the  flame :  the  hottest  point  of  the  blowpipe  flame,  where  neither 
fuel  nor  oxygen  is  in  excess,  appears  to  be  a  very  little  in  advance  of 
the  extremity  of  the  second  (reducing)  cone.  The  difference  in  the 
operation  of  the  two  flames  is  readily  shown  by  placing  a  little  red  lead 
(oxide  of  lead)  in  a  shallow  cavity  scooped  upon  the  surface  of  a  piece 
of  charcoal  (Fig.  136),  and  directing  the  flames  upon  it  in  succession) ; 


ANALYSIS   OF  HYDROCARBONS. 

the  inner  flame  will  reduce  a  globule  of  metallic  lead,  which  may  be 
reconverted  into  oxide  by  exposing  it  to  the  outer  flame.* 


Fig.  137. — Hot-blast  blowpipe. 


Fig.  136. — Keduction  of  metals  on  charcoal. 

The  immense  service  rendered  by  this  instrument  to  the  chemist  and 
mineralogist  is  well  known. 

By  forcing  a  stream  of  oxygen  through  a  flame,  from  a  gas-holder  or 
bag,  an  intensely  hot  blowpipe  flame  is  obtained,  in  which  pipeclay  and 
platinum  may  be  melted,  and  iron  burns  with  great  brilliancy. 

Fletcher's  hot-blast  blowpipe  (Fig.  137)  produces  a  much  higher  temperature  than 
the  ordinary  blowpipe.  Coal  gas  is  supplied  through  the  tube  g,  and  is  kindled 
at  the  Bunsen  burners  b  b  and  at  the  orifice/,  the 
supply  to  the  former  being  regulated  by  the  stop- 
cock £,  and  to  the  latter  by  the  stop-cock  d.  The 
flames  of  the  Bunsen  burners  heat  the  spiral  copper 
tube  e  to  redness,  so  that  the  air  blown  in  through 
the  flexible  tube  a  is  strongly  heated  before  being 
projected  into  the  flame  through  a  blowpipe  jet 
at  /.  Thin  platinum  wires  melt  easily  in  this  flame, 
and  thin  iron  wires  burn  away  rapidly. 

92.  Determination  of  the  composition  of 
gases  containing  carbon  and  hydrogen. — In 
order  to  ascertain  the  proportions  of  carbon 
and  hydrogen  present  in  a  gas,  a  measured 
volume  of  the  gas  is  mixed  with  an  excess 
of  oxygen,  the  volume  of  the  mixture  carefully  noted,  and  explosion 
determined  by  passing  the  electric  spark  ;  the  gas  remaining  after  the 
explosion  is  measured  and  shaken  with  potash,  which  absorbs  the 
carbonic  acid  gas,  from  the  volume  of  which  the  proportion  of  carbon 
may  be  calculated.  For  example, 

4  c.c.  of  marsh  gas,  mixed  with 
10     „         oxygen,  and  exploded,  left 
6     „        gas  ;  shaken  with  potash,  it  left 
2     „         oxygen, 

showing  that  4  c.c.  of  carbonic  acid  gas  had  been  produced.  This 
quantity  would  contain  4  c.c.  of  oxygen.  Deducting  this  last  from  the 
total  amount  of  oxygen  consumed  (8  c.c.),  we  have  4  c.c.  for  the  volume 
of  oxygen  consumed  by  the  hydrogen.  Now,  4  c.c.  of  oxygen  would 
combine  with  8  c.c.  of  hydrogen,  which  represents  therefore  the  amount 
of  hydrogen  in  the  marsh  gas  employed.  It  has  thus  been  ascertained 
that  the  marsh  gas  contains  twice  its  volume  of  hydrogen. 

The  method  by  which  the  composition  by  weight  of  a  gas  containing 

*  By  directing  the  reducing  flame  upon  the  metallic  oxide  in  the  cavity,  and  allowing  the 
oxidising  flame  to  sweep  over  the  surface  of  the  charcoal,  as  shown  in  the  figure,  a  yellow 
incrustation  of  oxide  of  lead  is  formed  upon  the  surface  of  the  charcoal,  which  affords 
additional  evidence  of  the  nature  of  the  metal. 


158  COAL. 

carbon  and  hydrogen  can  be  ascertained  will  be  appreciated  when  the 
section  on  ultimate  organic  analysis  has  been  studied.  In  the  case  of 
marsh  gas  such  an  analysis  shows  that  the  carbon  and  hydrogen  are 
present  in  the  gas  in  the  proportion  of  3  parts  by  weight  of  carbon 
to  one  part  by  weight  of  hydrogen.  If  the  atomic  weight  of  carbon  be 
12,  the  simplest  formula  for  marsh  gas,  expressing  this  ratio  of  C  to  H, 
will  be  CH4.  But  the  formula  02H8  would  equally  express  the  ratio 
3  :  i  —  (12  x  2  :  1x8);  this  cannot  be  the  formula  for  marsh  gas,  how- 
ever, because  the  specific  gravity  (H=  i)  of  the  gas  is  8,  therefore  its 
molecular  weight  must  be  16  (p.  9),  and  as  the  formula  is  to  represent 
one  molecular  weight  (p.  9),  the  formula  for  marsh  gas  must  be  CH4 
(12  +  4=16),  not  C2H8  (24  +  8  =  32). 

For  the  purpose  of  illustration,  the  analysis  of  marsh  gas  may  be  effected  in  a 
lire's  eudiometer  (Fig.  37),  but  a  considerable  excess  of  oxygen  should  be  added  to 
moderate  the  explosion.  The  eudiometer  having  been  filled  with  water,  i  c.  c.  of 
marsh  gas  is  introduced  into  it,  as  described  at  p.  44,  and  having  been  transferred  to 
the  closed  limb  and  accurately  measured  after  equalising  the  level  of  the  water,  the 
open  limb  is  again  filled  up  with  water,  the  eudiometer  inverted  in  the  trough,  and 
12  c.  c.  of  oxygen  added  ;  this  is  also  transferred  to  the  closed  limb  and  carefully 
measured.  The  electric  spark  is  passed  through  the  mixture  (see  p.  44),  the  open 
limb  being  closed  by  the  thumb.  The  level  of  the  water  in  both  limbs  is  then 
equalised,  and  the  volume  of  gas  measured.  The  open  limb  is  filled  up  with  a  strong 
solution  of  potash,  and  closed  by  the  thumb,  so  that  the  gas  may  be  transferred 
from  the  closed  to  the  open  limb  and  back,  until  its  volume  is  no  longer  diminished 
by  the  absorption  of  carbon  dioxide.  The  volume  of  residual  oxygen  having  been 
measured,  the  calculation  is  effected  as  described  above. 

The  results  are  more  exact  when  the  eudiometer  is  filled  with  mercury  instead  of 
water,  and  corrections  for  temperature  and  pressure  are  made. 

FUEL. 

93.  Whilst  any  combustible  substance  is  applicable  for  the  purpose 
of  producing  heat,  the  forms  of  fuel  actually  in  use  are  dependent  for 
their  calorific  value  on  the  combustion  of  carbon  and  hydrogen.*  A  table 
showing  the  composition  of  the  principal  fuels  will  be  found  on  p.  168. 

Coal. — The  various  substances  which  are  classed  together  under  the 
name  of  coal  are  characterised  by  the  presence  of  carbon  as  a  largely 
predominant  constituent,  associated  with  smaller  quantities  of  hydrogen, 
oxygen,  nitrogen,  sulphur,  and  certain  mineral  matters  which  compose 
the  ash.  Coal  appears  to  have  been  formed  by  a  peculiar  decomposition 
or  fermentation  of  buried  vegetable  matter,  resulting  in  the  separation 
of  a  large  proportion  of  its  hydrogen  in  the  form  of  marsh-gas  (CH4), 
and  similar  compounds,  and  of  its  oxygen  in  the  form  of  carbonic  acid 
gas  (C02),  the  carbon  accumulating  in  the  residue.  Thus,  cellulose 
(C6H10O5),  which  constitutes  the  bulk  of  woody  fibre,  might  be  imagined 
to  decompose  according  to  the  equation  2C6H10()5  =  5CH4  + 5C02  +  C9, 
and  the  occurrence  of  marsh  gas,  and  of  the  paraffin  hydrocarbons  of 
similar  compositions,  as  well  as  of  carbonic  acid  gas,  in  connexion  with 
deposits  of  coal,  supports  this  account  of  its  formation.  Marsh  gas 
and  carbonic  acid  gas  are  the  ordinary  products  of  the  fermentation  of 
vegetable  matter,  and  a  spontaneous  carbonisation  is  often  witnessed  in 
the  "  heating  "  of  damp  hay.  But  just  as  the  action  of  heat  upon  wood 

*  The  student  will  meet  with  a  few  cases  in  which  the  combustion  of  other  elements  affords 
heat  for  useful  purposes,  so  that  such  elements  are  fuels  under  the  particular  conditions. 
For  example,  the  sulphur  in  pyrites  or  the  aluminium  in  the  mixture  known  as  thermite 
may  be  regarded  as  fuels. 


COMBUSTION  OF   COAL.  159 

produces  a  charcoal  containing  small  quantities  of  the  other  organic 
elements,  so  the  carbonising  process  by  which  the  plants  have  been 
transformed  into  coal  has  left  behind  some  of  the  hydrogen,  oxygen, 
and  nitrogen  ;  the  last,  as  well  probably  as  a  little  of  the  sulphur, 
having  been  derived  from  the  vegetable  albumin  and  similar  substances 
which  are  always  present  in  plants.  The  chief  part  of  the  sulphur  is 
generally  present  in  the  form  of  iron  pyrites  (FeS2),  derived  from  some 
extraneous  source.  The  examination  of  a  peat-bog  is  very  instructive 
with  reference  to  the  formation  of  coal,  as  affording  examples  of 
vegetable  matter  in  every  stage  of  decomposition,  from  that  in  which 
the  organised  structure  is  still  clearly  visible,  to  the  black  carbonaceous 
mass  which  only  requires  consolidation  by  pressure  in  order  to  resemble 
a  true  coal.  In  some  cases  an  important  part  in  the  formation  of  coal 
may  have  been  played  by  slow  oxidation  or  decay  of  the  vegetable 
matter  at  the  expense  of  atmospheric  oxygen  held  in  solution  by  water  ; 
since  the  hydrogen  of  the  compound  would  be  removed  by  oxidation 
taking  place  at  a  low  temperature,  giving  rise  to  a  gradual  increase  in 
the  percentage  of  carbon. 

The  three  principal  varieties  of  coal — lignite,  bituminous  coal,  and 
anthracite — present  us  with  the  material  in  different  stages  of  carboni- 
sation ;  the  lignite,  or  broivn  coal,  presenting  indications  of  organised 
structure,  and  containing  considerable  proportions  of  hydrogen  and 
oxygen,  while  anthracite  often  contains  little  else  than  carbon  and  the 
mineral  matter  or  ash.  The  following  table  shows  the  progressive 
diminution  in  the  proportions  of  hydrogen  and  oxygen  in  the  passage 
from  wood  to  anthracite. 

Carbon.  Hydrogen.  Oxygen. 

Wood          .         .                  .                loo  ...  12. 18  ...  83.07 

Peat    ...                  .                100  ...  9.85  ...  55.67 

Lignite       .         .                 .                100  ...  8.37  ...  42.42 

Bituminous  coal                  .               100  ...  6.12  ...  21.23 

Anthracite          .                 .                100  ...  2.84  ...  1.74 

The  combustion  of  coal  is  a  somewhat  complex  process,  in  con- 
sequence of  the  re-arrangement  which  its  elements  undergo  when  the 
coal  is  subjected  to  the  action  of  heat. 

As  soon  as  a  flame  is  applied  to  kindle  the  coal,  the  heated  portion 
undergoes  destructive  distillation,  evolving  various  combustible  gases 
and  vapours,  which  take  fire  and  convey  the  heat  to  remoter  portions  of 
the  coal.  Whilst  the  elements  of  the  exterior  portion  of  coal  are  under- 
going combustion,  the  heat  thus  evolved  is  submitting  the  interior  of 
the  mass  to  destructive  distillation,  resulting  in  the  production  of 
various  compounds  of  carbon  and  hydrogen.  Some  of  these  products, 
such  as  marsh  gas  (CH4)  and  olefiant  gas  (C2H4),  burn  without  smoke  ; 
while  others,  like  benzene  (C6H6)  and  naphthalene  (C10H8),  which  con- 
tain a  very  large  proportion  of  carbon,  undergo  partial  combustion,  and 
a  considerable  quantity  of  carbon,  not  meeting  with  enough  heated  oxy- 
gen in  the  vicinity  to  burn  it  entirely,  escapes  in  a  very  finely  divided 
state  as  smoke  or  soot,  which  is  deposited  in  the  chimney,  mixed  with 
a  little  ammonium  carbonate  and  small  quantities  of  other  products  of 
the  distillation  of  coal.  "When  the  gas  has  been  expelled  from  the  coal, 
there  remains  a  mass  of  coke  or  cinder,  which  burns  with  a  steady  glow 
until  the  whole  of  its  carbon  is  consumed,  and  leaves  an  ash,  consisting 


160  COKE. 

of  the  mineral  substances  present  in  the  coal.*  The  final  results  of  the 
perfect  combustion  of  coal  would  be  carbonic  acid  gas  (CO.,),  water 
(H20),  nitrogen,  a  little  sulphurous  acid  gas  (S02),  and  ash.  The  pro- 
duction of  smoke  in  a  furnace  supplied  with  coal  may  be  prevented  by 
charging  the  coal  in  small  quantities  at  a  time  in  front  of  the  fire,  so 
that  the  highly  carbonaceous  vapours  must  come  in  contact  with  a 
large  volume  of  heated  air  before  reaching  the  chimney.  In  arrange- 
ments for  consuming  the  smoke,  hot  air  is  judiciously  admitted  at  the 
back  of  the  fire,  in  order  to  meet  and  consume  the  heated  carbonaceous 
particles  before  they  pass  into  the  chimney. 

The  difference  in  the  composition  of  the  several  varieties  of  coal  gives 
rise  to  a  great  difference  in  their  mode  of  burning. 

The  table  on  p.  168  exhibits  the  composition  of  representative  speci- 
mens of  the  four  principal  varieties,  namely,  lignite,  bituminous  coal, 
cannel,  and  anthracite. 

The  lignites  furnish  a  much  larger  quantity  of  gas  under  the  action 
of  heat  (and  therefore  burn  with  more  flame  than  the  other  varieties), 
leaving  a  coke  which  retains  the  form  of  the  original  coal  ;  while  bitu- 
minous coal  softens  and  cakes  together — a  useful  property,  since  it 
allows  even  the  dust  of  such  coal  to  be  burnt,  if  the  fire  be  judiciously 
managed.  Anthracite  (stone  coal  or  Welsh  coal)  is  much  less  easily  com- 
bustible than  either  of  the  others,  and,  since  it  yields  but  little  gas 
when  heated,  it  usually  burns  with  little  flame  or  smoke.  This  variety 
of  coal  is  so  compact  that  it  will  not  usually  burn  in  ordinary  grates, 
but  it  is  much  employed  for  boiler  furnaces. 

Jet  resembles  cannel  coal  in  composition. 

Accidents  occasionally  arise  from  the  spontaneous  combustion  of  coal. 
This  appears  to  be  due,  in  most  cases,  to  the  development  of  heat  by 
the  slow  combination  of  some  constituents  of  the  coal  with  atmospheric 
oxygen,  and  unless  due  provision  be  made  for  the  escape  of  the  heat,  its 
accumulation  may  raise  the  temperature  to  a  dangerous  degree.  The 
oxidation  is  more  likely  to  occur  if,  by  careless  loading  of  the  coal 
in  the  ship,  much  pulverisation  of  the  fuel  has  occurred  (compare 

P-  34)> 

Coke  is  the  residue  left  by  destructively  distilling  coal,  an  operation 
which  is  conducted  in  coke-ovens  when  the  object  is  to  produce  coke 
for  metallurgical  use  and  in  retorts  when  the  object  is  to  produce  coal 
gas,  the  coke  being  then  a  by-product.  There  is  no  essential  difference 
between  the  coke-oven  and  the  retort  save  that  the  former  is  con- 
siderably the  larger  of  the  two,  thus  distilling  a  greater  weight  of  coal 
and  producing  a  denser  coke.  As  all  the  volatile  portions  of  the  coal 
have  been  expelled  by  the  distillation,  coke  burns  without  flame  or 
smoke,  but  is  correspondingly  difficult  to  ignite. 

Wood  and  Charcoal  have  already  received  attention.  In  this 
country  the  use  of  the  former  as  fuel  is  limited  to  its  application  for 
kindling  less  inflammable  fuel,  like  coal.  Charcoal  is  useful  in  cases 
where  a  fuel  devoid  of  sulphur  is  desirable ;  it  stands  in  the  same 
relation  to  wood  that  coke  does  to  coal  as  has  already  been  explained 
(p.  in). 

*  This  ash  consists  chiefly  of  silica,  alumina  and  peroxide  of  iron.  When  lime  is  present 
in  the  ash,  it  is  liable  to  fuse  into  a  rough  glass  or  clinker,  which  adheres  to  the  grate  bars 
and  causes  much  inconvenience. 


COAL  GAS.  l6l 

Petroleum  finds  an  increasing  application  as  fuel,  particularly  the- 
residues  from  the  fractional  distillation  of  the  oil  (see  Organic  Chemistry)' 
for  obtaining  illuminating  oils.  Such  residues  are  known  as  astatkir 
and  when  sprayed  into  a  furnace  burn  with  a  high  heating  effect.  An 
advantage  of  this  form  of  fuel  is  its  freedom  from  ash. 

Gaseous  fuel. — The  fact  that  combustible  gases  can  be  burnt  without 
the  production  of  smoke  and  ash  renders  them  a  formidable  competitor 
of  coal  notwithstanding  that  for  an  equal  heating  effect  they  are  more1 
costly.  But  the  more  important  function  of  gaseous  fuel  is  as  a  source* 
of  power  by  its  combustion  in  the  cylinder  of  a  gas  engine.  So  far  as 
domestic  heating  is  concerned  coal  gas  is  still  the  sole  gaseous  fuel 
used  ;  an  air-gas  flame  (p.  154)  is  caused  to  play  upon  some  incombustible 
and  infusible  substance  like  asbestos  or  fireclay,  so  that  the  heat  of  the 
flame,  which  is  a  feeble  radiator,  may  be  converted  into  the  radiant 
heat  of  a  red-hot  solid.  The  cooling  of  the  flame  by  contact  with  the 
solid  necessarily  checks  the  combustion,  giving  rise  to  such  gases  as 
carbon  monoxide  and  acetylene  which  are  unwholesome  to  breathe.  A 
flue  for  carrying  away  the  products  of  the  combustion  is  therefore 
essential,  but  this  is  less  necessary  where  the  gas  is  allowed  to  burn 
with  a  luminous  flame,  the  radiation  from  which  is  considerable  while 
the  combustion  is  practically  complete. 

94.  Coal  gas. — The  manufacture  of  coal  gas  is  one  of  the  most  im- 
portant applications  of  the  principle  of  destructive  distillation,  and 
affords  an  excellent  example  of  the  tendency  of  this  process  to  develop 
new  arrangements  of  the  elements  of  a  compound  body.  The  action  of 
heat  upon  coal,  in  a  vessel  from  which  air  is  excluded,  gives  rise  to  the 
production  of  a  very  large  number  of  compounds  containing  some  two* 
or  more  of  the  five  elements  of  the  coal,  in  different  proportions,  or  in 
different  forms  of  arrangement.  Although  no  clue  has  yet  been  obtained 
to  indicate  the  true  arrangement  of  these  elements  in  the  original 
coal  (or,  as  it  is  termed,  the  constitution  of  the  coal),  it  is  certain  that 
these  various  compounds  do  not  exist  in  it  before  the  application  of 
heat,  but  are  really  the  results  of  this  application  ;  they  are  products, 
not  educts. 

The  illuminating  gas  obtained  from  coal  consists  essentially  of  free 
hydrogen,  marsh  gas,  olefiant  gas,  and  carbonic  oxide,  with  small! 
quantities  of  acetylene,  benzene  vapour,  and  some  other  substances. 
Its  specific  gravity  is  about  0.4,  and  is  higher  the  higher  the  illuminating 
value  of  the  gas. 

A  fair  general  idea  of  the  composition  of  coal  gas  is  given  in  the 
table  on  p.  168. 

The  constituents  which  contribute  most  largely  to  the  illuminating 
value  of  the  gas  are  the  vapour  of  benzene,  acetylene,  olefiant  gas  and 
similar  hydrocarbons,  represented  by  C2H4  in  the  table. 

The  most  objectionable  constituent  is  the  sulphur  present  in  very 
small  proportion  as  sulphuretted  hydrogen  and  bisulphide  of  carbon, 
for  this  is  converted  by  combustion  into  sulphurous  and  sulphuric  acids, 
which  seriously  injure  pictures,  furniture,  &c.  The  object  of  the 
manufacturer  of  coal  gas  is  to  remove,  as  far  as  possible,  everything 
from  it,  except  the  constituents  mentioned  as  essential,  and  at  the  same 
time  to  obtain  as  large  a  volume  of  gas  from  a  given  weight  of  coal  as 
is  consistent  with  good  illuminating  value. 

L 


l62 


ACETYLENE   IN   COAL   GAS. 


The  other  products  of  the  destructive  distillation  of  coal,  the  mode  of 
purifying  the  gas,  and  the  general  arrangements  for  its  manufacture, 
will  be  described  in  a  later  part  of  the  book. 

The  destructive  distillation  of  coal  may  be  exhibited  with  the  arrangement  repre- 
sented in  Fig.  138.  The  solid  and  liquid  products  (tar,  ammoniacal  liquor,  &c.)  are 
•condensed  in  a  globular  receiver  (A).  The  first  bent  tube  contains,  in  one  limb  (B) 
a  piece  of  red  litmus-paper  to  detect  ammonia  ;  and  in  the  other  (C)  a  piece  of  paper 
impregnated  with  lead  acetate,  which  will  be  blackened  by  the  sulphuretted 


Fig.  138. — Destructive  distillation  of  coal. 

hydrogen.  The  second  bent  tube  (D)  contains  enough  lime-water  to  fill  the  bend, 
which  will  be  rendered  milky  by  the  carbonic  acid  gas.  The  gas  is  collected  over 
water  in  the  jar  E,  which  is  furnished  with  a  jet  from  which  the  gas  may  be  burnt 
when  forced  out  by  depressing  the  jar  in  water. 

The  presence  of  acetylene  in  coal  gas  may  be  shown  by  passing  the  gas  from  the 
supply-pipe  (A,  Fig.  139),  first  through  a  bottle  (B) 
containing  a  little  ammonia,  then  through  a  bent 
tube  (C)  with  enough  water  to  fill  the  bend,  and  a 
piece  of  bright  sheet  copper  immersed  in  the  water  in 
each  limb.  After  a  short  time  the  bright  red  flakes 
of  the  copper  acetylide  will  be  seen  in  the  water. 


So  long  as  coal  gas  is  burnt  for  producing 
an  illuminating  flame  and  is  sold  at  so  much 
per  cubic  foot,  it  is  essential  that  the  maker 
should  be  compelled  to  supply  it  of  a  standard 
Fio.  illuminating  value.*  This  requirement,  which 

entails  considerable  expense  in  the  manufac- 
ture owing  to  the  necessity  for  "  enriching  "  the  gas  by  adding  to  it  petro- 
leum vapour  or  some  other  hydrocarbon  that  increases  the  illuminating 
value,  should  be  changed  into  a  standard  heating  value  now  that  so 
much  of  the  gas  is  used  for  heating  and  power  purposes,  and  that  the 
Welsbach  system  of  lighting  (which  depends  solely  on  the  heating  value 
of  the  gas)  is  displacing  illuminating  flames. 

Producer  gas. — In  the  manufacture  of  coal  gas  some  70  per  cent,  of 
the  carbon  of  the  coal  is  left  in  the  retort  as  coke.  It  is  possible  to 
convert  nearly  the  whole  of  the  carbon  of  the  coal  into  combustible  gas 
by  taking  advantage  of  the  fact  that  C02  is  reduced  to  CO  by  red -hot 
carbon,  C0,  +  0  =  2CO.  The  producer  in  which  this  change  is  effected, 
consists  of  a  deep  grate  into  which  the  fuel  is  fed  from  above,  the  air 
entering  below  the  charge.  The  bottom  portion  of  the  fuel  burns  to 
C02,  which  is  reduced  to  CO  t  by  the  hot  fuel  in  the  top  of  the  pro- 

*  In  London,  i6-candle  gas  must  be  supplied;  that  is,  when  the  g-as  is  burnt  from  a 
standard  burner  at  the  rate  of  5  cubic  feet  per  hour  the  flame  must  have  an  illuminating- 
value  equal  to  that  of  16  standard  caudles. 

t  See  foot-note,  p.  132. 


CALORIFIC  VALUE   OF  FUEL.  163 

ducer ;  this  escapes  through  a  flue  to  the  furnace  in  which  it  is  to  be 
burnt.  Of  course,  producer  gas  is  far  from  pure  CO  ;  it  must  neces- 
sarily contain  the  nitrogen  of  the  air  which  supplied  the  oxygen,  and, 
in  addition  to  this,  some  C02  and  the  products  of  the  destructive 
distillation  of  the  coal  used,  are  present. 

Water  gas. — A  gas  of  more  than  double  the  heating  effect  of  producer 
gas  can  be  obtained  from  the  original  fuel  by  converting  it  into  water 
gas.  This  process  depends  on  the  fact  that  when  steam  is  passed  over 
heated  carbon,  a  mixture  of  hydrogen  and  carbon  monoxide  is  obtained, 
C  +  H20  =  CO  +  H2.  Since  this  reaction  is  endothermic,  the  tempera- 
ture of  the  carbon  must  be  maintained  if  the  production  of  the  gas  is 
to  continue.  In  practice  water  gas  is  made  by  passing  steam  into 
a  producer  which  is  already  at  work,  until  the  temperature  has  so  far 
fallen  that  the  steam  is  no  longer  decomposed.  The  fuel  is  then  again 
brought  up  to  the  required  temperature  by  a  draught  of  air  (producer 
gas  being  formed  during  this  stage  of  the  process),  and  steam  is  again 
turned  in. 

It  will  be  obvious  that  by  blowing  an  appropriate  mixture  of  steam 
and  air  into  a  producer,  a  mixture  of  water  gas  and  producer  gas  (semi- 
water  gas,  Dowson  gas,  and  Mond  gas]  can  be  continuously  produced. 

Calorific  value  of  fuel. — For  all  practical  purposes  it  may  be 
stated  that  the  amount  of  heat  generated  by  the  combustion  of  a  given 
weight  of  fuel  depends  upon  the  weights  of  carbon  and  hydrogen,  re- 
spectively, which  enter  into  combination  with  the  oxygen  of  the  air 
when  the  fuel  burns. 

It  has  been  ascertained  by  experiment  that  i  gram  of  carbon  (in  the. 
form  in  which  it  exists  in  wood-charcoal),  when  combining  with  oxygen 
to  form  C02,  produces  a  quantity  of  heat  which  is  capable  of  raising 
8080  grams  of  water  from  o°  to  i°  C.  This  is  usually  expressed  by 
saying  that  the  calorific  value  of  carbon  is  8080,  or  that  carbon  produces 
8080  units  of  heat  during  its  combustion  to  C02.  If  the  fuel,  therefore, 
consisted  of  pure  carbon,  it  would  merely  be  necessary  to  multiply  its 
weight  by  8080  to  ascertain  its  calorific  value. 

One  gram  of  hydrogen,  during  its  conversion  into  water  by  combus- 
tion evolves  enough  heat  to  raise  34,400  Ibs.  of  water  from  o°  C.  to 
i°  C.,  so  that  the  calorific  value  of  hydrogen  is  34,400. 

If  the  fuel  consisted  of  carbon  and  hydrogen  only,  its  calorific  value 
would  be  calculated  by  multiplying  the  weight  of  the  carbon  in  i  Ib. 
of  the  fuel  by  8080,  and  that  of  the  hydrogen  by  34,400,  when  the  sum 
of  the  products  would  represent  the  theoretical  calorific  value.  But  if 
the  fuel  contains  oxygen  already  combined  with  it,  the  calorific  value 
will  be  diminished,  since  less  oxygen  will  be  required  from  the  air. 
For  example,  i  gram  of  wood  contains  0.5  gram  of  carbon,  0.06  of 
hydrogen,  and  0.44  of  oxygen.  Now,  oxygen  combines  with  one-eighth 
of  its  weight  of  hydrogen  to  form  water,  so  that  the  0.44  gram  of 
oxygen  will  convert  0.44  -r  8  =  0.055  of  the  hydrogen  into  water,  without 
evolution  of  available  heat,  leaving  only  0.005  available  for  the  produc- 
tion of  heat.  The  calorific  value  of  the  wood,  therefore,  would  be 
represented  by  the  sum  of  0.005x34400  (=172)  and  0.5x8080 
(  =  4040)  which  would  amount  to  4212  ;  or  i  gram  of  wood  should 
raise  4212  grams  of  water  from  o°  C.  to  i°  C. 

These  considerations  lead  to  the  following  general  formula  for  caku- 


164 


CALORIMETER. 


lating  the  calorific  value  of  a  fuel  containing  carbon,  hydrogen,  and 
oxygen,  where  c,  h,  and  o,  respectively  represent  the  carbon,  hydrogen, 
and  oxygen  in  i  gram  of  fuel. 

The  calorific  value  (or  number  of  grams  of  water  which  might  be 

heated  by  the  fuel  from  o°  C.  to  i  °  C)  =  8080  c  +  34400 


*  - 


The  calorific  value  of  a  coal,  as  determined  by  experiment  in  a  calorimeter  is 
generally  higher  than  that  calculated  by  the  above  formula.*  This  arises  from  lack 
of  knowledge  as  to  how  the  elements  of  the  coal  are  combined  together. 

A  convenient  form  of  calorimeter,  known  as  Mahler's  bomb,  is  shown  in  Fig.  140, 
and  to  a  smaller  scale  in  position  for  use  in  Fig.  141.  The  weighed  substance  to  be 
burnt  (or  the  mixture  the  reaction  between  the  constituents  of  which  is  to  be  started 
by  heat)  is  placed  in  a  platinum  boat  C  (Fig.  141),  attached  by  metal  rods  to  the 
cover  of  the  steel  bottle  B.  The  cover  is  screwed  on  to  the  bottle,  the  joint  being 
made  tight  by  means  of  a  lead  washer  P.  The  bomb  is  now  connected  at  N  with 


JV 


R 


Fig.  140. — Calorimetric  bomb. 


Fig.  141. — Calorimetric  bomb. 


a  tube  leading  from  a  bottle  of  compressed  oxygen,  and  having  a  pressure  gauge 
inserted  in  it,  and  is  filled  with  oxygen  under  pressure  by  slowly  turning  the  screw 
valve  R  and  closing  it  againiwhen  the  pressure  gauge  marks  5-10  atmospheres.  The 
bomb  is  now  placed  in  the  calorimeter  chamber  Z>,  containing  a  known  weight  of 
water,  and  surrounded  by  an  air  jacket  H,  itself  surrounded  by  a  water  jacket  A. 
One  of  the  rods  that  supports  the  tray  C  passes  through  an  insulating  plug  Ein  the 
cover  of  the  bottle  J5,  while  the  other  is  in  electrical  contact  with  the  bottle.  Thus,, 
by  connecting  the  end  of  the  insulated  wire  with  one  pole  of  a  battery,  and  the 
bottle  with  the  other  pole,  an  electric  current  may  be  passed  through  the  tray  C  (or 
through  a  platinum  spiral  embedded  in  the  substance  as  shown  in  Fig.  141),  so  as  to 
heat  it  to  ignite  the  substance  to  be  burnt.  (The  quantity  of  electric  current  used 
for  this  purpose  may  be  measured,  and  the  heat  thus  introduced  into  the  calori- 
meter may  be  calculated  from  the  known  equivalency  of  electric  energy  and  heat 
energy.)  The  battery  is  cut  off  as  soon  as  ignition  has  occurred,  and  the  stirrer  S' 
having  been  set  in  motion  the  thermometer  T  is  read  at  intervals,  note  being  taken  of 
the  highest  point  attained  and  the  time  occupied  in  attaining  it. 

*  Results  more  in  accord  with  the  practical  value  are  claimed  to  be  obtained  from  the 
following  formula,  where  Q  =  quantity  of  heat,  C'  =  carbon  left  as  coke  on  distilling  the 
coal,  and  C"=carbon  contained  in  the  volatile  products  :  Q  =  8080  C'  +11214  €"  +  34462  H.. 
If  much  O  be  present,  one-eighth  of  its  weight  must  be  deducted  from  the  H. 


CALORIFIC   INTENSITY   OF   FUELS.  165 

If  .all  the  heat  of  the  combustion  (or  reaction)  passed  into  the  water  of  the  calori- 
meter the  calculation  of  the  result  would  be  easy  ;  for  the  weight  of  the  water 
multiplied  by  the  rise  of  temperature  would  represent  the  heat  of  combustion.  As, 
however,  the  whole  apparatus  shares  the  heat  with  the  water  in  the  calorimeter 
chamber,  the  capacity  of  the  apparatus  for  heat  must  be  ascertained.  This  is  best 
effected  by  burning  a  known  weight  of  a  substance  of  known  calorific  value 
(naphthalene,*  for  example)  in  the  bomb,  and  observing  how  much  of  the  total  heat 
passes  into  the  water  in  the  calorimeter  ;  the  difference  between  this  quantity  and 
the  known  total  heat  is  the  amount  of  heat  absorbed  by  the  apparatus,  and  when 
divided  by  the  rise  of  temperature  shows  the  heat  capacity  of  the  apparatus. 

Suppose  that  I  gram  of  coal  has  been  burnt  in  the  manner  described,  that  the 
weight  of  water  in  the  calorimeter  is  w  grams,  that  the  rise  of  temperature  observed 
is  t°  C,  and  that  the  heat  capacity  of  the  apparatus  is  k  gram-units  ;  then  the  heat 
of  combustion  of  I  gram  of  coal  is  wt  +  lit.  In  accurate  work  a  correction  must 
be  made  for  the  heat  lost  by  radiation  and  convection  from  the  calorimeter  during 
the  time  occupied  by  the  experiment ;  for  the  methods  of  making  this  correction  a 
text-book  on  Physics  must  be  consulted. 

In  the  case  of  compounds  of  carbon  and  hydrogen,  it  has  been  ob- 
served, that  even  when  they  have  the  same  composition  in  100  parts, 
they  have  not  of  necessity  the  same  calorific  value,  the  latter  being 
affected  by  the  difference  in  the  arrangement  of  the  component  atoms 
of  the  compound,  which  causes  a  difference  in  the  quantity  of  heat 
absorbed  during  its  decomposition.  Thus,  olefiant  gas  (C2H4)  and 
cetylene  (C.6H32)  have  the  same  percentage  composition,  and  their 
calculated  calorific  values  would  be  identical,  but  the  former  is  found 
to  produce  11,858  units  of  heats,  and  the  latter  only  11,055. 

It  must  be  remembered  that  the  calorific  value  of  a  fuel  represents 
the  actual  amount  of  heat  which  a  given  weight  of  it  is  capable  of 
producing,  and  is  quite  independent  of  the  manner  in  which  the  fuel 
is  burnt.  Thus,  a  hundredweight  of  coal  will  produce  precisely  the 
same  amount  of  heat  in  an  ordinary  grate  as  in  a  wind-furnace, 
though  in  the  former  case  the  fire  will  scarcely  be  capable  of  melt- 
ing copper,  and  in  the  latter  it  will  melt  steel.  The  difference  resides 
in  the  temperature  or  calorific  intensity  of  the  two  fires  :  in  the  wind- 
furnace,  through  which  a  rapid  draught  of  air  is  maintained  by  a 
chimney,  a  much  greater  weight  of  atmospheric  oxygen  is  brought  into 
contact  with  the  fuel  in  a  given  time,  so  that,  in  that  time,  a  greater 
weight  of  fuel  will  be  consumed  and  more  heat  will  be  produced :  hence 
the  fire  will  have  a  higher  temperature,  for  the  temperature  represents, 
not  the  quantity  of  heat  present  in  a  given  mass  of  matter,  but  the  in- 
tensity or  extent  to  which  that  heat  is  accumulated  at  any  particular 
point.  In  the  case  of  the  wind-furnace  here  cited,  a  further  advantage 
is  gained  from  the  circumstance  that  the  rapid  draught  of  air  allows  a  J 
given  weight  of  fuel  to  be  -consumed  in  a  smaller  space,  and,  of  course,  y 
the  smaller  the  area  over  which  a  given  quantity  of  heat  is  distributed, 
the  higher  is  the  temperature  within  that  area  (as  exemplified  in  the 
use  of  the  common  burning-glass).  In  some  of  the  practical  applications 
of  fuel,  such  as  heating  steam  boilers  and  warming  buildings,  it  is  the 
calorific  value  of  the  fuel  which  chiefly  concerns  us  ;  but  the  case  is 
different  where  metals  are  to  be  melted,  or  chemical  changes  to  be 
brought  about  by  the  application  of  a  very  high  temperature,  for  it  is 
then  the  calorific  intensity,  or  actual  temperature  of  the  burning  mass, 
which  has  to  be  considered.  No  accurate  method  has  yet  been  devised 

*  One  gram  evolves  96,920  gram-units  of  heat. 


1 66  CALCULATING  CALORIFIC   INTENSITY. 

for  determining  by  direct  experiment  the  calorific  intensity  of  fuel,  nor 
can  this  value  be  ascertained  properly  by  calculation  owing  to  lack  of 
complete  data. 

It  will  be  instructive,  however,  to  consider  how  some  idea  of  calorific  intensity 
may  be  obtained  from  the  calorific  value. 

Let  it  be  required  to  calculate  the  calorific  intensity,  or  actual  temperature,  of 
carbon  burning  in  pure  oxygen  gas. 

Twelve  grams  of  carbon  combine  with  32  grams  of  oxygen,  producing  44  grams  of 
C02  ;  hence  I  gram  of  carbon  combines  with  2.67  grams  of  oxygen,  producing  3.67 
grams  of  CO2.  It  has  been  seen  above  that,  supposing  that  the  water  would  bear 
such  an  elevation  of  temperature,  and  that  its  specific  heat  would  remain  constant, 
the  i  gram  of  carbon  would  raise  i  gram  of  water  from  o°  to  8080°  C.  If  the 
specAjic  heat  (or  heat  required  to  raise  i  gram  through  i°)  of  C0.2  were  the  same  as 
that  of  water,  8080°  divided  by  3.67  would  represent  the  temperature  to  which  the 
3.67  grams  of  C02  would  be  raised,  and  therefore  the  temperature  to  which  the 
solid  carbon  producing  it  would  be  raised  in  the  act  of  combustion.  But  the 
specific  heat  of  carbonic  acid  gas  is  only  0.2163,  so  that  a  given  amount  of  heat 
would  raise  i  gram  of  C02  to  nearly  five  times  as  high  a  temperature  as  that  to 
which  it  would  raise  i  gram  of  water.  * 

Dividing  8080  units  of  heat  (available  for  raising  the  temperature  of  the  C02)  by 
0.2163  (the  quantity  of  heat  required  to  raise  i  gram  of  C02  through  i°),  we  obtain 
37355  f°r  the  number  of  degrees  through  which  i  gram  of  CO2  might  be  raised  by 
the  combustion  of  i  gram  of  carbon.  But  there  are  3.67  grams  of  CO2  formed  in 
the  combustion,  so  that  the  above  number  of  degrees  must  be  divided  by  3.67  in 
order  to  obtain  the  actual  temperature  of  the  C02  at  the  instant  of  its  production, 
that  is,  the  temperature  of  the  burning  mass.  The  calorific  intensity  of  carbon 
burning  in  pure  oxygen  is  therefore  (37355°  0.^3.67  =  )  10178°  C.  (or  18352°  F.). 
But  if  the  carbon  be  burnt  in  air,  the  temperature  will  be  far  lower,  because  the 
nitrogen  of  the  air  will  absorb  a  part  of  the  heat,  to  which  it  contributes  nothing. 
The  2.67  grams  of  oxygen  required  to  burn  i  gram  of  carbon  would  be  mixed,  in  air, 
with  8.93  grams  of  nitrogen,  so  that  the  8080  units  of  heat  would  be  distributed  over 
3.67  grams  of  C02  and  8.93  grams  of  nitrogen.  Since  the  specific  heat  of  COois 
0.2163,  the  product  of  3.67  x  0.2163  (or  °-794)  represents  the  quantity  of  heat  required 
to  raise  the  3.67  grams  of  C02  from  o°  to  i°  C. 

The  specific  heat  of  nitrogen  is  0.2438  ;  hence  8.93  x  0.2438  (or  2.177)  represents 
the  quantity  of  heat  required  to  raise  the  8.93  grams  of  atmospheric  nitrogen  from 
o°toi°C. 

Adding  together  these  products,  we  find  that  0.794  +  2.177  =  2.971  represents  the 
quantity  of  heat  required  to  raise  both  the  nitrogen  and  carbonic  acid  gas  from 
o°  to  i°  C. 

Dividing  the  8080°  by  2.971,  we  obtain  2720°  C.  (4928°  F.)  for  the  number  of 
degrees  through  which  these  gases  would  be  raised  in  the  combustion,  i.e.,  for  the 
calorific  intensity  of  carbon  burning  in  air.  By  heating  the  air  before  it  enters  the 
furnace  (as  in  the  hot-blast  iron  furnace),  of  course  the  calorific  intensity  would  be 
increased  ;  thus,  if  the  air  be  introduced  into  the  furnace  at  a  temperature  of  600°  F., 
it  might  be  stated,  without  serious  error,  that  the  temperature  producible  in  the 
furnace  would  be  5528°  F.  (4928° +  600°).  The  temperature  might  be  further  in- 
creased by  diminishing  the  area  of  combustion,  as  by  employing  very  compact  fuel 
and  increasing  the  pressure  of  the  blast. 

In  calculating  the  calorific  intensity  of  hydrogen  burning  in  air,  from  its  calorific 
value,  it  must  be  remembered  that,  in  the  experimental  determination  of  the  latter 
number,  the  steam  produced  in  the  combustion  was  condensed  to  the  liquid  form, 
so  that  its  latent  heat  was  added  to  the  number  representing  the  calorific  value  of 
the  hydrogen  ;  but  the  latent  heat  of  the  steam  must  be  deducted  in  calculating  the 
calorific  intensity,  because  the  steam  goes  off  from  the  burning  mass  and  carries  its 
latent  heat  with  it. 

One  gram  of  hydrogen,  burning  in  air,  combines  with  8  grams  of  oxygen,  pro- 
ducing 9  grams  of  steam,  leaving  26.77  grams  of  atmospheric  nitrogen,  and 
evolving  34400  units  of  heat. 

It  has  been  experimentally  determined  that  the  latent  heat  of  steam  is  537,  that  is, 

*  It  is  here  assumed  that  the  specific  heat  of  gases  is  constant  as  the  temperature  rises  ;  as 
a  fact  it  increases.  The  specific  heat  of  steam  is  calculated  to  be  doubled,  and  that  of  CO2  to 
be  more  than  doubled,  at  1200°  C. 


THE  REGENERATIVE  FURNACE.  167 

i  gram  of  water,  in  becoming  steam,  absorbs  537  units  of  heat  (or  as  much  heat  as 
would  raise  537  grams  of  water  from  o°  to  i°  0.)  without  rising  in  temperature  as 
indicated  by  the  thermometer.  The  9  grams  of  water  produced  by  the  combustion 
of  I  gram  of  hydrogen  will  absorb,  or  render  latent,  537x9  =  4833  units  of  heat. 
Deducting  this  quantity  from  the  34400  units  evolved  in  the  combustion  of  i  gram 
of  hydrogen,  there  remain  29567  units  of  heat  available  for  raising  the  temperature 
of  the  9  grams  of  steam  and  26. 77  grams  of  atmospheric  nitrogen.  The  specific  heat 
of  steam  being  0.480  the  number  (o. 480  x  9^)4.32  represents  the  quantity  of  heat 
required  to  raise  the  9  grains  of  steam  through  i°  C. ;  and  the  specific  heat  of  nitro- 
gen (0.2438)  multiplied  by  its  weight  (26.77  grams)  gives  6.53  units  of  heat  required 
to  raise  the  26.77  grams  of  nitrogen  through  i°  C.  By  dividing  the  available  heat 
(29567  units)  by  the  joint  quantities  required  to  raise  the  steam  and  nitrogen  through 
i°C.  (4.32  +  6.53=10.85),  we  obtain  the  number  2725°  C.  U937°  F.)  for  the  calorific 
intensity  of  hydrogen  burning  in  air. 

The  actual  calorific  intensity  of  the  fuel  is  not  so  high  as  it  should  be 
according  to  theory,  because  a  part  of  the  carbon  and  hydrogen  is  con- 
verted into  gas  by  destructive  distillation  of  the  fuel,  and  this  gas  is  not 
actually  burnt  in  the  fire,  so  that  its  calorific  intensity  is  not  added  to 
that  of  the  burning  solid  mass.  Again,  a  portion  of  the  carbon  is  con- 
verted into  carbonic  oxide  (CO),  especially  if  the  supply  of  air  be  im- 
perfect, and  much  less  heat  is  produced  than  if  the  carbon  were  converted 
into  carbon  dioxide ;  although  it  is  true  that  this  carbonic  oxide  may  be 
consumed  above  the  fire  by  supplying  air  to  it,  the  heat  thus  produced 
does  not  increase  the  calorific  intensity  or  temperature  of  the  fire  itself. 

One  gram  of  carbon  furnishes  2.33  grams  of  carbonic  oxide.  These  2.33  grams  of 
carbonic  oxide  evolve,  in  their  combustion,  5599  units  of  heat.  But  if  the  I  gram 
of  carbon  had  been  converted  at  once  into  carbon  dioxide,  it  would  have  evolved 
8080  units  of  heat,  so  that  8080-  5599,  or  2481,  represents  the  heat  evolved  during 
the  conversion  of  i  gram  of  carbon  into  carbonic  oxide,  showing  that  a  considerable 
loss  of  heat  in  the  fire  is  caused  by  ani  imperfect  supply  of  air.  It  has  been 
already  pointed  out  that  the  formation  of  carbonic  oxide  is  sometimes  encouraged 
with  a  view  to  the  production  of  a  flame  from  non-flaming  coal,  such  as 
anthracite. 

The  actual  calorific  intensity  of  fuel  is  diminished  by  the  heat  con- 
sumed in  bringing  the  portion  of  fuel  yet  unconsumed,  as  well  as  the 
surrounding  parts  of  the  grate,  up  to  the  temperature  of  the  fire. 

In  all  ordinary  fires  and  furnaces,  a  large  amount  of  heat  is  wasted  in 
the  current  of  heated  products  of  combustion  escaping  from  the  chimney. 
Of  course,  a  portion  of  this  heat  is  necessary  in  order  to  produce  the 
draught  of  the  chimney.  In  boiler  furnaces  it  is  found  that,  for  this 
purpose,  the  temperature  of  the  air  escaping  from  the  chimney  must 
not  be  lower  than  from  500°  to  600°  F.  If  the  fuel  could  be  consumed 
by  supplying  only  so  much  air  as  contains  the  requisite  quantity  of 
oxygen,  a  great  saving  might  be  effected,  but  in  practice  about  twice 
the  calculated  quantity  of  air  must  be  supplied  in  order  to  effect  the 
removal  of  the  products  of  combustion  with  sufficient  rapidity. 

Much  economy  of  fuel  results  from  the  use  of  furnaces  constructed 
on  the  principle  of  Siemens'  regenerative  furnace,  in  which  the  waste 
heat  of  the  products  of  combustion  is  absorbed  by  a  quantity  of  fire- 
bricks, and  employed  to  heat  the  air  before  it  enters  the  furnace,  two 
chambers  of  firebricks  doing  duty  alternately,  for  absorbing  the  heat 
from  the  issuing  gas,  and  for  imparting  heat  to  the  entering  air,  the 
current  being  reversed  by  a  valve  as  soon  as  the  firebricks  are  strongly 
heated.  This  system  is  best  adapted  for  the  use  of  gaseous  fuel  which 


i68 


CHEMICAL  TYPES. 


can  also  be  heated  by  the  hot  fire  bricks  before  its  combustion,  a  very 
high  temperature  being  thus  attainable. 

The  following  table  shows  the  percentage  composition  of  samples  of 
the  principal  varieties  of  fuel  together  with  their  calorific  values : — 


C. 

H. 

0. 

N. 

S. 

Ash. 

Calorific 
Value. 

Wood  (oak)       . 

50.18 

6.08 

42.64 

O.IO 



I.OO 

3,OOO 

Peat  . 

54.38 

5.08 

29-54 

1.31 

— 

8.69 

4,000 

Lignite      . 

66.32 

5.63 

22.86 

0.56 

2.36 

2.27 

5,000 

Bituminous  coal 

78.57 

5-29 

12.88 

1.84 

0-39 

1.03 

8,250 

Wigan  cannel    . 

80.06 

5-53 

8.09 

2.12 

1.50 

2.70 

8,750 

Charcoal    . 

81.97 

2.30 

14-  i  5 

— 

1.  60 

8,000 

Anthracite 

90-39 

3-28 

2.98 

0.83 

0.91 

1.61 

9,000 

Coke  . 

92.48 

0.47 

0-93 

0-73 

I.I4 

4-27 

8,000 

Petroleum  . 

85.00 

13.00 

2.OO 

11,000 

H. 

CH4 

CO 

C2H4* 

C02 

F. 

0. 

Calorific 
Value.! 

c°M™e} 

43-99 

39.36 

6.42 

4.12 

— 

5.40 

0.40 

170,000 

„        cannel 

41.72 

41.88 

4.98 

8.72 

— 

2.71  • 

) 

Producer  gas    . 

2.20 

7.40 

22.80 

3.60 

63.50    0.50 

28,000 

Water  gas 

48.00 

41.00 



6.00 

5.00  |    — 

74,000 

Mond  gas 

29.00 

2.OO 

I  I.OO 

— 

16.00 

42.00 

40,000 

TYPES  OF  CHEMICAL  COMPOUNDS. 

95.  It  has  been  seen  in  the  preceding  pages  that — 

One  vol.  chlorine  combines  with  one  vol.  hydrogen. 
One     „    oxygen  ,,  „     two  vols.         „ 

One    „    nitrogen        „  „     three  „  „ 

One    „    carbon  „  „     four    ,,  „ 

and  that  although  other  compounds  of  these  elements  with  hydrogen 
may  exist  they  are  less  stable  than  the  compounds  in  question  and 
contain,  moreover,  a  smaller  proportion  of  hydrogen. 

The  composition  of  the  four  compounds  in  question  may  be  repre- 
sented by  the  formulae  C1H,OH2,NH3  and  CH4  respectively,  and  if  the 
valency  of  an  element  be  defined  as  the  maximum  number  of  atoms  of 
hydrogen  with  which  one  atom  of  the  element  can  combine,  chlorine, 
oxygen,  nitrogen,  and  carbon  are  respectively  mono-  di-  tri-  and  tetra- 
valent  elements.  It  will  be  found  that  no  atom  can  combine  with  more 
than  four  atoms  of  hydrogen.  This  being  the  case,  the  hydrogen  com- 
pounds of  all  elements  must  fall  in  one  or  other  of  the  four  classes  of 
which  hydrochloric  acid,  water,  ammonia,  and  marsh  gas  are  the  types. 

One  of  the  atoms  of  H  in  each  of  these  typical  molecules  may  be  exchanged  for 
another  atom,  usually  a  metal  ;  thus  C1H  gives  CINa.  OH2  gives  OHNa,  NH3  gives 
NH2Na,  CH4  gives  CH3Na,  It  is  evident  that  the  groups  OH,  NH2,  and  CH3  are 
on  the  same  footing  as  the  elementary  atom  Cl  in  C1H  ;  as  already  explained,  each 
is  a  radicle — that  is.  a  group  capable  of  being  exchanged  for  an  element.  Since 

*  Including'  benzene  vapour,  acetylene,  etc. 
f  Gram  units  per  cubic  foot  (28.315  litres). 


CHLORINE.  169 

each  of  these  radicles  is  equivalent  to  Cl,  which  unites  with  one  atom  of  H,  and  is 
therefore  monovalent,  each  is  a  rnonovalent  radicle. 

The  elements  may  be  roughly  divided  into  those  which  form  stable  compounds 
with  hydrogen  and  those  which  are  substituted  for  hydrogen  ;  the  latter  class  is 
approximately  coincident  with  that  which  includes  the  elements  forming  basic 
oxides  (i.e.,  the  metals),  whilst  the  former  class  contains  those  elements  which  form 
acid  oxides  or  anhydrides  (i.0.,  the  non-metals).  The  valency  of  a  non-metal  is 
thus  fixed  by  the  number  of  atoms  of  hydrogen  in  a  molecule  of  its  maximum 
hydrogen  compound,  whilst  that  of  a  metal  is  determined  by  the  formula  for  its 
compound  with  Cl  or  with  0. 

Thus,  sulphur,  whose  maximum  hydrogen  compound  is  SH2,  falls  under  the  oxygen 
type,  and  is  divalent  towards  hydrogen  ;  phosphorus,  of  which  PH3  is  the  hydrogen 
compound  containing  the  largest  proportion  of  hydrogen,  falls  under  the  nitrogen 
type,  and  is  trivalent. 

Again,  the  analysis  of  zinc  oxide  shows  that  the  proportion  of  zinc  to  oxygen  in 
this  compound  is  represented  by  the  formula  OZn  ;  zinc  oxide,  therefore,  is  of  the 
type  OH2,  one  atom  of  the  metal  having  been  substituted  for  H2.  Thus,  Zn  falls  under 
the  oxygen  type,  and  is  divalent,  from  which  fact  it  would  be  possible  to  foretell  the 
composition  of  its  chloride  ;  for,  since  this  can  only  be  formed  by  the  substitution 
of  two  atoms  of  H,  the  type  C1H  must  be  doubled,  C12H2,  before  the  zinc  chloride 
can  be  formed  ;  the  formula  in  question  would  then  be  Cl2Zn. 

The  analysis  of  the  higher  chloride  of  iron  (two  are  known)  shows  that  the  formula 
for  this  chloride  is  FeCl3,  showing  that  the  iron  has  displaced  the  H  in  the  type 
C1H  trebled,  or  C13H3.  From  this  fact  the  formula  for  the  higher  oxide  of  iron  would 
be  prophesied  to  be  03Fe2  ;  for,  since  Fe  displaces  H3,  the  type  OH2  must  be 
trebled,  OgHg,  in  order  that  the  H  may  be  totally  displaced  by  the'h-on,  two  atoms  of 
which  will  displace  six  of  H. 

It  has  been  already  noted  that  the  valency  of  nitrogen  towards  H  is  not  the  limit 
of  the  atom-fixing  power  of  this  element.  It  will  be  noted  in  the  sequel  that  the 
atom-fixing  power  which  an  element  exhibits  towards  oxygen  is  generally  greater 
than  that  exhibited  towards  hydrogen. 


CHLORINE. 

Cl  =  35.5  parts  by  weight  =  I  volume. 

96.  This  element  is  never  found  in  the  uncombined  state,  but  is  very 
abundant  in  the  mineral  world  in  the  forms  of  sodium  chloride  (common 
salt)  and  potassium  chloride.  In  these  forms  also  it  is  an  important  con- 
stituent of  the  fluids  of  the  animal  body,  but  as  it  is  not  found  in  sufficient 
proportion  in  vegetable  food,  or  in  the  solid  parts  of  animal  food,  a 
quantity  of  salt  must  be  added  to  these  in  order  to  form  a  wholesome 
diet.  Sodium  chloride  is  indispensable  as  a  raw  material  for  several  of 
the  most  useful  arts,  such  as  the  manufacture  of  soaps  and  glass,  bleach- 
ing, &c.  ;  in  fact,  it  is  the  source  of  three  of  the  most  generally  useful 
chemical  products — viz.,  chlorine,  hydrochloric  acid,  and  soda. 

About  the  middle  of  the  seventeenth  century,  a  German  chemist 
named  Glauber  distilled  some  common  salt  with  sulphuric  acid,  and 
obtained  a  strongly  acid  liquid  to  which  he  gave  the  name  muriatic  acid 
(from  muria,  brine) ;  this  was  proved  to  be  identical  with  the  acid 
long  known  to  the  alchemist  as  spirit  of  salt  (obtained  by  distilling  salt 
with  clay).  The  saline  mass  which  was  left  after  the  experiment  was 
then  termed  Glauber's  salt,  but  afterwards  received  its  present  name  of 
sodium  sulphate. 

It  was  undoubtedly  a  natural  inference  from  this  experiment  that 
common  salt  was  composed  of  muriatic  acid  and  soda,  and  that  the 
sulphuric  acid  had  a  greater  attraction  for  the  soda  than  the  muriatic 
acid  had,  which  was  therefore  displaced  by  it.  In  accordance  with  this 


1 70  PEEPAEATION  OF  CHLORINE. 

view,  common  salt  was  called  muriate  of  soda,  without  further  question, 
until  the  year  1810,  when  the  experiments  of  Davy  proved  that  it  was 
really  composed  of  the  two  elementary  substances,  chlorine  and  sodium, 
and  must  therefore  be  styled,  as  it  now  is,  sodium  chloride,  and  repre- 
sented by  the  formula  Nad.  It  was  further  shown  by  Davy  that  the 
muriatic  acid  was  really  composed  of  chlorine  and  hydrogen,  and  that 
it  was,  in  fact,  HC1,  or  chloride  of  sodium  (NaCl),  in  which  the  sodium 
had  been  displaced  by  hydrogen. 

Preparation  of  chlorine. — In  order  to  extract  chlorine  from  common 
salt,  the  salt  is  heated  with  black  oxide  of  manganese  and  diluted 
sulphuric  acid,  when  the  sulphates  of  sodium  and  manganese  are  left  in 
solution,  and  chlorine  escapes  in  the  form  of  gas — 

2NaCl  +  Mn02  +  2H2S04  =  Na2S04  +  MnS04  +  2H20  +  C12. 

40  grins,  of  common  salt  may  be  mixed  with  30  grms.  of  binoxide  of  man- 
ganese, introduced  into  a  retort  (Fig.  142)  and  a  cold  mixture  of  44  c.c.  of 


Fi»-.  142. — Preparation  of  chlorine. 

strong  sulphuric  acid  with  no  c.c.  of  water  poured  upon  it.  The  retort  having  been 
well  shaken,  to  wet  the  powder  thoroughly  with  the  acid,  a  very  gentle  heat  is 
applied,  and  the  gas  collected  in  bottles  filled  with  water  and  inverted  in  the  pneu- 
matic trough  ;  the  stoppers,  previously  greased,  are  then  inserted  under  water  into 
the  bottles.  The  first  bottle  or  two  contains  the  air  from  the  retort,  and  therefore 
has  a  paler  colour  than  the  pure  chlorine  afterwards  collected.  It  is  advisable  to 
keep  a  jar  filled  with  water  standing  ready  on  the  shelf  of  the  trough,  so  that  any 
excess  of  chlorine  may  be  passed  into  it  instead  of  being  allowed  to  escape  into  the 
air  and  cause  serious  inconvenience.  The  bottles  of  moist  chlorine  must  always  be 
preserved  in  the  dark.  Chlorine  may  also  conveniently  be  prepared  by  gently  heat- 
ing 30  grms.  of  binoxide  of  manganese  with  no  c.c.  of  common  hydrochloric  acid  ; 
Mn02  +  4HC1  =  MnClg  +  2H20  +  C12.  Either  of  the  above  methods  will  furnish  about 
2800  c.c.  of  chlorine.  If  chlorine  be  required  free  from  HC1,  it  may  be  passed 
through  a  strong  solution  of  copper  sulphate — 

CuS04  +  2HC1  =  CuCla  +  H2S04. 

On  a  large  scale  chlorine  is  made  by  heating  manganese  dioxide  with  hydrochloric 
acid  in  stills  built  up  of  sandstone  slabs. 

In  Weldorfs  manganese  recovery  process  for  the  manufacture  of  chlorine,  the  man- 
ganese is  made  to  act  as  a  carrier  of  oxygen  from  the  atmosphere  to  the  hydrogen 
of  the  HC1,  setting  the  Cl  free.  For  this  purpose  the  chloride  of  manganese 
obtained  in  the  above  process  is  decomposed  by  lime  ;  MnCl2+CaO=:CaCl2+MnO. 
By  mixing  the  MnO  with  more  lime,  and  blowing  air  through  the  mixture  MnO2 
is  reproduced,  and  may  be  employed  for  decomposing  a  fresh  quantity  of  HC1.  In 
Deacon's  process,  a  mixture  of  air  and  hydrochloric  acid  gas  is  passed  over  hot  fire- 


PEOPERTIES   OF  CHLOEINE.  171 

brick  which  has  been  soaked  in  solution  of  copper  sulphate  and  sodium  sulphate,  and 
dried.  The  final  result  is  expressed  by  the  equation  2HC1  +  (N4  +  O)  =  H20  +  C12  +  N4, 
so  that  the  chlorine  obtained  is  mixed  with  twrice  its  volume  of  nitrogen,  which 
does  not  interfere  seriously  with  its  useful  application.  The  action  of  the  copper- 
salt  has  not  been  clearly  explained,  but  it  appears  to  depend  upon  the  instability  of 
the  chlorides  of  copper  under  the  influence  of  heat  and  oxygen. 

Chlorine  is  now  made  by  electrolysing  NaCl,  a  process  which,  among  others, 
will  receive  notice  under  Alkali. 

Properties  of  chlorine. — The  physical  and  chemical  properties  of 
chlorine  are  more  striking  than  those  of  any  element  hitherto  con- 
sidered. Its  colour,  whence  it  derives  its  name  (^Xwpo'c,  pale  green),  is 
bright  greenish-yellow,  its  odour  insupportable.  It  is  twice  and  a  half 
as  heavy  as  air  (sp.  gr.  2.47),  and  may  be  reduced  to  the  liquid  state  by 
cooling  it  to  -  34°  C.  (its  boiling-point),  or  by  a  pressure  of  8.5 
atmospheres  at  12.5°  C.  If  a  bottle  of  chlorine  be  held  mouth  down- 
wards in  water,  its  stopper  removed,  one-third  of  the  chlorine  decanted 
into  a  jar,  and  the  rest  of  the  gas  shaken  with  the  water  in  the  bottle, 
the  mouth  of  which  is  closed  by  the  palm  of  the  hand,  the  water  will 
absorb  about  twice  its  volume  of  chlorine,  producing  a  partial  vacuum 
in  the  bottle,  which  will  be  held  firmly  against  the  hand  by  atmospheric 
pressure.  If  air  be  then  allowed  to  enter,  and  the  bottle  again  shaken 
so  long  as  there  is  any  absorption,  a  saturated  solution  of  chlorine 
(liquor  chlori,  chlorine  water)  will  be  obtained.  By  exposing  this  yellow 
solution  to  a  temperature  approaching  o°  C.,  yellow  crystals  of  chlorine 
hydrate  (C1.4H20)  are  obtained,  the  liquid  becoming  colourless  ;  under 
atmospheric  pressure  the  crystals  decompose  into  water  and  chlorine  at 
9.6°  C. 

When  the  water  in  the  pneumatic  trough,  over  which  chlorine  is  being  collected, 
happens  to  be  very  cold,  the  gas  is  often  so  foggy  as  to  be  quite  opaque,  in  conse- 
quence of  the  deposition  of  minute  crystals  of  the  hydrate.  On  standing,  the  gas 
becomes  clear,  crystals  of  the  hydrate  being  deposited  like  hoar-frost  upon  the 
sides  of  the  bottle  ;  the  gas  also  becomes  clear  when  the  bottles  are  slightly 
warmed. 

Chlorine  hydrate  affords  a  convenient  source  of  liquid  chlorine.  The  crystals  are 
rammed  into  a  pretty  strong  tube  closed  at  one  end,  about  12  inches  long,  and  ^  an 
inch  in  diameter,  previously  cooled  in  ice.  The  tube,  having  been  nearly  filled  with 
the  crystals,  is  kept  surrounded  with  ice,  whilst  its  upper  end  is  gradually  softened 
in  the  blowpipe  flame  and  drawn  off  so  as  to  be  strongly  sealed.  When  this  tube  is 
immersed  in  water  at  38°  C.,  the  chlorine  separates  from  the  water,  and  two  layers 
of  liquid  are  formed,  the  lower  one  consisting  of  amber  yellow  liquid  chlorine  (sp. 
gr.  1.33),  and  the  upper  of  a  pale  yellow  aqueous  solution  of  chlorine.  On  allowing 
the  tube  to  cool  again,  the  crystalline  hydrate  is  reproduced,  even  at  common 
temperatures,  being  more  permanent  under  pressure.  It  may  even  be  sublimed  in  a 
sealed  tube. 

Liquid  chlorine  is  now  an  article  of  commerce,  being  transported  in  steel 
bottles. 

The  critical  temperature  of  chlorine  is  146°  C.,  and  its  critical  pressure  93.5  atm. 

The  most  characteristic  chemical  feature  of  chlorine  is  its  powerful 
attraction  for  many  other  elements  at  the  ordinary  temperature. 
Among  the  non-metals,  hydrogen,  bromine,  iodine,  sulphur,  selenium, 
phosphorus,  and  arsenic  combine  spontaneously  with  chlorine,  and 
nearly  all  the  metals  behave  in  the  same  way.* 

*  The  presence  of  moisture  appears  to  be  as  essential  for  the  combination  of  chlorine  with 
other  elements  as  it  is  for  the  combination  of  oxygen  with  other  elements.  Thus  sodium 
may  be  fused  in  absolutely  dry  chlorine  gas  without  alteration,  while  in  ordinary  chlorine 
violent  combustion  occurs.  When  the  sodium  is  heated  to  redness  in  the  dry  gas  it  burns 
explosively. 


172 


CHLORINE  AND   HYDROGEN. 


A  piece  of  dry  phosphorus  in  a  deflagrating  spoon,  immersed  in  a  bottle  of 
•chlorine  (Fig.  143),  takes  fire  spontaneously,  combining  with  the  chlorine  to  form 
phosphorous  chloride  (PC13).  A  tall  glass  shade  may  be  placed  over  the  bottle, 
which  should  stand  in  a  plate  containing  water,  so  that  the  fumes  may  not  escape 
into  the  air.  If  phosphorus  be  placed  in  a  bottle  of  oxygen,  to  which  a  small  quan- 
tity of  chlorine  has  been  added,  it  will  burst  out  after  a  minute  or  two  into  most 
brilliant  combustion. 

Powdered  antimony  (the  metal,  not  the  sulphide),  sprinkled  into  a  bottle  of 
•chlorine  (Fig.  144),  descends  in  a  brilliant  shower  of  white  sparks,  the  antimony 
burning  in  the  chlorine  to  form  antimonious  chloride  (SbCl3).  A  little  water 
.should  be  placed  at  the  bottom  of  the  bottle  to  prevent  it  from  being  cracked. 

If  a  flask,  provided  with  a  stop-cock  (Fig.  145),  be  filled  with  leaves  of  Dutch 
metal  (an  alloy  of  copper  and  zinc  resembling  gold-leaf),  exhausted  of  air,  and 
screwed  on  to  a  capped  jar  of  chlorine  standing  over  water,  on  opening  the  stop- 


Fig-.  143. 


Fig-.  144. 


oocks  so  that  the  chlorine  may  enter  the  flask,  the  metal  burns  with  a  red  light, 
forming  thick  yellow  fumes  containing  cupric  chloride  (CuCl2),  and  zinc  chloride 
<ZnCl2).  A  gold  leaf  suspended  in  chlorine  is  not  immediately  attacked,  but  gra- 
dually becomes  auric  chloride  (AuCl3). 

97.  The  most  important  useful  applications  of  chlorine  depend  upon 
its  powerful  chemical  attraction  for  hydrogen.  The  two  gases  may  be 
mixed  without  combining,  if  kept  in  the  dark ;  but  when  the  mixture 
is  exposed  to  light,  they  combine  to  form  hydrogen  chloride  (HOI) 
with  a  rapidity  proportionate  to  the  intensity  of  the  actinic  rays  (or 
rays  capable  of  inducing  chemical  change)  in  the  light  employed.  Ex- 
posed to  gas-light  or  ordinary  diffused  daylight,  the  H  and  Cl  combine 
slowly ;  but  direct  sunlight  causes  sudden  combination,  attended  with 
explosion,  resulting  from  the  expansion  which  the  hydrogen  chloride 
formed  suffers  by  the  heat  evolved  in  the  act  of  combination  (22,000 
gram  units  per  36.5  grams  of  HC1  formed).  The  light  of  magnesium 
burning  in  air,  and  some  other  artificial  lights,  also  cause  sudden  com- 
bination. The  gases  also  combine  at  about  300°  C.,  and  explode  on 
application  of  a  lighted  taper. 

Two  pint  gas-bottles  should  be  ground  so  that  their  mouths  may  be  fitted  accu- 
rately to  each  other,  and  filled  respectively  with  dry  hydrogen  and  dry  chlorine, 
both  gases  having  been  dried  by  passing  through  oil  of  vitriol,  and  collected,  the 
hydrogen  by  upward,  and  the  chlorine  by  downward,  displacement  of  air.  The 
mouths  should  be  slightly  greased  before  the  bottles  are  filled  with  gas,  and  after- 


CHLORINE  AND  HYDROGEN. 


'73 


wards  closed  with  glass  plates.  On  placing  the  bottles  together,  and  removing  the- 
plates  so  that  the  gases  may  come  in  contact  (see  Fig.  69),  the  yellow  colour  of  the 
chlorine  will  be  permanent  so  long  as  the  mixture  is  kept  in  the  dark,  but  on 
exposure  to  daylight  the  colour  will  gradually  disappear,  the  hydrochloric  acid  gas 
being  colourless.  If  the  bottles  be  now  closed  with  glass  plates,  the  small  quantity 
of  gas  which  escapes  during  the  operation  will  be  seen  to  fume  strongly  in  air,  a 
property  not  possessed  either  by  hydrogen  or  chlorine  ;  and  when  the  necks  of  the 
bottles  are  immersed  in  water,  and  the  glass  plates  withdrawn,  the  water  will  gradu- 
ally absorb  the  gas,  and  be  forced  into  the  bottles  so  as  to  fill  them,  with  the  excep- 
tion of  a  small  space  occupied  by  the  air  accidentally  admitted,  showing  that  the- 
hydrochloric  acid  gas  possesses  the 
joint  volumes  of  the  hydrogen  and 
chlorine.  If  the  water  be  tinged 
with  blue  litmus,  it  will  be  strongly 
reddened  as  it  enters  the  bottles. 

The  sudden  union  of  the  gases  with 
explosion  may  be  safely  exhibited  in 
a  Florence  flask.  The  flask  is  filled 
with  water,  which  is  then  poured  out 
into  a  measure.  Exactly  half  the 
water  is  returned  to  the  flask,  and 
its  level  in  the  latter  carefully  marked 
with  a  diamond  or  file.  The  flask, 
having  been  again  filled  with  water, 
is  closed  with  the  thumb  and  inverted 
in  the  pneumatic  trough,  so  that  Fig.  146. 

hydrogen  may  be  passed  up  into  it  to 

displace  one-half  of  the  water.  A  short-necked  funnel  is  then  inserted,  under  the 
water,  into  the  neck  of  the  flask,  and  chlorine  rapidly  decanted  up  from  a  gas-bottle 
(Fig.  146)  until  the  rest  of  the  water  has  been  displaced.  The  flask  is  now  raised 
from  the  water  and  quickly  closed  with  a  cork  (Fig.  147),  through  which  pass  two* 
gutta-percha-covered  copper  wires,  the  ends  of  which  have  been  stripped  and  brought 
sufficiently  near  to  each  other  to  allow  of  the  passage  of  the  electric  spark  within 
the  flask.  The  ends  external  to 
the  flask  are  also  stripped  and 
bent  into  hooks,  for  convenient 
connection  with  the  conducting 
wires.  The  flask  is  placed  upon 
the  ground,  and  covered  with  a 
wooden  box  to  prevent  the  pieces 
from  flying  about.  On  connecting 
the  copper  wires  with  the  conduct- 
ing wires  from  an  induction  coil 
or  an  electrical  machine,  it  will  be 
heard,  on  passing  the  spark,  that 
the  mixture  has  violently  ex- 
ploded ;  on  raising  the  box,  it  will 
be  found  filled  with  strong  fumes  Fig.  147. 

of  hydrochloric  acid,  and  a  heap 
of  small  fragments  of  glass  will  represent  the  flask. 

A  flask  filled  in  the  same  way  with  the  mixture  of  hydrogen  and  chlorine  may  be 
attached  to  the  end  of  a  long  stick,  and  thrust  out  into  the  sunlight,  when  it  explodes 
with  great  violence.  To  illustrate  the  direct  combination  of  H  and  Cl  under  the 
influence  of  artificial  light,  a  strong  half -pint  gas  cylinder  is  half  filled  with  H,  over 
water,  then  filled  up  quickly  with  Cl,  also  over  water,  closed  with  a  thin  plate  of  mica, 
placed  mouth  upwards  on  the  table,  and  a  piece  of  burning  magnesium  tape  held 
close  to  the  side  of  the  cylinder  ;  the  lightness  of  the  mica  plate  obviates  any  danger. 

A  mixture  of  H  and  Cl  which  is  to  be  exploded  by  light  must  consist  of  exactly 
equal  volumes,  for  a  slight  excess  of  either  gas  greatly  diminishes  the  sensitiveness 
of  the  mixture  to  light  ;  thus  a  mixture  of  100  vols.  of  Cl.  with  100.6  vols.  H  is 
38  per  cent,  less  sensitive  than  a  mixture  of  equal  volumes. 

The  attraction  of  chlorine  for  hydrogen   enables   it  to   decompose 
water.     Chlorine-water  may  be  preserved  in  the  dark  without  change  ; 


CHLOEINE  AND   HYDROGEN. 

but  when  exposed  to  light,  it  loses  the  smell  of  chlorine  and  becomes 
converted  into  weak  hydrochloric  acid,  the  oxygen  being  liberated  ; 
H20  +  C12  =  2HC1  +  0.*  The  decomposition  is  much  more  rapid  at  a 
red  heat,  so  that  oxygen  is  obtained  in  abundance  by  passing  a  mixture 
of  chlorine  and  steam  through  a  red-hot  tube. 

For  this  experiment  a  porcelain  tube  is  used,  loosely  filled  with  fragments  of  broken 
porcelain,  to  expose  a  large  heated  surface.  This  tube  is  gradually  heated  to  red- 
ness in  a  gas  furnace  (Fig.  148).  One  end  of  it  receives  the  mixture  of  chlorine  with 
steam,  obtained  by  passing  the  chlorine  evolved  from  hydrochloric  acid  and 


Fig.  148. — Steam  decomposed  by  chlorine. 

manganese  dioxide  in  A,  through  a  flask  (B)  of  boiling  water.  The  other  end  of 
the  tube  is  connected  with  a  bottle  (C)  containing  solution  of  potash,  to  absorb  any 
excess  of  chlorine  and  the  hydrochloric  acid  formed  ;  from  this  bottle  the  oxygen 
is  collected  over  the  pneumatic  trough. 

The  combination  of  hydrogen  with  chlorine  may  obviously  be 
regarded  as  the  substitution  of  an  atom  of  chlorine  for  an  atom  of 
hydrogen  in  a  molecule  of  hydrogen,  HH  +  C1C1  =  HC1 +  HC1,  the 
atom  of  hydrogen  substituted  having  been  removed  as  HC1.  Thus 
viewed  it  becomes  typical  of  a  large  number  of  cases  in  which  two 
atoms  of  chlorine  react  with  a  hydrogen  compound,  one  of  them  bear- 
ing away  a  hydrogen  atom  in  the  form  of  HC1  whilst  the  other  takes 
the  place  of  the  hydrogen  thus  removed.  Such  a  substitution  of  chlorine 
for  hydrogen  is  known  as  metalepsis,  and  is  a  very  common  reaction  of 
chlorine  with  hydrocarbons  ;  since  the  formation  of  hydrogen  chloride 
is  initiated  by  light  it  is  not  surprising  that  metalepsis  is  aided  by  this 
agency. 

When  equal  volumes  of  marsh  gas  (CH4)  and  chlorine  are  mixed  and  exposed  to 
sunlight  the  volume  of  the  mixture  remains  unaltered,  but  after  a  time  the  yellow 
colour  of  the  chlorine  is  no  longer  observed,  and  the  gas  is  found  to  consist  of  equal 
volumes  of  methyl  chloride  and  hydrogen  chloride,  CH4  +  C12=CH3C1  +  HC1.  The 
metalepsis  may  be  carried  further  by  mixing  methyl  chloride  with  more  chlorine, 
CH3C1  +  C12  =  CH2C12  +  HC1.  Again  CH2C12  with  Cla  will  yield  chloroform  CHC13, 
and  this  with  C12  will  yield  carbon  tetrachlorlde  CC14.  By  mixing  one  volume  of 
marsh  gas  with  its  own  volume  of  C02,  to  prevent  violent  action,  and  adding  four 
volumes  of  chlorine,  an  oily  mixture,  containing  chiefly  CHC13  and  CC14  is  formed 
under  the  influence  of  daylight. 

Since  water  is  decomposed  by  chlorine,  it  is  not  surprising  that  most 

*  A  portion  of  this  oxygen  beeomes  hypochlorous  acid  (HC1O),  chloric  acid  (HC1O3)  and 
perchloric  acid  (HC1O4),  particularly  if  the  light  be  not  very  intense. 


OXIDISING  ACTION   OF  CHLORINE.  175 

other  hydrogen  compounds  are  attacked  by  it.  Ammonia  (NH3)  is 
acted  on  with  great  violence.  If  a  stream  of  ammonia  gas  issuing  from 
a  tube  connected  with  a  flask  in  which  solution  of  ammonia  is  heated 
be  passed  into  a  bottle  of  chlorine,  it  takes  fire  immediately,  buring 
with  a  peculiar  flame,  and  yielding  thick  white  clouds  of  ammonium 
chloride;  4NH3  +  C13  =  3NH4C1  +  N.  A  piece  of  folded  filter-paper 
dipped  in  strong  ammonia,  and  immersed  in  a  bottle  of  chlorine,  will 
exhibit  the  same  effect.  When  the  chlorine  is  allowed  to  act  upon 
ammonium  chloride,  its  operation  is  less  violent,  and  one  of  the  most 
explosive  substances,  nitrogen  chloride,  NC13,  is  produced. 

Many  of  the  compounds  of  hydrogen  with  carbon  are  also  decomposed 
with  violence  by  chlorine.  When  a  piece  of  folded  filter-paper  is  dipped 
into  oil  of  turpentine  (010H16),  and  afterwards  into  a  bottle  of  chlorine, 
it  bursts  into  a  red  flame,  liberating  voluminous  clouds  of  carbon  and 
hydrochloric  acid.  Acetylene  (C2H2)  was  found  to  explode  spontaneously 
with  chlorine  when  exposed  to  light  (page  141).  The  striking  decom- 
position of  olefiant  gas  (C2H4)  by  chlorine  on  the  approach  of  a  flame 
has  already  been  noticed  (page  143).  When  a  lighted  taper  is  immersed 
in  pure  chlorine,  it  is  extinguished  ;  but  if  a  little  air  be  present,  it 
continues  to  burn  with  a  small  red  flame,  the  hydrogen  only  of  the  wax 
combining  with  the  chlorine,  whilst  the  carbon  separates  in  black 
smoke,  mixed  with  the  hydrochloric  fumes.  A  mixture  of  chlorine 
with  an  equal  volume  of  oxygen  burns  up  much  of  the  carbon,  with  a 
very  pretty  effect.  When  chlorine  is  brought  in  contact  with  the  flame 
of  a  spirit-lamp,  it  renders  the  flame  luminous  by  causing  the  separation 
of  solid  particles  of  carbon  (page  149).  It  has  been  seen,  in  the  case  of 
olefiant  gas,  that  chlorine  sometimes  combines  directly  with  the  hydro- 
carbons. 

The  attraction  of  chlorine  for  hydrogen  enables  the  moist  gas  to  act 
as  an  oxidising  agent.  Thus,  if  marsh  gas  and  chlorine  be  mixed  in  the 
presence  of  water,  and  exposed  to  daylight,  the  water  is  decomposed,  its 
hydrogen  combining  with  the  chlorine,  and  its  oxygen  with  the  carbon 
of  the  marsh  gas ;  CH4  +  2H20  +  C18  =  C02  +  8HC1. 

98.  The  powerful  bleaching  effect  of  chlorine  upon  organic  colour- 
ing matters  is  now  easily  understood.  If  a  solution  of  chlorine  in 
water  be  poured  into  solution  of  indigo  (sulphindigotic  acid),  the  blue 
colour  of  the  indigo  is  discharged,  and  gives  place  to  a  comparatively 
light  yellow  colour.  The  presence  of  water  is  essential  to  the  bleaching 
of  indigo  by  chlorine,  the  dry  gas  not  affecting  the  colour  of  dry  indigo. 
The  indigo  is  first  oxidised  at  the  expense  of  the  water  and  converted 
into  isatin,  which  is  then  acted  upon  by  the  chlorine  and  converted 
by  metalepsis  into  chlorisatin,  having  a  brownish-yellow  colour — 

C16H10N202  (Indigo')   +   2H,,0   +    C14  =  2C8H5N02      (Isatin)  +  4HC1 

CgHgNOo      (Isatin)   +     Cf2  =     C8H4C1N02  (C/ilor  isatin)    +     HC1. 

Nearly  all  vegetable  and  animal  colouring  matters  contain  carbon, 
hydrogen,  nitrogen,  and  oxygen,  and  are  converted  by  moist  chlorine 
into  products  of  oxidation  or  chlorination  which  happen  to  be  colour- 
less, or  nearly  so. 

It  might  be  thought  that,  since  water  is  decomposed  by  chlorine  only 
in  light,  chlorine  would  not  behave  as  an  oxidising  agent  in  the  dark. 
Bleaching  by  chlorine  can,  however,  proceed  in  the  absence  of  light 
because  the  colouring  matter,  being  ready  to  combine  with  oxygen,  exerts 


I76 


CHLORINE   AS   A  DISINFECTANT. 


Tig.  149, 


attraction  on  the  oxygen  of  the  water,  sufficiently  powerful  to  weaken 
the  union  between  the  H  and  0  so  that  the  chlorine  can  effect  the 
decomposition. 

That  dry  chlorine  will  not  bleach  may  be  shown  by  shaking  some  oil  of  vitriol  in 
a  bottle  of  the  gas  and  allowing  it  to  stand  for  an  hour  or  two,  so  that  the  acid 
may  remove  the  whole  of  the  moisture.  A  piece  of  crimson  paper  dried  at  a 
moderate  heat  and  suspended  in  the  bottle  while  warm,  remains  unbleached  for 
hours  ;  but  a  similar  piece  suspended  in  a  bottle  of  moist  chlorine  is  bleached 
almost  immediately.  If  characters  be  written  on  crimson  paper  with  a  wet  brush, 
and  the  paper  placed  in  a  jar  beside  a  bottle  of  chlorine 
(Fig.  149),  it  will  be  found  on  removing  the  stopper 
that  white  characters  soon  make  their  appearance  on  the 
red  ground. 

When  a  collection  of  coloured  linen  or  cotton  fabrics, 
or  of  artificial  flowers,  is  exposed  to  the  action  of  moist 
chlorine  or  of  chlorine-water,  those  which  are  dyed  with 
organic  colouring  matters  are  bleached  at  once,  whilst 
the  mineral  colours  for  the  most  part  remain  unaltered. 
Green  leaves  immersed  in  chlorine  acquire  a  rich  autum- 
nal brown  tint,  and  are  eventually  bleached.  All  flowers 
are  very  readily  bleached  by  the  gas. 

Chlorine  is  very  extensively  employed  for 
bleaching  linen  and  cotton,  the  gas  acting  upon 
the  colouring  matter  without  affecting  the  fibre  ; 
but  silk  and  wool  present  much  less  resistance 
to  chemical  action,  and  would  be  much  injured 
by  chlorine  so  that  they  are  always  bleached  by  sulphurous  acid  gas. 

Neither  chlorine  itself  nor  its  solution  in  water  can  be  very  con- 
veniently used  for  bleaching  on  the  large  scale,  on  account  of  the 
irritating  effect  of  the  gas,  so  that  it  is  usual  to  employ  it  in  the  form 
of  chloride  of  lime,  from  which  it  can  be  easily  liberated  as  it  is  wanted. 

99.  The  explanation  above  given  of  the  bleaching  effect  of  chlorine 
may  probably  be  applied  also  to  its  so-called   disinfecting  properties. 
The  atmosphere,  in  particular  localities,  is  occasionally  contaminated 
with  micro-organisms,  some  of  which  are  known  only  by  their  injurious 
effects  upon  the  health,  their  quantity  being  so  small  that  they  do  not 
appear  in  the  results  of  the  analysis  of  such  air.     Since,  however,  these 
minute  forms  of  life  appear  to  be  killed  by  the  same  agents  which  are 
usually  found  to  decompose  organic  compounds,  chlorine  has  been  very 
commonly  employed  to  combat  these  insidious  enemies  to  health. 

Among  the  offensive  and  unhealthy  products  of  putrefaction  of 
animal  and  vegetable  matter,  sulphuretted  hydrogen,  ammonia,  and 
like  bodies  are  found.  That  chlorine  breaks  up  these  hydrogen  com- 
pounds is  well  known ;  hence  its  great  value  for  removing  the  un- 
wholesome properties  of  the  air  in  badly  drained  houses,  &c. 

100.  The  discovery  of  chlorine,  and  the  discussions  which  ensued  with 
respect  to  its  real  nature,  contributed  very  largely  to  the  advancement 
of  chemical  science.     About  the  year  1770,  the  Swedish  chemist  Scheele 
(who  afterwards  discovered  oxygen)  first  obtained  chlorine  by  heating 
manganese  ore  with  muriatic  acid. 

The  construction  which  Scheele  put  upon  the  result  of  this  experiment 
was  one  which  was  consistent  with  the  chemistry  of  that  date.  He  sup- 
posed the  muriatic  acid  to  have  been  deprived  of  phlogiston,  and  hence 
chlorine  was  termed  by  him  dephlogisticated  muriatic  acid.  This  phlo- 
giston had  long  been  a  subject  of  contention  among  philosophers,  having 


HYDROGEN   CHLORIDE. 


177 


been  originally  assumed  to  exist  in  combination  with  all  combus- 
tible bodies,  and  to  be  separated  from  them  during  their  combustion. 
Towards  the  decline  of  the  phlogistic  theory,  attempts  were  made  to  prove 
the  identity  of  this  imaginary  substance  with  hydrogen,  which  shows 
how  very  nearly  Scheele's  reasoning  approached  to  the  truth,  even  with 
the  very  imperfect  light  which  he  then  possessed.  Berthollet's  move- 
ment was  retrograde,  when,  ten  years  afterwards,  he  styled  chlorine  oxy- 
genised  muriatic  or  oxymuriatic  acid  ;  but  the  experiments  of  Gay-Lussae 
and  Thenard,  and  more  particularly  those  of  Davy  in  1811,  proved  de- 
cisively that  hydrochloric  acid  was  composed  of  chlorine  and  hydrogen, 
and  that  the  effect  of  the  black  oxide  of  manganese  in  Scheele's  experi- 
ment was  to  remove  the  hydrogen  in  the  form  of  water,  thus  setting  the 
chlorine  at  liberty. 

HYDROCHLORIC  ACID,  OR  HYDROGEN  CHLORIDE. 
HCl  =  36-5  parts  by  weight  =  2  vols. 

101.  This  acid  is  found  in  nature  among  the  gases  emanating  from 
active  volcanoes,  and  occasionally  in  the  spring  and  river  waters  of 
volcanic  districts.  For  use  it  is  always  prepared  artificially  by  the 
action  of  sulphuric  acid  upon  common  salt — 

NaCl     +     H2S04     =     HC1     +     NaHS04 
Common  salt.  Hydrogen-sodium  sulphate. 

— the  sodium  of  the  common  salt  changing  places  with  the  hydrogen  of 
the  sulphuric  acid. 

20  grams  of  common  salt  (previously  dried  in  an  oven)  are  introduced  into  a  dry 
flask  (Fig.  150),  to  which  has  been  fitted,  by  means  of  a  perforated  cork,  a  tube  bent 
twice  at  right  angles,  to  allow  the  gas  to  be  collected  by  downward  displacement. 
30  c.c.  of  strong  H2S04  are  poured 
upon  the  salt,  and,  the  cork  having 
been  inserted,  the  flask  is  very  gently 
heated,  in  order  to  promote  the  dis- 
engagement of  the  hydrochloric  acid 
gas,  which  is  collected  in  a  perfectly 
dry  bottle,  the  mouth  whereof  when 
full,  may  be  covered  with  a  glass 
plate  smeared  with  a  little  grease. 
While  being  filled,  the  bottle  may  be 
closed  with  a  perforated  card. 

At  a  red  heat  the  whole  of  the 
hydrogen  in  the  H2S04  can  be  con- 
verted into  HC1.  2NaCl  +  H2S04  = 
Na.2S04  +  2HCl  ;  but  this  is  never 
effected  in  practice. 

Common  salt  in  powder  sometimes 
froths  to  a  very  inconvenient  extent 
with  sulphuric  acid  ;  it  is  therefore 
often  preferable  to  employ  fragments 
of  rock  salt  or  of  fused  salt,  prepared 
by  fusing  the  common  salt  in  a  clay  crucible,  and  pouring  it  on  to  a  clean  dry  stone. 

Hydrogen  chloride  is  also  conveniently  prepared  by  dropping  strong  H2S04  from  a 
funnel  provided  with  a  stopcock  into  commercial  strong  hydrochloric  acid.  The 
apparatus  may  take  the  form  shown  in  Fig.  156,  the  U-tube  being  omitted. 

The  bottle  will  be  known  to  be  filled  with  gas  by  the  abundant  escape 
of  the  dense  fumes  which  hydrogen  chloride,  itself  transparent,  pro- 
duces by  condensing  the  moisture  of  the  air  ;  for  since  the  gas  is  heavier 
than  air  (sp.  gr.  1.278),  it  will  not  escape  in  any  quantity  from  the 


Fig.  150. — Preparation  of  hydrochloric  acid  gas. 


HYDROCHLORIC  ACID. 


bottle  until  the  latter  is  full.  The  odour  of  the  gas  is  very  suffocating, 
but  not  nearly  so  irritating  as  that  of  chlorine.  The  powerful  attraction 
for  water  is  one  of  the  most  important  properties  of  this  gas. 

If  a  jar  of  hydrogen  chloride  be  closed  with  a  glass  plate  and  inverted  underwater, 
it  will  be  found  on  removing  the  plate  that  the  gas  is  absorbed  with  great  rapidity, 
the  water  being  forced  up  into  the  bottle  by  the  pressure  of  the  external  air,  in  pro- 
portion as  the  gas  is  absorbed.  The  experiment  may  also  be  made  as  in  the  case  of 
ammonia  (Fig.  69,  see  page  84). 

The  dissolution  of  36.5  grams  HC1  in  excess  of  water  evolves  17,200 
calories. 

The  liquid  hydrochloric,  or  muriatic  acid  of  commerce,  is  a  solution 
of  the  gas  in  water,  and  may  be  recognised  by  the  grey  fumes,  with  the 
peculiar  odour  of  the  acid,  which  it  evolves  when  exposed  to  the  air. 
One  pint  of  water  at  a  temperature  of  5°  C.  is  capable  of  absorbing 
480  pints  of  hydrochloric  acid  gas,  forming  ij  pints  of  the  solution, 
having  the  specific  gravity  1.21.  The  strength  of  the  acid  purchased 
in  commerce  is  usually  inferred  from  the  specific  gravity,  by  reference 
to  tables  indicating  the  weight  of  HOI  contained  in  solutions  of 
different  specific  gravities.  The  strongest  hydrochloric  acid  (sp.gr.  1.21) 
contains  43  per  cent.,  by  weight  of  the  gas.  At  -  18°  C.  it  deposits 
crystals  of  HC1.2Aq.  The  common  acid  has  usually  a  bright  yellow 
colour,  due  to  the  accidental  presence  of  a  little  ferric  chloride 
(Fe,016). 

This  acid  is  produced  in  enormous  quantities  in  the  alkali  works, 
where  common  salt  is  decomposed  by  sulphuric  acid  in  order  to  convert 
it  into  sodium  sulphate,  as  a  preliminary  step  to  the  production  of 

sodium  carbonate.  The  alkali 
manufacturer  is  compelled  to 
condense  the  gas,  for  it  is  found 
to  wither  up  the  vegetation  in  the 
neighbourhood.  For  this  purpose 
the  hydrochloric  acid  gas  is  drawn 
up  from  the  furnace  through 
vertical  cylinders  filled  with  coke, 
over  which  streams  of  water  are 
made  to  trickle.  The  water 
absorbs  the  acid,  and  is  drawn 
off  from  below  (see  Alkali). 

In  preparing  a  pure  solution  of  the 
acid  for  chemical  use  on  a  small  scale, 
the  gas  prepared  as  above  may  be  passed 
into  a  small  bottle  containing  a  very 
little  water,  to  wash  the  gas,  or  remove 

any  sodium  sulphate  which  may  splash  over,  and  then  into  a  bottle  about  two-thirds 
filled  with  distilled  waier,  the  tube  delivering  the  gas  passing  only  about  TV  inch 
below  the  surface,  so  that  the  heavy  solution  of  hydrochloric  acid  may  fall  to  the 
bottom,  and  fresh  water  may  be  presented  to  the  gas  (Fig.  151). 

Pure  solution  of  hydrochloric  acid  is  sometimes  prepared  on  a  large  scale  by 
allowing  concentrated  sulphuric  acid  to  run  into  the  common  hydrochloric  acid, 
when  the  gas  is  evolved,  and  is  washed  and  passed  into  water. 

When  the  concentrated  solution  of  hydrochloric  acid  is  heated  in  a 
retort  it  evolves  abundance  of  hydrochloric  acid  gas,  rendering  it  pro- 
bable that  it  is  not  a  true  chemical  compound  of  water  with  the  acid. 
The  evolution  of  gas  ceases  when  the  remaining  liquid  contains  20  per 


Fig.  151. — Preparation  of  solution  of 
hydrochloric  acid. 


HYDROCHLORIC  ACID  AND   METALS. 


179 


cent,  of  acid  (and  has  a  sp.  gr.  of  i.io).  If  a  weaker  acid  than  this 
be  heated,  it  loses  water  until  it  has  attained  this  strength,  when  it 
distils  unchanged  at  noj  C.* 

The  concentrated  solution  forms  a  very  convenient  source  from  which  to  procure 
the  gas.  It  may  be  heated  in  a  flask,  and  the  gas  dried  by  passing  through  a  bottle 
filled  with  fragments  of  pumice-stone  wetted  with  concentrated  sulphuric  acid, 
being  collected  over  the  mercurial  trough  (Fig.  152). 


Fig.  152. 

The  avidity  with  which  water  absorbs  hydrogen  chloride  is  the 
more  remarkable,  because  this  gas  can  be  liquefied  only  under  a  very 
high  pressure,  amounting  at  the  ordinary  temperature  to  about  40 
atmospheres.  The  liquid  boils  at  -  80°  C.  and  solidifies  at  a  lower 
temperature,  melting  at  -  112°  C.  The  sp.  gr.  of  the  liquid  is  0.91 
at  o°  C.  The  critical  temperature  of  the  gas  is  52°  C.  and  the  critical 
pressure  is  86  atmospheres. 

The  liquefied  hydrogen  chloride  has  comparatively  little  action  even 
upon  those  metals  which  decompose  its  aqueous  solution  with  great 
violence  ;  quicklime  is  unaffected  by  it,  and  solid  litmus  dissolves  in  it 
with  a  faint  purple  colour,  instead  of  the  bright  red  imparted  by  the 
aqueous  hydrochloric  acid.  Dry  hydrochloric  acid  gas  is  not  absorbed 
by  calcium  carbonate.t 

The  injurious  action  of  hydrochloric  acid  gas  upon  growing  plants  is 
probably  connected  with  its  attraction  for  water.  If  a  spray  of  fresh 
leaves  is  placed  in  a  bottle  of  hydrochloric  acid,  it  becomes  at  oncfe 
brown  and  shrivelled.  One  part  of  HC1  in  25,000  of  air  is  fatal  to  plants. 

1 02.  Action  of  hydrochloric  acid  upon  metals. — Those  metals  which 
have  the  strongest  attraction  for  oxygen  will  also  generally  have  the 
strongest  attraction  for  chlorine,  so  that  in  respect  to  their  capability  of 
decomposing  hydrochloric  acid,  they  may  be  ranked  in  pretty  nearly  the 
same  order  as  in  their  action  upon  water  (p.  19).  Since,  however,  the 
attraction  of  chlorine  for  the  metals  is  generally  superior  to  that  of 
oxygen,  the  metals  are  more  easily  attacked  by  hydrochloric  acid  than 

*  The  proportion  of  acid  thus  retained  by  the  water  varies-  directly  with  the  atmospheric 
pressure  to  which  it  is  exposed  during'  the  distillation.  A  hydrate  HC1.8H2O  would  contain 
20.2  per  cent.  HC1. 

f  The  realisation  of  the  fact  that  hydrochloric  acid  solution  behaves  similarly  to  the  oxy- 
acids,  led  to  the  ab  mdonment  of  the  view  that  oxygen  is  the  acid  former,  and  that  all  acids 
must  cont'in  this  element.  The  facts  quoted  with  regard  to  the  inactivity  of  anhydrous 
HC1  seem  to  inilicite  that  oxygen  (as  water)  is,  after  all,  essential  to  an  acid. 


180  HYDROCHLORIC  ACID  AND   METALLIC   OXIDES. 

by  water,  the  metal  taking  the  place  of  the  hydrogen,  and  a  chloride  of 
the  metal  being  formed. 

Even  silver,  which  does  not  decompose  water  at  any  temperature,  is 
dissolved,  though  very  slowly,  by  boiling  concentrated  hydrochloric  acid, 
the  chloride  of  silver  formed  being  soluble  in  the  strong  acid,  though  it 
may  be  precipitated  by  adding  water. 

Gold  and  platinum,  however,  are  not  attacked  by  hydrochloric  acid  ; 
but  if  a  little  free  chlorine  be  present,  it  converts  them  into  chlorides. 

Iron  and  zinc  decompose  the  acid  very  rapidly  in  the  cold,  forming 
ferrous  chloride  and  zinc  chloride  respectively,  and  liberating  hydrogen  ; 


When  potassium  or  sodium  is  exposed  to  hydrochloric  acid  gas,  it 
immediately  becomes  coated  with  a  white  crust  of  chloride,  which  partly 
protects  the  metal  from  the  action  of  the  gas  ;  but  when  these  metals 
are  heated  to  fusion  in  hydrochloric  acid  gas,  they  burn  vividly  ; 


The  composition  of  hydrogen  chloride  may  be  exhibited  by  confining  a 
measured  volume  of  the  gas  over  mercury  (see  Fig.  106,  p.  130),  and 
passing  up  a  freshly  cut  pellet  of  sodium.  On  gently  agitating  the 
tube,  the  gas  diminishes  in  volume,  and  after  a  time  will  have  contracted 
to  one-half,  and  will  be  found  to  have  all  the  properties  of  hydrogen. 
This  result  confirms  that  obtained  by  synthesis,  as  described  above, 
that  2  volumes  of  hydrogen  chloride  contain  i  volume  of  hydrogen 
and  i  volume  of  chlorine. 

The  electrolysis  of  hydrochloric  acid,  which  leads  to  the  same  con- 
clusion, has  been  described  at  p.  16. 

103.  Action  of  hydrochloric  acid  upon  metallic  oxides.  —  As  a  general 
rule,  it  may  be  stated  that,  when  hydrochloric  acid  acts  upon  the  oxide 
of  a  metal,  the  results  are  water  and  a  chloride  of  the  metal,  in  which 
each  atom  of  oxygen  in  the  oxide  has  been  displaced  by  2  atoms  of 
chlorine. 

Thus,  silver  oxide  acted  on  by  hydrochloric  acid  gas  gives  water  and 
silver  chloride  ;  Ag20  +  2HC1  =  H20  +  2  AgCl. 

Suboxide  of  copper  (cuprous  oxide)  yields  water  and  subchloride  of 
copper  (cuprous  chloride)  ;  Cu30  +  2HC1  =  H2O  +  Cu,Cl2. 

Ferric  oxide  gives  water  and  ferric  chloride;  Fe203  +  6HCl  = 
3H20  +  Fe2016. 

With  stannic  oxide,  water  and  stannic  chloride  are  obtained  ; 
Sn02  +  4HC1  =  3H2O  +  SnCl4. 

Antimonious  oxide  is  converted  into  water  and  antimonious  chloride  ; 
Sb2O3  +  6  HOI  =  3H20  +  2Sb013. 

104.  In  cases  where  the  corresponding  chloride  does  not  exist,  or  is 
not  stable  under  the  conditions  of  the  experiment,  a  chloride  is  formed 
containing  less  chlorine  than  is  equivalent  to  the  oxygen  in  the  oxide, 
and  the  balance  is  evolved  in  the  free  state.     Thus,  when  manganese 
sesquioxide  and  dioxide  are  heated  with  hydrochloric  acid  — 


Mn203  +  6HC1  =  3H20  +  2MnCl2  +  C10  ; 
Mn02    +  4HC1  =  2H2O  +   MnCl2  +  C12. 

It  would  seem  that  Mn2Cl6  and  MnCl4,  corresponding  with  Mn2O$ 
and  Mn02  respectively,  are  first  formed  and  that  these  decompose  into 
the  stable  chloride,  Mn012,  and  chlorine. 

Chromic  anhydride,  a  chloride  corresponding  with  which  is  not  known 


CHLOEINE   OXIDES.  l8l 

to  exist,  when  heated  with  hydrochloric  acid,  yields  chromic  chloride 
and  chlorine  ;   2  Cr03  +  1  2HC1  =  6H20  +  Cr2Cl6  +  C16. 

Most  metallic  oxides  containing  i  atom  of  oxygen  have  a  correspond- 
ing chloride  of  a  stable  character,  but  the  higher  oxides  less  frequently 
form  corresponding  chlorides  endowed  with  any  stability.  Basic  oxides 
rarely  evolve  chlorine  from  hydrochloric  acid.  When  an  oxide  gives  off 
chlorine  on  boiling  with  hydrochloric  acid  it  is  probably  a  peroxide  or 
an  add  oxide,  that  is,  an  oxide  containing  more  oxygen  than  suffices  to 
form  a  base  with  the  metal.  Thus,  the  basic  oxide  of  manganese  is  MnO, 
which  dissolves  in  HC1  with  evolution  of  chlorine  ;  but  the  dioxide 
Mn02,  or  MnO.O,  contains  an  extra  atom  of  oxygen  which  is  able  to 
oxidise  HOI;  2HC1  +  0  =  H20  +  C12. 

COMPOUNDS  OF  CHLORINE  WITH  OXYGEN. 

105.  It  is  worthy  of  notice,  that  whilst  chlorine  and  hydrogen  so 
readily  unite,  there  is  110  method  by  which  chlorine  can  be  made  to 
combine  in  a  direct  manner  with  oxygen,  the  compounds  of  these 
elements  having  been  hitherto  obtained  only  by  indirect  processes.  An 
excellent  illustration  is  thus  afforded  of  the  fact,  that  the  more  closely 
substances  resemble  each  other  in  their  chemical  relations,  the  less  will 
be  their  tendency  to  combine  ;  for  chlorine  and  oxygen  are  both  highly 
electro-negative  bodies,  and  therefore,  having  both  a  powerful  attrac- 
tion for  the  electro-positive  hydrogen,  their  attraction  for  each  other  is 
of  a  very  low  order. 

Three  oxides  of  chlorine,  C180,  C102  and  C1207,  and  four  oxyacids  of 
chlorine,  HC10,  HC102,  HC103,  and  HC104,  are  known. 

1  06.  Hypochlorous  anhydride  or  chlorine  monoxide  (01,0),  is 
of  some  practical  interest  in  connection  with  chloride  of  lime,  chloride  of 
soda,  and  other  bleaching  compounds.  It  is  prepared  by  passing  dry 
chlorine  gas  over  dry  precipitated  mercuric  oxide,  and  condensing  the 
product  in  a  tube  surrounded  with  a  mixture  of  ice  and  salt  ; 


The  hypochlorous  anhydride  is  thus  obtained  as  a  dark  brown  liquid, 
which  boils  at  6°  0.,  evolving  a  yellow  gas  thrice  as  heavy  as  air,  and 
having  a  very  powerful  and  peculiar  odour.  This  gas  is  remarkably 
explosive,  the  heat  of  the  hand  having  been  known  to  cause  its  separa- 
tion into  its  constituents,  when  2  volumes  of  the  vapour  yield  2  volumes 
of  chlorine  and  i  volume  of  oxygen.  As  might  be  expected,  most 
substances  which  have  any  attraction  for  oxygen  or  chlorine,  and 
therefore  raise  the  temperature  of  the  gas  by  combining  with  a  portion 
of  its  oxygen  or  chlorine,  will  decompose  the  gas,  sometimes  with 
explosive  violence.  This  instability  of  chlorine  monoxide  is  only  to  be 
expected  from  the  fact  that  it  evolves  heat  (17,800  gram  units  for  87 
grams)  in  its  decomposition,  and  is  therefore  an  endothermic  compound, 
i.e.,  one  which  could  only  be  formed  from  its  elements  by  the  absorp- 
tion of  heat.  It  is  generally  true  that  endothermic  compounds  can  be 
exploded  by  a  shock,  such  as  that  caused  by  a  sudden  rise  of  temperature. 
Even  hydrochloric  acid  decomposes  C120  :  i  volume  of  chlorine  mon- 
oxide is  entirely  decomposed  by  2  volumes  of  hydrochloric  acid,  yield- 
ing water  and  chlorine  ;  C12O  +  2HC1  =  H20  +  C14.  Chlorine  monoxide 
is  a  powerful  bleaching  agent,  both  its  chlorine  and  oxygen  acting  upon 
the  colouring  matter  in  the  manner  explained  at  page  175. 


1 82  HYPOCHLOROUS  ACID. 

Hypochlorous  anhydride  is  absorbed  in  large  quantity  by  water 
(200  vols.  in  i  vol.) ;  the  solution  is  supposed  to  contain  hypochlorous 
acid,  HC10  or  Cl.OH,  for  H20  +  C120  =  2HC1O ;  but  HC10  has  not  been 
obtained  in  the  separate  state.  The  solution  may  be  very  readily  pre- 
pared by  shaking  mercuric  oxide  with  water  in  a  bottle  of  chlorine  as 
long  as  the  gas  is  absorbed.  The  greater  part  of  the  mercuric  chloride 
which  is  produced  combines  with  the  excess  of  oxide  to  form  a  brown 
insoluble  oxychloride,  HgO.HgCl2,  whilst  the  hypochlorous  acid  and 
a  little  mercuric  chloride  remain  in  solution.  A  solution  of  the  acid, 
containing  calcium  chloride,  may  also  be  obtained  by  passing  Cl  into 
CaC03  suspended  in  water;  CaC03  +  H20  +  C14  =  CaCl2  +  2HC10  +  C02. 
This  solution  is  a  most  powerful  oxidising  and  bleaching  agent,  since  it 
readily  decomposes  into  HC1  and  0  ;  it  erases  writing  ink  immediately, 
and  does  not  corrode  the  paper  if  it  be  carefully  washed.  Printing  ink, 
which  contains  lamp  black  and  grease,  is  not  bleached  by  hypochlorous 
acid,  so  that  this  solution  is  very  useful  for  removing  ink  stains  from 
books,  engravings,  &c.  For  the  same  weight  of  01  it  is  twice  as  effective 
as  chlorine  water  ;  2HC1O  =  HC1  +  O2 ;  H20  +  01,  =  2HC1  +  0. 

The  action  of  some  metals  and  their  oxides  upon  solution  of  hypochlorous  acid  is 
instructive.  Iron  seizes  upon  the  oxygen,  whilst  the  chlorine  is  liberated  ;  copper 
takes  both  the  oxygen  and  chlorine  ;  whilst  silver  combines  with  the  chlorine,  and 
liberates  oxygen.  Mercury  yields,  on  shaking,  the  brown  mercuric  oxychloride. 
This  distinguishes  solution  of  HC1O  from  chlorine  water.  Oxide  of  lead  (PbO) 
removes  the  oxygen,  becoming  peroxide  of  lead  (Pb0.2),  and  liberating  chlorine,  but 
oxide  of  silver  converts  the  chlorine  into  chloride  of  silver,  and  liberates  the  oxygen  ; 
Ag.20  +  C120  =  2  AgCl  +  02. 

Hypochlorous  acid  is  formed  when  a  weak  solution  of  hydrogen  peroxide  is  added 
to  a  large  excess  of  chlorine  water  ;  C12  +  H202  =  2HC10.  With  an  excess  of  the 
peroxide,  HC10  +  H202  =  HC1  +  H20  +  02. 

The  salts  of  hypochlorous  acid,  or  hypochlorites,  are  obtained  in  solu- 
tion by  neutralising  hypochlorous  acid  with  bases,  only  a  few  of  them 
are  known  in  a  pure  state.  They  are  decomposed  even  by  carbonic 
acid,  with  liberation  of  hypochlorous  acid. 

"When  chlorine  is  passed  into  a  solution  of  a  metallic  hydroxide  the 
hypochlorite  and  chloride  of  the  metal  are  obtained,  2NaOH  +  Cl2  = 
NaOCl  +  NaCl  +  HOH ;  the  hypochlorite  may  be  supposed  to  be  formed 
by  metalepsis  (p.  174)  with  the  hydroxide  NaOH  +  C12  =  NaOCl  +  HC1, 
the  hydrochloric  acid  thus  formed  being  neutralised  by  another  portion 
of  NaOH. 

By  the  addition  of  any  acid  which  can  liberate  hydrochloric  acid,  and 
therefore  also  the  much  feebler  hypochlorous  acid,  to  the  solution  con- 
taining the  chloride  and  hypochlorite,  chlorine  will  be  evolved  since 
hydrochloric  and  hypochlorous  acids  react,  the  hydrogen  being  oxidised 
and  the  chlorine  set  free,  HC1  +  HC10  =  H20  +  C12.  If  only  a  small 
proportion  of  acid  is  added  to  the  solution  of  hypochlorite  and  chloride, 
the  hypochlorous  acid  will  alone  be  liberated,  and  may  be  distilled 
together  with  the  water. 

When  the  solution  of  a  hypochlorite  is  boiled,  it  undergoes  self- 
oxidation,  that  is,  one  part  of  the  hypochlorite  loses  oxygen,  becoming 
chloride,  whilst  the  remainder  is  oxidised  by  this  oxygen  to  chlorate  ; 
3KC1O  =  KC103  +  2KC1.  This  change  is  turned  to  practical  account  in 
the  manufacture  of  potassium  chlorate.  It  is  much  hindered  by  the 
presence  of  an  excess  of  alkali.  The  solution  of  hypochlorous  acid  itself, 


CHLORIDE   OF  LIME.  183 

when  exposed  to  light,  is  decomposed  into  chloric  acid  and  free  chlorine  • 
5  HC10  =  HC10,  +  2H2O  +  C14. 

A  solution  of  hypochlorous  acid  may  be  obtained  by  adding  boric  acid 
in  excess  to  a  solution  of  chloride  of  lime. 

107.  Chloride  of  lime  or  bleaching  powder,  or  calx  chlorata,  is  prepared 
by  passing  chlorine  gas  into  boxes  of  lead  or  stone  in  which  a  quantity 
of  moist  slaked  lime  is  spread  out.  The  temperature  is  not  allowed  to 
rise  above  25°  0.  (77°  F.),  which  is  ensured  by  acting  upon  the  fresh 
lime  with  chlorine  diluted  by  air.  The  lime  absorbs  nearly  half  its 
weight  of  chlorine,  and  forms  a  white  powder,  which  has  a  very  peculiar 
smell,  somewhat  different  from  that  of  chlorine. 

The  formula  of  chloride  of  lime  is  generally  written  CaCl.001. 

The  constitution  of  chloride  of  lime  is  not  known  with  certainty.  When  the 
calcium  hydroxide,  Ca(OH)2,  is  acted  on  by  chlorine,  the  simplest  reaction  would  be 
Ca(OH)2  +  Cl2  =  CaCl(OCl)  +  H20,  according  to  which  the  chloride  of  lime  would 
result  from  the  substitution  of  Cl  for  one  of  the  OH  groups,  and  the  removal  of  the 
H  of  the  other  as  H20,  this  atom  of  H  being  then  exchanged  for  Cl  ;  but  this  would 
require  the  calcium  hydroxide  to  absorb  nearly  an  equal  weight  of  chlorine,  whereas 
the  amount  is  not  much  more  than  half  this  quantity.  This  deficiency  is  partly 
explained  by  the  fact  that  a  small  portion  of  the  lime  is  not  attacked  by  the 
chlorine. 

Practically,  the  constitution  of  chloride  of  lime  itself  is  of  less  importance  than 
that  of  the  solution  obtained  by  treating  it  with  water,  which  is  generally  admitted 
to  contain  calcium  hypochlorite,  Ca(OCl)2,  and  calcium  chloride,  CaCl2,  with  some 
calcium  hydroxide,  Ca(OH)2,  of  which  a  quantity  is  left  in  the  undissolved  residue. 
The  decomposition  of  chloride  of  lime  by  water  should  be  represented  by  the  follow- 
ing equation  :  2CaCl(OCl)  =  CaCl2+Ca(OCl)2. 

If  the  solution  of  chloride  of  lime  is  added  to  blue  litmus,  it  exerts 
little  bleaching  action  ;  but  on  adding  a  little  acid  (sulphuric,  for 
example),  the  blue  colour  is  discharged,  the  acid  setting  free  the 
chlorine,  which  acts  upon  the  colouring  matter — 

Ca(OCl)2+CaCl2  +  2H2S04  =  2CaS04  +  2H20  +  C14. 
Solution  of  chloride  of  lime. 

Even  carbonic  acid  will  develop  the  bleaching  property  of  chloride  of 
lime  (by  liberating  hypochlorous  acid),  so  that  the  above  mixture  may 
be  decolorised  by  breathing  into  it  through  a  glass  tube. 

When  chloride  of  lime  is  used  for  bleaching  on  the  large  tcale,  the 
stuff  to  be  bleached  is  first  thoroughly  cleansed  from  any  grease  or 
weaver  s  dressing,  by  boiling  it  in  lime-water  and  in  a  weak  solution  of 
soda,  and  is  then  immersed  in  a  weak  solution  of  the  chloride  of  lime. 
This,  by  itself,  however,  exerts  very  little  action  upon  the  natural 
colouring  matter  of  the  fibre,  and  the  stuff  is  therefore  next  immersed 
in  very  dilute  sulphuric  acid,  when  the  colouring  matter  is  so  far  altered 
as  to  become  soluble  in  the  alkaline  solution  in  which  the  fabric  is  next 
immersed,  and  a  repetition  of  these  processes,  followed  by  a  thorough 
rinsing,  generally  perfects  the  bleaching. 

The  property  possessed  by  acids  of  liberating  chlorine  from  the  chloride 
of  lime  is  applied,  in  calico-printing,  to  the  production  of  white  patterns 
upon  a  red  ground.  The  stuff  having  been  dyed  with  Turkey-red,  the 
pattern  is  imprinted  upon  it  with  a  discharge  consisting  of  an  acid 
(tartaric,  phosphoric,  or  arsenic)  thickened  with  gum.  On  passing  the 
fabric  through  a  bath  of  weak  chloride  of  lime,  the  colour  is  discharged 
only  at  those  parts  to  which  the  acid  has  been  applied,  and  where,  con- 
sequently, chlorine  is  liberated. 


184  BLEACHING  POWDEE. 

Chloride  of  lime  is  one  of  the  most  convenient  forms  in  which  to 
apply  chlorine  for  the  purposes  of  fumigating  and  disinfecting.  If  a 
cloth  saturated  with  the  solution  be  suspended  in  the  air,  the  carbonic 
acid  gas  in  the  latter  causes  a  slow  evolution  of  hypochlorous  acid,  which 
is  even  a  more  powerful  disinfectant  than  chlorine  itself.  In  extreme 
cases,  where  a  rapid  evolution  of  chlorine  is  required,  the  bleaching 
powder  is  placed  in  a  plate,  and  diluted  sulphuric  acid  is  poured  over 
it,  or  the  powder  may  be  mixed  with  half  its  weight  of  powdered 
alum  in  a  plate,  when  a  pretty  rapid  and  regular  escape  of  chlorine  will 
ensue. 

The  best  bleaching  powder  contains  about  37  per  cent,  of  chlorine 
which  can  be  liberated  ("  available  chlorine ")  in  the  above  processes. 
It  is  liable  to  decomposition  when  kept,  evolving  oxygen,  and  becoming 
converted  into  calcium  chloride,  which  attracts  moisture  greedily,  and 
renders  the  bleaching  powder  deliquescent.  It  has  been  known  to 
shatter  the  glass  bottle  in  which  it  was  preserved,  in  consequence  of  the 
accumulation  of  oxygen ;  *  CaOCl2  =  CaCJ2  +  0. 

When  a  solution  of  a  salt  of  manganese  or  cobalt  is  added  to  solution 
of  chloride  of  lime,  a  black  precipitate  of  Mn02or  Co203  is  obtained.  If 
this  precipitate  be  boiled  with  an  excess  of  solution  of  chloride  of  lime, 
ib  causes  a  rapid  disengagement  of  oxygen,  in  some  manner  that  has 
not  yet  been  clearly  explained.  Large  quantities  of  oxygen  are  easily 
obtained  by  adding  a  few  drops  of  solution  of  cobalt  nitrate  to  solution 
of  chloride  of  lime,  and  applying  a  gentle  heat. 

Old  chloride  of  lime  always  contains  calcium  chlorate ;  6Ca0012  = 

a013  +  Ca(C103)2. 

Sodium  hypochlorite^  which  is  very  useful  for  removing  ink,  is  pre- 
pared in  solution  by  decomposing  solution  of  chloride  of  lime  with 
solution  of  sodium  carbonate,  and  separating  the  calcium  carbonate  by 
filtration.  The  solution  is  generally  called  "chloride  of  soda"  (liquor 
sodce  chloralce.  Eau  de  Javelle). 

1 08.  Chloric  acid  (HC103  or  C102(OH)).— This  acid  is  appropriately 
studied  here,  since  its  salts  are  usually  obtained  by  the  decomposition  of 
the  hypochlorites.  The  only  chlorate  which  possesses  any  great  practical 
importance  is  potassium  chlorate  (KC103),  which  is  largely  employed  as 
a  source  of  oxygen,  as  an  ingredient  of  several  explosive  compositions, 
and  in  the  manufacture  of  lucifer  matches. 

Potassium  chlorate,  or  chlorate  of  potash. — The  simplest  method  of 
obtaining  this  salt  consists  in  passing  an  excess  of  chlorine  rapidly  into 
a  strong  solution  of  potash  when  the  liquid  becomes  hot  enough  to 
decompose  the  hypochlorite  first  formed  into  potassium  chloride,  which 
remains  in  solution,  arid  potassium  chlorate,  which  is  deposited  in 
tabular  crystals,  the  ultimate  result  being  expressed  by  the  equation — 

6KOH  +  C16  =  KC103  +  5KC1  +  3H20. 

If  potassium  carbonate  or  a  weak  solution  of  potash  be  employed,  the 
liquid  will  require  boiling  after  saturation  with  chlorine,  in  order  to 
convert  the  hypochlorite  into  chlorate. 

The  following  proportions  will  be  found  convenient  for  the  preparation  of  potas- 
sium chlorate  on  the  small  scale  as  a  laboratory  experiment.  20  grins,  of  potassium 

*  When  rapidly  made  and  hastily  packed,  it  has  been  known  to  become  so  hot  as  to  set  fire 
to  the  casks. 


POTASSIUM   CHLORATE.  185 

carbonate  are  dissolved,  in  a  beaker,  with  60  c.c.  of  water.  40  grins,  of  NaCl  are 
mixed  with  30  grins,  of  Mn02,  and  very  gently  heated  in  a  flask  with  a  mixture  of 
40  c.c.  of  strong  H2S04  and  1 10  c.c.  of  water,  the  evolved  chlorine  being  passed 
through  a  rather  wide  bent  tube  into  the  solution  of  potassium  carbonate. 

At  first  no  action  appears  to  occur,  although  the  solution  absorbs  the  chlorine  ; 
because  the  first  portion  of  that  gas  converts  the  potassium  carbonate  into  a  mixture 
of  potassium  hypochlorite,  potassium  chloride,  and  hydropotassium  carbonate,  SDme 
crystals  of  which  will  probably  be  deposited;  2K.2C03  +  C1?  +  H20  =  KC1  +  KOC1  + 
2KHC03.  On  continuing  to  pass  chlorine,  these  crystals  will  redissolve,  and  brisk 
effervescence  will  be  caused  by  the  expulsion  of  the  carbonic  acid  gas  ;  2KHC03  + 
C12  =  KC1  +  KOC1  +  H.20  +  2CO2.  When  this  effervescence  has  ceased,  and  the 
chlorine  is  no  longer  absorbed  by  the  liquid,  the  change  is  complete,  the  ultimate 
result  being  represented  by  the'  equation  K2C03+C12:=KC1  +  KOC1  +  C02.  The 
solution  (which  often  has  a  pink  colour,  due  to  a  little  potassium  ferrate)  is  now 
poured  into  a  dish,  boiled  for  two  or  three  minutes,  filtered,  if  necessary,  from  any 
impurities  (silica,  &c.)  derived  from  the  potassium  carbonate,  and  set  aside  to  crys- 
tallise. The  ebullition  has  converted  the  potassium  hypochlorite  into  chlorate  and 
chloride  of  potassium  ;  3KOC1=KC103  +  2KC1.  The  latter,  being  soluble  in  about 
three  times  its  weight  of  cold  water,  is  retained  in  the  solution,  whilst  the  chlorate, 
which  would  require  about  sixteen  times  its  weight  of  cold  water  to  hold  it  dis- 
solved, is  deposited  in  brilliant  rhomboidal  tables.  These  crystals  may  be  collected 
on  a  filter,  and  purified  from  the  adhering  solution  of  potassium  chloride  by  pres- 
sure between  successive  portions  of  filter-paper.  If  they  be  free  from  chloride, 
their  solution  in  water  will  not  be  changed  by  silver  nitrate,  which  would  yield  a 
milky  precipitate  of  silver  chloride  if  potassium  chloride  were  present.  Should  this 
be  the  case,  the  crystals  must  be  redissolved  in  a  small  quantity  of  boiling  water, 
and  recrystallised. 

The  above  processes  for  preparing  potassium  chlorate  are  far  from 
economical,  since  five-sixths  of  the  potash  are  converted  into  chloride, 
being  employed  merely  to  furnish  oxygen  to  convert  the  chlorine  into 
chloric  acid.  In  manufacturing  the  chlorate  upon  the  large  scale,  a 
much  cheaper  material,  lime,  is  used  to  furnish  the  oxygen.  The 
lime  is  mixed  with  water,  and  saturated  with  chlorine  gas  in  closed 
leaden  tanks  ;  2Ca(OH)2  +  C14  =  Ca(OCl)2  +  CaCl2  +  2H2O.  The  liquid  is 
boiled  down,  when  the  calcium  hypochlorite  is  decomposed  into  calcium 
chlorate  and  chloride;  3Ca(OCl)2  =  Ca(C103)2  +  2CaCl2.  The  calcium 
chlorate  is  now  decomposed  by  boiling  with  potassium  chloride,  when  it 
yields  calcium  chloride  which  remains  in  solution,  and  potassium  chlorate 
which  crystallises  as  the  solution  cools — 

Ca(C103)2  +  2KC1  =  CaCl2  +  2KC103. 

Chlorate  of  potash  is  also  made  electrolytically  as  mentioned  in  the 
section  on  potassium. 

Chloric  acid  (HC103)  may  be  procured  by  decomposing  a  solution  of 
potassium  chlorate  with  hydrofluosilicic  acid,  when  the  potassium  is 
deposited  as  an  insoluble  silico-nuoride,  and  chloric  acid  is  found  in  the 
solution  ;  2KC103  +  H2SiF6  =  2HC1O3  +  K2SiF6. 

On  evaporating  the  solution  below  38°  C.,  the  chloric  acid  is  obtained 
as  a  yellow  liquid,  HC103.yAq,  with  a  peculiar  pungent  smell. 

In  its  chemical  characters,  chloric  acid  bears  a  very  strong  resemblance 
to  nitric  acid,  but  is  far  more  easily  decomposed.  It  cannot  even  be 
kept  unchanged  for  any  length  of  time,  and  at  temperatures  above 
40°  C.  it  is  decomposed  into  perchloric  acid,  chlorine,  and  oxygen  ; 
4HC103  =  2  HC104  +  H20  +  01,  +  03. 

Chloric  acid  is  one  of  the  most  powerful  oxidising  agents  :  a  drop  of 
it  will  set  fire  to  paper,  and  it  oxidises  phosphorus  (even  the  amorphous 
variety)  with  explosive  violence.  Like  hypochlorous  acid  it  will  oxidise 


1 86  COLOURED  FIEES. 

hydrochloric  acid  ;  HC103  +  5  HC1  =  3H20  +  C16.*     Yet  it  dissolves  Zn 
with  evolution  of  H. 

109.  Chlorates. — Chloric  acid,  like  nitric,  is  monobasic,  containing 
only  one  atom  of  hydrogen  which  can  be  exchanged  for  a  metal.  The 
chlorates  resemble  the  nitrates  in  their  oxidising  powder,  but  generally 
act  at  lower  temperatures,  in  consequence  of  the  greater  facility  with 
which  the  chlorates  part  with  their  oxygen. 

A  grain  or  two  of  potassium  chlorate,  rubbed  in  a  mortar  with  a  little  sulphur, 
for  example,  detonates  violently,  evolving  a  powerful  odour  of  chloride  of  sulphur. 
Potassium  chlorate  and  sulphur  were  used  in  some  of  the  first  percussion  caps,  but 
being  found  to  corrode  the  nipple  of  the  gun,  they  gave  place  to  the  anti-corrosive 
caps  containing  mercuric  fulminate. 

If  a  little  powdered  chlorate  be  mixed  on  a  card  with  some  black  antimony  sul- 
phide, and  wrapped  up  in  paper,  the  mixture  will  detonate  when  struck  with  a 
hammer.  The  earliest  lucifer  matches  were  tipped  with  a  mixture  of  potassium 
chlorate,  antimony  sulphide,  and  starch,  and  were  kindled  by  drawing  them  briskly 
through  a  doubled  piece  of  sand-paper. 

A  mixture  of  potassium  chlorate  and  lead  ferrocyanide  is  used  in  toy  detonating 
crackers. 

At  high  temperatures  the  chlorates  act  violently  upon  combustible 
bodies.  A  little  potassium  chlorate  sprinkled  upon  red-hot  coal  causes 
a  very  violent  deflagration.  If  a  little  of  the  chlorate  be  melted  in  a 
deflagrating  spoon,  and  plunged  into  a  bottle  or  flask  containing  coal 
gas,  the  salt  burns  with  great  brilliancy,  its  oxygen  combining  with  the 
carbon  and  hydrogen  in  the  gas,  which  becomes  in  this  case  the  supporter 
of  combustion. 

Potassium  chlorate  is  much  used  in  the  manufacture  of  fireworks, 
especially  as  an  ingredient  of  coloured  fire  compositions,  which  generally 
consist  of  potassium  chlorate  mixed  with  sulphur,  and  with  some 
metallic  compound,  to  produce  the  desired  colour  in  the  flame. 

They  are  not  generally  made  of  the  best  quality  on  the  small  scale,  from  want  of 
attention  to  the  very  finely  powdered  state  of  the  ingredients,  the  absence  of  all 
moisture,  and  the  most  intimate  mixture,  but  if  these  precautions  are  attended  to, 
the  following  prescriptions  will  give  very  good  coloured  fires  : 

Red  fire. — 40  grains  of  strontium  nitrate,  thoroughly  dried  over  a  lamp,  are 
mixed  with  10  grains  of  potassium  chlorate,  and  reduced  to  the  finest  possible 
powder.  In  another  mortar  13  grains  of  sulphur  are  mixed  with  4  grains  of  black 
sulphide  of  antimony  (crude  antimony).  The  two  powders  are  then  placed  upon 
a  sheet  of  paper,  and  very  intimately  mixed  with  a  bone  knife,  avoiding  any  great 
pressure.  A  little  heap  of  the  mixture  touched  with  a  red-hot  iron  ought  to  burn 
with  a  uniform  red  flame,  the  colour  being  due  to  the  strontium.f 

Blue  fire. — 15  grains  of  potassium  chlorate  are  mixed  with  10  grains  of  potassium 
nitrate  and  30  grains  of  oxide  of  copper,  in  a  mortar.  The  finely  powdered  mixture 
is  transferred  to  a  sheet  of  paper,  and  mixed,  by  a  bone  knife,  with  15  grains  of 
sulphur.  The  colour  of  the  fire  is  given  chiefly  by  the  copper. 

Green  fire. — 10  grains  of  barium  chlorate  are  mixed  with  10  grains  of  barium 
nitrate  in  a  mortar,  and  afterwards  on  paper  with  12  grains  of  sulphur.  The  barium 
is  the  cause  of  the  bright  green  colour  of  the  flame. 

These  compositions  are  rather  dangerous  to  keep,  since  they  are  liable  to  sponta- 
neous combustion. 

White  gunpowder  is  a  mixture  of  two  parts  of  potassium  chlorate  with  one  part 
of  dried  yellow  prussiate  of  potash,  and  one  part  of  sugar,  which  explodes  very 
easily  under  friction  or  percussion. 

The  decomposition  KC1O3  =  KC1  +  O3  is  exothermic,  9700  calories  being 
evolved  per  gram  molecule  of  potassium  chlorate.  If  the  chlorate  be 

*  Perchloric  acid  and  chlorine  peroxide  are  also  produced. 

f  The  red  fire  made  by  pyrotechnists  commonly  contains  charcoal  i  part,  shellac  4  parts, 
sulphur  8  parts,  potassium  chlorate  12  parts,  strontium  nitrate  40  parts. 


PERCHLORIC   ACID.  I  8/ 

heated  to  the  point  at  which  it  begins  to  decompose,  and  a  little  ferric 
oxide  be  thrown  into  it,  enough  heat  will  be  evolved  to  bring  the  mass 
to  a  red  heat,  although  the  ferric  oxide  is  not  oxidised.  This  evolution 
of  heat  must  of  course  contribute  to  increase  the  energy  of  explosive 
mixtures  containing  the  chlorate,  and  may  be  accounted  for  on  the 
supposition  that  the  heat  evolved  by  the  combination  of  the  Kwith  the 
01  to  form  KC1  exceeds  that  which  is  absorbed  in  effecting  the  chemical 
decomposition  of  the  chlorate. 

no.  Perchloric  acid  (HC1O4  or  C103(OH)),  is  obtained  by  evapo- 
rating, at  a  boiling  heat,  the  solution  of  chloric  acid  obtained  by  de- 
composing potassium  chlorate  with  hydrofluosilicic  acid  (see  page  185), 
when  the  chloric  acid  is  decomposed  into  perchloric  acid,  chlorine,  and 
oxygen;  4HC1O3  =  2HC1O4  +  H2O  +  C12  +  03.  The  pure  acid  is  best 
obtained  by  distilling  potassium  perchlorate  (see  below)  with  four  times 
its  weight  of  strong  H2S04  in  a  vacuum.  At  56  mm.  pressure  it  boils 
at  39°  C. 

The  pure  perchloric  acid  is  a  colourless,  very  heavy  liquid  (sp.  gr. 
i. 764  at  22°  C.),  which  soon  becomes  yellow  from  decomposition.  It 
cannot  be  kept  for  any  length  of  time,  but  it  is  more  stable  than  any 
of  the  other  oxyacids  of  chlorine.  When  heated,  it  decomposes,  often 
with  explosion.  In  its  oxidising  properties  it  is  more  powerful  than 
chloric  acid.  It  burns  the  skin  in  a  very  serious  manner,  and  sets  fire 
to  paper,  charcoal,  &c.,  with  explosive  violence.  This  want  of  stability, 
however,  belongs  only  to  the  pure  acid.  If  water  be  added  to  it,  heat 
is  evolved,  and  a  crystalline  acid,  HC104.H20,  melting  at  50°  C.,  may 
be  obtained.  Diluted  perchloric  acid  is  much  more  stable  than  the 
pure  acid  ;  il  does  not  even  bleach,  but  reddens  litmus  in  the  ordinary 
way.  It  dissolves  Zn  with  evolution  of  H. 

Perchloric  acid  is  monobasic.  The  perchlorates  are  decomposed  by 
heat,  evolving  oxygen,  and  leaving  chlorides  ;  thus — -KC104  =  KC1  +  04. 

The  potassium  perchlorate  is  one  of  the  least  soluble  of  the  potassium 
salts,  requiring  150  times  its  weight  of  cold  water  to  dissolve  it.  It  is 
always  formed  in  the  first  stage  of  the  decomposition  of  potassium 
chlorate  by  heat ;  2KC1O3  =  KC104  +  KC1  +  O2. 

If  a  few  crystals  of  potassium  chlorate  be  heated  in  a  test-tube,  they  first  melt  to 
a  perfectly  clear  liquid,  which  soon  evolves  bubbles  of  oxygen.  After  a  time  the 
liquid  becomes  pasty,  and  if  the  contents  of  the  tube,  after  cooling,  be  dissolved  by 
boiling  with  water,  the  latter  will  deposit,  as  it  cools,  crystals  of  potassium  perchlo- 
rate. These  are  readily  distinguished  from  the  chlorate  by  their  not  yielding  a 
yellow  gas  (C102)  when  "treated  with  strong  sulphuric  acid.  Neither  perchloric  acid 
nor  any  of  its  salts  is  applied  to  any  useful  purpose. 

in.  Chlorine  dioxide  or  chlorine  peroxide  (C102)  is  dangerous  to 
prepare  and  examine  on  account  of  its  great  instability  and  violently 
explosive  character.  It  is  obtained  by  the  action  of  strong  sulphuric 
acid  upon  potassium  chlorate— 

3KC103  +  2H2S04  =  KC104  +  2KHS04  +  2C102  +  H20. 

It  is  a  bright  yellow  gas,  with  a  chlorous  and  somewhat  aromatic  smell, 
and  sp.  gr.  2.32  ;  condensable  to  a  red,  very  explosive  liquid  (b.p.  9°  C.). 
The  gas  is  gradually  decomposed  into  its  elements  by  exposure  to  light, 
and  a  temperature  of  60°  C.  causes  it  to  decompose  with  violent  ex- 
plosion into  a  mixture  of  chlorine  and  oxygen,  the  volume  of  which  is 
one  and  a  half  times  that  of  the  compound. 


1 88  CHLORINE  PEROXIDE. 

On  a  small  scale,  chlorine  peroxide  may  be  prepared  with  safety  by  pouring  a 
little  strong  sulphuric  acid  upon  one  or  two  crystals  of  potassium  chlorate,  in  a 
test-tube  supported  in  a  holder.  The  crystals  at  once  acquire  a  red  colour,  which 
gradually  diffuses  itself  through  the  liquid,  and  the  bright  yellow  gas  collects  in  the 
tube.  If  heat  be  applied,  the  gas  will  explode,  and  the  colour  and  odour  of  chlorine 
peroxide  will  be  exchanged  for  those  of  chlorine.  If  the  chlorate  employed  in  this 
experiment  contains  potassium  chloride,  explosion  often  happens  in  the  cold, 
since  the  hydrochloric  acid  evolved  by  the  action  of  the  acid  upon  that  salt  decom- 
poses a  part  of  the  chlorine  peroxide,  and  thus  provokes  the  decomposition,  of  the 
remainder. 

C102  is  easily  absorbed  by  water,  f ormiDg  chlorous  and  chloric  acids  ; 
the  solution  has  powerful  bleaching  properties.  Combustible  bodies, 
such  as  sulphur  and  phosphorus,  decompose  the  gas,  as  might  be  expected, 
with  great  violence.  This  powerful  oxidising  action  of  chlorine  peroxide 
upon  combustible  substances  appears  to  be  the  cause  of  the  property 
possessed  by  mixtures  of  such  substances  with  potassium  chlorate,  to 
inflame  when  touched  with  strong  sulphuric  acid. 

If  a  few  crystals  of  potassium  chlorate  be  thrown  into  a  glass  of  water  (Fig.  153), 
one  or  two  small  fragments  of  phosphorus  dropped  upon  them,  and  some  strong 
sulphuric  acid    poured  down  a  funnel  tube  to  the  bottom  of 
the  glass,  the  chlorine  peroxide  will  inflame  the  phosphorus 
with  bright  flashes  of  light  and  slight  detonations. 

Powdered  sugar  mixed  with  potassium  chlorate  on  paper, 
will  burn  brilliantly  when  touched  with  a  glass  rod  dipped  in 
strong  sulphuric  acid.  Matches  may  be  prepared,  which 
inflame  when  moistened  with  sulphuric  acid,  by  dipping  the 
end  of  splinters  of  wood  in  melted  sulphur,  and,  when  cool, 
tipping  them  with  a  mixture  of  5  grains  of  sugar  and  15  grains 
of  potassium  chlorate  made  into  a  paste  with  4  drops  of 
water.  When  dry,  they  may  be  fired  by  dipping  them  into  a 
bottle  containing  asbestos  moistened  with  strong  sulphuric 
acid.  These  matches,  under  the  names  of  Eupyrion  and  Vesta 
matches,  were  used  before  the  introduction  of  phosphorus  into 
general  use.  The  Promethean  light  was  an  ornamental  scented 
paper  spill,  one  end  of  which  contained  a  small  glass  bulb  of 
sulphuric  acid  surrounded  with  a  mixture  of  chlorate  and 
sugar,  which  inflamed  when  the  end  of  the  spill  was  struck  or 
squeezed,  so  as  to  break  the  bulb  containing  the  sulphuric  acid. 
The  paper  was  waxed  in  order  to  make  it  inflame  more  easily.  Percussion  fuses, 
&c.,  have  been  often  constructed  upon  a  similar  principle. 

Chlorous  acid,  HC102  or  CIO(OH),  is  contained,  together  with 
chloric  acid,  in  the  aqueous  solution  of  chlorine  peroxide  (2C102  +  H20  = 
HC1O,  +  HC103)  which  thus  resembles  nitric  peroxide  in  not  being  a 
separate  anhydride. 

The  chlorous  acid  may  be  separated  by  neutralising  the  solution  with  potash  and 
evaporating  until  the  potassium  chlorate  crystallises,  leaving  the  chlorite  (KC102) 
in  solution.  Little  is  known  about  the  acid  or  its  salts  ;  they  readily  undergo 
self-oxidation,  like  hypochlorous  acid  and  its  salts,  yielding  chloric  acid  and 
chlorates. 

112.  Euchlorine,  the  deep  yellow,  dangerously  explosive  gas  evolved  by  the 
action  of  strong  HC1  upon  KC103,  appears  to  be  a  mixture  of  chlorine  peroxide  with 
chlorine.  It  is  resolved  by  explosion  into  2  vols.  Cl  and  i  vol.  0.  Mercurous 
chloride  absorbs  Cl  from  it,  leaving  C102.  Hence  its  production  may  be  explained 
by  the  equation,  4KC1O?+  I2HC1  =  4KC1  +  6H20  +  3C102  +  C19. 

Cillorine  heptoxide,  presumably  C1207,  is  obtained  by  dropping  perchloric 
acid  on  to  phosphoric  anhydride  cooled  below  —  10°  C.  and  after  a  day  or  two  warm- 
ing the  retort  until  the  heptoxide  distils.  It  is  a  colourless  volatile  oil,  boiling  at 
82°  C.,  and  easily  exploded.  It  is  probably  perchloric  anhydride. 


CARBON   TETEACHLORIDE. 


CHLORIDES  OF  CARBON. 


189 


113.  It  has  already  been  seen  that  chlorine  has  no  direct  attraction 
for  carbon,  the  two  elements  not  being  known  to  enter  into  direct  com- 
bination ;  but  several  chlorides  of  carbon  may  be  obtained  by  the 
action  of  chlorine  upon  other  compounds  of  carbon,  particularly  by 
metalepsis  with  hydrocarbons. 

Carbon  tetrachloride,  CC14,  has  been  mentioned  (p.  174)  as  the  final 
result  of  the  action  of  chlorine  upon  marsh  gas  (CH4)  and  upon  chloro- 
form (CHC13).  It  is  easily  obtained  in  large  quantity,  by  passing 
chlorine  (dried  by  passage  through  a  tube  containing  pumice  wetted 
with  strong  H2S04)  (Fig.  154),  through  a  bottle  containing  carbon  bisul- 
phide, and  afterwards  through  a  porcelain  tube,  filled  with  fragments 
of  broken  porcelain  and  maintained  at  a  red  heat  by  a  gas  furnace ; 
the  products  are  condensed  in  a  bottle  surrounded  by  ice.  A  mixture 


Fig.  154. — Preparation  of  carbon  tetrachloride. 

of  carbon  tetrachloride  and  sulphur  dichloride  is  thus  obtained ; 
CS2  +  C16  =  CC14  +  S2C12.  This  is  shaken  with  potash,  whereupon  the 
sulphur  dichloride  is  decomposed  and  dissolved,  whilst  the  carbon 
tetrachloride  separates  and  falls  to  the  bottom.  The  two  layers  having 
been  separated  by  a  separating  funnel  (p.  139),  the  tetrachloride  maybe 
purified  by  distillation. 

Another  method  of  preparing  CC14  consists  in  distilling  carbon  bisul- 
phide with  antimonic  chloride  in  a  stream  of  chlorine. 

Carbon  tetrachloride  is  a  colourless  liquid,  much  heavier  than  water 
(sp.  gr.  1.6),  having  a  peculiar  odour,  and  boiling  at  77°  C.  It  may  be 
solidified  at  -23°  C.  The  tetrachloride  is  insoluble  in  water,  but 
dissolves  in  alcohol  and  in  ether.  It  is  a  very  useful  solvent  for  fats, 
and  also  finds  application  in  making  dyestufls. 

It  will  be  obvious  that  since  the  number  of  hydrocarbons  is  very 
large  there  must  be  a  considerable  number  of  chlorides  of  carbon 
obtained  by  the  complete  substitution  of  chlorine  for  hydrogen,  gener- 
ally by  metalepsis.  Some  of  these  are  of  very  high  molecular  weight, 
such  as  octachloronaphthalene  C10C18,  obtained  from  naphthalene  C10H8. 

Carbon  trichloride,  perchlorethane  or  hexachlor ethane,  C2C16,  is  pro- 
duced by  treating  Dutch  liquid  (p.  143)  with  excess  of  chlorine  in  sunlight. 


190  NITROGEN   CHLORIDE. 

It  is  a  white  crystalline  solid,  melting  at  187°  C.  By  treatment  with 
nascent  hydrogen  (zinc  and  sulphuric  acid)  it  yields  carbon  dichloride, 
or  tetrachlorethylene,  C2C14,  a  colourless  liquid  which  boils  at  121°  C. 

114.  Carbonyl  chloride,  carbon  oxychloride,  or  phosgene  gas,  COC12, 
is  produced  by  the  direct  combination  of  equal  volumes  of  carbonic  oxide 
and  chlorine  gases  under  the  influence  of  sunlight  (whence  its  last  name), 
when  the  mixture  condenses  to  half  its  volume  of  a  colourless  gas,  con- 
densable by  cold  (b.p.  8.4°  C.),  having  a  very  peculiar  pungent  smell,  and 
fuming  strongly  when  exposed  to  moist  air  by  decomposing  the  moisture 
and  producing  hydrochloric   acid;    COC12  +  H20  =  C02  + 2HC1.     It   is 
decomposed  by  alkalies,  producing  chlorides  and  carbonates.    It  is  used 
in  the  manufacture  of  some  artificial  dyestuffs. 

COC12  may  also  be  prepared  by  passing  a  mixture  of  equal  volumes  of  CO  and  Cl 
through  a  long  tube  filled  with  granulated  animal  charcoal,  which  favours  the  com- 
bination of  the  gases  ;  or  by  passing  dried  carbonic  oxide  through  antimony  penta- 
chloride  ;  SbCl5  +  CO  =  COC12  +  SbCl3. 

Phosgene  gas  has  also  been  obtained  by  heating  carbon  tetrachloride  with  phos- 
phoric anhydride,  in  a  sealed  tube  ;  3CC14  +  P205  =  2?OC13  +  3COC12  ;  and  by  heating 
chloroform  with  sulphuric  acid  and  potassium  dichromate. 

A  convenient  method  for  preparing  phosgene  gas  consists  in  dropping  fuming  sul- 
phuric acid  (containing  80  per  cent.  S03)  down  an  inverted  condenser  into  a  flask 
in  which  carbon  tetrachloride  is  boiling.  The  gas  escapes  through  a  side  tube  at 
the  top  of  the  condenser  and  is  washed  by  passage  through  strong  H2S04  ; 
CC14  +  2S03  =  COC12  +  S205C12  (jpyrosulphuryl  chloride). 

115.  Nitrogen  chloride  is  the  name  usually  given  to  the  very  explo- 
sive compound  before  referred  to  as  being  produced  by  the  action  of 
chlorine  on  ammonium  chloride.     The  oily  liquid  thus  produced  is  a 
mixture  of  several  compounds  which  have  been  formed  from  the  NH4C1 
by  the  substitution  of  chlorine  for  hydrogen.     Nitrogen  chloride,  NC13, 
is  the  most  explosive  constituent  of  the  mixture,  and  can  be  isolated  by 
a  process  attended  with  considerable  danger. 

It  is  a  yellow,  heavy,  oily  liquid  (sp.  gr.  1.7),  which  volatilises  easily, 
yielding  a  vapour  of  very  characteristic  odour,  which  affects  the  eyes. 
When  heated  to  about  93°  C.  it  explodes  with  great  violence,  emitting 
a  loud  report  and  a  flash  of  light.*  Its  instability  is,  of  course, 
attributable  to  the  feeble  attraction  which  holds  its  elements  together ; 
and  the  violence  of  the  explosion,  to  the  sudden  expansion  of  a  small 
volume  of  the  liquid  into  a  large  volume  of  nitrogen  and  chlorine. 

As  might  be  expected,  its  explosion  is  at  once  brought  about  by  contact  with 
substances  which  have  an  attraction  for  chlorine,  such  as  phosphorus  and  arsenic  ; 
the  oils  and  fats  cause  its  explosion,  probably  by  virtue  of  their  hydrogen  ;  oil  of 
turpentine  explodes  it  with  greater  certainty  than  the  fixed  oils.  Alkalies  also 
decompose  it  violently  ;  whilst  acids,  having  no  action  upon  the  chlorine,  are  not 
so  liable  to  explode  it.  At  71°  C.  this  substance  has  actually  been  distilled  with- 
out explosion. 

Although  practically  unimportant,  the  violently  explosive  properties  of  this  sub- 
stance render  it  so  interesting  that  it  may  be  well  to  give  some  directions  for  its 
safe  preparation,  which  may  be  effected  by  the  action  of  solution  of  hypochlorous 
acid  upon  ammonium  chloride. 

Fifty  grains  of  red  oxide  of  mercury  are  very  finely  powdered  and  thrown  into 
a  pint  bottle  of  chlorine  together  with  ^  oz.  of  water.  The  stopper  is  replaced, 
and  the  bottle  well  shaken,  loosening  the  stopper  occasionally,  as  long  as  the 
chlorine  is  absorbed.  The  solution  of  hypochlorous  acid  thus  produced  is  filtered 
from  the  residual  mercuric  oxychloride,  and  poured  into  a  clean  thumb-glass 

*  It  is  said  to  absorb  38,478  gram  units  of  heat  per  equivalent,  in  the  process  of  forma- 
tion, and  would  therefore  disengage  that  amount  of  heat  in  the  act  of  decomposition. 


ACID   CHLORIDES.  19! 

(Fig.  155).  A  lump  of  ammonium  chloride  weighing  20  grains  is  then  dropped 
into  the  solution,  and  the  glass  is  placed  under  a  stout  wooden  box.  After  the 
lapse  of  twenty  minutes,  the  chloride  of  nitrogen  may  be  exploded 
by  inserting,  through  a  hole  in  the  box,  a  stick  dipped'in  turpentine, 
fixed  at  right  angles  to  a  longer  stick.  The  glass  will  be  shattered 
into  very  small  fragments. 


1  1  6.  Aqua  regia.  —  This  name  has  been  bestowed  upon 
the    mixture   of  i    measure  of    nitric,  and   3   measures  of 
hydrochloric  acid  (nitromuriatic  acid),   which  is  employed      Fig.  155. 
for  dissolving  gold,  platinum,  and  other  metals  which  are 
not  soluble  in   the  separate  acids.     A  little  gold  leaf  placed  in  hydro- 
chloric and  nitric  acids  contained  in  separate  glasses  remains  unaffected 
even  on   warming  the   acids;  but  if    the  contents    of   the  glasses  be 
mixed,  the  gold  will  be  immediately  dissolved  by  the  chlorine,  which 
is  liberated  in  the  action  of  the  acids  upon  each  other  ;  HN03  +  3HC1  = 


The  nitrosyl  chloride  (NOC1)  is  a  red  gas,  condensable  in  a  freezing  mixture 
to  a  dark  red  liquid,  which  boils  at  -  8°  C.  and  dissociates  above  700°  C.  It  has 
a  very  peculiar  odour,  and  is  decomposed  by  contact  with  water,  nitrous  acid  and 
hydrochloric  acid  being  produced.  Nitrosyl  chloride  is  also  produced  by  mixing 
2  volumes  of  nitric  oxide  with  I  volume  of  chlorine  ;  it  condenses  to  a  red  liquid 
when  cooled.  When  nitrosyl  chloride  is  passed  into  oil  of  vitriol  cooled  to  o°  C., 
crystals  of  the  acid  nitrosyl  sulphate  (NOHS04)  are  deposited;  NO*C1  + 
S02(OH)(OH)  =  HC1  +  S02(OH)(ONO)*. 

Nitrosyl  sulphate  is  also  obtained  by  passing  S02  into  nitric  acid,  or  N203  into 
sulphuric  acid,  or  by  burning  a  mixture  of  I  part  of  sulphur  and  3  parts  of  nitre 
in  moist  air. 

Nitrosyl  chloride  is  best  prepared  by  heating  nitrosyl  sulphate  with  sodium 
chloride;  NO'HS04  +  NaCl  =  NO'Cl  +  NaHS04.  It  is  a  useful  reagent  in  organic 
chemistry. 

It  has  been  proposed  to  manufacture  chlorine  by  oxidising  hydrochloric  acid  with 
nitric  acid  as  shown  by  the  above  equation  for  the  decomposition  of  aqua  regia. 
The  mixture  of  NOC1  and  C12  is  passed  through  strong  sulphuric  acid  whereby 
the  NOC1  is  absorbed  and  HC1  evolved  in  its  stead  ;  this  is  removed  from  the  Cl 
by  passage  through  water.  By  diluting  the  sulphuric  acid  containing  the  nitrosyl 
sulphate  and  passing  air  through  the  liquid,  N02  is  evolved,  which  may  be  passed 
(together  with  air)  into  water  to  form  HN03.  In  this  way  the  nitric  acid  would 
serve  as  a  carrier  of  oxygen  from  the  air  to  the  hydrogen  of  the  hydrochloric  acid. 

Nitrosyl  chloride,  NOC1,  is  an  example  of  a  large  class  of  compounds 
known  as  acid  chlorides  or  chlor  anhydrides.  An  acid  chloride  is  formed 
by  the  substitution  of  01  for  OH  in  an  acid  ;  thus  nitrosyl  chloride  is 
formed  from  nitrous  acid,  NO  'OH.  The  reaction  which  most  generally 
produces  an  acid  chloride  is  that  between  an  oxy-acid  and  phosphoric 
chloride,  PC15  (see  Phosphorus)  ;  if  R  represent  the  group  of  atoms  com- 
bined with  OH  in  an  acid,  this  reaction  may  be  expressed  by  the  equa- 
tion, R-OH-f  PC15  =  R/C1  +  POC13  +  HC1,  or,  since  the  acid  residue 
may  be  combined  with  several  OH  groups,  R(OH)w  +  ?iPCl5  = 
RCln  +  nPOC]3  +  ?iHCl.  It  is  from  this  fact,  namely,  that  for  every 
atom  of  chlorine  introduced  into  an  acid  by  the  action  of  phosphoric 
chloride,  one  atom  of  oxygen  and  one  atom  of  hydrogen  are  removed 
(as  POC13  and  HCl  respectively),  that  the  inference  is  drawn  that  the 
hydrogen  in  an  oxyacid  exists  in  the  form  of  hydroxyl  groups.  For  it 

*  In  this  formula  for  nitrosyl  sulphate  the  nitrosyl  group  is  exchanged  for  hydrogen  in 
one  of  the  hydroxyl  groups  of  sulphuric  acid.  Some  chemists  regard  the  compound  as 
nitrosulphuric  or  nitrosulphonic  acid,  that  is,  sulphuric  acid  in  which  NO2  has  been  substi- 
tuted for  H  :—  SO2(OH)(NO2). 


1 92  BROMINE. 

is  obvious  that  a  moriovalent  atom  like  Cl  can  only  be  substituted  for 
another  monovalent  atom  or  a  monovalent  radicle,  so  that  if  0  and  H 
are  together  exchanged  for  Cl  they  must  be  present  as  -  OH  ;  were  they 
present  independently  of  each  other  they  would  represent  three  atom- 
fixing  powers  (-O-and  H-),  and  could  not  be  exchanged  for  the 
monovalent  atom  Cl.  It  will  be  found,  particularly  in  organic 
chemistry,  that  acids  frequently  contain  0  and  H,  for  which  Cl  cannot 
be  substituted,  and  therefore  exist  in  some  other  relationship  to  the- 
molecule  than  that  represented  by  -  OH. 

The  characteristic  behaviour  of  acid  chlorides  is,  that  when  brought- 
into  contact  with  water  they  exchange  their  chlorine  for  hydroxyl,  and 
are  converted  into  the  acids  from  which  they  were  derived  ;. 
RClM  +  wHOH  =  R(OH)M  +  wHCl.  It  is  because  these  chlorides  form 
acids,  in  this  way,  when  brought  in  contact  with  water,  that  they  are- 
also  termed  chloranhydrides. 

It  is  noteworthy  that  whilst  the  acid  chlorides  yield  acid  hydroxides- 
and  hydrochloric  acid  by  treatment  with  water,  the  basic  hydroxides,, 
such  as  NaOH,  Ca(OH)2,  yield  basic  chlorides  and  water  by  treatment 
with  hydrochloric  acid  ;  thus  it  is  instructive  to  compare  the  reactions  i 

NO-C1  +  HOH  =  NO-OH  +  HC1, 
and  NaOH  +  HC1    =  NaCl      +  HOH. 

Nitroxyl  chloride  or  nitryl  chloride,  N02C1,  is  the  acid  chloride  from, 
nitric  acid,  N02.OH.  It  is  produced  by  heating  N02  with  Cl,  NO,  +  CL 
=  NO2C1,  and  is  a  yellowish  red  liquid  boiling  at  5°  C. 

Carbonyl  chloride,  COC12,  is  the  acid  chloride  of  carbonic  acid,, 
CO(OH)2. 

BROMINE. 

Br  =  79.5  Pafts  by  weight. 

117.  It  generally  happens  that  elements  between  which  any  strong 
family  likeness  exists  are  found  associated  in  nature.  This  remark  par- 
ticularly applies  to  the  three  elements — chlorine,  bromine,  and  iodine — 
all  of  which  are  found  in  sea  water,  though  the  first  predominates  to- 
such  an  extent  that  the  others  for  a  long  time  escaped  notice.  Bromine 
was  brought  to  light  in  the  year  1826  by  Balard  in  the  examination  of 
bittem,which  is  the  liquid  remaining  after  the  sodium  chloride  and  some 
other  salts  have  been  made  to  crystallise  by  evaporating  sea  water,  which 
contains  bromine  in  the  forms  of  bromide  of  magnesium  and  bromide  of 
sodium.*  It  has  also  been  extracted  from  the  waters  of  certain  mineral 
springs,  as  those  of  Kreuznach  and  Kissingen,  which  contain  much 
larger  quantities  of  bromine,  combined  with  potassium,  sodium,  or  mag- 
nesium. Now,  almost  the  sole  sources  of  bromine  are  the  mother-liquors  of 
the  salt-works  at  Stassfurt,  and  from  certain  saline  springs  in  the  United 
States. 

In  extracting  the  bromine  from  these  waters,  advantage  is  taken  of 
the  circumstance  that  chlorine  displaces  bromine  from  its  combinations 
with  the  metals.  Aftermost  of  the  other  salts,  such  as  sodium  chloride,, 
sodium  sulphate,  and  magnesium  sulphate,  which  are  less  soluble  than 
the  bromides,  have  been  separated  from  the  water  by  evaporation  and 

*  4.9  grams  of  magnesium  bromide  per  gallon  have  been  found  in  the  water  of  the  Irish. 


PROPERTIES  OF  BROMINE,  195. 

crystallisation,  the  remaining  liquid,  containing  about  0.3  per  cent,  of 
bromine,  is  run  down  a  tower  packed  with  earthenware  balls,  where  it 
meets  a  current  of  steam  conveying  chlorine  which  has  been  passed  into- 
it  from  a  chlorine  still.  The  bromine  is  liberated  from  the  bromides,. 
the  chief  of  which  is  magnesium  bromide  (MgBr2  +  Cl,  =  Mg012  +  Br2), 
and  passes  as  vapour  from  the  top  of  the  tower  through  a  condenser  in 
which  it  is  condensed  to  the  liquid  state. 

The  chief  impurity  in  the  crude  bromine  thus  obtained  is  bromine  chloride,  BrCl, 
formed  by  the  combination  of  excess  of  chlorine  with  the  bromine.  This  is  decom- 
posed by  shaking  the  crude  product  with  potassium  bromide,  KBr  +  BrCl  =  KCl  + 
Br2  ;  and  the  bromine  is  distilled  away  from  the  KC1. 

To  illustrate  on  a  small  scale  the  manufacture  of  bromine,  chlorine  water  may  be 
added  to  a  solution  of  potassium  bromide,  which  will  at  once  become  orange  from 
the  liberation  of  the  bromine,  KBr  +  Cl  =  KC1  +  Br.  The  bromine  thus  set  free  exists 
now  diffused  through  a  large  volume  of  water,  which  cannot  be  separated  from  it  in 
the  usual  way,  by  evaporation,  because  bromine  is  itself  very  volatile.  An  ingenious 
expedient  is  therefore  resorted  to,  of  shaking  the  orange  liquid  briskly  with  ether, 
which  has  a  greater  solvent  power  for  bromine  than  is  possessed  by  water,  and  there- 
fore abstracts  it  from  the  aqueous  solution  :  since  ether  does  not  mix  to  any  great 
extent  with  water,  it  now  rises  to  the  surface  of  the  liquid,  forming  a  layer  of  a 
beautiful  orange  colour,  due  to  the  bromine  which  it  holds  in  solution.  This  orange 
layer  is  carefully  separated  and  shaken  with  solution  of  potash,  which  immediately 
destroys  the  colour  by  removing  the  bromine,  leaving  the  ether  to  rise  to  the 
surface  in  a  pure  state,  and  fit  to  be  employed  for  abstracting  the  bromine  from  a 
fresh  portion  of  the  water.  The  action  of  the  bromine  upon  potash  is  precisely 
similar  to  that  of  chlorine  ;  6KOH  +  Br6  =  5KBr  +  KBr03  +  3H2O. 

After  the  solution  of  potash  has  been  several  times  shaken  with  the  ethereal  solu- 
tion of  bromine,  and  has  become  highly  charged  with  this  element,  it  is  evaporated 
so  as  to  expel  the  water,  leaving  a  solid  residue  containing  the  potassium  bromide 
and  bromate.  This  saline  mass  is  strongly  heated  to  decompose  the  bromate,  and 
convert  it  into  bromide;  KBr03  =  KBr  +  03.  From  this  salt  the  bromine  is  ex- 
tracted by  distilling  it  with  manganese  dioxide  and  sulphuric  acid,  when  the  bro- 
mine is  liberated  and  condensed  in  a  receiver  kept  cold  by  iced  water;  2KBr  + 


The  aspect  of  bromine  is  totally  different  from  that  of  any  othei 
element,  for  it  distils  over  in  the  liquid  condition,  and  preserves  that 
form  at  ordinary  temperatures,  being  the  only  liquid  non-metallic  ele- 
ment. Its  dark  red-brown  colour,  and  the  peculiar  orange  colour  of  the 
vapour  which  it  exhales  continually,  are  also  characteristic  ;  but,  above 
all,  its  extraordinary  and  disagreeable  odour,  from  which  it  derives  its 
name  (/Spw/zor,  a  stench),  leaves  no  doubt  of  its  identity.  The  odour 
has  some  slight  resemblance  to  that  of  chlorine,  but  is  far  more  intoler- 
able, often  giving  rise  to  great  pain,  and  sometimes  even  to  bleeding  at 
the  nose. 

Liquid  bromine  is  thrice  as  heavy  as  water  (sp.  gr.  3.18  at  o°  C.),  and 
boils  at  63°  C.,  yielding  a  vapour  5^  times  as  heavy  as  air  (sp.gr.  5.54).* 
It  may  be  frozen  at  -  7°  C.  to  a  brown  crystalline  solid.  It  requires 
33  times  its  weight  of  cold  water  to  dissolve  it,  and  forms  a  crystalline 
hydrate  (Br.5H20)  corresponding  with  chlorine  hydrate. 

In  its  bleaching  power,  its  aptitude  for  direct  combination,  and  its 
other  chemical  characters,  it  very  closely  resembles  chlorine,  so  closely, 
indeed,  that  it  is  difficult  to  distinguish,  in  many  cases,  between  the 
compounds  of  chlorine  and  bromine  with  other  substances,  unless  the 
elements  themselves  be  isolated.  A  necessary  consequence  of  so  great  a 
similarity  is,  that  very  little  use  has  been  made  of  bromine,  since  the  far 

*  At  high  temperatures  the  vapour  density  (sp.  gr.)  of  bromine  decreases  considerably. 

N 


194  HYDRO BKOMIC   ACID. 

more  abundant  chlorine  fulfils  nearly  all  the  purposes  to  which  bromine 
might  otherwise  be  applied.  In  the  daguerreotype  and  photographic 
arts,  however,  some  special  applications  of  bromine  have  been  discovered, 
and  for  some  chemical  operations,  such  as  the  determination  of  the  illu- 
minating hydrocarbons  in  coal  gas,  bromine  is  sometimes  preferred  to 
chlorine.  It  is  applied  in  the  manufacture  of  artificial  dyestuffs  and  has 
also  been  used  in  America  as  a  disinfectant.  The  bromides  of  potassium 
and  ammonium  are  frequently  employed  in  medicine.  Bromide  of  cad- 
mium is  used  in  photography.  Commercial  bromine  sometimes  contains 
bromoform  and  cyanogen  bromide.  In  the  composition  of  their  com- 
pounds chlorine  and  bromine  exhibit  great  analogy,  but  no  compound 
of  bromine  with  oxygen  has  been  obtained. 

Hypobromous  acid  (HOBr)  has  been  obtained  in  solution  by  shaking 
mercuric  oxide  with  water  and  bromine.  The  solution  is  very  unstable, 
decomposing,  especially  when  heated,  with  liberation  of  bromine  and 
formation  of  bromic  acid.  The  action  of  bromine  upon  diluted  solutions 
of  the  alkalies,  and  upon  the  alkaline  earths,  produces  bleaching  liquids 
similar  to  those  formed  by  chlorine,  and  apparently  containing  the 
hypobromites  of  the  metals. 

Bromic  acid  (HBr03)  can  be  prepared  in  a  similar  manner  to  that 
described  for  the  preparation  of  chloric  acid,  to  which  it  has  a  great 
general  resemblance,  the  bromates  being  also  similar  to  the  chlorates. 

1 1 8.  Hydrogen  bromide  or  hydrobromic  acid  (HBr  =  8i  parts  by 
weight  =  2  vols.) — The  inferiority  of  bromine  to  chlorine  in  chemical 
energy  is  well  exemplified  in  its  relations  to  hydrogen ;  for  the  vapour 
of  bromine  mixed  with  hydrogen  will  not  explode  under  the  action  of 
flame  or  of  the  electric  spark,  like  the  mixture  of  chlorine  and  hydrogen. 
Direct  combination  may  be  induced  by  contact  with  heated  platinum. 

When  it  is  attempted  to  prepare  this  acid  by  distilling  bromide  of 
sodium  or  potassium  with  sulphuric  acid  (as  in  the  preparation  of  hydro- 
chloric acid)  the  inferior  stability  of  hydrobromic  acid  is  shown  by  the 
decomposition  of  a  part  of  it,  the  hydrogen  being  oxidised  by  the 
sulphuric  acid,  and  the  bromine  set  free;  2HBr  +  H9S04  =  2H20  +  S02 
+  Br2. 

If  a  strong  solution  of  phosphoric  acid  be  employed  instead  of  the 
sulphuric,  pure  hydrobromic  acid  may  be  obtained. 

But  the  most  instructive  method  of  obtaining  hydrobromic  acid  con- 
sists in  attacking  water  with  bromine  and  phosphorus  simultaneously, 
when  the  phosphorus  takes  the  oxygen  of  the  water,  forming  phosphoric 
acid,  and  the  bromine  combines  with  the  hydrogen  to  form  hydrobromic 
acid;  3H2O  +  Br5  +  P  =  HPO3  +  5HBr. 

Phosphoric  acid. 

The  experiment  may  be  made  in  the  apparatus  shown  in  Fig.  156.  20  grams  of 
red  phosphorus  are  introduced  into  the  flask  and  are  covered  with  40  c.c.  of  water. 
1 20  grams  (40  c.c.)  of  bromine  are  allowed  to  fall,  drop  by  drop,  from  the  stop- 
cock funnel  into  the  flask.  The  hydrogen  bromide  is  passed  through  a  U-tube  con- 
taining fragments  of  glass  mixed  with  moist  red  phosphorus,  to  absorb  bromine, 
and  is  collected  by  downward  displacement.  After  a  time  the  flask  may  be  gently 
heated. 

Hydrogen  bromide  is  very  similar  to  hydrogen  chloride  ;  it  boils  at 
-  73°  C.  Like  that  gas,  it  is  very  soluble  in  water,  and  the  solution 
acts  upon  metals  and  their  oxides  in  the  same  manner  as  does  hydro- 
chloric acid.  Chlorine  removes  the  hydrogen  from  hydrobromic  acid, 


IODINE. 


195 


liberating  bromine,  which  it  converts  into  bromine  chloride  if  employed 
in  excess. 


Fig.  156. — Preparation  of  hydrobromic  acid. 

Nitrogen  bromide  has  been  obtained  by  the  action  of  bromide  of  potassium  upon 
chloride  of  nitrogen,  which  it  resembles  in  general  character  and  explosive  pro- 
perties. 

Carbon  tetrabromlde,  CBr4,  is  obtained  by  heating  CS2  with  Br  at  160°  C.  It 
crystallises  in  white  tables,  melts  at  91°  C.  and  boils  at  189.5°  @. 

Bromine  chloride,  BrCl,  is  a  very  volatile  red-brown  liquid  of  pungent  odour. 
It  is  dissociated  above  10°  C.  That  chlorine  should  unite  directly  with  bromine, 
which  it  so  much  resembles  in  chemical  character,  illustrates  its  great  tendency  to 
direct  chemical  combination. 

IODINE. 

1  =  126  parts  by  weight. 

119.  Iodine  is  contained  in  sea  water  in  even  smaller  quantity  than 
bromine  is, and  appears  to  be  present  as  calcium  iodate,  Ca  (IO3)2,of  which 
4  parts  are  contained  in  a  million  of  sea  water,*  but  the  iodine  appears 
to  constitute  a  portion  of  the  necessary  food  of  certain  varieties  of  sea- 
weed, which  extract  it  from  the  sea  water,  and  concentrate  it  in  their 
tissues.  The  ash  remaining  after  sea-weed  has  been  burnt  was  long 
used,  under  the  name  of  kelp,  in  soap-making,  because  it  contains  a 
considerable  quantity  of  sodium  carbonate;  and  in  the  year  1811, 
Courtois,  a  soap-boiler  of  Paris,  being  engaged  in  the  manufacture  of 
soda  from  kelp,  obtained  from  the  waste  liquors  a  substance  which 
possessed  properties  different  from  those  of  any  form  of  matter  with 
which  he  was  acquainted.  He  transferred  it  to  a  French  chemist, 
Clement,  who  satisfied  himself  that  it  was  really  a  new  substance ;  and 
Oay-Lussac  and  Davy  having  examined  it  still  more  closely,  it  took  its 
rank  among  the  non-metallic  elementary  substances,  under  the  name  of 

*  The  iodate  may  be  detected  in  sea  water  by  shaking-  with  carbon  disulphide  and  a  little 
of  the  water  in  which  phosphorus  has  been  kept ;  the  phosphorous  acid  reduces  the  iodate, 
liberating  iodine,  which  dissolves  in  the  CS2  with  a  rose  colour.  It  has  been  shown  that  the 
amount  of  iodine  (2.3  milligrams  per  litre)  in  sea  water  is  constant  at  all  depths,  but  while  it 
is  in  inorganic  combination  at  great  depths  it  is  organically  combined  near  the  surface. 


196  EXTEACTION   OF   IODINE. 

iodine    (toeiS?)?,  violet-coloured),    conferred    upon  it   in   allusion    to   the 
magnificent  violet  colour  of  its  vapour. 

The  history  of  the  discovery  of  iodine  affords  a  very  instructive 
example  of  the  advantage  of  training  persons  engaged  in  manufactures 
to  habits  of  accurate  observation,  and,  if  possible,  of  accurate  chemical 
observation  ;  for  had  Courtois  passed  over  this  new  substance  as  acci- 
dental, or  of  no  consequence,  the  community  would  have  lost,  at  least 
for  some  time,  the  benefits  derived  from  the  discovery  of  iodine. 

For  some  years  the  new  element  was  only  known  as  a  chemical 
curiosity,  but  an  unexpected  demand  for  it  at  length  arose  on  the  part 
of  the  physician,  for  it  had  been  found  that  the  efficacy  of  the  ashes  of 
sponge,  which  had  long  been  used  in  some  particular  maladies,  was  due 
to  the  small  quantity  of  iodine  which  they  contained,  and  it  was  of 
course  thought  desirable  to  place  this  remedy  in  the  hands  of  the  medical 
profession  in  a  purer  form  than  the  ash  of  sponge,  where  it  is  associated 
with  very  large  quantities  of  various  saline  substances.  Much  more 
recently,  the  demand  for  this  element  has  greatly  increased  on  account 
of  its  employment  in  photography,  and  in  the  manufacture  of  artificial 
dyes,  and  large  quantities  of  it  were  at  one  time  produced  from  kelp. 

Although  the  production  of  iodine  from  kelp  is  a  dead  industry,  a  brief  de- 
scription of  it  may  be  given  as  an  excellent  example  of  how  an  element  may  be 

extracted  from  an  enormously  pre- 
ponderating mass  of  other  matter. 
The  sea- weed*  is  spread  out  to  dry, 
and  burnt  in  shallow  pits  at  as  low 
a  temperature  as  possible ;  for  the 
sodium  iodide  is  converted  into- 
vapour  and  lost  if  the  temperature 
is  very  high.  The  ash,  which  is  in 
a  half-fused  state,  is  broken  up  and 
treated  with  hot  water,  which  dis- 
solves about  half,  leaving  a  residue 
consisting  of  calcium  carbonate  and 
sulphate,  sand,  &c.  The  whole  of 
the  sodium  iodide  is  contained  in 
the  portion  dissolved  by  the  water, 
but  is  mixed  with  much  larger 
quantities  of  sulphate,  carbonate f 
Fig.  157. — Extraction  of  iodine.  hyposulphite,  sulphide  and  bro- 

mide of  sodium,  together  with  sul- 
phate and  chloride  of  potassium.  A  portion  of  the  water  is  expelled  by  evaporation, 
when  the  sulphate  and  carbonate  of  sodium  and  chloride  of  potassium,  being  far  less 
soluble  than  the  iodide  of  sodium,  crystallise.  In  order  to  decompose  the  hyposul- 
phite and  sulphide  of  sodium,  the  liquid  is  mixed  with  an  eighth  of  its  bulk  of  oil 
of  vitriol,  which  decomposes  these  salts,  evolving  sulphurous  and  hydrosulphuric  acid 
gases,  with  deposition  of  sulphur,  and  forming  sodium  sulphate,  which  is  deposited 
in  crystals.  The  liquor  thus  prepared  is  next  mixed  with  manganese  dioxide,  and 
heated  in  an  iron  still  lined  with  lead  (Fig.  157),  when  the  iodine  is  evolved  as  a 
magnificent  purple  vapour,  which  condenses  in  the  bottle-shaped  glass  or  stoneware 
receivers  (aludels)  in  the  form  of  dark  grey  scales  with  metallic  lustre,  and  having 
considerable  resemblance  to  black  lead.  The  liberation  of  the  iodine  is  explained 
by  the  following  equation— 2NaI  +  Mn02  +  2H2S04  =  Na-jSO^  +  MnS04  +  2H20  + 12. 

When  no  more  iodine  passes  over,  some  manganese  dioxide  is  added,  and  "the 
bromine  then  distils.  The  quantity  of  bromine  obtained  is  about  one-tenth  that  of 
the  iodine.  A  ton  of  kelp  yields  about  10  Ibs.  of  iodine.  The  crude  iodine  is  re- 
sublimed  to  purify  it. 

A  far  more  economical  process  for  the  treatment  of  sea-weed  consists  in  distilling 

*  The  Laminaria  digitata,  or  deep  sea  tangle,  contains  most  iodine,  amounting  to  0.45  per 
cent,  of  the  dried  weed. 


PEOPEETIES   OF   IODINE.  197 

it,  when  ammonia,  acetic  acid,  naphtha,  tar,  and  illuminating  gas  are  obtained, 
whilst  a  porous  charcoal  remains  in  the  retort,  which  is  treated  with  water  in  order 
to  extract  the  iodides  and  other  soluble  salts.  This  charcoal  somewhat  resembles 
animal  charcoal  in  character,  containing  much  phosphate  and  carbonate  of  calcium 
and  magnesium  ;  it  is  useful  as  a  decolorising  and  deodorising  agent.  In  France 
the  iodine  is  generally  precipitated  from  the  concentrated  solution  of  kelp  by 
passing  chlorine  into  the  solution.  The  precipitate  is  washed  and  resublimed. 

Iodine  is  now  imported  from  Chili  and  Peru,  where  it  is  obtained 
from  caliche,  the  crude  nitrate  of  soda  found  in  certain  districts 
of  those  countries.  In  this  mineral  the  iodine  (about  o.i  per  cent.) 
occurs  as  sodium  iodate  (IS"aI03)  which  remains  dissolved  in  the  water 
from  which  the  sodium  nitrate  has  been  recrystallised  for  the  market. 
These  mother  liquors,  containing  about  22  per  cent,  of  NaIO3,  are 
mixed  with  a  solution  containing  sodium  sulphite  (Na2S03)  and  sodium 
hydrogen  sulphite  (NaHSO3),  when  the  iodine  is  precipitated  according 
to  the  equation — 

2NaI03  +  3Na2S03  +  2NaHS03  =  5X8.5804  +  L2  +  H20. 

The  precipitate  is  drained,  pressed,  and  resublimed. 

Besides  non- volatile  matter  (sand  and  calcium  sulphate),  which  may  be 
eliminated  by  resublimation,  commercial  iodine  is  liable  to  contain  chlorine, 
bromine,  and  cyanogen  iodide.  It  may  be  freed  from  these  volatile  impurities 
by  dissolving  it  in  a  strong  solution  of  potassium  iodide,  precipitating  it  by 
the  addition  of  water  and  resubliming  the  dried  precipitate  after  it  has  been 
mixed  with  barium  oxide  to  complete  its  desiccation. 

The  features  of  this  element  are  extremely  well  marked  :  its  metallic 
lustre  and  peculiar  odour  sufficiently  distinguish  it  from  all  others,  and 
the  effect  of  heat  upon  it  is  very  striking,  in  first  easily  fusing  it  (at 
116°  C.),  and  afterwards  converting  it  (boiling-point,  183°)  into  the 
most  exquisitely  purple  vapour,  which  is  nearly  nine  times  as  heavy  as 
air  (sp.  gr.  8.72),*  and  condenses  upon  a  cool  surface  in  shining  scales. 
Iodine  stains  the  skin  intensely  brown.  The  specific  gravity  of  solid 
iodine  is  4.95. 

When  iodine  is  shaken  with  cold  water,  a  very  small  quantity  is  dis- 
solved (about  0.05  per  cent.),  forming  a  light-brown  solution.  Hot 
water  dissolves  a  larger  quantity,  but  alcohol  is  one  of  the  best  solvents 
for  iodine,  producing  a  dark  red-brown  solution  from  which  part  of  the 
iodine  may  be  precipitated  by  adding  water.  A  solution  of  potassium 
iodide  also  dissolves  iodine  freely  (Lugol's  solution  ;  liquor  iodi).  Tincture 
of  iodine  contains  iodine  with  half  its  weight  of  potassium  iodide 
dissolved  in  alcohol.  Benzene  and  carbon  bisulphide  dissolve  it  abun- 
dantly, producing  fine  violet-red  solutions,  which  deposit  the  iodine,  if 
allowed  to  evaporate  spontaneously,  in  minute  rhombic  octahedral 
crystals  aggregated  into  very  beautiful  fern- like  forms.  If  an  extremely 
weak  aqueous  solution  of  iodine  be  shaken  with  a  little  carbon  bi- 
sulphide, the  latter  will  remove  the  iodine  from  the  solution,  and,  on 
standing,  will  fall  to  the  bottom  of  the  liquid,  having  a  beautiful  rose 
colour.  By  dissolving  a  large  quantity  of  iodine  in  carbon  bisulphide,  a 
solution  is  obtained  which  is  perfectly  opaque  to  rays  of  light,  though  it 
allows  heat  rays  to  pass  freely,  and  is  therefore  of  great  value  in  physical 
experiments.  A  solution  of  iodine  in  carbon  teti  achloride  is  also  used 
for  the  same  purpose. 

*  The  vapour  density  of  iodine  vapour  falls  with  rise  of  temperature. 


198  IODINE  AND   STARCH. 

Existing,  as  iodine  does,  in  very  minute  quantity  in  the  water  from 
various  natural  sources,  it  would  often  be  overlooked  if  the  chemical 
analyst  did  not  happen  to  possess  a  test  of  the  most  delicate  description 
for  it.  Iodine,  in  the  uncombined  state,  dyes  starch  of  a  beautiful 
blue  colour,  as  may  be  proved  by  heating  a  grain  or  two  of  the  element 
with  water,  and  adding  to  the  cold  solution  a  little  thin  starch,  or  by 
placing  a  minute  fragment  of  iodine  in  a  stoppered  bottle,  and  sus- 
pending in  it  a  piece  of  paper  clipped  in  thin  starch.  This  test,  however, 
though  sensitive  to  the  smallest  quantity  of  free  iodine,  gives  no  indica- 
tion whatever  with  iodine  in  combination,  as  it  always  exists  in  nature ; 
in  order,  therefore,  to  test  for  iodine,  a  little  starch-paste  is  added  to  the 
suspected  liquid,  and  then  a  drop  of  a  weak  solution  of  chlorine,  which 
will  set  free  the  iodine,  and  cause  the  production  of  the  blue  colour.  It 
is  necessary,  however,  carefully  to  avoid  adding  too  much  chlorine,  since 
it  would  immediately  destroy  the  colour  of  the  iodised  starch  :  if  this 
has  been  done,  a  very  little  sulphurous  acid  will  bring  back  the  blue  tint, 
which  will  be  again  bleached  by  more  sulphurous  acid.*  Alkalies  also 
bleach  it,  and  the  colour  of  a  mixture  of  the  iodised  starch  with  water  is 
removed  by  heating,  but  returns  in  great  measure  when  the  solution 
cools.  The  starch  appears  to  be  only  dyed  by  the  iodine,  and  not 
combined  with  it ;  on  shaking  the  blue  iodised  starch  for  some  time  with 
CS2,  the  blue  colour  is  removed,  and  the  red  solution  of  iodine  in  CS2  is 
obtained. 

This  delicate  test  for  iodine  has  enabled  the  chemist  to  show  that  the 
element  is  widely  distributed  in  very  small  quantities.  It  has  been 
found  in  the  floating  matter  of  the  air,  in  various  fungi,  in  forest  trees, 
and  in  the  animal  body,  particularly  the  thyroid  gland. 

Though  very  closely  connected  with  chlorine  and  bromine  in  its  general 
chemical  relations,  there  are  several  points  in  the  history  of  iodine  which 
cause  it  to  stand  out  in  marked  contrast  by  the  side  of  these  elements. 
The  attraction  which  binds  it  to  hydrogen  and  the  metals  is  certainly 
weaker  than  that  exerted  by  chlorine  and  bromine,  so  that  either  of 
these  is  capable  of  displacing  it  from  its  compounds,  and  its  bleaching 
properties  are  very  feeble.  01,  uniting  with  H,  produces  22,000  heat- 
units;  gaseous  Br  produces  12,100,  but  gaseous  I  produces  practically  no 
thermal  effect.t  Hence  HI  is  much  less  stable  than  HBr  or  HC1.  On  the 
other  hand,  iodine  exhibits  a  more  powerful  tendency  to  unite  with 
oxygen  ;  for  boiling  nitric  acid  converts  it  into  iodic  acid  (HI03),  though 
this  oxidising  agent  would  not  affect  chlorine  or  bromine.  Iodine  is 
also  capable  of  direct  oxidation  by  ozone. 

Iodine  pentoxide,  I205,  is  the  only  oxide  of  iodine  which  is  known  with 
certainty;  it  is  the  anhydride  of  iodic  acid  (H2O.I2O5=:2HI03),  and  is  a  white 
crystalline  substance  obtained  by  heating  the  acid.  The  product  of  the  oxidation 
of  iodine  by  ozone  is  a  yellow  deliquescent  powder  (formerly  supposed  to  be 
I203),  the  exact  composition  of  which  has  not  been  elucidated, 

Evidence  has  been  obtained,  from  the  existence  of  certain  organic  compounds, 
that  iodine  is  able  to  form  a  base  on  the  type  of  ammonia.  When  this  base  is 
isolated  it  will  probably  have  the  formula  IH2  (OH),  being  the  analogue  of  hydroxyl- 
amine  NH2  (OH). 

Some  of  the  compounds  of  iodine  with  the   metals   are  remarkable  for  their 

*  The  following  equations  explain  these  changes  : 

(i)  KI  +  Cl  =  KC1  +  I  ;  (2)  I  +  3H2O  +  C15  =  HIO3  +  5HC1  ; 

(3)  2HIO3  +  H2S03=5H2SO4  +  I2  +  H2O;         (4)  I2  +  H2CH-H2SO3  =  2HI  +  H2SO4. 
t  The  formation  of  HI  from  H  and  solid  I  absorbs  6000  heat-units. 


IODIC   ACID. 


I99 


beautiful  colours.  The  mercuric  iodide,  produced  by  mixing  solutions  of  potassium 
iodide  and  mercuric  chloride,  forms  a  tine  scarlet  precipitate,  which  dissolves  in 
an  excess  of  potassium  iodide  to  a  colourless  solution. 

Lead  iodide  has  a  bright  yellow  colour,  as  may  be  seen  by  precipitating  potas- 
sium iodide  with  a  solution  of  lead  acetate.  The  precipitate  is  dissolved  by 
boiling  with  water  (especially  on  adding  a  little  hydrochloric  acid),  forming  a 
colourless  solution,  from  which  the  lead  iodide  crystallises  in  very  brilliant  golden 
scales  on  cooling.  Silver  iodide  is  produced  as  a  yellow  precipitate  when  silver 
nitrate  is  added  to  potassium  iodide.  The  bromide  and  chloride  of  silver  would 
form  white  precipitates.  Silver  iodide  is  more  stable  than  the  chloride  or 
bromide  ;  when  exposed  to  light  it  appears  to  be  unchanged,  but  if  a  reducing 
agent,  such  as  ferrous  sulphate  or  pyrogallin,  be  afterwards  poured  over  it,  that 
portion  of  the  iodide  which  has  been  exposed  to  light  is  immediately  blackened, 
from  the  separation  of  silver  in  the  metallic  state.  This  is  the  principle  of  the 
process  for  developing  the  negative  photograph  taken  on  a  collodion  film  rendered 
sensitive  by  silver  iodide.  The  iodides  of  potassium,  ammonium,  and  cadmium 
are  also  used  in  photography. 

120.  lodic  acid,  HI03  or  I02(OH),  is  most  easily  prepared  by  boiling 
iodine  with  the  strongest  nitric  acid  in  a  long-necked  flask,  when  it  is 
dissolved  in  the  form  of  iodic  acid,  which  is  left,  on  evaporating  the 
nitric  acid,  as  a  white  mass.  This  may  be  purified  by  dissolving  in  water 
and  crystallising,  when  the  iodic  acid  forms  white  hexagonal  tables. 
Heated  to  180°  C.  the  iodic  acid  is  decomposed  into  water  and  iodic 
anhydride,  2HI03  =  H90  + 1905.  This  last  is  decomposed  at  about 
370°  C.  into  iodine  and  oxygen.  The  iodic  anhydride  oxidises  combus- 
tible bodies,  but  not  with  any  great  violence.  The  acid  is  far  more 
stable  than  chloric  or  bromic  acid.  Its  solution  first  reddens  litmus- 
paper,  and  afterwards  bleaches  it  by  oxidation.  Its  salts,  the  iodates, 
are  less  easy  soluble  in  water  than  are  the  chlorates  and  bromates,  which 
they  resemble  in  their  oxidising  action  upon  combustible  bodies.  They 
are  all  decomposed  by  heat,  evolving  oxygen,  and  sometimes  even 
iodine,  showing  how  much  inferior  this  element  is  to  chlorine  and  bromine 
in  its  attraction  for  metals. 

Potassium  iodide  may  be  oxidised  directly  to  potassium  iodate,  KI03,  by  potas- 
sium permanganate.  Iodic  acid  forms  acid  potassium  salts  of  the  formula?  KHI206 
and  KH2I309,  the  existence  of  which,  together  with  the  fact  that  the  acid  readily 
yields  an  anhydride  and  water  when  heated  (an  uncommon  reaction  for  a  mono- 
basic acid),  and  with  other  evidence,  indicates  that  the  acid  is  di-  or  even  tri-basic. 

Periodates. — The  periodates  (such  as  AgI04),  analogous  to  the  perchlorates,  are 
known,  but  the  simple  acid  HI04  has  not  been  isolated.  The  periodic  acid,  H5I06  or 
IO(OH)5.  is  prepared  as  follows  :  Chlorine  is  passed  through  a  solution  of  sodium 
iodate  containing  NaOH,  whereupon  the  salt  IO(OH)3(ONa)2  crystallises  from  the 
solution  ;  NaI03  +  3NaOH  +  C12  ==  aNaCl  +  IO(OH)3(ONa)2.  This  sodium  salt  is  dis- 
solved in  HN03  and  AgNO3  is  added  ;  a  brown  precipitate  of  Ag2HI05  is  obtained. 
When  this  is  dissolved  in  HN03  and  the  solution  is  evaporated  red  crystals  of 
AgI04.H20  separate,  and  by  treating  these  with  water  HglOg  passes  into  solution, 
whilst  Ag4I209.3H20  remains  undissolved.  Periodic  acid  crystallises  from  this 
solution  in  colourless  prisms  ;  it  decomposes  when  heated,  yielding  H20,  O  and 
Io05.  A  solution  of  the  acid  is  a  powerful  oxidant. 

"  The  periodates  are  referable  to  four  types,  termed  respectively,  the  meta-salts, 
from  the  acid  HI04  or  I03(OH)  ;  the  meso-salts,  from  the  acid  H3I05  or  I02(OH)3  ; 
the  para-salts,  from  the  acid  H5I06  or  IO(OH)5  ;  and  the  dimeso-salts,  from  the 
acid  H4I209  or  2l02(OH)3-H20.  It  thus  happens  that  a  large  number  of  these 
salts  are  known  ;  they  are  sparingly  soluble. 

When  iodine  is  dissolved  in  an  alkali  an  iodide  and  an  iodate  are 
formed  ;  6NaOH  +  I6  =  sNal  +  NaIO3  +  3HOH.  In  the  case  of  chlorine 
and  bromine  the  analogous  reaction  yields  a  hypochlorite  and  a  hypo- 
bromite  respectively  ;  but  the  evidence  for  the  existence  of  a  hypoiodite 


200  HYDRIODIC   ACID. 

in  the  alkaline  solution  of  iodine  is  very  feeble.  When  such  an  alkaline 
solution  of  iodine  is  acidified,  all  the  iodine  is  liberated,  for  the 
hydriodic  acid  and  the  iodic  acid  set  free  immediately  react,  the  iodic 
acid  oxidising  the  hydriodic  acid  ;  HI03  +  5  HI  =  3HOH  + 16. 

121.  Hydrogen  iodide  or  hydriodic  acid  (111  =  128  parts  by 
weight  =2  vols.). — Iodine  vapour  combines  with  hydrogen  at  450°  C. 
to  form  hydrogen  iodide.  The  gas  is  best  prepared  by  decomposing 
water  with  iodine  in  the  presence  of  phosphorus  ;  P  + 15  +  4.HOH  = 
PO(OH)3  +  5HI  or,  if  a  smaller  proportion  of  iodine  be  used 
P(OH)3 


6.5  grams  of  potassium  iodide  are  dissolved  in  3  c.c.  of  water  in  a  retort  (Fig.  158), 
and  13  grams  of  iodine  are  added  ;  when  this  has  dissolved,  0.65  gram  of  red 

phosphorus  are  introduced,  and  the  mixture 
heated  very  gradually,  the  gas  being  collected 
by  downward  displacement  in  stoppered 
bottles,  which  must  be  placed  in  readiness,  as 
the  gas  comes  off  very  rapidly.  These  quan- 
tities will  fill  four  pint  bottles  with  the  gas. 

Hydrogen  iodide  is  very  similar  in  its 
properties  to  hydrogen  chloride  and 
bromide,  fuming  strongly  in  moist  air, 
very  readily  absorbed  by  water,  lique- 
fied only  under  strong  pressure,  and 
solidified  by  extreme  cold.  It  is  much 
heavier,  its  specific  gravity  being  4.44. 
If  a  bottle  of  hydriodic  acid  gas  be  placed  in  contact  with  a  bottle  con- 
taining chlorine  or  bromine  vapour  diluted  with  air  (Fig.  69)  the  HI 
will  be  instantly  decomposed,  with  separation  of  the  beautiful  violet 
vapour  of  iodine.  The  gas  is  decomposed  by  light  at  the  ordinary 
temperature  and  is  dissociated  when  heated.* 

The  aqueous  solution  of  hydriodic  acid  is  most  conveniently  prepared 
by  passing  hydrosulphuric  acid  gas  through  water  in  which  iodine  is 
suspended,  H2S  +  I?  =  2  HI  +  S,  the  separated  sulphur  being  filtered  off, 
and  the  solution  boiled  to  expel  the  excess  of  hydrosulphuric  acid.  By 
this  method  it  is  not  possible  to  obtain  a  solution  of  HI  of  greater 
sp.  gr.  than  1.56  (50  per  cent.  HI  ;  the  strongest  solution  has  asp.  gr. 
of  1.99),  for  a  strong  solution  of  hydriodic  acid  converts  sulphur  into 
H2S. 

The  iodine  is  only  able  to  decompose  the  H2S  by  virtue  of  the  fact  that  the 
HI  produced  has  an  affinity  for  the  water  ;  since  this  affinity  diminishes  as  the 
liquid  grows  stronger,  a  period  is  soon  reached  when  the  dissolution  of  the  HI 
in  the  water  can  no  longer  supply  enough  energy  to  enable  the  iodine  to 
decompose  the  H2S.  In  other  words,  the  reaction  only  occurs  so  long  as  it  is 
exothermic,  which  will  be  the  case  until  the  heat  produced  by  the  dissolution 
of  the  HI  in  water  is  equal  to  that  absorbed  in  the  decomposition  of  the  H2S  by 
the  iodine. 

Solution  of  hydriodic  acid  differs  greatly  from  hydrochloric  and 
hydrobromic  acids,  in  being  decomposed  by  exposure  to  air,  particularly 
in  light,  its  hydrogen  being  oxidised  and  iodine  separated,  which  dis- 
solves in  the  liquid,  and  renders  it  brown. 

This  tendency  of  the  hydrogen  of  hydriodic  acid  to  combine  with 

*  At  350°  C.  17.3  per  cent.,  at  394°  C.  19.5  per  cent.,  and  at  448°  C.  21.5  per  cent,  of  the 
gas  is  dissociated. 


I  UNIVERSE 

NITROGEN   IODIDE.  2OI 

oxygen  renders  that  acid  a  powerful  reducing  agent.     It  is  even  capable 
of  reducing  sulphuric  acid  to  hydrosulphuric  acid — 
H2S04  +  SHI  =  H2S  +4H20  +  I8 

so  that  when  potassium  iodide  is  heated  with  concentrated  sulphuric 
acid,  hydrosulphuric  acid  is  evolved  in  considerable  quantity.  It  will  be 
remembered  that  HC1  does  not  reduce  H2S04,  whilst  HBr  only  reduces 
it  to  H2S03. 

The  action  of  hydriodic  acid  upon  the  metals  and  their  oxides  is  gene- 
rally similar  to  that  of  the  other  hydrogen  acids.  In  organic  chemistry, 
hydriodic  acid  is  often  employed  for  introducing  hydrogen  into  a  coin- 
pound  ;  thus,  by  heating  benzene  with  hydriodic  acid  it  may  be  made 
to  take  up  6  atoms  of  hydrogen  ;  C6H6  +  6HI  =  C6H12  + 16.  Since  the 
attraction  of  iodine  for  hydrogen  is  so  feeble,  metalepsis  does  not  occur 
between  this  halogen  and  hydrocarbons. 

The  circumstance  that  the  organic  compounds  containing  iodine  are 
generally  much  less  volatile,  and  therefore  more  manageable,  than  those 
of  chlorine  and  bromine,  leads  to  the  extensive  employment  of  this 
element  in  researches  upon  organic  substances. 

When  potassium  is  heated  in  a  measured  volume  of  gaseous  hydriodic 
acid,  the  iodine  is  removed,  and  the  hydrogen  occupies  half  the  original 
volume.  Hence  i  volume  of  hydrogen  is  combined  with  i  volume  of 
iodine  vapour  in  2  volumes  of  hydriodic  acid. 

122.  Compounds  of  carbon  with  iodine,  analogous  in  composition  to 
the  chlorine  compounds  of  this  element,  are  known.  They  are  solids,  it 
being  generally  the  case  that  iodine  compounds  are  less  volatile  than  the 
corresponding  chlorine  compounds. 

Nitrogen  iodide. — The  action  of  chlorine,  bromine,  and  iodine  upon 
ammonia  exemplifies  the  difference  in  their  attraction  for  hydrogen ;  for 
whilst  chlorine  and  bromine,  acting  upon  ammonia,  cause  the  liberation 
of  a  certain  amount  of  nitrogen,  iodine  simply  removes  part  of  the 
hydrogen,  and  itself  fills  up  the  vacancies  thus  occasioned,  no  nitrogen 
being  liberated,  the  hydriodic  acid  thus  formed  combining  with  more 
ammonia  to  form  ammonium  iodide.  Nitrogen  iodide,  NI3,  is  formed 
at  the  same  time. 

It  appears  that  when  iodine  is  dissolved  in  dilute  ammonia  NH41  and  hypo- 
iodous  acid  are  formed  ;  NH3  +  I2  +  H20  =  NH4I  +  HOI.  The  hypoiodous  acid  then 
reacts  with  more  ammonia  to  form  nitrogen  iodide  ;  NH3  +  3HOI  =  NI3  +  3H20. 

By  another  theory  the  nitrogen  iodide,  alleged  to  have  the  formula  N2H3I3,  is 
formed  as  a  decomposition  product  of  ammonium  hypoiodite ;  3NH4OI  = 
N2H3I3  +  NH3  +  2H20.  The  hypoiodite  would  be  formed  when  the  iodine  dis- 
solved in  excess  of  ammonia  ;  I2  +  2NH3  +  H20  =  NH4I  +  ]SrH4OL 

To  prepare  the  iodide  of  nitrogen  1.3  gram  of  iodine  is  rubbed  to  powder 
in  a  mortar  and  mixed  with  14  c.c.  of  strong  ammonia  :  the  mortar  is  covered 
with  a  glass  plate,  and  after  about  half  an  hour  the  iodide  of  nitrogen  is  collected 
in  separate  portions  upon  four  niters,  which  are  allowed  to  drain  and  spread 
out  to  dry.  The  brown  solution  contains  iodine  dissolved  in  ammonium  iodide. 

Another  method  consists  in  dissolving  iodine  in  a  mixture  of  hydrochloric  with 
a  little  nitric  acid,  with  the  aid  of  heat,  and  adding  ammonia,  which  decomposes 
the  IC1  in  solution,  and  gives  a  black  precipitate  of  the  iodide  of  nitrogen. 

When  dry  NH3  gas  is  passed  over  iodine  the  two  combine,  several  compounds, 
such  as  (NH3)2I,  being  formed. 

The  iodide  is  a  black  powder,  which  explodes  with  a  loud  report  even 
when  touched  with  a  feather,  the  violence  of  the  explosion  being 
accounted  for  by  the  sudden  evolution  of  a  large  volume  of  gas  and 


202  HYDROFLUORIC   ACID. 

vapour  from  a  small  volume  of  solid.  Even  when  allowed  to  fall  from 
the  height  of  a  few  feet  upon  the  surface  of  water,  it  explodes  if  perfectly- 
dry.  In  the  moist  state  it  slowly  undergoes  decomposition. 

123.  Iodine  forms  two  compounds  with  chlorine,  mono  chloride   (IC1)  and  tri- 
chloride (IC13).     The  former  is  obtained  by  passing  dry  chlorine  over  dry  iodine 
until  it  becomes  a  red-brown  liquid.     This  solidifies  when  cooled  and  then  melts 
at  14°  C.,  but  is  unstable,  readily  passing  to  another  form  which  melts  at  27°  C. 

The  trichloride  forms  fine  red  needle-like  crystals,  and  is  produced  when  iodine 
or  hydriodic  acid  gas  is  acted  upon  with  an  excess  of  chlorine.  It  is  useful  as  a 
germicide.  The  chlorides  of  iodine  are  decomposed  by  water,  yielding  HI03, 
HC1,  and  iodine.  From  the  aqueous  solution  of  IC1,  ether  extracts  a  yellow 
volatile  compound  having  the  composition  IC1.HC1. 

Iodine  bromide,  IBr,  is  a  crystalline  solid  resembling  iodine,  fusing  at  36°  C. 
and  subliming  with  partial  decomposition.  Water  decomposes  it,  iodine  being 
separated. 

FLUORINE. 

F  =  19  parts  by  weight. 

124.  The  most  ornamental  mineral  substance  occurring  in  any  abun- 
dance in  this  country  is  known  as  fluor  spar,  Derbyshire  spar,  or  blue 
John  (fluoride  of  calcium),  and  is  found  with  several  beautiful  shades  of 
colour — blue,  purple,  violet,  or  green,  and  sometimes  perfectly  colour- 
less, either  in  large  masses  or  in  crystals,  which   have  the  form  of  a 
cube  or  of  some  solid  derived  from  it.     The  use  of  this  mineral  as  a  flux 
in  smelting  ores  dates  from  a  very  remote  period,  and  from  this  use  the 
name  fluor  appears  to  have  been  originally  derived ;  but  we  have  no 
record  of  its  chemical  examination  until  1764,  when  Margraf  found  his 
glass  retort  powerfully  corroded   in   distilling   this  mineral  with  sul- 
phuric acid,  and  Scheele  soon  after  announced  that  it  contained  lime 
and  fluoric  acid.     But  though  this  chemist  had  fallen  into  the  error  to 
which  analysts  are  continually  liable,  of  mistaking  products  for  educts, 
his  experiments,  as  they  were  afterwards  perfected  by  Gay-Lussac  and 
Thenard,  deserve  particular  consideration. 

125.  Hydrogen  fluoride  (HF  =  20  parts  by  weight  =  2  volumes).* — 
If  powdered  fluor  spar  be  mixed  with  twice  its  weight  of  oil  of  vitriol, 

and  heated  in  a  leaden  retort  (Fig.  159)7 
the  neck  of  which  fits  tightly  into  a  leaden 
condensing-tube,  cooled  in  a  mixture  of 
ice  and  salt,  a  colourless  liquid  distils 
over,  arid  the  residue  in  the  retort  is 
found  to  consist  of  calcium  sulphate  ;  "t* 
CaF2  +  H2S04  =  CaS04  +  2HF.  The 
colourless  liquid  (hydrofluoric  acid)  pos- 

sesses  most  remarkable  properties ;  it  is 

Fio.  powerfully  acid,  fumes  strongly  in  the  air, 

and  has  a  most  pungent  irritating  odour. 
If  the  air  is  at  all  warm,  the  liquid  begins  to  boil  when  taken  out  of  the 
freezing-mixture.  Should  the  operator  have  the  misfortune  to  allow  a 

*  The  vapour  density  of  hydrogen  fluoride  is  25.6  at  26.4°  C.,  and  gradually  diminishes 
until  the  temperature  reaches  89°  C.,  when  it  remains  constant  at  10 ;  this  shows  that  at 
temperatures  below  89°  C.  the  molecule  of  this  gas  is  more  complex  than  is  represented  by 
the  formula  HF,  but  becomes  HF  at  89°  C. 

f  The  mineral  kryolite  (fluoride  of  aluminium  and  sodium)  may  be  advantageously  substi- 
tuted for  fluor  spar,  being  more  easily  obtained  in  a  pure  state. 


THE   ETCHING   OF   GLASS.  203 

drop  to  fall  upon  his  hand,  it  will  produce  a  very  painful  sore,  even  its 
vapour  producing  pain  under  the  finger  nails.  Its  attraction  for  water 
is  so  great,  that  the  acid  hisses  like  red-hot  iron  when  brought  in  contact 
with  water.  But  its  most  surprising  property  is  that  of  rapidly  corro- 
ding glass,  which  has  already  been  alluded  to  as  noticed  by  Margraf . 
Experiment  soon  proved  that  great  analogy  existed  between  the  pro- 
perties of  this  new  acid  and  those  of  hydrochloric  acid  :  and  Ampere 
was  led  to  believe  that  the  acid  was  a  hydrogen  acid,  containing  a  new 
salt  radicle,  which  he  named  fluorine  ;  the  name  of  the  acid  was  then 
changed  from  fluoric  to  hydrofluoric  acid. 

This  liquid  has  since  been  proved  to  be  a  solution  of  hydrofluoric 
acid  in  water;  for  if  it  be  distilled  with  phosphoric  anhydride,, 
which  retains  the  water,  it  evolves  hydrofluoric  acid  gas,  which  re- 
sembles hydrochloric  acid  gas  in  fuming  strongly  on  contact  with  moist 
air  and  being  eagerly  absorbed  by  water,  but  has  a  far  more  pungent 
odour. 

Pure  hydrogen  fluoride  is  prepared  by  heating  dry  potassium  hydrogen 
fluoride  (KHF2)  to  redness  in  a  platinum  still.  It  is  then  obtained  as  a 
colourless  liquid,  which  boils  at  19°  C.,  and  has  the  specific  gravity 
0.985  at  12°  C.  It  solidifies  at -102°  C.  and  melts  again  at  -92°. 
The  pure  acid  scarcely  affects  metals,  excepting  potassium  and  sodium. 
It  corrodes  glass,  however,  rapidly,  though  its  vapour  has  little  action 
on  glass  unless  moisture  be  present.  It  combines  eagerly  with  sul- 
phuric and  phosphoric  anhydrides,  with  great  evolution  of  heat,  a 
circumstance  in  which  it  resembles  water,  and  differs  altogether  from 
its  more  obvious  analogue,  hydrochloric  acid.  It  is  also  found  that  it 
combines  energetically  with  the  fluorides  of  potassium  and  sodium, 
precisely  as  water  combines  with  the  oxides  of  those  metals. 

It  is  remarkable  that  the  solution  of  hydrofluoric  acid,  in  its  concen- 
trated form,  is  not  so  heavy  as  a  somewhat  weaker  acid.  Thus  the  acid 
of  spr  gr.  i  .06  acquires  the  sp.  gr.  1.15  on  addition  of  a  little  water  ;  but 
on  adding  more  water,  its  sp.  gr.  is  again  reduced.  It  would  hence 
appear  that  the  acid  of  1.15  is  a  definite  hydrate  of  hydrofluoric  acid ; 
its  composition  corresponds  with  HF.2H20.  It  distils  unchanged  at 
248°  F.  (120°  C.). 

The  solution  of  hydrofluoric  acid  is  generally  kept  in  bottles  made  of 
gutta-percha.  Its  action  on  metals  and  their  oxides  resembles  that  of 
hydrochloric  acid.  It  dissolves  all  ordinary  metals  except  gold, 
platinum,  silver,  mercury,  and  lead.  Strange  to  say,  it  has  but  little 
action  on  magnesium. 

The  property  which  renders  this  acid  so  useful  to  the  chemist  is  its 
power  of  dissolving  silica  even  in  its  most  refractory  form.  When  sand 
or  flint  reduced  to  powder  is  digested  in  a  leaden  or  platinum  vessel 
with  hydrofluoric  acid,  it  is  gradually  dissolved ;  and  if  the  solution 
be  evaporated,  the  whole  of  the  silica  will  be  found  to  have  disappeared 
in  the  form  of  gaseous  silicon  tetrafluoride  ;  SiO,  +  4-HF  =  SiF4  +  2lI2O. 
If  the  silica  be  combined  with  a  base,  the  metal  will  be  left  as  a  fluoride 
decomposable  by  sulphuric  or  hydrochloric  acid.  This  renders  hydro- 
fluoric acid  a  most  valuable  agent  in  the  analysis  of  the  numerous 
mineral  silicates  which  resist  the  action  of  other  acids. 

The  corrosion  of  glass  by  hydrofluoric  acid  is  now  easily  explained. 
Ordinary  glass  consists  of  silicate  of  sodium  or  potassium  combined  with 


204 


ISOLATION   OF   FLUORINE. 


silicate  of  calcium  or  lead.     The  hydrofluoric  acid  attacks  and  removes 
the  silica,  and  thus  eats  its  way  into  the  glass. 

In  order  to  demonstrate  the  action  of  this  acid  upon  glass,  a  glass  plate  is 
warmed  sufficiently  to  melt  wax,  a  piece  of  which  is  then  rubbed  over  it,  until  the 
glass  is  covered  with  a  thin  and  pretty  uniform  coating.  Upon  this  a  word  or 
drawing  may  be  engraved  with  a  sharp  point  so  that  the  lines  shall  expose  the 
glass.  The  glass  plate  is  then  placed,  wax  downwards,  over  a  leaden  or  platinum 
dish  containing  a  mixture  of  fluor  spar  and  strong  sulphuric  acid,  exposed  to  a 
very  gentle  heat,  and  allowed  to  remain  for  a  quarter  of  an  hour  ;  the  plate  is 
then  gently  warmed  to  melt  the  wax,  which  may  be  wiped  off  with  a  little  tow, 
when  it  will  be  found  that  the  hydrofluoric  acid  evolved  from  the  mixture  has 
•corroded  those  portions  of  the  glass  from  which  the  graver  had  removed  the 
wax.  This  process  is  applied  to  the  marking  of  glass  instruments. 

The  solution  of  hydrofluoric  acid  etches  glass  without  deadening  the  surface,  as 
is  the  case  with  the  vapour  ;  but  a  solution  of  fluoride  of  potassium  or  ammonium 
mixed  with  sulphuric  acid  does  produce  a  dead  surface,  and  is  much  used  for 
•engraving  on  glass.  An  ink  sold  for  writing  on  glass  with  a  steel  pen  is  composed 
of  barium  and  ammonium  fluorides  and  sulphuric  acid. 

126.  When  hydrofluoric  acid  was  tirst  obtained  it  was  soon  evident 
that  it  was  not  an  element,  because  it  yielded  hydrogen  when  treated 
with  metals,  and  its  analogy  to  hydrochloric  acid  led  naturally  to  the 
assumption  that  it  was  a  compound  of  hydrogen  with  only  one  other 
element,  which  was  called  fluorine.  All  attempts  to  isolate  this  element, 
however,  failed,  owing  to  the  great  attraction  which  it  possesses  for 
other  elements.  It  was  not  until  Moissan,  in  1886,  prepared  very  pure 
hydrogen  fluoride,  and  discovered  that  an  alloy  of  platinum  with  10  per 

cent,  of  iridium  would 
withstand  the  attack  of 
fluorine,,  that  he  suc- 
ceeded in  electrolysing 
HF  with  liberation  of 
fluorine  at  the  anode  in 
quantity  sufficient  for 
the  properties  of  the 
element  to  be  examined. 

Fig.  1 60  illustrates  the 
electrolytic  cell  used  by 
Moissan.  The  U-tube  A  is 
made  of  the  aforesaid  alloy, 
as  also  are  the  electrodes  iB 
passing  through  stoppers  C 
made  of  fluor  spar,  which 
insulates  them  from  the 
metal  of  the  U-tube.  The 
cell  contains  pure  liquid 
hydrogen  fluoride,  having 
about  20  per  cent,  of  potas- 
sium fluoride  dissolved  in  it, 
and  is  immersed  in  a  bath  of 
methyl  chloride  whereby  it 
is  cooled  to  -  23°  C.  ;  a  cur- 
rent from  25  Bunsen's  cells 
is  passed  through  the  liquid. 
The  liberated  gases  escape  by  the  side  tube  D,  the  hydrogen  being  set  free  at  the 
negative  electrode  and  the  fluorine  at  the  positive  electrode.  To  free  the  fluorine 
from  the  HF  it  is  passed  over  dry  KF. 

Fluorine  is  a  greenish-yellow  gas,  which  becomes  liquid  at  -  185°  C. 


Fig.  1 60.— Isolation  of  fluorine. 


THE  HALOGENS.  205 

and  has  the  properties  of  chlorine,  but  much  more  strongly  marked. 
It  decomposes  water  immediately,  seizing  upon  its  hydrogen  ^and 
liberating  oxygen  in  the  ozonised  condition  ;  it  explodes  with  hydrogen 
even  in  the  dark,*  and  nearly  all  non-metals  and  many  metals  take  fire 
in  it  at  ordinary  temperatures. 

Some  metal?,  however,  become  coated  with  fluoride  and  need  to  be  heated  before 
they  burn  in  the  gas.  Gold  and  platinum  resist  attack  at  temperatures  below 
300°  C.,  and  carbon  is  fairly  resistant  unless  finely  divided.  Oxygen,  nitrogenr 
chlorine,  and  argon  appear  to  be  unattacked  by  fluorine  ;  hydrogen  chloride 
explodes  with  it,  yielding  HF  and  Cl. 

Fluorine  can  also  be  obtained  by  heating  the  tetrafluorides  of  certain 
metals  (just  as  chlorine  is  evolved  from  their  tetrachlorides).  By  this 
method  the  element  has  been  prepared  from  the  tetrafluorides  of  lead 
and  of  cerium.  The  great  activity  of  the  gas  has  rendered  a  detailed 
study  of  its  properties  difficult  ;  it  appears,  however,  that  its  vapour 
density  is  slightly  lower  than  19,  indicating  that  the  gas  contains  free 
atoms,  as  well  as  molecules  of  F2,  at  the  ordinary  temperature.  This 
may  account  for  its  activity. 

Fluorides.  —  Solutions  of  the  fluorides  of  potassium  and  the  other 
alkali  metals  corrode  glass  slowly,  like  hydrofluoric  acid.  The  fluorides 
are  capable  of  combining  with  the  acid  ;  thus  potassium  fluoride  forms 
KF.HF,  which,  when  dry,  is  a  convenient  source  of  HF  gas  when 
moderately  heated.  The  only  fluoride  possessed  of  much  practical 
interest,  beside  the  fluoride  of  calcium,  is  the  mineral  kryolite  (xpvos, 
frost),  which  is  a  double  fluoride  of  aluminium  and  sodium  (Na3AlF6), 
found  abundantly  in  Greenland,  and  valuable  as  a  source  of  aluminium. 

The  topaz  contains  fluorine,  but  in  what  form  of  combination  is  not  certain  ;  its 
other  constituents  are  alumina  and  silica.  Tourmaline  also  contains  fluorine, 
together  with  alumina,  silica,  and  FeO.  In  such  minerals  it  is  probable  that  the 
F  is  substituted  for  part  of  the  0. 

Magnesium  fluoride  (MgF2)  forms  the  mineral  Sellaite  which  is  found,  crystal- 
lised, in  Savoy.  Fluorides  are  also  found,  though  in  very  small  quantity,  in  sea 
water,  and  they  have  been  discovered  in  plants  and  animals.  Human  bone  con- 
tains about  2  per  cent,  of  calcium  fluoride. 

No  compound  of  fluorine  with  oxygen  is  known. 

Carbon  tetrafluoride,  CF4,  is  a  colourless  gas  made  by  burning  lamp  black  in 
fluorine  ;  it  boils  at—  15°  C.  and  is  said  to  be  produced  in  quantity,  when  kryolite  is 
electrolysed  for  winning  aluminium 


127.  General  review  of  chlorine,  bromine,  iodine,  and  fluorine. 

—  These  four  elements  compose  a  natural  group,  the  members  of  which 
are  connected  by  the  similarity  of  their  chemical  properties  far  more 
closely  than  those  of  any  other  group  of  elements.  They  are  usually 
styled  the  halogens,  from  their  tendency  to  produce  salts  resembling  sea 
salt  in  their  composition  (a\s,  the  sea),  and  such  salts  are  called  haloid 
salts.  These  elements  are  also  called  salt-radicles,  from  their  property  of 
forming  salts  by  direct  union  with  the  metals.  Each  is  monatomic, 
and  combines  with  an  equal  volume  of  hydrogen  to  form  an  acid  which 
occupies  the  joint  volumes  of  its  constituents. 

The  halogens  also  supply  the  most  prominent  example  of  the  grada- 
tion in  properties  observed  among  the  members  of  the  same  natural 
group  of  elements. 

In  the  order  of  their  chemical  energy,  that  is,  of  the  force  with  which 

*  Evolving  39,000  calories  per  20  grams  of  HF  formed. 


206  SULPHUR   ORES. 

they  hold  other  elements  in  chemical  combination  with  them,  fluorine 
should  stand  first,  its  combining  energy  being  so  great  as  to  cause  a 
serious  difficulty  in  isolating  it ;  chlorine  would  rank  next,  then  bromine, 
and  iodine  last. 

The  atomic  weights  follow  the  inverse  order  of  their  chemical  energies  : 
fluorine,  19;  chlorine,  35.5  ;  bromine,  80  ;  iodine,  127 — numbers  which, 
of  course,  also  represent  their  relative  specific  gravities  in  the  state  of 
vapour. 

A  similar  gradation  is  observed  in  their  physical  state  and  colour, 
fluorine  being  a  yellow  gas,  chlorine  a  yellow  gas,  bromine  a  red  liquid 
boiling  at  63°  C.,  and  iodine  a  black  solid  boiling  at  183°  C. 

Even  in  the  exceptions  which  occur  to  the  order  of  chemical  energy 
above  alluded  to,  the  same  progression  is  noticed  :  thus  fluorine  has  so 
little  attraction  for  oxygen  that  no  oxide  is  known  ;  chlorine  has  less 
attraction  for  oxygen  than  bromine  (chloric  acid  being  less  stable  than 
bromic) ;  whilst  bromine  has  less  than  iodine,  which  is  capable  even  of 
uniting  directly  with  ozonised  oxygen. 

The  compounds  of  these  elements  with  hydrogen  are  all  gases  distin- 
guished by  a  powerful  attraction  for  moisture  and  great  similarity  of 
odour.  Their  potassium  salts  all  crystallise  in  the  same  (cubical)  form. 

The  silver  fluoride  is  deliquescent  and  soluble  in  water  ;  the  chloride 
is  insoluble  in  water,  but  dissolves  very  easily  in  ammonia;  the  bromide 
dissolves  with  some  difficulty  in  ammonia ;  and  the  iodide  is  insoluble, 
In  some  other  particulars,  fluorine  stands  apart  from  the  other  halogens  ; 
thus,  the  fluoride  of  calcium  is  a  very  insoluble  substance,  whilst  the 
chloride,  bromide,  and  iodide  are  very  soluble.  Hydrofluoric  acid  forms 
KHF2,  which  corresponds  in  composition  with  KHO. 

It  is  noteworthy  that  these  halogen  elements  are  par  excellence  acid 
elements ;  that  is  to  say,  not  only  their  oxygen  compounds  but  their 
hydrogen  compounds  exhibit  acid  properties.  The  carbon  family  gives 
neutral  hydrogen  compounds ;  the  nitrogen  family  gives  basic  hydrogen 
compounds,  whilst  the  sulphur  family  gives  feebly  acid  hydrogen 
compounds. 

SULPHUR. 

8  =  32  parts  by  weight  =  I  volume  (at  1000°  C.). 

128.  Sulphur  is  remarkable  for  its  abundant  occurrence  in  nature 
in  the  uncombined  state  in  many  volcanic  districts.  It  is  also  found, 
as  sulphuretted  hydrogen,  in  many  mineral  waters,  and  very 
abundantly  in  combination  with  metals,  forming  the  numerous  ores 
known  as  sulphurets  or  sulphides,  of  which  the  following  are  the  most 
abundant : 

Iron  pyrites,  Iron  disulphide,  FeS2 

Copper  pyrites,  Sulphide  of  iron  and  copper,  Cu.2S.Fe2S3 

Galena,  Sulphide  of  lead,  PbS 

Blende,  Sulphide  of  zinc,  ZnS 

Crude  antimony,  Sulphide  of  antimony,  Sb2S3 

Cinnabar,  Sulphide  of  mercury,  HgS. 

Sulphur  is  plentifully  distributed  also,  in  combination  with  oxygen 
and  a  metal,  in  the  form  of  sulphates,  of  which  the  most  conspicuous 
are 


EXTRACTION  OF  SULPHUR.  2O/ 

Gypsum,  Sulphate  of  calcium,  CaS04.2H20 

Heavy  spar,  Sulphate  of  barium,  BaS04 

Celestine,  Sulphate  of  strontium,  SrS04 

Epsom  salts,  Sulphate  of  magnesium,  MgSO4.7H20 

Glauber's  salt,  Sulphate  of  sodium,  Na,S04.ioH20. 

In  plants,  sulphur  is  also  found  in  the  form  of  sulphates,  and  as  a 
constituent  of  the  vegetable  albumin  (of  which  it  forms  about  1.5  per 
cent.)  present  in  the  sap.  It  is  also  contained  in  certain  of  the  essential 
oils  remarkable  for  their  peculiar  pungent  odour,  such  as  those  of  garlic 
and  mustard. 

In  animals,  sulphur  occurs  as  sulphates,  as  a  constituent  of  albumin, 
fibrin,  and  casein  (in  none  of  which  does  it  exceed  2  per  cent.),  and 
in  bile,  one  of  the  products  from  which,  taurine,  contains  25  per  cent, 
of  sulphur. 

For  our  supplies  of  sulphur  we  are  chiefly  indebted  to  Sicily,  where 
large  quantities  of  it  are  found  in  an  uncombined  state  in  beds  of  blue 
clay.  Magnificent  crystalline  masses  of  strontium  sulphate  are  often 
found  associated  with  it ;  the  sulphur  itself  sometimes  occurs  in  the 
form  of  transparent  yellow  octahedra,  but  more  frequently  in  opaque, 


Fig-.  161. — Distillation  of  sulplmr. 

amorphous  masses.  The  districts  in  which  sulphur  is  found  are  usually 
volcanic,  and  those  which  border  the  Mediterranean  are  particularly  rich 
in  it.  Sulphur  has  also  been  found  in  Iceland  and  New  Zealand. 

The  native  sulphur,  being  commonly  distributed  in  veins  through 
masses  of  gypsum  and  celestine,  has  to  be  separated  from  these  by  the 
action  of  heat.  When  the  ores  contain  more  than  12  per  cent,  of 
sulphur,  the  bulk  of  it  is  melted  out,  the  ore  being  thrown  into  rough 
furnaces  or  cauldrons  with  a  little  fuel,  and  smothered  up  with  earth, 
so  as  to  prevent  the  combustion  of  the  sulphur,  which  runs  down  in  the 
liquid  state  to  the  bottom  of  the  cauldron,  and  is  drawn  out  into  wooden 
moulds.*  But  when  the  proportion  of  sulphur  is  small,  the  ore  is 
heated  so  as  to  convert  the  sulphur  into  vapour,  which  is  condensed  in 
another  vessel.  The  operation  is  conducted  in  rows  of  earthen  jars 
(A,  Fig.  161)  heated  in  a  long  furnace,  and  provided  with  short  lateral 

*  High  pressure  steam  has  been  applied  with  advantage  for  melting  the  sulphur  out  of 
the  ores,  which  are  enclosed  in  an  iron  vessel  ;  or  the  ores  are  heated  in  a  boiler  with  a 
66  per  cent,  solution  of  calcium  chloride  at  120°  C.  The  sulphur  is  sometimes  extracted  by 
dissolving  it  with  carbon  bisulphide.  When  sulphur  ores  containing  calcium  sulphate  are 
distilled,  part  of  the  sulphur  is  lost  as  sulphur  dioxide,  which  goes  off  as  gas— 
CaSO4  +  S2  =  CaS  +  2SO2. 


208 


DISTILLATION   OF  SULPHITE. 


pipes,  which  convey  the  sulphur  into  similar  jars  (B)  standing  outside* 
the  furnace,  in  which  the  vapour  of  sulphur  condenses  in  the  liquid 
state,  and  flows  out  into  pails  of  water.  The  sulphur  obtained  by  this 
process  is  imported  as  rough  sulphur,  and  contains  3  or  4  per  cent,  of 
earthy  impurities.  In  order  to  separate  these,  it  is  redistilled,  in  this 
country,  in  an  iron  retort  (A,  Fig.  162),  from  which  the  vapour  is  con- 
ducted into  a  large  brick  chamber  (B),  upon  the  sides  of  which  it  is- 


Fig.  162. — Sulphur  refinery. 

deposited  in  the  form  of  a  pale  yellow  powder  (flowers  of  sulphur,  or 
sublimed  sulphur).  When  the  operation  has  been  continued  for  some 
time,  the  walls  of  the  chamber  become  sufficiently  hot  to  melt  the 
sulphur,  which  is  allowed  to  collect,  and  afterwards  cast  in  wooden 
moulds,  forming  roll  sulphur  or  brimstone.  Distilled  sulphur  is  obtained 
by  allowing  the  vapour  to  pass  from  the  retort  into  a  small  receiving 
vessel  (C)  cooled  by  water,  where  it  condenses  in  the  liquid  state  ;  this 
variety  of  sulphur  is  preferred  for  the  manufacture  of  gunpowder,  for 
reasons  which  will  be  stated  hereafter. 

Sulphur  is  readily  distilled  on  a  small  scale  in  a  Florence  flask  (Fig.  163),. 
another  flask  cut  off  at  the  neck  being  employed  as  a  receiver.  The  flask  con- 
taining the  sulphur  should  be  supported  upon  a  thin 
iron  wire  triangle,  and  heated  by  a  gauze  burner,  at 
first  gently,  and  afterwards  to  the  full  heat.  Flowers 
of  sulphur  will  at  first  condense  in  the  receiver,  and 
will  be  followed  by  distilled  sulphur  when  the  tem- 
perature increases.  A  slight  explosion  of  the  mix- 
ture of  sulphur  vapour  and  air  may  occur  at  the 
commencement  of  the  distillation.  An  ounce  of 
sulphur  may  be  distilled  in  a  few  minutes. 

We  are  by  no  means  entirely  dependent 

Fig.  ^.-Distillation  of  sulphur,   upon  Sicily  for  sulphur,  for    this    element 

can  be  easily  extracted  from  iron  and  copper 
pyrites,  both  of  which  are  found  abundantly  in  this  country. 

Iron  pyrites  forms  the  yellow  metallic-looking  substance  which  is 
often  met  with  in  masses  of  coal,  sometimes  in  distinct  cubical  crystals, 
and  is  to  be  picked  up  in  large  quantities  on  some  sea-beaches,  where 
it  occurs  in  rounded  nodules,  rusty  outside,  but  having  a  fine  radiated 
metallic  fracture.  When  this  mineral  is  strongly  heated,  it  gives  up 
part  of  its  sulphur ;  at  a  very  high  temperature  one-half  of  the  sulphur 


PROPERTIES  OF  SULPHUR.  209 

may  be  separated,  FeS2  =  FeS  +  S,  but  by  an  ordinary  furnace  heat  only 
about  one-fourth  can  be  obtained.  The  distillation  of  iron  pyrites  is 
sometimes  effected  in  conical  fireclay  retorts,  but  it  is  riot  now  much 
practised.  The  sulphur  obtained  in  this  way  has  a  green  colour,  due  to 
the  presence  of  a  little  sulphide  of  iron  carried  over  mechanically  during 
the  distillation  :  in  order  to  purify  it,  it  is  melted  and  allowed  to  cool 
slowly,  when  the  sulphide  of  iron  subsides ;  the  upper  portion  of  the 
mass  is  then  further  purified  by  distillation. 

Sulphur  may  also  be  obtained  from  copper  pyrites  (Cu2S.Fe2S3)  in  the  process  of 
roasting  the  ore,  previously  to  the  extraction  of  the  copper.  The  ore  is  heaped  up 
into  a  pyramid,  the  base  of  which  is  about  30  feet  square  :  a  layer  of  powdered  ore 
is  placed  at  the  bottom,  to  prevent  too  rapid  access  of  air  :  above  this  there  is  a 
layer  of  brushwood  :  a  wooden  chimney  is  placed  in  the  centre,  and  is  lhade  to 
communicate  with  air-passages  left  between  the  faggots  :  around  this  chimney  the 
large  fragments  of  the  ore  are  piled  to  a  height  of  about  8  feet,  and  a  layer  of 
powdered  ore,  about  12  inches  deep,  is  strewn  over  the  whole.  The  heap  contains 
about  2000  tons  of  pyrites,  and  will  yield  20  tons  of  sulphur.  The  fire,  being 
kindled  by  dropping  lighted  faggots  down  the  chimney,  burns  very  slowly,  because 
of  the  limited  access  of  air,  and  after  a  few  days  sulphur  is  seen  to  exude  from  the 
surface,  and  is  received  in  cavities  made  for  the  purpose  in  different  parts  of  the 
heap.  The  roasting  requires  five  or  six  months  for  its  completion.  In  this 
operation  a  part  of  the  sulphur  has  been  separated  by  the  mere  action  of  heat,  and 
another  part  has  been  displaced  by  the  oxygen  of  the  air,  which  has  converted  a 
portion  of  the  iron  into  an  oxide.  A  part  of  the  separated  sulphur  has  been  burnt, 
the  rest  having  escaped  combustion  on  account  of  the  limited  access  of  air.  The 
sulphur  extracted  from  pyrites  is  generally  found  to  contain  a  little  arsenic,  which 
is  frequently  associated  with  minerals. 

Much  sulphur  is  now  prepared  from  the  sulphuretted  hydrogen  from 
the  tank-waste  of  the  alkali  works,  and  from  the  aminoniacal  liquor  of 
gas  works,  by  a  process  which  will  be  described  under  the  manufacture 
of  carbonate  of  soda. 

Immense  quantities  of  sulphur  are  consumed  in  this  country  for  the 
manufacture  of  sulphuric  acid,  gunpowder,  lucifer  matches,  vulcanised 
caoutchouc,  and  for  making  the  sulphurous  acid  gas  employed  in  bleach- 
ing processes. 

129.  Properties  of  sulphur. — In  its  ordinary  forms  sulphur  has  a 
characteristic  yellow  colour,  though  milk  of  sulphur,  or  precipitated 
sulphur  (obtained  by  adding  an  acid  to  the  solution  of  sulphur  in  an 
alkali),  is  white.  It  suffers  electrical  disturbance  with  remarkable  faci- 
lity, so  that  when  powdered  in  a  dry  mortar  it  clings  to  the  mortar 
with  great  pertinacity. 

Finely  divided  sulphur,  especially  sublimed  sulphur,  is  gradually 
oxidised  and  converted  into  sulphuric  acid  when  exposed  to  moist  air. 

One  of  the  most  remarkable  features  of  sulphur  is  its  inflammability, 
due  to  its  tendency  to  combine  with  oxygen  at  a  moderately  elevated 
temperature.  It  melts  at  115°  C.  (239°  F.),  and  inflames  at  about 
260°  C.  (500°  F.),  burning  with  a  pale  blue  flame  and  emitting  the  well- 
known  suffocating  odour  of  sulphurous  acid  gas  (S02).  The  changes  in 
the  physical  condition  of  this  element  under  the  influence  of  heat  are 
very  extraordinary.  If  a  quantity  of  sulphur  be  introduced  into  a 
Florence  flask  and  subjected  to  a  gradually  increasing  heat  (Fig.  164), 
it  is  soon  converted  into  a  pale  yellow  limpid  liquid  (120°  0.),  the  colour 
of  which  becomes  gradually  brown  as  the  temperature  rises,  until,  at 
about  200°  C.,  it  is  nearly  black  and  opaque,  and  is  so  viscid  that  the 

o 


210  ALLOTBOPIC  STATES  OF  SULPHUR. 

flask  may  be  inverted  without  spilling  it :  at  this  point  the  temperature 
of  the  sulphur  remains  stationary  for  a  time,  notwithstanding  that  it  is 
still  over  the  flame,  showing  that  heat  is  becoming  latent  in  converting 
the  sulphur  into  the  new  modification.  On  continuing  the  heat  the 
sulphur  once  more  becomes  liquid,  though  not  so  mobile  as  at  first,  and 
at  a  much  higher  temperature,  440°  C.  (836°  F.), 
it  boils,  and  is  converted  into  a  brownish  red, 
very  heavy  vapour :  at  this  point  of  the  experi- 
ment an  explosion  of  the  mixture  of  sulphur 
vapour  with  air  often  occurs.  The  flask  may  now 
be  removed  from  the  flame,  and  a  little  of  the 
sulphur  poured  into  a  vessel  of  water,  through 
which  it  will  descend  in  a  continuous  stream, 
forming  a  soft  elastic  string  like  india-rubber  : 
the  portion  remaining  in  the  flask  will  be  observed, 
as  it  cools,  to  pass  again  through  the  same  states, 
becoming  viscid  at  200°  C.,  and  very  liquid  at 
-  164  I20°  ^'  >  another  portion  may  now  be  poured 

into  water,  through  which  it  will  fall  in  isolated 
drops,  solidifying  into  yellow  brittle  crystalline  buttons  of  ordinary 
sulphur.  As  the  portion  of  sulphur  left  in  the  flask  cools,  it  will  be 
found  to  deposit  small  tufts  of  crystals,  and  ultimately  to  solidify  alto- 
gether to  a  yellow  crystalline  mass.  » 

The  brown  ductile  sulphur,  when  kept  for  a  few  hours,  will  become 
yellow  and  brittle,  passing,  in  great  measure,  spontaneously  into  the 
crystalline  sulphur.  The  change  is  accelerated  by  a  gentle  heat,  and  is 
attended  with  evolution  of  the  heat  which  the  sulphur  was  found  to 
absorb  at  200°  C.  Both  these  varieties  of  sulphur  are,  of  course,  inso- 
luble in  water,  and  they  are  not  dissolved  to  any  great  extent  by 
alcohol  and  ether ;  but  these,  when  heated,  will  dissolve  enough  to  be 
deposited  in  white  silvery  needles  on  cooling.  Glacial  acetic  acid  also 
dissolves  sulphur,  and  deposits  it  in  needles.  If  the  crystalline  variety 
be  shaken  with  a  little  carbon  bisulphide,  it  rapidly  dissolves,  and  on 
allowing  the  solution  to  evaporate  spontaneously,  it  deposits  beautiful 
octahedral  crystals,  resembling  those  of  native  sulphur  (Fig.  165). 
Ductile  sulphur,  however,  is  practically  insoluble  in  carbon  bisul- 
phide. 

"When  flowers  of  sulphur  are  shaken  with  carbon  bisulphide,  a  con- 
siderable quantity  passes  into  solution,  the  remainder  consisting  of  the 
amorphous,  or  insoluble  sulphur.  Roll  sulphur  dissolves  to  a  greater- 
extent,  and  sometimes  entirely,  in  the  bisulphide,  and  distilled  sulphur 
is  always  easily  soluble. 

According  to  the  older  investigations  of  Berthelot  and  others,  when  a  solution  of 
sulphuretted  hydrogen  (H2S)  is  electrolysed  the  sulphur  is  separated  at  the  anoder 
and  is  therefore  the  electro-negative  element  of  the  compound.  This  sulphur  was 
found  to  be  soluble  in  carbon  bisulphide.  So,  also,  the  sulphur  precipitated  by  an 
acid  from  a  solution  of  sulphur  in  an  alkali  sulphide  is  soluble  in  carbon  bisulphide, 
the  assumed  reason  being  that  it  is  electro-negative  to  the  metal  with  which  it  was 
combined. 

When,  however,  a  solution  of  sulphurous  acid  is  electrolysed  the  sulphur  is 
separated  at  the  cathode  showing  that  in  this  combination  it  is  electro-positive  ; 
this  sulphur  is  insoluble  in  carbon  bisulphide.  These  observations  do  not  appear 
to  have  been  satisfactorily  confirmed. 

It  is  well  known  that  when  a  solution  of  sulphur  in  carbon  bisulphide  is  exposed 


OCTAHEDRAL  AND  PEISMATIC   SULPHITE.  211 

to  light  sulphur  is  separated  from  it,  showing  that  under  this  influence  the  soluble- 
variety  is  converted  into  the  insoluble. 

Crystalline  or  soluble  sulphur  exists  in  several  forms,  of  which  two  are> 
well  known.  The  natural  form  of  crystallised  sulphur  is  derived  from 
the  octahedron  with  a  rhombic  base  (Fig.  165),  and  it  is  a  modification  of 
this  form  which  sulphur  assumes  when  crystallised  from  its  solutions. 
But  if  sulphur  be  melted  in  a  covered  cruci- 
ble, allowed  to  cool  until  the  surface  has 
congealed,  and  the  remaining  liquid  portion 
poured  out  after  piercing  the  crust  (with 
two  holes,  one  for  admission  of  air),  the 
crucible  will  be  lined  with  beautiful  needles, 
which  are  derived  from  an  oblique  prism 
(Fig.  1 66).  These  crystals  are  brownish- 
yellow  and  transparent,  when  freshly  made, 
but  they  soon  become  opaque  yellow  ;  and  Fig-.  165.  Fig.  166. 
ulthough  they  retain  their  prismatic  appear- 
ance, they  have  now  changed  into  minute  rhombic  octahedra,  the  change 
being  attended  with  evolution  of  heat.*  On  the  other  hand,  if  a  crystal 
of  octahedral  sulphur  be  exposed  for  a  short  time  to  a  temperature  of 
about  230°  F.  (no0  C.),  in  a  boiling  saturated  solution  of  common  salt, 
for  example,  it  becomes  opaque,  in  consequence  of  the  formation  of  a 
number  of  minute  prismatic  crystals  in  the  mass."}" 

Both  crystalline  forms  of  sulphur  may  be  obtained  at  the  same  tem- 
perature from  super/used  sulphur,  or  from  a  supersaturated  solution  of 
sulphur  in  benzene,  by  dropping  in  a  crystal  of  the  form  required. 

The  difference  between  these  two  forms  of  crystalline  sulphur 
extends  to  their  fusing-points  and  specific  gravities,  the  prismatic 
sulphur  fusing  at  248°  F.  (120°  C.).,  and  the  octahedral  sulphur  at. 
239°  F.  (115°  C.),  the  specific  gravity  of  the  prisms  being  1.98,  and  that 
of  the  octahedra  2.05. 

Boll  sulphur,  when  freshly  made,  consists  of  a  mass  of  oblique  pris- 
matic crystals,  but  after  being  kept  for  some  time,  it  consists  of  octa- 
hedra, although  the  mass  generally  retains  the  specific  gravity  proper  to- 
the  prismatic  form.  This  change  in  the  structure  of  the  mass,  taking 
place  when  its  solid  condition  prevented  the  free  movement  of  the- 
particles,  gives  rise  to  a  state  of  tension  which  may  account  for  the 
extreme  brittleness  of  roll  sulphur.  If  a  stick  of  sulphur  be  held  in 
the  warm  hand,  it  often  splits,  from  unequal  expansion.  These  pecu- 
liarities of  sulphur  deserve  careful  study,  as  helping  to  elucidate  the 
spontaneous  alterations  in  the  structure  of  glass,  iron,  &c.,  under  certain 
conditions. 

Flowers  of  sulphur  do  not  present  a  crystalline  structure,  but  consist 
of  spherical  globules  composed  of  insoluble  sulphur  enclosing  soluble 
sulphur.  Hot  oil  of  turpentine  dissolves  sulphur  freely,  and  when  the 
solution  is  allowed  to  stand,  the  crystals  which  are  deposited  whilst  the 
solution  is  hot  have  the  prismatic  form,  but  as  it  cools,  octahedra  are 
separated. 

*  Spring-  has  shown  that  a  pressure  of  6000  atmospheres  converts  prismatic  sulphur  and 
plastic  sulphur  into  the  octahedral  variety. 

f  The  change  from  octahedral  to  prismatic  sulphur  is  accompanied  by  the  absorption  of 
650  cals.  per  gram  molecule. 


212          COMBINATION   OF   SULPHUR   WITH   OTHER   ELEMENTS. 
The  following  table  exhibits  the  chief  allotropic  forms  of  sulphur : 

Sp.  gr.  Fusing-point.     In  Carbon  Bisulphide. 

Octahedral     .         .          2.05  115°  C.  Soluble. 

Prismatic        .         .  1.98  120°  Soluble. 

Amorphous:         I}      '-95      Becomes  octahedral.  Insoluble. 

The  octahedral  is  by  far  the  most  stable  of  the  three,  and  is  the  ulti- 
mate condition  which  the  others  assume.  Melted  with  a  little  iodine, 
sulphur  remains  amorphous  when  it  solidifies,  and  retains  this  form  for 
some  time. 

As  has  been  seen  the  two  forms  of  sulphur  are  easily  converted  the  one  into  the 
other  by  changing  the  conditions  under  which  they  exist.  This  is  not  an  uncommon 
phenomenon  and  is  quite  analogous  to  the  relationship  between  a  solid  and  the 
liquid  which  it  becomes  when  melted.  Ice  and  water,  for  example,  are  convertible 
into  each  other  by  varying  the  temperature,  and  there  is  a  definite  temperature, 
o°  C.,  at  which  they  are  in  equilibrium,  that  is,  neither  the  ice  nor  the  water  in- 
creases in  quantity.  So  with  the  two  forms  of  sulphur  :  at  96.5°  C.  both  octahedra 
and  prisms  may  exist  in  equilibrium,  but  a  slight  rise  of  temperature  will  increase 
the  mass  of  the  prisms  while  a  slight  fall  will  increase  that  of  the  octahedra.  The 
temperature  is  therefore  known  as  the  transition-point,  and  theitwo  forms  are  said 
to  be  enantiotropes. 

Other  varieties  of  sulphur,  such  as  a  black  and  a  red  modification, 
have  been  described,  but  it  is  doubtful  if  they  are  pure  sulphur.-  A 
colloidal  variety,  soluble  in  water,  has  been  found  in  the  solution  formed 
by  passing  hydrogen  sulphide  through  an  aqueous  solution  of  sulphur 
dioxide. 

Sulphur  enters  into  direct  combination  with  several  other  elements. 
It  unites  with  chlorine  and  with  some  of  the  metals,  if  finely  divided, 
even  at  the  ordinary  temperature,  and  at  a  high  temperature  with  all 
the  non-metals  except  nitrogen,  and  with  most  metals. 

A  mixture  of  5  parts  of  iron-powder  (ferruin  redactum)  and  3  parts  of  flowers 
of  sulphur  will  burn  when  kindled  by  a  match,  leaving  a  black  mass  of  ferrous 
sulphide.      Zinc-dust  mixed  with  half  its  weight  of  sulphur  also   burns  freely, 
leaving  white  zinc  sulphide. 

The  so-called  I/emery's  volcano  was  made  by  mixing 
iron  filings  with  two-thirds  of  their  weight  of  powdered 
sulphur,  and  burying  several  pounds  of  the  moist  mixture 
in  the  earth,  when  the  heat  evolved  by  the  rusting  of  part 
of  the  iron  provoked  the  energetic  combination  of  the 
remainder  with  the  sulphur,  and  the  consequent  develop- 
ment of  much  steam.*  Firework  compositions  contain- 
ing iron  filings  and  sulphur  may  cause  ignition  if  damp. 

Several  metals  may  be  made  to  burn  in  sulphur  vapour, 
as  in  oxygen,  by  heating  the  sulphur  in  a  Florence  flask, 
with  a  gauze  burner,  so  as  to  keep  the  flask  constantly 
filled  with  the  brown  vapour.  Potassium  and  sodium, 
introduced  in  deflagrating  spoons,  take  fire  spontaneously 
in  the  vapour  (Fig.  167).  A  coil  of  copper  wire  glows 
vividly  in  sulphur  vapour,  and  becomes  converted  into  a 
Fig-.  167.  brittle  mass  of  sulphide  of  copper.  When  sulphur  is  ex- 

posed to  sunshine  in  an  atmosphere  of  hydride  of  anti- 
mony or  arsenic,  it  becomes  converted  into  hydrosulphuric  acid  gas  and  sulphide  of 
antimony  or  arsenic. 

Sulphur  dissolves,  though  slowly,  in  boiling  concentrated  nitric  and 

*  Rust-joint  cement  is  a  mixture  of  80  p  vrts  iron  filings,  i  of  sal  ammoniac,  and  2  of  sul- 
phur, made  into  a  paste  with  water ;  it  is  very  useful  for  making  the  joints  of  iron  tubes 
air-tight,  for  it  sets  into  a  hard  cement,  the  iron  combining  with  the  sulphur. 


HYDROGEN   SULPHIDE. 


2I3 


sulphuric  acids,  being  oxidised  by  the  former  into  sulphuric  acid,  and  by 
the  latter  into  sulphur  dioxide.  It  is  far  more  readily  converted  into 
sulphuric  acid  by  a  mixture  of  nitric  acid  and  potassium  chlorate.  The 
alkalies  dissolve  sulphur  when  heated,  yielding  yellow  or  red  solutions 
which  contain  hyposulphites  and  sulphides  of  the  alkali  metals. 

There  is  a  very  general  resemblance  in  composition  between  the  com- 
pounds of  sulphur  and  those  of  oxygen  with  the  same  elements. 

Sulphur  forms  a  good  example  of  the  diminution  which  may  occur  in 
the  vapour-density  of  an  element  as  the  temperature  rises,  a  full  dis- 
cussion of  which  must  be  postponed  to  the  chapter  on  General  Principles. 
Sulphur  boils  at  444°  C.,  and  if  its  vapour  be  weighed  at  a  temperature 
of  480°  C.,  it  is  found  to  weigh  6.617  times  as  much  as  an  equal  volume 
of  air  at  480°  C.,  so  that  it  is  96  times  as  heavy  as  hydrogen,  or  i  atom 
of  sulphur  would  occupy  J  volume.  But  if  the  vapour  of  sulphur  be 
weighed  at  1000°  C.,  it  is  found  to  weigh  only  2.23  times  as  much  as  an 
equal  volume  of  air  at  the  same  temperature  and  pressure,  so  that  it  is 
only  32  times  as  heavy  as  hydrogen,  and  i  atom  of  sulphur  occupies  i 
volume. 

HYDROGEN  SULPHIDE,  OR  HYDROSULPHURIC  ACID. 
H2S  =  34  parts  by  weight  =  2  vols. 

130.  Sulphuretted  hydrogen,  or  hydrogen  sulphide,  or  hydrosulphuric 
acid,  has  been  already  mentioned  as  occurring  in  some  mineral  waters,  as 
at  Harrogate.  It  is  also  found  in  the  gases  emanating  from  volcanoes, 
sometimes  amounting  to  one-fourth  of  their  volume.  It  is  a  product  of 
the  putrefaction  of  organic  substances  containing  sulphur,  and  is  one  of 
the  causes  of  the  sickening  smell  of  drains,  &c.  Eggs,  which  contain  a 
considerable  portion  of  sulphur,  evolve  sulphuretted  hydrogen  as  soon 
as  they  begin  to  change,  and  hence  the  association  between  this  gas  and 
the  "  smell  of  rotten  eggs."  The  same  smell  is  observed  when  a  kettle 
boils  over  upon  a  coke  or  coal  fire,  the  hydrogen  liberated  from  the 
water  combining  with  the  sulphur  present  in  the  fuel. 

Hydrosulphuric  acid  is  also  found  among  the  products  of  destructive 
distillation  of  organic  substances  containing  sulphur  ;  it  was  mentioned 
among  the  products  from  coal,  in  which  it  is  for  the  most  part  combined 
with  the  ammonia  formed  at  the  same  time,  producing  ammonium 
sulphide. 

It  may  be  produced,  though  not  in  large  quantity,  by  the  direct 
union  of  hydrogen  with  sulphur  vapour  at  a  temperature  about  the 
boiling-point  of  the  sulphur,  or  by  passing  a  mixture  of  sulphur  vapour 
and  steam  through  a  tube  filled  with  red-hot  pumice  stone  (the  latter 
encouraging  the  action  by  its  porosity).  Hydrosulphuric  acid  is  more 
readily  formed  by  heating  a  damp  mixture  of  sulphur  and  wood 
charcoal,  and  may  be  obtained  in  large  quantity  by  heating  a  mixture 
of  equal  weights  of  sulphur  and  tallow  or  paraffin  wax,  the  latter 
furnishing  the  hydrogen. 

Preparation  of  hydrosulphuric  acid. — For  use  in  the  laboratory,  where 
it  is  very  largely  employed  in  testing  for  and  separating  metals,  hydro- 
sulphuric  acid  is  generally  prepared  by  decomposing  ferrous  sulphide 
with  diluted  sulphuric  acid  ;  FeS  +  H2S04  =  H2S  +  FeS04 

To  obtain  ferrous  sulphide,  a  mixture  of  3  parts  of  iron  filings  with  2  parts  of 


2I4 


HYDROSULPHUEIC  ACID. 


flowers  of  sulphur  is  thrown,  by  small  portions  at  a  time,  into  an  earthen  crucible 
(A,  Fig.  1 68)  heated  to  redness  in  a  charcoal  fire,  the  crucible  being  covered  after 
each  portion  has  been  added.  The  iron  and  sulphur  combine,  with  combustion, 

and  when  the  whole  of  the  mix- 
ture has  been  introduced,  the 
crucible  is  allowed  to  cool,  the 
mass  of  ferrous  sulphide  broken 
out,  and  a  few  fragments  of  it 
are  introduced  into  a  bottle  (Fig. 
169)  provided  with  a  funnel  tube 
for  the  addition  of  the  acid,  and 
a  bent  tube  for  conducting  the 
gas  through  a  small  quantity  of 
water,  to  remove  any  splashes 
of  ferrous  sulphate.  From  the 
second  bottle  the  gas  is  con- 
ducted by  a  glass  tube  with  a 
caoutchouc  joint,  either  down 
into  a  gas-bottle,  or  into  water, 
or  any  liquid  upon  which  the  gas 
is  intended  to  act.  The  frag- 
ments of  ferrous  sulphide  should 


Fig.  168. 


Fig.  169. — Preparation  of 
hydrosulphuric  acid. 


be  covered  with  enough  water  to 
fill  the  gas-bottle  to  about  one- 
third,  and  strong  sulphuric  acid 
poured  by  degrees  through  the  funnel,  the  bottle  being  shaken  until  effervescence 
is  observed.     An  excess  of  strong  sulphuric  acid  stops  the  evolution  of  gas  by 
precipitating  a  quantity  of  white  anhydrous  ferrous  sulphate,  which  coats  the 
sulphide  and  defends  it  from  the  action  of  the  acid. 
When  no  more  gas  is  required,  the  acid  liquid  should 
be  at  once  poured  away,  leaving  the  fragments  of 
ferrous  sulphide  at  the  bottom  of  the  bottle  for  a 
fresh  operation.     The  liquid,  if  set  aside,  will  deposit 
beautiful  green  crystals  of  copperas  or  ferrous  sul- 
phate (FeS04.7H20). 

Since  the  ferrous  sulphide  prepared  as  above  gene- 
rally contains  a  little  metallic  iron,  the  sulphuretted 
hydrogen  is  mixed  with  free  hydrogen,  which  does 
not  generally  interfere  with  its  uses.  The  pure  gas 
may  be  prepared  by  heating  antimony  sulphide  (crude 
antimony)  in  a  flask  with  hydrochloric  acid — 

Sb2S3  +  6HC1  =  3H2S  +  2SbCl3. 
If  hydrochloric  acid  be  diluted  with  more  than  6  molecular  proportions  of  water, 
it  cannot  decompose  the  antimony  sulphide  ;  hence,  when  the  sulphide  is  heated 
with  an  acid  somewhat  stronger  than  this,  the  subsequent  addition  of  water  repre- 
cipitates  the  antimony  sulphide  with  the  orange  colour  which  it  always  presents 
when  precipitated. 

Generally  speaking,  it  is  only  the  sulphides  of  those  metals  which  evolve 
hydrogen  from  dilute  acids  that  yield  H2S  when  treated  with  acids  ;  thus  copper 
and  mercury  which  do  not  dissolve  in  HC1  with  evolution  of  H,  yield  sulphides 
which  are  not  attacked  by  HC1.  Antimony,  however,  is  an  exception  to  this 
statement. 

Properties  of  hydrosulphuric  acid. — This  gas  is  at  once  distinguished 
from  all  others  by  its  disgusting  odour.  It  is  one-fifth  heavier  than 
air  (sp.  gr.  1.1912).  The  gaseous  state  is  not  permanent,  but  a  pressure  of 
17  atmospheres  is  required  to  reduce  it  to  a  liquid  (sp.  gr.  0.9),  which  is 
colourless,  boils  at  —  62  °  0.,  and  congeals  to  a  transparent  solid  at  —  85  °  C. 
Water  absorbs  about  three  times  its  volume  of  sulphuretted  hydrogen 
at  the  ordinary  temperature;  both  the  gas  and  its  solution  are  feebly 
acid  to  blue  litmus-paper.  The  gas  is  very  combustible,  burning  with 
a  blue  flame  like  that  of  sulphur,  and  yielding,  as  the  chief  products, 


OXIDATION  OF  SULPHURETTED   HYDROGEN.  215 

water  and  sulphurous  acid  gas,  H2S  +  O3  =  H20  +  S02  ;  a  little  sulphuric 
acid  (H2S04)  is  also  formed,  and  unless  the  supply  of  air  be  very  good, 
some  of  the  sulphur  will  be  separated ;  thus,  if  a  taper  be  applied  to  a 
bottle  filled  with  sulphuretted  hydrogen,  a  good  deal  of  sulphur  will  be 
deposited  upon  the  sides.  This  combustibility  of  sulphuretted  hydrogen 
is  of  the  greatest  importance  in  those  processes  of  chemical  manufacture 
in  which  this  gas  is  evolved  (as  in  the  preparation  of  ammoniacal  salts 
from  gas  liquor),  enabling  it  to  be  disposed  of  in  the  furnace  instead  of 
becoming  a  nuisance  to  the  neighbourhood.  The  gas  causes  fainting 
when  inhaled  in  large  quantity,  and  appears  much  to  depress  the  vital 
energy  when  breathed  for  any  length  of  time  even  in  a  diluted  state. 

When  dissolved  in  water,  hydrosulphuric  acid  is  slowly  acted  upon  by 
the  oxygen  of  the  air  (particularly  in  light),  which  converts  its  hydrogen 
into  water,  and  causes  a  white  deposit  of  sulphur. 

This  is  a  great  drawback  to  the  use  of  this  indispensable  chemical  in  the 
laboratory,  since  the  solution  of  H2S  is  soon  rendered  useless.  To  obviate  it  as  far 
as  possible,  the  solution  should  be  made  either  with  boiled  water  (free  from  dissolved 
air),  or  with  water  which  has  already  been  once  charged  with  the  gas  and  spoilt  by 
keeping,  for  all  the  oxygen  dissolved  in  this  water  will  have  been  consumed  by  the 
former  portion  of  gas.  The  gas  should  be  passed  through  the  water  until,  on 
closing  the  bottle  with  the  hand  and  shaking  violently,  the  pressure  is  found  to 
act  outwards,  showing  the  water  to  be  saturated  with  the  gas.  In  an  inverted 
bottle  with  a  greased  stopper,  the  solution  may  be  preserved  for  some  weeks,  even 
though  occasionally  opened  for  use.  The  solution  in  glycerine  keeps  better,  and  is 
sold  as  a  reagent. 

In  preparing  the  solution  of  hydrosulphuric  acid,  a  certain  quantity  of  the  gas 
always  escapes  absorption.  To  prevent  this  from  becoming  a  nuisance,  the  bottle 
containing  the  water  to  be  charged  with  gas  may  be  covered  with  an  air-tight 
caoutchouc  cap  having  two  tubes,  through  one  of  which  passes  the  glass  tube 
conve3ring  the  gas  down  into  the  water,  and  through  the  other,  a  tube  con- 
ducting the  excess  of  gas  either  into  a  gas  burner,  where  it  may  be  consumed,  or 
into  a  solution  of  ammonia  which  will  absorb  it,  forming  the  very  useful 
ammonium  sulphide. 

Hydrogen  sulphide  is  dissociated  by  a  high  temperature,  just  as  water 
is.  Concentrated  nitric  acid  acts  upon  hydrogen  sulphide,  oxidising  the 
hydrogen  and  a  part  of  the  sulphur,  ammonium  sulphate  being  found 
in  the  solution,  and  a  pasty  mass  of  sulphur  separated.  Chlorine, 
bromine,  and  iodine  at  once  appropriate  its  hydrogen  and  separate  the 
sulphur.  Nitrous  acid  acts  very  readilv  upon  hydrogen  sulphide,  yielding 
much  ammonia  ;  HONO  +  3H2S  =  KH3  +  2H20  +  S3. 

In  its  action  upon  the  metals  and  their  oxides,  hydrosulphuric  acid 
resembles  hydrochloric  and  the  other  hydrogen  acids.  Many  of  the 
metals  displace  the  hydrogen  and  form  metallic  sulphides.  This  usually 
requires  the  assistance  of  heat,  but  mercury  and  silver  act  upon  the  gas 
at  the  ordinary  temperature.  Thus,  if  hydrogen  sulphide  be  collected 
over  mercury,  the  surface  of  the  latter  becomes  coated  with  a  black 
film  of  mercurous  sulphide  ;  H2S  +  Hg2  =  H2  +  Hg2S.  In  a  similar  way 
the  surface  of  silver  is  slowly  tarnished  when  exposed  to  air  containing 
sulphuretted  hydrogen,  its  surface  being  covered  with  a  black  film  of 
silver  sulphide.  It  is  on  this  account  that  silver  plate  is  so  easily 
blackened  by  the  air  of  towns.  An  egg-spoon  is  always  blackened  by 
the  sulphur  from  the  egg.  Silver  coins  kept  in  the  pocket  with  lucifer 
matches  are  blackened,  from  the  formation  of  a  little  silver  sulphide. 
The  original  brightness  of  the  coin  may  be  restored  by  rubbing  it  with 
a  solution  of  potassium  cyanide,  which  dissolves  the  silver  sulphide. 


2l6  SULPHIDES. 

Friction  with  strong  ammonia  will  also  remove  the  tarnish,  and  its 
application  is  safer  than  that  of  the  poisonous  cyanide. 

When  heated  in  the  gas,  several  metals  displace  the  hydrogen  from 
it.  Thus,  potassium  acts  upon  it  in  a  similar  manner  to  that  in  which 
it  acts  upon  water,  forming  potassium  hydrosulphide  (KHS). 

Tin  removes  the  whole  of  the  sulphur  from  hydrosulphuric  acid  at  a 
moderate  heat ;  Sn  +  H2S  =  H2  +  SnS.  The  hydrogen  which  is  left  may 
be  measured,  and  thus  the  fact  that  two  volumes  of  H2S  contain  two 
volumes  of  hydrogen  may  be  demonstrated. 

When  hydrosulphuric  acid  acts  upon  a  metallic  oxide,  it  generally 
converts  it  into  a  sulphide  corresponding  with  the  oxide,  whilst  the 
hydrogen  and  oxygen  unite  to  form  water.  Lead  oxide  in  contact 
with  the  gas  yields  black  lead  sulphide  and  water ;  PbO  +  H0S  = 
PbS  -j-  H20.  Paper  impregnated  with  a  salt  of  lead  is  used  as  a  test 
for  the  presence  of  this  gas.  Thus,  if  paper  be  spotted  with  a  solution 
of  lead  nitrate  (or  acetate)  it  will  indicate  the  presence  of  even  minute 
quantities  of  hydrogen  sulphide  (in  impure  coal  gas,  for  example)  by 
the  brown  colour  imparted  to  the  spots;  Pb(NO3)2  +  H2S  -  2HNO3  +  PbS. 

It  is  in  this  manner  that  paints  containing  white  lead  (lead  carbonate) 
are  darkened  by  exposure  to  the  air  of  towns.  Cards  glazed  with  white 
lead,  and  engravings  on  paper  whitened  with  that  substance,  suffer  a 
similar  change.  Paintings,  whether  in  oil  or  water-colours,  in  which 
lead  is  an  ingredient,  are  also  injured  by  air  containing  sulphuretted 
hydrogen.  It  has  been  found  that  such  colours,  damaged  by  the  forma- 
tion of  lead  sulphide,  are  restored  by  the  continued  action  of  light  and 
air,  the  black  sulphide  becoming  oxidised  and  converted  into  the  white 
sulphate,  PbS  +  04  =  PbS04.  In  the  dark  this  restoration  does  not  occur, 
so  that  it  is  often  a  mistake  to  screen  pictures  from  the  light  by  a 
curtain. 

The  action  of  hydrosulphuric  acid  upon  the  chlorides  and  other 
haloid  salts  of  the  metals  generally  resembles  its  action  upon  the  oxides 
of  the  same  metals. 

Most  of  the  sulphides  of  the  metals,  like  the  corresponding  oxides, 
are  insoluble  in  water,  but  many  of  the  sulphides  are  also  insoluble  in 
diluted  acids  and  in  alkalies,  so  that  when  hydrosulphuric  acid  is 
brought  into  contact  with  the  solutions  of  metals,  it  will  in  many  cases 
precipitate  the  metal  in  the  form  of  a  sulphide  having  some  charac- 
teristic colour  or  other  property  by  which  the  metal  may  be  identified. 

Any  solution  of  lead  will  give  a  black  precipitate  with  solution  of  H2S,  the  lead 
sulphide  being  insoluble  in  dilute  acids  and  in  alkalies. 

A  solution  of  antimony  (tartar-emetic,  the  tartrate  of  antimony  and  potassium, 
for  example),  mixed  with  an  excess  of  hydrochloric  acid,  gives  an  orange- 
coloured  precipitate  (Sb2S3)  on  adding  H2S  ;  but  if  another  portion  be  mixed  with 
an  excess  of  potash  before  adding  the  H2S,  there  will  be  no  precipitate,  for  the 
antimony  sulphide  is  soluble  in  alkalies. 

Cadmium  chloride  gives  a  brilliant  yellow  precipitate  of  cadmium  sulphide. 

Zinc  sulphate  yields  a  white  precipitate  of  zinc  sulphide  (ZnS),  but  if  a  little 
hydrochloric  acid  be  previously  added,  no  precipitate  is  formed,  the  zinc  sulphide 
being  soluble  in  acids.  On  neutralising  the  hydrochloric  acid  with  ammonia, 
the  zinc  sulphide  is  at  once  precipitated. 

It  is  evident  that,  in  a  solution  containing  cadmium  and  zinc,  the  metals  may 
be  separated  by  acidifying  the  liquid  with  hydrochloric  acid  and  adding  excess 
of  hydrosulphuric  acid,  which  precipitates  the  cadmium  sulphide  only.  On 
filtering  the  solution,  and  adding  ammonia,  the  zinc  sulphide  is  precipitated. 


OXIDATION   OF  SULPHIDES.  217 

Those  sulphides  which  are  soluble  in  the  alkalies  are  often  designated 
sulphur-acids,  whilst  the  sulphides  of  the  alkalies  are  sulphur-bases. 
These  two  classes  of  sulphides  combine  to  form  sulphur-salts  analogous 
in  composition  to  the  oxygen-salts  of  the  same  metals.  Thus,  there 
have  been  crystallised,  the  salts — 

Sodium  sulphostannate Na4SnS4 

„        suiphantimonate          ....     Na  SbS3 
„        sulpharsenate Na3AsS4 

Speaking  generally,  those  metals  which  give  feebly  acid  oxides  also 
give  feebly  acid  sulphides,  whilst  the  sulphides,  which  correspond  with 
powerful  bases  are  themselves  basic,  for  H2S  is  not  capable  of  completely 
neutralising  the  alkalies. 

The  action  of  air  upon  the  sulphide.s  of  the  metals  is  often  turned  to 
account  in  chemical  manufactures.  At  the  ordinary  temperature,  the 
sulphides  of  those  metals  which  form  alkaline  oxides  (such  as  sodium 
and  calcium),  when  exposed  to  the  air  in  the  presence  of  water,  yield 
sulphite  and  thiosulphate  (hyposulphite).  This  change  is  sometimes 
turned  to  account  for  the  manufacture  of  sodium  hyposulphite. 

When  the  metal  forms  a  less  powerful  base  with  oxygen,  the  sul- 
phide is  often  converted  into  sulphate  by  exposure  to  moist  air ;  thus, 
CuS  +  O4  =  CuS04,  which  is  taken  advantage  of  for  the  separation  of 
copper  from  its  ores. 

The  black  ferrous  sulphide  (FeS),  when  exposed  to  moist  air,  becomes 
converted  into  red  ferric  oxide,  with  separation  of  sulphur,  2FeS  +  03  = 
Fe203  +  S2,  a  change  which  enables  the  gas  manufacturer  to  revive,  by 
the  action  of  air,  the  ferric  oxide  employed  for  removing  the  sulphuretted 
hydrogen  from  coal  gas. 

When  roasted  in  air  at  a  high  temperature,  the  sulphides  correspond- 
ing with  the  more  powerful  bases  are  converted  into  sulphates ;  thus, 
ZnS  +  04  =  ZnSO4,  which  explains  the  production  of  zinc  sulphate  by 
roasting  blende.  But  in  most  cases  part  of  the  sulphur  is  converted  into 
sulphurous  acid  gas  at  the  same  time.  Cuprous  sulphide,  for  instance,  is 
partly  converted  into  cupric  oxide  by  roasting,  Cu2S  +  04=  2CuO  +  S02, 
a  change  of  great  importance  in  the  extraction  of  copper  from  its  ores. 

131.  Hydrogen  per  sulphide. — The  composition  of  this  substance  is  not  yet  satis- 
factorily ascertained.  The  similarity  of  its  chemical  properties  to  those  of 
hydrogen  peroxide  prompts  the  wish  that  its  formula  may  be  H2S2.  Some 
analyses,  however,  seem  to  lead  to  the  formula  H2S5,  but  since  the  persulphide 
is  a  liquid  capable  of  dissolving  free  sulphur,  which  is  not  easily  separated  from 
it,  there  is  much  difficulty  in  determining  the  exact  proportion  of  this  element 
with  which  the  hydrogen  is  combined. 

When  equal  weights  of  slaked  lime  and  sulphur  are  boiled  with  water,  an 
orange-coloured  liquid  is  formed,  which  contains  calcium  hyposulphite,  calcium 
disulphide,  and  calcium  pentasulphide  (CaS5)  ;  3CaO  +  S6=CaS203  +  2CaS2. 

When  HC1  is  added  to  the  filtered  solution  an  abundant  precipitation  of  sulphur 
occurs,  and  much  H2S  is  evolved;  CaS2  +  2HCl  =  CaCl2  +  H2S  + S.  But  if  the 
solution  be  poured  by  degrees  into  a  slightly  warm  mixture  of  HC1  with  twice  its 
bulk  of  water,  and  constantly  stirred,  a  yellow  heavy  oily  liquid  collects  at  the 
bottom,  which  is  the  hydrogen  persulphide;  CaS2  +  2HCl  =  H2S2(?)-r  CaCl2.  The 
acid  having  been  kept  in  excess,  the  persulphide  has  been  preserved  from  the 
decomposition  which  it  suffered  in  the  presence  of  the  alkaline  solution  in  the 
former  experiment.  For  the  hydrogen  persulphide  very  closely  resembles  the  per- 
oxide in  the  facility  with  which  it  may  be  decomposed  into  hydrosulphuric  acid 
and  sulphur  ;  it  undergoes  spontaneous  decomposition  even  in  sealed  tubes,  and 
the  hydrosulphuric  acid  then  becomes  liquefied  by  its  own  pressure.  Most  of 


2lS  SULPHUEOUS  ACID   GAS. 

the  substances,  the  contact  of  which  promotes  the  decomposition  of  H202,  have 
the  same  effect  upon  the  persulphide.  This  compound  has  a  peculiar  odour,  which 
affects  the  eyes  ;  of  course,  its  vapour  is  mixed  with  H2S  resulting  from  its  decom- 
position. Its  specific  gravity  is  1.73. 

OXIDES  OF  SULPHUR. 

132.  Only  two  important  compounds  of  sulphur  with  oxygen  have 
been  obtained  in  the  separate  state — viz.,  sulphurous  anhydride  (SO.,) 
and  sulphuric  anhydride  (S03).      fiulphur  sesquioxide   (S203)  and  per- 
sulphuric  oxide  (S207)  also  exist. 

SULPHUR  DIOXIDE  OR  SULPHUROUS  ANHYDRIDE. 
S02  =  64  parts  by  weight  =  2  vols. 

133.  In  nature,  sulphur  dioxide  (sulphurous  acid  gas)  is  but  rarely 
met  with  ;  it  exists  in  the  gases  issuing  from  volcanoes.     Although  con- 
stantly discharged  into  the  air  of  towns  by  the  combustion  of  coal  (con- 
taining sulphur),  it  is  so  easily  oxidised  and  converted  into  sulphuric 
acid  that  no  considerable  quantity  is  ever  found  in  the  atmosphere. 
Sulphurous  acid  gas  has  been  already  mentioned  as  the  sole  product  of 
the  combustion  of  sulphur  in  dry  air  or  oxygen,*  but  it  is  generally 
prepared  in  the  laboratory  from  sulphuric  acid,  by  heating   it  with 
metallic  copper,  2H2S04  +  Cu  =  CuS04  +  2H20  +  S02. 

20  grams  of  copper  clippings  are  heated  in  a  flask  with  no  c.c.  of  strong  H2S04, 
the  gas  being  conducted  by  a  bent  tube  down  to  the  bottom  of  a  dry  bottle  closed  with 
a  perforated  card  (see  Fig.  150,  p.  177).  Some  time  elapses  before  the  gas  is  evolved  ; 
for  sulphuric  acid  attacks  copper  only  at  a  high  temperature  ;  but  when  the  evolution 
of  gas  fairly  begins  it  proceeds  very  rapidly,  so  that  it  is  necessary  to  remove  the 
flame  from  under  the  flask.  The  gas  will  contain  a  little  suspended  vapour  of 
sulphuric  acid,  which  renders  it  turbid. 

When  the  operation  is  finished,  and  the  flask  has  been  allowed  to  cool,  it  will  be 
found  to  contain  a  grey  crystalline  powder  at  the  bottom  of  a  brown  liquid.  The 
latter  is  the  excess  of  H2S04  used,  and  retains  very  little  copper,  since  cupric 
sulphate  is  insoluble  in  the  strong  acid.  If  the  liquid  be  poured  off',  and  the  flask 
filled  up  with  water,  and  set  aside  for  some  time,  the  crystalline  powder  will  dis- 
solve, forming  a  blue  solution  of  sulphate  of  copper,  yielding  that  salt  in  fine 
prismatic  crystals  by  evaporation  and  cooling.  The  dark  powder  remaining  un- 
dissolved  after  extracting  the  whole  of  the  sulphate,  consists  chiefly  of  cuprous 
sulphide  (Cu2S),  the  production  of  which  is  interesting,  as  showing  how  far  the 
•de-oxidising  effect  of  the  copper  may  be  carried  in  this  experiment. 

Sulphur  dioxide  is  a  very  heavy  (sp.  gr.  2.25)  colourless  gas,  charac- 
terised by  its  odour  of  burning  brimstone.  It  condenses  to  a  clear  liquid 
at  o°  F.  (the  temperature  of  a  mixture  of  ice  and  salt,  -  18°  C.)  even  at 
the  ordinary  pressure  of  the  air,  and  has  been  frozen  to  a  colourless 
crystalline  solid  at  -  76°  C.  The  liquid  has  the  sp.  gr.  1.4  at  15°  C., 
and  boils  at  -8°  C.  As  would  be  anticipated  from  its  comparatively 
high  boiling-point  S02  is  a  very  imperfect  gas  (p.  28).  The  cold  pro- 
duced by  the  evaporation  of  the  liquefied  gas  is  about  6500  cals.  per 
gram  mol.,  and  the  liquid  finds  application  in  some  forms  of  freezing- 
machines.  The  critical  temperature  is  157°  C.,  and  the  pressure 
79  atmospheres. 

The  liquefaction  of  the  gas  is  easily  exhibited  by  passing  it  down  to  the  bottom 
of  a  tube  (A,  Fig.  170)  closed  at  one  end,  and  surrounded  with  a  mixture  of 

*  According  to  Berthclot,  a  notable  quantity  of  SO3  is  produced  at  the  same  time. 


SULPHUR   DIOXIDE.  219 

pounded  ice  with  half  its  weight  of  salt.  The  tube  should  have  been  previously 
drawn  out  to  a  narrow  neck  at  B,  which  may  afterwards  be  sealed  by  the  blow- 
pipe, the  lower  part  of  the  tube  being  still  surrounded  by  the  freezing-mixture. 
The  tube  need  not  be  very  strong,  for  at  the  ordinary 
temperature  the  vapour  exerts  a  pressure  of  only  2.5 
atmospheres.  Liquid  sulphur  dioxide  is  a  convenient 
agent  for  producing  (by  its  rapid  evaporation)  the  low 
temperature  (  -  39°  F.)  required  to  effect  the  solidifi- 
cation of  mercury.  A  small  globule  of  this  metal  may 
readily  be  frozen  by  dropping  some  liquid  sulphur 
dioxide  upon  it  in  a  watch-glass  placed  in  a  strong 
draught  of  air.  The  tube  containing  the  sulphur 
dioxide  should  be  held  in  a  woollen  cloth  or  glove. 
The  attractive  experiment  of  freezing  water  in  a  red- 
hot  crucible  may  also  be  made  with  the  liquid.  A 
platinum  crucible  being  heated  to  redness,  and  some 
liquid  sulphur  dioxide  poured  into  it,  from  a  tube 
which  has  been  cooled  for  half  an  hour  in  ice  and 
salt,  the  liquid  becomes  surrounded  with  an  atmo- 
sphere of  sulphurous  acid  gas,  which  prevents  its  Fig.  170. 
contact  with  the  metal  (assumes  the  spheroidal  state), 

and  its  temperature  is  reduced  by  its  own  evaporation  to  so  low  a  degree  that  a 
little  water  allowed  to  flow  into  it  will  at  once  become  converted  into  opaque  ice. 
Liquid  S02  is  now  sold  in  glass  "  siphons  "  similar  to  those  in  which  soda-water  is 
supplied,  and  these  form  a  convenient  store  of  the  gas. 

Sulphurous  acid  gas  is  very  easily  absorbed  by  water,  as  may  be  shown 
by  pouring  a  little  water  into  a  bottle  of  the  gas,  closing  the  bottle  with 
the  palm  of  the  hand,  and  shaking  it  violently,  when  the  diminished 
pressure  due  to  the  absorption  of  the  gas  will  cause  the  bottle  to  be 
sustained  against  the  hand  by  the  pressure  of  the  atmosphere.  Water 
absorbs  43.5  times  its  bulk  of  the  gas  at  the  ordinary  temperature.  The 
solution  is  believed  to  contain  sulphurous  acid,  H2S03,  formed  by  the 
reaction  H20  +  S02  =  H2SO3,  but  this  body  has  not  been  obtained  in  the 
separate  state.  If  the  solution  be  exposed  to  a  low  temperature,  a 
crystallised  hydrate,  H2S03.i4H20,  is  obtained;  this  melts  at  2°  C. 
When  the  solution  of  sulphurous  acid  is  kept  for  some  time  in  a  bottle 
containing  air,  its  smell  gradually  disappears,  the  acid  absorbing  oxygen 
and  becoming  converted  into  sulphuric  acid. 

Sulphur  dioxide,  like  carbon  dioxide,  possesses  in  a  high  degree  the 
power  of  extinguishing  flame.  A  taper  is  at  once  extinguished  in  a 
bottle  of  the  gas,  even  when  containing  a  considerable  proportion  of  air. 
One  of  the  best  methods  of  extinguishing  burning  soot  in  a  chimney 
consists  in  passing  up  sulphurous  acid  gas  by  burning  a  few  ounces  of 
sulphur  in  a  pan  placed  over  the  fire. 

The  principal  uses  of  sulphur  dioxide  depend  upon  its  property  of 
bleaching  many  animal  and  vegetable  colouring-matters.  Although  a 
far  less  powerful  bleaching  agent  than  chlorine,  it  is  preferred  for 
bleaching  silks,  straw,  wool,  sponge,  isinglass,  baskets,  &c.,  which  would 
be  injured  by  the  great  chemical  energy  of  chlorine.  The  articles  to  be 
bleached  are  moistened  with  water  and  suspended  in  a  chamber  in  which 
sulphurous  acid  gas  is  produced  by  combustion  of  sulphur.  The 
colouring-matters  do  not  appear  in  general  to  be  decomposed  by  the 
acid,  but  rather  to  form  colourless  combinations  with  it,  for  in  course  of 
time  the  original  colour  often  reappears,  as  is  seen  in  straw,  flannel,  &c., 
which  becomes  yellow  from  age,  the  sulphurous  acid  probably  being 
oxidised  into  sulphuric  acid.  Stains  of  fruit  and  port  wine  on  linen  are 


220 


SULPHUROUS  ACID. 


conveniently  removed  by  solution  of  sulphurous  acid.  Hops  are  sulphured 
by  exposure  to  fumes  of  burning  sulphur  with  the  object  of  improving 
their  appearance. 

The  red  solution  obtained  by  boiling  a  few  chips  of  logwood  with  river  water 
(distilled  water  does  not  give  so  fine  a  colour)  serves  to  illustrate  the  bleaching 
properties  of  sulphurous  acid.  A  few  drops  of  the  solution  of  the  acid  will  at 
once  change  the  red  colour  of  the  solution  to  a  light 
yellow  ;  but  that  the  colouring  power  is  suspended,  and 
not  destroyed,  may  be  shown  by  dividing  the  yellow  liquid 
into  two  parts,  and  adding  to  them,  respectively,  potash 
and  diluted  sulphuric  acid,  which  will  restore  the  colour 
in  a  modified  form.  To  contrast  this  with  the  complete 
decomposition  of  the  colouring-matter,  a  little  sulphurous 
acid  may  be  added  to  a  weak  solution  of  the  potassium 
permanganate,  when  the  splendid  red  solution  at  once 
becomes  perfectly  colourless,  and  neither  acid  nor  alkali 
can  effect  its  restoration. 

If  a  bunch  of  damp  coloured  flowers  be  suspended  in  a 
bell-jar  over  a  crucible  containing  a  little  burning  sulphur 
(Fig.  171),  many  of  the  flowers  will  be  completely  bleached 
Fig.  171.  by  the  sulphurous  acid  ;  and  by  plunging  them  afterwards 

into   diluted  sulphuric  acid  and  ammonia,    their  colours 
may  be  partly  restored  with  some  very  curious  modifications. 

Another  very  useful  property  of  sulphurous  acid  is  that  of  arresting 
fermentation  (or  putrefaction),  apparently  by  killing  the  vegetable  or 
animal  growth  which  is  the  cause  of  the  fermentation.  This  is  commonly 
designated  the  antiseptic  or  antizymotic  property  of  sulphurous  acid,  and 

is  turned  to  account  when  casks  for  wine 
and  beer  are  sulphured  in  order  to  prevent 
the  action  of  any  substance  contained  in 
the  pores  of  the  wood,  and  capable  of 
exciting  fermentation,  upon  the  fresh 
liquor  to  be  introduced.  If  a  little  solu- 
tion of  sugar  be  fermented  with  yeast  in  a 
flask  provided  with  a  funnel  tube  (Fig. 
172),  a  solution  of  sulphurous  acid  poured 
in  through  the  latter  will  at  once  arrest 
the  fermentation.  The  salts  of  sulphurous 
acid  (sulphites)  are  also  occasionally  used  to 
arrest  fermentation,  in  the  manufacture  of  sugar,  for  instance.  Clothes 
are  sometimes  fumigated  with  sulphurous  acid  gas  to  destroy  vermin, 
and  the  air  of  rooms  is  disinfected  by  burning  sulphur  in  it,  4  Ibs.  of 
sulphur  being  recommended  for  every  1000  cubic  feet  of  space. 

The  disposition  of  sulphurous  acid  to  absorb  oxygen  and  pass  into 
sulphuric  acid,  renders  it  a  powerful  de-oxidising  or  reducing  agent. 
Solutions  of  silver  and  gold  are  reduced  to  the  metallic  state  by  sul- 
phurous acid  and  sulphites.  As  usual,  however,  the  reducing  power  of 
sulphur  dioxide  is  only  a  comparative  phenomenon.  Towards  several 
substances  the  acid  behaves  as  an  oxidising  agent,  a  noteworthy  case 
being  its  reaction  with  hydrogen  sulphide,  which  (in  presence  of  water) 
occurs  in  the  sense  of  the  equation,  2H2S  +  S02  =  2H0O  +  S3. 

An  aqueous  solution  of  stannous  chloride  gives  a  precipitate  of  stannic  sulphide 
with  sulphurous  acid. 

If  a  solution  of  sulphurous  acid  be  heated  for  some  time  in  a  sealed  tube  at 
150°  C..  one  portion  of  the  acid  de-oxidises  another,  sulphur  is  separated,  and 
sulphuric  acid  formed  ;  3H2S03  =  2H2S04  + 


Fig.  172. 


SULPHITES. 


221 


S02  and  NH3  combine  to  form  two  solid  compounds  (NH3)2S02  and  NH3.S02. 

The  unsaturated  character  of  S02  finds  illustration  in  the  fact  that  chlorine 
combines  with  an  equal  volume  of  the  gas,  under  the  influence  of  bright  sunshine, 
or  in  presence  of  charcoal,  to  produce  a  colourless  liquid,  the  vapour  of  which  is 
very  acrid  and  irritating  to  the  eyes.  This  is  the  chloranhydride  (p.  191)  of 
sulphuric  acid,  sulphuryl  chloride,  SO2C12.  Its  decomposition  by  water  occurs 
in  two  stages:  (i)  S02C12  +  H20  =  S02.C1.0H  +  HC1 ;  (2)  S02.C1.0H  +  H20  = 
S02.OH.OH  -t-HCl  ;  the  final  products  being  sulphuric  and  hydrochloric  acids,  so 
thalt  the  formula  S02.OH.OH  for  sulphuric  acid  is  justified.  The  chloride  of 
thionyl*  or  sulphurosyl  chloride,  SOC12,  is  a  colourless  volatile  liquid  obtained  by 
the  action  of  sulphurous  acid  gas  on  phosphorus  pentachloride.  It  is  decomposed  by 
water,  yielding!  hydrochloric  and  sulphurous  acids,  being  the  chloranhydride  of 
the  latter. 

Potassium  and  sodium,  when  heated  in  sulphur  dioxide,  burn  vividly,  producing 
the  oxides  and  sulphides  of  the  metals.  Iron,  lead,  tin,  and  zinc  are  also  con- 
verted into  oxides  and  sulphides  when  heated  in  the  gas  ;  S02  +  Zn3  =  ZnS  +  2ZnO. 

Lead  peroxide,  Pb02,  is  the  best  absorbent  for  S02  with  which  it  combines  (with 
incandescence  in  the  pure  gas)  to  form  lead  sulphate  :  Pb02  +  S02  =  PbS04. 

That  sulphur  dioxide  contains  its  own  volume 
of  oxygen  is  best  shown  by  burning  sulphur 
in  a  given  volume  of  oxygen  in  the  apparatus 
represented  in  Fig.  173. 

The  stopper  A  having  been  removed,  mercury  is  poured 
into  the  open  limb  of  the  U-tube  until  it  stands  at  a 
point  just  below  the  bulb  B,  the  air  in  which  is  then 
displaced  by  oxygen.  A  pellet  of  sulphur  is  placed  in 
the  metal  spoon  attached  to  the  stopper  and  the  latter 
is  inserted  directly  the  tube  delivering  the  oxygen  has 
been  removed.  A  platinum  helix  rests  upon  the  sulphur 
and  is  now  heated  to  redness  by  a  current  of  electricity 
passed  through  the  wires  attached  to  the  spoon  and  the 
helix.  When  the  sulphur  has  burnt  itself  out  and  the 
apparatus  has  cooled,  it  will  be  found  that  the  volume  of 
gas  has  not  varied,  showing  that  the  S02  produced  con- 
tains its  own  volume  of  oxygen.  To  relieve  the  pressure 
produced  by  the  heat  of  the  combustion,  it  is  well  to 
diminish  the  initial  pressure,  after  the  gas  has  been 
measured,  by  drawing  off  some  of  the  mercury  through 
the  stop-cock  C. 

Sulphites. — The  acid  character  of  sulphurous 
acid  is  rather  feeble,  although  stronger  than 
that  of  carbonic  acid.  There  is  much  general 
resemblance  between  the  sulphites  and  carbonates  in  point  of  solubility, 
the  sulphites  of  the  alkali  metals  being  the  only  salts  of  sulphurous  acid 
which  are  freely  soluble  in  water.  Sulphurous  acid,  SO(OH)2,  being 
dibasic  like  carbonic  acid,  forms  two  classes  of  salts,  the  normal  sulphites 
(for  example,  sodium  sulphite,  Na2S03)  and  acid  sulphites  (as  hydrogen 
potassium  sulphite,  KHS03). 

Sodium  sulphite  is  extensively  manufactured  for  the  use  of  the  paper- 
maker,  who  employs  it  as  an  antichlore  for  killing  the  bleach,  that  is, 
neutralising  the  excess  of  chlorine  after  bleaching  the  rags  with  chloride 
of  lime  (see  p.  183);  Na2SO3  +  H20  +  012  =  Na2S04  + 2HC1.  It  is  pre- 
pared by  passing  sulphurous  acid  gas  over  damp  crystals  of  sodium 
carbonate,  when  CO.,  is  expelled,  and  sodium  sulphite  formed,  which  is 
dissolved  in  water  and  crystallised.  It  forms  oblique  prisms,  having 
the  composition  Na2S03.yAq,  which  effloresce  in  the  air,  becoming 

*  Oetof,  sulphur. 


Fig'.  173- 
Composition  of  SO2  gas. 


222 


SULPHUR    TRIOXIDE. 


opaque,  and   slowly  absorbing  oxygen,  passing  into  sodium  sulphate 
(Na2S04).     Its  solution  is  slightly  alkaline  to  test-papers. 

For  the  manufacture  of  sodium  sulphite  the  SO.,  is  obtained  either  by 
the  combustion  of  sulphur  or  by  heating  sulphuric  acid  with  charcoal  ; 
2H2S04  +  C  =  2H20  +  C02  +  2SO,.  The  carbon  dioxide  of  course  will 
not  interfere  with  this  application  of  the  sulphur  dioxide. 

The  existence  of  sulphurosyl  chloride,  SO.CI2,  and  its  behaviour  with  water 
justify  the  formula  SO(OH)2  for  sulphurous  acid.  There  is  some  evidence,  derived 
from  organic  chemistry  (see  Sulplionic  Acids),  that  the  i  metallic  sulphites  are  not 


S 


which 


derived  from  SO(OH)2,  but  from  an  acid  of  the  form  Q>        H   ,    wc        may 

be  regarded  as  the  parent  substance  of  the  sulphonic  acids,  and  may  therefore  be 
termed  sulplionic  acid.  The  potassium  sulphite  is  supposed  to  be  02S.OK.K.  and 
not  SO.OK.OK.  Two  potassium-sodium  sulphites  have  been  prepared  which 
differ  in  properties  and  appear  to  be  02S.OK.Na  and  02S.ONa.K  respectively. 

Solutions  of  the  sulphites  absorb  nitric  oxide  in  the  cold,  yielding  nitro  sulphites^ 
such  as  the  potassium  salt  K2S03.2NO.  At  higher  temperatures  the  sulphites 
reduce  NO  to  N20. 

Pyrosulpliites,  derived  from  hypothetical  pyrosulplmrous  acid,  H2S205,  crystal- 
lise from  hot  strong  solutions  of  bisulphites,  2KHS03  =  K2S205  +  H20.  Possibly 
they  are  compounds  of  normal  sulphites  with  S02-K2S03.S02. 


SULPHUR  TRIOXIDE  OR  SULPHURIC  ANHYDRIDE. 
S03  =  8o  parts  by  weight. 

Sulphur  dioxide  and  oxygen  combine  to  form  sulphur  trioxide  when 
passed  through  a  tube  containing  heated  platinum  or  certain  metallic 
oxides,  such  as  those  of  iron  and  chromium,  the  action  of  which  in 

promoting  the  combination  is  not 
thoroughly  understood.  The  reaction 
is  exothermic,  evolving  some  103,000 
cals.  per  80  grams  of  S03  formed. 

The  combination  may  be  shown  by  pass- 
ing oxygen  from  the  tube  A  (Fig.  174), 
connected  with  a  gas-holder,  through  a 
strong  solution  of  sulphurous  acid  (B),  so 
that  it  may  take  up  a  quantity  of  S02  ; 
afterwards  through  a  tube  (C)  containing 
pumice-stone  soaked  with  oil  of  vitriol  to 
remove  the  water  ;  and  then  through  a 
bulb  (D)  containing  platinised  asbestos 
(see  p.  98).  The  mixture  of  the  gases  issuing  into  the  air  is  quite  invisible,  but 
when  the  bulb  is  gently  heated  combination  occurs,  and  dense  white  clouds  are 
formed  in  the  air,  from  the  combination  of  the  sulphuric  anhydride  (S03)  produced, 
with  the  atmospheric  moisture.  The  clouds  are  best  shown  by  conducting  themT 
through  a  bent  tube  attached  to  D,  into  a  large  flask. 

Pure  sulphur  trioxide,  prepared  by  repeated  distillation  out  of  con- 
tact with  moisture,  is  a  mobile  liquid  which  crystallises  when  cooled, 
in  long  transparent  prisms  like  nitre,  which  fuse  at  14°.  8  C.  and  boil 
at  46°  C.  At  temperatures  below  25°  C.  these  crystals  easily  change, 
especially  if  they  have  absorbed  a  little  water,  into  an  opaque,  fibrous, 
crystalline  mass  which  does  not  fuse,  but  vaporises  at  about  50°  C.,  the 
vapour  condensing  again  to  the  prismatic  variety  which  melts  at  14.8°. 
The  formula  of  the  fibrous  form  appears  to  be  S2O6,  and  it  is  much  less 
active  than  the  prismatic  form  (SO3).  When  sulphuric  acid  in  small 
quantity  is  added  to  S03  it  dissolves  it,  and  on  cooling  to  8°  C.  crystals 


Fig-.  174. 


PROPERTIES   OF   SULPHURIC  ANHYDRIDE.  223 

of  H2S04.3SO3  are  deposited.  "When  more  H2SO4  is  added,  it  forms- 
pyrosulphuric  acid,  H,S04.S03  or  H2S207  (m.p.  35°  C.).  S03  can  dis- 
solve much  SO2. 

When  exposed  to  air,  sulphur  trioxide  emits  strong  white  fuines,  its 
vapour  combining  with  the  moisture  of  the  air.  It  soon  deliquesces- 
and  becomes  sulphuric  acid  —  S03  +  H20  =  H2S04. 

When  thrown  into  water  it  hisses  like  red-hot  iron,  from  the  sudden 
formation  of  steam.  The  vapour  is  decomposed  into  SO2  and  0,  when, 
passed  through  a  red-hot  tube  ;  but  if  the  tube  contain  platinum,  or 
another  "  contact  substance,"  the  vapour  is  only  in  a  dissociated  state, 
for  the  SO,  and  0  recombine  on  cooling  in  contact  with  the  platinum. 
Phosphorus  burns  in  its  vapour,  combining  with  the  oxygen  and 
liberating  sulphur.  Baryta  glows  when  heated  in  the  vapour,  com- 
bining with  it  to  form  barium  sulphate,  unless  both  be  quite  dry. 

Sulphuric  anhydride  mixes  in  all  proportions  with  sulphuric  acid,  the 
mixture  being  known  as  fuming  sulphuric  acid.  The  melting-point  of 
the  mixture  varies  with  the  percentage  of  S03  in  it  ;  that  containing 
80  per  cent,  is  the  most  convenient  for  use,  as  it  remains  liquid  at 
ordinary  temperature.  Fuming  sulphuric  acid  finds  extended  applica- 
tion in  Organic  Chemistry  for  making  sulphonic  acids  (q.v.).  By  gently 
warming  it,  much  S03  can  be  distilled  from  it  for  small  experiments. 

The  pyrosulphuric  acid,  or  anhydrosulpJiuric  acid,  H2S207,  referred  to  above,. 
contains  45  per  cent,  of  S03  and  is  solid  at  ordinary  temperature  ;  it  may  be 
regarded  as  S03  which  has  insufficient  water  to  form  H2S04  (H4S208),  and  since  the- 
acid  chloride  S205C12  (formed  by  the  action  of  excess  of  PC15  on  H2S04)  exists,  its 

02S/OH  02S/C1 

constitution  may  be  represented  as          /O     ,  the  chloride  being          /O  .      An 


acid  containing  a  larger  proportion  of  S03  remains  liquid  at  low  temperatures. 

Sulphuric  anhydride  is  capable  of  combining  with  olefiant  gas  (C2H4) 
and  similar  hydrocarbons,  and  absorbs  these  from  mixtures  of  gases. 
In  the  analysis  of  coal  gas,  a  fragment  of  coke  wetted  with  fuming 
sulphuric  acid  is  passed  up  into  a  measured  volume  of  the  gas  standing 
over  mercury  to  absorb  these  illuminating  hydrocarbons.  S03  also- 
combines  with  HC1,  forming  S02.C1.0H,  which  may  also  be  obtained  by 
distilling  sulphuric  acid  with  phosphoric  chloride  — 

3S02(OH)2  +  PC15  =  3(S02.C1.0H)  +  P02.OH  +  2HC1. 

An  interesting  method  of  obtaining  the  sulphuric  anhydride  consists. 
in  pouring  2  parts  by  weight  of  oil  of  vitriol  over  3  parts  of  phosphoric 
anhydride,  contained  in  a  retort  cooled  in  ice  and  salt,  and  afterwards 
distilling  at  a  gentle  heat,  when  the  phosphoric  anhydride  retains  water,. 
and  the  S03  may  be  condensed  in  a  cooled  receiver. 

SULPHURIC  ACID,  OR  HYDROGEN  SULPHATE. 
H2S04  or  S02(OH)2  =  98  parts  by  weight. 

134.  More  than  four  centuries  ago  the  alchemist  Basil  Valentine 
subjected  green  vitriol,  as  it  was  then  called  (sulphate  of  iron),  to  dis- 
tillation, and  obtained  an  acid  liquid  which  he  named  oil  of  vitriol. 
The  process  discovered  by  this  laborious  monk  is  even  now  in  use  at 
Nordhausen  in  Saxony,  and  the  Nordhausen  oil  of  vitriol  was  at  one 


224  HISTORY   OF   SULPHURIC   ACID. 

time  an  important  article  of  commerce.  The  crystals  of  ferrous  sulphate 
(FeS04.yH20)  exposed  to  the  air  absorb  oxygen,  and  become  basic  ferric 
sulphate  ;  6FeS04  +  03  =  2Fe2(S04)3.Fe203. 

When  this  salt  is  partially  dried,  and  distilled  in  earthenware  retorts, 
a  mixture  of  sulphuric  acid  and  sulphuric  anhydride  distils  over,  and 
constitutes  Nordhausen  or  fuming  sulphuric  acid  ;  Fe.,(S04)3+ 2H2O  = 
Fe2O3+2H2SO4  +  S03.  The  ferric  oxide  (Fe2O3)  which  is  left  in  the 
retorts,  is  the  red  powder  known  as  colcothar,  which  is  used  for  polishing 
plate  glass  and  metals. 

The  green  vitriol  employed  for  preparing  the  Nordhausen  acid  was  obtained 
from  iron  pyrites  (FeS2).  A  particular  variety  of  this  mineral,  white  pyrites  (or 
efflorescent  pyrites),  when  exposed  to  moist  air,  undergoes  oxidation,  yielding 
ferrous  sulphate  and  sulphuric  acid  ;  FeS2  +  H20  +  Ol7  =  FeS04  +  H2S04. 

Large  masses  of  this  variety  of  pyrites  in  mineralogical  cabinets  may  often  be 
seen  broken  up  into  small  fragments,  and  covered  with  an  acid  efflorescence  of 
ferrous  sulphate  from  this  cause.  Ordinary  iron  pyrites  is  not  oxidised  by 
exposure  to  the  air  unless  it  be  first  subjected  to  distillation  in  order  to  separate 
a  portion  of  the  sulphur  which  it  contains. 

The  first  step  towards  the  discovery  of  the  process  which,  until 
within  the  last  few  years,  has  been  the  only  profitable  one  by  which 
this  acid  could  be  manufactured  on  a  large  scale  was  also  made  by 
Valentine,  when  he  prepared  his  oleum  sulphuris  per  campanum,  by 
burning  sulphur  under  a  bell-glass  over  water,  and  evaporating  the 
acid  liquid  thus  obtained.  The  same  experimenter  also  made  a  very 
important  advance  when  he  burnt  a  mixture  of  sulphur,  antimony 
sulphide  and  nitre  under  a  bell-glass  placed  over  water ;  but  it  was  not 
until  the  middle  of  the  eighteenth  century  that  it  was  suggested  by 
some  French  chemists  to  burn  the  sulphur  and  nitre  alone  over  water  ; 
a  process  by  which  the  acid  appears  actually  to  have  been  manufactured 
upon  a  pretty  large  scale.  The  substitution  of  large  chambers  of  lead 
for  glass  vessels  by  Dr.  Roebuck  was  a  great  improvement  on  the  pro- 
cess, and  about  the  year  1770  the  preparation  of  the  acid  formed  an 
important  branch  of  manufacture ;  since  then  the  process  has  been 
steadily  improving  until,  at  the  present  time,  a  very  large  quantity  is 
manufactured  by  this  method.  The  diminution  in  the  price  of  oil  of 
vitriol  well  exhibits  the  progress  of  improvement  in  its  production,  for 
the  original  oil  of  sulphur  appears  to  have  been  sold  for  about  half  a 
crown  an  ounce,  and  that  prepared  by  burning  sulphur  with  nitre  in 
glass  vessels  at  the  same  price  per  pound ;  but  when  leaden  chambers 
were  introduced,  the  price  fell  to  a  shilling  per  pound,  and  at  present 
oil  of  vitriol  can  be  purchased  at  the  rate  of  five  farthings  per  pound. 

The  description  of  the  present  "  chamber  process  "  of  manufacture 
will  be  best  understood  after  a  consideration  of  the  principles  of  the 
chemical  changes  upon  which  it  depends. 

It  has  been  seen  that  when  sulphur  is  burnt  in  air  sulphur  dioxide  is 
produced.  When  this  acts  on  nitric  acid,  in  the  presence  of  water, 
sulphuric  acid  and  nitric  oxide  are  produced,  3S02+ 2HNO3+ 2H20  = 
3H2SO4  +  2NO.*  The  nitric  oxide,  in  contact  with  air  becomes  nitric 
peroxide,  NO  +  O  =  N02,  which,  in  the  presence  of  H20.  serves  to 
convert  a  further  quantity  of  S02  into  H2S04,  S02  +  N02  +  H20  = 

*  According  to  some  authorities,  N2O3  is  the  oxide  of  nitrogen  produced  ;  since,  however, 
it  has  been  shown  that  this  compound  can  only  exist  at  low  temperatures,  the  view  that 
nitric  oxide  is  the  oxide  formed  in  the  chambers  is  here  adopted. 


OIL  OF  VITRIOL.  225 

H2S04  +  NO;  nitric  oxide  is  thus  regenerated  and  serves  to  convert 
more  SO2  into  sulphuric  acid  if  the  requisite  quantities  of  air  and  steam 
be  supplied,  the  two  last  equations  being  repeated. 

When  the  supply  of  steam  is  deficient,  nitrosyl  sulphate  is  found  deposited  in 
crystals  (chamber  crystals)  in  the  sulphuric  acid  chambers.  This  has  been  formed 
according  to  the  equation  2S02  +  2N02  +  0  +  H20  =  2S02.OH.ONO.  In  the  presence 

of  a  further  quantity  of  S02  and  H20  the  nitrosyl  sulphate  is  decomposed  thus 

2S02.OH.ONO  +  SO2  +  2H2O  =  3H2S04  +  2NO. 

It  is  generally  believed  that  these  two  equations  represent  the  reactions  in  the 
chamber  rather  than  those  quoted  above. 

It  appears,  therefore,  that  NO  may  be  employed  to  absorb  oxygen 
from  the  air  and  to  convey  it  to  the  S02,  so  that,  theoretically,  an 
unlimited  quantity  of  sulphur  might  be  converted  into  sulphuric  acid 
by  a  given  quantity  of  NO,  with  a  sufficient  supply  of  air  and  steam. 

The  actual  reactions  involved  in  this  process  have  received  much 
attention,    and  a   full   dis- 
cussion of  the  probabilities 
will  be  found  in  works  on 
sulphuric  acid  manufacture. 

To  illustrate  the  chemical 
principles  of  the  manufacture  of 
sulphuric  acid,  a  large  glass 
flask  or  globe  (A,  Fig.  175)  is 
fitted  with  a  cork  through  which 
are  passed  («)  a  tube  connected 
with  a  flask  (D)  containing 
copper  and  strong  sulphuric  acid 
for  evolving  S02 ;  (i)  a  tube 
connected  with  a  flask  (B)  con- 
taining copper  and  dilute  nitric 
acid  (sp.  gr.  1.2)  for  supplying 
nitric  oxide  ;  (c)  a  tube  pro- 
ceeding from  a  small  flask  (E)  Fig.  175. — Preparation  of  sulphuric  acid, 
containing  water. 

On  heating  the  flask  containing  nitric  acid  and  copper,  the  NO  passes  into  the 
globe  and  combines  with  the  oxygen  of  the  air,*  filling  the  globe  with  a  red 
mixture  of  nitric  peroxide  and  nitrous  anhydride.  The  nitric  oxide  flask  may  then 
be  removed.  Sulphur  dioxide  is  now  generated  by  heating  the  flask  containing 
sulphuric  acid  and  copper  ;  the  S02  soon  decolourises  the  red  gas,  the  contents  of 
the  globe  becoming  colourless,  and  the  crystalline  compound  forming  abundantly 
on  the  sides  ;  the  sulphur  dioxide  flask  may  then  be  removed.  Steam  is  sent  into 
the  globe  from  the  flask  containing  water,  when  the  crystalline  compound  dissolves, 
and  sulphuric  acid  collects  at  the  bottom  of  the  globe. 

If  the  experiment  be  repeated,  the  steam  being  introduced  simultaneously  with 
the  sulphur  dioxide,  no  crystalline  compound  will  be  formed,  the  sulphur  dioxide 
being  at  once  converted  into  sulphuric  acid. 

Since  the  cork  is  somewhat  corroded  in  this  experiment,  it  is  preferable  to  have 
the  mouth  of  the  flask  ground  and  closed  by  a  ground  glass  plate,  perforated  with 
holes  for  the  passage  of  the  tubes.  The  perforations  are  easily  made  by  placing 
the  glass  plate  flat  against  the  wall  and  piercing  it  with  the  point  of  a  revolving 
rat's-tail  file  dipped  in  turpentine  ;  the  file  is  then  gradually  worked  through  the 
hole  until  the  latter  is  of  the  required  size. 

The  process  employed  for  the  manufacture  of  English  oil  of  vitriol 
will  now  be  easily  understood. 

A  series  of  chambers  (about  100  ft.  x  20  ft.  x  20  ft.,  shown  in  trans- 
verse section  at  F,  Fig.  176),  is  constructed  of  leaden  plates,  the  edges 

*  The  operation  is,  of  course,  more  striking  if  oxygen  is  employed  instead  of  air,  the  globe 
in  Fig.  175  being  filled  with  oxygen  by  displacement  at  the  commencement. 

P 


226 


MANUFACTURE   OF  SULPHURIC  ACID. 


of  which  are  united  by  autogenous  soldering  (that  is,  by  fusing  together 
their  edges  without  solder,  which  would  be  rapidly  corroded  by  the  acid 
vapours.)  The  bottom  or  saucer  (G)  of  the  chamber  is  not  attached  to 


the  upper  portion  or  curtain  (F),  the"  sulphuric  acid  which  collects  in 
the  saucer  serving  to  seal  the  communication  between  the  interior  of 
the  chamber  and  the  outer  air.  A  framework  of  timber  supports  the 
curtain. 

The  sulphurous  acid  gas  is  generated  by  burning  iron  pyrites*  or 
*  2FeS2  +  On  =  Fe2O3  +  4SO2. 


REACTIONS   IN  THE  VITRIOL  CHAMBERS.  227 

sulphur  in  suitable  furnaces  (A)  adjoining  the  chambers,  and  so  arranged 
that  the  gas  produced  may  be  mixed  with  about  the  proper  quantity  of 
air  to  furnish  the  oxygen  required  for  its  conversion  into  sulphuric  acid.. 

Nitric  acid  vapour  is  evolved  from  a  mixture  of  sodium  nitrate  and 
oil  of  vitriol  (see  page  89)  contained  in  iron  nitre  pots  (C)  which  are 
heated  by  being  placed  in  the  flue  (B),  leading  from  the  pyrites  burners, 
to  the  chamber,  so  that  the  nitric  acid  is  carried  into  the  chambers  with 
the  current  of  sulphurous  acid  gas  and  air  (through  D). 

Jets  of  steam  are  introduced  at  different  parts  of  the  chambers  from 
an  adjacent  boiler. 

The  sulphurous  acid  gas  acts  upon  the  nitric  acid  vapour,  in  the 
presence  of  the  water,  forming  nitric  oxide  and  sulphuric  acid  which 
rains  down  into  the  water  on  the  floor  of  the  chambers.  If  the  NO 
were  permitted  to  escape  from  the  chambers,  and  a  fresh  quantity  of 
nitric  acid  vapour  introduced  to  oxidise  another  portion  of  sulphur 
dioxide,  2  molecules  (170  parts  by  weight)  of  sodium  nitrate  would  be 
required  to  furnish  the  nitric  acid  for  the  conversion  of  2  atoms  (64 
parts  by  weight)  of  sulphur,  whereas,  in  practice,  only  4  parts  by  weight 
of  nitrate  are  employed  for  96  parts  of  sulphur. 

The  nitrogen  of  the  air  takes  no  part  in  the  change ;  and  since  the 
oxygen  consumed  in  converting  the  sulphur  into  sulphuric  acid  is  accom- 
panied by  four  times  its  volume  of  nitrogen,  there  is  a  very  large  accu- 
mulation of  this  gas  in  the  chambers,  and  provision  must  be  made  for 
its  removal  in  order  to  allow  space  for  those  gases  which  take  part  in 
the  change.  The  obvious  plan  would  appear  to  be  the  erection  of  a 
simple  chimney  for  the  escape  of  the  nitrogen  at  the  opposite  end  of 
the  chamber  to  that  at  which  the  sulphurous  acid  gas  and  air  enter  it, 
and  this  plan  was  formerly  adopted  ;  but  the  nitrogen  carries  off  with 
it  a  portion  of  the  oxides  of  nitrogen  which  are  so  valuable  in  the 
chamber,  and  to  save  this  the  escaping  nitrogen  is  now  generally  passed 
through  a  lead-lined  tower  (Gay-Lussac's  tower)  (H)  filled  with  per- 
forated stoneware  plates,  through  which  oil  of  vitriol  (sp.  gr.  1.72)  is 
allowed  to  trickle  :  the  oil  of  vitriol  absorbs  the  nitrogen  oxides,  and  flows 
into  a  cistern  (acid  egg),  wherefrom  it  is  forced  up,  by  air  pressure,  to 
a  cistern  (K)  at  the  top  of  another  tower  (Glover's  tower)  (E)  packed 
with  acid-proof  bricks,  through  which  the  hot  SO,  and  air  are  made  to 
pass  as  they  enter,  when  they  take  up  the  nitrogen  oxides  from  the 
"  nitrous  vitriol,"  and  carry  them  into  the  chamber. 

A.  saving  of  over  50  per  cent,  of  the  weight  of  sodium  nitrate  used  is 
thus  effected. 

The  sulphuric  acid  is  allowed  to  collect  on  the  floor  of  the  chamber 
until  it  has  a  specific  gravity  of  about  1.6,  and  contains  70  per  cent, 
of  oil  of  vitriol  (H2S04).  If  it  were  allowed  to  become  more  concen- 
trated than  this,  it  would  both  attack  the  lead  and  absorb  some  of  the 
oxides  of  nitrogen  in  the  chamber,  so  that  it  is  now  drawn  off. 

This  acid  (chamber  acid)  is  quite  strong  enough  for  some  of  the  appli- 
cations of  sulphuric  acid,  particularly  for  that  which  consumes  the 
largest  quantity  in  this  country,  viz.,  the  conversion  of  common  salt  into 
sodium  sulphate  as  a  preliminary  step  in  the  manufacture  of  carbonate 
of  soda.  To  save  the  expense  of  transporting  the  acid  for  this  purpose, 
the  vitriol  chambers  form  part  of  the  plant  of  the  alkali  works. 

To  convert  this  weak  acid  into  the  ordinary  oil  of  vitriol  of  commerce, 


228  CONCENTRATION   OF   SULPHURIC  ACID. 

it  is  run  off  into  shallow  leaden  pans  set  in  brickwork  and  supported  on 
iron  bars  over  the  flue  of  a  furnace,  where  it  is  heated  until  so  much 
^water  has  evaporated  that  the  specific  gravity  of  the  acid  has  increased 
to  1.72.  The  concentration  cannot  be  carried  further  in  leaden  pans, 
because  the  strong  acid  acts  upon  the  lead,  and  converts  it  into  sulphate  — 
2H2S04  +  Pb  =  PbS04  +  2H20  +  S02. 

When  a  Glover's  Tower  is  used  the  whole  of  the  chamber  acid  is 
passed  down  the  tower  together  with  the  nitrous  vitriol.  The  chamber 
acid  is  thus  concentrated  by  the  heat  of  the  furnace  gases  to  sp.  gr.  1.72 
and  the  gases  are  at  the  same  time  cooled. 

The  acid  of  1.72  sp.  gr.  contains  about  80  per  cent,  of  true  oil  of 
vitriol,  and  is  largely  employed  for  making  superphosphate  of  lime,  and 
in  other  rough  chemical  manufactures.  It  is  technically  called  brown 
acid  (brown  oil  of  vitriol,  B.O.V.),  having  acquired  a  brown  colour  from 
organic  matter  accidentally  present  in  it. 

To  convert  this  brown  acid  into  commercial  oil  of  vitriol,  it  is  boiled 
down,  either  in  glass  retorts  or  platinum  stills,  when  water  distils  over, 
accompanied  by  a  little  sulphuric  acid,  and  the  acid  in  the  retort  becomes 
colourless,  the  brown  carbonaceous  matter  being  oxidised  by  the  strong 
sulphuric  acid,  with  formation  of  carbonic  and  sulphurous  acid  gases. 
When  dense  white  fumes  of  oil  of  vitriol  begin  to  pass  over,  showing 
that  all  the  superfluous  water  has  been  expelled,  the  acid  is  drawn  off 
by  a  siphon.  The  strongest  acid  obtainable  by  this  process  still  contains 
about  2  per  cent,  of  water,  formed  by  the  decomposition  of  some  of  the 
H3S04  into  H20  and  S03,  which  escapes  as  vapour. 

The  cost  of  the  acid  is  very  much  increased  by  this  concentration.  It  cannot 
be  conducted  in  open  vessels,  partly  on  account  of  the  loss  of  sulphuric  acid, 
partly  because  concentrated  sulphuric  acid  absorbs  moisture  from  the  open  air 
even  at  the  boiling-point.  The  loss  by  breakage  of  the  glass  retorts  is  very  con- 
siderable. although  it  is  reduced  as  far  as  possible  by  heating  them  in  sand,  and 
keeping  them  always  at  about  the  same  temperature  by  supplying  them  with  hot 
acid.  But  the  boiling-point  of  the  concentrated  acid  is  very  high  (640°  F.,  338°  C.), 
and  the  retorts  consequently  become  so  hot  that  a  current  of  cold  air  or  an 
accidental  splash  of  acid  will  frequently  crack  them  at  once.  Moreover,  the  acid 
boils  with  succussion  or  violent  bumping,  caused  by  sudden  bursts  of  vapour,  which 
endanger  the  safety  of  the  retort. 

With  platinum  stills  the  risk  of  fracture  is  avoided,  and  the  concentration  may 
be  conducted  more  rapidly,  the  brown  acid  (sp.  gr.  1.72)  being  admitted  at  the  top, 
and  the  oil  of  vitriol  (sp.  gr.  1.84)  drawn  off  by  a  platinum  siphon  from  the 
bottom  of  the  still,  which  is  protected  from  the  open  fire  by  an  iron  jacket.  But 
since  a  platinum  still  costs  ^2000  or  ^3000,  the  interest  upon  its  value  increases 
the  cost  of  production  of  the  acid.  It  is  stated  to  be  economical  to  protect  the 
platinum  from  the  slight  action  of  the  vitriol  on  it  by  a  lining  of  gold,  which  is 
less  attacked. 

When  the  perfectly  pure  acid  is  required,  it  is  actually  distilled  so  as  to  leave 
the  solid  impurities  (sulphate  of  lead,  &c.)  in  the  retort.  Some  fragments  of  rock 
crystal  should  be  introduced  into  the  retort  to  moderate  the  bursts  of  vapour,  and 
heat  applied  by  a  ring  gas-burner  with  somewhat  divergent  jets. 

Commercial  sulphuric  acid  is  liable  to  contain  nitrogen  oxides,  lead  sulphate, 
arsenic  (from  the  iron  pyrites  burnt  in  the  kilns),  and  iron.  Arsenic-free  acid 
may  be  made  by  passing  H2S  through  the  diluted  acid,  filtering  off  the  precipitate 
of  As2S3,  and  concentrating.  It  is  generally  made,  however,  by  using  sulphur  in 
the  kilns  in  place  of  pyrites.  Nitrogen  oxides  are  eliminated  by  adding  a  little 


ammonium  sulphate  during  concentration  ;  NO  +  N02  +  (NH4)2S04  =  N4  + 
3H20.     To  eliminate  iron  and  lead  sulphate  the  acid  must  be  distilled. 

For  many  years  it  has  been  the  dream  of  the  sulphuric  acid  maker  to 


CONTACT-PROCESS   FOR  MAKING   SULPHURIC   ACID.  2 2Q 

combine  sulphur  dioxide  and  atmospheric  oxygen,  by  the  method 
described  at  p.  222  for  making  sulphuric  anhydride,  and  to  absorb  the 
product  in  water  to  obtain  sulphuric  acid.  In  such  a  process  the  "  con- 
tact substance  "  has  the  same  function  as  that  of  the  nitric  oxide  in  the 
chamber-process,  that  is  to  say,  it  acts  as  a  carrier  of  oxygen  from  the 
air  to  the  sulphur  dioxide,  although  in  what  manner  is  unknown.  The 
contact-substance  has  the  great  advantage  over  nitric  oxide  that,  being 
a  solid,  it  requires  less  room  in  which  to  do  its  work,  and  is  not  liable  to 
loss  by  leakage.  Thus  the  unit  of  plant  might  be  expected  to  be  con- 
siderably smaller  in  a  "  contact-process "  for  making  sulphuric  acid 
than  in  the  chamber-process.  An  economy  of  greater  importance  than 
the  saving  of  interest  on  plant,  however,  consists  in  the  possibility  of 
making  by  the  contact-process  strong  sulphuric  acid,  or  even  a  fuming 
acid,  at  once,  thus  eliminating  the  cost  of  concentration  ;  for  it  is  obvious 
that  by  abjusting  the  proportion  of  water  by  which  the  sulphuric  anhy- 
dride is  absorbed,  an  acid  of  any  degree  of  concentration  may  be 
obtained. 

Unfortunately,  there  are  several  conditions  which  affect  unfavourably 
the  combination  of  SO2  and  0  in  the  contact-process.  The  only  contact- 
substance  which  has  proved  so  far  sufficiently  active  in  inducing  the 
combination  is  platinum,  most  economically  used  by  spreading  it  over  a 
large  surface  as  in  the  form  known  as  platinised  asbestos  (p.  98).  The 
activity  of  this  material,  however,  rapidly  diminishes  if  the  gases  contain 
impurities,  because  these  are  either  deposited  on  the  platinum  or  they 
combine  with  it  and  render  it  ineffective.  Such  impurities  are  said  to 
*'  poison  "  the  metal,  and  the  worst  of  them  in  this  respect  are  com- 
pounds of  arsenic,  phosphorus,  and  mercury.  The  first  of  these  is 
nearly  always  present  in  the  pyrites  burnt  lor  the  production  of  S02, 
and,  passing  into  the  gases,  is  sufficient,  together  with  the  dust  arising 
from  the  pyrites  burners,  to  render  the  platinum  useless  in  a  very  short 
time.  It  was  the  necessity  for  constantly  renewing  the  platinum  by 
dissolving  it  from  the  asbestos  by  aqua-regia,  and  again  precipitating  it 
thereon,  that  prevented  the  success  of  the  contact- process  in  the  past. 

Another  difficulty  to  be  met  in  the  contact-process  (or  catalytic  pro- 
cess) arises  from  the  fact  that  the  heat  evolved  when  S02  and  O  combine 
(p.  222)  is  apt  to  accumulate  until  the  temperature  of  the  contact-sub- 
stance is  so  high  that  much  of  the  S03  produced  is  decomposed  again 
into  S02  and  0,  or  these  gases  never  combine. 

The  demand  for  strong  and  fuming  sulphuric  acid  by  the  manu- 
facturers of  artificial  dyestuffs  and  other  organic  preparations,  having 
increased  rapidly  during  the  last  few  years,  strenuous  efforts  have  again 
been  made  to  produce  the  acid  by  the  contact-process,  and  by  rigorous 
care  in  purifying  the  sulphur  dioxide  and  air  before  they  enter  the 
chamber  containing  the  contact-substance,  and  by  careful  regulation  of 
the  temperature  of  the  latter  great  success  has  been  attained.  Indeed, 
it  is  claimed  that  so  much  as  96  per  cent,  of  the  S02  may  be  converted 
into  S03,  and  there  is  little  reason  to  doubt  that  the  process  will  ulti- 
mately displace  the  chamber-process. 

Sulphur  dioxide  is  produced  in  a  pyrites  burner  as  in  the  chamber- 
process,  sufficient  air  for  its  conversion  into  S03  being  drawn  in  through 
the  burner.  This  mixture  of  gases  is  then  thoroughly  washed,  dried, 
and  passed  into  a  chamber  containing  platinised  asbestos  spread  on 


230 


CONTACT-PEOCESS   FOE  MAKING  SULPHURIC  ACID. 


shelves.  At  first  the 
chamber  must  be 
artificially  heated  to  a 
temperature  of  about 
250°  to  300°  C.  in 
order  to  induce  the 
combination,  but  after 
this  has  once  set  in,  it 
becomes  necessary  to 
withdraw  the  arti- 
ficial heat  and  to  cir- 
culate the  gases  which 
are  to  be  combined, 
around  the  contact- 
chamber  in  order  that 
they  may  equalise  the 
temperature  therein, 
and  prevent  it  from 
rising  at  any  one 
point  to  that  at  which 
decomposition  of  the 
S03  occurs.  The 
sulphuric  anhydride 
is  finally  absorbed  in 
water  to  produce  sul- 
phuric acid. 

Fig.  177  illustrates  the 
kind  of  plant  used  in  the 
contact-process  for  the 
manufacture  of  sulphuric 
acid.  The  gases  from 
the  pyrites  kiln  A  pass 
through  a  dust  chamber 
B,  where  they  are  sub- 
mitted to  the  action  of 
steam  jets  in  order  to 
mix  them,  and  at  the 
same  time  to  dilute  the 
sulphuric  acid,  which  is 
always  produced  during 
the  combustion  in  the 
pyrites  burner,  so  that 
afterwards  it  may  not 
attack  the  metal  of  the 
apparatus.  The  gases 
next  pass  through  lead 
pipes  6',  exposed  to  the 
atmosphere,  in  order  to 
cool  them  below  100°  C., 
and  then  up  through 
washing  towers  D  sup- 
plied with  water.  As 
the  presence  of  moisture 
in  the  gases  leads  to 
formation  of  H2S04  in 
the  contact  -  chamber, 
which  damages  the  plati- 
num, the  gases  are  next 


PROPERTIES   OF  SULPHURIC  ACID.  23 1 

dried  in  a  tower  E  supplied  with  strong  sulphuric  acid.  To  ensure  continued 
activity  of  the  platinum,  it  is  desirable  to  watch  carefully  over  the  purity  of  the 
gases  entering  the  contact-chamber  ;  for  this  purpose  they  are  passed  through  a 
long  box  F,  having  glass  ends  so  that  the  operative  can  observe  from  one  end  a  light 
burning  at  the  other,  and  thus  determine  whether  the  gases  are  free  from  suspended 
matter.  A  periodical  chemical  testing  of  the  gases  is  also  made  by  passing  some 
of  them  through  water,  which  is  afterwards  analysed  for  arsenic  and  other 
impurities. 

The  contact-chamber  G  (which  is  drawn  to  an  exaggerated  scale  for  the  sake 
of  clearness)  contains  columns  of  perforated  shelves  on  which  platinised  asbestos 
is  spread.  At  first  the  chamber  is  heated  by  the  gas  jets  g,  the  products  of  com- 
bustion of  which  pass  up  the  flue  Ji.  The  cold  gases  being  admitted  at  i,  and 
passing  around  the  columns  of  shelves,  become  heated  by  transmission  through  the 
walls  of  the  flue  and  enter  the  columns,  as  indicated  by  the  arrows,  at  a  tempera- 
ture high  enough  to  combine  under  the  influence  of  the  platinum.  The  gas  jets 
may  now  be  turned  off,  for  the  heat  of  combination  is  communicated  to  the  gases 
as  they  pass  around  the  columns,  and  the  whole  apparatus  may  be  maintained  at 
the  most  favourable  temperature  for  combination,  about  350°  C. 

The  S03  produced  is  absorbed  by  water  in  a  series  of  vessel  like  H. 

No  means  of  circulating  the  gases  is  shown  in  the  figure,  but  this  is  best  effected 
by  pumps. 

Properties  of  oil  of  vitriol. — The  properties  of  concentrated  sulphuric 
acid  are  very  characteristic.  Its  great  weight  (sp.  gr.  1.84),*  freedom 
from  odour,  and  oily  appearance,  distinguish  it  from  any  other  liquid 
commonly  met  with,  which  is  fortunate,  because  it  is  difficult  to  preserve 
a  label  upon  the  bottles  of  this  powerfully  corrosive  acid.  Although,  if 
absolutely  pure,  it  is  perfectly  colourless,  the  ordinary  acid  used  in  the 
laboratory  has  a  peculiar  grey  colour,  due  to  traces  of  organic  matter. 
Its  high  boiling-point,  338°  C.  (640°  F.)  has  been  already  noticed ;  it 
mast  be  added  that  vapour  of  H2S04  is  not  evolved  by  the  ebullition 
but  the  products  of  its  dissociation,  H20  +  S03.  When  acid  of  100  per 
cent,  strength  is  heated  it  begins  to  (apparently)  boil  at  290°  C.  and 
loses  SO3  until  its  strength  has  fallen  to  98  per  cent.,  when  both  water 
and  S03  distil  over  and  condense  together  in  the  receiver.  The  vapour 
is  perfectly  transparent  in  the  vessel  in  which  the  acid  is  boiled  ;  as  soon 
as  it  issues  into  the  air  it  condenses  into  voluminous,  dense  clouds  of  a 
most  irritating  description.  Even  a  drop  of  the  acid  evaporated  in  an 
open  dish  will  fill  a  large  space  with  these  clouds.  Oil  of  vitriol  solidifies 
when  cooled  to  about  -  34°  C.  ( -  30°  F.),  though  pure  H2S04  melts  at 
10°. 5  C.  (51°  F.).  Oil  of  vitriol  rapidly  corrodes  the  skin  and  other 
organic  textures  upon  which  it  falls,  usually  charring  or  blackening 
them  at  the  same  time.  Poured  upon  a  piece  of  wood  the  latter  speedily 
assumes  a  dark  brown  colour ;  and  if  a  few  lumps  of  sugar  be  dissolved 
in  a  very  little  water,  and  stirred  with  oil  of  vitriol,  there  is  a  violent 
action,  and  a  semi-solid  black  mass  is  produced.  This  property  of  sul- 
phuric acid  is  turned  to  account  in  the  manufacture  of  blacking,  in  which 
treacle  and  oil  of  vitriol  are  employed.  These  effects  are  to  be  ascribed 
to  the  powerful  attraction  of  oil  of  vitriol  for  water.  Woody  fibre 
(C6H1005)  (which  composes  the  bulk  of  wood,  paper,  and  linen)  and 
sugar  (d19H92On),  may  be  regarded,  for  the  purpose  of  this  explanation, 
as  composed  of  carbon  associated  with  5  and  1 1  molecules  of  water, 
respectively,  and  any  cause  tending  to  remove  the  water  would  tend  to 
eliminate  the  carbon. 

*  The  acid  containing  97.7  per  cent,  has  the  highest  sp.  gr.  1.8413 ;  that  of  98  per  cent., 
1.8412  ;  99  per  cent.,  1.8403  ;  99.47  per  cent.,  1.8395  ;  100  per  cent.,  1.8384. 


232  SULPHUEIC  ACID  AND   WATEK. 

The  great  attraction  of  this  acid  for  water  is  shown  by  the  high  tem- 
perature (often  exceeding  the  boiling-point  of  water)  produced  on  mixing 
oil  of  vitriol  with  water,  which  renders  it  necessary  to  be  careful  in 
diluting  the  acid. 

The  water  should  be  placed  in  a  jug,  and  the  oil  of  vitriol  poured  into  it  in  a 
thin  stream,  a  glass  rod  being  used  to  mix  the  acid  with  the  water  as  it  flows  in. 
Ordinary  oil  of  vitriol  becomes  turbid  when  mixed  with  water,  from  the  separation 
of  lead  sulphate  (formed  from  the  evaporating  pans),  which  is  soluble  in  the 
concentrated,  but  not  in  the  diluted  acid,  so  that  if  the  latter  be  allowed  to  stand 
for  a  few  hours,  the  lead  sulphate  settles  to  the  bottom,  and  the  clear  acid  may 
be  poured  off  free  from  lead.  Diluted  sulphuric  acid  has  a  smaller  bulk  than  is 
occupied  by  the  acid  and  water  before  mixing. 

The  heat  evolved  on  combining  one  gram-molecule  of  H2S04  with  one  gram- 
molecule  of  water  amounts  to  69.7  gram-units.  Decreasing  quantities  of  heat  are 
evolved  for  successive  additions  of  water,  until  200  gram-molecules  of  water  have 
been  added. 

The  heat  thus  evolved  must  be  regarded  as  equivalent  to  a  chemical  affinity 
exerted  between  the  acid  and  water  ;  several  compounds  of  sulphuric  acid  with 
water  have  been  crystallised.  The  most  notable  of  these  is  H2S04.H20,  corre- 
sponding with  an  acid  of  sp.  gr.  1.78  ;  it  is  called  dihydrated  sulphuric  acid 
(S03.2H20).  in  contradistinction  to  oil  of  vitriol,  which  is  monohydrated  sulphuric 
acid  (S03.H20)  ;  it  solidifies  to  a  mass  of  ice-like  crystals  at  8°  0.,  and  on  this 
account  is  called  glacial  sulphuric  acid.  When  sold  instead  of  oil  of  vitriol  it  may 
be  recognised  by  its  freezing  in  winter.  The  hydrate  H2S04.2H20  corresponds  with 
the  maximum  contraction  which  occurs  when  H2S04  and  water  are  mixed,  and  with 
an  acid  of  sp.  gr.  1.63  ;  it  is  called  trihydrated  sulphuric  acid  or  orthosulphuric 
acid. 

The  so-called  "solidified  sulphuric  acid  "  is  sodium  hydrogen  sulphate  saturated 
with  sulphuric  acid. 

Even  when  largely  diluted,  sulphuric  acid  corrodes  textile  fabrics 
very  rapidly,  and  though  the  acid  be  too  dilute  to  appear  to  injure  them 
at  first,  it  will  be  found  that  the  water  evaporates  by  degrees,  leaving 
the  acid  in  a  more  concentrated  state,  and  the  fibre  is  then  perfectly 
rotten.  The  same  result  ensues  at  once  on  the  application  of  heat;  thus, 
if  characters  be  written  on  paper  with  the  diluted  acid,  they  will  remain 
invisible  until  the  paper  is  held  to  the  fire,  when  the  acid  will  char  the 

paper,  and  the  writing  will  appear 
intensely  black. 

If  oil  of  vitriol  be  left  exposed  to 
the  air  in  an  open  vessel,  it  very  soon 
increases  largely  in  bulk  from  the 
absorption  of  water,  and  a  flat  dish 
of  oil  of  vitriol  under  a  glass  shade 
(Fig.  178)  is  frequently  employed  in 
the  laboratory  for  drying  substances 
without  the  assistance  of  heat.  The 
Fig.  178,-Desiccator  for  drying  drying  is  of  course  much  accelerated 

over  oil  of  vitriol.  by  placing  the  dish  on  the  plate  of 

an  air-pump,  and  exhausting  the  air 

from  the  shade,  so  as  to  effect  the  drying  in  vacuo.    It  will  be  remem- 
bered also  that  oil  of  vitriol  is  in  constant  use  for  drying  gases. 

At  a  red  heat,  the  vapour  of  oil  of  vitriol  is  decomposed  into  water, 
sulphur  dioxide,  and  oxygen ;  H2S04  =  H20  +  S02  +  O. 

When  sulphur  is  boiled  with  oil  of  vitriol,  the  latter  gradually  dis- 
solves the  melted  sulphur,  converting  it  into  sulphur  dioxide — 

S  +  2H2S04  -  3S02  +  2H20. 


COMPOSITION   OF  SULPHURIC  ACID.  233 

All  ordinary  metals  are  acted  upon  by  concentrated  sulphuric  acid 
when  heated,  except  gold  and  platinum  (the  latter  does  not  quite 
escape  when  long  boiled  with  the  acid),  the  metal  being  oxidised  by  one 
portion  of  the  acid,  which  is  thus  converted  into  sulphur  dioxide,  the 
oxide  reacting  with  another  part  of  the  sulphuric  acid  to  form  a  sul- 
phate. Thus,  when  silver  is  boiled  with  strong  sulphuric  acid,  it  is 
converted  into  silver  sulphate,  which  is  soluble  in  hot  water — 
Ag2  +  2H2S04  =  Ag2S04  +  2H20  +  S02. 

Should  the  silver  contain  any  gold,  this  is  left  behind  in  the  form  of  a 
dark  powder.  Sulphuric  acid  is  extensively  employed  for  the  separation 
or  parting  of  silver  and  gold.  This  acid  is  also  employed  for  extract- 
ing gold  from  copper,  and  when  sulphate  of  copper  is  manufactured 
by  dissolving  that  metal  in  sulphuric  acid  (see  p.  218),  large  quan- 
tities of  gold  are  sometimes  extracted  from  the  accumulated  residue 
left  undissolved  by  the  acid.  If  the  sulphuric  acid  contains  nitric  acid, 
it  dissolves  a  considerable  quantity  of  gold,  which  separates  again  in 
the  form  of  a  purple  powder  when  the  acid  is  diluted  with  water,  the 
sulphate  of  gold  formed  being  reduced  by  the  nitrous  acid  when  the 
solution  is  diluted. 

Some  of  the  uses  of  sulphuric  acid  depend  upon  its  specific  action  on 
certain  organic  substances,  the  nature  of  which  has  hot  yet  been  clearly 
explained.  Of  this  kind  is  the  conversion  of  paper  into  vegetable  parch- 
ment by  immersion  in  a  cool  mixture  of  two  measures  of  oil  of  vitriol 
and  one  measure  of  water,  and  subsequent  washing.  The  conversion  is 
not  attended  by  any  change  in  the  weight  of  the  paper. 

Proof  of  the  composition  of  sulphuric  acid. — 10  grams  of  sulphuric  acid  are 
neutralised  by  22.7  grams  of  PbO,  when  heated,  giving  off  1.82  grams  of  H20  and 
leaving  30.9  grams  of  lead  sulphate.  Hence  sulphuric  acid  contains  2.02  per  cent, 
of  H.  10  grams  galena  (PbS),  containing  8.66  Pb  and  1.34  S,  when  converted  into 
lead  sulphate  (PbS04)  by  nitric  acid,  yield  12.68  grams.  Hence  12.68  grams  lead 
sulphate  contain  1.34  S  and  2.68  0,  being  the  difference  between  the  lead  sulphate 
and  the  lead  sulphide.  The  30.9  grams  of  lead  sulphate  furnished  by  10  grams  of 
sulphuric  acid  would  therefore  contain  3.26  S  and  65.2  0,  so  that  100  parts  of 
sulphuric  acid  contain  2.02  H,  32.6  S,  and  65.2  0,  which  numbers,  divided  by  the 
atomic  weights,  give  2  atoms  of  H.  I  atom  of  S,  and  4  atoms  of  0.  The  molecular 
weight  of  sulphuric  acid  cannot  be  deduced  from  the  sp.  gr.  of  its  vapour  because  it 
is  dissociated  into  H20  and  S03.  But  it  yields  with  KOH  two  salts,  one  containing 
an  atom  of  K  and  an  atom  of  H,  and  the  other  containing  two  atoms  of  K. 
Hence  these  salts  must  be  KHS04  and  K2S04,  and  the  molecule  of  the  acid  must  be 
H2S04. 

135.  /Sulphates. — At  common  temperatures  sulphuric  acid  displaces 
all  other  acids  from  their  salts  ;  many  cases  will  be  remembered  in 
which  this  power  of  sulphuric  acid  is  turned  to  account. 

So  great  is  the  acid  energy  of  sulphuric  acid,  that  when  it  is  allowed 
to  act  011  an  indifferent  or  acid  metallic  oxide,  it  causes  the  separation 
of  a  part  of  the  oxygen,  and  reacts  with  the  basic  oxide  so  produced. 
Advantage  is  sometimes  taken  of  this  circumstance  for  the  preparation 
of  oxygen ;  for  instance,  when  manganese  dioxide  is  heated  with 
sulphuric  acid,  sulphate  of  manganese  is  produced,  and  oxygen  dis- 
engaged ;  MnO>2  +  H2S04  =  MnS04  +  O  +  H20. 

Again,  if  chromic  "anhydride  be  treated   in  the  same  way,  chromic 
sulphate  will  be  produced,  with  liberation  of  oxygen — 
2Cr03  +  3H2S04  =  Cr.2.3S04  +  03  +  3H20. 


234 


SULPHATES. 


A  mixture  of  potassium  bichromate  (K20.2Cr03)  and  sulphuric  acid  is 
sometimes  used  as  a  source  of  oxygen. 

Sulphuric  acid  is  a  dibasic  acid,  that  is,  it  contains  two  atoms  of 
hydrogen  which  may  be  exchanged  for  a  metal.  In  normal  sulphates, 
both  atoms  of  H  are  so  exchanged,  as  in  K2SO4,  the  normal  potassium 
sulphate.  When  only  a  part  of  the  H  is  exchanged,  acid  sulphates  are 
produced  \  thus  KHS04  is  acid  potassium  sulphate,  which  is  very  use- 
ful in  blcwpipe  and  metallurgic  chemistry,  because,  when  heated,  it 
yields  normal  potassium  sulphate  and  sulphuric  acid;  2KHS04  = 
K2SO4  +  H2S04.  When  the  two  atoms  of  H  in  H2S04  are  exchanged 
for  different  metals,  double  sulphates  are  formed  ;  potassium  alum, 
KA1(SO4)2,  is  an  example  of  this  class,  in  which  one-fourth  of  the  H  in 
2H2S04  is  exchanged  for  potassium,  and  the  other  three  atoms  by  tri- 
atomic  aluminium. 

The  following  table  exhibits  the  composition  of  the  sulphates  most 
frequently  met  with  : 


Chemical  Xame. 

Common  Name. 

Formula. 

Potassium  sulphate 

Sal  polychrest  . 

K2S04 

Sodium  sulphate     .... 

Glauber's  salt  . 

Na2S04.  ioH20 

Hydropotassium  sulphate 

Bisulphate  of  potash 

KHSO* 

Ammonium  sulphate 
Barium  sulphate     .... 

Heavy  spar 

(NH4)2S04 
BaS04 

Calcium  sulphate    .... 

Gypsum  . 

CaS04.2H20 

Magnesium  sulphate 

Epsom  salts 

MgS04.7H2O 

Potassium-aluminium  sulphate 

Potash-alum     . 

KAl(S04)2.i2H20 

Ammonium-aluminium  sulphate    . 

Ammonia-alum 

NH4Al(S04)2.i2H20 

Potassium-chromium  sulphate 

Chrome-alum  . 

KCr(S04)2.i2H20 

Ferrous  sulphate     . 

Green  vitriol    .         ) 
Copperas  .         .         / 

FeS04.7H20 

Manganese  sulphate 

MnS04.5H20 

Zinc  sulphate  

White  vitriol   . 

ZnS04.7H2O 

Lead  sulphate         .... 

PbS04 

Cupric  sulphate 

Blue  vitriol      .         ^ 
Blue  stone        .         J 

CuS04,5H20 

In  consequence  of  the  tendency  of  sulphuric  acid  to  break  up  into  sulphur  dioxide 
and  oxygen  at  a  high  temperature,  most  of  the  sulphates  are  decomposed  by  heat ; 
cupric  sulphate,  for  example,  when  very  strongly  heated,  leaves  cupric  oxide,  whilst 
sulphur  dioxide  and  oxygen  escape;  CuS04=CuO  +  S0.2  +  0.  Ferrous  sulphate  is 
more  easily  decomposed,  some  of  the  S03  escaping  decomposition,  whilst  the 
remainder  breaks  up  into  S02  and  0,  the  latter  oxidising  the  ferrous  oxide  which 
would  otherwise  be  left ;  2FeS04  =  Fe203  +  S02+S03. 

The  normal  sulphates  of  potassium,  sodium,  barium,  strontium,  calcium,  and 
lead  are  not  decomposed  by  heat,  and  sulphate  of  magnesium  is  only  partly  decom- 
posed at  a  very  high  temperature. 

When  a  sulphate  of  an  alkali  or  alkaline  earth  metal  is  heated  with  charcoal,  the 
carbon  removes  the  whole  of  the  oxygen,  and  a  sulphide  of  the  metal  remains,  thus  : 
K2S04  (Potassium  sulphate)  +  C4  =  K2S  (Potassium  sulphide)  +  4.CO .  Hydrogen,  at 
a  high  temperature,  effects  a  similar  decomposition. 

Even  at  the  ordinary  temperature,  calcium  sulphate  in  solution  is  sometimes  de- 
oxidised by  organic  matter  ;  this  may  occasionally  be  noticed  in  well  and  river 
waters  when  kept  in  closed  vessels ;  they  acquire  a  strong  smell  of  hydrogen  sul- 
phide, in  consequence  of  the  conversion  of  a  part  of  the  calcium  sulphate  into 
sulphide  by  the  organic  constituents  of  the  water,  and  the  subsequent  decomposi- 
tion of  the  calcium  sulphide  by  the  carbonic  acid  present  in  the  water. 


THIOSULPKATES.  235 

Sulphur  sesquioxide,  S203,  is  an  unstable,  blue,  crystalline  solid,  obtained  by 
the  gradual  addition  of  sulphur  to  sulphuric  anhydride  in  the  cold.  It  dissolves 
in  fuming  sulphuric  acid  to  a  blue  liquid,  but  is  decomposed  by  water,  alcohol,  or 
ether,  sulphur  being  liberated. 

Persulphuric  anhydride,  S207,  is  a  crystalline  compound  formed  by  electrising 
<j).  65)  a  mixture  of  S02  and  O.  It  is  also  produced  by  the  interaction  of  hydro- 
gen dioxide  andH2SO4.  It  is  very  volatile  and  unstable,  but  its  solution  in  fairly 
•concentrated  sulphuric  acid  possesses  oxidising  properties  and  probably  con- 
tains per  sulphuric  acid  HS04(?H2S208).  Such  a  solution  is  formed  at  the  anode 
during  the  electrolysis  of  sulphuric  acid  of  medium  strength,  and  its  presence  is  to  be 
detected  in  the  ordinary  lead  electric  accumulator.  The  persulphate*  are  easily  pre- 
pared by  the  electrolysis  of  solutions  of  the  sulphates  in  dilute  sulphuric  acid.  To 
prepare  potassium  persulphate,  KS04  (?K2S208),  a  saturated  solution  of  KHS04  is  con- 
tainedin  a  platinum  dish,  kept  cool;  a  porous  pot  containing  dilute  H2S04is  immersed 
in  the  solution,  and  in  this  a  platinum  wire  is  introduced  to  serve  as  a  cathode  ;  the 
platinum  dish  is  made  the  anode.  By  continuing  the  electrolysis  (current  =  2- 3 
amperes)  for  some  time,  crystals  of  KS04  are  deposited  in  the  dish.  When  dried 
and  heated  they  evolve  S03  and  0,  K2S04  being  left.  Barium  chloride  gives  no 
precipitate  with  a  solution  of  a  persulphate  until  heated,  when  the  Ba(S04)2 
decomposes,  BaSO4  being  precipitated.  The  persulphates  behave  as  oxidising 
agents  in  solution,  and  find  application  as  bleaching  agents,  although  the  use  of  the 
ammonium  salt  as  a  "reducer"  in  photography  can  hardly  be  explained  by  refer- 
ence to  its  oxidising  power. 

It  has  been  found  that  when  a  persulphate  is  treated  with  strong  H2S04the  solu- 
tion rapidly  liberates  iodine  from  an  iodide,  whereas  persulphuric  acid  does  so  only 
slowly.  Hence  such  a  solution  (Cards  acid}  is  supposed  to  contain  another  per- 
sulphuric acid,  to  which  the  formula  H2S05  has  been  given. 

Besides  the  oxyacids  of  sulphur  already  described  the  following  are 
known  : — 

Sulphurous H2S03 

Sulphuric H2S04 

Thiosulphuric  (formerly  hyposulphurous) H2S203 

Hydrosulphurous H2S204 

Dithionic H2S206 

Trithionic H2S306 

Tetrathionic H2S406 

Pentathionic ,  H2S506 

136.  Thiosulphuric  acid  (H2S203  or  S02.OH.SH).— This  acid  has  not 
been  obtained  in  the  separate  state ;  but  many  salts  are  known  which 
are  evidently  derived  from  it,  and  such  salts  are  called  hyposulphites  or 
thiosulphates. 

The  sodium  thiosulphate  is  by  far  the  most  important  of  these  salts, 
being  very  largely  employed  in  photography,  under  the  name  of  hypo- 
sulphite, and  as  a  substitute  for  sodium  sulphite  as  an  antichlore.  The 
simplest  method  of  preparing  it  consists  in  digesting  powdered  roll 
sulphur  with  solution  of  sodium  sulphite  (Na2S03),  when  the  latter  dis- 
solves an  atom  of  sulphur  and  becomes  thiosulphate  (Na2S203),  which 
crystallises  from  the  solution,  when  sufficiently  evaporated,  in  fine 
prismatic  crystals,  having  the  formula  Na2S2O3.5H2O. 

On  a  large  scale,  sodium  thiosulphate  is  more  economically  prepared  from  the 
calcium  thiosulphate  obtained  by  exposing  the  refuse  (tank-waste  or  soda-ioaste) 
of  the  alkali  works  to  the  air  for  some  days.  This  refuse  contains  a  large  propor- 
tion of  calcium  sulphide,  which  becomes  converted  into  thiosulphate  by  oxidation  ; 
2CaS  +  04  +  H20  =  CaS203  +  Ca(OH)2. 

The  thiosulphate  is  dissolved  out  by  water,  and  solution  mixed  with  sodium 
carbonate,  when  calcium  carbonate  is  precipitated  and  sodium  thiosulphate  remains 
in  solution  ;  CaS203  +  Na2CO3  =  CaC03  +  Na^S203. 

The  most  remarkable  and  useful  property  of  the  sodium  thiosulphate 


236  FIXING  PHOTOGRAPHIC  PRINTS. 

is  that  of  dissolving  the  chloride  and  iodide  of  silver,  which  are  insoluble 
in  water  and  most  other  liquids ;  hence  its  use  in  photography. 

On  mixing  a  solution  of  silver  nitrate  with  one  of  sodium  chloride,  a  white  pre- 
cipitate of  silver  chloride  is  obtained,  the  separation  of  which  is  promoted  by  stir- 
ring the  liquid  ;  AgN03  +  NaCl  =  AgCl  +  NaNO3.  The  precipitate  may  be  allowed  to- 
settle  and  washed  twice  or  thrice  by  decantation.  One  portion  of  the  silver 
chloride  is  transferred  to  another  glass,  mixed  with  water,  and  solution  of  sodium 
thiosulphate  added  by  degrees.  The  silver  chloride  is  very  easily  dissolved,  yield- 
ing an  intensely  sweet  solution,  which  contains  the  thiosulphate  of  sodium  and 
silver,  produced  by  double  decomposition  between  the  silver  chloride  and  sodium 
thiosulphate  ;  2AgCl  +  sNa^Og  =  Ag2Na4(S203)3  +  2NaCl.  The  sodium  silver  thio- 
sulphate may  be  obtained  in  crystals  from  the  solution. 

When  the  silver  chloride  is  acted  on  by  a  weaker  solution  of  the  thiosulphate,. 
another  thiosulphate  of  sodium  and  silver  is  formed,  which  is  very  insoluble  in 
water  ;  AgCl  +  Na.2S203  =  NaCl  +  NaAgS203.  Hence  the  necessity  for  using  a  strong 
solution  of  the  hyposulphite  in  fixing  photographic  prints. 

If  the  other  portion  of  the  silver  chloride  be  exposed  to  the  action  of  light,  and 
especially  of  direct  sunlight,  it  assumes  by  degrees  a  dark  slate  colour,  possibly 
from  the  formation  of  silver  subchloride  :  4AgCl  +  H20  =  2Ag.2Cl  +  HCl  +  HOCl.  By 
treating  this  darkened  silver  chloride  with  the  hyposulphite,  as  before,  the  un- 
altered silver  chloride  will  be  entirely  dissolved,  but  the  subchloride  will  be  decom- 
posed into  monochloride,  which  dissolves  in  the  hyposulphite,  and  metallic  silver, 
which  is  left  in  a  very  finely  divided  state  as  a  black  powder.  The  application  of 
these  facts  in  photography  is  well  illustrated  by  the  following  experiments  :  A 
sheet  of  paper  is  soaked  for  a  minute  or  two  in  a  solution  of  10  grains  of  common 
salt  in  an  ounce  of  water  contained  in  a  flat  dish.  It  is  then  dried,  and  soaked  for 
three  minutes  in  a  solution  of  50  grains  of  silver  nitrate  in  an  ounce  of  water.  The 
paper  thus  becomes  impregnated  with  silver  chloride  formed  by  the  decomposition 
between  the  sodium  chloride  and  the  silver  nitrate.  It  is  now  hung  up  in  a  dark 
place  to  dry.  If  a  piece  of  lace,  or  a  fern  leaf,  or  an  engraving  on  thin  paper,  with 
well-marked  contrast  of  light  and  shade,  be  laid  upon  a  sheet  of  the  prepared 
paper,  pressed  down  upon  it  by  a  plate  of  glass  and  exposed  for  a  short  time  to  sun- 
light, a  perfect  representation  of  the  object  will  be  obtained,  those  parts  of  the 
sensitive  paper  to  which  the  light  had  access  having  been  darkened  by  the  forma- 
tion of  silver  subchloride,  whilst  those  parts  which  were  protected  from  the  light 
remain  unchanged. 

But  if  this  photographic  print  were  again  exposed  to  the  action  of  light,  it  would 
soon  be  obliterated,  the  unaltered  silver  chloride  in  the  white  parts  being  acted  on 
by  light  in  its  turn.  The  print  is  therefore  J&gfti  by  soaking  it  for  a  short  time  in  a 
saturated  solution  of  sodium  thiosulphate,  which  dissolves  the  white  unaltered  silver 
chloride  entirely,  and  decomposes  the  subchloride  formed  by  the  action  of  light, 
leaving  the  black,  finely  divided  metallic  silver  in  the  paper.  The  print  should  now 
be  washed  for  two  or  three  hours  in  a  gentle  stream  of  water,  to  remove  all  the 
silver  thiosulphate,  when  it  will  be  quite  permanent. 

The  power  of  sodium  thiosulphate  to  dissolve  silver  chloride  has  also 
been  turned  to  account  for  extracting  silver  from  its  ores,  in  which  it  is 
occasionally  present  in  the  form  of  chloride. 

The  behaviour  of  solution  of  sodium  thiosulphate  with  powerful  acids 
explains  the  circumstance  that  the  thiosulphuric  acid  has  not  been 
isolated,  for  if  the  solution  be  mixed  with  a  little  dilute  sulphuric  or 
hydrochloric  acid,  it  remains  clear  for  a  few  seconds,  and  then  becomes 
suddenly  turbid  from  the  separation  of  sulphur,  at  the  same  time  evolv- 
ing a  powerful  odour  of  sulphur  dioxide ;  H2S203  =  H2O  +  S  +  S03.  This 
disposition  of  the  thiosulphuric  acid  to  break  up  into  sulphur  dioxide 
and  sulphur  also  explains  the  precipitation  of  metallic  sulphides,  which 
often  occurs  when  sodium  thiosulphate  is  added  to  the  acid  solu- 
tions of  the  metals.  Thus,  if  an  acid  solution  of  antimonious  chloride 
(obtained  by  boiling  crude  antimony  ore  (Sb2S3)  with  hydrochloric  acid) 
be  added  to  a  boiling  solution  of  sodium  "thiosulphate,  the  sulphur, 


THIONIC  ACIDS.  237 

separated  from  the  thiosulphuric  acid,  combines  with  the  antimony  to 
form  a  fine  orange-red  precipitate  of  antimonious  sulphide  (Sb2S3), 
which  is  used  in  painting  under  the  name  of  antimony  vermilion.  On 
the  large  scale,  the  solution  of  calcium  thiosulphate  obtained  from  the 
alkali  waste  is  employed  in  the  preparation  of  antimony  vermilion,  as 
being  less  expensive  than  the  sodium-salt.  Lead  thiosulphate  dissolved 
in  sodium  thiosulphate  is  used  as  a  hair-dye,  depositing  the  black  lead 
sulphide. 

A  solution  of  sodium  thiosulphate  bleaches  iodine  solution,  becoming 
changed   into   a   solution    of    sodium   tetrathionate  ;     2Na,S,O,  +  I9  = 


When  crystals  of  sodium  thiosulphate  are  heated  in  the  air,  they  first  fuse  in 
their  water  of  crystallisation,  then  dry  up  to  a  white  mass,  which  burns  with  a 
blue  flame,  leaving  a  residue  of  sodium  sulphate.  If  heated  out  of  contact  with 
air,  sodium  pentasulphide  will  be  left  with  the  sodium  sulphate  ;  4/Na9S0Oo. 

H0       Na.S0      Na.S. 


Some  of  the  reactions  of  sodium  thiosulphate  become  more  intelligible  when  the 
salt  is  represented  as  sodium  sulphate,  S02(OJSTa)2,  in  which  an  atom  of  sulphur  has 
displaced  an  atom  of  oxygen,  S02.ONa.SNa. 

Hydrosulphurous  acid  (H2S204).  —  In  an  aqueous  solution  of  sulphurous  acid 
zinc  dissolves,  forming  a  yellow  solution,  without  the  usual  evolution  of  hydrogen  ; 
the  solution  contains  zinc  hydrosulphite  ;  2H2S03  +  Zn  =  ZnS204  +  2H20. 

The  solution  bleaches  organic  colours,  even  Prussian  blue,"and  reduces  the  salts 
of  silver,  mercury,  and  copper  to  the  metallic  state  ;  it  is  used  in  the  indigo  vat  for 
reducing  the  indigo.  It  is  very  unstable,  soon  becoming  colourless  zinc  sulphite  ; 
ZnS204  +  0  +  H20  =  ZnS03  +  H2S03. 

The  sodium  salt,  Na^S^,  is  obtained  by  digesting  zinc  in  solution  of  NaHS03  ; 
2NaHS03  +  Zn  =  Na2S2O4  +  Zn(OH)2.  It  forms  needle-like  crystals  very  soluble  in 
water,  insoluble  in  strong  alcohol,  and  becoming  NaHS03,  by  absorption  of  oxygen 
from  the  air.  By  decomposing  the  sodium  hydrosulphite  with  oxalic  acid.  H2S204 
is  obtained  as  an  orange-yellow  unstable  liquid. 

137.  Dithionic  acid,  or  hyposulphuric  acid  (H2S206),  has  not  at  present  acquired 
any  practical  importance.     To  prepare  a  solution  of  the  acid,  manganese  dioxide 
in  a  state  of  fine  division  is  suspended  in  water  and  exposed  to  a  current  of  sulphur 
dioxide,  the  water  being  kept  very  cold  whilst  the  gas  is  passing.     A  solution  of 
manganese  dithionate  is  thus  obtained  ;  2S02  +  Mn02  =  MnS206.     Some  manganese 
sulphate  is  always  formed  at  the  same  time  ;  S02+MnO2  =  MnS04,  and  if  the  tem- 
perature be  allowed  to  rise,  this  will  be  produced  in  large  quantity. 

The  solution  containing  the  sulphate  and  dithionate  is  decomposed  by  solution 
of  baryta  (baryta-water),  when  manganous  oxide  is  precipitated,  together  with 
barium  sulphate,  and  barium  dithionate  is  left  in  solution.  To  the  filtered  solution 
dilute  sulphuric  acid  is  carefully  added  until  all  the  barium  is  precipitated  as 
BaS04,  when  the  solution  of  dithionic  acid  is  filtered  and  evaporated  in  vacua  over 
oil  of  vitriol.  It  is  a  colourless,  inodorous  liquid,  which  is  decomposed,  when 
heated,  into  sulphuric  acid  and  sulphur  dioxide  ;  H2S206  =  H2S04  +  S02.  Oxidising 
agents  (HNO3,C1,  &c.)  convert  it  into  H2S04. 

The  dithionates  are  not  of  any  practical  importance  ;  they  are  all  soluble,  and  are 
decomposed  by  heat,  leaving  sulphates,  and  evolving  sulphur  dioxide.  They  are 
distinguished  from  the  thiosulphates  in  that  they  evolve  S02  when  heated  with 
HC1,  without  depositing  sulphur. 

138.  Trithionic  acid  (H2S306)  is  also  a  practically  unimportant  acid.     It  is  pre- 
pared from  the  potassium  trithionate  which  is  formed  by  boiling  a  strong  solution 
of    potassium    bisulphite   with   sulphur    until    the  solution  becomes    colourless, 
and  filtering  the   hot   solution  from    any   undissolved    sulphur;  6KHS03  +  S  = 
2K2S306  +  K2S03  +  3H20.     The  solution  deposits  potassium  trithionate  in  prismatic 
crystals.     By  dissolving  these  in  water,  and  decomposing  the  solution  with  per- 
chloric acid,  the  potassium  is  precipitated  as  perchlorate,  and  a  solution  of  trithi- 
onic  acid  is  produced,  from  which  the  acid  has  been  obtained  in  crystals.     It  is, 
however,  very  unstable,  being;  easily  resolved  into  sulphur  dioxide,  sulphuric  acid, 
and  free  sulphur  ;  H2S306  =  H2S04  +  S02  +  S. 

139.  Tetrathionic  acid  (H2S406)  is  rather  more  stable  than  the  preceding  acid, 


238  CARBON   BISULPHIDE. 

though  equally  devoid  of  practical  importance.  It  is  formed  when  barium  thio- 
sulphate,  suspended  in  a  little  water,  is  treated  with  iodine,  when  the  tetrathionate 
is  obtained  in  crystals;  2(BaS.203)  +  I2  =  BaI2  +  BaS406.  (Compare  the  action  of 
iodine  on  sodium  thiosulphate,  p.  237.)  By  exactly  precipitating  the  barium  from 
a  solution  of  BaS406  by  dilute  H2S04,  a  solution  of  tetrathionic  acid  may  be 
obtained.  When  boiled,  it  is  decomposed  into  sulphuric  acid,  sulphur  dioxide,  and 
free  sulphur  ;  HaS4O6=H8SO4+SOa-tS^. 

When  solution  of  ferric  chloride  is  added  to  sodium  thiosulphate,  a  fine  purple 
colour  is  at  first  produced,  which  speedily  vanishes,  leaving  a  colourless  solution. 
The  purple  colour  appears  to  be  due  to  the  formation  of  the  ferric  thiosulphate- 
which  speedily  decomposes,  the  ultimate  result  being  expressed  by  the  equation 
F&2C16  +  2(Na2S203)  =  Na.jS406  +  2FeCl2  +  2NaCl. 

140.  Pentathionic  acid  (H2S506)  possesses  some  interest  as  resulting  from  the 
action  of  hydrogen  sulphide  upon  sulphurous  acid,  when  much  sulphur  is  deposited, 
and  pentathionic  acid  remains   in   solution;  5H2S  +  5H2S03  =  H2S506  +  9H20  +  S5. 
Besides  pentathionic  acid,  a  colliodal  form  of  sulphur,  sulphuric  acid,  tetrathionic 
acid  and  hexathionic  acid  (?)  are  found  in  the  solution.     To  obtain  a  concentrated 
solution  of  the  acid,  H2S  and  S02  are  passed  alternately  through  the  same  portion,, 
of  water  until  a  large  deposition  of  sulphur  has  occurred.     This  is  allowed  some 
hours  to  settle  ;  the  clear  liquid  poured  off  and  the   solution   concentrated  by 
evaporation,  first  over  a  water-bath,  and  finally,  in  vacua,  over  oil  of  vitriol ;  for  a 
concentrated  solution  of  pentathionic  acid  is  decomposed  by  heat  into  H2S04  and 
S02.  with  separation  of  sulphur  ;  H2S506-H2S04-t-S02+S3. 

BISULPHIDE  OF  CARBON,  OR  CARBON  BISULPHIDE. 

CS2  =  76  parts  by  weight. 

141.  This  very  important  compound  (also  called  bisulphuret  of  carbon) 
is  found  in  small  quantity  among  the  products  of  destructive  distilla- 
tion of  coal,  and  is  very  largely  manufactured  for  use  as  a  solvent  for 
sulphur,  phosphorus,  caoutchouc,  fatty  matters,  &c.     It  is  one  of  the 
few  compounds  of  carbon  which  can  be  obtained   by  the  direct  union  of 

their  elements,  and  is 
^^•^  1 1  '  .  i  "i  prepared  by  passing 
vapour  of  sulphur 
over  charcoal  heated 
to  redness.  The  com- 
bination is  probably 
endothermic. 


In  small  quantity  car- 
bon disulphide  is  easily 

Fig.  179.  prepared    in    a    tube    of 

German   glass    (combus- 
tion-tube) about  two  feet  long  and  half  an  inch  in  diameter  (Fig.  179). 

This  tube  is  closed  at  one  end,  and  a  few  fragments  of  sulphur  dropped  into  it 
so  as  to  occupy  two  or  three  inches.  The  rest  of  the  tube  is  filled  up  with  small 
fragments  of  recently  calcined  wood  charcoal.  The  tube  is  placed  in  a  combustion- 
furnace,  and  its  open  end  connected  by  a  perforated  cork  with  a  glass  tube,  which 
dips  just  below  the  surface  of  water  contained  in  a  bottle  placed  in  a  vessel,  of  very 
cold  water.  The  part  of  the  tube  which  contains  the  charcoal  is  heated  first,  and 
when  it  is  red-hot  the  end  containing  the  sulphur  is  heated,  so  that  the  vapour  of 
sulphur  maybe  slowly  passed  over  the  red-hot  charcoal.  The  disulphide  being- 
insoluble  in  water,  and  much  heavier  (sp.  gr.  1.2  at  o°  C.),  is  deposited  beneath  the 
water  in  the  receiver.  To  purify  it  from  the  water  and  the  excess  of  sulphur  which 
is  deposited  with  it,  the  water  is  carefully  drawn  off  with  a  small  siphon,  the  CS2 
transferred  to  a  flask,  and  a  few  fragments  of  calcium  chloride  dropped  into  it  to 
absorb  the  water.  A  condenser  is  attached  to  the  flask  (Fig.  180)  by  a  perforated 
cork,  and  the  flask  is  gently  heated  in  a  water-bath,  when  the  CS2  is  distilled  over 
as  a  perfectly  colourless  liquid.  The  inflammability  of  the  disulphide  renders 
great  care  necessary. 


CARBON  BISULPHIDE.  239 

On  a  large  scale,  a  fire-clay  or  cast-iron  retort  is  filled  with  fragments 
of  charcoal  and  heated  to  redness,  pieces  of  sulphur  being  occasionally 
dropped  in  through  an  earthenware  tube  passing  to  the  bottom  of  the 
retort.  When  very  large  quantities  are  made,  coke  is  employed,  and 
the  vapour  of  sulphur  is  obtained  from 
iron  pyrites.  The  carbon  disulphide  is 
possessed  of  some  very  remarkable  pro- 
perties :  it  is  a  very  brilliant  liquid,  the 
light  passing  through  which  at  certain 
angles  is  partly  decomposed  into  its  com- 
ponent coloured  rays  before  it  reaches 
the  eye.  These  properties  are  dependent 
upon  its  high  refractive  and  dispersive 
powers,  which  are  turned  to  great  ad- 
vantage in  optical  experiments,  especially 
in  spectrum  analysis,  where  the  rays 
emanating  from  a  coloured  flame  are 
analysed  by  passing  them  through  a  Fig-.  180. 

prismatic  bottle  filled  with  carbon  disul- 
phide. It  is  also  highly  diathermic,  that  is,  it  allows  rays  of  heat  to 
pass  through  it  with  comparatively  little  loss,  so  that  if  it  be  rendered 
opaque  to  light  by  dissolving  iodine  in  it,  the  rays  of  light  emanating 
from  a  luminous  object  may  be  arrested,  whilst  the  calorific  rays  are 
allowed  to  pass.  Carbon  disulphide  is  a  very  volatile  liquid,  readily 
assuming  the  form  of  vapour  at  the  ordinary  temperature,  and  boiling 
at  46°  C.  Its  vapour,  when  diluted  with  air,  has  a  very  disgusting  and 
exaggerated  odour  of  sulphuretted  hydrogen,  but  the  smell  at  the  mouth 
of  the  bottle  is  ethereal  and  not  unpleasant  if  the  disulphide  has  been 
carefully  purified. 

The  rapid  evaporation  of  carbon  disulphide  is,  of  course,  productive  of  great 
cold.  If  a  few  drops  be  placed  in  a  watch-glass  and  blown  upon,  they  soon  pass  off 
in  vapour,  and  the  temperature  of  the  glass  is  so  reduced  that  some  of  the  disul- 
phide is  frozen  ;  *  this  melts  when  the  glass  is  placed  in  the  palm  of  the  hand.  If 
a  glass  plate  be  covered  with  water,  a  watch-glass  containing  carbon  disulphide 
placed  on  it,  and  evaporation  promoted  by  blowing  through  a  tube,  the  watch- 
glass  will  be  frozen  on  to  the  plate,  so  that  the  latter  may  be  lifted  up  by  it. 

The  carbon  disulphide  is  exceedingly  inflammable  ;  it  takes  fire  at  a 
temperature  far  below  that  required  to  inflame  ordinary  combustible 
bodies,  and  burns  with  a  bright  blue  flame,  producing  carbon  dioxide 
and  sulphur  dioxide  (CS2  +  O6  =  CO,  +  2S02),  and  having  a  great  tendency 
to  deposit  sulphur  unless  the  supply  of  air  be  very  good. 

If  a  little  carbon  disulphide  be  dropped  into  a  small  beaker,  it  may  be  inflamed 
by  holding  in  its  vapour  a  test-tube  containing  oil  heated  to  about  300°  F.  (149°  C.), 
which  will.be  found  incapable  of  firing  gunpowder  or  of  inflaming  any  ordinary 
combustible  substance. 

The  abundance  of  sulphur  separated  in  the  flame  of  carbon  disulphide  enables 
it  to  burn  iron  by  converting  it  into  sulphide.  If  some  carbon  disulphide  be 
boiled  in  a  test-tube  provided  with  a  piece  of  glass  tube  from  which  the  vapour 
may  be  burnt,  and  a  piece  of  thin  iron  wire  be  held  in  the  flame  (Fig.  181),  it  will 
burn  with  vivid  scintillation,  the  fusible  ferrous  sulphide  dropping  off. 

Carbon  disulphide  is  endothermic  (p.  96),  76  grams  of  the  liquid  absorbing 
19,610  gram  units  in  its  formation  ;  like  most  other  endothermic  gases  (C2H2,  C2N2, 
N20,  &c.),  it  may  be  suddenly  decomposed  into  its  elements  by  a  violent  shock.  This 

*  This  solid  matter  is  probably  a  cryohydrate  of  CS2.     Dry  CS2  melts  at  -  113°  C. 


240  THIOCARBONATES. 

experiment  is  performed  by  detonating  0.05  gram  of  mercuric  fulminate,  by  means 
of  an  electric  spark,  in  an  inclined  tube  open  at  one  end,  in  which  a  paper  satu- 
rated with  carbon  disulphide  has  been  suspended.  After  the  explosion  the  carbon 

and  sulphur  are  seen  deposited  on  the  walls  of 

the  tube. 

The  vapour  of  carbon  disulphide  acts 
very  injuriously  if  breathed  for  any 
length  of  time,  producing  symptoms 
somewhat  resembling  those  caused  by 
sulphuretted  hydrogen.  Its  poisonous 
properties  have  been  turned  to  account 
for  killing  insects  in  grain  without 
injuring  the  grain. 

The  chief  application  of  carbon  disul- 
phide depends  upon  its  power  of  dissolv- 
ing the  oils  and  fats.  After  as  much 
oil  as  possible  has  been  extracted  from 
seeds  and  fruits  by  pressure,  a  fresh 
quantity  is  obtained  by  treating  the 
rig.  181.  pressed  cake  with  carbon  disulphide, 

which  is  afterwards  recovered  by  dis- 
tillation from  the  oil.  In  Algiers  it  is  employed  for  extracting  the 
essential  oils  in  which  reside  the  perfumes  of  roses,  jasmine,  lavender,  &c. 
Carbon  disulphide  has  often  been  made  a  starting-point  in  the 
attempts  to  produce  organic  compounds  by  synthesis.  It  may  be 
employed  in  the  formation  of  the  hydrocarbons  which  are  usually  derived 
from  organic  sources ;  for  if  it  be  mixed  with  hydrogen  sulphide  (by 
passing  that  gas  through  a  bottle  containing  the  disulphide  gently 
warmed),  and  passed  over  copper-turnings  heated  to  redness  in  a  porcelain 
tube,  olefiant  gas  will  be  produced;  2CS2  +  2H2S  +  Cu6  =  6CuS  +  C2H4. 
Marsh  gas  may  be  obtained  in  the  same  way.  When  passed  through  a 
red  hot  tube  the  vapour  of  CS2  is  decomposed  into  C  and  S. 

The  action  of  carbon  disulphide  upon  ammonia  is  practically  impor- 
tant for  the  easy  production  of  ammonium  sulphocyanide,  which  is 
formed  when  the  disulphide  is  dissolved  in  alcohol,  and  acted  on  by 
ammonia  with  the  aid  of  heat ;  CS2  +  2NH3  =  H2S  +  NH4CNS. 

Carbon  disulphide  is  often  called  sulphocarbonic  or  thiocarbonic 
anhydride  to  emphasise  its  analogy  to  carbonic  anhydride  ;  it  combines 
with  some  of  the  sulphur-bases  to  form  sulphocarbonates  or  thiocarbonates, 
which  correspond  with  the  carbonates,  containing  sulphur  in  place  of 
oxygen.  Thus,  when  a  solution  of  potassium  sulphide  is  mixed  with  an 
excess  of  carbon  disulphide,  potassium  thiocarbonate  is  obtained  in 
orange-yellow  crystals.  Even  the  hydrogen  compound  corresponding  in 
composition  with  the  unknown  H2C03  may  be  obtained  as  a  yellow  oily 
liquid  by  decomposing  potassium  thiocarbonate  with  hydrochloric  acid  ; 
K9CS3  +  2HC1  =  H2CS3  +  2KC1.  Potassium  thiocarbonate  is  applied  for 
the  destruction  of  the  phylloxera  insect  which  infests  vines.  As  would 
be  expected,  the  thiocarbonates,  when  boiled  with  water,  exchange  their 
sulphur  for  oxygen,  becoming  carbonates;  K2CS3  +  3H20  =  K2C03  +  3H2S. 

Small  quantities  of  CS2  may  be  identified  by  dissolving  in  alcoholic  potash  and 
adding  cupric  sulphate,  which  gives  a  yellow  precipitate  of  cuprous  xantliate, 
Cu2S.CS.OC2H5. 


SULPHUR  CHLORIDE.  241 

The  carbon  disulphide  vapour  in  coal  gas  is  one  of  the  most  injurious  of  the 
impurities,  and  one  of  the  most  difficult  to  remove  with  economy. 

It  is  especially  injurious,  because,  when  burning  in  the  presence  of  aqueous 
vapour,  a  part  of  its  sulphur  is  converted  into  sulphuric  acid,  the  corrosive  effects 
of  which  are  so  damaging.  Several  processes  have  been  devised  for  its  removal, 
but  that  which  is  now  almost  universally  adopted  consists  in  absorbing  it  in  lime 
which  has  already  become  saturated  with  H2S  in  the  course  of  the  purification  of 
the  gas,  and  thus  contains  calcium  hydrosulphide,  Ca(SH)2.  This  compound  com- 
bines with  the  CS2  to  form  calcium  thiocarbonate,  Ca(SH)2+CS2=:CaCS3  +  H2S. 

Carbon  monoswlphide,  CS,  is  deposited  when  CS2  is  exposed  to  sunlight,  or  left 
for  some  weeks  in  contact  with  iron  wire  ;  2CS2  +  Fe  =  FeS2  +  2CS.  The  FeS2  is 
dissolved  out  by  HC1,  leaving  the  CS  as  a  red-brown  powder,  of  sp.  gr.  1.66, 
insoluble  in  alcohol  and  benzene,  slightly  soluble  in  hot  ether  and  CS2.  It  is 
soluble  in  boiling  nitric  acid  and  in  boiling  strong  potash.  At  about  200°  C.  it 
is  decomposed  into  carbon,  sulphur,  and  a  little  disulphide.  It  is  converted  into 
the  latter  by  heating  with  excess  of  sulphur. 

Tricarbon  disulphide,  C3S2,  has  been  obtained  by  boiling  CS2in  a  flask,  the  upper 
portion  of  which  contains  an  electric  arc,  and  condensing  the  vapour,  after  it  has 
been  thus  heated,  so  that  it  may  fall  back  into  the  flask.  It  is  a  deep  red  liquid 
(sp.  gr.  1.27)  which  has  a  very  irritating  odour.  When  heated  it  is  changed  to  a 
black  mass  of  the  same  percentage  composition. 

Cartoon  Oxysulphide  (COS  =  60  parts  by  weight  =  2  volumes).  —  This  com- 
pound, which  may  be  regarded  as  C02  in  which  S  has  been  substituted  for  0,  is 
formed  when  a  mixture  of  carbonic  oxide  with  sulphur  vapour  is  acted  on  by 
electric  sparks,  or  passed  through  a  red-hot  porcelain  tube  ;  also  when  carbon 
disulphide  vapour  is  passed  over  white-hot  clay,  and  when  CdS  is  heated  in 
COC12. 

It  is  easily  prepared  by  gently  heating  potassium  sulphocyanide,  KCNS,  with 
oil  of  vitriol  diluted  with  four-fifths  of  its  volume  of  water,  and  collecting  the  gas 
over  mercury.  The  action  of  the  sulphuric  acid  upon  the  sulphocyanide  produces 
hydrosulphocyanic  acid  ;  KCNS  +  H2S04  =  HCNS  +  KHS04  ;  which  is  then  decom- 
posed by  the  water  in  the  presence  of  the  excess  of  sulphuric  acid,  into  COS  and 
NH3,  the  latter  combining  with  the  sulphuric  acid  ;  HCNS  +  H20  =  NH3  +  COS.  The 
gas  has  a  peculiar,  disagreeable  odour,  recalling  that  of  carbon  disulphide  ;  it  is  more 
than  twice  as  heavy  as  air  (sp.  gr.  2.  n),  and  is  very  inflammable,  burning  with  a 
blue  flame,  and  yielding  C02  and  S02.  Potash  absorbs  and  decomposes  it,  yielding 
carbonate  and  sulphide  of  potassium;  COS  +  4KOH  =  K2S  +  K2C03  +  2H20.  Am- 
monia absorbs  it  freely,  and,  on  evaporation,  evolves  H2S  and  deposits  crystals  of 
urea  ;  COS  +  2NH3  =  H2S  +  CO^H^. 

141.  Nitrogen  tetrasulphide  (N4S4)  is  produced  when  chloride  of  sulphur,  dissolved 
in  benzene,  is  acted  on  by  gaseous  ammonia,  i6NH3  +  6S2Cl2=  I2NH4C1  +  N4S4+S8. 
The  precipitate  obtained  is  washed  with  water  to  remove  NH4C1  and  is  then 
fractionally  crystallised  from  CS2  to  separate  the  N4S4  and  S,  the  latter  being  the 
more  soluble.  This  substance  melts  at  178°  C.  and  is  remarkable  for  its  sparing 
solubility,  its  irritating  odour,  and  its  explosibility  when  struck  or  sharply  heated, 
its  elements  being  held  together  by  a  very  feeble  attraction. 

Nitrogen  pentasulphide,  N2S5,  is  a  red  oil  obtained  by  heating  the  tetrasulphide, 
dissolved  in  CS2,  in  a  sealed  tube  at  100°  C.,  distilling  the  CS2,  and  extracting 
the  residue  with  ether  which  leaves  the  N2S5  on  evaporation.  Its  sp.  gr.  is  1.9  and 
it  melts  at  10°  C.  It  resembles  iodine  in  odour  and  burns  the  skin. 

142.  Chlorides  of  Sulphur.  —  The  subchloride,  or  sulphur  mono- 
chloride  (S2C12  =  135  parts  by  weight),  is  the  most  important  of  these, 
since  it  is  employed  in  the  process  of  vulcanising  caoutchouc.  It  is  very 
easily  prepared  by  passing  dry  chlorine  over  sulphur  very  gently  heated 
in  a  retort  (Fig.  182);  the  sulphur  quickly  melts,  and  the  sulphur  mono- 
chloride  distils  over  into  the  receiver  as  a  yellow  volatile  liquid,  boiling 
at  280°  F.  (138°  0.),  which  has  a  most  peculiar  odour.  It  fumes  strongly 
in  air,  the  moisture  decomposing  it,  forming  hydrochloric  and  sulphurous 
acids  and  causing  a  deposit  of  sulphur  upon  the  neck  of  the  bottle  ; 


9C12  +  3HOH  =  4H01  +  SO(OH)2  +  S3. 
When  poured  into  water  it  sinks  (sp.gr.  1.68)  and  slowly  decomposes  ; 

Q 


242  SELENIUM. 

the  solution  contains,  beside  hydrochloric  arid  sulphurous  acids,  some  of 
the  acids  containing  a  larger  proportion  of  sulphur.  If  phosphorus  dis- 
solved in  carbon  disulphide  be  mixed  with  sulphur  monochloride,  the 
liquid  will  take  fire  on  addition  of  ammonia.  The  specific  gravity  of 
the  vapour  of  S2C12  is  4.7,  showing  that  it  is  68  times  as  heavy  as- 
hydrogen  and  therefore  cannot  have  the  formula  SCI. 


Fig.  182. — Preparation  of  sulphur  monochloride. 

'iur  dlchloride  (SC12)  is  a  far  less  stable  compound  than  the  preceding 
chloride,  from  which  it  is  obtained  by  the  action  of  an  excess  of  chlorine.  It  is  a 
dark-red  fuming  liquid,  easily  resolved,  even  by  sunlight,  into  free  chlorine  and 
sulphur  monochloride.  Sulphur  tetrachlorlde  (SC14)  has  also  been  obtained. 

Corresponding  bromides  and  iodides  of  sulphur  are  known.  Of  these  the 
di-iodide  (SI2)  is  a  crystalline  unstable  substance,  produced  by  the  direct  union  of 
its  elements,  and  occasionally  employed  in  veterinary  medicine  under  the  name 
of  black  sulphur. 

SELENIUM. 
80  =  78.5  parts  by  weight. 

143.  Selenium  (SeX^?;,  the  moon)  is  a  rare  element,  very  closely  allied  to  sulphur 
in  its  natural  history,  physical  characters,  and  chemical  relations  to  other  bodies. 
It  is  found  sparingly  in  the  free  state  associated  with  some  varieties  of  native 
sulphur,  but  more  commonly  in  combination  with  metals,  forming  selenides,  which 
are  found  together  with  the  sulphides.  The  iron  pyrites  of  Fahlun,  in  Sweden, 
is  especially  remarkable  for  the  presence  of  selenium,  and  was  the  source  whence 
this  element  was  first  obtained.  The  Fahlun  pyrites  is  employed  for  the  manu- 
facture of  oil  of  vitriol,  and  in  the  leaden  chambers  a  reddish-brown  deposit  is 
found,  which  was  analysed  by  Berzelius  in  1817,  and  found  to  contain  the  new 
element. 

In  order  to  extract  selenium  from  the  seleniferous  deposit  of  the  vitriol  works 
this  may  be  boiled  with  sulphuric  acid  diluted  with  an  equal  volume  of  water,  and 
nitric  acid  added  in  small  portions  until  the  oxidation  is  completed,  when  no 
more  red  fumes  will  escape.  The  solution,  containing  selenious  and  selenic  acids, 
is  largely  diluted  with  water,  filtered  from  the  undissolved  matters,  mixed  with 
about  one-fourth  of  its  bulk  of  hydrochloric  acid,  and  somewhat  concentrated  by 
evaporation,  when  the  hydrochloric  acid  reduces  the  selenic  to  selenious  acid — 
H2Se04  +  2HC1  =  H2Se03  +  H2O  +  C12. 

A  current  of  sulphurous  acid  gas  is  now  passed  through  the  solution,  when  the 
selenium  is  precipitated  in  fine  red  flakes,  which  collect  into  a  dense  black  mass 
when  the  liquid  is  gently  heated  ;  H2Se03  +  H20  +  2S02=:2H2S04  +  Se. 

The  proportion  of  selenium  in  the  deposit  from  the  leaden  chambers  is  variable. 
The  author  has  obtained  3  per  cent,  by  this  process. 


SELENIUM. 


243- 


Like  sulphur,  selenium  exists  in  an  amorphous  and  a  crystalline  form,  and  more 
than  one  of  the  latter  appear  to  exist.  Amorphous  selenium  is  the  red  precipitate 
formed  by  precipitating  the  element,  either  as  described  above  or  by  adding  an 
acid  to  a  solution  of  it  in  potassium  cyanide.  When  kept  at  100°  C.  for  some  time 
this  form  of  selenium  suddenly  changes  into  the  grey  crystalline  variety  with 
much  evolution  of  heat.  Amorphous  selenium  has  sp.  gr.  4.26  and  is  soluble 
in  CS2  ;  it  becomes  plastic  a  little  above  100°  C.  and  if  melted  and  cooled  quickly 
it  forms  a  vitreous  mass  (sp.  gr.  4.28),  still  amorphous,  but  if  carefully  cooled  so 
that  it  may  superfuse  it  solidifies  to  the  grey  crystalline  form  (sp.  gr.  4.8)  ;  but 
when  less  carefully  cooled  it  solidifies  to  a  mass  of  red  monoclinic  prisms 
isomorphous  with  monoclinic  sulphur  and  of  sp.  gr.  4.47.  These  crystalline  forms 
are  insoluble  in  CS,2. 

Amorphous  and  monoclinic  selenium  are  very  poor  conductors  of  electricity,  but 
the  grey  crystalline  form  is  a  fair  conductor  and  a  better  one  in  light  than  in 
darkness,  a  property  which  is  applied  in  apparatus  for  seeing  at  a  distance. 

Selenium  boils  at  680°  C.  and  its  vapour  shows  much  the  same  variation  in 
density  as  that  exhibited  by  sulphur. 

Selenium  is  less  combustible  than  sulphur  ;  when  heated  in  air  it  burns  with  a 
blue  flame,  and  emits  a  peculiar  odour  like  that  of  putrid  horse-radish,  which 
appears  to  be  due  to  the  formation  of  a  little  selenietted  hydrogen  from  the 
moisture  of  the  air.  The  odour  serves  for  the  detection  of  selenium  compounds 
when  they  are  heated  on  charcoal.  When  heated  with  oil  of  vitriol,  selenium 
forms  a  green  solution  which  deposits  the  selenium  again  when  poured  into  water. 

Selenium  dioxide  (Se02),  corresponding  with  sulphur  dioxide,  is  the  product  of 
combustion  of  selenium  in  oxygen.  It  is  best  obtained  by  dissolving  selenium  in 
boiling  nitric  acid  (which  would  convert  sulphur  into  sulphuric  acid),  and  evapo- 
rating to  dryness,  when  the  selenium  dioxide  remains  as  a  white  solid  which 
sublimes  in  needle-like  crystals  when  heated.  When  dissolved  in  boiling  water 
it  yields  crystalline  selenious  acid,  SeO(OH)2. 

Selenle  acid  (H2Se04  or  SeO2(OH)2).— Potassium  selenate  is  formed  when  selenium 
is  oxidised  by  fused  nitre  ;  2KN03+Se  =  K2Se04  +  2NO.  By  dissolving  the  potas- 
sium selenate  in  water,  and  adding  lead  nitrate,  a  precipitate  of  lead  selenate 
(PbSe04)  is  obtained,  and  if  this  be  suspended  in  water  and  decomposed  by  passing 
hydrosulphuric  acid  gas,  lead  will  be  removed  as  insoluble  sulphide,  and  a  solution 
of  selenic  acid  will  be  obtained  :  PbSe04  +  H2S  =  H2Se04  +  PbS.  This  solution  may 
be  evaporated  till  it  has  a  sp.  gr.  of  2.6  (when  it  very  closely  resembles  oil  of 
vitriol)  and  heated  in  a  vacuum  at  180°  C.  so  long  as  any  distils  over  ;  the  residue 
will  crystallise  on  cooling.  The  crystals  (sp.  gr.  2.95)  melt  at  58°  C.  and  are 
deliquescent  ;-the  hydrate,  H2Se04.H20,  melts  at  25°  C.  It  is  decomposed  at  260°  C. 
into  H205  Se02,  and  0.  It  oxidises  the  metals  as  oil  of  vitriol  does,  and  even  dis- 
solves gold.  The  selenates  closely  resemble  the  sulphates,  but  they  are  decomposed 
when  heated  with  hydrochloric  acid,  chlorine  being  evolved  and  selenious  acid 
produced. 

Hydroselenicacid,  or  selenietted  hydrogen  (H2Se),  is  the  analogue  of  sulphuretted 
hydrogen,  and  is  produced  by  a  similar  process.  It  is  even  more  offensive  and 
poisonous  than  that  gas,  and  acts  in  a  similar  way  upon  metallic  solutions,  precipi- 
tating the  selenides. 

There  are  two  chlorides  of  selenium :  the  monochloride,  Se2Cl2,  a  brown  volatile 
liquid  corresponding  with  sulphur  monochloride  ;  and  the  tetrachloride,  SeCl4,  a 
white  crystalline  solid.  SeOCl2  is  also  known. 

Notwithstanding  the  resemblance  between  the  two  elements,  sulphides  oj 
selenium  are  known,  probably  SeS2  and  SeS3.  The  former  is  obtained  as  a  yellow 
precipitate  when  hydrogen  sulphide  is  passed  into  solution  of  selenious  acid. 

TELLURIUM. 

Te=  126  parts  by  weight. 

144.  Tellurium  (from  tellus,  the  earth)  is  connected  with  selenium  by  analogies 
stronger  than  those  which  connect  that  element  with  sulphur.  It  is  even  less 
frequently  met  with  than  selenium,  being  found  chiefly  in  certain  Transylvanian 
gold  ores.  It  occasionally  occurs  in  an  uncombined  form,  but  more  frequently  in 
combination  with  metals.  It  has  recently  been  found  in  Colorado,  masses  of 
native  tellurium  up  to  12  kilos,  in  weight  having  been  met  with  ;  also  coloradoite, 


244  TELLURIUM. 

•or  murcuric  telluride,  HgTe.  Bismuth  telluride,  or  tetradymite,  Bi2Te3,  has  been 
found  in  California,  and  lead  telluride,  or  altaite,  in  North  Carolina.  Foliated  or 
.graphic  tellurium,  or  sylvanite,  is  a  black  material  containing  the  tellurides  of 
•silver  and  gold.  Arsenical  pyrites  sometimes  contains  tellurium,  apparently  as 
TeS2. 

Tellurium  is  extracted  from  the  foliated  ore  by  a  process  similar  to  that  for 
'obtaining  selenium.  From  bismuth  telluride  it  is  procured  by  strongly  heating  the 
•ore  with  a  mixture  of  potassium  carbonate  and  charcoal,  when  potassium  telluride 
is  formed,  which  dissolves  in  water  to  a  purple-red  solution,  wherefrom  tellurium 
is  deposited  on  exposure  to  air  ;  K2Te  -\-  0  +  H20  =  2KOH  +  Te.  It  is  purified  by 
sublimation  in  hydrogen  when  it  is  deposited  as  white  lustrous  hexagonal  rhornbo- 
liedra,  isomorphous  with  S  and  Se. 

Considerable  quantities  of  tellurium  are  now  obtainable  from  the  sludge 
deposited  in  the  electrolytic  cells  in  which  copper  is  refined,  the  crude  metal 
having  collected  the  tellurium  contained  in  the  original  ore. 

Tellurium  much  more  nearly  resembles  the  metals  than  the  non-metals  in  its 
physical  properties  (sp.  gr.  6.2),  and  is  on  that  account  often  classed  among  the 
former,  but  it  is  not  capable  of  forming  a  true  basic  oxide.  In  appearance  it  is 
very  similar  to  bismuth  (with  which  it  is  so  frequently  found),  having  a  pinkish 
metallic  lustre,  and  being,  like  that  metal,  crystalline  and  brittle.  When  precipi- 
tated it  is  a  black  amorphous  powder,  which  becomes  crystalline,  with  evolution  of 
much  heat,  when  warmed.  It  fuses  at  455°  C.  and  boils,  yielding  a  yellow  vapour, 
of  normal  vapour  density,  at  1390°  C.  When  heated  in  air  it  burns  with  a  blue 
flame  edged  with  green,  and  emits  fumes  of  tellurium  dioxide  (Te02)  and  a  peculiar 
odour. 

Like  selenium,  tellurium  is  dissolved  by  strong  sulphuric  acid,  yielding  a  purple- 
red  solution,  from  which  water  precipitates  it  unchanged. 

The  oxides  of  tellurium  correspond  in  composition  with  those  of  sulphur.  Tellu- 
rous  acid  (H2Te03)  is  precipitated  when  a  solution  of  tellurium  in  dilute  nitric  acid 
is  poured  into  water.  If  the  nitric  solution  is  boiled,  a  crystalline  precipitate  of 
tellurous  anhydride,  Te02,  is  obtained,  but  when  the  solution  is  evaporated  a  well 
crystallised  basic  nitrate,  Te2O3(OH)N03,  separates.  Unlike  selenious  acid  tellurous 
acid  is  sparingly  soluble  in  water.  The  anhydride  is  easily  fusible,  forming  a 
yellow  glass,  which  becomes  white  on  cooling,  and  may  be  sublimed  unchanged. 
Tellurous  acid  is  rather  a  feeble  acid,  and  with  some  of  the  stronger  acids  the 
anhydride  forms  soluble  compounds  in  which  it  takes  the  part  of  a  very  feeble  base. 

Telluric  acid  (H2Te04)  is  also  a  feeble  acid  obtained  by  oxidising  tellurium  with 
nitre,  precipitating  the  potassium  tellurate  with  barium  chloride,  and  decomposing 
the  barium  tellurate  with  sulphuric  acid.  On  evaporating  the  solution,  crystals  of 
telluric  acid  (H2Te04.2H20)  are  obtained,  which  become  H2Te04  at  a  moderate  heat, 
and  when  heated  nearly  to  redness  are  converted  into  an  orange-yellow  powder, 
which  is  the  anhydride,  Te03.  In  this  state  it  is  insoluble  in  acids  and  alkalies. 
When  strongly  heated  it  evolves  oxygen,  and  becomes  tellurous  anhydride.  The 
tellurates  are  unstable  salts  which  are  converted  into  tellurites  when  heated.  Solu- 
tions of  alkali  tellurates  yield  a  precipitate  of  tellurium  when  boiled  with  alkali 
carbonates  and  glucose. 

Telluretted  hydrogen  or  hydrotelluric  acid  (H2Te)  exhibits  in  the  strongest 
manner  the  chemical  analogy  of  tellurium  with  selenium  and  sulphur.  It  is  a  gas 
of  dreadful  odour  and  similar  to  H2S  in  most  of  its  properties.  When  its  aqueous 
solution  is  exposed  to  the  air,  it  yields  a  brown  deposit  of  tellurium.  When  passed 
into  metallic  solutions  it  precipitates  the  tellurides.  The  gas  is  prepared  by  decom- 
posing telluride  of  zinc  with  hydrochloric  acid. 

The  most  characteristic  property  of  tellurium  compounds  is  that  of  furnishing 
the  purple  solution  of  potassium  telluride  when  fused  with  potassium  carbonate 
and  charcoal,  and  treated  with  water  ;  in  the  total  absence  of  oxygen,  however, 
the  solution  is  colourless.  Two  solid  chlorides  of  tellurium  have  been  obtained  ; 
TeCl2  is  a  black  solid  with  a  violet-coloured  vapour,  and  is  decomposed  by  water 
into  tellurium  and  TeCl4.  The  latter  may  be  obtained  as  a  white  crystalline  volatile 
solid,  decomposed,  by  much  water,  into  hydrochloric  and  tellurous  acids. 

145.  Review  of  the  sulphur  group  of  elements. — The  three 
divalent  elements — sulphur,  selenium,  and  tellurium — exhibit  a  relation 
of  a  similar  character  to  that  observed  between  the  members  of  the 
chlorine  group,  both  in  their  physical  and  chemical  properties. 


BORIC   ACID. 


245 


Sulphur  is  a  pale  yellow  solid,  easily  fusible  and  volatile,  without  any 
trace  of  metallic  lustre,  and  of  sp.  gr.  2.05,  melting  at  118°  and  boiling 
at  444°  C.  Selenium  is  either  a  red  powder  or  a  lustrous  mass  appearing 
black,  but  transmitting  red  light  through  thin  layers,  of  specific  gravity 
4.8,  melting-point  217°  C.,  and  boiling-point  680°  C.  Tellurium  has  a 
brilliant  metallic  lustre,  sp.  gr.  6.2,  melting-point  455°  C.,  and  boiling- 
point  1390°  C. 

Sulphur  (atomic  weight  32)  has  the  most  powerful  attraction  for 
oxygen,  hydrogen,  and  the  metals.  Selenium  (atomic  weight  79)  ranks 
next  in  the  order  of  chemical  energy.  Tellurium  (atomic  weight  126.5) 
has  a  less  powerful  attraction  for  oxygen,  hydrogen,  and  the  metals, 
than  either  sulphur  or  selenium  has.  This  element  appears  to  stand  on 
neutral  ground  between  the  non-metallic  bodies  and  the  less  electro- 
positive metals. 

BORON. 

B'"=  II  parts  by  weight. 

This  element  resembles  carbon  in  several  respects,  but  is  not  properly 
classed  therewith  because  it  is  of  the  trivalent  type,  while  carbon  is 
tetravalent.  The  element  itself  does  not  possess  much  importance  ;  it 
is  found  only  in  combination  with  oxygen  in  the  mineral  world,  whence 
very  small  quantities  find  their  way  into  some  plants  such  as  the  grape- 
vine and  into  sea-water.  The  oxide  will  be  considered  first. 

Boric  anhydride,  or  Anhydrous  Boric  Acid  (B2O3  =  69.8  parts  by 
weight). — A  saline  substance  called  borax  (Na2B4O7.ioAq)  has  long 
been  used  in  medicine,  in  working  metals,  and  in  making  imitations  of 
precious  stones ;  this  substance  was  originally  imported  from  India  and 
Thibet,  where  it  was  obtained  in  crystals  from  the  waters  of  certain 
lakes,  and  came  into  this  country  under  the  native  name  of  tincal, 
consisting  of  impure  borax,  surrounded  with  a  peculiar  soapy  substance. 
Borax  has  recently  been  found  in  abundance  in  the  bed  of  a  dried-up 
lake  in  the  Sierra  Nevada. 

In  1702,  in  the  course  ot  one  of  those  experiments  to  which,  though 
empirical  in  their  nature,  scientific  chemistry  is  now  so  deeply  indebted, 
Homberg  happened  to  distil  a  mixture  of  borax  and  green  vitriol  (ferrous 
sulphate),  when  he  obtained  a  new  substance  in  pearly  plates,  which  was 
found  useful  in  medicine,  and  received  the  name  of  sedative  salt.  A 
quarter  of  a  century  later  Lemery  found  that  this  substance  might  be 
separated  from  borax  by  employing  sulphuric  acid  instead  of  ferrous 
sulphate,  and  that  it  possessed  acid  properties,  whence  it  was  called 
boracic  acid,  now  abbreviated  to  boric  acid. 

Much  more  recently  this  acid  has  been  obtained  in  a  free  state  from 
natural  sources,  and  is  now  largely  imported  into  this  country  from  the 
volcanic  districts  in  the  north  of  Italy,  where  it  issues  from  the  earth 
in  the  form  of  vapour,  accompanied  by  violent  jets  of  steam,  which  are 
known  in  the  neighbourhood  as  soffioni.  It  would  appear  easy  enough, 
by  adopting  arrangements  for  the  condensation  of  this  steam,  to  obtain 
the  boric  acid  which  accompanies  it,  but  it  is  found  necessary  to  cause 
the  steam  to  deposit  its  boric  acid  by  passing  it  through  water,  for 
which  purpose  basins  of  brickwork  (lagunes,  Fig.  183)  are  built  up 
around  the  soffioni,  and  are  kept  filled  with  water  from  the  neighbouring 


246 


BOEIC   ACID. 


springs  or  brooks ;  this  water  is  allowed  to  flow  successively  into  the 
different  lagunes,  which  are  built  upon  a  declivity  for  that  purpose,  and 
it  thus  becomes  impregnated  with  about  i  per  cent,  of  boric  acid.  The 
necessity  for  expelling  a  large  proportion  of  this  water,  in  order  to 
obtain  the  boric  acid  in  crystals,  formed  for  a  long  time  a  great  obstacle 
to  the  success  of  this  branch  of  industry  in  a  country  where  fuel  is  very 
expensive.  In  1817,  however,  Larderello  conceived  the  project  of 
evaporating  this  water  by  the  steam-heat  afforded  by  the  soffioni  them- 
selves, and  several  hundred  tons  of  boric  acid  are  now  annually  produced 
in  this  manner.  The  evaporation  is  conducted  in  shallow  leaden  evapo- 
rating pans  (A,  Fig.  183),  under  which  the  steam  from  the  soinoni  is 
conducted  through  the  flues  (F)  constructed  for  that  purpose.  As  the 
demand  for  boric  acid  increased  on  account  of  the  immense  consumption 
of  borax  in  the  porcelain  manufacture,  the  experiment  was  made,  with 
success,  of  boring  into  the  volcanic  strata,  and  thus  producing  artificial 
sofiiom,  yielding  boric  acid. 


Fig.  183. — Boracic  lagune  and  evaporating  pans. 

The  crystals  of  boric  acid,  as  imported  from  these  sources,  contain 
salts  of  ammonia  and  other  impurities.  They  dissolve  in  about  three 
times  their  weight  of  boiling  water,  and  crystallise  on  cooling,  since 
they  require  26  parts  of  cold  water  to  dissolve  them.  These  crystals 
have  the  sp.  gr.  1*435  an(^  are  represented  by  the  formula  3H2O.B2O3 
(or  H3B03,  or  B(OH)3).  If  they  are  sharply  heated  in  a  retort  they 
partly  distil  unchanged,  together  with  the  water  derived  from  the 
decomposition  of  another  part ;  but  if  they  be  not  heated  above  212°  F., 
they  effloresce  and  become  H2O.B2O3.*  When  heated  for  a  long  time  to 
140°  C.  this  becomes  H20. 2 B203," sometimes  written  H2B4O7,  and  called 
pyroboric  acid,  whilst  H2O.B203  is  HB02,  metaboric  acid,  and  the  crystals, 
H3B03,  are  orthoboric  acid.  When  pyroboric  acid  is  heated  further 
the  whole  of  the  water  passes  off,  carrying  with  it  a  little  boric  acid, 
and  the  B203  fuses  to  a  glass,  which  remains  perfectly  transparent  on 
cooling  (vitreous  boric  acid}.  This  is  slowly  volatilised  by  the  continued 
action  of  a  very  high  temperature.  It  dissolves  very  slowly  in  water. 
Boric  acid  is  an  antiseptic,  i.e.,  it  hinders  putrefaction,  and  is  applied, 
either  alone  or  in  combination  with  glycerine,  for  the  preservation  of 
milk,  meat,  and  other  foods.  It  is  also  said  to  kill  grass. 

*  According  to  Hehner,  boric  acid  can  be  completely    volatilised  at  100°  C.  without    at 
any  stage  having  the  composition  H2O.B2OS. 


BORATES. 


247 


A  characteristic  property  of  boric  acid  is  that  of  imparting  a  green 
colour  to  flames.  Its  presence  may  thus  be  detected  in  the  steam 
issuing  from  a  boiling  solution  of  boric  acid  in  water  ;  for  if  a  spirit- 
flame  or  a  piece  of  burning  paper  is  held  in  the  steam,  the  flame  acquires 
a  green  tint,  especially  at  the  edges. 

The  colour  is  more  distinctly  seen  when  the  crystallised  boric  acid  is  heated  on 
platinum  foil  in  a  spirit-flame  or  an  air-gas  flame  ;  and  still  better  when  the 
crystals  are  dissolved  in  boiling  alcohol,  and  the  solution  burnt  on  a  plate.  The 
presence  oi!  boric  acid  in  borax  may  be  ascertained  by  mixing  the  solution  of  borax 
with  strong  sulphuric  acid  to  liberate  the  boric  acid,  and  adding  enough  alcohol  to 
make  the  mixture  burn  ;  or  by  moistening  the  borax  with  glycerine,  when  it  gives 
a  green  flame  in  the  Bunsen  burner.  Another  peculiar  property  of  boric  acid  is  its 
action  upon  turmeric.  If  a  piece  of  turmeric  paper  be  dipped  in  solution  of  boric 
acid  and  dried  at  a  gentle  heat,  it  assumes  a  fine  brown-red  colour,  which  is 
changed  to  green  or  blue  by  potash  or  its  carbonate.  In  applying  this  test  to  borax, 
the  solution  is  slightly  acidified  with  hydrochloric  acid,  to  set  free  the  boric  acidj 
before  dipping  the  paper.  In  the  presence  of  oxalic  acid  the  test  is  more  delicate. 

Bwates. — Boric  acid,  like  carbonic,  must  be  classed  among  the  feeble 
acids.  It  colours  litmus  violet  only,  like  carbonic  acid,  and  does  not 
neutralise  the  action  of  the  alkalies  upon  test-papers.  At  high  tem- 
peratures, fused  boric  anhydride  combines  with  the  alkalies  and 
metallic  oxides  to  form  transparent  glassy  borates,  which  have,  in  many 
cases,  very  brilliant  colours,  and  upon  this  property  depend  the  chief 
uses  of  boric  acid  in  the  arts. 

Unlike  the  silicates,  the  borates  are  comparatively  rare  in  the 
mineral  world.  No  very  familiar  mineral  substance,  except  borax, 
contains  boric  acid.  A  double  borate  of  sodium  and  calcium,  called 
boro-natrocalcite,  Na2B4O7.(CaB4O7)2.i8H20,  is  imported  from  Peru  for 
the  manufacture  of  borax,  and  the  mineral  known  as  boracite  is  a 
magnesium  borate.  The  mineral  tourmaline,  an  aluminium-ferrous 
silicate,  contains  a  considerable  proportion  of  B203,  apparently  sub- 
stituted for  part  of  the  A12O3. 

In  determining  the  proportion  of  base  which  boric  acid  requires  to  form  a  chemi- 
cally neutral  salt,  the  same  difficulties  are  met  with  as  in  the  case  of  silicic  acid 
(p.  280)  ;  but  since  it  is  found  that  69.8  parts  of  boric  anhydride  (the  weight  repre- 
sented by  B203)  displace  54  parts  of  water  (three  molecules)  from  sodium  hydroxide 
and  from  barium  hydroxide,  each  employed  in  excess,  it  would  appear  that  the 
boric  acid  requires  three  molecules  of  an  alkali  fully  to  satisfy  its  acid  character, 
6NaOH  +  B2O3=2Na3B03  +  3H.,O.  Hence,  boric  acid  is  a  tribasic  acid  represented 
by  the  formula  H3BO3,  which  is  the  composition  of  the  crystallised  acid,  but  the 
formula?  of  the  common  borates  cannot  be  made  to  accord  with  this  view.  The 
only  orthoborate  yet  obtained  is  Mg3(BO3)2. 

The  acid  character  of  boron  oxide  (B203)  is  so  feeble  as  compared  with  that  of 
such  anhydrides  as  S03  and  P205,  that  boron  oxide  can  even  behave  as  a  feeble 
base  towards  these  powerful  acid  oxides,  forming  salts  such  as  B203.  P205. 

By  treating  borates  with  H2O2,  or  by  electrolysing  them  as  for  the  production  of 
persulphates  (p.  235),  perborates  such  as  Na3B04  are  obtained.  They  are  unstable 
and  rapidly  lose  oxygen. 

146.  Boron. — It  was  in  the  year  1808  that  Gay-Lussac  and  Thenard 
succeeded,  by  fusing  boric  anhydride  with  potassium,  in  isolating  boron. 
The  element  is  more  easily  prepared  by  fusing  magnesium  with  an 
excess  of  boric  acid  and  treating  the  product  successively  with  alkalies 
and  acids.  The  amorphous  boron  thus  obtained  is  a  maroon-coloured 
powder  of  sp.  gr.  2.45.  It  is  infusible,  burns  with  a  green  flamo  at 
700°  C.,  and  is  a  very  poor  conductor  of  electricity.  This  form  of 


248  BOEON  CHLORIDE. 

boron  is  attacked  by  hot  concentrated  mineral  acids  ;  it  behaves  like 
charcoal  in  its  tendency  to  absorb  gases. 

The  so-called  diamond  of  boron  is  obtained  by  very  strongly  heating 
amorphous  boron  with  aluminium,  extracting  the  aluminium  from  the 
mass  with  hydrochloric  acid,  and  afterwards  separating  the  crystals  of 
mixed  boron  and  aluminium  from  those  of  boron  by  boiling  with  nitric 
acid.  These  crystals  are  brilliant  transparent  octahedra  (sp.  gr.  2.68), 
which  are  sometimes  nearly  colourless,  and  resemble  the  diamond  in 
their  power  of  refracting  light,  and  in  their  hardness,  which  is  so  great 
that  they  will  scratch  rubies,  and  will  even  wear  away  the  surface  of 
the  diamond.*  This  form  of  boron  cannot  be  attacked  by  any  acid, 
but  is  dissolved  by  fused  alkalies.  It  only  undergoes  superficial  con- 
version into  boric  anhydride  when  heated  to  whiteness  in  oxygen. 

Boron  forms  a  compound  with  hydrogen  which  has  never  been 
obtained  free  from  admixed  hydrogen,  but  probably  has  the  formula 
BH3  ;  it  is  an  inflammable  gas,  burning  with  a  green  flame,  and  is 
obtained  by  heating  fused  boric  anhydride  with  magnesium  and  treating 
the  mass  with  hydrochloric  acid.  Boron  shows  greater  disposition  to 
combine  with  nitrogen  than  is  manifested  by  most  other  elements.  It 
absorbs  nitrogen  readily  when  heated  to  redness,  forming  a  white  in- 
fusible insoluble  powder,  the  boron  nitride  (BN). 

Boron  nitride  is  also  obtained  by  heating  to  redness  anhydrous  borax 
with  twice  its  weight  of  ammonium  chloride  and  extracting  with  dilute 
HC1  which  leaves  the  nitride  undissolved.  When  heated  in  steam  it 
yields  boric  acid  and  ammonia;  BN  +  3H2O  =  H3B03  +  NH3.  When 
heated  in  air  it  phosphoresces  greenish. 

Boron  carbide,  CB6,  is  produced  when  boron  and  carbon  are  heated  together  in 
the  electric  furnace,  best  in  the  presence  of  silver  which  dissolves  both  elements 
and  enables  the  carbide  to  crystallise.  It  is  black  and  remarkably  hard,  ranking 
next  to  diamond  in  this  respect.  It  burns  in  oxygen  at  a  high  temperature,  and  is 
attacked  by  fused  alkalies  but  not  by  acids. 

Boron  trichloride,  BC13.  —  Boron  burns'^when  heated  at  410°  C.  in 
chlorine  forming  the  trichloride,  which  is  more  conveniently  prepared 
by  heating  a  mixture  of  boric  acid  and  charcoal  in  chlorine; 
B203  +  C3  +  C16=2BC13  +  3CO.  It  is  a  liquid  of  sp.gr.  1.35  and  boils 
at  17°  C.  It  is  the  chloranhydride  (p.  191)  of  metaboric  acid,  being 
decomposed  by  water  thus:  BC13  +  3H20  =  B(OH)3  +  3HC1.  It  has  a 
remarkable  tendency  to  combine  with  other  chlorides. 

147.  Boron  trifluoride  (BF3),  may  be  prepared  by  strongly  heating  a  mixture 
of  powdered  boric  anhydride  with  twice  its  weight  of  fluor  spar  in  an  iron  tube  ; 
3CaF2  +  B203  =  3CaO  +  2BF3. 

The  boron  fluoride  is  a  gas  which  fumes  strongly  in  moist  air,  like  the  silicon 
fluoride.  It  is  absorbed  eagerly  by  water,  with  evolution  of  heat.  One  volume  of 
water  at  o°  C.  is  capable  of  dissolving  1057  volumes  of  boron  fluoride,  producing  a 
corrosive  heavy  liquid  (sp.  gr.  1.77),  which  fumes  in  air,  and  chars  organic  sub- 
stances on  account  of  its  attraction  for  water.  This  solution  is  known  as  fluo  ~boriv 
or  boro  fluoric  acid,  and  its  formation  is  explained  by  the  equation  2BF3  +  3H2O  = 
B203.6HF  (Fluoloric  acid). 

When  the  solution  is  heated,  it  evolves  boron  fluoride,  until  its  specific  gravity  is 
reduced  to  1.58,  when  it  distils  unchanged. 

Hydrofluoboric  acid  is  obtained  in  solution  by  adding  a  large  quantity  of  water 
to  fluoboric  acid  ;  2(B203.6HF)  =  H3B03  +  3H20  +  3HBF4  (hydrofuoboric  acid). 


*  The  author  has  known  them  to  cut  through  the  bottom  of  the  beaker  used  in  separa- 
ting them  from  the  aluminium. 


SOURCES   OF  PHOSPHORUS.  249 

The  hydrogen  of  this  acid  may  be  exchanged  for  metals  to  form  borqfliwrides,. 
which  have  been  applied  as  antiseptics.  Ammonium  borofluoride  NH4BF4  is  pro- 
duced when  boron  nitride  is  heated  with  hydrofluoric  acid. 

Boron  trimlpltide,  B2S3,  is  made  by  strongly  heating  boron  in  H2S  ;  it  forms 
white  needles,  melts  at  310°  C.,  and  yields  B(OH)3  and  H2S  when  in  contact  with 
water.  Bo ron  pentasulphide,  B2S5,  is  a  white  crystalline  powder  (m.p.  390°  C.)made 
by  heating  BI3  with  S  in  CS2  at  60°.  It  is  decomposed  by  water  into  B(OH)3,  H2S 
and  S. 

PHOSPHORUS. 

P  =  3i  parts  by  weight.* 

148.  This  element  is  never  known  to  occur  uncombined  in  nature,, 
but  is  found  abundantly  in  the  form  of  phosphate  of  lime  or  tricalcic 
diphosphate,  3CaO.P205  or  Ca3(P04)2,  which  is  contained  in  the  minerals 
coprohte,  phosphorite,  and  apatite,  and  occurs  diffused,  though  generally 
in  small  proportion,  through  all  soils  upon  which  plants  will  grow  ;  for 
phosphorus,  probably  in  this  form,  is  an  essential  constituent  of  the 
food  of  plants,  and  especially  of  the  cereal  plants,  which  form  so  large  a 
proportion  of  the  food  of  animals.  The  seeds  of  such  plants  are  espe- 
cially rich  in  the  phosphates  of  calcium  and  magnesium. 

Animals  feeding  upon  these  plants  still  further  accumulate  the  phos- 
phorus, for  it  enters,  chiefly  in  the  form  of  calcium  phosphate,  into  the 
composition  of  almost  every  solid  and  liquid  in  the  animal  body,  and  is 
especially  abundant  in  the  bones,  which  contain  about  three-fifths  of 
their  weight  of  calcium  phosphate. 

Composition  of  the  Bones  of  Oxen. 

Fat 5.4 

Nitrogenous  matter 28.6 

Calcium  phosphate 56.5 

„           fluoride 1.2 

„          carbonate 7.3 

Magnesium  phosphate i.o 

100.00 

What  is  here  termed  nitrogenous  matter  is  a  cartilaginous  substance,  converted 
into  gelatine  when  the  bones  are  heated  with  water  under  pressure,  and  containing^ 
C,  H,  N  and  0.  It  was  formerly  the  custom  to  get  rid  of  this  by  burning  the  bones 
in  an  open  lire,  but  the  increased  demand  for  chemical  products,  and  the  diminished 
supply  of  bones,  have  taught  economy,  so  that  the  cartilaginous  matter  is  now 
dissolved  out  by  heating  the  bones  with  water  at  a  high  pressure  for  the  manufac- 
ture of  glue  ;  or  the  bones  are  subjected  to  destructive  distillation,  so  as  to  save 
the  ammonia  which  they  evolve,  and  the  bone  charcoal  thus  produced  is  used  by 
the  sugar-refiner  until  its  decolorising  powers  are  exhausted,  when  it  is  heated  in 
contact  with  air  to  burn  away  the  charcoal,  and  leave  the  bone-asli,  consisting 
chiefly  of  calcium  phosphate,  Ca3(P04)2,  and  valuable  as  a  manure, 

Originally,  phosphorus  was  made  from  bone-ash,  but  now  the  cheaper 
calcium  phosphate  of  mineral  origin  is  employed  as  the  raw  material. 
The  coprolites,  or  other  phosphates,  are  ground  to  powder  and  mixed 
with  enough  chamber  acid  (H2S04)  to  convert  the  calcium  into  sulphate 
and  to  liberate  the  phosphoric  acid  ;  Ca3(P04)2  +  3H2S04  =  3CaS04  + 
2H3P04.  The  liquor  is  evaporated  and  the  solution  of  phosphoric  acid 

*  The  vapour  of  phosphorus  is  62  times  as  heavy  as  hydrogen,  so  that  its  atom  only 
occupies  half  a  volume,  if  the  atom  of  hydrogen  be  taken  to  occupy  one  volume ;  and  the 
molecule  of  phosphorus  (P4)  occupying  two  volumes,  would  consist  of  four  atoms  instead  of 
two.  At  very  high  temperatvu-es  the  specific  gi'avity  of  phosphorus  vapour  diminishes, 
showing  a  tendency  to  conform  with  the  ordinary  law  of  volumes. 


250  PROPERTIES   OF  PHOSPHORUS. 

separated  from  the  calcium  sulphate  by  filtration.  This  solution  is 
further  evaporated  to  a  syrup,  absorbed  by  charcoal  and  dried,  during 
which  the  phosphoric  acid  loses  water,  becoming  inetaphosphoric  acid, 
H3P04  =  HPO3-f  2H20.  It  is  now  only  necessary  to  distil  the  mixture 
of  charcoal  and  metaphosphoric  acid  in  bottle-shaped  fireclay  retorts 
set  in  a  furnace.  The  phosphorus  distils,  hydrogen  and  carbon  mon- 
oxide being  evolved  at  the  same  time  (4HP03  +  C12=  i2CO  +  P4  +  H4), 
and  is  condensed  under  warm  water  in  which  it  melts.  It  is  far  from 
pure,  having  a  mahogany  colour  ;  to  eliminate  this  it  is  remelted  with 
a  mixture  of  sulphuric  acid  and  potassium  bichromate ;  the  impuri- 
ties are  thus  oxidised  and  the  phosphorus  becomes  yellow.  It  is 
cast  into  sticks  or  wedges  which  are  packed  in  tins,  containing  water, 
for  the  market.  The  yield  is  only  70  per  cent,  of  the  theoretical 
yield. 

Instead  of  liberating  the  phosphoric  acid  from  the  calcium  phosphate 
by  sulphuric  acid  as  described  above,  advantage  may  be  taken  of  the 
fact  that  at  very  high  temperatures  silicic  anhydride  (SiO2),  being  less 
volatile  than  phosphoric  anhydride  (P2O5),  can  expel  the  latter  from 
its  combination  with  lime,  although  a  less  powerfully  acid  oxide ; 
Ca3(P04)2  +  3SiO2  =  30aSiO3  +  P2O5.  The  temperature  of  the  electric 
furnace  (p.  138),  however,  is  essential  for  this  reaction;  accordingly, 
on  a  commercial  scale  a  mixture  of  calcium  phosphate,  sand  (Si02)  and 
coke  (C)  is  heated  in  such  a  furnace  provided  with  an  arrangement  for 
collecting  the  phosphorus  which  distils  from  the  mixture.  The  carbon 
of  the  coke  reduces  the  P2O5  liberated  according  to  the  above  equation  ; 
P.O.  +  O.-P.  +  sCO. 

On  a  small  scale,  for  the  sake  of  illustration,  phosphorus  may  be  prepared  by  a 
process  which  has  also  been  successfully  employed  for  its  manufacture  in  quantity, 
and  consists  in  heating  a  mixture  of  bone-ash  and  charcoal  in  a  stream  of  hydro- 
chloric acid  gas  ;  Ca3(P04)2  +  6HC1  +  C8  =  3CaCl2  +  SCO  +  H6  +  P2. 

A  mixture  of  equal  weights  of  well-dried  charcoal  and  bone-ash,  both  in  fine 
powder,  is  introduced  into  a  porcelain  tube,  and  placed  in  a  gas  furnace.  One  end 
of  the  tube  is  connected  with  a  flask  evolving  HC1  (p.  177),  and  the  other  is 
cemented  with  putty  into  a  bent  tube  for  conveying  the  phosphorus  into  a  vessel 
of  water.  On  heating  the  porcelain  tube  to  bright  redness,  phosphorus  distils  in 
abundance.  The  hydrogen  and  carbonic  oxide  inflame  as  they  escape  into  the  air, 
from  their  containing  phosphorus  vapour. 

Pure  ordinary,  or  vitreous,  phosphorus  is  almost  colourless  and  trans- 
parent, but  when  exposed  to  light,  and  especially  to  direct  sunlight,  it 
gradually  acquires  an  opaque  red  colour,  from  its  conversion  into  the 
allotropic  variety  known  as  red  phosphorus.  By  tying  bands  of  black 
cloth  round  a  stick  of  phosphorus  and  exposing  it,  under  water,  to  the 
action  of  sunlight,  alternate  zones  of  red  may  be  produced. 

Even  though  the  phosphorus  be  screened  from  light,  it  will  not  re- 
main unchanged  unless  the  water  be  kept  quite  free  from  air,  which 
irregularly  corrodes  the  surface  of  the  phosphorus,  rendering  it  white 
and  opaque.  This  action  is  accelerated  by  exposure  to  light. 

The  most  remarkable  character  of  ordinary  phosphorus  is  its  easy 
inflammability.  It  inevitably  takes  fire  in  air  when  heated  a  little 
above  its  melting-point,  44°  C.  (m°.5  F.),  burning  with  a  brilliant 
white  flame,  which  becomes  insupportable  when  the  combustion  is  in 
oxygen  (p.  34),  and  evolving  dense  white  clouds  of  phosphoric  anhydride. 
When  a  piece  of  dry  phosphorus  is  exposed  to  the  air,  it  combines 


PHOSPHORESCENCE.  251 

slowly  with  oxygen,*  and  its  temperature  often  becomes  so  much 
elevated  during  this  slow  combustion,  that  it  melts  and  takes  fire, 
especially  if  the  combustion  be  encouraged  by  the  warmth  of  the  hand 
or  by  friction.  Hence,  ordinary  phosphorus  must  never  be  handled  or 
cut  in  the  dry  state,  but  always  under  water,  for  it  causes  most  painful 
burns. 

The  slow  oxidation  of  phosphorus  is  attended  with  that  peculiar 
luminous  appearance  which  is  termed  phosphorescence  (0ws,  light,  0f'(ow, 
to  bear),  but  this  glow  is  not  seen  in  pure  oxygen,  except  under 
diminished  pressure,  or  in  air  containing  a  minute  proportion  of  olefiant 
gas  or  oil  of  turpentine  ;  nor  will  phosphorus  glow  in  compressed  air  at 
the  ordinary  temperature.  It  will  be  remembered  that  the  slow 
oxidation  of  phosphorus  in  moist  air  is  attended  with  the  formation 
of  ozone. 

The  glow  of  phosphorus,  which  maybe  regarded  as  an  incipient  flame, 
is  in  some  way  connected  with  this  ozone  (possibly  produced  during  the 
oxidation  of  the  phosphorus  to  P2O5;  P2  +  363  =  P2O5  +  O  and  02  +  0  =  03). 
When  phosphorus  is  exposed  to  pure  oxygen  at  the  ordinary  pressure, 
oxidation  seems  to  proceed  very  slowly  at  the  ordinary  temperature  ; 
tout  at  an  elevated  temperature  (25°  C),  or  in  oxygen  at  diminished 
pressure,t  the  phosphorus  is  oxidised  with  formation  of  P205  (and 
ozone)  and  P406.  This  latter  oxide  is  readily  oxidised  to  P2O5  and 
phosphoresces  during  the  change,  particularly  in  the  presence  of  ozone. 
Moisture  is  essential  to  the  oxidation  (and  the  glow)  of  phosphorus  at 
any  pressure.  . 

Ordinary  phosphorus  is  slowly  vapourised  at  common  temperatures, 
and  emits  in  the  air  white  fumes  with  a  peculiar  alliaceous  odour, 
which  appear  phosphorescent  in  the  dark.  It  boils  at  278°  C.,  yielding 
a  colourless  vapour. 

The  characteristic  behaviour  of  phosphorus  in  air  is  best  observed  when  the 
phosphorus  is  in  a  finely  divided  state.  The  experiment  described  on  p.  34  (Fig.  26) 
will  serve  as  an  illustration. 

If  phosphorus  be  dissolved  in  olive  oil,  at  a  gently  heat,  the  solution  is  strongly 
phosphorescent  when  shaken  in  a  bottle  containing  air,  or  rubbed  upon  the  hand. 

Characters  may  be  written  on  paper  with  a  stick  of  phosphorus  held  in  a 
thickly  folded  piece  of  damp  paper  (having  a  vessel  of  water  at  hand  into  which 
to  plunge  the  phosphorus  if  it  should  take  fire).  When  the  paper  is  held  with  its 
back  to  the  fire,  or  to  a  hot  iron,  in  a  darkened  room,  a  twinkling  combustion  of 
the  finely  divided  phosphorus  ensues  and  the  letters  are  burnt  into  the  paper. 
Phosphorus  which  has  been  partly  oxidised  is  even  more  easily  inflamed  than  pure 
phosphorus.  If  a  few  small  pieces  of  phosphorus  be  placed  in  a  dry  stoppered 
bottle,  gently  warmed  till  they  melt,  and  then  shaken  round  the  sides  of  the  bottle 
so  as  to  become  partly  converted  into  red  oxide  of  phosphorus,  it  will  be  found, 
long  after  the  bottle  is  cold,  to  be  spontaneously  inflammable,  so  that  if  a  wooden 
match  tipped  with  sulphur  be  rubbed  against  it,  the  phosphorus  which  it  takes  up 
will  ignite  when  the  match  is  brought  into  the  air.  kindling  the  sulphur,  which  will 
inflame  the  wood.  This  was  one  of  the  earliest  forms  in  which  phosphorus  was 
employed  for  the  purpose  of  procuring  an  instantaneous  light.  If  the  stopper  be 
greased,  the  phosphorus  may  be  preserved  unchanged  for  a  long  time. 

In  the  last  experiment,  if  the  wood  had  not  been   tipped  with   sulphur,  the 

*  The  white  fumes  evolved  by  phosphorus  in  moist  air  are  said  to  consist  partly  of 
ammonium  nitrate,  formed  by  the  action  of  the  ozonised  oxygen  (p.  65)  upon  the  air  and 
aqueous  vapour. 

f  It  will  be  remembered  that  the  pressure  of  the  oxygen  in  the  air  is  only  about  one-fifth 
of  the  total  pressure,  BO  that  air  contains  oxygen  at  diminished  pressure.  The  extent  to 
which  the  pressure  must  be  diminished  for  the  production  of  the  glow  depends  on  the  tem- 
perature. 


252  EED   PHOSPHORUS. 

phosphorus  would  not  have  kindled  it,  the  flame  of  phosphorus  generally  being" 
unable  to  ignite  solid  combustibles,  because  it  deposits  upon  them  a  coating  of 
P205,  which  protects  them  from  the  action  of  air.  Hence,  in  the  manufacture  of 
lucifer  matches,  the  wood  is  first  tipped  with  sulphur,  or  wax,  or  paraffin,  which 
easily  give  off  combustible  vapours  to  be  kindled  by  the  flame  of  the  phosphorus 
composition,  and  thus  to  inflame  the  wood. 

If  a  small  stick  of  phosphorus  be  carefully  dried  with  filtering  paper,  and  dropped 
into  a  cylinder  of  oxygen,  which  is  afterwards  covered  with  a  glass  plate,  no- 
luminosity  will  be  observed  in  a  darkened  room  until  the  cylinder  is  placed  under 
the  air-pump  receiver,  and  the  air  slowly  exhausted.  When  the  oxygen  has  thus 
been  rarefied  to  about  one-fifth  of  its  former  density,  the  phosphorescence  will  be 
seen.  A  similar  effect  may  be  produced  by  covering  the  cylinder  of  oxygen  con- 
taining the  phosphorus  (having  removed  the  glass 
plate)  with  another  cylinder,  about  four  times  its 
size  (Fig.  184),  filled  with  carbonic  acid  gas,  which 
will  gradually  dilute  the  oxygen  and  produce  the 
phosphorescence.  By  suspending — in  a  bottle  of 
air  containing  a  strongly  luminous  piece  of  phos- 
phorus— a  piece  of  paper  with  a  drop  of  oil  of  turpen- 
tine upon  it,  the  glow  may  be  almost  instantane- 
ously destroyed.  A  small  tube  of  olefiant  gas  or 
coal  gas  dropped  into  the  bottle  will  also  extinguish 
the  luminosity.* 

The  luminosity  of  phosphorus  vapour  is  seen  to 
advantage  when  a  piece  of  phosphorus  is  boiled  with 
water  in  a  narrow-necked  flask  or  retort,  or  a  test- 
Fig-.  184.  tube  with  a  cork   and  narrow  tube.     The  steam 
charged  with   vapour  of  phosphorus   has   all  the 

appearance  of  a  blue  flame,  in  a  darkened  room,  but  of  course  combustibles  are 
not  inflamed  by  it,  since  its  temperature  is  not  higher  than  100°  C.  Phos- 
phorus may  be  distilled,  with  perfect  safety,  in  an  atmosphere  of  carbonic  acid 
gas,  the  neck  of  the  retort  being  allowed  to  dip  under  water  in  the  receiver. 

Advantage  is  taken  of  the  fact  that  phosphorus  distils  in  steam  and  renders  it 
luminous  in  testing  for  this  poison  in  organic  liquids.  Very  small  quantities  may 
thus  be  detected.  Conversely,  the  glow  of  phosphorus  vapour  may  serve  as  a  delicate 
test  for  oxygen,  as  it  can  be  detected  until  the  last  trace  of  this  gas  has  dis- 
appeared. 

Although  ordinary  phosphorus  is  of  a  decidedly  glassy  or  vitreous 
structure,  it  may  be  obtained  in  dodecahedral  crystals,  by  allowing  its 
solution  in  carbon  disulphide  to  evaporate  in  an  atmosphere  of  carbonic 
acid  gas,  or  by  fusing  it  in  a  tube  exhausted  by  a  Sprengel  pump,  and 
letting  it  cool  in  the  dark. 

The  conversion  of  ordinary  phosphorus  into  the  red  phosphorus  is  one 
of  the  most  striking  instances  of  allotropic  modification.  When  phos- 
phorus is  heated  for  a  considerable  length  of  time  to  about  450°  F. 
(232°  C.)  in  vacuo,  or  in  an  atmosphere  in  which  it  cannot  burn,  it 
becomes  converted  into  an  infusible  mass  of  red  phosphorus,  27,000 
gram  units  of  heat  being  evolved  for  every  31  grams  converted.  This 
form  of  phosphorus  differs  as  widely  from,  the  vitreous  form  as  graphite 
differs  from  diamond.  It  is  only  slowly  oxidised  in  warm  moist  air, 
evolves  no  vapour,  is  not  luminous,  cannot  be  inflamed  by  friction,  or 
even  by  any  heat  short  of  500°  F.  (260°  C.)  When  it  is  heated  above 
350°  C.  it  slowly  sublimes  as  yellow  phosphorus.  By  heating  vitreous 
phosphorus  in  an  exhausted  and  sealed  tube  to  about  500°  C.,  it  is  con- 
verted into  a  violet-black  fused  mass  with  cavities  containing  crystals. 
Red  phosphorus  is  insoluble  in  the  solvents  for  ordinary  phosphorus. 
The  two  varieties  also  differ  greatly  in  specific  gravity,  that  of  the 

*  Chappuis  finds  that  when  phosphorus  is  suspended  in  oxygen,  the  space  glows  for  a 
short  time  on  adding  a  little  ozone. 


PROPERTIES   OF  RED   PHOSPHORUS. 


253 


Fig-.  185. 


•ordinary  phosphorus  being  1.83,  and  of  the  red  variety  2.14.     Of  the 
two,  the  red  variety  is  the  better  conductor  of  electricity. 

The  conversion  of  vitreous  into  red  phosphorus,  or  amorphous  phosphorus  as  it  was 
•called  before  it  was  proved  to  be  microscopically  crystalline,  may  be  effected  by 
heating  it  in  a  flask  (A,  Fig.  185)  placed  in  an  oil-bath  (B),  maintained  at  a  tempera- 
ture ranging  from  450°  to  460°  F.  (232°  to  238°  C.),  the  flask  being  furnished  with 
;abent  tube  (C)  dipping  into  mercury,  and  with  another  tube  (D)  for  supplying  car- 
bonic acid  gas,  dried  by  passing  over  calcium  chloride.  The  flask  should  be 
thoroughly  filled  with  carbonic  acid  gas  before  applying  heat,  and  the  tube  delivering 
it  may  then  be  closed  with  a  small  clamp  (E).  After  exposure  to  heat  for  about 
forty  hours,  but  little  ordinary  phosphorus  will  remain,  and  this  may  be  removed 
by  allowing  the  mass  to  remain  in 
-contact  with  carbon  disulphide  for 
some  hours,  and  subsequently  washing 
it  with  fresh  disulphide  till  the  latter 
•leaves  no  phosphorus  when  evaporated. 

On  the  large  scale,  the  red  phos- 
phorus is  prepared  by  heating  about 
200  Ibs  of  vitreous  phosphorus  to  450° 
F.  (232°  C.)  in  an  iron  boiler.  After 
three  or  four  weeks  the  phosphorus  is 
found  to  be  converted  into  a  hard  red 
brittle  mass,  which  is  ground  by  mill- 
stones under  water,  and  separated 
from  the  ordinary  phosphorus  either 
by  carbon  disulphide  or  caustic  soda, 
in  which  the  latter  is  soluble.  The 
temperature  requires  careful  regula- 
tion, for  if  it  be  allowed  to  rise  to 
350°  C.,  the  red  phosphorus  resumes 
the  vitreous  condition.  This  reconversion  may  be  shown  by  heating  a  little  red 
phosphorus  in  a  narrow  test-tube,  when  drops  of  vitreous  phosphorus  condense  on 
the  cool  part  of  the  tube.  The  colour  of  different  specimens  of  red  phosphorus 
varies  considerably,  depending  upon  the  temperature  at  which  the  conversion  has 
been  effected  ;  that  prepared  on  the  large  scale  is  usually  of  a  dark  purplish  colour, 
but  it  may  be  obtained  of  a  bright  scarlet  colour.  Rhombohedral  crystals  of  the 
red  phosphorus,  resembling  crystals  of  arsenic  in  form  and  metallic  appearance,  have 
been  obtained  by  fusing  phosphorus  with  lead,  and  dissolving  out  the  latter  with 
•diluted  nitric  acid  (sp.  gr.  i.i).  Similar  crystals  have  been  obtained  by  heating 
red  phosphorus  to  530°  C.  hi  a  vacuous  tube. 

Ordinary  phosphorus  is  very  poisonous  (o.  i  gram  being  fatal),  whilst 
red  phosphorus  appears  to  be  harmless.  The  former  is  employed, 
mixed  with  fat  by  substances,  for  poisoning  rats  and  beetles.  Cases  are, 
unhappily,  not  very  rare,  of  children  being  poisoned  by  sucking  the 
phosphorus  composition  on  lucif  er  matches.  The  vapour  of  phosphorus 
also  produces  a  very  injurious  effect  upon  the  persons  engaged  in  the 
manufacture  of  lucifer  matches,  resulting  in  the  decay  of  the  lower 
jaw-bone.  The  evil  is  much  mitigated  by  good  ventilation,  or  by  diffus- 
ing turpentine  vapour  through  the  air  of  the  workroom,  and  attempts 
have  been  made  to  obviate  it  entirely  by  substituting  red  phosphorus 
for  the  ordinary  variety,  but,  as  might  be  expected,  the  matches  thus 
made  are  not  so  sensitive  to  friction  as  those  in  which  the  vitreous 
phosphorus  is  used. 

The  difference  between  the  two  varieties  of  phosphorus,  in  respect  to 
chemical  energy,  is  seen  when  they  are  placed  in  contact  with  a  little 
iodine  on  a  plate,  when  the  ordinary  phosphorus  undergoes  combustion 
and  the  red  phosphorus  remains  unaltered. 

Ordinary  phosphorus,  when  moist,  is  capable  of  direct  union  with 


254  LUCIFEE    MATCHES. 

oxygen,  chlorine,  bromine,  iodine,  sulphur,  and  most  of  the  metalsr 
with  which  it  forms  phosphides  or  phosphurets.  Even  gold  and  plati- 
num unite  with  this  element  when  heated,  so  that  crucibles  of  these 
metals  are  liable  to  corrosion  when  heated  in  contact  with  a  phosphate 
in  the  presence  of  a  reducing  agent,  such  as  carbon.  Thus  the  inside 
of  a  platinum  dish  or  crucible  is  roughened  when  vegetable  or  animal 
substances  containing  phosphates  are  incinerated  in  it.  The  presence 
of  small  quantities  of  phosphorus  in  iron  or  copper  produces  consider- 
able effect  upon  the  physical  qualities  of  these  metals. 

Phosphorus  has  the  property,  a  very  remarkable  one  in  a  non-metal,, 
of  precipitating  some  metals  from  their  solutions  in  the  metallic  state. 
If  a  stick  of  phosphorus  be  placed  in  a  solution  of  sulphate  of  copper,  it 
becomes  coated  with  metallic  copper,  the  phosphorus  appropriating  the 
oxygen.  This  has  been  turned  to  advantage  in  copying  very  delicate 
objects  by  the  electrotype  process,  for  by  exposing  them  to  the  action  of 
a  solution  of  phosphorus  in  ether  or  carbon  disulphide,  and  afterwards 
to  that  of  a  solution  of  copper,  they  acquire  the  requisite  conducting 
metallic  film,  even  on  their  finest  filaments.  Solutions  of  silver  and  gold 
are  reduced  in  a  similar  manner  by  phosphorus. 

By  floating  very  minute  scales  of  ordinary  phosphorus  upon  a  dilute  solution  of 
chloride  of  gold,  the  metal  will  be  reduced  in  the  form  of  an  extremely  thin  film, 
which  may  be  raised  upon  a  glass  plate,  and  will  be  found  to  have  various  shades 
of  green  and  violet  by  transmitted  light,  dependent  upon  its  thickness,  whilst  ita 
thickest  part  exhibits  the  ordinary  colour  of  the  metal  to  reflected  light.  By 
heating  the  films  on  the  plate,  various  shades  of  amethyst  and  ruby  are  developed. 
If  a  very  dilute  solution  of  chloride  of  gold  in  distilled  water  be  placed  in  a 
perfectly  clean  bottle,  and  a  few  drops  of  ether,  in  which  phosphorus  has  been 
dissolved,  poured  into  it,  a  beautiful  ruby-coloured  liquid  is  obtained,  the  colour 
of  which  is  due  to  metallic  gold  in  an  extremely  finely  divided  state,  and  on 
allowing  it  to  stand  for  some  months,  the  metal  subsides  as  a  purple  powder, 
leaving  the  liquid  colourless.  If  any  saline  impurity  be  present  in  the  gold 
solution,  the  colour  of  the  reduced  gold  will  be  amethyst  or  blue.  These  ex- 
periments illustrate  very  strikingly  the  use  of  gold  for  imparting  ruby  and  purple 
tints  to  glass  and  the  glaze  of  porcelain. 

149.  Lucifer  matches  are  made  by  tipping  the  wood  with  sulphur,  or 
wax,  or  paraffin,  to  convey  the  flame,  and  afterwards  with  the  match  com- 
position, which  is  generally  composed  of  saltpetre  or  potassium  chlorate, 
phosphorus,  red  lead,  and  glue,  and  depends  for  its  action  on  the  easy 
inflammation,  by  friction,  of  phosphorus  when  mixed  with  oxidising 
agents  like  saltpetre  (KNO3),  potassium  chlorate  (KC1O3),  or  red  lead 
(Pb3O4),  the  glue  only  serving  to  bind  the  composition  together  and 
attach  it  to  the  wood.  The  composition  used  by  different  makers  varies 
much  in  the  nature  and  proportions  of  the  ingredients.  In  this 
country,  potassium  chlorate  is  most  commonly  employed  as  the  oxi- 
dising agent,  such  matches  usually  kindling  with  a  slight  detonation  ; 
but  the  German  manufacturers  prefer  either  potassium  nitrate  or  lead 
nitrate,  together  with  lead  dioxide  or  red  lead,  which  produce  silent 
matches. 

Sulphide  of  antimony  (which  is  inflamed  by  friction  with  potassium 
chlorate,  see  p.  186)  is  also  used  in  those  compositions  in  which  a  part 
of  the  phosphorus  is  employed  in  the  red  form,  and  fine  sand  or 
powdered  glass  is  very  commonly  added  to  increase  the  susceptibility  of 
the  mixture  to  inflammation  by  friction. 

The  match  composition  is  coloured  either  with  ultramarine  blue,  Prus- 


LUCIFER    MATCHES.  255 

sian  blue,  or  vermilion.  In  preparing  the  composition,  the  glue  and  the 
nitre  or  chlorate  are  dissolved  in  hot  water,  the  phosphorus  then  added 
and  carefully  stirred  in  until  intimately  mixed,  the  whole  being  kept  at 
a  temperature  of  about  100°  F.  (38°  C.).  The  fine  sand  and  colouring 
matter  are  then  added,  and  when  the  mixture  is  complete,  it  is  spread 
out  upon  a  stone  slab  heated  by  steam,  and  the  sulphured  ends  of  the 
matches  are  dipped  into  it. 

The  safety  matches,  which  refuse  to  ignite  unless  rubbed  upon  the 
sides  of  the  box,  are  tipped  with  a  mixture  of  antimony  sulphide,  potas- 
sium chlorate  and  powdered  glass,  which  is  not  sufficiently  sensitive  to 
be  ignited  by  any  ordinary  friction,  but  inflames  at  once  when  rubbed 
upon  the  red  phosphorus  mixed  with  glass,  which  coats  the  rubber  on 
the  sides  of  the  box. 

It  would  be  very  desirable  to  dispense  entirely  with  the  use  of  phos- 
phorus in  lucifer  matches,  not  only  because  of  the  danger  from  accident 
and  disease  in  the  manufacture,  but  because  a  certain  quantity  of  phos- 
phate of  lime  is  diverted  from  agricultural  purposes  to  the  preparation 
of  phosphorus,  of  which  many  tons  are  consumed  annually  for  the 
manufacture  of  matches.  The  most  successful  attempt  in  this  direc- 
tion appears  to  be  the  employment  of  a  mixture  of  potassium  chlorate 
and  lead  hyposulphite,  in  place  of  the  ordinary  phosphorus  com- 
position. 

For  illustration,  very  excellent  matches  may  be  made  upon  the  small  scale  in 
the  following  manner.  The  slips  of  wood  are  dippped  in  melted  sulphur  so  as  to 
acquire  a  slight  coating.  Thirty  grains  of  gelatine  or  isinglass  are  dissolved  in 
2  drachms  of  water  in  a  porcelain  dish  placed  upon  a  steam-bath  ;  20  grains  of 
ordinary  phosphorus  are  then  added,  and  well  mixed  in  with  a  piece  of  wood  ;  to 
this  mixture  are  added,  in  succession,  15  grains  of  red  lead  and  50  grains  of 
powdered  potassium  chlorate.  The  sulphured  matches  are  dipped  into  this  paste, 
and  left  to  dry  in  the  air. 

To  make  the  safety  matches  :  10  grains  of  powdered  potassium  chlorate  and 
10  grains  of  antimony  sulphide  are  made  into  a  paste  with  a  few  drops  of  a  warm 
solution  of  20  grains  of  gelatin  in  2  drachms  of  water,  the  sulphured  matches 
being  tipped  with  this  composition.  The  rubber  is  prepared  with  20  grains  of 
red  phosphorus,  and  10  grains  of  finely-powdered  glass,  mixed  with  the  solution 
of  gelatine,  and  painted  on  paper  or  cardboard  with  a  brush. 

150.  A  very  sensitive  detonating  composition  formerly  used  for  igniting  per- 
cussion shells,  may  be  prepared  with  care  in  the  following  manner  :  Four  grains 
of  powdered  potassium  chlorate  are  moistened  on  a  plate  with  6  drops  of  spirit  of 
wine,  4  grains  of  powdered  red  phosphorus  are  added,  and  the  whole  mixed,  at 
arm's  length,  with  a  bone-knife,  avoiding  great  pressure.  The  mixture,  which 
should  be  quite  moist,  is  spread  in  small  portions  upon  ten  or  twelve  pieces  of 
filtering  paper,  and  left  in  a  safe  place  to  dry.  If  one  of  these  be  gently  pressed 
with  a  stick,  it  explodes  with  great  violence. '  It  is  dangerous  to  press  it  with  the 
blade  of  a  knife,  as  the  latter  is  commonly  broken,  and  the  pieces  projected  with 
considerable  force.  A  stick  dipped  in  oil  of  vitriol  of  course  explodes  it  imme- 
diately. If  a  bullet  be  placed  very  lightly  upon  one  of  the  pellets,  and  the  paper 
tenderly  wrapped  round  it,  a  percussion  shell  may  be  extemporised,  which  explodes 
with  a  loud  report  when  dropped  upon  the  floor. 

The  detonating  toys  known  as  amorces  fulminantes  are  made  by  enclosing  this 
composition  between  two  pieces  of  thin  paper.  1000  of  them  contain  70  grains  of 
the  composition. 

151.  Oxides  of  Phosphorus. — Four  compounds  of  phosphorus  and 
oxygen  are  known,  their  formulae  being  P4O,  P4O6,  P2O4,  and  P205.  Of 
these  P4O6  and  P2O5  are  anhydrides,  the  others  are  neutral  oxides. 


256  PHOSPHORIC  ACID. 

PHOSPHORIC  ACIDS  AND  PHOSPHATES. 

152.  The  phosphates  are  by  far  the  most  important  of  the  compounds 
of  phosphorus.  They  have  been  already  noticed  as  almost  the  only 
forms  of  combination  in  which  that  element  is  met  with  in  nature,  and 
as  indispensable  ingredients  in  the  food  of  plants  and  animals.  No 
other  mineral  substance  can  bear  comparison  with  calcium  phosphate  as 
a  measure  of  the  capability  of  a  country  to  support  animal  life.  Phos- 
phoric acid  itself  is  very  useful  in  calico-printing  and  in  some  other 
arts. 

The  mineral  sources  of  this  acid  appear  to  be  phosphorite,  coprolite, 
and  apatite,  all  consisting  essentially  of  calcium  phosphate,  Ca3(PO4)2, 
but  associated  in  each  case  with  calcium  fluoride,  which  is  also  contained, 
with  calcium  phosphate,  in  bones,  and  would  appear  to  indicate  an 
organic  origin  for  these  minerals.  Phosphorite  is  any  earthy-looking 
substance,  forming  large  deposits  in  Estremadura.  Apatite  (from 
anarda),  to  cheat,  in  allusion  to  mistakes  in  its  early  analysis)  occurs  in 
prismatic  crystals,  and  is  met  with  in  the  Cornish  tin-veins.  Both 
these  minerals  are  largely  imported  from  Spain,  Norway,  and  Florida, 
for  use  in  this  country  as  a  manure.  Coprolites  (KOKPOS,  dung,  \i6os,  a 
stone,  from  the  idea  that  they  were  petrified  dung)  are  rounded  nodules 
of  calcium  phosphate,  which  are  found  abundantly  in  this  country. 

Large  quantities  of  phosphates  of  calcium  and  magnesium  are 
imported  in  the  form  of  guano,  the  partially  decomposed  excrement  of 
sea-fowl. 

Phosphoric  acid  is  obtained  from  bone-ash,  or  mineral  phosphate,  by 
decomposing  it  with  sulphuric  acid,  so  as  to  remove  as  much  of  the  lime 
as  possible  in  the  form  of  sulphate,  which  is  strained  off,  and  the  acid 
liquid  neutralised  with  ammonium  carbonate,  which  precipitates  any 
unchanged  calcium  phosphate,  and  converts  the  phosphoric  acid  into 
ammonium  phosphate.  On  evaporating  the  solution,  and  heating  the 
ammonium  phosphate,  ammonia  and  water  are  expelled,  and  meta- 
phosphoric  acid  (HP03)  is  left  in  a  fused  state,  solidifying  to  a  glass  on 
cooling.  Thus  prepared,  however,  it  always  retains  some  ammonia. 

This  method  of  preparing  phosphoric  acid  is  illustrative  of  one  very 
generally  employed  in  the  preparation  of  those  acids  which  cannot  be 
distilled.  In  the  case  of  most  of  the  acids  heretofore  considered,  advan- 
tage is  taken  of  their  great  volatility,  compared  with  that  of  sulphuric 
acid,  to  obtain  them  from  their  sodium  salts.  It  is  possible  to  liberate 
phosphoric  acid  from  its  sodium  salt  by  the  action  of  sulphuric  acid ; 
but  since  phosphoric  acid  is  not  more  volatile  than  sulphuric  acid,  it  is 
difficult  to  separate  the  sodium  sulphate  produced  by  the  combination 
of  the  sulphuric  acid  with  the  sodium  of  the  sodium  phosphate,  from 
the  phosphoric  acid,  both  of  them  remaining  in  solution.  In  such  cases 
advantage  is  taken  of  the  insolubility  of  calcium  sulphate  or  of  barium 
sulphate ;  when  a  calcium  or  barium  salt  of  the  required  acid  is  treated 
with  sulphuric  acid,  calcium  sulphate  or  barium  sulphate  is  precipitated, 
and  may  be  separated  from  the  solution  containing  the  desired  acid  by 
nitration.  The  treatment  of  a  lead  salt  of  the  acid  with  hydrosulphuric 
acid,  whereby  lead  sulphide  is  precipitated,  is  another  method  for  pre- 
paring acids,  based  on  the  same  principle. 

Pure  phosphoric  acid  is  prepared  by  oxidising  phosphorus  with  dilute 


PHOSPHORIC  ANHYDRIDE. 


257 


nitric  acid  (sp.  gr.  1.197)  and  evaporating  the  solution  until  the  phos- 
phoric acid  begins  to  volatilise  in  white  fumes;  5HNO3  +  P3  =  3HP03-t- 
H2O  +  5NO.*  Some  phosphorous  acid  is  formed  at  an  intermediate 
stage.  A  transparent  glass  (glacial  phosphoric  acid)  is  thus  obtained, 
which  eagerly  absorbs  moisture  from  the  air,  and  becomes  liquid.  That 
which  is  sold  in  sticks  contains  much  sodium  metaphosphate. 

The  addition  of  a  little  bromine  greatly  facilitates  the  action  of  nitric  acid  upon 
phosphorus,  apparently  by  forming  the  phosphorus  pentabromide,  which  is  then 
decomposed  by  water  ;  PBr5  +  4H20  =  H3P04  +  sHBr.  The  hydrobromic  acid  being 
then  acted  on  by  nitric  acid,  bromine  is  set  free  to  act  upon  a  fresh  quantity  of 
phosphorus;  3HBr  +  HN03  =  Br3  +  2H2O  +  NO.  When  iodine  is  also  added,  the 
action  is  still  better.  28  grams  of  phosphorus  are  placed  in  170  c.c.  of  water  and 
0.32  gram  of  iodine  are  added  ;  then,  drop  by  drop,  1.94  grams  of  bromine.  When 
the  action  is  over,  1700.0.  of  HNO3  (sp.  gr.  1.42)  are  added,  and  the  vessel  is  placed 
in  cold  water.  When  the  phosphorus  has  dissolved,  the  solution  is  evaporated  till 
its  temperature  rises  to  about  204°  C.  in  order  to  expel  the  excess  of  nitric  acid, 
the  bromine,  and  the  iodine. 

Phosphoric  anhydride,  or  phosphorus  pentoxide  (P,O5),  is  pre- 
pared by  burning  phosphorus  in  dry  air. 

When  required  in  considerable  quantity,  the  anhydride  is  prepared  by  burning 
the  phosphorus  in  a  small  porcelain  dish  (A,  Fig.  186)  placed  under  a  bell-jar 
which  fits  in  a  groove  containing  mercury  and  surrounding  a  glass  funnel.  Air 


Fig.  186. 

is  drawn  through  the  apparatus  by  an  aspirator  attached  to  the  tube  C,  the  empty 
bottle  serving  to  catch  the  P205  carried  over  by  the  current.  A  drying- tube,  con- 
taining pumice  moistened  with  oil  of  vitriol,  is  attached  to  the  lateral  neck  of  the 
bell-jar  in  order  to  dry  the  entering  air.  When  all  the  phosphorus  has  been  burnt 
the  bell  may  be  removed,  and  the  P205  swept  down  the  stem  of  the  funnel  into  a 
dry  bottle.  A  small  quantity  of  phosphoric  anhydride  is  more  conveniently 
prepared  by  burning  phosphorus  under  a  large  bell-jar,  as  shown  in  Fig.  25. 

Phosphoric  anhydride  as  thus  prepared  is  amorphous ;  it  may  be  fused 
at  a  very  high  temperature,  and  even  sublimed,  when  it  condenses  as 
microscopic  crystals.  Its  great  feature  is  its  attraction  for  water;  left 
exposed  to  the  air  for  a  very  short  time  it  deliquesces  entirely,  becoming 
converted  into  phosphoric  acid.  It  is  often  used  by  chemists  as  a 

*  Orthophosphoric  acid  is  first  formed,  5NO2.OH  +  P3  +  2HOH  =  3PO(OH)3  +  sNO ;  but 
this  loses  water  during  the  evaporation,  PO(OH)3-H2O  =  PO2(OH). 

B 


258  PHOSPHOKIC  ACIDS. 

de-hydrating  agent,  and  will  even  remove  water  from  oil  of  vitriol. 
When  thrown  into  water  it  hisses  like  a  red-hot  iron,  but  does  not 
entirely  dissolve  at  once,  a  few  flakes  of  metaphosphoric  acid  (?)  remain- 
ing suspended  in  the  liquid  for  some  time.  The  commercial  anhydride 
is  apt  to  contain  lower  oxides  of  phosphorus,  and  even  red  phosphorus. 

The  solution  obtained  by  dissolving  phosphoric  anhydride  in  water 
contains  monohydrated  phosphoric  acid  or  metaphosphoric  acid  (H2O.P2O5 
or  HP03)  the  analogue  of  nitric  acid.  If  a  little  silver  nitrate  be  added 
to  a  portion  of  it,  a  transparent  gelatinous  precipitate  is  formed,  which 
is  the  silver  metaphosphate  ( AgN08  +  HP03  =  HNO3  +  AgP03). 

If  the  solution  of  metaphosphoric  acid  is  heated  in  a  flask  for  a  short 
time,  it  loses  the  property  of  yielding  a  precipitate  with  silver  nitrate, 
unless  one  or  two  drops  of  ammonia  be  added  to  neutralise  it,  when  an 
opaque  white  precipitate  of  silver  pyrophosphate  (2  Ag2O.P205  or  Ag4P2O7) 
is  obtained,  for  the  phosphoric  acid  has  now  been  converted  into  the 
dihydrated  or  pyrophosphoric  acid  (2H2O.P2O5  or  H4P2O7).  The  forma- 
tion of  the  precipitate  is  thus  expressed — 

H4P207  +  4AgN03  +  4NH3  =  Ag4P207  +  4NH4N03. 

When  the  solution  of  pyrophosphoric  acid  is  mixed  with  more  water 
and  boiled  for  a  long  time,  it  gives,  when  tested  with  silver  nitrate  and 
a  little  ammonia,  a  yellow  precipitate  of  silver  orthophosphater 
(3Ag2O.P,05  or  Ag3PO4) ;  the  phosphoric  acid  having  become  converted 
into  trihydrated  phosphoric  acid  or  orthophosphoric  acid  (3H2O.P2O5  or 
H3P04),  and  acting  upon  the  silver  nitrate  in  the  presence  of  ammoniar 
thus  H3P04  +  3AgN03  +  3NH3  =  Ag3P04  +  3NH4N03. 

The  reverse  changes  occur  when  orthophosphoric  acid  is  heated,  this- 
becoming  pyrophosphoric  acid  at  300°  C.,  and  metaphosphoric  acid  at  a 
red  heat. 

The  pyrophosphoric  acid  (H4P207)  cannot  be  obtained  by  the  above 
process  without  an  admixture  of  one  of  the  other  acids,  but  it  has  been 
obtained  in  crystals  by  decomposing  the  lead  pyrophosphate  (Pb2P207) 
with  hydrosulphuric  acid,  and  evaporating  the  filtered  solution  in  vacuo 
over  oil  of  vitriol. 

Trihydrated  phosphoric  acid  may  also  be  obtained  in  prismatic  crystals,, 
by  evaporating  its  solution  in  a  similar  way.  This  acid  is  also  called 
orthophosphoric  acid  (opQdg,  true),  and  common  phosphoric  acid,  in  allu- 
sion to  the  circumstance  that  the  phosphates  found  in  nature  and 
commonly  met  with  and  employed  in  the  arts  are  the  salts  of  this  acid. 

Metaphosphoric  acid  is  distinguished  from  the  other  two  acids  by  the 
fact  that  it  coagulates  white  of  egg  (albumin). 

It  will  be  perceived,  from  their  formulae,  that  metaphosphoric.  HP03,  ortho- 
phosphoric,  H3P04,  and  pyrophosphoric  acid,  H4P207,  are  respectively  monobasic,, 
tribasic,  and  tetrabasic  acids.  The  normal  sodium  salts  of  these  acids  are,  re- 
spectively, metaphosphate,  NaP03,  orthophosphate,  Na3P04,  and  pyrophosphate, 
Na4P207.  The  hydrogen  in  orthophosphoric  and  pyrophosphoric  acids  may  be 
only  partly  exchanged  for  a  metal  ;  thus  there  are  two  other  orthophosphates  of 
sodium,  viz.,  hydrogen-disodium  phosphate,  HNa^PO^  and  dihydrogen-sodium  phos- 
phate, H2NaP04. 

The  phosphates  commonly  met  with  are  all  derived  from  orthophosphoric  acid  : 
for  example,  bone-ash,  or  tricalcium  orthophosphate,  Ca3(P04)2  ;  superphosphate, 
or  monocalcium  orthophosphate,  CaH4(PO4)2 ;  common  phosphate  of  soda,  or 
hydrogen-disodium  orthophosphate,  HNa.2P04  ;  microcosmic  salt,  or  hydrogen- 
ammonium  sodium  orthophosphate,  HNH4Na(P04). 

Pyrophosphates  and  metaphosphates  may  be  obtained  by  the  action  of  heat  on. 


PHOSPHOROUS  ACID.  259 

the  orthohydrogen  phosphates.  Thus,  if  a  crystal  of  the  common  rhombic  sodium 
phosphate  (HNa.2PO4.i2Aq)  be  heated  gently  in  a  crucible,  it  melts  in  its  water  of 
crystallisation,  and  gradually  dries  up  to  a  white  mass,  the  composition  of  which, 
if  not  heated  beyond  149°  C.,  will  be  Na.2HPO4.  A  little  of  this  white  mass  dis- 
solved in  water  gives  a  solution  alkaline  to  red  litmus-paper  ;  and  if  silver  nitrate 
(itself  neutral  to  test-papers)  is  added  to  it,  a  yellow  precipitate  of  silver  ortho- 
phosphate  is  obtained,  and  the  solution  becomes  strongly  acid  — 

Na2HP04  +  3AgX03  =  Ag3P04  +  2NaNO3  +  HNO  . 

If  the  dried  sodium  phosphate  be  now  strongly  heated  over  a  lamp,  it  will  lose 
water,  and  become  pyrophosphate  (jrvp,  fi  re)  ;  2Na,2H  P04  =  H.2O  +  Na4P2O7.  On  dis- 
solving this  in  water,  the  solution  will  be  alkaline,  and  will  give  with  silver  nitrate 
a  white  precipitate  and  a  neutral  solution  ;  Na4P2O7  -H  4AgNO3  =  Ag4P.207  +  4NaN03. 

Microcosmic  salt  (NaNH4HP04.4Aq),  when  dissolved  in  water,  yields  an  allta- 
line  solution  which  gives  a  yellow  precipitate  with  silver  nitate,  the  liquid  becom- 
ing acid;  NaNH4HPO4  +  3AgN03  =  Ag3P04  +  NaNO3  +  NH4N03  +  HN03. 

But  if  the  salt  be  heated  in  a  crucible,  it  fuses,  evolving  water  and  ammonia, 
and  leaving  a  transparent  glass  of  sodium  metaphosphate  ;  NaNH4HPO4  = 
H2O  +  NH3  +  NaPO3,  which  may  be  dissolved  by  soaking  in  water,  yielding  a 
slightly  acid  solution,  which  gives  a  white  gelatinous  precipitate  with  silver  nitrate, 
the  liquid  being  neutral;  NaP03  +  AgN03  =  AgP03  +  NaNO3. 

All  the  phosphates  may  be  converted  into  orthophosphates,  by  fusing  them  with 
an  alkali,  or  by  boiling  them  for  some  time  with  a  dilute  acid.* 

153.  Phosphorus  anhydride  (P406)  is  a  product  of  tl^e  slow  combustion  of 
phosphorus,  and,  by  carefully  regulating  the  combustion,  may  be  made  to  consti- 
tute 50  per  cent,  of  the  oxides  produced,  the  remainder  being  P205.  It  is  prepared 
by  drawing  a  slow  current  of  air  over  ignited  phosphorus  and  causing  the  product 
to  pass,  first  through  a  tube  maintained  at  about  60°  C..  a  temperature  at  which 
P.205  condenses,  and  then  through  a  U-tube  surrounded  by  a  freezing-mixture 
wherein  the  P4O6  solidifies.  It  forms  feathery  crystals  which  melt  at  22.5°  C.  ;  it 
boils  at  173°  C.,  and  is  decomposed  at  higher  temperatures  (in  a  sealed  tube) 
according  to  the  equation  2P406  =  3P.204  +  P.2.  It  dissolves  slowly  in  cold  water, 
forming  phosphorous  acid,  P406  +  6HOH  =  4P(OH)3  ;  hot  water  decomposes  it  with 
great  violence.  It  burns  in  oxygen,  forming  P.205,  and  in  chlorine,  forming 
POC13  and  POr>Cl  (?).  Its  combustion  in  oxygen  is  attended  by  all  the  phenomena 
of  phosphorescence  shown  by  phosphorus,  but  no  ozone  is  produced. 

Phosphorus  tetroxide,  P204,  corresponding  with  N204,  is  obtained  as  a  very 
deliquescent  crystalline  sublimate  by  heating  P406  to  about  440°  C.  in  a  sealed 
tube  filled  with  C02  ;  the  white  P4O6  becomes  orange,  from  the  production  of  red 
phosphorus,  and  P204  sublimes  in  deliquescent  colourless  crystals.  When  dissolved 
in  water  it  is  converted  into  a  mixture  of  phosphorous  and  orthophosphoric  acids, 
just  as  nitric  peroxide,  N2O4,  is  converted  into  nitrous  and  nitric  acids  ; 
P004  +  3H20  =  H3P04  +  H3P03. 

"Phosphorous  acid,  H3P03  or  P(OH)3,  or  PHO(OH)2,  is  obtained  in  solution, 
mixed  with  phosphoric  acid,  when  sticks  of  phosphorus  arranged  in  separate  tubes 
open  at  both  ends  and  placed  in  a  funnel  over  a  bottle,  are  exposed  under  a  bell- 
jar,  open  at  the  top,  to  air  saturated  with  aqueous  vapour.  To  obtain  the  pure 
acid,  chlorine  is  very  slowly  passed  through  phosphorus  fused  under  water,  when 
the  phosphorous  chloride  first  formed  is  decomposed  by  the  water  into  phosphorous 
and  hydrochloric  acids  ;  PC13  +  3H20  =  P(OH)3  +  3HC1.  The  hydrochloric  acid  is 
expelled  by  a  moderate  heat,  when  the  phosphorous  acid  is  deposited  in  prismatic 
crystals.  When  heated,  it  is  decomposed  into  phosphoric  acid  and  gaseous  phos- 


phoretted  hydrogen  ;        33  =       34  3. 

Solution  of  phosphorous  acid  gradually  absorbs  oxygen  from  the  air,  becoming 
phosphoric  acid.  This  tendency  to  absorb  oxygen  causes  it  to  act  as  a  reducing- 
agent  upon  many  solutions  ;  thus  it  precipitates  finely  divided  metallic  silver 
from  a  solution  of  the  nitrate,  by  which  its  presence  may  be  recognised  in  the 
water  in  which  ordinary  phosphorus  has  been  kept.  The  solution  of  phosphorous 
acid  even  reduces  sulphurous  acid,  producing  sulphuretted  hydrogen  and  sulphur, 
the  latter  being  formed  by  the  action  of  the  sulphuretted  hydrogen  upon  the  sul- 
phurous acid;  H2SO3  +  3*H3P03  =  3H3P04  +  H2S.  Some  metals  dissolve  in  it, 
evolving  PH3. 

*  It  has  been  remarked  that  the  pliancy  of  the  acid  character  of  phosphoric  acid  particu- 
larly fits  it  to  take  part  in  the  vital  phenomena.  It  may  be  regarded  as  three  acids  in  one. 


260  STRUCTURE   OF  ACIDS. 

If  solution  of  phosphorous  acid  be  poured  into  a  hydrogen  apparatus,  some  PH3 
is  formed  which  imparts  a  fine  green  tint  to  the  hydrogen  flame. 

'  It  is  doubtful  whether  phosphorous  acid  is  dibasic  or  tribasic,  that  is,  whether  it 
•contains  2  or  3  hydroxyl  groups.  In  the  former  case  its  formula  should  be 
PHO(OH)2  in  the  latter,  P(OH)3. 

As  the  salt  Na3P03  has  been  prepared,  the  formula  P(OH)3  is  indicated  ;  it  is  sup- 
ported by  the  reaction  between  PC13  and  HOH. 

154.  Hypophosphorous  acid,  H3P02  or  PH20(OH).  —  When  phosphorus  is  boiled 
with  barium  hydroxide  and  water,  the  latter  is  decomposed,  its  hydrogen  com- 
bining with  part  of  the  phosphorus  to  form  hydrogen  phosphide  (spontaneously  in- 
flammable), which  escapes,  whilst  the  oxygen  of  the  water  unites  with  another 
part  of  the  phosphorus,  forming  hypophosphorous  acid,  which  acts  on  the  baryta 
to  form  barium  hypophosphite  ;  this  may  be  obtained,  by  evaporating  the  solution 
in  crystals  having  the  composition  (PH20.0)2Ba.  The  action  of  phosphorus  upon 
barium  hydroxide  may  be  represented  by  the  equation  — 

3Ba(OH)2  +  6H20   +   P8  =   3(PH20.0)2Ba  +   2PH3. 
Barium  hydroxide.  Barium  hypophosphite. 

Some  barium  orthophosphate  is  also  formed  at  the  same  time,  as  the  result  of  a 
secondary  action. 

By  dissolving  the  barium  hypophosphite  in  water,  and  decomposing  it  with  the 
requisite  quantity  of  sulphuric  acid,  so  as  to  precipitate  the  barium  as  sulphate,  a 
solution  is  obtained  which  may  be  concentrated  by  careful  evaporation.  If  this 
hypophosphorous  acid  be  heated,  it  evolves  hydrogen  phosphide,  and  becomes  con- 
verted into  phosphoric  acid  ;  2H3P02  =  H3P04  +  PH3.  When  exposed  to  the  air  it 
absorbs  oxygen,  and  becomes  converted  into  phosphorous  and  phosphoric  acids. 
It  is  a  more  powerful  reducing-agent  than  phosphorous  acid.  The  latter  acid  does 
not  reduce  a  solution  of  cupric  sulphate,  but  hypophosphorous  acid,  when  gently 
warmed  with  it,  gives  a  brown  precipitate  of  cuprous  hydride  (CuH),  which  is 
decomposed  by  boiling,  evolving  H  and  leaving  Cu. 

When  heated,  the  hypophosphites  evolve  hydrogen  phosphide,  and  are  converted 
into  phosphates.  The  sodium  hypophosphite,  PH2O.ONa,  is  sometimes  used  in 
medicine  ;  its  solution  has  been  known  to  explode  with  great  violence  during 
evaporation,  probably  from  a  sudden  disengagement  of  hydrogen  phosphide.  Hy- 
pophosphites, when  boiled  with  caustic  alkalies,  are  converted  into  phosphates, 
hydrogen  being  evolved  ;  phosphites  are  unchanged. 

Hypophoxphorio  acid,  H4P206  or  PO(OH)2.PO(OH)2,  exists  in  the  water  in  which 
phosphorus  has  been  kept. 

The  following  is  a  summary  of  the  acids  formed  ~by  phosphorus  with  oxygen  and 
hydrogen: 


Hypophosphorous  acid      .         .         .         .         .         .     PH20(OH) 

Hypophosphoric  acid        ......     P202(OH)4  •&  fi 

Phosphorous  „  ......     P(OH)3 

Metaphosphoric     ,  .......     PO2.(OH) 

Orthophosphoric    „  .         .....  /PO(OH)3  Hvttjl 

Pyrophosphoric      ,  .......     P203(OH)4        ^    - 

155.  Su'boxide  of  phosphorus,  P40,  is  supposed  to  constitute  the  yellow  or  red 
residue  which  is  left  in  the  dish  when  phosphorus  burns  in  air,  but  it  is  always 
mixed  with  much  phosphoric  anhydride.  It  is  also  said  to  be  obtained  by  allowing 
phosphorus  to  dissolve  slowly  in  an  alcoholic  solution  of  NaOH,  and  then  adding 
an  acid,  whereupon  an  orange  red  powder  is  precipitated. 

Structure  of  acids.  —  Attention  has  already  been  called  to  the  theory 
that  oxy-acids  contain  hydroxyl  groups  and  that  they  owe  their  basicity 
to  the  number  of  these  groups  (pp.  104,  191).  Since  the  group  OH  is 
monovalent  it  is  reasonable  to  suppose  that  the  atom  of  an  element 
would  be  capable  of  combining  with  one  of  these  groups  for  each  atom 
fixing-power  which  the  element  possesses.  Thus,  the  maximum  valency  of 
phosphorus  being  five  (as  seen  from  the  chloride  PC15)  the  acid  P(OH)5 
might  be  expected  to  exist,  although  it  is  not  known.  It  is  customary  to 
term  such  hydroxyl  compounds  of  the  elements  ortho-acids,  and  to  regard 


ANHYDRO-ACIDS.  261 

other  oxy-acids  as  being  derived  from  the  ortho-acids  by  loss  of  water  ; 
these  other  oxy-acids  are  called  auhydro-  acids  to  express  this  view. 

According  to  this  conception,  the  name  orthophosphoric  acid,  which 
has  been  given  to  H3P04,  is  a  misnomer,  for  this  acid  is  really  the  first 
anhydro-acid  of  true  orthophosphoric,  P(OH)5,  which  is  unknown. 
Pyro-phosphoric  acid  is  the  second  and  metaphosphoric  acid  the  third 
anhydro-acid  from  true  orthophosphoric  acid,  as  will  be  apparent  from 
the  following  :  — 

P(OH)5  -  H20         =  PO(OH)3,  "  orthophosphoric  acid  "  ; 
/0(OH)2 

~~ 


f  ~~  / 

\0(OH)2 
PO(OH)3  -  H20      =  P02(OH),  metaphosphoric  acid. 

Only  a  few  ortho-acids  are  known,  although  the  existence  of  several  others  is 
indicated  by  the  fact  that  some  of  their  salts  (chiefly  organic  salts)  have  been 
isolated.  The  ortho-acids  are  generally  very  unstable,  tending  to  lose  water  and 
to  become  anhydro-acids.  Thus,  orthocarbonic  acid,  C(OH)4,  has  never  been 
prepared,  although  several  organic  ortho-carbonates  of  the  type  C(OM)4,  in  which 
M  is  an  organic  basic  radicle,  are  known.  It  will  be  remembered  that  the 
anhydro-acid,  CO(OH)2(=:C(OH)4-  H20),  carbonic  acid,  is  supposed  to  exist  in 
the  aqueous  solution  of  C02  ;  but  this  also  readily  loses  water,  yielding  the  true 
anhydride,  C02(  =  CO(OH)2-H20).  Ortlionulphuric  acid,  S(OHJ6,  probably  exists 
in  an  aqueous  solution  of  sulphuric  acid,  for  the  maximum  contraction  which 
occurs  when  H2S04  and  H20  are  mixed  takes  place  when  the  proportion  of  acid  to 
water  is  expressed  by  the  formula  H2S04.2H20  or  H6S06.  It  very  readily  loses 
water,  however,  when  heated,  and  if  the  evaporated  solution  be  cooled  to  8°  C.  the 
anhydro-acid,  SO(OH)4  or  H2S04.H20,  crystallises,  which  in  its  turn  loses  water 
when  heated,  becoming  the  most  stable  anhydro-acid  of  sulphur,  H2S04  or 
S02(OH)2.  The  solution  of  S03  in  H2S04(H2S207),  which  melts  at  35°  C.  and  is 
called  anhydrosulphuric  acid,  must  be  regarded  as  a  further  anhydride  of  sulphuric 
acid  — 

2(OH) 


_ 
S02(OH)2/  '      2      ~ 

b\02(OH) 

Orthoxilicic  acid,  Si(OH)4,  is  believed  to  exist  in  solution  (p.  278),  but  it  very 
easily  loses  water,  becoming  the  anhydro-acid,  SiO(Ofl)2,  metasilicic  acid.  By 
the  loss  of  water  from  several  molecules  of  orthosilicic  acid,  anhydro-acids  of  com- 
plex type  would  be  produced  ;  thus  — 

Si/(OH)3 

Si(OH)4]  )o 

Si(OH)4  I  -  2H20  =  Sif  (OH)2 
Si(OH)J  )0 

S<(OH)3 

The  mineral  silicates  are  undoubtedly  derived  from  such  complex  silicic  acids,  the 
existence  of  which  is,  in  many  cases,  also  indicated  by  the  isolation  of  acid 
chlorides  (p.  191)  corresponding  with  them. 

Orthoboric  acid,  B(OH)3,  is  well  known.  OrtJwnitric  acid,  N(OH)5,  is  not  known  : 
ordinary  nitric  acid  is  the  anhydro-acid  N02(OH). 

The  ortho-acid  of  chlorine  should  be  C1(OH)7,  for  this  element  is  probably, 
heptavalent  to  elements  other  than  hydrogen  ;  but  no  anhydro-acid  intermediate 
between  this  and  C103(OH),  perchloric  acid,  is  known.  Ortlwwdic  add,  I(OH)7, 
is  unknown  ;  periodic  acid,  IO(OH)5,  is  the  first  anhydro-acid  from  orthoiodio; 
acid. 

On  reviewing  the  highest  oxy-acids  of  the  non-metallic  elements,  it  will  be  found. 
to  be  generally  true  that  those  acids  are  the  most  stable  which  contain  the  same, 


262 


PHOSPHINE. 


number  of  hydroxyl  groups  in  the  molecule  as  there  are  hydrogen  atoms  in  the 
highest  hydrogen  compound  of  the  element. 

PHOSPHIDES  OF  HYDROGEN. 

156.  Although  phosphorus  and  hydrogen  do  not  combine  directly, 
there  are  three  compounds  of  these  elements  producible  by  processes  of 
substitution,  viz.,  PH3,  gas ;  P2H4,  liquid  5  P4H2,  solid. 

Gaseous  hydrogen  phosphide,  or  phosphoretted  hydrogen,  or 
phosphine  (PH3  =  34  parts  by  weight),  is  by  far  the  most  important  of 
these.  It  has  been  mentioned  above  as  produced  by  the  action  of  heat  upon 
phosphorous  acid,  and  when  prepared  by  this  process,  it  is  a  colourless 
gas,  with  a  most  powerful  odour  of  putrid  fish,  inflaming  on  the  approach 
of  a  light,  and  burning  with  a  brilliant  white  flame,  producing  thick 
clouds  of  phosphorus  pentoxide.  It  is  slightly  heavier  than  air  (sp.  gr. 
1.18),  and  has  been  liquefied  at  -90°  0.  and  solidified  at  -  133°  C.  ; 
it  boils  at  -85°. 

The  ordinary  method  of  preparing  this  gas  for  experimental  purposes  consists  in 
"boiling  phosphorus  with  a  strong  solution  of  potash,  when  water  is  decomposed,  its 
hydrogen  combining  with  one  part  of  the  phosphorus,  and  its  oxygen  with  another 
part  forming  hypophosphorous  acid,  which  unites  with  the  potash — 

P4  +  sKOH  +  3H2O  =  PH3  +  3PH20(OK). 

A  few  fragments  of  phosphorus  are  introduced  into  a  small  retort  (Fig.  187). 
which  is  then  nearly  filled  with  a  strong  solution  of  potash  (45  grams  of  stick 

potash  in  100  c.c.  of  water),  and  heated. 
The  extremity  of  the  neck  of  the  retort 
should  not  be  plunged  under  water  until 
the  spontaneously  inflammable  gas  is  seen 
burning  at  the  orifice,  and  the  retort  must 
not  be  placed  close  to  the  face  of  the 
operator,  since  explosions  sometimes 
happen  in  preparing  the  gas,  and  the  boil- 
ing potash  produces  dangerous  effects. 
The  gas  may  be  collected  in  small  jars 
filled  with  water,  taking  care  that  no 
bubble  of  air  is  left  in  them.  It  contains 
hydrogen  phosphide  mixed  with  free 
hydrogen,  the  latter  being  formed  from 
the  de-oxidation  of  water  by  the  potas- 
sium hypophosphite.  As  each  bubble  of 
this  gas  escapes  into  the  air  through  the 
water  of  the  pneumatic  trough,  it  burns 
with  a  vivid  white  flame,  producing 
beautiful  wreaths  of  smoke  (phosphoric 
anhydride),  resembling  the  gunner's  ring* 
sometimes  seen  in  firing  cannon.  Small 
bubbles  sometimes  escape  without  spon- 
taneously inflaming.  If  a  bubble  be  sent  up  into  a  jar  of  oxygen,  the  flash  of  light 
is  extremely  vivid,  and  the  jar  must  be  a  strong  one  to  resist  the  concussion.  It  is 
advisable  to  add  a  trace  of  chlorine  to  the  oxygen,  to  ensure  the  inflammation  of 
each  bubble,  for  an  accumulation  of  the  gas  would  shatter  the  jar. 

It  is  stated  that  phosphoretted  hydrogen  may  be  added  to  pure  oxygen  without 
ignition  until  the  pressure  is  reduced,  when  explosion  suddenly  occurs  (compare 
the  phenomenon  of  phosphorescence,  p.  251). 

If  the  phosphoretted  hydrogen  be  passed  through  a  tube  cooled  in  a  freezing- 
mixture  of  ice  and  salt,  the  gas  escaping  from  the  tube  is  found  to  have  lost  its 
spontaneous  inflammability,  although  it  takes  fire  on  contact  with  flame.  The 
cold  tube  contains  the  liquid  hydrogen  phosphide  (P2H4),  which  was  present  in  the 
gas  in  the  state  of  vapour,  and  caused  its  spontaneous  inflammability,  for  as  soon  as 
the  liquid  comes  in  contact  with  air  it  takes  fire.  When  exposed  to  light,  the 


Fig.  187. 
Preparation  of  phosphoretted  hydrogen. 


CHLORIDES   OF  PHOSPHORUS.  263 

liquid  phosphide  is  decomposed  into  the  gaseous  phosphide,  and  a  yellow  solid 
phosphide  (P4H2),  which  is  not  spontaneously  inflammable  ;  5P2H4  =  P4H2  +  6PH3. 
It  is  for  this  reason  that  the  spontaneously  inflammable  gas  loses  that  property 
when  kept  (unless  in  the  dark),  depositing  the  solid  phosphide  upon  the  sides  of 
the  jar. 

By  passing  a  few  drops  of  oil  of  turpentine  up  through  the  water  into  a  jar  of  the 
spontaneously  inflammable  gas,  this  property  will  be  entirely  destroyed. 

Hydrogen  phosphide,  when  passed  through  solutions  of  some  of  the  metals,  pre- 
cipitates their  phosphides.  For  example,  with  cupric  sulphate  it  gives  a  black 
precipitate  of  cupric  phosphide  ; 


When  this  black  precipitate  is  heated  with  solution  of  potassium  cyanide,  it 
evolves  self-lighting  hydrogen  phosphide.  *  In  fact,  this  is  one  of  the  easiest  and 
safest  methods  of  preparing  this  gas  ;  for  the  cupric  phosphide  is  readily  obtained 
by  simply  boiling  phosphorus  in  a  solution  of  cupric  sulphate. 

Phosphine  is  absorbed  by  strong  sulphuric  acid,  and,  after  a  time,  acts  upon  it 
with  great  evolution  of  heat,  S02  being  formed  and  sulphur  deposited.  Sulphur 
decomposes  it  in  sunshine  ;  2PH3+S6  =  P2S3  +  3H2S. 

The  spontaneously  inflammable  hydrogen  phosphide  may  also  be  obtained  by 
throwing  fragments  of  calcium  phosphide  into  water  ;  this  substance  is  prepared  by 
passing  vapour  of  phosphorus  over  red-hot  quicklime,  or  simply  by  heating  small 
lumps  of  quicklime  to  bright  redness  in  a  crucible  and  throwing  in  fragments  of 
phosphorus,  closing  the  crucible  immediately.  The  dark  brown  mass  thus  obtained 
is  a  mixture  of  pyrophosphate  and  phosphide  of  calcium,  of  somewhat  variable 
composition.  The  calcium  phosphide  has  been  used  in  life-buoys  for  indicating  by 
the  flare  their  position  on  the  water. 

Phosphine  has  great  pretensions  to  rank  as  the  chemical  analogue  ot 
ammonia,  for  although  it  has  no  alkaline  properties,  it  is  capable  of 
combining  with  hydrobromic  and  hydriodic  acids  to  form  crystalline 
compounds  such  as  phosphonium  iodide,  PH4I,  analogous  to  ammonium 
bromide  and  iodide  ;  these  compounds,  however,  are  decomposed  by 
water.  It  will  be  seen  hereafter,  that  when  the  hydrogen  in  phosphine 
is  displaced  by  certain  compound  radicles,  such  as  ethyl,  powerful 
organic  bases  are  produced. 

When  phosphine  is  decomposed  by  a  succession  of  electric  sparks,  2  volumes  of 
the  gas  yield  3  volumes  of  hydrogen,  the  phosphorus  being  deposited  in  the  red 
form. 

157.  Two  chlorides  of  phosphorus  are  known.  The  trichloride  or  phosphorous 
chloride  (PC13),  the  acid  chloride  of  phosphorous  acid,  is  prepared  by  acting 
upon  phosphorus  with  perfectly  dry  chlorine  in  the  apparatus  employed  (p.  242)  for 
preparing  the  chloride  of  sulphur.  Red  phosphorus  may  be  used,  and  the  product 
redistilled  with  a  little  vitreous  phosphorus  to  decompose  any  PC15.  Phosphorous 
chloride  distils  over  very  easily  (boiling-point,  76°  C.),  as  a  colourless,  pungent 
liquid  (sp.  gr.  1.61),  which  fumes  strongly  in  air,  its  vapour  decomposing  the 
moisture  of  the  air  and  producing  hydrochloric  acid  fumes.  In  contact  with  water 
the  liquid  is  immediately  decomposed,  yielding  hydrochloric  and  phosphorous 
acids,  as  described  for  the  preparation  of  the  latter  acid  (p.  251).  Its  analogy  to 
phosphorous  anhydride  is  shown  by  its  absorbing  oxygen  when  boiled  in  the  pre- 
sence of  that  gas,  and  forming  the  phosphorus  oxy  chloride  or  phosphoryl  chloride 
POC13.  the  acid  chloride  of  phosphoric  acid.  It  also  absorbs  chlorine  with  avidity, 
becoming  converted  into  pentachlorlde  of  phosphorus  ex  phosphoric  chloride  (PC15). 
This  compound,  however,  is  more  conveniently  prepared  by  passing  chlorine 
through  a  solution  of  phosphorus  in  carbon  disulphide,  carefully  cooled.  On 
evaporation,  the  pentachloride  of  phosphorus  is  deposited  in  white  prismatic 
crystals,  which  volatilise  below  100°  C.,  and  fume  when  exposed  to  air,  from  the 
production  of  hydrochloric  acid.  When  PC15  is  heated  above  148°  C.  it  is  disso- 
ciated into  PC13  and  C12,  but  this  may  be  prevented  by  volatilising  it  in  an 
atmosphere  of  PC13,  and  thus  its  vapour  density  has  been  determined.  When 
thrown  into  wrater,  it  is  decomposed  into  phosphoric  and  hydrochloric  acids  ; 
PC15  +  4H20  =  H3PO4+5HC1.  But  if  it  be  allowed  to  deliquesce  in  air,  only  a 

*  Cupric  cyanide  and  potassium  phosphide  being  formed,  and  the  latter  decomposed  by 
water,  giving  hydrogen  phosphide  and  potassium  hypophosphite. 


264 


PHOSPHORUS  SULPHIDES. 


partial  decomposition  occurs,  and  the  phosphorus  oxychloride  is  formed  ; 
PC15  +  H20  =  POC13  +  2HC1.  The  same  compound  is  obtained  by  distilling  P205 
with  NaCl  ;  2P205  +  sNaCl  =  POC13  +  3NaP03. 

This  oxychloride  may  also  be  produced  by  heating  phosphoric  chloride  with 
phosphoric  anhydride  ;  P205  +  3PC15  =  5POC13.  A  more  instructive  method  of  pre- 
paring it  consists  in  distilling  the  phosphoric  chloride  with  crystallised  boric  acid  ; 
3PC15  +  2B(OH)3  =  3POC13  +  6HC1  +  B203. 

Some  of  the  organic  acids  (succinic,  for  example)  may  be  converted  into  anhy- 
drides, as  the  boric  acid  is  in  this  case,  by  distilling  with  phosphoric  chloride. 
The  phosphorus  oxychloride  distils  over  (boiling-point,  107°  C.)  as  a  heavy  (sp.  gr. 
1.7)  colourless  fuming  liquid  of  pungent  odour.  Of  course,  it  is  decomposed  by 
water,  yielding  hydrochloric  and  phosphoric  acids.  It  will  be  found  of  the  greatest 
use  in  effecting  certain  transformations  in  organic  substances. 

Pyropkogphoryl  chloride,  P203C14,  the  acid  chloride  of  pyrophosphoric  acid,  is  a 
product  of  the  action  of  N02  on  PC13.  It  is  a  fuming  liquid. 

The  analogy  between  water  and  hydrosulphuric  acid  would  lead  to  the  expecta- 
tion that  a  snip  ko  chloride  of  phosphorus  or  thiopJiosphoryl  chloride  (PSC13),  corre- 
sponding with  the  oxychloride,  would  be  formed  by  the  action  of  hydrosulphuric 
acid  upon  phosphoric  chloride  ;  PC15  +  H2S  =  PSC13  +  2HC1.  It  is  a  colourless 
fuming  liquid  (boiling-point  125°  C.,  sp.  gr.  1.68),  which  is  slowly  decomposed  by 
water,  giving  phosphoric,  hydrochloric,  and  hydrosulphuric  acids  ;  PSC13  +  4H20  = 
H3P04  +  3HC1  +  H2S.  When  attacked  by  solution  of  soda,  it  loses  its  chlorine  to 
the  sodium,  and  acquires  the  equivalent  of  oxygen,  a  sodium  thiophosphate 
(Na3POpS.i2H20)  being  deposited  in  crystals.  This  salt  evidently  corresponds  in 
composition  with  sodium  orthophosphate  (Na3P04.i2H20),  and  its  production  is 
expressed  by  the  equation—  PS013  +  6NaOH  =  3NaCl-f  Na3P03S  +  3H20.  Salts  of 
similar  composition  may  be  obtained  with  other  metallic  oxides. 

The  bromides  and  oxybromide  of  phosphorus  correspond  with  the  chlorine 
compounds  ;  as  also  do  the  fluorides.  The  latter  are  gaseous  under  ordinary 
conditions. 

Iodine  in  the  solid  state  combines  very  energetically  with  phosphorus,  but  if 
the  two  elements  be  brought  together  in  a  state  of  solution  in  carbon  disulphide, 
a  more  moderate  action  ensues,  and  two  iodides  of  phosphorus  may  be  obtained  in 
crystals  ;  a  tri-iodide.  (P13)  corresponding  with  the  trichloride,  and  phosphorus 
di-iodide  (P2I4),  which  has  no  analogue  either  among  the  oxygen,  chlorine,  or 
bromine  compounds  of  phosphorus.  P2I4  forms  orange-red  crystals,  which  are 
decomposed  by  water,  with  separation  of  red  phosphorus;  3P2I4+  I2H20  = 


The  addition  of  a  very  small  quantity  of  iodine  to  ordinary  phosphorus,  fused 
in  a  flask  filled  with  carbonic  acid  gas,  materially  accelerates  its  conversion  into 
the  red  modification,  and  allows  the  change  to  be  effected  at  a  much  lower  tem- 
perature than  that  required  when  the  phosphorus  is  heated  alone,  probably  because 
successive  portions  of  vitreous  phosphorus  combine  with  the  iodine  to  form  an 
unstable  iodide,  which  is  in  turn  decomposed  by  the  heat  into  red  phosphorus 
and  iodine. 

158.  The  sulphides  of  phosphorus  may  be  formed  by  the  direct  combination 
of  their  elements.  Yellow  phosphorus  liquefies  when  mixed  with  sulphur  (an  opera- 
tion not  unattended  by  danger),  and  the  liquid  dissolves  as  much  as  25  per  cent,  of 
sulphur.  It  fumes  in  air  and  readily  ignites,  but  it  appears  to  be  only  a  solution 
of  sulphur  in  phosphorus,  which,  like  most  other  solutions,  has  a  lower  melting- 
point  than  that  of  the  solvent  (phosphorus).  When  a  mixture  of  red  phosphorus 
and  sulphur  is  heated,  combination  occurs,  and  either  P2S3  or  P2S5  is  formed 
according  to  the  proportions  used.  A  clay  crucible  is  heated  by  a  bunsen  burner 
and  a  mixture  of  red  phosphorus  (31  parts)  and  sulphur  (48  parts)  is  added  by 
degrees,  the  crucible  being  covered  after  each  addition  until  the  reaction  is  over. 
The  crucible  is  allowed  to  cool  until  the  mass  is  about  to  solidify,  and  the  phos- 
phorus trisulphide  is  then  poured  on  to  an  iron  plate.  It  is  a  dirty  yellow  crystal- 
line mass  of  sp.  gr.  2.0  and  melting-point  167°  C. 

Phosphorus  pentasulphide,  P2S5,  is  similarly  prepared  and  melts  at  275°  C.  and 
boils  at  530°  C.  ;  from  CS2  it  separates  in  nearly  colourless  crystals.  Both  sul- 
phides deliquesce  in  air,  being  decomposed  into  oxyacids  of  phosphorus  with 
evolution  of  H2S,  and  both  are  used  in  organic  chemistry  for  substituting  S  for  0. 

P2S5   combines   with   alkali   sulphides,  forming  thlophosp  hates 
2K3PS4. 


ARSENIC.  265 

159.  Amides. — A  general  reaction  between  ammonia  and  an  acid 
chloride  is  the  production  of  the  amide  corresponding  with  the  acid 
whose  chloride  is  being  treated.     The  amide  of  an  acid  contains  NH2 
(amidogen)  in  place  of  the  hydroxyl  of  the  acid ;  the  reaction  may  be 
regarded  as  consisting  of  an  exchange  of  01  for  ]SH2 ;  thus,  the  action 
of   ammonia  on   phosphoryl  chloride  produces  the  amide  of  "  ortho- 
phosphoric  acid,"  PO(NH2)3,  called  phospho-triamide.     The  change  may 
be  written  POC13  +  3NH"2'H  =  PO(NHa)3  +  3HC1,  but  it  will  not  occur 
unless  excess  of  ammonia  be  present  to  combine  with  the  liberated  HC1, 
§o  that  the  actual  reaction  is  POC13  +  6NH3  =  3NH4C1  +  PO(NH2)3. 

When  an  amide  is  boiled  with  an  acid  or  an  alkali  it  reacts  with  the 
water,  producing  the  acid  from  which  it  is  derived,  and  ammonia.  Such 
a  decomposition  by  water  is  termed  hydrolysis;  PO(NH,)3  +  3HOH  = 
PO(OH)3  +  3NH3. 

If  an  acid  be  present  the  N  H3  will  immediately  become  an  ammonium 
salt.  If  an  alkali  be  present  the  ammonia  will  be  evolved  and  the 
alkali  will  combine  with  the  phosphoric  acid.  If  neither  acid  nor 
alkali  be  present  the  change  will  not  proceed  far. 

If  the  sulphochloride,  PSCl3,be  substituted  for  the  oxychloride  and  treated  with 
ammonia,  the  corresponding  sulphosphotriamide,  PS(KH2)3,  is  obtained. 

The  action  of  ammonia  on  phosphoric  chloride  yields  chlorophosphamide^ 
PC13(NH2)2  ;  PC15  +  2NH3  =  2HC1  +  PC1?(NH2)3,  and  phospham,  PN2H,  a  white  solid 
which  is  the  analogue  of  hydrogen  nitride,  N3H. 

When  chlorophosphamide  is  boiled  with  water,  a  very  stable  insoluble  substance 
is  obtained,  which  is  phosphodiamide  ;  N2H4PC13  +  H20  =  3HC1  +  N2H3PO  (phospho- 
diamide). 

When  heated,  it  evolves  ammonia  and  becomes  phosphonitrile.  the  analogue  of 
nitrous  oxide  ;  N2H3PO  =  NH3  +  NPO. 

The  phosphamides  may  be  regarded  as  being  derived  from  the  ammonium  ortho- 
phosphates  by  the  abstraction  of  3H20  ;  thus— 

(NH4)3P04    minus  jH,/)  =  N3H6PO  or  PO(NH2)3,  Phosphotriamide. 
(NH4)2HP04     „         „        =  N2H3PO  or  PO(NH2)NH,  Phosphamide-imide. 
NH4H2P04        „         „        =  NPO,  Phosphonitrile. 

Nitrogen  chlurophosphi'de,  NV3P'"3C16,  is  obtained  by  distilling  phosphoric  chloride 
with  ammonium  chloride  ;  3PC15  +  3NH4C1  =  N3P3C16+  I2HC1.  It  forms  colourless 
rhombic  prisms,  melting  at  114°  C.  and  insoluble  in  water,  but  slowly  decomposed 
by  it;  2P3N3C16+ I5H20  =  I2HC1  +  3P203(NH2)2(OH)2,  pyrophosphodiamic  acid, 
or  pyrophosphoric  acid,  P203(OH)4,  in  which  two  NH2  groups  have  been  substi- 
tuted for  two  OH  groups. 

ARSENIC. 
As  =  74.5  parts  by  weight.* 

1 60.  This  element  is  often  classed  among  the  metals,  because  it  has  a 
metallic  lustre  and  conducts  electricity,  but  it  is  not  capable  of  forming 
a  base  with  oxygen,  and  the  chemical  character  and  composition  of  its 
compounds  connect  it  in  the  closest  manner  with  phosphorus. 

In  its  mode  of  occurrence  in  nature  it  more  nearly  resembles  the 
sulphur  group  of  elements,  for  it  is  occasionally  found  in  the  uncombined 
state  (native  arsenic),  but  far  more  abundantly  in  combination  with 
various  metals,  forming  arsenides,  which  frequently  accompany  the  sul- 
phides of  the  same  metals.  The  following  are  some  of  the  chief  arsenides 
and  arsenio-sulphides  found  in  the  mineral  kingdom  : — 

*  The  specific  gravity  of  the  vapour  of  arsenic,  like  that  of  phosphorus,  indicates  that 
74.5  parts  by  weight  only  occupy  half  a  volume.  Hence  the  molecule  of  arsenic  must  be 
represented  as  As4  =  2  volumes  ;  but  at  very  high  temperatures  a  disposition  to  conform  with 
the  law  is  shown  by  a  diminution  in  the  vapour  density. 


266  EXTRACTION   OF   ARSENIC. 


Kupfernickel  NiAs 

Arsenical  nickel  NiAs2 

Tin- white  cobalt  CoAs2 

Arsenical  iron  Fe2As3 


Mispickelor  \ 

Arsenical  pyrites    J 

Cobalt-glance  CoS2.  CoAs2 

Nickel-glance  NiS2.NiAs2 


But  arsenic  also  occurs,  like  the  metals,  in  combination  with  sulphur ; 
thus  we  have  red  orpiment  or  realgar,  As2S2,  and  yellow  orpiment, 
As2S3.  It  is  from  these  minerals  that  arsenic  derives  its  name 
(apcrfviK&v,  orpiment). 

The  sulphides  of  arsenic  are  also  found  in  combination  with  other  sulphides  ; 
thus  Proustite  is  a  compound  of  the  sulphides  of  silver  and  arsenic  (3Ag2S.As2S3)  ; 
Tennantite  contains  sulphide  of  arsenic  combined  with  the  sulphides  of  iron  and 
copper  ;  and  grey  copper  ore  is  composed  of  sulphide  of  arsenic  with  sulphides  of 
copper,  silver,  zinc,  iron,  and  antimony.  In  an  oxidised  form  arsenic  is  found  in 
condurrite,  which  contains  arsenious  anhydride  (As406)  and  cuprous  oxide. 
Cobalt-bloom  consists  of  cobalt  arsenate,  Co3(As04)2. 

Arsenical  pyrites  is  one  of  the  principal  sources  of  arsenic  and  its 
compounds,  though  a  considerable  quantity  is  also  obtained  in  the  form 
of  arsenious  oxide  as  a  secondary  product  in  the  working  of  certain  ores, 
especially  those  of  copper,  tin,  cobalt,  and  nickel. 

The  substance  used  in  the  arts  under  the  name  of  arsenic  is  really 
the  arsenious  oxide  (As406) ;  pure  arsenic  itself  has  very  few  useful 
applications,  so  that  it  is  not  the  subject  of  an  extensive  manufacture. 
Arsenic  can  be  extracted  from  mispickel  (Fe2S2As2)  by  heating  it  in 
earthern  cylinders  fitted  with  iron  receivers  in  which  the  arsenic 
condenses  as  a  metallic-looking  crust,  the  heat  expelling  it  from  the 
mineral  in  the  form  of  vapour. 

On  a  small  scale  it  may  be  obtained  by  heating  a  mixture  of  white  arsenic 
with  half  its  weight  of  recently  calcined  charcoal  in  a  crucible  (Fig.  188),  the 

mixture  being  covered  with  two  or  three  inches 
of  charcoal  in  very  small  fragments,  and  the 
crucible  so  placed  that  this  charcoal  may  be 
heated  to  redness  first,  in  order  to  ensure  the 
reduction  of  any  oxide  which  might  escape  from 
below.  In  order  to  collect  the  arsenic,  another 
crucible,  having  a  small  hole  drilled  through  the 
bottom  for  the  escape  of  gas,  is  cemented  on 
to  the  first,  in  an  inverted  position,  with  fire- 
clay, and  protected  from  the  fire  by  an  iron  plate 
with  a  hole  in  it  for  the  crucible.  The  reduc- 
tion of  arsenious  anhydride  by  charcoal  is  thus 
represented — As406  +  C6  =  As4  +  6CO. 

For  the  sake  of  illustration,  a  small  quantity 
of  arsenic  may  be  prepared  from  white  arsenic 
by  a  method  commonly  employed  in  testing  for 
that  substance.     A  small  tube  of  German  glass 
Fig.  188. — Extraction  of  arsenic.       is  drawn  out  to  a  narrow  point  (A,  Fig.   189), 

and  sealed  with  the  aid  of  the  blow-pipe.     A 

very  minute  quantity  of  white  arsenic  is  introduced  into  the  point  of  the  tube,  and 
a  few  fragments  of  charcoal  are  placed  in  the  tube  itself  at  B.  The  charcoal  is 
heated  to  redness  with  a  blow-pipe  flame,  and  the  point  is  then  heated  so  as  to 
drive  the  white  arsenic  in  vapour  over  the  red-hot  charcoal,  when  a  shining  black 
ring  of  arsenic  (C)  will  be  deposited  upon  the  cooler  portion  of  the  tube. 

The  arsenic  thus  obtained  is  a  brittle  mass  of  a  dark  steel-grey  colour 
and  brilliant  metallic  lustre  (sp.  gr.  5.7).  It  vaporises  at  180°  C. 
without  melting  unless  it  is  heated  in  a  sealed  tube  under  the  pressure 
of  its  own  vapour,  when  it  melts  at  480°  C.  It  is  not  changed  by 
exposure  to  air,  unless  powdered  and  moistened,  when  it  is  slowly 


OXIDES   OF  ARSENIC.  267 

Converted  into  As4O6.  When  heated  in  air  it  oxidises  rapidly  at  about 
71°  C.,  giving  off  white  fumes  of  arsenious  oxide  and  a  characteristic 
garlic  odour  (recalling  that  of  phosphorus),  which  is  also  produced  when 
arsenical  pyrites  is  struck  with  a  hammer  or  pick.  At  a  red  heat  it 
burns  in  air  with  a  bluish-white  flame,  and  in  oxygen  with  great 
brilliancy.  1 1  is  not  dis- 
solved by  water  or  any 
simple  solvent,  but  is 
oxidised  and  dissolved  by 
nitric  acid, 

In  its  chemical  relations 
to  other  elements,  arsenic 
much  resembles  phos- 
phorus, undergoing  spon- 
taneous combustion  in 
chlorine,  and  easily  com- 
bining with  sulphur.  Fig.  l85._Reduction  of  arsenious  oxide. 
Like  phosphorus  also,  it 

•combines  with  many  metals,  even  with  platinum,  to  form  arsenides,  and 
its  presence  often  affects  materially  the  properties  of  the  useful  metals. 

Pure  arsenic  does  not  produce  symptoms  of  poisoning  till  a  consider- 
able period  after  its  administration,  being  probably  first  oxidised  in  the 
stomach  and  intestines,  and  converted  into  arsenious  acid. 

Arsenic  vapour  is  colourless,  but  when  rapidly  cooled  it  appears 
yellow  owing  to  the  condensation  of  a  cloud  of  minute  yellow  crystals 
which  are  an  allotropic  modification  of  arsenic,  soluble  in  CS2  and  re- 
markably sensitive  to  light,  which  converts  it  into  the  black  variety. 

When  arsenic  is  sublimed  in  a  tube  filled  with  hydrogen,  ordinary 
or  crystalline  arsenic  condenses  on  the  warmer  part  of  the  tube,  but 
on  the  cooler  part,  amorphous  arsenic  is  deposited,  of  sp.  gr.  only  4.7. 
This  is  not  so  easily  oxidised  in  moist  air  as  the  crystalline  variety. 
At  360°  C.  it  evolves  heat  and  becomes  converted  into  crystalline 
arsenic.* 

161.  Oxides  of  Arsenic. — Arsenic  forms  two  oxides,  corresponding 
with  phosphorous  and  phosphoric  anhydrides,  viz.,  As406  and  As205. 

Arsenious  oxide  (As406  =  396  parts  by  weight) — Unlike  phosphorus, 
arsenic,  when  burning  in  air,  only  combines  with  oxygen  to  form  its 
lower  oxide.  Arsenious  oxide,  or  white  arsenic,  is  a  very  useful  sub- 
stance in  many  branches  of  industry.  It  is  employed  in  the  manufac- 
ture of  glass,  and  of  several  colouring-matters.  A  large  quantity  is 
also  consumed  for  the  preparation  of  arsenic  acid  and  arsenate  of  soda ; 
it  is,  indeed,  the  source  from  which  nearly  all  the  compounds  of  arsenic 
are  procured.  Small  quantities  of  crystalline  arsenious  oxide  are  occa- 
sionally found  associated  with  the  ores  of  nickel  and  cobalt. 

White  arsenic  is  manufactured  by  roasting  the  arsenical  pyrites, 
chiefly  obtained  from  the  mines  of  Silesia,  in  muffles  or  ovens,  through 
which  air  is  allowed  to  pass,  when  the  arsenic  is  converted  into  As4O6, 
and  the  sulphur  into  SO2,  which  are  conducted  into  large  chambers 
wherein  the  As406  is  deposited  as  a  very  fine  powder.  The  iron  of  the 

*  Another  amorphous  variety  of  arsenic  has  been  described  as  a  brownish-black  powder 
of  sp.  gr.  3.7.  Doubt  has  been  expressed  concerning  the  amorphous  character  of  this  allo- 
trope  of  arsenic. 


268  WHITE  AESENIC. 

pyrites  is  left  partly  as  oxide,  and  partly  as  sulphate  of  iron.  The 
removal  of  the  As4O6  from  the  condensing- chambers  is  a  very  unwhole- 
some operation,  owing  to  its  dusty  and  very  poisonous  character.  The 
workmen  are  cased  in  leather,  and  protect  their  mouths  and  noses  with 
damp  cloths,  so  as  to  avoid  inhaling  the  fine  powder. 

This  rough  white  arsenic  is  subjected  to  a  second  sublimation  on  a 
smaller  scale  in  iron  vessels,  when  it  is  obtained  in  the  form  of  a  semi- 
transparent  glassy  mass  known  as  vitreous  arsenious  acid,  which  gradually 
becomes  opaque  from  crystallisation  when  kept,  and  ultimately  resembles 
porcelain.  The  white  arsenic  sold  in  the  shops  is  a  fine  powder, 
dangerously  resembling  flour  in  appearance,  but  so  much  heavier  (sp. 
gr.  3.7)  that  it  ought  not  to  be  mistaken  for  it.  When  examined  under 
the  microscope  it  appears  in  the  form  of  irregular  glassy  fragments, 
mixed  with  octahedral  crystals.  White  arsenic  softens  when  gently 
heated,  but  does  not  fuse  (unless  in  a  sealed  tube),  being  converted  into 
vapour  at  193°  C.,  and  depositing  in  brilliant  octahedral  crystals  upon 
a  cool  surface.  The  experiment  may  be  made  in  a  small  tube  sealed  at 
one  end,  the  upper  part  of  which  should  be  slightly  warmed  before 
heating  the  arsenious  oxide,  so  as  to  prevent  too  rapid  condensation, 
which  is  unfavourable  to  the  formation  of  distinct  crystals.  The 
octahedra  are  best  examined  with  a  binocular  microscope.  By  satura- 
ting a  boiling  solution  of  KOH  with  As406,  and  allowing  the  liquid 
to  cool,  prismatic  crystals  (sp.  gr.  4)  separate.  Thus  As406  is  both 
amorphous  and  dimorphous,  the  amorphous  form  (sp.  gr.  3.7)  being 
condensed  from  the  vapour  on  a  hot  surface,  the  octahedral  (sp.  gr.  3.7) 
condensing  on  a  cool  surface,  and  the  prismatic  crystallising  as  described 
above.  When  crystallised  from  water  both  the  other  forms  become 
octahedral.  The  change  from  amorphous  to  crystalline  arsenious  oxide 
is  attended  by  evolution  of  heat. 

The  amorphous  and  octahedral  forms  differ  in  solubility,  one  part 
of  the  former  dissolving  in  108  parts  of  water  at  15°  C.,  and  one  part 
of  the  crystalline  in  355  parts.  At  the  boiling-point  these  numbers 
become  30  and  46  respectively. 

This  common  poison  may  fortunately  be  easily  recognised  by  sprink- 
ling it  upon  a  red-hot  coal,  when  a  strong  odour  of  garlic  is  percep- 
tible, due  to  the  reduction  of  the  As4O6  by  the  heated  carbon  ;  the 
vapour  of  white  arsenic,  or  that  of  arsenic,  is  itself  inodorous.  The 
sparing  solubility  of  white  arsenic  in  water  is  very  unfavourable  to  its 
action  as  a  poison,  for,  when  thrown  into  ordinary  liquids,  it  is  dissolved 
in  very  small  quantity,  the  greater  part  of  it  collecting  at  the  bottom. 
Even  when  taken  into  the  stomach  in  a  solid  state,  its  want  of  solubility 
delays  its  operation  sufficiently  to  give  a  better  chance  of  antidotal 
treatment  than  in  the  case  of  most  other  common  poisons.  Its  com- 
parative insolubility  is  shown  by  its  being  almost  tasteless.  Although 
so  little  as  2.5  grains  of  white  arsenic  have  been  known  to  prove  fatal, 
the  exhibition  of  gradually  increasing  doses  will  so  inure  the  system  to 
the  poison  that  comparatively  large  quantities  can  be  administered  at 
frequent  intervals.  When  exhibited  in  this  manner,  white  arsenic 
appears  to  have  a  remarkable  effect  on  the  animal  body.  Grooms 
occasionally  employ  it  to  improve  the  appearance  of  horses,  and  in  Styria, 
it  seems,  it  is  taken  by  men  and  women  for  the  same  purpose,  apparently 
favouring  the  secretion  of  fat.  It  is  said  that  a  continuance  of  the 


SOLUBILITY   OF  WHITE  AESENIC.  269 

custom  develops  a  craving  for  this  drug,  and  enables  it  to  be  taken 
without  immediate  danger,  though  the  ultimate  consequences  are  very 
serious.  The  antidote  to  the  poison  is  ferric  hydroxide,  made  by  mixing 
magnesia  with  ferric  chloride  solution ;  this  acts  by  rendering  the 
arsenic  insoluble. 

The  very  general  distribution  of  arsenic  through  the  mineral  kingdom 
makes  it  necessary  that  the  analyst  should  ever  be  on  the  watch  for 
this  insidious  poison.  As  has  been  already  seen  the  arsenic  in  ordinary 
pyrites  finds  its  way  into  the  sulphuric  acid  made  therefrom,  and  then 
into  the  commercial  hydrochloric  acid  distilled  with  aid  of  this  sulphuric 
acid.  The  use  of  sulphuric  acid  containing  arsenic  for  converting  starch 
into  glucose  subsequently  used  in  making  beer  has  been  the  cause  of 
many  deaths  in  the  district  consuming  the  beer.  This  beverage  appears 
to  be  liable  also  to  contain  arsenic  derived,  it  is  alleged,  from  pyrites  in 
the  fuel  used  to  dry  the  malt,  from  which  the  beer  is  brewed. 

When  thrown  into  water,  white  arsenic  exhibits  great  repulsion  for  the  particles 
of  that  liquid,  and  collects  in  a  characteristic  manner  round  little  bubbles  of  air 
forming  small  white  globes  which  are  not  wetted  by  the  water.  Even  if  stirred, 
with  the  water,  and  allowed  to  remain  in  contact  with  it  for  some  hours,  a  pint  of 
water  (20  oz.)  would  not  take  up  more  than  20  grains.  If  boiling  water  be  poured 
upon  powdered  white  arsenic,  and  allowed  to  remain  in  contact  with  it  till  cold, 
it  will  dissolve  about  ^^th  of  its  weight  (22  grains  in  a  pint). 

When  powdered  white  arsenic  is  boiled  with  water  for  two  or  three  hours,  ico 
parts  by  weight  of  \\ater  may  be  made  dissolve  11.5  parts,  and  when  the  solution 
is  allowed  to  cool,  about  9  parts  will  be  deposited  in  octahedral  crystals,  leaving 
2.5  parts  dissolved  in  100  of  water  (219  grains  in  a  pint). 

This  great  increase  in  the  solubility  of  the  arsenious  oxide  by  long  boiling  with 
water  is  usually  attributed  to  the  conversion  of  the  opaque  or  crystalline  variety, 
which  always  composes  the  powder,  into  the  vitreous  modification,  which  is  the 
more  soluble  in  water  (4  parts  in  100  of  water).  Water,  heated  with  white  arsenic 
in  a  sealed  tube,  may  be  made  to  dissolve  its  own  weight  of  it  ;  as  the  solution 
cools,  it  first  deposits  prismatic  crystals,  and  afterwards  the  ordinary  octahedral 
form.  The  solution  is  very  feebly  acid  to  blue  litmus-paper.  Glycerine  dissolves 
As406  easily  when  heated. 

White  arsenic  dissolves  abundantly  in  hot  hydrochloric  acid  (a  part  of 
it  being  converted  into  arsenious  chloride),  and  as  the  solution  cools, 
part  of  the  oxide  is  deposited  in  large  octahedral  crystals.  The  forma- 
tion of  these  crystals  is  attended  by  flashes  of  light,  visible  in  a 
darkened  room. 

This  experiment,  which  is  exceedingly  beautiful,  is  best  performed  by  boiling 
60  grams  of  arsenious  oxide  in  500  c.c,  of  a  mixture  of  equal  volumes  of  strong 
hydrochloric  acid  and  water  in  a  flask,  and  allowing  the  solution  to  cool  slowly  ; 
after  a  time  the  crystals  begin  to  form,  a  flash  of  light  accompanying  the  formation 
of  each,  and  the  effect  may  be  enhanced  by  carefully  shaking  the  flask.  It  is  said 
that  it  is  only  the  vitreous  form  which  exhibits  this  phenomenon  ;  but  the  same 
solution  will  generally  serve  for  the  above  experiment  any  number  of  times  if  it 
be  reheated,  although  the  arsenious  oxide  has,  of  course,  been  deposited  in 
the  crystalline  form  ;  it  is,  however,  remarkable  that  the  experiment  sometimes 
unaccountably  fails. 

Solutions  of  the  alkalies  readily  dissolve  arsenious  oxide,  forming 
alkali  arsenites,  the  solutions  of  which  are  capable  of  dissolving  arsenious 
oxide  more  easily  than  water  can,  and  deposit  it  in  crystals  on  cooling 
(see  above).  On  adding  a  small  quantity  of  hydrochloric  acid  to  the 
solution  of  the  alkali  arsenite,  a  white  precipitate  of  arsenious  oxide 
is  formed. 

White  arsenic  has  the  property  of  preventing  the  putrefaction  of  skin 


270  ARSENITES. 

and  similar  substances,  and  is  occasionally  employed  for  the  preservation 
of  objects  of  natural  history,  &c. 

Arsenites. — Arsenious  acid, properly  so  called. has  not  yet  been  obtained 
in  the  separate  state.  The  aqueous  solution  of  white  arsenic,  when 
neutralised  exactly  with  ammonia,  yields,  with  silver  nitrate,  a  yellow 
precipitate  having  the  composition  Ag'3AsO3 ;  with  cupric  sulphate,  a 
green  precipitate  having  the  composition  Cu"HAsO3;  with  zinc  sulphate, 
a  white  precipitate  containing  Zn"3(AsO3)2  ;  and  with  magnesium 
sulphate,  a  white  precipitate  of  Mg"HAsO3.  It  would  appear,  therefore, 
that  the  arsenious  acid  from  which  these  salts  are  derived  is  a  tribasic 
acid  having  the  formula  H3AsO3,  or  As(OH)3,  corresponding  with  boric 
acid,  H3BO3.  Arsenious  acid  does  not  destroy  the  alkaline  reaction  of 
the  alkalies,  and  it  does  not  decompose  the  alkaline  carbonates  unless 
heat  is  applied,  proving  it  to  be  a  feeble  acid.  The  ammonium  arsenite 
is  very  unstable,  evolving  ammonia  freely  when  exposed  to  the  air. 
When  arsenious  oxide  is  dissolved  in  a  hot  solution  of  ammonia, 
octahedral  crystals  of  it  are  deposited  on  cooling,  notwithstanding  the 
presence  of  ammonia  in  large  excess.  The  alkali  arsenites  are  more 
correctly  metarsenites,  for  they  are  derived  from  HAs02,  or  AsO(OH), 
metarsenious  acid  ;  the  potassium  arsenite  is  KAsO2. 

When  the  carbonates  of  potassium  and  sodium  are  fused  with  an  excess  of 
arsenious  oxide,  brilliant  transparent  glasses  are  obtained  which  are  similar  in 
composition  to  glass  of  borax  (K2As407  and  Na,2As407). 

If  an  alkali  arsenite  be  fused  in  contact  with  platinum,  the  latter  is  easily  melted,, 
combining  with  a  small  proportion  of  arsenic  to  form  a  fusible  platinum  arsenide, 
a  portion  of  the  arsenite  being  converted  into  arsenate.  The  alkali  arsenates 
(from  arsenic  acid,  H3As04)  are  so  much  more  stable  than  the  arsenites  that  the 
latter  exhibit  a  great  tendency  to  pass  into  the  former,  with  separation  of  arsenic. 

The  arsenites  of  potassium  and  sodium  in  solution  are  sometimes  employed  as 
sheep-dipping  compositions  ;  and  an  arsenical  soap,  composed  of  potassium  arsenite,. 
soap,  and  camphor,  is  used  by  naturalists  to  preserve  the  skins  of  animals.  Sodium 
arsenite  is  also  occasionally  employed  for  preventing  incrustations  in  steam  boilers, 
being  prepared  for  that  purpose  by  dissolving  2  molecules  of  white  arsenic  and 
I  molecule  of  sodium  carbonate. 

Scheele's  green  is  an  arsenite  of  copper  (CuHAsO3)  prepared  by  dissolv- 
ing white  arsenic  in  a  solution  of  potassium  carbonate,  and  decomposing 
the  arsenite  of  potassium  thus  produced  by  adding  sulphate  of  copper, 
when  the  arsenite  of  copper  is  precipitated.  This  poisonous  colour  i& 
used  to  impart  a  bright  green  tint  to  paper  hangings,  and  is  sometimes 
injurious  to  the  health  of  the  occupants  of  rooms  thus  decorated,  since 
the  arsenite  of  copper  is  often  easily  rubbed  off  the  paper,  and  diffused 
through  the  air  in  the  form  of  a  fine  dust,  a  small  portion  of  which  is 
inhaled  with  every  breath. 

The  presence  of  the  arsenite  of  copper  in  a  sample  of  such  paper  is  readily  proved 
by  soaking  it  in  a  little  ammonia,  which  will  dissolve  the  arsenite  of  copper  to  a 
blue  liquid,  the  presence  of  arsenic  in  which  may  be  shown  by  acidifying  it  with  a 
little  pure  hydrochloric  acid,  and  boiling  with  one  or  two  strips  of  pure  copper, 
which  will  become  covered  with  a  steel-grey  coating  of  arsenide  of  copper.  On 
washing  the  copper,  drying  it  on  filter-paper,  and  heating  it  in  a  small  tube 
(Fig.  190),  the  arsenic  will  be  converted  into  arsenious  oxide,  which  will  deposit  in 
brilliant  octahedral  crystals  on  the  cool  part  of  the  tube.  It  is  obvious  that,  to 
avoid  mistakes,  the  ammonia,  hydrochloric  acid,  and  copper  should  be  examined 
in  precisely  the  same  way,  without  the  suspected  paper,  so  as  to  render  it  certain 
that  the  arsenic  is  not  derived  from  them. 

The  effective  green  colour  of  the  arsenite  of  copper  also  leads  to  its 


AESENIC  ACID.  271 

employment  as  a  colour  for  feathers,  muslin,  &c.,  where  it  is  very  in- 
jurious to  the  health  of  the  workpeople.     It  has  even  been  ignorantly 
or   recklessly   used   for  colouring 
twelfth-cake  ornaments,  &c. 

Emerald-green  (Paris  green)  is 
a  combination  of  arsenite  and 
acetate  of  copper  obtained  by 
mixing  hot  solutions  of  equal 
weights  of  white  arsenic  and 
acetate  of  copper.  Solution  of 
potassium  arsenite  (Fowler's  solu- 
tion) has  long  been  used  in  medi- 
cine. 

Both  Scheele's  green  and  Paris 
green  are  used  as  insecticides  on 
growing  crops. 

162.  Arsenic  acid  (H3AsO4  or  AsO(OH)3).  Arsenic  acid  is  prepared 
by  oxidising  white  arsenic  with  three-fourths  of  its  weight  of  nitric  acid 
of  sp.  gr.  1.35,  when  it  dissolves  with  evolution  of  much  heat  and 
abundant  red  fumes  of  nitrous  anhydride — 

As406  +  4HN03  +  4H.20  =  2N203  +  4H3As04. 

After  cooling,  the  solution  deposits  very  deliquescent  prismatic 
crystals  containing  2H3AsO4.H.,O.  When  heated  to  100°  C.,  these 
melt,  and  the  liquid  deposits  needle-like  crystals  of  ortho-arsenic  acidf 
H3AsO4,  corresponding  with  orthophosphoric ;  at  180°  C.,  2H3As04  = 
H20  -f  H4As207,  pyro-arsenic  acid,  corresponding  with  pyrophosphoric  ; 
at  206°  C.,  H4As207=  H2O  +  2HAs03,  metarsenic  acid,  corresponding 
with  metaphosphoric  ;  but  here  the  resemblance  ceases,  for  at  260°  C.r 
2HAsO3  =  H2O  +  As,O5,  whereas  HPO3  may  be  vaporised  without  decom- 
position. When  metarsenic  and  pyro-arsenic  acids  are  dissolved  in 
water,  they  at  once  become  ortho-arsenic  acid.  The  meta-  and  pyro- 
arsenates  are  known  only  in  the  solid  state.  As2(X  is  decomposed  at  a 
red  heat  into  As4O6  and  oxygen. 

Arsenic  anhydride,  As2O5,  has  very  much  less  attraction  for  water  than 
has  the  phosphoric  anhydride  with  which  it  corresponds  ;  it  deliquesces 
slowly  in  air,  and  dissolves  rather  reluctantly  in  water.  Neither  does  it 
appear  that  its  combinations  with  water  differ  from  each  other,  like  the 
phosphoric  acids,  in  the  salts  to  which  they  give  rise,  arsenic  acid  form- 
ing tribasic  salts  only,  like  common  phosphoric  acid.  The  arsenates 
correspond  very  closely  with  the  orthophosphates,  with  which  they  are 
isomorphous  (i.e.,  identical  in  crystalline  form).  Thus  the  three 
arsenates  of  sodium  are  similar  in  composition  to  the  three  ortho- 
phosphates,  the  formulae  being  Na3AsO4.i2Aq  ;  Na2HAsO4.i2Aq  ;  and 
2(NaH2AsO4).Aq. 

The  common  arsenate  of  soda  (Na2HAsO4>7Aq)  is  largely  used  by 
calico-printers  as  a  substitute  for  the  dung-baths  formerly  employed, 
since,  like  the  common  phosphate  of  soda,  it  possesses  the  feebly  alkaline 
properties  required  in  that  particular  part  of  the  process.  It  is  manu- 
factured by  combining  arsenious  oxide  with  soda,  and  heating  the 
resulting  arsenite  with  sodium  nitrate,  from  which  it  acquires  oxygen, 
becoming  converted  into  sodium  arsenate. 


272 


MARSH'S  TEST  FOR  ARSENIC. 


Calcium  arsenate,  2CaHAs04.7H2O,  has  been  found  in  crystalline 
crusts  at  Joachimsthal.  Arsenio-siderite  and  xantho-siderite  are  calcium 
ferric  arsenates. 

Arsenic  acid  is  used  by  the  calico-printer  as  an  acid  and  by  the  dye- 
stuff  maker  as  an  oxidant.  It  is  a  much  more  powerful  acid  than  arsenious 
acid,  being  comparable,  in  this  respect,  with  phosphoric  acid.  It  is  less 
stable  than  phosphoric  acid,  and  acts  as  an  oxidising  agent.  Sulphurous 
acid,  which  is  without  action  on  phosphoric,  reduces  arsenic  acid  to 
arsenious  acid ;  H3AsO4  +  H2S03  =  H3AsO3  +  H2S04. 

1 63.  Arsenetted  hydrogen,  hydrogen  arsenide,  or  arsine  ( AsH3  = 
78  parts  by  weight). — The  only  compound  of  arsenic  and  hydrogen  the 
existence  of  which  has  been  satisfactorily  established  is  that  which 
corresponds  with  ammonia  and  phosphine.  It  is  prepared  by  the  action 
of  sulphuric  acid  diluted  with  three  parts  of  water  upon  the  zinc 
arsenide,  obtained  by  heating  equal  weights  of  zinc  and  arsenic  in  an 
earthern  retort;  Zn3As2  + 3H2S04=  2AsH3  + 3ZnS04.  The  gas  is  so 
poisonous  in  its  character  that  its  preparation  in  the  pure  state  is 
attended  with  danger.  It  has  a  sickly  alliaceous  odour,  and  may  be 
liquefied  at  -55°  C.  and  solidified  at  -113°  0.  It  is  inflammable, 
burning  with  a  peculiar,  livid  flame,  producing  water  and  fumes  of 
arsenious  oxide;  4AsH3  +  012  =  As4O6  +  6H20.  The  chief  interest  at- 
taching to  this  gas  depends  upon  the  circumstance  that  its  production 
allows  of  the  detection  of  very  minute  quantities  of  arsenic  in  cases  of 
poisoning. 

The  application  of  this  test,  known  as  Marsh's  test,  is  the  safest  method  of 
preparing  arsenetted  hydrogen  in  order  to  study  its  properties,  for  it  is  obtained 
so  largely  diluted  with  free  hydrogen  that  it  ceases  to  be  so  very  dangerous. 
Some  fragments  of  granulated  zinc  are  introduced  into  a  half-pint  bottle  (Fig.  191), 

provided  with  a  funnel 
tube  (A),  and  a  narrow 
tube  (B)  bent  at  right 
angles  and  drawn  out  to 
a  jet  at  the  extremity  ; 
this  tube  should  be  made 
of  German  glass,  so  that 
it  may  not  fuse  easily. 
The  bottle  having  been 
about  one-third  filled 
with  water,  a  little  diluted 
sulphuric  acid  is  poured 
down  the  funnel-tube  so 
as  to  cause  a  moderate 
evolution  of  hydrogen, 
and  after  about  five 
minutes  (to  allow  the 
escape  of  the  air)  the 
hydrogen  is  kindled  at 

the  jet.  If  a  few  drops  of  a  solution  obtained  by  boiling  white  arsenic  with  water 
be  now  poured  down  the  funnel,  arsenetted  hydrogen  will  be  evolved  together  with 
the  hydrogen  ;  As406  +  Zn12  +  i2H2S04  =  4AsH3  +  i2ZnS04  +  6H20. 

The  hydrogen  flame  will  now  acquire  the  livid  hue  above  referred  to,  and  a 
white  smoke  of  As406  will  rise  from  it.  If  a  piece  of  glass  or  porcelain  be  depressed 
upon  the  flame  (Fig.  192),  it  will  acquire  a  brown  coating  of  arsenic,  just  as  carbon 
would  be  deposited  from  an  ordinary  gas-flame.  Arsenetted  hydrogen  is  easily 
decomposed  by  heat  (230°  C.),  so  that  if  the  glass  tube  through  which  it  passes  be 
heated  with  a  spirit-lamp  (Fig.  193)  a  dark  mirror  of  arsenic  will  be  deposited  a 
little  in  front  of  the  heated  part,  and  the  flame  of  the  gas  will  lose  its  livid  hue. 
These  deposits  of  arsenic  are  extremely  thin,  so  that  a  very  minute  quantity  of 


Fig-.  192. 


Fig.  193. 


ARSENIOUS   CHLORIDE.  2/3 

arsenic  is  required  to  form  them,  thus  rendering  the  test  one  of  extraordinary 
delicacy.  It  must  be  remembered,  however,  that  both  sulphuric  acid  and  zinc  are 
liable  to  contain  arsenic,  so  that  erroneous  results  may  be  very  easily  arrived  at  by 
this  test. 

An  electrolytic  test  for  arsenic  may  also  be  employed  which  depends  upon  the 
circumstance  that  when  a  fairly  powerful  galvanic  current  is  passed  through  an 
acid  liquid  containing  arsenic,  arsenetted  hydrogen  is  evolved  at  the  negative  ter- 
minal along  with  the  hydrogen  of  the  decomposed  water. 

Arsenetted  hydrogen,  like  sulphuretted  hydrogen,  causes  dark  precipitates  in 
many  metallic  solutions. 

Silver  nitrate  is  reduced  to  the  metallic  state  by  AsH3  ;  AsH3  +  6AgN03  +  3H20  = 
H3As03  +  6HN03  +  3Ag2.  A  piece  of  filter-paper,  spotted  with  silver  nitrate 
solution,  will  have  the  spots  blackened  if  held  before  the  tube  from  which  the 
gas  issues.  The  simplest  test  for  arsenic  in  wall-paper,  &c.,  is  to  drop  a  piece 
of  the  paper  into  a  glass  containing  some  zinc  and  sulphuric  acid,  and  to  cover 
the  mouth  of  the  glass  with  a  piece  of  paper  wetted  with  silver  nitrate,  which 
will  be  blackened  if  arsenic  be  present.  The  purity  of  the  materials  should  be 
tested  first  in  the  same  way,  and  the  absence  of  sulphur,  which  also  blackens 
silver  nitrate,  should  be  proved  by  lead  acetate,  which  is  not  blackened  by  arsenic. 

Hydrogen  phosphide,  hydrogen  arsenide,  and  ammonia  constitute  a 
group  of  hydrogen  compounds  having  certain  properties  in  common, 
which  distinguish  them  from  the  compounds  of  hydrogen  with  other 
elements. 

Two  volumes  of  each  of  these  gases  contain  three  volumes  of  hydrogen. 

They  are  all  possessed  of  peculiar  odours,  that  of  ammonia  being  the 
most  powerful  and  that  of  hydrogen  arsenide  the  least.  Ammonia  is 
powerfully  alkaline,  phosphine  exhibits  some  tendency  to  play  an  alka- 
line part,  whilst  arsine  seems  devoid  of  alkaline  disposition.  They  are 
all  inflammable,  ammonia  being  the  least  so  of  the  group,  and  are 
decomposed  by  heat,  ammonia  least  easily,  and  hydrogen  arsenide  most 
easily.  They  are  all  producible  from  their  corresponding  oxygen  com- 
pounds, viz.,  N203,P406,  and  As4O6,  by  the  action  of  nascent  hydrogen 
(e.g.,  by  contact  with  zinc  and  diluted  sulphuric  acid). 

All  three  are  the  prototypes  of  various  organic  bases  which  contain 
some  compound  radicle  in  place  of  the  hydrogen,  thus  — 

NH3  is  the  prototype  of  triethylamine  N(C2H5)3 

PH3        „  „  triethylphosphine    P(C2H5)3 

AsH3      „  „  triethylarsine  As(C2H5)3 

164.  Arsenic  trichloride,  or  arsenious  chloride.  —  Only  one  compound  of  chlorine 
with  arsenic  (AsCl3)  is  well  known.*  The  trichloride  may  be  formed  by  the  direct 
union  of  its  elements,  but  the  simplest  laboratory  process  for  procuring  it  consists 
in  heating  white  arsenic  in  dry  chlorine,  in  a  tubulated  retort  (A,  Fig.  194).  The 
arsenious  anhydride  soon  melts,  and  the  trichloride  distils,  leaving  a  melted 
mass  in  the  flask,  which  is  a  brilliantly  transparent  glass  when  cool  ;  its  composition 
varies  somewhat  with  the  temperature  used,  but  appears  to  be  essentially  As406.As205. 
The  same  vitreous  compound  may  be  obtained  by  fusing  arsenious  and  arsenic 
oxides  together.  The  reaction  may  be  represented  by  the  equation  — 

1  1  As406  +  C124  =  8AsCl3  +  6(As406.Asa05). 

Arsenic  trichloride  bears  a  great  general  resemblance  to  phosphorus  trichloride  ; 
it  is  a  heavy  (sp.  gr.  2.2,  b.p.  134°  C.),  pungent,  fuming  liquid,  decomposed  by  the 
moisture  of  the  air,  its  vapours  depositing  a  white  coating  upon  the  objects  in 
its  immediate  neighbourhood.  When  poured  into  water  it  deposits  arsenious 
oxide  ;  4AsCl3  +  6H2O  =  As4O6+  I2HC1  ;  but  when  dissolved  in  the  smallest  possible 


quantity  of  water  it  deposits  crystals  of  the  formula  AsOCl.  H20  or  AsCl(OH)2. 

When  white   arsenic   is   dissolved  in  hydrochloric  acid,  arsenious  chloride   is 
formed,  As406+  i2HCl  =  4As013  +  6H20,  and  remains  undecomposed  by  the  water 

*  It  is  said  that  the  pentachloride  can  be  formed  by  the  action  of  hydrochloric  acid  gas 
on  As2O5  in  presence  of  ether. 

S 


274 


ORPIMENT. 


in  the  presence  of  strong  hydrochloric  acid,  but  if  water  be  added,  arsenious  oxide 
is  precipitated.  When  the  solution  in  hydrochloric  acid  is  distilled,  the  arsenious 
chloride  distils  over,  and  this  is  sometimes  a  convenient  method  of  separating 
arsenic  from  articles  of  food,  &c.,  in  testing  for  that  poison.  When  heated  in 

dry  hydrochloric  acid  gas,  white  arsenic 
yields  a  glassy  compound,  which  con- 
tains As4O6.2AsOCl  ;  3As4O6  +  4HCl  = 
2(As406.2AsOCl)  +  2H20. 

AsCl3    and  AsH3  decompose    each 
other,  yielding  3HC1  and  As2. 

Arsenious  bromide  much  resembles 
the  chloride  in  its  chemical  characters, 
but  is  a  solid  crystalline  substance, 
fusing  at  25°  C.  and  boiling  at  220°  C. 
165.  Arsenic  tri-iodide,  or  arsenious 
iodide  (AsI3),  is  remarkable  for  not 
being  decomposed  by  water,  like  the 
corresponding  phosphorus  compound. 
When  obtained  by  heating  together 
arsenic  and  iodine,  it  sublimes  in  brick- 
Fig-.  194.  red  flakes,  which,  if  prepared  on  a 
large  scale,  hang  in  long  laminae,  like 

sea-weed.  It  may  be  dissolved  in  boiling  water,  and  crystallises  unchanged.  It 
may  even  be  prepared  by  heating  3  parts  of  arsenic  with  10  of  iodine  and  100  of 
water,  when  the  solution  deposits  red  crystals  of  the  hydrated  tri-iodide,  from  which 
the  water  may  be  expelled  by  a  gentle  heat. 

AsI3  is  precipitated  as  a  golden  crystalline  powder  on  mixing  a  hot  solution  of 
As406  in  HC1  with  a  strong  solution  of  KI. 

Arsenic  di-iodide,  AsI2,  is  obtained  by  heating  i  part  of  arsenic  and  2  parts  of 
iodine  in  a  sealed  tube  to  230°  C.,  and  crystallising  from  CS2  in  an  atmosphere  of 
C02.  It  forms  red  prismatic  crystals  which  become  black  when  treated  with 
water,  according  to  the  equation  3 AsI2  =  2AsI3  +  As. 

When  iodine  is  dissolved  in  a  solution  of  arsenious  acid,  this  is  oxidised  to 
arsenic  acid  ;  H2As03  +  H20  +  I2  =  H3As04  +  2HI.  When  the  solution  is  concentrated 
by  evaporation,  the  change  is  reversed,  and  iodine  liberated. 

The  arsenic  tri-fluoride  (AsF3)  resembles  the  trichloride,  but  is  much  more 
volatile  (b.p.  63°  C.)  It  may  be  obtained  by  distilling  4  parts  of  arsenious  oxide 
with  5  of  fluor  spar  and  10  of  strong  sulphuric  acid,  in  a  leaden  retort  (see 
p.  202).  It  does  not  attack  glass  unless  water  be  present,  which  decomposes  it  into, 
arsenious  and  hydrofluoric  acids.  PC15  converts  it  into  FP5  and  AsCl3. 

1 66.  Sulphides  of  Arsenic. — There  are  three  well-known  sulphides 
of  arsenic,  having  the  composition  As2S2,  As2S3,  and  As2S3,  the  two- 
former  being  found  in  nature. 

Realgar  (As2S2)  is  a  beautiful  mineral,  crystallised  in  orange-red 
prisms  ;  but  the  red  orpiment  used  in  the  arts  is  generally  prepared  by 
heating  a  mixture  of  white  arsenic  and  sulphur,  when  sulphurous  acid 
gas  escapes,  and  an  orange-coloured  mass  of  realgar  is  left.  Another 
process  for  preparing  it  consists  in  distilling  arsenical  pyrites  with, 
sulphur  or  with  iron  pyrites ;  FeS2.FeAs2  +  2FeS2  =  4FeS  +  As2S9.  The 
realgar  distils,  and  condenses  to  a  red  transparent  solid.  Realgar  burns 
in  air  with  a  blue  flame,  yielding  arsenious  and  sulphurous  oxides.  If 
it  be  thrown  into  melted  saltpetre,  it  burns  with  a  brilliant  white  flame, 
being  converted  into  arsenate  and  sulphate  of  potassium.  This  brilliant 
flame  renders  realgar  an  important  ingredient  in  Indian  fire  and  similar 
compositions  for  fireworks  and  signal  lights.  A  mixture  of  one  part  of 
red  orpiment  with  3.5  parts  of  sublimed  sulphur  and  14  parts  of  nitre 
is  used  for  signal  light  composition. 

Eealgar  is  not  easily  attacked  by  acids  ;  nitric  acid,  however,  dissolves  it,  with 
the  aid  of  heat,  forming  arsenic  acid  and  sulphuric  acid,  with  separation  of  part 


SULPHIDES  OF  ARSENIC.  2/5; 

of  the  sulphur  in  the  free  state.  Alkalies  (KOH  for  example)  partly  dissolve^ 
it,  leaving  a  dark  brown  substance,  which  appears  to  contain  free  arsenic  ; 
3As2S2  =  2As2S3  +  As2.  When  exposed  to  air  realgar  is  partly  oxidised  and  con- 
verted into  a  mixture  of  As.2S.2  and  As406. 

Yellow  orpiment,  or  arsenious  sulphide  (As2S3),  is  found  native  in 
yellow  prismatic  crystals.  The  pigment  known  as  Kings  yellow  is  a 
mixture  of  arsenious  sulphide  and  arsenious  anhydride,  prepared  by  sub- 
liming excess  of  sulphur  with  white  arsenic;  S9  +  As406=  2As2S3  +  3S02. 
It  is,  of  course,  very  poisonous. 

This  substance,  like  realgar,  is  not  much  affected  by  acids,  excepting  nitric  acid  ; 
but  it  dissolves  entirely  in  potash,  forming  potassium  arsenite  and  thwarsenite  ; 
6KOH  +  As2S3:=  K3AsS3  +  K3AsO3  +  3H2O.*  Ammonia  also  dissolves  it  easily,  form- 
ing a  colourless  solution  which  is  employed  for  dyeing  yellow,  since,  if  a  piece  of 
stuff  be  dipped  into  it  and  exposed  to  air,  the  ammonia  will  volatilise,  leaving  the 
yellow  orpiment  behind.  When  As2S3  is  boiled  with  a  strong  solution  of  sodium 
carbonate,  H2S  is  evolved  and  As2S2  is  deposited  as  a  crystalline  powder. 

The  formation  of  the  characteristic  yellow  sulphide  is  turned  to  account  in 
testing  for  arsenic  ;  if  a  solution  prepared  by  boiling  white  arsenic  with  distilled 
water  be  mixed  with  a  solution  of  hydrosulphuric  acid,  a  bright  yellow  liquid  is 
produced,  which  looks  opaque  by  reflected,  but  transparent  by  transmitted,  light, 
and  may  be  passed  through  a  filter  without  leaving  any  solid  matter  behind. 
This  solution  probably  contains  a  soluble  colloidal  form  of  arsenious  sulphide  ;  this 
is,  however,  rendered  insoluble  by  evaporation.  The  addition  of  a  little  hydro- 
chloric acid,  or  of  sal-ammoniac,  and  many  other  neutral  salts,  will  also  cause  a 
separation  of  the  sulphide  from  this  solution;  even  the  addition  of  hard  water 
will  have  that  effect.  If  the  solution  of  arsenious  acid  be  acidified  with  hydro- 
chloric acid  before  adding  the  hydrosulphuric  acid,  the  bright  yellow  sulphide  is 
precipitated  at  once,  and  may  be  distinguished  from  any  other  similar  precipitate 
by  its  ready  solubility  in  solution  of  ammonium  carbonate. 

Arsenic  sulphide  (As2S5)  possesses  far  less  practical  importance  than  the  preced- 
ing sulphides  ;  it  may  be  obtained  by  fusing  As2S3  with  sulphur,  when  it  forms 
an  orange-coloured  glass,  easily  fusible,  and  capable  of  being  sublimed  without 
change.  When  hydrosulphuric  acid  gas  is  passed  slowly  through  solution  of 
arsenic  acid,  very  little,  if  any,  arsenic  sulphide  is  formed,  a  white  precipitate  of 
sulphur  being  first  obtained,  the  hydrogen  reducing  the  arsenic  acid  to  arsenious 
acidf;  H3As04  +  H2S  —  H3As03  +  H20  +  S  ;  and  if  the  passage  of  the  gas  be  con- 
tinued, the  arsenious  acid  is  decomposed,  and  arsenious  sulphide  is  precipitated  ; 
these  changes  are  much  accelerated  by  heat.  But  a  rapid  current  of  H2S  passed 
through  a  solution  of  arsenic  acid  in  presence  of  much  free  hydrochloric  acid 
throws  down  pure  arsenic  sulphide.  If  a  solution  of  sodium  arsenate  be  saturated 
with  H2S,  it  is  converted  into  sodium  tJiioarsenate,  NagAsS4.  On  adding  hydro- 
chloric acid  to  this  solution,  a  bright  yellow  precipitate  of  arsenic  sulphide 
is  obtained.  Cuprous  sulphar  senate,  or  Clarite  (Cu3AsS4),  is  found  in  the  Black 
Forest. 

167.  Review  of  Nitrogen,  Phosphorus,  and  Arsenic. — These 
elements  are  connected  together  by  the  general  analogy  of  their  hydrogen 
and  oxygen  compounds,  the  two  last  members  of  the  group  being  far 
more  closely  connected  with  each  other  than  with  nitrogen.  With  the 
metals  they  are  connected  through  arsenic,  the  hydrogen-compound  of 
which  is  very  similar  in  properties,  and  probably  in  composition,  to 
antimonetted  hydrogen ;  arsenious  oxide  (As406)  is  also  capable  of 
occupying  the  place  of  antimonious  oxide  (Sb406)  in  certain  salts  of 
that  oxide ;  and  the  sulphides  of  antimony  correspond  in  composition, 
and  in  some  of  their  properties,  with  those  of  arsenic.  One  form  of 

*  Since  the  metarsenite,  KAsO2,  is  the  only  potassium  arsenite  which  has  been  prepared, 
and  the  metathioarsenite,  KAsS2,  appears  to  exist  in  the  solution,  the  reaction  is  better  ex- 
pressed by  the  equation,  2As2S3  +  4KOH=:KA8O2  +  3KAsS2  +  2H2O. 

t  Under  some  conditions  the  solution  remains  clear  at  first,  sulphoxyarsenic  acid  being- 
formed  which  is  decomposed  by  more  H2S  with  precipitation  of  As2S5.  (i)  H3AsO4  +  H2S  = 
H3AsO3S  +  H2O;  (2)  2 


276  FORMS   OF   SILICA. 

.arsenious  oxide  (the  prismatic)  is  isomorphous  with  native  oxide  of 
-antimony,  and  this  oxide  may  be  obtained  in  octahedra,  the  ordinary 
form  of  arsenious  oxide,  so  that  these  oxides  are  isodimorphous. 

These  elements  are  also  connected  with  the  oxygen  group  through 
'Sulphur,  selenium,  and  tellurium,  the  relations  of  which  to  hydrogen  and 
the  metals  are  somewhat  similar  to  those  of  phosphorus  and  arsenic. 

SILICON. 

Siiv  =  28.2  parts  by  weight. 

168.  In  many  of  its  chemical  relations  to  other  bodies  this  element 
will  be  found  to  bear  a  great  resemblance  to  carbon  ;  but  whilst  carbon 
is  the  characteristic  element  of  organic  substances,  silicon  is  the  most 
abundant  in  the  mineral  world,  where  it  is  chiefly  found  in  combination 
with  oxygen,  as  silica  (Si02),  either  alone  or  as  silicates. 

Silica  (SiO2  =  60  parts  by  weight). — The  purest  natural  form  of 
silica  is  the  transparent  and  colourless  variety  of  quartz  known  as  rock 
crystal,  the  most  widely  diffused  ornament  of  the  mineral  world,  often 
seen  crystallised  in  beautiful  six-sided  prisms,  terminated  by  six-sided 
pyramids  (Fig.  195),  which  are  always  easily  distinguished  by  their 

great  hardness,  scratch- 
ing glass  almost  as  readily 
as  the  diamond.  Coloured 
of  a  delicate  purple,  pro- 
bably by  a  little  organic 
matter,  these  crystals  are 
known  as  amethysts  ;  and 
Fig.  195.— Crystal  of  quartz.  when  of  a  brown  colour, 

as  Cairngorm   stones    or 

Scotch  pebbles.  Losing  its  transparency  and  crystalline  structure,  we 
meet  with  silica  in  the  form  of  chalcedony  and  of  carnelian,  usually 
coloured,  in  the  latter,  with  oxide  of  iron. 

Hardly  any  substance  has  so  great  a  share  in  the  lapidary's  art  as 
silica,  for  in  addition  to  the  above  instances  of  its  value  for  ornamental 
purposes,  we  find  it  constituting  jasper,  agate,  cat's  eye,  onyx,  so  much 
prized  for  cameos,  opal,  and  some  other  precious  stones.  In  opal  the 
silica  is  combined  with  water. 

/Sand,  of  which  the  whiter  varieties  are  nearly  pure  silica,  appears  to 
have  been  formed  by  the  disintegration  of  siliceous  rocks,  and  has 
generally  a  yellow  or  brown  colour,  due  to  the  presence  of  oxide  of 
iron. 

The  resistance  offered  by  silica  to  all  impressions  has  become  pro- 
verbial in  the  case  oi  flint,  which  consists  essentially  of  that  substance 
coloured  with  some  impurity.  Flints  are  generally  found  in  compact 
masses,  distributed  in  regular  beds  throughout  the  chalk  formation ; 
their  hardness,  which  even  exceeds  that  of  quartz,  rendered  them  useful, 
before  the  days  of  matches,  for  striking  sparks  with  steel ;  small 
particles  of  metal  are  thus  detached,  and  are  so  heated  by  the  percussion 
as  to  continue  to  burn  (see  p.  37)  in  the  air,  and  to  inflame  tinder  or 
gunpowder  upon  which  they  are  allowed  to  fall. 

The  part  taken  by  silica  in  natural  operations  appears  to  be  chiefly 
a  mechanical  one,  for  which  its  stability  under  ordinary  influences 


DISSOLVING  SILICA.  277 

peculiarly  fits  -it,  for  it  is  found  to  constitute  the  great  bulk  of  the  soil 
which  serves  as  a  support  and  food-reservoir  for  land  plants,  and  enters 
largely  into  the  composition  of  the  greater  number  of  rocks. 

But  that  this  substance  is  not  altogether  excluded  from  any  share  in 
life,  is  shown  by  its  presence  in  the  shining  outer  sheath  of  the  stems 
of  the  grasses  and  cereals,  particularly  in  the  hard  external  coating  of 
the  Dutch  rush  used  for  polishing,  and  in  the  joints  of  the  bamboo, 
where  it  forms  the  greater  part  of  the  matter  known  as  tabasheer. 
This  alone  would  lead  to  the  inference  that  silica  could  not  be 
absolutely  insoluble,  since  the  capillary  vessels  of  plants  are  known  to 
be  capable  of  absorbing  only  such  substances  as  are  in  a  state  of  solu- 
tion. Many  natural  waters  also  present  us  with  silica  in  a  dissolved 
state,  and  often  in  considerable  quantity,  as,  for  example,  in  the 
geysers  of  Iceland,  which  deposit  a  coating  of  silica  upon  the  earth 
around  their  borders. 

Pure  water,  however,  has  no  solvent  action  upon  the  natural  varieties 
of  silica.  The  action  of  an  alkali  is  required  to  bring  it  into  a  soluble 
form. 

To  effect  this  upon  the  small  scale,  some  white  sand  is  very  finely 
powdered  (in  an  agate  mortar),  mixed  with  about  four  times  its  weight 
of  dried  sodium  car- 
bonate, placed  upon  a 
piece  of  platinum  foil 
slightly  bent  up  (Fig. 
196),  and  fused  by 
directing  the  flame  of 
a  blowpipe  upon  the 
under  side  of  the  foil. 
Effervescence  will  be 
observed,  due  to  the 
escape  of  carbonic  acid 
gas.  The  piece  of 

platinum      foil,      when  Fig".  196.— Fusion  on  platinum  foil. 

cool,  may  be  placed  in 

a  little  warm  water,  and  allowed  to  soak  for  some  time,  when  the  melted 
mass  will  gradually  dissolve,  forming  a  solution  of  sodium  silicate.  This 
solution  will  be  found  decidedly  alkaline  to  test-papers. 

If  a  portion  of  the  solution  of  sodium  silicate  in  water  be  poured  into 
a  test-tube,  and  two  or  three  drops  of  hydrochloric  acid  added  to  it,  with 
occasional  agitation,  effervescence  will  be  produced  by  the  expulsion  of 
any  carbonic  acid  gas  still  remaining,  and  the  solution  will  be  converted 
into  a  gelatinous  mass  by  the  separation  of  silicic  acid.  But  if  another 
portion  of  the  solution  be  poured  into  an  excess  of  dilute  hydrochloric 
acid  (i.e.,  into  enough  to  render  the  solution  distinctly  acid),  the  silicic 
acid  will  remain  dissolved  in  the  water,  together  with  the  sodium 
chloride  formed. 

In  order  to  separate  the  sodium  chloride  from  the  silicic  acid,  the 
process  of  dialysis  *  must  be  adopted. 

Dialysis  is  the  separation  of  dissolved  substances  from  each  other  by 
taking  advantage  of  the  different  rates  at  which  they  pass  through  moist 
diaphragms  or  septa.  It  is  found  that  those  substances  which  crystallise 

*  From  SiaAv'w,  to  part  asunder. 


2/8  SILICIC   ACID. 

(crystalloids)  and  the  mineral  acids  pass  through  such  septa  in  a  solution 
faster  than  do  amorphous  substances  (colloids). 

If  the  mixed  solution  of  sodium  chloride  and  silicic  acid  were  poured  upon  an 
ordinary  paper  filter,  it  would  pass  through  without  alteration  ;  but  if  parchment 
paper  be  employed,  which  is  not  pervious  to  water,  although  readily  moistened  by 
it,  none  of  the  liquid  will  pass  through.  If  the  cone  of  parchment  paper  be  sup- 
ported upon  a  vessel  filled  with  distilled  water  (Fig.  197),  so  that  the  water  maybe 
in  contact  with  the  outer  surface  of  the  cone,  the  hydrochloric  acid  and  the  sodium 
chloride  will  pass  through  the  substance  of  the  parchment  paper,  and  the  water 


Fig-.  197.  Fig.  198.— Dialyser. 

charged  with  them  may  be  seen  descending  in  dense  streams  from  the  outside  of 
the  cone.  After  a  few  hours,  especially  if  the  water  be  changed  occasionally,  the 
whole  of  the  hydrochloric  acid  and  sodium  chloride  will  have  passed  through,  and 
a  pure  solution  of  silicic  acid  in  water  will  remain  in  the  cone. 

A  convenient  form  of  dialyser  is  represented  in  Fig.  198  ;  it  consists  of  parchment 
paper  stretched  over  a  gutta-percha  ring  and  held  in  this  position  by  a  concentric 
ring.  It  is  suspended  on  a  surface  of  water  and  the  solution  to  be  dialysed  is  poured 
upon  it. 

This  solution  is  believed  to  contain  the  orthosilicic  acid,  H20.2Si02,  or 
H4Si04,  or  Si(OH)4.  It  is  very  feebly  acid  to  blue  litmus-paper,  and 
not  perceptibly  sour  to  the  taste.  It  has  a  great  tendency  to  set  into  a 
jelly  in  consequence  of  the  sudden  separation  of  silicic  acid.  If  it  be 
slowly  evaporated  in  a  dish,  it  soon  solidifi.es;  but,  by  conducting  the 
evaporation  in  a  flask,  so  as  to  prevent  any  drying  of  the  silicic  acid  at 
the  edges  of  the  liquid,  it  may  be  concentrated  until  it  contains  14  per 
cent,  of  silicic  acid.  When  this  solution  is  kept,  even  in  a  stoppered 
or  corked  bottle,  it  sets  into  a  transparent  gelatinous  mass,  which 
gradually  shrinks  and  separates  from  the  water.  When  evaporated,  in 
vacuo,  over  sulphuric  acid,  it  gives  a  transparent  lustrous  glass  which  is 
composed  of  22  per  cent,  of  water  and  78  percent,  of  silica  (H2O.Si02). 
This  is  also  the  composition  of  the  gelatinous  precipitate  produced  by 
acids  in  the  solution  of  sodium  silicate.  It  is  sometimes  written  H2Si03 
or  SiO(OH)2,  and  called  metasilicic  acid. 

This  behaviour  of  silicic  acid  is  typical  of  colloids  ;  they  can  generally 
exist  in  solution  (the  hydrosol  form),  but  are  apt  to  separate  as  a  jelly 
(the  hydrogel  form)  from  such  solutions.  Gelatine  is  a  familiar  example. 

The  hydrated  silica  cannot  be  redissolved  in  water,  and  is  only  soluble 
to  a  slight  extent  in  hydrochloric  acid.  If  it  be  heated  to  expel  the 
water,  the  silica  which  remains  is  insoluble  both  in  water  and  in  hydro- 
chloric acid,  but  is  dissolved  when  boiled  with  solution  of  potash  or  soda, 
or  their  carbonates. 

Silica  in  the  naturally  crystallised  form,  as  rock  crystal  and  quartz, 


MODIFICATIONS  OF  SILICA. 


279 


is  insoluble  in  boiling  solutions  of  the  alkalies,  and  in  all  acids  except 
hydrofluoric ;  but  amorphous  silica  (such  as  opal  and  tripoli)  is  readily 
dissolved  by  boiling  alkalies.  These  represent,  in  fact,  two  distinct 
modifications  of  silica,  which  may  be  said  to  be  dimorphous*  A  trans- 
parent piece  of  rock  crystal  may  be  heated  to  bright  redness  without 
change,  but  if  it  be  powdered  previously  to  being  heated,  its  specific 
gravity  is  diminished  from  2.6  to  2.4,  and  it  becomes  soluble  in  boiling 
alkalies,  having  been  converted  into  the  amorphous  modification.  The 
natural  forms  of  amorphous  silica  of  sp.  gr.  2.2  are  always  hydrated,  and 
even  some  of  the  varieties  of  sp.  gr.  2.6,  such  as  flint,  agate,  and  chalce- 
dony, contain  a  little  water,  pointing  to  the  aqueous  origin  of  all  silica. 
Crystals  of  quartz  have  been  obtained  artificially  by  the  prolonged 
action  of  water  upon  glass  at  a  high  temperature  under  pressure.  When 
fused  with  the  oxyhydrogen  blowpipe,  silica  does  not  crystallise,  being 
thus  converted  into  the  amorphous  variety  of  sp.  gr.  2.2,  which  may  be 
worked  while  soft  into  threads  and  even  tubes,  much  as  glass  is.  The 
threads  are  useful  in  electrical  apparatus  on  account  of  their  excellent 
insulating  property,  far  surpassing  that  of  glass  in  a  moist  atmosphere. 
The  tubes  are  useful  on  account  of  the  high  temperature  and  rapid 
changes  of  temperature  they  can  withstand  without  fusion  or  fracture. 

To  prepare  the  amorphous  modification  of  silica  artificially,  white  sand  in  very 
fine  powder  may  be  fused,  in  a  platinum  crucible,  with  six  times  its  weight  of  a 
mixture  of  equal  weights  of  the  potassium  and  sodium  carbonates,  the  mixture 
being  more  easily  fusible  than  either  of  the  carbonates  separately.  The  crucible 
may  be  heated  over  a  gas  burner  supplied  with  a  mixture  of  gas  and  air,  or  may 
be  placed  in  a  little  calcined  magnesia  contained  in  a  fire-clay  crucible,  which  may 
be  covered  up  and  introduced  into  a  good  fire.  The  platinum  crucible  is  never 
heated  in  direct  contact  with  fuel,  since  the  metal  would  become  brittle  by  com- 
bining with  carbon,  silicon,  and  sulphur  derived  from  the  fuel.  The  magnesia  is 
used  to  protect  the  platinum  from  contact  with  the  clay  crucible.  When  the 
action  of  the  silica  upon  the  alkali  car- 
bonates is  completed,  which  will  be 
indicated  by  the  cessation  of  the  efferves- 
cence, the  platinum  crucible  is  allowed 
to  cool,  placed  in  an  evaporating  dish, 
and  soaked  for  a  night  in  water,  when 
the  mass  should  be  almost  entirely  dis- 
solved. Hydrochloric  acid  is  then  added 
to  the  solution,  with  occasional  stirring, 
until  it  is  distinctly  acid  to  litmus-paper. 
On  evaporating  the  solution,  it  will,  at  a 
certain  point,  solidify  to  a  gelatinous 
mass  of  hydrated  silica,  which  would  be 
ejected  from  the  dish  if  evaporation  over 
the  flame  were  continued.  To  prevent 
this,  the  dish  is  placed  over  an  empty 
iron  saucepan  so  that  the  heat  from  the 
flame  may  be  equally  distributed  over 
the  bottom  of  the  dish.  When  the  mass 
is  quite  dry  the  dish  is  allowed  to  cool, 
and  some  water  is  poured  into  it,  which 
dissolves  the  chlorides  of  potassium  and 
sodium  (formed  by  the  action  of  the 
hydrochloric  acid  upon  the  silicates),  and  leaves  the  silica  in  white  flakes.  These 
may  be  collected  upon  a  filter,  and  washed  several  times  with  distilled  water.  The 

*  If  tridymite—a,  mineral  which  occurs  in  anhydrous  hexagonal  crystals,  has  a  sp.  gr.  of 
2.3,  and  is  not  attacked  by  alkalies— be  regarded  as  the  type  of  another  crystalline  variety  of 
silica,  this  must  be  said  to  be  trimorphous. 


I99>_Air-gas  blowpipe. 


280  SILICATES. 

filter  is  then  carefully  spread  out  upon  a  hot  iron  plate,  or  upon  a  hot  brick,  and 
allowed  to  dry,  when  the  silica  is  left  as  a  dazzling  white  powder,  which  must  be 
strongly  heated  in  a  porcelain  or  platinum  crucible  to  expel  the  last  traces  of  water. 
It  is  remarkable  for  its  extreme  lightness,  especially  when  heated,  the  slightest 
current  of  air  easily  blowing  it  away. 

169.  For  effecting  such  fusions  as  that  just  described,  an  air-gas  blowpipe  (Fig. 
199)  supplied  with  air  from  a  double-action  bellows,  worked  by  a  treadle,  will  be 
found  most  convenient. 

170.  Silicates. — The  acid  properties  of  silicic  acid  are  so  feeble  that  it 
is  a  matter  of  great  difficulty  to  determine  the  proportion  of  any  base 
which  is  required  to  react  with  it  in  order  to  form  a  chemically  neutral 
salt.  Like  carbonic  acid,  it  does  not  destroy  the  action  of  the  alkalies 
upon  test-papers,  and  we  are  therefore  deprived  of  this  method  of 
ascertaining  the  proportion  of  alkali  which  neutralises  it  in  a  chemical 
sense.  In  attempting  to  ascertain  the  quantity  of  alkali  with  which 
silica  combines,  from  that  of  the  carbon  dioxide  which  it  expels  when 
heated  with  an  alkaline  carbonate,  it  is  found  that  the  proportion  of 
carbon  dioxide  expelled  varies  considerably,  according  to  the  temperature 
and  the  proportion  of  alkaline  carbonate  employed.  The  limits  of  the 
reaction  however  appear  to  be  the  formation  of  the  alkali  metasilicate 
on  the  one  hand  and  the  alkali  orthosilicate  on  the  other : 
SiO2  +  Na2C03  =  CO,  +  Na.,Si03  (metasilicate) 
Si02  +  2Na2C03  =  C02  +  Na4SiO4  (orthosilicate). 

By  heating  silica  with  sodium  hydroxide  (NaOH),  it  is  found  that  60 
parts  of  silica  expel  36  parts  of  water,  however  much  NaOH  is  employed, 
and  the  same  proportion  of  water  is  expelled  from  barium  hydroxide, 
Ba(OH)2,  when  heated  with  silica. 

The  formula  Si02  represents  60  parts  by  weight  of  silica,  and  36  parts 
represent  two  molecules  of  water.  Hence  it  would  appear  that  the 
action  of  silica  upon  sodium  hydroxide  is  represented  by  the  equation — 
4NaOH  +  Si02  =  Na4Si04  +  2H2O  ;  and  that  upon  barium  hydroxide  by 
2Ba(OH)2  +  Si02  =  Ba2Si04  + 2H20 :  and  since  it  is  found  that  several 
of  the  crystallised  mineral  silicates  contain  a  quantity  of  metal  equiva- 
lent to  H4,  it  is  usual  to  represent  silicic  acid  as  a  tetrabasic  acid,  H4Si04, 
containing  4  atoms  of  hydrogen  exchangeable  for  metals. 

The  circumstance  that  silica  is  not  capable  of  being  converted  into 
vapour  at  a  high  temperature,  enables  it  to  decompose  the  salts  of  many 
acids  which,  at  ordinary  temperatures,  are  able  to  displace  silicic  acid. 
The  feebly  acid  character  of  Si02  will  recall  that  of  C02.  Other  com- 
parison between  these  analogues  is  hardly  possible  on  account  of  their 
different  physical  condition. 

The  silicates  form  by  far  the  greatest  number  of  minerals.  The 
different  varieties  of  clay  consist  of  aluminium  silicate ;  felspar  is 
a  silicate  of  aluminium  and  potassium  ;  meerschaum  is  a  silicate  of 
magnesium. 

The  different  kinds  of  glass  are  composed  of  silicates  of  potassium, 
sodium,  calcium,  lead,  &c.  None  but  the  silicates  of  the  alkali  metals 
are  appreciably  soluble  in  water. 

Scarcely  any  of  the  silicates  are  represented  by  formulae  which  express 
their  derivation  from  the  acid  H4Si04 ;  they  are  generally  represented 
as  derivatives  of  metasilicic  acid  and  of  polysilicic  acids,  i.e.,  compounds 
of  7iH20  with  Si02  (compare  p.  261). 

This   tendency  of   silicon  to  form    complex   mineral    compounds   is 


SILICON.  281 

comparable  with  that  of  its  analogue,  carbon,  to  form  complex  organic 
compounds,  but  whereas  oxygen  is  the  other  element  mostly  concerned 
in  the  formation  of  mineral  silicates,  hydrogen  is  the  predominant 
companion  of  carbon  in  organic  derivatives. 

171.  Silicon  or  silicium. — From  the  remarkably  unchangeable 
character  of  silica,  it  is  not  surprising  that  it  was  long  regarded, 
as  an  elementary  substance.  In  1813,  however,  Davy  succeeded 
in  decomposing  it  by  the  action  of  potassium,  and  in  obtaining  an 
impure  specimen  of  silicon.  It  has  since  been  produced,  far  more 
easily,  by  converting  the  silica  into  potassium  silico-fluoride  (K2SiF6), 
and  decomposing  this  at  a  high  temperature  with  potassium  or  sodium, 
which  combines  with  the  fluorine  to  form  a  salt  capable  of  being  dis- 
solved out  by  water,  leaving  the  silicon  in  the  form  of  a  brown  powder 
(amorphous  silicon),  which  resists  the  action  of  all  acids,  except  hydro- 
fluoric, which  it  decomposes,  forming  silicon  fluoride,  and  evolving 
hydrogen  (Si +  4HF  =  SiF4  + H4).  It  is  also  dissolved  by  solution  of 
potash,  with  evolution  of  hydrogen,  and  formation  of  potassium  silicate. 
It  burns  brilliantly  when  heated  in  oxygen,  but  not  completely,  for  it 
becomes  coated  with  silica  which  is  fused  by  the  intense  heat  of  the 
combustion.  When  heated  with  the  blowpipe  on  platinum  foil,  it  eats 
a  hole  through  the  metal,  with  which  it  forms  the  fusible  platinum 
silicide. 

If  potassium  silico-fluoride  be  fused  with  aluminium,  a  portion  of  the 
latter  combines  with  the  fluorine,  and  the  remainder  combines  with  the 
silicon,  forming  aluminium  silicide.  By  boiling  this  with  hydrochloric 
and  hydrofluoric  acids  in  succession,  the  aluminium  is  extracted,  and 
crystalline  scales  of  silicon,  with  a  metallic  lustre  resembling  black  lead, 
are  left  (graphitoid  silicon).  In  this  form  the  silicon  has  a  specific 
gravity  of  about  2.5,  and  refuses  to  burn  in  oxygen,  or  to  dissolve  in 
hydrofluoric  acid.  A  mixture  of  nitric  and  hydrofluoric  acids,  however, 
dissolves  it.  It  burns  spontaneously  in  fluorine,  and  when  heated  in 
chlorine.  Like  graphite,  this  variety  of  silicon  conducts  electricity, 
though  amorphous  silicon  is  a  non-conductor.  The  amorphous  silicon 
becomes  converted  into  this  incombustible  and  insoluble  form  under  the 
action  of  intense  heat.  It  is  worthy  of  remark  that  the  combustibility 
of  amorphous  carbon  (charcoal)  is  also  very  much  diminished  by  exposure 
to  a  high  temperature. 

Unlike  carbon,  however,  silicon  is  fusible  at  a  temperature  somewhat 
above  the  melting-point  of  cast-iron  ;  on  cooling,  it  forms  a  brilliant 
metallic-looking  mass,  which  may  be  obtained,  by  certain  processes, 
crystallised  in  octahedra  so  hard  as  to  scratch  glass  like  a  diamond. 

In  their  chemical  relations  to  other  substances  there  is  much  resem- 
blance between  silicon  and  carbon.  Silicon,  however,  is  capable  of  dis- 
placing carbon,  for  if  potassium  carbonate  be  fused  with  silicon,  the 
latter  is  dissolved,  forming  potassium  silicate,  and  carbon  is  separated. 
Silicon  also  resembles  carbon  in  its  disposition  to  unite  with  certain 
metals  to  form  compounds  which  still  retain  their  metallic  appearance. 
Thus  silicon  is  found  together  with  carbon  in  cast-iron,  and  it  unites 
directly  with  aluminium,  zinc,  and  platinum,  to  form  compounds  resem- 
bling metallic  alloys.  Nitrogen  enters  into  direct  union  with  silicon  at 
a  high  temperature,  though  it  refuses  to  unite  with  carbon  except  in 
the  presence  of  alkalies. 


282  CARBORUNDUM. 

The  most  important  analogy  between  carbon  and  silicon  from  a 
theoretical  point  of  view,  resides  in  the  fact  that  each  of  them  combines 
with  hydrogen  in  the  proportion  of  one  atom  of  the  element  to  four 
atoms  of  hydrogen,  showing  that  each  is  a  tetravalent  element. 

Silicon  carbide,  SiC. — As  might  be  expected  from  their  similarity, 
carbon  and  silicon  do  not  combine  easily.  At  the  temperature  of  the 
electric  furnace  (3500°  C.),  however,  the  compound  SiC  is  produced  in 
the  form  of  colourless,  transparent  hexagonal  plates  of  sp.  gr.  3.12.  It 
is  hard  enough  to  scratch  the  ruby,  and  on  this  account  is  made  on  a 
considerable  scale  for  use  as  an  abrasive  material  under  the  name  car- 
borundum which  is  generally  dark  coloured  from  impurities.  It  resists 
the  attack  of  all  acids,  but  succumbs  to  fused  alkali ;  it  does  not  oxidise 
even  at  a  white  heat. 

In  the  manufacture  of  carborundum  the  electric  furnace  consists  of  a  brick  box, 
having  a  carbon  electrode  projecting  into  each  end.  The  bottom  of  the  box  having 
been  covered  up  to  the  level  of  the  electrodes  with  a  mixture  of  sand,  coke,  and  a 
little  salt,  a  layer  of  crushed  coke  of  the  same  cross-section  as  the  electrodes  is  built 
up  between  the  electrodes.  The  furnace  is  then  filled  with  the  aforesaid  mixture. 
When  the  electric  current  is  supplied  to  the  electrodes  the  layer  of  coke  between 
them  attains  a  very  high  temperature  owing  to  the  resistance  it  offers  to  the  passage 
of  the  current,  and  the  radiation  from  .this  hot  core  causes  the  carbon  in  the  charge 
to  reduce  the  silica  and  to  combine  with  the  silicon  for  a  certain  distance  around 
the  core  ;  SiO2  +  C3  =  SiC  +  2CO. 

Silicon  nitride,  SiN  (?),  has  been  obtained  by  heating  silica  with  carbon  in  a 
blast  furnace  and  treating  the  product  successively  with  hydrofluoric  acid  and 
potash,  when  the  nitride  is  left  as  a  green  infusible  powder  which  is  attacked  by 
potash  at  a  red  heat,  yielding  potassium  silicate,  hydrogen,  and  ammonia.  Si2N3  is 
formed  by  heating  silicon  in  nitrogen. 

Silicon  hydride,  SiH4,  is  the  analogue  of  marsh  gas,  CH4,  but  is  much  less  stable. 
It  is  prepared  by  decomposing  magnesium  silicide  Mg2Si  (made  by  heating  mag- 
nesium with  ;silica)  with  dilute  HC1.  It  is  a  colourless  gas  which,  unlike  CH4, 
ignites  spontaneously  in  air,  burning  with  a  brilliant  white  flame  which  emits 
clouds  of  silica  and  deposits  a  brown  film  of  silicon  upon  a  cold  surface.  Pure 
SiH4  does  not  appear  to  be  spontaneously  inflammable,  resembling  pure  PH3  in  this 
respect,  and  also  in  the  influence  which  pressure  has  upon  its  spontaneous  explosion 
when  mixed  with  oxygen. 

Silico-acetylene,  Si2H2,  is  produced  when  calcium  silicide,  CaSi2,  the  analogue  of 
calcium  carbide  (p.  137),  is  treated  with  dilute  acid  ;  CaSi2  +  2HCl  =  CaCl2+Si2H2. 
The  silicide  is  made  by  heating  a  mixture  of  lime,  silica,  and  carbon  in  the  electric 
furnace,  and  the  silico-acetylene  is  a  yellow  crystalline  substance. 

When  cast-iron  containing  silicon  is  boiled  with  hydrochloric  acid  until  the 
whole  of  the  iron  is  dissolved,  a  grey  frothy  residue  is  left.  If  this  be  collected  on 
a  filter,  well  washed  and  dried,  it  is  found  to  consist  of  black  scales  of  graphite, 
mixed  with  a  very  light  white  powder.  On  boiling  it  with  potash,  hydrogen  is 
evolved  and  the  white  powder  dissolves,  forming  a  solution  containing  potassium 
silicate.  This  white  powder  appears  to  be  identical  with  a  substance  obtained  by 
other  processes,  and  called  leucone,*  which  is  believed  to  have  the  composition 
Si2H203  or  0(8iOH)2.  Its  action  upon  solution  of  potash  would  be  explained  by 
the  equation — 

Si2H203  +  4KOH  =  2K2Si03  +  H20  +  H4 

Leucone  is  slowly  converted  into  silicic  acid,  even  by  the  action  of  water,  hydrogen 
being  disengaged.     It  burns  when  heated  in  air. 

Other  compounds  of  this  character  have  been  prepared. 

172.  Silicon  tetrachloride,  SiCl4,  unlike  the  chlorides  of  carbon,  may 
be  formed  by  the  direct  union  of  silicon  with  chlorine  at  a  high  tempera- 
ture ;  but  it  is  best  prepared  by  passing  dry  chlorine  over  a  mixture  of 
silica  and  charcoal,  heated  to  redness  in  a  porcelain  tube  connected  with 

*  Aev/ebs,  white. 


SILICON  FLUORIDE.  283 

a  receiver  kept  cool  by  a  freezing-mixture.  Neither  C  nor  01  separately 
attacks  the  silica,  but  when  they  are  employed  together,  the  combined 
attractions  of  the  carbon  for  the  oxygen  and  the  chlorine  for  the  silicon 
decomposes  the  silica  ;  Si02  +  C2  +  C14  =  SiCl4  +  200. 

The  tetrachloride  is  a  colourless  heavy  liquid  (sp.  gr.  1.52),  which  is 
volatile  (boiling-point,  59°  C.),  and  fumes  when  exposed  to  air,  the 
moisture  of  which  decomposes  it  yielding  hydrochloric  acid  and  silicic 
acid  ;  Si014  +  4HOH  -  Si(OH)4  +  4HC1. 

When  silicon  is  heated  in  hydrogen  chloride  a  compound,  which, 
from  its  analogy  with  chloroform,  CHC13,  is  termed  silico-chloroform, 
SiHCls,  is  obtained;  Si  +  3HC1  =  SiH013  +  H2.  This  is  a  colourless 
liquid  which  boils  at  36°  C.,  and,  unlike  most  chlorine  compounds 
(including  chloroform),  is  inflammable,  burning  with  a  greenish  flame, 
and  producing  Si02  and  HOI. 

The  chlorides  of  silicon  have  not  received  any  practical  application 
on  a  large  scale,  but  they  are  of  theoretical  importance  as  forming  the 
starting-point  of  a  number  of  silicon  compounds  which  are  the  analogues 
of  organic  carbon  compounds,  C  being  exchanged  for  Si. 

Silicon  hexachloride,  Cl3Si  -  SiCl3,  is  produced  when  SiCl4  is  passed  over  fused 
silicon  at  a  very  high  temperature.  It  forms  colourless  crystals  melting  at-  i°  C. 
and  boiling  at  147°  C.  Cold  water  decomposes  it  with  formation  of  silico-oxalic 
acid,  Cl3Si  •Si013  +  4HOH  =  HOOSi-SiOOH  +  6HCl. 

Silicon  tetrabromide.  SiBr4,  is  a  colourless  liquid  of  sp.  gr.  2.82,  b.p.  150°  C.  and 
m.p.  -  12°  C.  Silicon  tetraiodide,  SiI4,  crystallises  in  colourless  octahedra,  melts  at 
120°  C.,  and  boils  at  290°  C. 

173.  Silicon  tetrafluoride  (SiF4=  104  parts  by  weight). — If  a  mix- 
ture of  powdered  fluor  spar  and  glass  be  heated,  in  a  test-tube  or  small 
flask,  with  concentrated  sulphuric  acid,  a  gas  is  evolved  which  has  a 
very  pungent  odour,  and  produces  thick  white  fumes  in  contact  with 
the  air  :  *  it  might  at  first  be  mistaken  for  hydrofluoric  acid,  but  a  glass 
rod  or  tube  moistened  with  water  and  exposed  to  the  gas,  becomes 
coated  with  a  white  film,  which  proves,  on  examination,  to  be  silica. 
This  result  originated  the  belief  that  the  gas  consisted  of  fluoric  (now 
hydrofluoric)  acid  and  silica ;  but  Davy  corrected  this  view  by  showing 
that  it  really  contained  no  oxygen,  and  consisted  solely  of  silicon  and 
fluorine.  The  gas  is  now  called  silicon  tetrafluoride,  and  represents 
silica  in  which  the  oxygen  has  been  displaced  by  fluorine  :  the  change 
of  places  between  these  two  elements  in  the  above  experiment  is  repre- 
sented by  the  equation — 

2CaF2  +  Si02  +  2H2S04  =  2CaS04  +  SiF4  +  2H20. 

The  formation  of  the  crust  of  silica  upon  the  wetted  surface  of  the 
glass  is  due  to  a  reaction  between  the  tetrafluoride  and  the  water,  in 
which  the  oxygen  and  fluorine  again  change  places;  SiF4  +  2H20  = 
Si02  +  4HF.f  Since  this  latter  equation  shows  that  hydrofluoric  acid 
is  again  formed,  it  would  be  expected  that  the  glass  beneath  the  deposit 

*  SiF4  becomes  solid  at  -  102°  C.,  and,  at  a  higher  temperature,  evaporates  without 
fusing1. 

f  It  will  be  noticed  that  the  proportion  of  SiF4  to  H2O  in  this  equation,  representing  the 
decomposition  of  the  gas  by  water,  is  the  same  as  that  in  the  preceding  equation,  represent- 
ing the  evolution  of  the  gas  together  with  water,  so  that  the  equations  seem  to  contradict 
each  other.  In  reality  it  depends  on  the  actual  masses  of  water  and  other  substances  pre- 
sent, and  also  on  the  temperature,  whether  SiF4  and  H2O  can  exist  together  or  will  at  once 
decompose  each  other.  The  excess  of  sulphuric  acid  used  in  the  manufacture  of  SiF4  will 
combine  with  the  water,  and  will  prevent  it  from  decomposing  the  SiF4. 


284 


HYDROFLUOSILICIC  ACID. 


of  silica  would  be  found  corroded  by  the  acid ;  this,  however,  is  not  the 
case,  and  when  the  experiment  is  repeated  upon  a  somewhat  larger 
scale,  so  that  the  water  which  has  attacked  the  gas  may  be  examined, 
it  is  found  to  hold  in  solution,  not  hydrofluoric  acid,  but  an  acid  which 
has  little  action  upon  glass,  and  is  composed  of  hydrofluoric  acid  and 
silicon  fluoride,  the  hydrofluoric  acid  produced  when  water  acts  on  the 
fluoride  having  combined  with  a  portion  of  the  latter  to  produce  the 
new  acid,  2HF.SiF4,  or  H2SiF6,  hydrofluosilicic  acid. 

For  the  preparation  of  silicon  tetrafluoride,  30  grams  of  fluor  spar  and  an  equal 
weight  of  powdered  glass  are  mixed  together,  and  heated  in  a  Florence  flask,  with 
200  c.c.  of  oil  of  vitriol,  the  gas  being  collected  in  dry  bottles  by  downward  dis- 
placement (see  Fig.  150,  p.  177).  If  a  little  of  the  gas  be  poured  from  one  of  the 
bottles  into  a  flask  filled  up  to  the  neck  with  water,  the  surface  of  the  latter  will 
become  covered  with  a  layer  of  silica,  so  that  if  the  flask  be  quickly  inverted,  the 
water  will  not  pour  from  it,  and  will  seem  to  have  been  frozen.  In  a  similar 
manner,  a  small  tube  filled  with  water  and  lowered  into  a  bottle  of  the  gas,  will 
appear  to  have  been  frozen  when  withdrawn.  A  stalactite  of  silica  some  inches  in 
length  may  be  obtained  by  allowing  water  to  drip  gently  from  a  pointed  tube  into 
a  bottle  of  the  gas.  Characters  written  on  glass  with  a  wet  brush  are  rendered 
opaque  by  pouring  some  of  the  gas  upon  them. 

The  fact  that  silica  is  so  easily  volatilised  in  the  form  of  SiF4  is  of 
immense  service  in  analytical  chemistry  for  "  opening  up "  mineral 
silicates.  By  heating  the  silicate  with  H2SOt  and  HF  in  a  platinum 
vessel  all  the  silica  may  be  expelled,  leaving  the  bases  in  the  form  of 
sulphates. 

174.  Hydrofluosilicic  acid  (H2SiF6=  144  parts  by  weight). — This 
acid  is  obtained  in  solution  by  passing  silicon  tetrafluoride  into  water ; 
3$iF4  +  2H20  =  2H2SiF6  +  SiO2. 

The  gas  must  not  be  passed  directly  into  the  water,  lest  the  separated 
silica  should  stop  the  orifice  of  the  tube,  to  prevent  which  the  latter 

should  dip  into  a  little  mercury 
at  the  bottom  of  the  water, 
when  each  bubble,  as  it  rises 
through  the  mercury  into  the 
water,  will  become  surrounded 
with  an  envelope  of  gelatinous 
silica,  and  if  the  bubbles  be  very 
regular,  they  may  even  form 
tubes  of  silica  extending  through 
the  whole  height  of  the  water. 

Crystals  of  H2SiF6.2Aq  have 
been  obtained  by  passing  SiF4 
into  solution  of  HF. 

For  preparing  hydrofluosilicic  acid, 
it  will  be  found  convenient  to  employ 
a  gallon  stoneware  bottle  (Fig.  200), 
furnished  with  a  wide  tube  dipping 
into  a  cup  of  mercury  placed  at  the 
bottom  of  the  water.  500  grams  of 
finely  powdered  fluor  spar,  an  equal 

weight  of  fine  sand,  and  2  litres  of  oil  of  vitriol  are  introduced  into  the  bottle,  which 
is  gently  heated  upon  a  sand-bath,  the  gas  being  passed  into  about  3  litres  of  water. 
After  six  or  seven  hours  the  water  will  have  become  pasty,  from  the  separation  of 
gelatinous  silica.  It  is  poured  upon  a  filter,  and  when  the  liquid  has  drained  through 
as  far  as'  possible,  the  filter  is  wrung  in  a  cloth,  to  extract  the  remainder  of  the  acid 
solution,  which  will  have  a  sp.  gr.  of  about  1.078. 


Fig.  200. — Preparation  of  hydrofluosilicic  acid. 


CAEBON  GKOUP  OF  ELEMENTS.  285 

A  dilute  solution  of  hydrofluosilicic  acid  may  be  concentrated  by 
evaporation  up  to  a  certain  point,  when  it  begins  to  decompose,  evolving 
fumes  of  SiF4,  HF  remaining  in  solution  and  volatilising  in  its  turn  if 
the  heat  be  continued.  Of  course,  the  solution  corrodes  glass  and  porce- 
lain when  evaporated  in  them.  If  the  solution  of  hydofluosilicic 
acid  be  neutralised  with  potash,  and  stirred,  a  very  characteristic 
crystalline  precipitate  of  potassium  silica  -fluoride  (potassium  fluosilicate), 
K2SiF6,  is  formed  ;  H2SiF6  +  2KHO  =  K2SiF6  +  2H?O. 

But  if  an  excess  of  potash   be  employed,  a  precipitate  of  gelatinous 
silica  will  be  separated,  potassium  fluoride  remaining  in  the  solution — 
H2SiF6  +  6KHO  =  6KF  +  4H20  +  SiOa. 

One  of  the  chief  uses  of  hydrofluosilicic  acid  is  to  separate  the  potas- 
sium from  its  combination  with  certain  acids,  in  order  to  obtain  these 
in  the  separate  state. 

Tin  and  lead,  which  belong  to  the  same  group  of  elements  as  silicon 
(see  "  Periodic  Law  "),  form  fluostannates  and  jluoplumbates,  such  as 
Na2SnF6  or  2NaF.SnF4,  and  K2PbF6  or  2KF.PbF4,  analogous  to  the 
fluosilicates. 

175.  Silicon  disulpliide  (SiS2),  corresponding  with  carbon  disulphide,  is  obtained 
by  burning  silicon  in  sulphur  vapour,  or  by  passing  vapour  of  carbon  disulphide 
over  a  mixture  of  silica  and  charcoal,  in  the  form  of  volatile  needles.  Unlike  the 
carbon  compound,  it  is  a  white  amorphous  solid,  absorbing  moisture  when 
exposed  to  air,  and  soluble  in  water,  which  gradually  decomposes  it  into  silica 
and  hydrogen  sulphide.  When  heated  in  air  it  burns  slowly,  yielding  silica  and 
sulphur  dioxide. 

176.  The  elements  carbon,  boron,  and  silicon  possess  many  properties 
in  common.  They  all  exist  in  the  amorphous  and  the  crystalline  forms ; 
all  are  incapable  of  being  converted  into  vapour  ;  all  exhibit  a  want  of 
disposition  to  dissolve  ;  all  form  feeble  acid  oxides  by  direct  union  with 
oxygen,  for  which  the  order  of  their  aflinity  is  boron,  silicon,  carbon  ; 
and  all  unite  with  several  of  the  metals  to  form  compounds  which 
resemble  each  other.  Boron  and  silicon  are  capable  of  direct  union 
with  nitrogen,  and  so  is  carbon  if  an  alkali  be  present.  Recent  re- 
searches attribute  to  silicon  the  power  of  occupying  the  place  of  carbon 
in  some  organic  compounds,  and  the  formula  of  leucone,  Si2H203  strongly 
reminds  us  of  the  organic  compounds  of  carbon  with  hydrogen  and 
oxygen.  In  many  of  its  physical  and  chemical  characters  silicon  is 
closely  allied  with  the  metals,  and  it  will  be  found  that  tin  and  titanium 
bear  a  particular  resemblance  to  it  in  their  chemical  relations. 

Notwithstanding  these  points  of  similarity  between  boron,  carbon, 
and  silicon,  boron  is  not  regarded  as  belonging  to  the  family  of  elements 
which  includes  carbon  and  silicon,  because  whilst  C  and  Si  are  tetra- 
valent  elements,  boron  is  trivalent,  and  must,  therefore,  be  classed  with 
nitrogen  and  phosphorus. 


CERTAIN  GENERAL  PRINCIPLES 


ATOMS  AND  MOLECULES. 

177.  It  is  only  after  numerous  facts  have  been  observed,  and  accu- 
rately described,  that  it  is  possible  to  deduce  such  general  principles  as 
may  enable  future  workers  to  conduct  their  experiments  in  such  a 
manner  that  they  may  discover  and  arrange  fresh  facts  with  the  smallest 
possible  expenditure  of  energy  and  time.  Thus,  the  generalisation 
which  receives  the  name  of  the  Atomic  Theory,  and  upon  which  the 
science  of  Chemistry  is  now  constructed,  was  enunciated  at  the  begin- 
ning of  the  last  century  only  after  the  gravimetric  and  volumetric 
composition  of  a  large  number  of  compounds  had  been  determined  by 
both  synthetical  and  analytical  methods. 

The  theory  arose  from  the  contemplation  of  the  quantitative  com- 
position of  various  compounds,  when  it  was  seen  that  chemical  combina- 
tion does  not  occur  between  masses  of  matter  in  indefinite  quantities, 
but  is  controlled  by  the  following  three  laws : 

(1)  Law  of  Constant  Proportions. — In  every  compound  the  masses  of 
the  constituent  elements  bear  the  same  ratio  to  each  other,  from  what- 
ever source  the  compound  may  be  obtained. 

It  is  this  law  which  determines  how  much  of  an  element  in  a  mixture 
will  enter  into  combination.  For  example,  when  a  mixture  of  zinc  and 
sulphur  is  heated,  complete  combination  will  only  occur  when  the  ratio 
of  the  mass  of  zinc  to  that  of  sulphur  is  65*5  :  32  ;  if  the  mixture 
contain  the  elements  in  any  other  ratio,  either  zinc  or  sulphur  will 
remain  uncombined  after  the  heating. 

(2)  Law  of  Multiple  Proportions. — When  two  elements  combine  to 
form  more  than  one  compound,  the  masses  of  the  one  element  com- 
bining with  a  constant  mass  of  the  other,  must  be  simple  multiples  of 
the  smallest  mass  among  them. 

The  hydrocarbons  yield  abundant  examples  of  this  law ;  thus, 
quantitative  analysis  of  marsh  gas,  defiant  gas,  and  acetylene  shows 
that  they  have  the  following  gravimetric  compositions  per  cent.  : 

Carbon.  Hydrogen.  Ratio  of  C  :  H. 

Marsh  gas  75  25  3:1 

Olefiant  gas  85.7  14.3  6:1 

Acetylene  92.3  7.7  12  :  i 

It  is  apparent  from  the  ratios  that  the  proportion  of  carbon  that 
combines  with  one  part  by  weight  of  hydrogen  in  the  second  and  third 
compounds,  is  a  multiple  of  that  in  the  first  compound  by  a  simple 
whole  number. 


= 

18.7 

6.2 

or 

3 

:    i 

= 

18.7 

100 

or 

3 

:  16 

= 

6.2 

100 

or 

i 

:  16 

LAWS  OF  COMBINATION.  287 

Another  striking  example  is  afforded  by  the  oxides  of  nitrogen ;  in 
these  there  are,  for  100  parts  of  nitrogen,  57.1,  114.2,  171.3,  228.4  a^d 
285.5  Parts  of  oxygen  respectively,  figures  in  the  ratio  1:2:3:4:5. 

(3)  Law  of  Reciprocal  Proportions. — When  an  element  forms  a  com- 
pound with  each  of  several  other  elements,  the  masses  of  the  several 
other  elements  which  combine  with  a  constant  mass  of  the  first  element, 
are  also  the  masses  of  these  elements  which  combine  with  each  other, 
or  they  bear  some  simple  ratio  to  these  masses. 

Thus,  sulphuretted  hydrogen,  sulphur  dioxide,  and  carbon  bisulphide 
have  the  following  gravimetric  compositions : 

Per  cent.  Per  cent. 

Sulphuretted  hydrogen     .         Sulphur     94.1  .  .  Hydrogen       5.9 

Sulphur  dioxide         .         .         Sulphur     50.0  .  .  .  Oxygen         50.0 

Carbon  bisulphide    .         .         Sulphur     84.2  .  .  Carbon          15.8 

When  these  figures  are  calculated  for  100  parts  of  sulphur  in  each 
case,  they  become — 

Sulphuretted  hydrogen     .         Sulphur     100         .         .         Hydrogen       6.2 
Sulphur  dioxide        .         .         Sulphur     100         .         .         Oxygen      100 
Carbon  bisulphide    .      .  .        Sulphur     100        .        .         Carbon          18.7 

The  ratios  of  the  proportions  of  C,  H  and  0  which  combine  with  100 
parts  of  sulphur  in  the  above  table  are  : — 

C  :H 
C  :0 
H:  0 

Now  3  compounds  of  carbon  with  hydrogen,  2  of  carbon  with  oxygen, 
and  2  of  hydrogen  with  oxygen  are  known,  and  the  ratios  of  the  ele- 
ments in  these  compounds  are  : 

C:H     =     3:1         6  :    i         12  :  i 
C  :  O      =     3:8         3  :  16 
H  :  0     =      i  :  8         I  :  16 

Thus  the  ratio  in  which  any  pair  of  these  elements  combine  with  each 
other  is  either  the  same  as  that  in  which  they  combine  with  a  constant 
mass  of  sulphur  or  is  some  multiple  or  submultiple  thereof  by  a  simple 
whole  number. 

In  order  to  account  for  the  existence  of  these  laws,  Dalton  revived 
the  atomic  theory.  The  fundamental  conception  on  which  this  theory 
is  based  has  been  stated  in  the  Introduction;  the  new  significance  with 
which  Dalton  invested  it  was,  that  each  of  the  indivisible  particles 
(atoms)  of  which  a  kind  of  matter  is  composed  has  an  invariable  weight, 
and  that  this  weight  is  the  same  for  each  atom  of  the  same  kind  of 
matter.  Furthermore,  when  combination  of  one  kind  of  matter  with 
another  occurs,  the  union  takes  place  between  the  atoms  of  these  kinds 
of  matter,  and  consists  in  the  addition  of  one  or  more  atoms  of  the  first 
kind  to  one  or  more  atoms  of  the  second  kind.  If  these  postulates 
be  granted,  it  at  once  becomes  apparent  why  a  compound  always  con- 
tains its  elements  in  the  same  gravimetric  ratio  ;  water,  for  instance,  is 
always  composed  of  oxygen  and  hydrogen  in  the  ratio  of  8  :  i  by  weight ; 
and  this,  according  to  Dalton,  is  clue  to  the  fact  that  water  is  a  compound 
of  one  atom  of  oxygen  with  one  atom  of  hydrogen,  the  atom  of  oxygen 
weighing  8  times  as  much  as  the  atom  of  hydrogen.  The  "  atom  "  of 


288  DALTON'S  ATOMIC   WEIGHTS. 

water,  as  Dalton  called  it,  should  therefore  be  represented  as  HO.  The 
considerations  which  led  to  the  adoption  of  H,0  for  the  formula  of 
water  will  be  dealt  with  presently. 

Again,  the  law  of  multiple  proportions  follows  of  necessity  from  Dalton's  hypo- 
thesis. For  if  a  compound  of  x  atoms  of  one  element  with  y  atoms  of  another 
element  exist,  a  new  compound  can  only  be  formed  by  adding  another  atom  or  by 
taking  one  away  ;  and  since  each  atom  of  the  same  element  weighs  the  same,  the 
addition  or  subtraction  of  each  atom  must  cause  the  same  variation  in  the  propor- 
tional composition.  Thus,  if  there  be  a  compound  of  one  atom  of  nitrogen  with  one 
atom  of  oxygen,  and  the  ratio  between  the  weights  of  these  atoms  be  7  :  8  (or 
loo  :  114.2),  it  is  only  possible  to  produce  another  compound  of  these  two  elements 
by  adding  one  or  more  atoms  of  nitrogen,  each  weighing.  7,  or  one  or  more 
atoms  of  oxygen,  each  weighing  8  ;  so  that  any  other  oxide  of  nitrogen 
must  contain  the  elements  in  the  ratio  7  x  n  :  8  x  m  by  weight,  n  and  m  being 
integers. 

The  third  law  of  chemical  combination  is  equally  explicable,  for  the  ratio  by 
weight  in  which  two  elements  combine  is  either  the  ratio  between  the  weights  of 
their  atoms,  or  that  between  some  multiples  of  these.  Hence  the  ratio  between 
the  weights  of  two  elements  in  a  compound  must  be  represented  by  the  same 
numbers  as  those  representing  the  weights  of  these  elements  in  their  compounds 
with  any  other  elements,  or  by  some  simple  multiple  or  submultiple  of  these 
weights.  If  the  compound  of  carbon  with  sulphur  which  contains  these  elements 
in  the  proportion  of  18.7  :  100  or  3  :  16  parts  by  weight,  contain  only  one  atom  of 
sulphur  and  one  atom  of  carbon,  then  any  compound  of  sulphur  with  another 
element,  itself  capable  of  combining  with  carbon  in  the  proportion  of  x  :  3,  must 
contain  the  sulphur  and  the  other  element  in  the  proportion  of  16  :  x  or  16  x  n  :  a?, 
where  n  is  an  integer  ;  if,  on  the  other  hand,  the  compound  of  carbon  with  sulphur 
contain  2  or  4  atoms  of  sulphur,  other  compounds  of  this  element  may  contain  it 
in  the  proportion  of  8  or  4  parts  by  weight. 

Dalton  endeavoured  to  construct  a  table  of  atomic  weights — that  is,  a 
table  of  the  relative  weights  of  the  atoms — by  determining  how  many 
parts  by  weight  of  each  element  combine  with  one  part  by  weight  of 
hydrogen,  the  atomic  weight  of  which  he  took  as  unity,  hydrogen  being 
the  lightest  kind  of  matter.  His  numbers,  however,  agree  only  in  a 
few  cases  with  the  modern  atomic  weights,  for  two  reasons.  In  the 
first  place,  except  in  those  cases  in  which  two  elements  form  more  than 
one  compound — the  difference  between  which  compounds  he  attributed 
to  their  containing  different  numbers  of  atoms — except  in  these  cases, 
he  concluded  that  combination  occurs  between  one  atom  and  one  atom, 
whereas  now  the  hypothesis  is  that  in  many  cases  the  combination  is 
between  2  or  3  atoms  and  i  atom,  or,  generally,  between  n  and  m  atoms. 
For  instance,  if  the  compound  of  carbon  and  hydrogen  in  which  the 
ratio  by  weight  of  C  :  H  is  3  :  i  be  a  compound  of  i  atom  of  C  with 
i  atom  of  H  the  atomic  weight  of  carbon  will  be  3  ;  if,  as  now  believed, 
it  is  a  compound  of  i  atom  of  C  with  4  atoms  of  H,  the  atomic  weight 
of  carbon  is  1 2 . 

In  the  second  place,  Dalton  had  not  conceived  the  existence  of  a 
second  kind  of  ultimate  particle,  now  called  a  molecule.  Thus,  he  spoke 
of  an  "  atom  "  of  water  and  other  compounds,  notwithstanding  that  by 
his  hypothesis  an  atom  is  indivisible,  while  by  definition  a  compound  is 
divisible.  His  studies  of  gases  were  limited  to  their  combination  by 
weight.  Gay-Lussac  (1809)  studied  their  combination  by  volume,  and 
experienced  a  difficulty  in  applying  Dalton's  hypothesis,  which  led  to 
the  conception  of  molecules. 

The  difficulty  is  easily  appreciated  from  the  contemplation  of  the 
combination  of  hydrogen  with  chlorine.  Equal  volumes  of  these  gases 


DALTON'S   ATOMIC  WEIGHTS.  28^ 

combine,  and  the  product  occupies  twice  the  volume  of  either  of  its 
constituents  :  one  volume  of  H  combines  with  one  volume  of  01  to  form 
two  volumes  of  HC1.  According  to  Dalton's  theory,  one  atom  of 
hydrogen  combines  with  one  atom  of  chlorine  to  form  one  "  atom  "  of 
hydrogen  chloride.  If  this  be  the  case,  equal  volumes  of  hydrogen  and 
chlorine  must  contain  the  same  number  of  atoms,  for  it  is  found  that 
equal  volumes  of  these  gases  combine  exactly — that  is,  no  residue  of 
either  gas  is  left.  This  reasoning  applies  to  the  combination  of  several 
other  gases,  whence  Gay-Lussac  attempted  to  deduce  the  generalisation 
that  equal  volumes  of  all  gases  contain  the  same  number  of  atoms. 
But  if  this  be  the  case,  the  two  volumes  of  HC1,  produced  by  the 
combination  of  one  volume  of  H  with  one  volume  of  01,  must  contain 
twice  as  many  atoms  as  the  one  volume  of  chlorine  or  of  hydrogen 
contains ;  therefore  one  atom  of  01  combines  with  one  atom  of  H  to 
form  two  atoms  of  HC1,  and  consequently  one  atom  of  HC1  must  contain 
half  an  atom  of  01,  which  is  impossible,  an  atom  being  indivisible. 
Gay-Lussac's  generalisation,  however,  corrected  some  of  Dalton's  atomic 
weights  to  the  present  values  ;  that  of  oxygen  will  serve  as  an  example. 
Two  volumes  of  H  combine  with  one  volume  of  O  to  form  water ;  but 
equal  volumes  of  gases  contain  the  same  number  of  atoms,  therefore 
2  atoms  of  H  combine  with  one  atom  of  0 ;  the  ratio  by  weight  of  H  to 
O  in  water  is,  however,  i  :  8,  so  that  2  atoms  of  H  weighing  i  combine 
with  i  atom  of  0  weighing  8 ;  but,  as  already  denned,  i  atom  of 
hydrogen  is  to  weigh  i,  therefore  water  contains  2  atoms  of  hydrogen 
weighing  2,  combined  with  one  atom  of  oxygen  weighing  16,  and  its 
formula  is  H2O. 

Avogadro  (1811)  conceived  the  existence  of  two  kinds  of  ultimate 
particle.  Starting  with  the  conception  that  gases  are  composed  of 
ultimate  particles,  which  he  preferred  to  call  molecules,  he  attempted  to 
explain  the  combination  of  gases  by  volume,  but  encountered  the  diffi- 
culty experienced  by  Gay-Lussac.  To  overcome  this  difficulty  he  had 
recourse  to  the  supposition  that  the  molecules  of  the  gases  are  shattered 
before  combination  occurs,  and  that  the  parts  of  the  molecules  then  re- 
combine  to  form  the  molecules  of  the  new  gas.  The  particles  produced 
by  the  scission  of  the  molecules  were  the  true  indivisibles,  or  Dalton's 
atoms.  Thus,  Avogadro  was  able  to  support  the  generalisation  now 
known  as  Avogadro' s  Law.  namely,  that  equal  volumes  of  gases  at  the 
same  temperature  and  pressure  contain  the  same  number  of  molecules. 
The  combination  of  hydrogen  with  chlorine  is  now  easily  explained ; 
one  volume  of  hydrogen  contains  the  same  number  of  molecules  as  is 
contained  in  one  volume  of  chlorine  ;  when  these  volumes  combine,  the 
molecules  are  shattered  and  their  component  atoms  recombine  to  form 
molecules  of  hydrogen  chloride ;  one  molecule  of  chlorine  thus  reacts 
with  one  molecule  of  hydrogen  to  form  two  molecules  of  hydrogen 
chloride,  which  (according  to  Avogadro's  law)  must  therefore  occupy 
twice  the  volume  occupied  by  either  the  chlorine  or  the  hydrogen. 

The  definitions  of  an  atom  and  of  a  molecule  have  been  given  on 
p.  8.  The  hypothesis  that  the  hydrogen  molecule  consists  of  two  atoms 
may  be  supported  as  follows  :  Hydrogen  chloride  contains  half  its  volume 
of  hydrogen,  and  therefore  half  as  much  hydrogen  as  is  contained  in  an 
equal  volume  of  hydrogen ;  but  equal  volumes  of  hydrogen  chloride  and 
hydrogen  contain  the  same  number  of  molecules  (Avogadro's  law), 


290  MOLECULAR  MOTION. 

therefore  one  molecule  of  hydrogen  chloride  contains  half  as  much 
hydrogen  as  one  molecule  of  hydrogen  contains.  Now  one  molecule  of 
hydrogen  chloride  is  supposed  to  consist  of  one  atom  of  hydrogen  com- 
bined with  one  atom  of  chlorine,  therefore  one  molecule  of  hydrogen 
must  be  supposed  to  consist  of  one  atom  of  hydrogen  combined  with  one 
atom  of  hydrogen.  The  same  reasoning  will  apply  to  the  molecule  of 
chlorine. 

It  is  difficult  to  account  for  the  spontaneous  intermixture  or  diffusion 
of  gases  (p.  25)  unless  it  be  granted  that  their  molecules  are  always  in 
motion,  and  if  this  be  postulated  an  explanation  of  the  pressure  of  a  gas 
is  at  once  found.  For  if  the  molecules  are  in  constant  motion  they 
must  continually  strike  the  sides  of  the  containing  vessel  and  the 
numerous  impacts  must  exert  a  pressure  on  those  sides. 

Liquids  also  have  the  property  of  diffusion,  but  the  property  is  not 
universal  between  all  liquids;  thus,  oil  and  water  do  not  intermix. 
Moreover,  the  diffusion  occupies  a  much  longer  time  than  that  of  gases. 
It  seems  therefore  that  molecular  motion  must  also  exist  in  liquids, 
but  at  a  slower  rate  or  more  limited  than  that  in  gases.  Diffusion 
among  solids  is  rare  though  not  unknown  (p.  25),  but  the  process  is  so 
exceedingly  slow  that  molecular  motion  of  solids  must  be  more  limited 
than  that  of  liquids. 

Now  by  heating  a  gas  its  pressure  is  increased,  and  if  the  pressure  is 
due  to  the  motion  of  the  molecules,  it  follows  that  increase  of  the  tem- 
perature of  the  gas  means  increase  of  molecular  motion.  Conversely, 
cooling  a  gas  decreases  its  pressure,  and  therefore  also  its  molecular 
motion.  All  gases  save  hydrogen  (which  requires  pressure)  can  be 
liquefied  by  merely  cooling  them,  that  is,  by  depriving  their  molecules 
of  motion  to  a  sufficient  extent. 

The  movement  of  the  molecules  of  a  solid  may  be  regarded  as 
limited  to  a  species  of  oscillation,  that  is  to  say,  the  molecules  cannot 
move  far  from  their  original  positions.  As  this  movement  is  increased 
by  rise  of  temperature  there  is  a  tendency  for  the  molecules  to  move  so 
fast  that  they  break  away  from  the  influence  of  each  other,  and  are 
imbued  with  much  more  freedom  of  motion.  The  temperature  at  which 
this  happens  is  the  melting-point  of  the  solid,  and  is  constant  until  the 
whole  mass  is  liquid,  since  heat  is  absorbed  in  order  to  effect  the  work 
of  separating  the  molecules. 

The  molecules  of  a  liquid  are  still  considerably  under  the  influence  of 
each  other,  although  those  at  the  surface  escape  and  move  about  in  the 
space  above  the  liquid  without  influencing  each  other  to  any  but  a  very 
limited  extent ;  this  is  the  evaporation  of  the  liquid.  When  the  space 
is  confined,  it  soon  becomes  saturated  with  these  vapour  molecules,  and 
evaporation  apparently  ceases.  This  happens  when  as  many  molecules 
of  vapour  attach  themselves  to  the  surface  of  the  liquid  as  escape  from 
it,  in  unit  time. 

As  the  temperature  of  the  vapour  is  raised,  the  motion  of  the  mole- 
cules becomes  more  rapid,  and  the  latter  are  less  and  less  influenced  by 
each  other.  The  vapour  is  then  a  gas,  and  conforms  with  the  laws 
which  connect  the  volume  of  a  gas  with  its  pressure  and  temperature 
(see  p.  27). 

If  an  ideal  gas  (see  p.  28)  consists  of  a  number  of  elastic  solid  particles 
in  motion,  its  properties  can  be  investigated  by  mathematics ;  this 


KINETIC   THEORY   OF  GASES.  291 

has  been  done,  and  the  results  are  generally  spoken  of  as  the  kinetic 
theory*  of  gases,  which  may  be  succinctly  stated  thus  :  The  molecules 
of  a  gas  are  in  constant  and  rapid  motion  in  straight  lines,  and  continue 
moving  in  the  same  direction  until  they  are  reflected  by  striking  each 
other  or  the  walls  of  the  containing  vessel.  The  impacts  against  the 
sides  of  the  vessel  give  rise  to  the  pressure  of  the  gas.  whilst  the  tem- 
perature of  the  gas  is  a  measure  of  the  velocity  of  motion  of  the 
molecules. 

The  theory  is  not  strictly  within  the  province  of  the  chemist,  but  in 
that  of  the  physicist  ;  the  former,  however,  finds  in  it  an  explanation 
of  many  chemical  changes,  and,  above  all,  a  confirmation  of  Avogadro's 
hypothesis,  originally  deduced  from  purely  chemical  considerations,  that 
equal  volumes  of  gases  at  the  same  temperature  and  pressure  contain 
the  same  number  of  molecules.  Moreover,  the  theory  teaches  him  that 
the  hypothesis  is  absolutely  true  only  of  perfect  gases. 

A  mathematical  expression  for  the  pressure  of  a  gas  may  be  deduced  from  con- 
sideration of  molecules  moving  in  a  hollow  cube.  Let  a  molecule  of  mass  m  in 
such  a  vessel  be  moving  in  any  direction  with  velocity  w  ;  this  can  be  resolved 
into  three  components  (a1,  y.  z)  in  directions  parallel  to  the  sides  of  the  cube  and 
according  to  the  principle  of  the  resolution  of  velocities,  w2  =  a?  +  y2  +  z2.  When  the 
molecule  moving  towards  the  side  of  the  cube  with  velocity  x  strikes  the  side,  it 
exerts  a  force  equivalent  to  its  momentum,  which  is  mas,  not  only  at  the  impact 
but  when  it  rebounds,  making  a  total  of  2m  A:  If  I  is  the  distance  that  the  molecule 
has  to  move  from  one  side  of  the  cube  to  the  other,  that  is,  the  length  of  the  side 
of  the  cube,  this  force  is  repeated  &/1  times  every  unit  of  time.  Thus  the  force 
exerted  in  unit  time  becomes  2m&x&'/l  =  2mas2/l.  What  is  true  of  components- 
applies  to  the  other  components,  so  the  expression  becomes  2  w  (*2  +  y^  +  z2)/l  =  2mwz/l, 
and  for  the  whole  number  n  of  the  molecules,  2nmw2/l.  The  pressure  p  of  a  gas  is 
expressed  per  unit  area,  so  the  foregoing  expression  must  be  divided  by  6Z2,  the 

number  of  units  of  surface  in  a  cube  ;  hence  the  final  formula  is  p  =  —  n™   .    Is  is  the 
volume  (r)  of  the  cube,  so  the  expression  may  be  written  pv=—    —  ,  or  for  unit 


volume  p  = 

It  is  more  instruct!  veto  write  this  formula  ^=-1.%-^-,  for  —   is   the  kinetic 

32  2 

energy  of  the  moving  molecule  and  nmw'2/2  that  of  all  the  molecules.  Now  if  p  is 
varied  by  altering  the  temperature  of  the  gas,  this  variation  can  be  due  only  to  the 
variation  of  the  kinetic  energy  of  the  molecules  for  n  is  constant.  Hence  the  tem- 
perature of  a  gas  must  be  a  measure  of  its  kinetic  energy,  and  if  unit  volumes  of 
two  gases  have  the  same  temperature  they  must  also  have  the  same  kinetic  energy, 
or  mwz/2  =  mlw-^/2.  Let  the  unit  volumes  be  also  at  the  same  pressure,  then 

_  n  mw  ,      ^-n1m'lWl-  or  mnw2=mlnlii<l2,   or   since  niio2  =  mlw-f  by  the  previous 

equation,  n  =  %,  that  is  to  say,  when  gases  are  at  the  same  temperature  and  pressure 
the  number  of  molecules  in  unit  volume  is  the  same  (Avogadro's  hypothesis). 

The  mass  of  a  volume  of  gas  must  be  the  product  of  the  mass  of  each  molecule 
and  the  number  of  molecules  ;  hence  mn  in  the  foregoing  equations  is  the  mass  of 
the  gas.  Taking  I  gram  of  hydrogen  which  measures  11,110  C.G.  at  760  mm. 
pressure  and  o°  C.,  mn  will  be  i,  and  we  have  pv  =  w2/$  or  w=  V^pv.  The  pres- 
sure of  760  mm.  of  mercury  in  absolute  units  of  mass  is  76  x  13.5  xff  =  ioi3i3Q. 
Hence  the  rate  w  at  which  the  hydrogen  molecules  move  is  —  ^3  x  1013130  x  uiio 
cm.  per  second,  or  1838  metres  per  second. 

The  mass  of  unit  volume  is  identical  -with  density,  hence  for  mn  in  the  foregoing 
equations  might  be  written  d,  and  it  will  be  obvious  that  if  p  and  v  are  constants 
must  vary  inversely  as  VdT  That  is  to  say,  the  velocity  of  the  molecules  of  a  gas 

*  KIITJ<TIS=  motion. 


2Q2        DETERMINATION  OF  MOLECULAR  WEIGHT. 

varies  inversely  as  the  square  root  of  the  density  of  the  gas.  Since  in  equal 
volumes  of  two  gases  at  the  same  temperature  and  pressure  mnuP  =  ml<nlw-f  it 
follows  that  dw2  =  dlw12  ;  that  is  to  say,  the  rates  of  movement  of  the  molecules 
of  different  gases  vary  inversely  as  the  square  roots  of  their  specific  gravities. 

Molecular  Weights. — The  weight  of  a  single  molecule  has  never 
been  determined,  and  it  is  assumed  that  all  the  molecules  of  any  single 
substance  have  the  same  weight.  To  compare  the  weights  of  the  mole- 
cules of  different  substances  is  possible  if  Avogadro's  hypothesis  be  true. 
For  if  equal  volumes  of  gases  at  the  same  temperature  and  pressure  con- 
tain the  same  number  of  molecules,  the  relative  weights  of  these  volumes 
must  also  be  the  relative  weights  of  the  molecules  of  the  gases.  The 
molecule  of  hydrogen  being  selected  as  the  standard  of  comparison,  the 
unit  of  molecular  weights  is  2,  since  it  is  accepted  that  there  are  two 
parts  or  atoms  in  each  molecule  of  hydrogen,  and  the  molecular  weight 
of  any  other  gas,  be  it  element  or  compound,  is  twice  the  number  of  times 
that  a  volume  of  it  in  the  state  of  gas  is  heavier  than  an  equal  volume  oj 
hydrogen  at  the  same  temperature  and  pressure.  This  is  expressed 
by  the  equation  M  =  2D,  where  M  is  the  molecular  weight,  and  D  the 
vapour  density  *  of  the  gas,  for  the  latter  is  the  number  of  times  that 
the  gas  is  heavier  than  hydrogen. 

Hence,  in  order  to  ascertain  the  molecular  weight  of  a  substance  it  is- 
necessary  to  determine  the  vapour  density  and  to  double  this  value. 
When  the  substance  is  a  gas  at  the  ordinary  temperature,  the  operation 
consists  in  weighing  a  volume  of  the  gas  ;  this  weight  is  then  divided 
by  that  of  the  same  volume  of  hydrogen  at  the  same  temperature  and 
pressure,  calculated  on  the  basis  of  the  ascertained  weight  of  one  litre 
of  hydrogen  at  o°C.  and  760  mm.  pressure,  namely  0.09  gram. 

In  the  actual  process,  the  capacity  (about  500  c.c.)  of  a  globe  (closed 
by  a  stop-cock  such  as  that  shown  in  Fig.  50)  is  determined  by  weighing 
it,  first  empty,  and  then  full  of  water ;  the  weight  of  the  water  which 
it  can  contain,  and,  therefore,  its  volume  (i  c.c.  of  water  weighs  i  gram 
at  4°C.)  is  thus  ascertained.  The  dried  globe  may  then  be  filled  with 
the  purified  gas,  the  temperature  and  pressure  being  noted  at  the 
moment  when  the  stop-cock  is  closed,  and  again  weighed. 

Let  the  weight  of  the  empty  globe  be  w  grams,  and  that  of  the  globe  full 
of  water  at  4°  C.  be  W  grams ;  then  the  capacity  (V)  of  the  globe  is 
W-w  c.c.  Let  Wj  be  the  weight  of  the  globe  filled  with  carbon  dioxide. 
(C02)  at  15°  C.  and  770  mm.  bar.  Then  Wj  — ifl  grams  is  the  weight  of 
V  c.c.  of  G0.2  at  15°  and  770  mm.  bar.  Since  the  volume  of  a  gas  varies  in- 
versely as  its  pressure,  and  directly  with  its  absolute  temperature  (degrees 

c  +  273),  V  c.c.  of  hydrogen  at  15°  C.  and  770  mm.  bar.  will  be  V    x    ^|?  x  ?I3  c.c. 

at  o°  C.  and  760  mm.,  and  will  weigh  Y  x  ZZSL  x  -Zi    x     0.0009     =     A      grams. 

760       285 

Thus  — *        —  vapour  density  of  C02,  and  — J~ —       is   the   molecular  weight   of 
C02. 

When  the  substance  has  to  be  heated  to  convert  it  into  a  gas,  the 
same  method  may  be  adopted,  the  solid  or  liquid  substance  being  intro- 
duced into  the  globe,  which  is  then  heated  in  a  bath  of  liquid  at  a  suffi- 
ciently high  temperature  to  volatilise  the  substance  entirely;  the  vapour,, 

*  The  term  vapour  density  is  used  here  because  so  few  substances  being  gaseous  at  the 
ordinary  temperature,  it  is  nearly  always  necessary  to  vaporise  the  substance  before  it  can 
be  regarded  as  a  gas. 


VICTOR   MEYER'S   METHOD. 


293 


in  escaping  from  the  globe,  expels  the  air,  and  when  no  more  vapour 
issues  from  the  narrow  orifice  of  the  neck  (which  is  substituted  for  the 
stop-cock),  a  blowpipe  flame  is  applied  to  seal  this  orifice,  the  tempera- 
ture of  the  bath  and  the  pressure  of  the  atmosphere  being  noted  at  the 
moment  of  sealing.  The  calculations  involved  are  the  same  as  those 
stated  above.  For  substances  which  volatilise  at  temperatures  above 
that  at  which  glass  becomes  soft,  globes  made  of  porcelain  must  be 
employed ;  these  are  sealed  by  the  oxyhydrogen  blowpipe.  When 
modified  in  this  way  for  solids  and  liquids,  the  method  is  known  as 
Dumas'  method. 

The  foregoing  method  for  deter- 
mining vapour  densities  consists  in 
weighing  a  known  volume  of  vapour. 
The  value  can  be  equally  well,  and 
somewhat  more  easily,  ascertained  by 
measuring  the  volume  occupied  by  a 
known  weight  of  vapour,  an  operation 
which  is  most  easily  effected  by  the 
Victor  Meyer  method.  In  this,  a 
weighed  quantity  of  the  substance  is 
converted  into  vapour  in  a  vessel  con- 
taining air  (or  some  other  gas),  and  the 
volume  of  air  displaced  by  the  vapour 
is  collected  and  measured. 


Take,  for  example,  the  determination  of  the 
vapour  density  of  alcohol,  which  boils  at 
78.3°  C.  The  vapourising  tube  (&,  Fig.  201), 
well  closed  by  a  cork,  is  heated  in  the  cylinder 
of  boiling  water  a  so  long  as  any  bubbles 
of  air  pass  from  the  opening  of  the  delivery- 
tube  d  through  the  water  in  the  trough. 
The  end  of  the  delivery-tube  is  then  inserted 
into  the  graduated  tube  /,  which  is  full  of 
water.  About  o.i  gram  of  alcohol  is  weighed 
out  into  a  small  tube,  which  is  dropped  into 
the  opening  of  the  vapourising-tube,  this  being 
then  quickly  corked.  A  little  asbestos  is 
placed  at  the  bottom  of  the  vapourising-tube 
c  to  prevent  breakage. 

The  alcohol  vapour  expels  a  volume  of  air 
equal  to  its  own,  and  this  is  collected  in  the 
tube  /,  and  accurately  measured,  with  the 
usual  corrections  for  temperature  and  pres- 
sure. The  volume  of  a  known  weight  of 
alcohol  in  the  form  of  vapour  having  been 
thus  ascertained,  the  vapour  density  may  be  calculated. 

For  example,  o.i  gram  of  alcohol  expelled  a  volume  of  air  which  measured 
48.5  c.c.  when  corrected  to  o°  C.  and  760  mm.  bar.  Hence,  supposing  that  alcohol 
could  retain  the  state  of  vapour  at  that  temperature  and  pressure,  48.5  c.c.  of 
alcohol  vapour  would  weigh  o.  i  gram. 

Now,  48.5  c.c.  of  hydrogen  at  o°  C.  and  760  mm.  weighs  0.00434  gram,  so  that 

the  vapour  density  of  alcohol  is  — : =   23,    and    its    molecular    weight     is 

0.00434 
23x2  =  46. 

For  substances  which  can  only  be  volatilised  at  very  high  temperatures  porcelain 
must  be  substituted  for  glass,  and  a  liquid  of  high  boiling-point  must  be  used  in  the 
bath  surrounding  the  vapourising  tube. 


Fig.  201. — Victor  Meyer's  apparatus. 


294  ABNORMAL  VAPOUR  DENSITY. 

It  will  be  obvious  that  the  molecular  weight  of  a  compound  which  is 
not  capable  of  being  vapourised  without  decomposition  cannot  be  ascer- 
tained from  the  vapour  density.  There  are,  however,  other  criteria,  by 
means  of  which  the  molecular  weight  of  a  compound  may  be  ascertained ; 
these  will  receive  notice  presently. 

Inasmuch  as  Avogadro's  law  is  true  only  of  the  ideal  gas,  the 
foregoing  method  of  determining  molecular  weights  can  give  accurate 
results  only  with  gases  which  are  far  removed  in  temperature  from  the 
boiling-point  of  the  corresponding  liquids,  and  thus  approach  perfection. 
A  criterion  for  the  degree  of  gaseous  character  is  the  amount  by  which 
a  gas  deviates  from  Boyle's  law ;  if,  for  instance,  on  doubling  the 
pressure  on  1000  c.c.  the  volumes  becomes}  400  c.c.  instead  of  500  c.c., 
the  gas  is  far  removed  from  perfection. 

Another  criterion  is  the  behaviour  of  the  gas  when  heated  ;  if 
1000  c.c.  at  o°  C.  (273°  absolute)  expand  to  2100  c.c.  instead  of  2000 
c.c.  when  heated  to  273°  0.  (546°  absolute),  the  molecules  of  the  gas 
must  have  been  considerably  under  the  influence  of  each  other  at  the 
lower  temperature,  for  the  volume  of  a  true  gas  must  vary  proportionally 
to  the  absolute  temperature.  If  on  heating  the  gas  in  question  beyond 
273°  C.  its  volume  increases  in  direct  proportion  to  the  absolute 
temperature,  it  may  be  concluded  that  at  these  higher  temperatures 
the  gas  is  nearly  a  true  gas. 

Now  hydrogen,  the  standard  for  vapour  densities,  expands  like  a 
true  gas,  so  that  if  the  vapour  density  *  of  a  gas  which  expands  more 
rapidly  than  a  true  gas  (hydrogen)  is  determined  at  different  tempera- 
tures it  is  found  not  to  be  constant,  but  to  grow  less  as  the  temperature 
rises.  For  example,  at  273°  C.,  1000  c.c.  of  hydrogen  contain  1/2  the 
matter  contained  in  1000  c.c.  at  o°  C.,  whereas  in  1000  c.c.  of  the  gas 
cited  above  (as  expanding  to  2100  c.c.  at  273°  C.)  there  is  at  273°  (X 
only  1/2. i  the  matter  that  is  contained  in  1000  c.c.  at  o°  C.  Hence  if 
the  vapour  density  were  x  at  o°  C.  it  would  be  only  x-x/2i  at 
273°  C. 

It  follows  that  in  order  to  apply  Avogadro's  law  to  determine  the 
vapour  density  of  a  substance  the  observations  should  be  made  at 
successively  higher  temperatures  until  the  value  remains  constant. 
In  most  cases  the  fall  in  vapour  density  with  rise  of  temperature  is 
very  slight,  bnt  in  some  it  is  very  considerable ;  compare  sulphur 
(p.  213). 

It  is  supposed  that  in  the  case  of  sulphur  and  certain  other  sub- 
stances, there  is  more  in  this  decrease  of  vapour  density  than  a  mere 
improvement  of  gaseous  character,  as  will  be  explained  a  little  later. 

It  will  presently  be  made  clear  that  by  the  chemist  the  determina- 
tion of  vapour  density  for  ascertaining  molecular  weights  is  used  solely 
as  an  indication  as  to  which  of  two  values  is  correct ;  for  this  method 
lacks  the  accuracy  attainable  by  that  which  is  particularly  the  chemist's 
own — gravimetric  analysis.  The  whole  system  of  molecular  and  atomic 
weights  has  been  built  up  by  use  of  the  balance  to  determine  chemical 
equivalents. 

*  Vapour  density  is  distinct  from  specific  gravity.  Of  course  the  latter  decreases  with 
rise  of  temperature  because  it  is  the  ratio  between  the  Weight  of  a  volume  of  the  gas  at  the 
particular  temperature  and  that  of  an  equal  volume  of  the  standard  gas  at  standard  tempe- 
rature and  pressure.  The  vapour  density  is  determined  by  weighing  both  gases  at  the  same 
temperature,  whatever  that  may  be,  and  should  be  a  constant. 


ATOMIC  WEIGHTS. 


295 


Chemical  Equivalents. — It  was  seen  above  that  Dalton  constructed 
a  table  of  atomic  weights,  the  figures  in  which  represented  the  number 
of  parts  by  weight  of  the  respective  elements  which  combine  with  one 
part  by  weight  of  hydrogen.  These  figures  are  what  are  now  called 
chemical  equivalents  and  are  determined  by  analysing  the  compounds 
of  the  elements  with  hydrogen  ;  thus,  it  having  been  found  that  100  parts 
of  the  compound  of  sulphur  with  hydrogen  contain  94.1  of  sulphur  and 
5.9  of  hydrogen,  the  chemical  equivalent  of  sulphur  is  94.1  ^5.9  =  16. 
But  the  majority  of  elements  do  not  combine  with  hydrogen,  or  do  not 
combine  with  it  to  form  compounds  which  may  easily  be  analysed  with 
accuracy.  However,  nearly  all  combine  with  oxygen,  and  as  the 
chemical  equivalent  of  the  latter  is  well  established  as  8,  the  chemical 
equivalent  of  other  elements  may  be  ascertained  by  analysing  their 
oxygen  compounds  to  find  what  weight  of  the  element  combines  with 
8  parts  by  weight  of  oxygen. 

In  cases  where  the  element  forms  more  than  one  compound  with 
hydrogen  or  oxygen,  as  for  instance  carbon  (p.  137),  there  may  be  said 
to  be  more  than  one  equivalent.  The  lowest  number,  however,  is 
selected  ;  thus  3  is  the  equivalent  of  carbon,  although  6  and  12  parts 
of  it  also  combine  with  i  part  of  hydrogen. 

Had  the  chemist  to  concern  himself  with  weights  alone,  a  list  of 
chemical  equivalents  would  suffice ;  indeed,  until  recently  no  account 
was  taken  of  any  other  numbers  by  the  purely  analytical  chemist ;  for 
him  the  symbol  of  an  element  represented  its  chemical  equivalent. 
The  progress  of  chemical  investigation,  however,  would  have  been  far 
less  rapid  had  not  the  chemist  sought  an  insight  into  the  actual 
mechanism  of  chemical  change  by  aid  of  an  atomic  hypothesis,  which, 
as  explained  for  oxygen  on  p.  289,  necessitates  the  abandonment  of  the 
chemical  equivalent  as  the  unit  weight  of  an  element  that  enters  into 
chemical  change,  that  is,  the  atomic  weight. 

Atomic  Weights. — Except  in  certain  cases  which  have  been  satis- 
factorily explained  (as  will  be  shown  later  in  this  work),  there  has 
never  been  evidence  that  in  any  compound  of  hydrogen  the  ratio 
between  the  number  of  atoms  of  H  and  the  other  element.  X,  is  less 
than  1:1.  That  is  to  say,  compounds  of  the  formula  HX2,  HX3,  &c., 
are  not  known,  except  as  aforesaid  ;  they  are  limited  to  the  form  HX. 
On  the  other  hand,  compounds  of  the  types  H2X,  H3X,  H4X  are 
quite  common. 

From  this  it  is  evident  that  (i)  the  atomic  weight  cannot  be  less  than 
the  equivalent;  (2)  the  atomic  weight  of  an  element  forming  the  com- 
pound HX  must  be  identical  with  the  equivalent ;  and  (3)  the  atomic 
weights  of  elements  forming  H2X,  H3X,  and  H4X  respectively,  must 
be  twice,  thrice,  and  four  times  the  equivalents  respectively. 

There  are  three  methods  for  determining  whether  i,  2,  3,  or  4  is  the 
factor  for  ascertaining  the  atomic  weight  from  the  equivalent. 

(i)  This  method  is  best  explained  by  an  example.  The  vapour 
density  of  a  compound  of  nitrogen  is  ascertained,  as  described  at  p.  292, 
to  be  15,  so  that  the  molecular  weight  of  the  compound  is  30.  Gravi- 
metric analysis  shows  that  the  compound  contains  45.16  per  cent,  of 
nitrogen.  Hence  30  parts  by  weight  of  it  contain  13.55  parts  of  this 
element,  that  is  to  say,  one  molecule  of  the  compound  contains 
n  atoms  of  nitrogen  weighing  13.55.  If  n  is  one,  then  13.55  *s 


296  ATOMIC   HEATS. 

approximately  the  atomic  weight  of  nitrogen ;  if  n  is  2  the  atomic 
weight  is  6.77,  and  so  on.  It  is  impossible  to  decide  the  value  of  n 
from  this  experiment ;  all  that  can  be  said  is  that  by  hypothesis  it 
cannot  be  less  than  i,  so  that  the  atomic  weight  of  nitrogen,  according 
to  this  experiment,  is  not  greater  than  13.55  or  a  number  very  near 
this.  Supposing,  however,  that  many  other  compounds  of  nitrogen 
have  been  submitted  to  similar  experiments,  and  it  has  been  found  that 
in  none  of  them  does  the  molecular  weight  contain  less  than  13.55 
parts  of  nitrogen,  the  presumption  is  large  that  this  is  indeed  the 
approximate  atomic  weight. 

By  analysing  ammonia,  the  compound  of  nitrogen  with  hydrogen,  it 
is  found  to  contain  for  every  part  of  hydrogen  4.66  parts  of  nitrogen  ; 
4.66  is  therefore  the  chemical  equivalent  of  this  element.  Now  13.55 
is  nearly  3  times  4.66,  so  3  is  the  factor  required  and  4.66  x  3  =  14  is 
the  atomic  weight  of  nitrogen. 

This  method  consists,  then,  in  determining  the  molecular  weights  of 
compounds  of  the  element,  and  ascertaining  how  many  parts  by  weight 
of  the  element  the  molecular  weight  contains  in  each  case.  The  lowest 
value  obtained  is  the  maximum  possible  value  for  the  atomic  weight 
and  comparison  with  the  chemical  equivalent  gives  the  required  factor. 

(2)  It  was  observed  by  Dulong  and  Petit  (1819),  from  the  study  of 
elements  of  known  atomic  weight  that  the  quantity  of  heat  necessary  to 
raise  the  temperature  of  one  atomic  weight  of  any  solid  element  is  approxi- 
mately the  same,  or,  more  generally,  "  the  atoms  of  all  the  simple  bodies 
have  exactly  the  same  capacity  for  heat." 

It  will  be  remembered  that  the  specific  heat  of  a  substance  is  the 
quantity  of  heat  required  to  raise  its  temperature  through  i  °  as  com- 
pared with  the  quantity  of  heat  required  to  raise  the  temperature  of  an 
equal  weight  of  water  through  i  °  ;  or,  more  concisely,  the  quantity  of 
heat  required  to  raise  one  part  by  weight  of  the  substance  i  °  (referred 
to  water  as  the  unit).  Thus,  the  specific  heats  of  potassium,  sodium, 
and  lithium  are,  respectively,  0.1696,  0.2934,  and  0.9408,  these  numbers 
representing  the  relative  quantities  of  heat  required  to  raise  one  part 
by  weight  of  each  of  these  elements  through  i  °  in  temperature,  suppos- 
ing that  an  equal  weight  of  water  would  be  raised  through  i  °  by  a 
quantity  of  heat  expressed  by  one.  No  simple  relation  can  be  traced 
between  these  numbers,  but  if  the  quantities  of  heat  be  calculated  which 
are  required  to  raise  atomic  weights  of  these  elements  through  i  ° ,  the 
case  will  be  different. 

If  0.1696  be  the  quantity  of  heat  required  to  raise  the  temperature 
of  onepartby  weight  of  potassium  through  ic,  0.1696  x  39,  or  6.61,  will 
represent  the  quantity  of  heat  required  to  raise  the  temperature  of  39 
parts  b}'  weight  (one  atomic  weight)  of  potassium  through  i°.  In  the 
same  way  0.2934  x  23,  or  6.75,  is  the  quantity  of  heat  required  to  raise 
the  temperature  of  one  atomic  weight  of  sodium  through  i°  ;  and 
0.9408  x  7,  or  6.59,  is  the  quantity  required  to  raise  one  atomic  weight 
of  lithium  through  i °.  Allowing  for  experimental  error  in  the  deter- 
mination of  the  specific  heats,  these  numbers,  6.61,  6.75,  and  6.59,  may 
be  regarded  as  representing  the  same  quantity  of  heat,  and  they  are  the 
atomic  heats  of  these  metals. 

The  atomic  heat  of  an  element  is  the  quantity  of  heat  required 
to  raise  the  temperature  of  the  number  of  unit  weights  of  the  solid 


VALENCY.  297 

•element  expressed  by  the  atomic  weight  through  i  °  ;  it  is  ascertained 
by  multiplying  the  specific  heat  by  the  atomic  weight  and  is  approxi- 
mately a  constant,  6.4. 

It  is  obvious  that  since  specific  heat  x  atomic  weight  =  6.4,  the  atomic 

weight  =  —     .  '    , — - ,  and  that  from  the  equation  an  approximate  value 

for  the  atomic  weight  of  an  element  can  be  ascertained  if  the  specific 
heat  of  the  solid  element  is  known. 

When  efforts  to  determine  the  specific  heat  of  an  element  have  failed,  it  is 
sometimes  possible  to  arrive  at  a  value  for  the  atomic  heat  by  a  consideration  of 
the  molecular^  heat  of  compounds  containing  the  element.  The  molecular  heat  of 
£k  compound*  is  the  quantity  of  heat  required  to  raise  the  temperature  of  the 
number  of  unit  weights  of  the  compound  expressed  by  the  molecular  weight, 
through  i°.  It  is  supposed  that  the  molecular  heat  of  a  compound  is  the  sum  of 
the  atomic  heats  of  each  of  the  atoms  which  the  molecule  contains — a  generali- 
sation which  is  not  fully  substantiated. 

Thus,  the  specific  heat  of  solid  chlorine  is  not  known,  but  if  the  specific  heats 
of  the  chlorides  of  potassium,  sodium,  and  rubidium  are  multiplied  by  the  mole- 
cular weights  of  these  chlorides,  the  product  in  each  case  approaches  very  nearly 
to  the  number  12.69.  Supposing  these  chlorides  to  contain  one  atom  of  each  of 
their  constituents,  then,  by  subtracting  the  mean  atomic  heat  (6.65)  of  the  three 
metals  from  the  mean  molecular  heat  (12.69)  °f  the  three  chlorides,  a  value  (6.04) 
for  the  atomic  heat  of  solid  chlorine  will,  according  to  the  above  generalisation,  be 
obtained. 

The  specific  heat  of  barium  has  not  been  determined  so  that  its  atomic  weight 
has  not  been  ascertained  directly  by  this  method  ;  but  the  specific  heat  of  barium 
chloride  is  0.09.  Barium  chloride  contains  68.5  parts  of  barium  for  every  35.5 
parts  of  chlorine  ;  if  68.5  be  the  atomic  weight  of  barium,  the  formula  for  the 
chloride  will  be  BaCl,  and  its  molecular  heat  0.09x104  =  9.36;  this  only  allows 
an  atomic  heat  of  3.36  for  barium,  because  that  of  chlorine  is  6.0.  If  the  atomic 
weight  of  barium  be  137  the  formula  for  the  chloride  will  be  BaCl2,  and  the  mole- 
cular heat  will  be  208x0.09=18.72  ;  this  will  allow  an  atomic  heat  of  6.72  for 
barium,  for  two  atomic  heats  of  chlorine  must  be  subtracted  from  18.72.  As  6.72 
is  more  nearly  normal  for  the  atomic  heat  than  is  3.16,  the  atomic  weight  of 
barium  may  be  taken  as  137. 

The  specific  heat  of  all  substances  varies  with  the  temperature  ;  this  is  parti- 
cularly noticeable  in  the  case  of  carbon,  boron,  silicon,  and  a  few  other  elements. 
At  low  temperatures  the  specific  heats,  and  therefore  the  atomic  heats,  of  C,  B, 
and  Si  are  very  low,  but  at  higher  temperatures  they  increase  until  the  atomic 
heats  are  about  5.5.  Thus,  the  specific  heat  of  diamond  at  10°  C.  is  0.112,  corre- 
sponding with  the  atomic  heat  1.34,  whilst  at  985°  C.  the  specific  heat  is  0.458, 
corresponding  with  atomic  heat  5.5. 

All  elements  whose  atomic  weight  is  above  30,  obey  Dulong  and  Petit's  law. 

(3)  On  page  1 1  the  term  valency  was  used  to  express  the  number  of 
atoms  of  hydrogen  one  atom  of  an  element  can  combine  with.  It  is 
evident  that  the  number  expressing  this  valency  is  none  other  than  the 
factor  now  under  discussion.  The  third  method  consists  in  studying 
the  general  chemical  analogies  of  the  element  with  some  other  element 
of  known  valency  for  the  purpose  of  deciding  the  unknown  valency. 

In  this  respect  the  isomorphism  of  the  compounds  of  the  element  with 
those  of  other  elements  of  known  atomic  weight,  and  therefore  of 
known  valency,  is  most  important.  The  principle  of  isomorphism, 
originally  stated  by  Mitscherlich  (1821),  is  that  certain  elements  may  be 
substituted  for  each  other  in  their  crystalline  compounds  ivithout  alteration 
of  the  form  of  the  crystals.  Such  elements  are  said  to  be  isomorphous 
with  each  other,  and  the  crystalline  compounds,  in  which  the  substitution 
occurs,  are  said  to  be  isomorphous  compounds.  Thus,  aluminium, 
chromium,  and  iron  are  isomorphous  elements  because  they  all  form 


298  EXAMPLE   OF  ATOMIC  WEIGHT  DETERMINATION. 

alums  of  the  type  KR'"(SO4)2.i2H20  (where  R'"  is  Fe,  Al,  or  Or),  which 
crystallise  in  octahedra,  and  are  capable  of  forming  mixed  crystals,  the 
most  important  criterion  of  isomorphism.  For  example,  when  a 
mixture  of  solutions  of  aluminium  alum  and  chromium  alum  is  allowed 
to  crystallise,  the  crystals  contain  both  aluminium  and  chromium  in 
proportion  varying  with  the  conditions  of  crystallisation.  Supposing 
that  the  valency  of  chromium  were  unknown  it  could  be  deduced  from 
this  isomorphism  with  aluminium.  For  the  valency  of  aluminium  is 
three,  hence  it  is  probable  that  the  valency  of  chromium  is  also  three, 
in  which  case  the  atomic  weight  of  the  metal  is  thrice  its  equivalent. 

As  an  example  of  the  application  of  these  three  methods,  the  following  experi- 
ments may  be  supposed  to  have  been  performed  with  a  view  of  ascertaining  the 
atomic  weight  of  cadmium  : 

(1)  0.7232  gram  of  cadmium  bromide  *  was  dissolved  in  water,  and  the  bromine 
was  exactly  precipitated  by  adding  a  solution  of  silver  nitrate  (with  the  precautions 
necessary  to  an  accurate  result).     This  solution  was  made  by  dissolving  10  grams 
of  pure  silver  in  I  litre  of  dilute  nitric  acid,  and  57.43  c.c.  were  required  for  the  pre- 
cipitation.    Hence  0.5743  gram  of  silver  will  combine  with  the  bromine  in  0.7232 
gram  of  cadmium  bromide  ;  but  from  the  careful  synthesis  of  silver  bromide,  it  i& 
known  that  this  weight  of  silver  will  combine  with  0.4254  gram  of  Br  ;  therefore 
the  0.7232  gram  of  cadmium  bromide  contains  0.2978  gram  of  Cd  combined  with 

0.4254  gram  of  Br.     Since  the  equivalent  of  bromine  is  80.  — =56  will 

be  the  equivalent  of  cadmium — that  is,  the  number  of  parts  by  weight  of 
Cd  which  will  combine  with  one  equivalent  of  Br.  The  atomic  weight  of  cadmium 
must,  therefore,  be  56  x  %,  where  n  is  a  small  integer. 

(2)  The  vapour  density  of  cadmium  bromide  was  found  to  be  136,  therefore  its 
molecular  weight  is   272  ;  but,  according  to  the   above   analysis,  this  number  of 
grams  will  contain  112  grams  of  Cd  and  160  grams  of  Br,  for  these  elements  are 
present  in  the  ratio  56  :  80.     It  follows  that  the  atomic  weight  of  cadmium  cannot 
be  greater  than  112,  or  n  cannot  be  greater  than  2. 

(3)  A  piece  of  cadmium  weighing  100  grams  was  heated  in  boiling  water  until 
it  had  attained  the  temperature  of  the  water  (100°  C.)  ;  it  was  then  transferred  to 
a  calorimeter  containing  ]  oo  grams  of  water  at  o°  C.     The  temperature  of  this 
water  (allowing  for  the  heat  left  in  the  calorimeter)  rose  to  5.3°  C.     Therefore  the 
loo  grams  of  cadmium,  in  cooling   from    100°   to   5.3°,  have   lost    100x5.3  =  530 
gram-units  of  heat,f  so  that  in  cooling  through  i°  C.  the  100  grams  would  lose 

53° 

Q -— -  =5.6  units,  or  i  gram  would  lose  0.056  unit — that  is,  the  specific  heat  of 

cadmium  is  0.056.  But  the  specific  heat  x  atomic  weight  will  probably  —  6.4, 
so  that  the  atomic  weight  of  cadmium  should  be — —^—ii^  (nearly).  This  is 

approximately  56  x  2,  therefore  n  is  probably  2. 

(4)  Many  cadmium  salts  are  found  to  crystallise  together  with  zinc  salts,  being 
isomorphous  with  them  ;  but  zinc  is  divalent,  therefore  cadmium  is  probably  also 
divalent,  in  which  case  its  atomic  weight  must  be  twice  its  equivalent,  or  112. 

With  regard  to  the  standard  for'  the  atomic  weights,  it  may  be  said  that  many 
chemists  prefer  to  fix  arbitrarily  16  as  the  atomic  weight  of  oxygen,  rather  than 
to  adhere  to  Dalton  s  standard— viz.,  H=i.  The  reason  for  this  is  that  the 
equivalents  of  the  elements  are  far  more  frequently  determined  from  oxygen- 
compounds  than  from  hydrogen-compounds,  because  the  former  are  both  more 
numerous  and  better  capable  of  exact  analysis. 

Atomicity  of  Molecules. — The  following  paragraphs  deal  with 
methods  of  ascertaining  the  number  of  atoms  in  a  molecule,  that  is,  the 
atomicity  of  the  molecule. 

*  It  will  be  evident  that  the  analysis  of  any  compound  of  the  element  with  another 
element  of  well-established  equivalent  will  serve  to  fix  the  equivalent  of  the  first  element. 

f  No  allowance  is  here  made  for  the  slight  alteration  in  the  specific  heat  of  water  with 
rise  of  temperature. 


ATOMICITY  OF  MOLECULES.  299 

Considering  first  the  atomicity  of  elementary  molecules,  the  molecular 
weight  having  been  determined  from  the  vapour  density  and  the  atomic 
weight  from  the  chemical  equivalent,  the  atomicity  is  ascertained  by 
simply  dividing  the  atomic  weight  into  the  molecular  weight.  For 
instance,  the  vapour  density  of  nitrogen  being  14,  and  its  atomic 
weight  also  14,  its  atomicity  is  two — there  are  two  atoms  in  the  mole- 
cule ;  it  is  diatomic  ;  its  molecular  symbol  is  ~N2. 

In  the  case  of  certain  elements,  the  type  of  which  is  the  newly  discovered  argon, 
there  is  difficulty  in  ascertaining  the  atomic  weight  because  the  element  shows  so 
little  tendency  to  combine  that  the  equivalent  cannot  be  determined.  A  method 
exists  whereby  it  is  possible  to  decide  whether  an  element  of  this  kind  is  mon- 
atomic,  diatomic,  or  polyatomic  ;  it  depends  on  the  following  considerations  :  The 
amount  of  heat  required  to  raise  the  temperature  of  an  ideal  gas  through  i°  C. 
should  be  that  expended  in  increasing  the  kinetic  energy  of  its  molecules,  provided 
the  gas  is  not  allowed  to  expand,  that  is,  if  its  volume  is  kept  constant.  If  the  gas 
is  allowed  to  expand  the  molecules  do  work  in  overcoming  the  external  pressure,  and 
the  heat  required  to  raise  the  temperature  i°  C.  will  be  more  than  that  necessary  to 
increase  the  kinetic  energy  by  an  amount  equivalent  to  the  work  done.  In  the 
former  case  the  pressure  of  the  gas  increases  when  it  is  heated,  while  in  the  latter 
case  it  remains  constant.  It  follows  that  the  specific  heat  of  a  gas  at  constant 
pressure,  Cp,  is  greater  than  that  of  the  gas  at  constant  volume,  Cr.  While  Cp  is 
easily  determined,  Cv  is  very  difficult  to  determine  ;  but  the  ratio  Cp  :  Cv  may  be 
calculated,  from  the  kinetic  theory  of  gases,  to  be  1.66.  A  discussion  of  the 
calculations  cannot  be  entered  upon  here,  but  it  will  be  obvious  from  what  was 
said  at  p.  291  that  if  the  molecular  weight  of  the  gas  be  considered,  the  increase  in 
kinetic  energy  will  be  proportional  to  mw  2/2,  while  the  work  done  in  overcoming 
the  external  pressure  is  proportional  to  mw  2/3.  Hence,  while  C'i<  is  measured  by 
the  former  value,  Cp  is  measured  by  (mw  2/2  +  w*  iv  2/3)  and  the  ratio  of  the  latter 
to  the  former  5/6  :  1/2  or  1.66  :  I. 

Now  experimental  methods  have  been  devised  for  determining  the  ratio  Cp  :  Cv, 
chief  of  which  is  that  depending  on  the  velocity  (u)  of  sound  in  the  gas  for  which 
the  ratio  is  to  be  ascertained.  The  velocity  is  given  by  the  equation  u  =  */kpjd,  where 
p  is  the  pressure,  d  the  density,  and  k  the  ratio  Cp  :  Cv.  The  velocity  of  sound  in 
air  is  a  well-known  experimental  constant,  and  therefrom  k  is  found  to  be  1.4  for 
air.  By  filling  a  glass  tube,  clamped  at  one  end,  with  a  gas  and  rubbing  the  tube 
so  as  to  produce  a  musical  note,  the  wave  length  of  the  note  can  be  ascertained  if 
the  tube  contain  a  dust  capable  of  marking  the  nodes  by  the  disturbance  it  suffers. 
By  comparison  of  this  wave  length  with  that  known  for  the  note  in  air,  the  value 
of  u,  and  therefore  of  &,  for  the  gas  may  be  calculated. 

In  gases  that  are  known  to  have  diatomic  molecules,  £=1.4 — that  is,  the  specific 
heat  at  constant  volume  is  more  than  it  would  be  in  the  ideal  gas.  The  assumption 
is  that  in  a  diatomic  gas,  the  atoms  in  the  molecule  have  a  movement  relative  to 
each  other,  an  intra-niolecular  motion,  which  is  increased  by  heat.  Thus  heat  would 
be  absorbed  which  would  not  increase  the  kinetic  energy  of  the  moving  molecules. 

The  method  in  question,  therefore,  consists  in  ascertaining  the  value  Cp  :  Cv  for 
the  gas  the  atomicity  of  whose  molecules  is  to  be  ascertained.  If  this  ratio  is  1.66 
the  molecules  are  monatomic  ;  if  it  is  1.4  the  molecules  are  diatomic.  For  poly- 
atomic gases  the  ratio  is  still  lower.  Mercury  vapour  and  the  gases  of  the  argon 
group  are  found  by  this  method  to  be  monatomic. 

As  already  indicated  (p.  294),  the  vapour  density  of  some  elements 
decreases  as  the  temperature  rises.  It  follows  that  the  atomicity  of 
the  molecules  decreases ;  thus,  sulphur  vapour  at  480°  0.  ha,s  a  density  of 
95.1,  which,  divided  by  32,  the  atomic  weight 'of  sulphur,  gives  S6  as  the 
molecular  symbol ;  but  at  1000°  C.  the  density  falls  to  32.1,  giving  S2 
for  the  molecular  symbol.  It  is  supposed  that  in  such  cases  the  mole- 
cule suffers  a  dissociation  as  the  temperature  rises  quite  analogous  to 
that  which  undoubtedly  occurs  in  the  case  of  many  compound  molecules, 
and  noticed  at  page  86. 

The  elements  may  be  classified  in  this  respect  as  follows  :     (i)  Those  whose 


300  DETERMINATION   OF   FORMULAE. 

vapour  densities  are  identical  with  their  atomic  weights  at  all  temperatures  ;  * 
H,  O  and  N  are  the  chief  of  these.  Since  M  =  2D,  the  molecular  weights  of  these 
atoms  must  be  twice  their  atomic  weights,  and  the  molecule  must  therefore 
contain  two  atoms,  it  is  diatomic  at  all  temperatures.  (2)  Those  whose  vapour 
densities  are  identical  with  their  atomic  weights  at  low  temperatures  but  become 
one-half  at  high  temperatures.  These  are  Cl,  Br,  I ;  their  molecules  are  diatomic 
at  low  temperatures  but  monatomic  at  high  temperatures.  (3)  Those  whose  vapour 
densities  are  one-half  of  their  atomic  weights  at  all  temperatures,  so  that  their 
molecular  weights  are  identical  with  their  atomic  weights  at  all  temperatures. 
These  are  Na,  K,  Zn,  Cd,  Hg,  A,  He.  Their  molecules  are  monatomic  at  all  tem- 
peratures. (4)  Those  whose  A'apour  densities  are  twice  their  atomic  weights  at 
low  temperatures  but  identical  with  them  at  high  temperatures.  Such  are  P. 
As,  Sb.  Since  M  =  2D,  the  molecular  weights  of  each  of  these  gaseous  elements  must 
be  four  times  their  atomic  weight  at  low  temperatures,  but  only  twice  at  high  tem- 
peratures. They  are  tetratomic  at  low,  but  diatomic  at  high,  temperatures. 
(5)  Those  whoseVapour  densities  are  a  greater  multiple  than  twice  their  atomic 
weights  at  low  temperatures,  becoming  equal  to  their  atomic  weights  at  high 
temperatures.  Sulphur  is  the  only  example. 

Turning  now  to  the  determination  of  the  atomicity  of  a  compound 
molecule,  that  is,  the  selection  of  the  formula  for  the  compound,  this 
resolves  itself  into  three  steps  : 

(1)  Quantitative  analysis  of  the  compound  to  determine  the  per- 
centage composition  of  it.     Here  a  distinction  must  be  drawn  between 
a  proximate  analysis  and  an  ultimate  analysis.     For  instance,  a  sample 
of  beer  may  be  analysed  to  determine  the  percentage  of  alcohol,  water, 
hop-extract,  <fcc.,  in  it ;  this  is  a  proximate  analysis.     If  the  operations 
were  directed  to  the  determination  of  the  carbon,  hydrogen,  oxygen, 
<fcc.,  in  the  beer — that  is  to  say,  its   ultimate  constituents — an  ultimate 
analysis  would  have  been   performed.     Taking  alcohol  as  an  example, 
the  result  of  an  ultimate  analysis  would  be,   carbon  52.16  per  cent., 
hydrogen  13.04  per  cent.,  oxygen  34.80  per  cent.     As  these  numbers 
add  up  to  100  no  other  element  can  be  present. 

(2)  Division  of  the  percentage  of  each  element  by  the  atomic  weight 
of  the  element  to  ascertain  the  relative  number  of  atoms  of  each  in  the 
compound. 

In  the  case  of  alcohol  the  following  figures  would  be  obtained  : 

52.16  divided  by  12  gives    4.34  atomic  weights  of  carbon. 
13.04       ..       „       i     ..       13.04         „  „  hydrogen. 

34.80       „        ,.     16     ,.         2.17         „  ,,  oxygen. 

In  its  lowest  terms  the  ratio  4.34  :  13.04  :  2.17  is  2:6:1;  that  is,  the 
atoms  of  C,  H  and  O  are  present  in  the  molecule  of  alcohol  in  this 
ratio.  An  experimental  or  empirical  formula  for  alcohol  is  thus  ob- 
tained, and  it  is  evidently  C,H6O.  This,  however,  may  not  be  the 
formula  for  the  molecule  or  the  molecular  formula.  It  is  certainly  the 
minimum  formula,  for  by  hypothesis  it  is  impossible  for  the  molecule  to 
contain  half  an  atom,  as  would  be  the  case  if  the  formula  be  written 
CH3Oj.  But  the  true  formula  may  be  a  multiple  of  C2H60,  such  as 
C4H1202  or  C6H1803— all  that  is  known  so  far  is  that  the  ratio  of  C:H:O 
must  be  2:6:1. 

(3)  The  vapour  density  of  the  compound  is   determined.     It  will  be 
obvious  that  this  settles  the  molecular  formula,  or  the  atomicity  of  the 
molecule.     For  M  =  2D,  so  that  if  the  molecule  is  C2H60  the  vapour 

density  must  be  I2  x  2  +  *  x  6  +  l6  x  I  =  23  ;  if  it  is  C4H1202  the  vapour 

*  The  temperatures  referred  to  in  this  classification  range  from  100°  C.  to  1700°  C. 


DISSOCIATION.  301 

density  must  be 2  =  46.     Now  the  determination 

2 

of  the  vapour  density  of  alcohol,  as  described  at  p.  293,  gives  a  number 
near  23  ;  therefore  the  molecular  weight  is  46  and  the  molecular 
formula  is  C2H6O,  9  atoms  in  the  molecule. 

Dissociation. — The  only  difficulty  in  following  the  foregoing  steps 
for  determining  the  molecular  formula  for  a  compound,  provided  that 
this  is  volatile,  is  in  the  doubt  which  sometimes  exists  whether  the 
vapour  or  gas  into  which  the  compound  is  converted  by  heat  is  indeed 
the  same  compound.  The  gas  produced  by  the  vaporisation  may  con- 
sist of  products  of  decomposition  or  of  dissociation  of  the  compound. 
The  difference  between  these  two  phenonena  has  already  been  explained 
(p.  86).  An  example  will  make  clear  how  dissociation  affects  the 
determination  of  molecular  formulae.  The  ultimate  analysis  of  am- 
monium chloride  shows  that  its  empirical  formula  is  NH4C1,  and  this 
must  be  the  minimum  molecular  formula,  because  the  molecule  cannot 
contain  less  than  one  atom  of  N  or  one  atom  of  Cl.  A  determination 
of  the  vapour  density  of  ammonium  chloride,  however,  gives  the  number 
13.35,  corresponding  with  molecular  weight  26.7.  Now,  the  formula 
NH4C1  corresponds  with  molecular  weight  14+1x4  +  35.5  =  53.5  or 
double  that  found  from  the  vapour  density,  which  indeed  corresponds 
with  the  impossible  formula  NjHgClj. 

The  experiment  cited  at  p.  86  shows  that  the  vapour  of  ammonium 
chloride  consists  not  of  this  compound  but  of  a  mixture  of  ammonia, 
NH3,  and  hydrogen  chloride,  HC1.  That  is,  instead  of  being  composed 
of  NH4C1  molecules,  the  vapour  consists  of  a  mixture  of  NH3  +  HC1 
molecules.  Unless  the  vapour  itself  had  been  tested  this  change  would 
not  have  been  detected,  for  it  is  a  dissociation,  not  a  decomposition,  so 
that  when  the  vapour  is  cooled  the  ammonium  chloride  is  re-formed, 
just  as  water  is  obtained  again  when  the  steam  from  it  is  condensed. 

To  make  clear  how  this  dissociation  affects  the  vapour  density,  it 
must  be  explained  that  ammonium  chloride  is  found  to  be  produced 
when  equal  volumes  of  NH3  and  HC1  are  mixed.  Hence  the  dissociated 
vapour  of  ammonium  chloride  must  consist  of  equal  volumes  of  these 
gases.  Now  a  mixture  of  gases  in  equal  volumes  always  has  a  vapour 
density  which  is  the  mean  of  the  vapour  densities  of  the  constituent 
gases.  In  this  case  the  vapour  density  of  NH3  being  8.5,  and  that  of 
HC1  1 8. 2,  that  of  the  mixture  would  be  half  the  sum  of  these  values, 
or  13.35. 

Classification  of  the  Elements— The  Periodic  Law.— It  has 
been  already  shown  that  the  elements  may  be  classified  into  groups  which 
contain  individuals  possessed  of  similar  chemical  properties.  Newlands, 
in  1864,  pointed  out  that  when  the  elements  are  arranged  in  the  order 
of  their  atomic  weights,  this  similarity  is  seen  to  exist  between  every 
eighth  element,  the  first  being  similar  to  the  eighth,  the  second  to  the 
ninth,  and  so  on  (law  of  octaves).  In  1869  Mendeleeff  and  Lothar 
Meyer  made  a  similar  discovery. 

In  seeking  for  a  basis  for  a  classification  of  the  elements,  it  is 
natural  that  the  chemist  should  turn  to  the  most  strictly  chemical 
property  of  the  elements,  namely,  their  tendency  to  combine  with 
each  other.  Mendeleeff  has  pointed  out  that  the  limit  to  this  tendency 
is  expressed  by  saying  that  one  equivalent  of  an  element  never  com- 


302 


THE  PERIODIC   LAW. 


bines  with  more  than  eight  equivalents  of  another  element.  If  oxygen 
and  hydrogen  betaken  as  typical  elements,  it  will  be  noticed  that  there 
are  never  more  than  four  atoms  of  oxygen  or  four  atoms  of  hydrogen 
united  to  one  atom  of  an  element.  Furthermore,  the  sum  of  the 
equivalents  of  O  and  H,  which  can  combine  with  one  atom  of  an 
element  is  eight.  Thus,  if  an  element  R  forms  as  its  highest  salt- 
forming  oxide*  a  compound  of  the  type  RO2,  it  will  form  a  hydride 
RH4 ;  if  an  oxide,  R03,  a  hydride,  RH2,  and  so  on.  For  example,  N 
forms  N205  as  its  maximum  oxide — that  is,  a  compound  of  five  equiva- 
lents of  oxygen  with  one  atom  of  nitrogen — and  its  maximum  hydride 
is  NH3  ;  S  forms  S03  (6  equivalents  of  oxygen),  and  SH2.  01  forms 
C1H,  so  that  its  highest  salt-forming  oxide  should  be  C12O7  (7  equivalents 
of  O  to  i  atom  of  01),  which,  however,  is  only  known  in  such  com- 
pounds as  K2O.C1207=  2KC104. 

It  follows  that  there  are  eight  types  of  higher  salt-forming  oxides, 
viz.  :  R2O,  R2O2,  R203,  R2O4,  R205,  R206,  R2O7,  and  R308. 

Those  elements  which  form  higher  salt-forming  oxides  of  the  same 
type  are  alone  analogous.  If  this  proposition  be  admitted,  the  ele- 
ments must  be  classified  in  eight  groups.  Such  a  classification  reveals 
the  fact  that  when  the  elements  are  arranged  in  the  order  of  their 
atomic  weights,  they  follow  the  same  order  as  that  of  their  higher 
oxides,  so  that  the  valency  of  the  elements  towards  oxygen  returns  to 
the  same  value  at  every  eighth  element,  that  is,  periodically.  This 
return  is  noticeable  in  the  case  of  all  other  properties  of  the  elements 
which  have  been  accurately  examined,  that  is  to  say,  the  properties  of  the 
elements  are  periodic  functions  of  their  atomic  weights.  In  general  terms, 
if  the  elements  be  arranged  in  the  order  of  their  atomic  weights,  the  proper- 
ties of  consecutive  elements  will  be  found  to  differ,  but  the  properties 
will  return  to  approximately  the  same  value  at  definite  periods. 

Such  an  arrangement  of  the  elements  is  shown  in  the  appended  table  : 


Group  . 

i. 

ii. 

iii. 

iv. 

v. 

vi. 

vii. 

viii. 

Series    i 

H      • 

He 

2 

Li     • 

Be    • 

B      • 

c    • 

N      • 

o    • 

F      • 

Ne 

3 

Na    • 

Mg  • 

Al     • 

Si     • 

P      • 

S       • 

ci    • 

Ar 

4 

K      • 

Ca    • 

Sc     • 

Ti     ' 

v    • 

Or     ' 

Mn  • 

Fe  :  Co.Ni.Cu 

5 

•(Cu) 

•    Zn 

•    Ga 

•    Ge 

•    As 

•     Se 

•     Br 

Kr 

6 

Rb    • 

Sr     • 

Y      • 

Zr     • 

Nb   • 

Mo   • 

— 

Ru  :  Rh.Pd.Ag 

7 

'(Ag) 

•    Cd 

•     In 

•     Sn 

•     Sb 

•     Te 

I 

Xe 

8 

Cs     • 

Ba    • 

La    • 

Ce    • 

Pr     • 

Nd   • 

Sa    • 



9 

•    Gd 

— 

•    Tb 

— 

•     Er 



•    Tu 

10 

—    . 

— 

Yb    • 

—    . 

Ta    • 

w   • 

— 

Os  :  lr.Pt.Au 

ii 

•(Au) 

'   Hg 

•     Tl 

•    Pb 

•     Bi 

.     — 

.     — 

,       12 

Th    • 

— 

u    • 

— 

Higher  oxide 
type  . 

R20 

R202 
(BO) 

R203 

R204 

BA 

R206 
(R03) 

BA 

R2O8 
(R04) 

Hydrides 

RH4 

RH3 

RH2 

RH 

Capable  of  behaving-  as  an  anhydride  or  as  a  base. 


FAMILIES   OF   ELEMENTS.  303 

In  drawing  up  this  table  two  main  difficulties  occurred.  In  the  first 
place,  Co,  being  next  to  Fe  in  atomic  weight,  should  have  been  written 
in  group  i.  ;  but  neither  this  metal  nor  Ni  shows  any  analogy  with  the 
elements  in  group  i.  Cu,  on  the  other  hand,  shows  some  analogy 
with  the  elements  of  both  group  viii.  and  group  i.,  consequently  its  true 
position  is  somewhat  doubtful.  Thus  Co  and  Ni  have  to  remain  in 
group  viii.,  an  arrangement  also  necessary  in  the  case  of  Rh,  Pd,  Ir, 
and  Pt. 

Within  the  last  few  years  much  difficulty  has  arisen  owing  to  the 
discovery  of  the  helium  and  argon  group  of  elements,  as  these  do  not 
appear  to  form  any  chemical  compounds  and  therefore  have  no  valency. 
In  the  foregoing  table  they  are  placed  in  group  viii.  pending  a  more 
satisfactory  elucidation  of  their  probable  position. 

In  the  second  place,  the  element  Ru,  which  is  next  in  atomic  weight 
to  Mo,  should  come  in  group  vii.,  but  its  position  there  is  untenable, 
because  its  higher  oxide  is  of  the  type  RO4  and  not  R207.  Consequently, 
Ru  must  be  placed  in  group  viii.,  whilst  the  position  in  group  vii.  re- 
mains vacant.  Thus  it  is  not  always  possible  to  locate  each  element  in 
the  table  immediately  succeeding  the  next  lower  in  atomic  weight,  so 
that  a  certain  number  of  blanks  must  be  left.  Where  such  blanks 
occur  elements  are  believed  to  exist,  but  to  be  as  yet  unknown. 
Credence  is  afforded  to  this  view  by  the  fact  that  the  number  of  such 
blanks  was  larger  when  the  table  was  first  drawn  up,  some  of  these 
spaces  having  been  since  filled  by  the  discovery  of  elements  (such  as 
Oa,  Ge,  and  Sc),  the  atomic  weights  of  which  showed  that  they  were 
the  missing  elements. 

It  will  be  found  that  elements  in  the  same  group,  and  in  even  series, 
are  completely  similar  to  each  other,  as,  for  example,  Ca,  Sr,  and  Ba ; 
this  is  also  the  case  with  the  elements  in  the  same  group  and  in  odd 
series,  such  as  P,  As,  and  Sb.  The  members  of  the  odd  series,  however, 
do  not  so  closely  resemble  those  of  the  even  series,  though  in  the  same 
group.  Thus,  Ca  and  Zn  have  far  fewer  properties  in  common  than 
have  Ca  and  Sr.  It  seems,  then,  that  the  periodic  return  of  properties 
to  the  same  value  only  occurs  after  two  series  have  been  traversed,  so 
that  each  period  of  the  table  is  constituted  by  two  series  ;  thus,  K,  Rb, 
and  Cs  resemble  each  other  very  closely.  It  will  be  seen  that  since 
this  is  the  case,  each  group  must  consist  of  two  sub-groups,  indicated  in 
the  table  by  the  setting  of  the  symbols  in  two  vertical  lines  in  each 
group. 

The  members  of  these  sub-groups  or  families  resemble  each  other 
more  closely  than  do  the  members  of  a  group  taken  as  a  whole.  Whilst 
this  is  true  of  the  elements  which  follow  Na,  it  is  not  true  up  to  this 
point ;  thus,  Be  is  more  nearly  allied  to  Mg  than  to  Ca ;  B  to  Al  than 
to  Sc  ;  and  C  to  Si  than  to  Ti.  These  elements,  therefore,  do  not  appear 
to  be  in  their  right  places,  a  difficulty  which  is  met  by  supposing  that 
they,  and  those  from  Na  to  Cl  (inclusive)  constitute  two  short  periods ; 
these  elements  have  been  termed  the  typical  elements  of  the  table. 

It  is  only  possible  here  to  call  attention  to  a  very  few  of  the  properties  of  the 
elements  which  return  periodically  to  about  the  same  value.  The  elements  of  the 
same  family  form  oxides  which,  when  bases,  are  of  the  same  order  of  basicity  and, 
when  acid  oxides,  of  the  same  order  of  acidity  ;  this  is  well  illustrated  by  K,  Rb, 
Cs  ;  Ca,  Sr,  Ba  ;  P,  As,  Sb. 

The  specific  gravities  (mass  of  unit  volume)  of  the  elements  exhibit  a  periodicity. 


304  APPLICATION   OF   THE   PERIODIC   LAW. 

Instead  of  comparing  specific  gravities  it  is  better  to  compare  atomic  volumes  (or 
number  of  unit  volumes  in  the  atomic  weight).  The  atomic  volume  of  an  element 
is  the  quotient  of  its  atomic  weight  divided  by  its  specific  gravity  at  the  melting- 
point,  A/d  (at  melting-point).  Those  elements  which  are  most  chemically  active 
have  the  lowest  specific  gravities  and  therefore  the  highest  atomic  volumes  ;  thus  it 
is  found  that  the  atomic  volume  falls  from  the  beginning  to  the  middle  of  a  period, 
but  rises  again  from  the  middle  to  the  end ;  for  instance,  the  atomic  volume  of  K  is- 
45,  of  Ni  6.8,  and  of  Br  26.  In  the  same  family  the  atomic  volume  rises  with  the 
atomic  weight  ;  e.g.,  Li=i2,  K  =  45,  Eb  =  57,  Cs  =  7i.  Similar  relations  are  main- 
tained between  the  molecular  volumes  (molecular  weight  divided  by  specific  gravity) 
of  the  oxides  and  of  some  other  compounds  of  the  elements. 

The  same  periodic  fluctuation  is  to  be  noted  in  the  melting-points,  the  electro- 
positiveness,  the  brittleness  and  the  ductility  of  the  elements,  and  extends  to  the 
colour  of  their  salts.  If,  therefore,  the  atomic  volumes  be  plotted  on  a  curve,  the 
same  curve  will  apply  to  many  other  of  the  properties. 

The  Periodic  Table  has  found  a  twofold  application  :  (i)  It  has  served  to  enable 
chemists  to  foretell  the  existence  and  properties  of  elements  which  have  subsequently 
been  discovered  ;  (2)  it  has  afforded  a  means  for  deciding  the  atomic  weights  of 
some  elements. 

An  example  of  the  first  of  these  is  the  prophecy  by  Mendeleeff  of  the  existence 
and  properties  of  germanium  ;  the  principle  upon  wrhich  such  predictions  are  made, 
is  that  the  properties  of  an  element  are  approximately  the  mean  of  those  of  the  four 
elements  which  immediately  surround  it.  There  was  a  vacancy  in  the  table  between  Si 
and  Sn  ;  Mendeleeff  termed  the  element  which  had  to  be  discovered  to  fill  the  gap,, 
ekasilicon  (eka  is  "  one  "  in  Sanscrit).  According  to  the  above  principle,  ekasilicon 
when  discovered  should  have  properties  identical  with  the  mean  of  those  of  Si,  As, 
Sn,  and  Ga  ;  but  Ga  was  itself  unknown  at  the  time,  so  Mendeleeff  had  to  use  Zn  as 
a  member  of  the  quorum.  The  mean  of  the  atomic  weights  of  these  four  elements 
is  71.5,  so  that  this  would  be  the  atomic  weight  of  ekasilicon  ;  that  found  for  ger- 
manium is  72.  Ekasilicon  (Es)  would  probably  form  two  oxides,  EsO  and  Es02, 
an  acid  oxide  ;  for  although  SiO  is  not  known,  SnO  is  known,  and  both  Si02  and 
Sn02  are  stable,  acid  oxides ;  Ge02,  an  acid  oxide,  is  well  known,  and  GeO  probably 
exists.  EsCl4  and  EsCl2  should  exist,  because  SnCl4  and  SnCl2  exist,  but  GeCl2 
should  be  less  stable  than  SnCl2,  for  SiCl2  is  not  known.  As  a  fact,  both  GeCl4  and 
GeCl2  exist,  the  latter  being  less  stable  than  SnCl2.  Further,  the  boiling-point  of 
EsCl4  should  be  the  mean  of  those  of  SnCl4  and  SiCl4 — namely,  88.5°  ;  it  is  found 
to  be  86°. 

The  second  application  of  the  table  is  illustrated  by  the  fixation  of  the  atomic 
weight  of  beryllium.  The  equivalent  of  beryllium  is  4.5,  and  its  atomic  weight  was 
at  first  said  to  be  13.5,  because  its  oxide  was  supposed  to  be  Be203  on  account  of  its- 
similarity  to  A1203.  With  this  atomic  weight,  however,  this  element  would  have  to 
follow  carbon  in  the  periodic  table,  a  position  certainly  at  variance  with  its  proper- 
ties. It  was  therefore  suggested  that  its  atomic  weight  is  really  9,  in  which  case  its- 
oxide  would  be  BeO  and  the  element  would  fall  into  the  then  vacant  place  in 
group  ii.,  a  position  which  has  since  been  confirmed  by  the  determination  of  the 
vapour  density  of  BeCl2,  from  which  the  maximum  atomic  weight  of  9  is 
obtained. 

THE  MEASUREMENT  OF  CHEMICAL  AFFINITY. 

Chemical  affinity  is  a  name  conveniently  employed  to  designate  the 
unknown  force  by  which  chemical  change  is  effected. 

Energy  is  that  fundamental  property  which,  in  addition  to  mass,  is  possessed 
by  every  kind  of  matter,  and  for  the  present  purpose  it  may  be  defined  as  ability 
to  effect  a  change  in  the  relative  position  of  masses  of  matter,  be  they  molar, 
molecular,  or  atomic.  It  is  of  several  kinds,  of  which  chemical  energy  is  one. 
Heat  energy,  electrical  energy,  kinetic  energy  (or  that  resident  in  moving  matter), 
and  potential  energy  (or  that  resident  in  matter  by  virtue  of  its  position),  are  other 
kinds  of  energy. 

The  nature  of  chemical  energy  is  unknown  ;  but  it  rnaj-  be  compared  with 
potential  energy,  for  it  appears  to  depend  upon  the  position  of  the  matter  in 
which  it  resides.  Thus  a  mixture  of  hydrogen  and  oxygen  may  be  said  to  possess 
a  potential  energy  due  to  the  position  of  close  proximity  of  the  molecules ;  for, 
just  as  the  potential  energy  of  a  stone  on  the  edge  of  a  cliff  requires  an  impulse 


PRINCIPLES   OF   THERMOCHEMISTRY.  305 

in  order  to  convert  it  into  another  form  of  energy — the  kinetic  energy  of  its  fall 
to  the  foot  of  the  cliff — so  the  potential  energy  of  a  mixture  of  hydrogen  and 
oxygen  requires  an  impulse,  such  as  the  heat  of  an  electric  spark,  in  order  to 
convert  it  into  another  form  of  energy — heat  energy. 

The  potential  energy  of  a  stone  on  a  cliff  is  measured  by  multiplying  the  force 
which  impels  the  stone  to  fall  to  the  foot  of  the  cliff  by  the  space  through  which 
it  has  to  fall,  so  that  potential  energy  =  force  x  space.  Chemical  energy  may 
also  be  regarded  as  composed  of  two  factors  ;  one  of  these  is,  perhaps,  chemical 
affinity,  the  other  is  unknown. 

It  is  not  necessary  to  know  the  force  impelling  the  stone  to  fall,  or  the  space 
through  which  it  falls,  in  order  to  ascertain  the  potential  energy  of  a  stone  on  a 
cliff.  If  the  stone  be  allowed  to  fall,  and  steps  be  taken  to  receive  it  in  such  a 
manner  that  all  the  heat  generated  by  its  impact  with  the  earth  is  measured,  then, 
by  the  principle  of  the  Conservation  of  Energy,*  the  potential  energy  can  be  cal- 
culated from  this  heat,  which  is  exactly  equivalent  to  it.  (The  mechanical  equiva- 
lent of  heat  is :  one  gram-unit  of  heat  =  the  energy  represented  by  one  gram 
falling  through  42.350  centimetres.) 

It  should  be  equally  possible  to  measure  the  chemical  energy  of  a  mixture  of 
hydrogen  with  oxygen  by  ascertaining  the  quantity  of  heat  evolved  during  the 
combination  of  the  gases,  and  although  this  method  would  not  necessarily  measure 
the  chemical  affinity  of  the  hydrogen  for  the  oxygen,  yet  the  value  obtained  would 
probably  be  proportional  to  this  affinity. 

There  are  two  methods  by  which  a  force  may  be  directly  measured  :  (i)  A 
force  of  known  magnitude  may  be  brought  to  bear  upon  the  force  to  be  measured 
in  such  a  manner  that  the  two  are  in  equilibrium.  The  two  forces  will  then  be 
equal.  Such  a  method  may  be  called  a  static,  wet/tod,  and  would  be  employed  if  a 
force  of  known  value  were  brought  to  bear  upon  a  falling  stone  so  as  to  bring  it 
to  rest ;  the  force  of  the  stone  would  then  be  equal  to  the  opposing  force  ;  (2)  by 
measuring  the  velocity  of  a  moving  mass  in  successive  seconds,  the  force  impelling 
the  motion  is  measured  by  the  change  which  occurs  in  this  velocity.  This  may  be 
called  a  kinetic  method. 

The  attempts  which  have  been  made  to  measure  chemical  affinity  involve 
methods  analogous  to  these  two  methods  of  measuring  dynamical  force.  But  the 
attempt  to  measure  the  chemical  energy  of  chemical  reactions  by  ascertaining 
their  heat  changes,  and  thus  to  obtain  measurements  which  may  be  regarded  as 
proportional  to  chemical  affinity,  has  been  made  to  a  much  greater  extent  than 
have  attempts  to  apply  the  static  or  the  kinetic  method  ;  the  measurement  of 
chemical  energy  by  measuring  thermal  changes  will  therefore  be  considered  first. 

Thermochemistry  is  that  branch  of  the  science  of  chemistry  which 
deals  with  the  study  of  the  thermal  changes  accompanying  chemical  re- 
actions. The  prime  object  of  the  study  is  to  obtain  relative  measure- 
ments of  the  chemical  affinities  inducing  the  reactions. 

Attention  has  been  called  in  the  preceding  pages  to  some  of  the 
principles  of  thermochemistry,  but  they  may  aptly  be  summarised  here, 
(i)  Every  chemical  change  is  accompanied  by  a  thermal  change,  which 
is  a  constant  quantity.  (2)  The  thermal  change  occurring  during  the 
combination  of  elements  to  form  a  compound  is  called  the  heat  of 
formation  of  the  compound.  It  is  generally  a  positive  quantity,  that 
is,  heat  is  evolved — the  compound  is  exothermic ;  sometimes,  however, 
it  is  a  negative  quantity,  that  is,  heat  is  absorbed — the  compound  is 
endothermic.  (3)  The  thermal  change  occurring  during  the  decomposi- 
tion of  a  compound  is  called  the  heat  of  decomposition  of  the  compound. 
(4)  The  heat  of  decomposition  of  a  compound  is  identical  with,  but  of 
opposite  sign  to,  the  heat  of  formation  of  that  compound. 

*  This  principle  may  be  expressed  thus  :  In  any  space  the  total  quantity  of  energy  remains 
the  same,  although  the  energy  may  be  transferred  from  one  part  of  the  space  to  another,  or 
transformed  from  one  kind  of  energy  into  another.  An  example  of  the  principle  is  furnished 
by  the  firing  of  a  mixture  of  H2-f-O  in  a  vessel  from  which  loss  of  heat  is  impossible.  There 
is  the  same  quantity  of  energy  in  the  vessel  before  the  explosion  und  after  it,  bnt  after  the 
explosion  the  energy  is  in  the  form  of  heat  energy  instead  of  chemical  energy. 

U 


306  DETERMINATION   OF   THERMOCHEMICAL  DATA. 

The  last  proposition  follows  from  the  principle  of  the  conservation  of 
energy  (see  foot-note,  p.  305).  The  potential  energy  of  a  mixture  of 
elements  is  lost  to  the  system  in  the  form  of  heat  energy  when  the 
elements  combine ;  and  in  order  that  the  elements  may  be  again 
imbued  with  the  same  potential  energy,  heat  energy,  or  some  other 
form  of  energy,  must  be  restored  to  the  system. 

The  measurement  of  the  thermal  changes  of  chemical  reactions  is 
effected  by  causing  the  reaction  to  occur  in  a  closed  chamber  which  is 
immersed  in  a  calorimeter,  such  as  that  described  at  p.  164. 

The  heat  of  formation  of  a  compound  is  expressed  thus  :  H,OJ  = 
22,000,  meaning  that  the  combination  of  i  gram  of  hydrogen  with 
35-5  grams  of  chlorine  evolves  22,000  gram-units  of  heat.  Again, 
N,02  =  —  7700,  means  that  when  14  grams  of  nitrogen  combine  with 
32  grams  of  oxygen,  7700  gram-units  of  heat  are  absorbed.  Again, 
H20,S03=  21,320  means  that  when  18  grams  of  water  combine  with 
80  grams  of  SO3,  21,320  gram-units  of  heat  are  evolved.  The  heat  of 
decomposition  is  expressed  similarly,  but  with  reversed  signs,  thus  ; 
-H,C1=  -  22,000  ;  -N,02= +7700. 

The  value  obtained  in  a  calorimeter  for  the  thermal  change  of  a 
reaction  is  not  necessarily  the  thermal  change  due  to  that  chemical 
reaction  whose  heat  is  to  be  measured.  Allowance  must  frequently  be 
made  for  secondary  chemical  reactions  and  for  changes  of  physical  state. 

Two  examples  may  be  quoted  in  order  to  make  this  clear  : 

(1)  80  grams  of  S03  were  mixed  with  a   large  excess  of  water    (the    quantity 
being  known)  with  the  view  of  ascertaining  the  thermal  change  S03,  H.2O.     The 
value   obtained  was  39,177  ;    but  this  obviously  includes  two  thermal    changes  : 

(a)  that  due  to  the  combination  of  80  grams  of  S03  with  18  grams  of  H20,  and 

(b)  that  due  to  the  combination  of  the  H2S04  produced  with  an  excess  of  water. 
When  sulphuric  acid  is  diluted  with  water  in  a  calorimeter,  it  is  found  that  heat 
continues  to  be  evolved  until  the  weight  of  water  amounts  to  about  thirty-six 
times  that  of  the  sulphuric  acid   (corresponding  with  the  formula  H2S04.2ooH20)  ; 
this  thermal  change  amounts  to   17,857  gram-units  per  98  grains  of  H2SO4,   and 
must  be  subtracted  from  that  observed  on  mixing  80  grams  of  S03  with  a  large 
excess  of  water  in  order  to  arrive  at  the  value  S03,H20.     This  now  becomes  21,320. 
A  similar  action  of  excess  of  water  has  to  be  taken  into  account  in  many  cases,  and 
it  is  customary  to  use  the  symbol  Aq  for  such  an  excess.     Thus,  S03,Aq:=39,i77 
means  that  when  S03  is  dissolved  in  so  much  water  that  the  addition  of  a  further 
quantity   will  produce   no   further   thermal   change,    39,177   gram-units  of    heat 
are  evolved. 

(2)  O'l   gram  of  hydrogen  and  o-8  gram  of  oxygen  were  mixed  and  fired  in  a 
calorimeter,  the  final  temperature  of  which   was  20°  C.     The  gram-units  of  heat 
evolved  by  the  reaction  (calculated  from  the  rise  of  temperature)  amounted  to  3418. 
This  corresponds  with  H2,0  =  68.360.     But  since  we  know  of  at  least  three  sources 
from  which  this  thermal  change  is  derived,  this  value  cannot  be  regarded  as   ex- 
pressing the  amount  of  heat  energy  equivalent  to  the  chemical  energy  of  the  com- 
bination.    The  first  source  is  the  chemical  energy  of  the  combination.     The  second 
and  third  sources  are  due  to  the  change  of  aggregation  which  occurs  after  the  gases 
have  combined. 

The  steain  produced  by  the  combination  of  H2+0  occupies  two- thirds  of  the 
volume  previously  occupied  by  the  mixed  gases  ;  now  the  contraction  of  the 
volume  of  a  gas  always  involves  a  transformation  of  some  of  the  kinetic  energy 
of  the  gas  into  heat  energy  ;in  other  words,  heat  is  evolved  by  the  contraction.  It 
is  unreasonable  to  suppose  that  the  condensation  of  H2  +  0  into  steam  is  an 
exception  to  this  rule,  so  that  the  heat  evolved  by  this  condensation  must  be 
allowed  for  in  the  present  case  ;  a  value  for  it,  however,  can  only  be  calculated 
when  the  kinetic  energy  of  the  molecules  of  hydrogen  and  oxygen,  and  that  of 
the  molecules  of  steam  are  known.  The  method  by  which  these  kinetic  energies 
are  calculated  cannot  be  given  here  ;  suffice  it  to  say  that  the  difference  between. 


HEATS   OF  FORMATION  CALCULATED.  307 

the  kinetic  energy  of  18  grams  of  H2  +  0  and  that  of  18  grams  of  steam  has  been 
calculated  to  be  equivalent  to  193  gram-units  of  heat. 

Of  much  greater  importance  than  the  above  item,  is  the  difference  between  the 
kinetic  energies  of  steam  molecules  at  ioo°C.  and  water  molecules  at  the  same- 
temperature.  This  difference  is  well  known,  and  is  expressed  by  the  heat  of  con- 
densation of  steam.  One  gram  of  steam  at  100°  C.  evolves  536*5  gram-units  of 
heat  in  becoming  water  at  100°  C.  Therefore  18  grams  will  evolve  9666-,gram- 
units.  In  the  calorimeter  the  water  formed  by  the  reaction  does  not  remain  at 
100°  C.,  but  cools  to  20°  C.  before  the  temperature  of  the  outside  water  in  the 
calorimeter  is  measured.  In  cooling  from  100°  to  20°,  i  gram  of  water  loses 
80  gram-units  of  heat  (supposing  that  the  specific  heat  of  water  is  constant  over 
this  range  of  temperature)  ;  therefore  18  grams  of  water  lose  1440  gram-units. 

From  these  remarks  it  will  be  seen  that  of  the  total  68,360  gram-units  evolved  by 
the  reaction  in  the  calorimeter,  11,299  are  due  to  the  changes  of  aggregation, 
namely,  193  to  the  contraction  of  H2  +  O  to  steam,  9666  to  the  condensation  of  the 
steam  to  water  at  100°  C.,  and  1440  to  the  cooling  of  water  from  100°  C.  to  20°  C. 
By  deducting  these  11,299  units  from  the  total,  57,061  gram-units  are  obtained  as 
the  thermal  equivalent  of  the  potential  chemical  energy  of  a  mixture  of  hydrogen 
and  oxygen,  rendered  kinetic  by  the  combination. 

It  must  be  remembered  that  even  when  every  allowance  has  been 
made  for  such  secondary  reactions  and  such  changes  of  aggregation,  it 
is  by  no  means  certain  that  the  thermal  value  obtained  represents  the 
energy  of  combination  of  the  atoms  concerned  in  the  chemical  change. 
If  the  hypothesis  be  adopted  that  the  molecules  of  hydrogen  and 
oxygen,  for  example,  must  be  separated  into  their  constituent  atoms 
before  combination  can  occur,  it  must  be  admitted  that  some  energy 
is  absorbed  in  this  preliminary  process.  This  energy  will  become 
potential  in  the  atoms,  and  may  or  may  not  be  completely  rendered 
kinetic,  and  therefore  evolved  as  heat,  when  the  atoms  combine  to  form 
molecules  of  water.  Thus  it  may  happen  that  the  heat  evolved  in  the- 
combination  of  hydrogen  and  oxygen,  is  only  the  excess  of  that  due  to 
the  combination  of  the  atoms  of  H  and  0  over  that  absorbed  by  the- 
decomposition  of  the  molecules  of  H  and  0  into  atoms.  It  will  be 
obvious,  however,  that  for  all  practical  purposes,  such  as  for  the  calcu- 
lation of  the  calorific  value  of  a  gaseous  fuel  (see  Fuel),  the  calorimetrical 
value  for  the  combination  of  hydrogen  and  oxygen  is  a  perfectly  correct 
one,  inasmuch  as  the  gases  employed  in  the  experiment  are  in  the  same 
condition  as  those  used  in  practice. 

The  heat  of  formation  of  many  compounds  cannot  be  directly  deter- 
mined because  the  compounds  are  not  formed  by  the  direct  combination 
of  their  elements.  In  such  cases  the  value  is  calculated  by  methods 
which  can  receive  but  short  notice  here. 

The  principle  underlying  one  of  these  methods  is  that  the  thermal 
change  of  any  reaction  in  which  a  compound  AB  is  concerned,  must  be 
smaller  or  greater*  than  the  thermal  change  of  a  reaction — having  the 
same  products — in  which  the  constituents  A  and  Bare  concerned,  by  the 
heat  of  formation  of  AB.  For  example,  the  combustion  of  CH4  is  ther- 
mally expressed  thus  :  CH4,O4  =  2 1 1,930  gram-units  ;  but  it  is  supposed 
that  the  mechanism  of  this  combustion  consists  in  the  decomposition  of 
CH4  into  its  elements  which  are  then  burnt,  and  it  will  be  at  once  evident 
that  in  the  two  reactions,  CH4  +  O4  =  C02  + 2H?O  and  C  +  H4  +  O4  = 
C02  +  2H20,  the  heat  evolved  in  the  latter  will  differ  from  that  evolved 
in  the  former  by  an  amount  representing  the  heat  of  decomposition  of 
CH4.  Now  C,O2  =  96,96o  gram-units  when  solid  carbon  is  burnt, 

*  Accordingly  as  AB  is  exothermic  or  endothermic. 


3O8  APPLICATION  OF  THERMOCHEMICAL  DATA. 

•and  H4,02=  136,720  gram-units  for  gaseous  hydrogen;  therefore 
•(C  +  H4),04  =  96, 960+  136,720  =  233,680  gram-units.  But  CH4,O4  = 
2 1 1,930,  that  is,  the  heat  of  combustion  of  the  constituents  of  CH4  exceeds 
that  of  CH4  itself  by  21,750  ;  consequently,  CH4  must  have  absorbed  this 
amount  of  heat  in  being  decomposed  into  its  elements  before  these  were 
burnt.  Thus  it  is  concluded  that  marsh  gas  is  an  exothermic  com- 
pound, and  that  C,H4=2i,75o  gram-units,  supposing  that  the  gas 
were  produced  from  solid  carbon  and  gaseous  hydrogen. 

Another  instance  :  N2O  cannot  be  formed  directly  from  its  elements, 
but  the  heat  of  combustion  of  carbon  in  the  gas  is  easily  determined, 
••and  it  is  found  that  the  reaction  C  4-  2lN"2O  =  C02  +  N4  evolves  133,900 
gram-units.  Now  this  reaction  involves  the  decomposition  of  2N2O  and 
the  formation  of  C02,  so  that  the  heat  evolved  should  be  smaller  or 
greater  than  that  evolved  in  the  reaction  of  C  +  02  =  C02  by  the  heat  of 
decomposition  of  2N20.  Since  0,03  =  96,960,  the  heat  of  decomposition 
of  2N2O  must  be  133,900  -  96,960  =  36.940  gram-units,  and  that  of  N2O 
must  be  18,470  gram-units;  in  other  words,  nitrous  oxide  evolves  heat 
in  its  decomposition,  and  is  therefore  an  endothermic  compound,  or 
N2,0=  -18,470. 

Another  method  for  indirectly  determining  the  heat  of  formation  of 
a  compound  depends  upon  the  fact  that  the  total  energy  change  in  a 
reaction  is  the  same  whether  the  reaction  occurs  in  one  stage  or  in 
several.  This  is  only  an  application  of  the  principle  of  the  conservation 
of  energy  ;  the  total  energy  of  a  stone  falling  to  the  earth  is  the  same 
whether  the  fall  occur  in  one  stage  or  in  several.  An  example  of  the 
method  is  furnished  by  the  determination  of  the  heat  of  formation  of 
H2S04.  This  compound  cannot  be  made  from  its  elements  directly, 
but  the  heat  of  the  reaction  H20  +  SO2  +  0  =  H2S04  is  determinate, 
and  that  of  H2  +  0  =  H20,  and  of  S  +  02  =  S02,  are  well  known.  The 
total  heat  evolved  in  the  formation  of  H2S04  will  be  the  same  whether 
the  change  is  in  one  stage,  H2  + S  +  04  =  H2S04,  or  in  three,  viz., 
)  H2  +  0-H20  +  68,360;  (2)  S  +  02  =  S02+ 71,080;  (3)  H20  +  SO2  + 
=  H2S04  +  53,480;  consequently,  H2,S,O4  =  68, 360+ 71,080  + 53,480  = 
192,920. 

From  what  has  been  said,  it  will  be  apparent  that  the  thermal  changes 
of  chemical  reactions,  as  they  are  at  present  determined,  cannot  be 
regarded  with  certainty  as  equivalent  to  the  total  chemical  energy  con- 
cerned in  the  reaction.  They  cannot,  therefore,  be  said  to  be  an  abso- 
lute measure  of  the  chemical  affinity  of  elements  for  each  other. 

Nevertheless,  the  thermochemical  data  which  have  been  accumulated,  and  are 
to  be  found  in  most  books  of  chemical  constants,  are  useful  aids  to  the  chemist 
when  it  is  remembered  (i)  that  endothermic  reactions  rarely  occur  save  by  the 
application  of  external  energy  (generally  applied  in  the  form  of  heat  energy)  ; 
(2)  that  of  two  exothermic  reactions,  that  is  more  likely  to  occur,  under  ordinary 
conditions,  which  is  the  more  exothermic  ;  and  (3)  that  of  two  exothermic  com- 
pounds that  which  is  the  more  exothermic  is  the  more  stable. 

For  example,  it  is  seen  from  the  thermal  values  Ca,O=  132,000  and  0,02  =  96,960 
that  it  is  not  probable  that  carbon  will  reduce  CaO  at  any  but  a  very  high 
temperature  ;  for  the  reaction  2CaO  +  C  =  CO2  +  Ca2  is  highly  endothermic,  since  it 
involves  the  heat  of  decomposition  of  2CaO  (  -  264,000),  and  the  heat  of  formation 
of  C02,  leaving  a  balance  of  — 167,040  gram-units.  As  a  fact  the  reaction  does 
not  occur  at  any  temperature  hitherto  attained,  for  although  in  the  manufacture  of 
calcium  carbide  reduction  of  CaO  may  be  said  to  occur,  it  must  be  aided  by  the 
affinity  of  Ca  for  C  at  the  high  temperature  used. 


REVERSIBLE   REACTIONS. 


3°9 


Again,  in  any  competition  between  chlorine  and  bromine  for  hydrogen,  chlorine 
may  be  expected  to  prevail,  for  H,C1  =  22,000  and  H,Br  =  13,500.  HC1  is  the  more 
stable  of  these  two  because  it  is  the  more  exothermic. 

In  attempting  to  use  thermal  data  as  a  guide  for  prophesying  what  will  occur  in 
a  chemical  reaction,  it  must  not  be  forgotten  that  they  have  nearly  all  been 
determined  at  an  initial  and  final  temperature  of  about  20°  C.,  and  are  only  true 
for  the  elements  in  their  usual  condition  at  this  temperature.  There  is  no  reason 
to  suppose  that  the  thermal  change  at  a  high  temperature  is  the  same  as  it  is  at 
20°  C.  Thus  it  has  been  shown  that  the  heat  of  formation  of  hydrogen  iodide  is 
negative  at  low  temperatures,  but  positive  at  400°  C. 

Static  method  of  measuring  chemical  energy. — For  practical 
purposes  chemical  reactions  may  be  classified  into  complete  and  reversible 
reactions.  The  former  class  includes  those  changes  in  which  the  whole  of 
the  reacting  substances  is  converted  into  the  products  of  the  reaction ; 
for  example,  when  a  mixture  of  equal  volumes  of  H  and  01  is  fired,  the 
two  gases  combine  completely  and  are  entirely  converted  into  HC1.  A 
reversible  reaction  is  of  such  a  nature  that  the  products  of  the  reaction 
will,  under  a  slight  alteration  of  conditions,  react  with  each  other  to 
re-form  the  original  substances.  Thus,  when  steam  and  iron  are  heated 
together,  a  reaction  expressed  by  the  equation  Fe3  +  4H2O  =  Fe3O4  +  H8 
occurs  ;  but  it  is  equally  true  that  when  hydrogen  and  Fe304  are  heated 
together  the  reaction  Fe3O4  +  H8  =  4H20  +  Fe3  occurs.  N  ow  either  of 
these  reactions  may  be  carried  to  approximate  completion  under  certain 
conditions  ;  thus,  by  passing  steam  over  red-hot  iron  the  whole  of  the 
iron  can  be  converted  into  Fe3O4;  so  also  by  passing  hydrogen  over  Fe304 
at  the  same  temperature  the  whole  of  this  can  be  reduced  to  metallic 
iron.  But  if  iron  and  steam  be  heated  together  in  a  closed  vessel,  the 
iron  will  never  be  completely  oxidised.  This  is  because  the  reaction  is 
reversible,  that  is  to  sa,y,  as  soon  as  any  Fe3O4and  Hare  produced  these 
tend  to  react  with  each  other  to  form  H2O  and  Fe ;  in  other  words,  the 
reaction  Fe3  +  4H2O^Fe3O4  +  H8,  can  take  place  in  either  direction  at 
the  same  time,  a  fact  expressed  by  the  substitution  of  ^  for  =  in  the 
equation. 

It  has  been  seen,  however,  that  by  passing  steam  over  red-hot  iron 
the  latter  can  be  completely  oxidised — that  is  to  say,  the  equation 
Fe3  +  4H20  =  Fe304  +  H8  can  be  realised.  This  is  only  possible  because 
one  of  the  products  of  the  reaction  (the  hydrogen)  is  in  such  a  physical 
condition  that  it  can  be  removed  from  the  sphere  of  action  (the  tube  in 
which  the  reaction  is  performed)  ;  indeed,  for  the  complete  oxidation  of 
the  iron  a  large  excess  of  steam  over  that  indicated  as  necessary  by  the 
equation  (72  parts  of  steam  for  168  parts  of  iron)  must  be  passed 
through  the  apparatus  containing  the  iron  in  order  to  sweep  away  the 
hydrogen.  If  the  hydrogen  could  not  be  removed  in  this  manner,  the 
completion  of  the  reaction  would  be  impossible.  The  same  remarks, 
mutatis  mutandis,  apply  to  the  complete  reduction  of  Fe3O4  by  hydrogen. 

A  reversible  reaction  can  only  become  complete  when  one  of  the 
products  of  the  reaction  is  removed  from  the  sphere  of  action.  Under 
any  other  conditions  the  vessel  in  which  the  reaction  is  proceeding  will 
contain  some  of  each  of  the  reacting  substances,  and  some  of  each  of 
the  products  of  the  reaction. 

The  question  naturally  arises,  When  iron  and  steam  are  heated  in  a 
closed  vessel,  so  that  nothing  can  escape  from  the  sphere  of  action,  how 
far  will  the  reaction  proceed  ?  How  much  iron  oxide  and  hydrogen  will 


310  THE  ACTION  OF  MASS. 

be  produced  ?  How  much  steam  and  iron  will  be  left  ?  To  fully  appre- 
ciate the  state  of  the  case  it  must  be  realised  that  both  the  reactions  ex- 
pressed by  the  equation  Fe3  +  4H2O^Fe3O4  +  H8  are  proceeding  at  the 
same  time,  and  during  the  whole  time,  and  that  if  the  temperature  be 
kept  constant  a  period  will  soon  be  reached,  when  the  amount  of  iron 
oxidised  per  unit  time  will  be  exactly  equivalent  to  the  amount  of  iron 
oxide  reduced  per  unit  time. 

When  this  state  of  affairs  prevails  the  equation  in  the  direction  repre- 
sented by  the  arrow->,  which  may  conveniently  be  termed  the  equation 
representing  the  positive  change,  will  be  realised  to  exactly  the  same 
extent  as  the  equation  represented  by  the  arrow<-(the  negative  change) 
is  realised,  per  second.  This  is  called  the  equilibrium  stag  erf  the  rever- 
sible reaction,  and  when  it  is  attained  an  analysis  of  the  contents  of 
the  vessel  will  show  the  same  proportion  of  iron,  steam,  iron  oxide  and 
hydrogen  to  be  present,  however  long  the  vessel  is  maintained  at  the 
same  temperature.  An  alteration  in  the  temperature  will  cause  an 
alteration  in  the  extent  to  which  either  the  positive  or  negative  change 
will  occur  per  second  ;  so  that  with  every  such  change  of  temperature 
a  new  equilibrium  stage  will  be  established,  and  an  analysis  will  show  a 
new  proportion  between  the  quantities  of  the  four  substances  present. 

There  is  another  factor  besides  temperature  which  influences  the 
quantity  of  each  of  the  substances  present  at  the  equilibrium  stage  of 
a  reversible  reaction.  This  is  the  mass  of  any  one  of  the  substances. 
Thus,  if  iron  and  steam  be  heated  in  the  proportion  represented  by 
the  equation  (168  parts  of  iron:  72  parts  of  steam)  at  any  given  tem- 
perature, exactly  the  same  quantity  of  iron  oxide  and  hydrogen  will  be 
produced  as  would  remain  undecomposed  if  iron  oxide  and  hydrogen 
were  heated  in  the  proportion  represented  by  the  equation  (232  parts 
of  Fe3O4 :  8  parts  of  hydrogen),  at  the  same  temperature.  But  if  the 
mass  of  either  the  steam  or  the  hydrogen  be  increased,  then  the  quan- 
tities of  steam  or  hydrogen  present  at  the  equilibrium  stage  will  be 
altered.  If  the  proportion  of  either  of  the  constituents  on  the  left  hand 
of  the  equation  be  increased,  the  positive  change  will  have  occurred  to 
a  greater  extent — that  is,  more  Fe304  and  H  will  have  been  produced 
— when  the  equilibrium  stage  is  reached,  than  was  the  case  with  the 
former  proportion.  If  the  proportion  of  either  of  the  substances  on 
the  right  hand  of  the  equation  be  increased,  the  negative  change 
will  occur  to  a  greater  extent  than  before.  Since  Fe  and  Fe3O4  are 
solids  while  hydrogen  and  steam  are  gases,  the  system  is  in  this  case 
heterogeneous,  and  of  the  four  substances  only  the  H2O  and  H  can 
intermix.  Hence,  here,  an  alteration  of  the  proportion  of  Fe  or  Fe304 
has  but  little  effect  upon  the  change. 

This  mass  action  is  of  great  importance  in  chemical  change,  and  may 
be  generally  expressed  by  stating  that  in  a  homogeneous  system  chemical 
change  is  pi'oportional  to  the  active  mass  of  each  of  the  substances  taking 
part  in  the  reaction.  By  active  mass  is  meant  the  number  of  molecules 
of  the  substance  in  unit  volume,  such  as  gram -molecules  per  litre. 

From  a  practical  point  of  view  mass  action  frequently  influences  chemical 
change,  a  large  mass  compensating  a  feeble  affinity,  it  being  possible  for  reactions 
to  proceed  which,  considering  the  relative  affinities,  could  not  occur  unless  one  of 
the  products  were  sufficiently  insoluble  to  be  removed  from  the  homogeneous 
system.  Such  a  case  wrill  be  met  in  the  description  of  the  manufacture  of  caustic 
soda,  where  the  comparatively  feeble  affinity  of  lime  for  C0.2  is  nevertheless  suffi - 


COEFFICIENTS   OF  AFFINITY.  311 

cient  to  allow  the  reaction  Na2C03  +  Ca(OH)2  =  2NaOH  +  CaC03  to  occur  in  solution, 
because  the  CaCO.{  immediately  separates  from  the  liquid  and  the  reaction  in  the 
left  hand  direction  cannot,  in  consequence,  occur  so  rapidly  as  that  in  the  right 
hand  direction.  Nevertheless  care  must  be  taken  that  the  active  mass  of  the  NaOH 
does  not  increase  too  much,  for  then  even  the  precipitated  CaC03  will  be  attacked  to 
reproduce  Na2C03  and  Ca(OH)2.  In  other  words,  the  solution  must  not  be  too 
concentrated. 

It  is  not  difficult  to  imagine  the  mechanism  of  this  mass  action  ;  the  greater 
the  number  of  molecules  in  a  given  space  the  more  frequently  will  they  come 
into  contact  with  each  other,  and  since  chemical  change  appears  to  occur  only 
between  molecules  in  contact,  the  greater  will  be  the  amount  of  chemical  change 
produced.  In  the  case  of  steam  and  red-hot  iron,  it  is  obvious  that  the  greater 
the  number  of  steam  molecules  present,  the  more  frequently  these  will  come  in 
contact  with  the  iron,  and  the  more  oxide  of  iron,  and  consequently  hydrogen, 
will  be  produced. 

The  subject  of  dissociation  furnishes  numerous  examples  of  mass  action. 

The  chemical  equilibrium  between  two  opposing  reactions,  such  as 
those  concerned  in  the  action  of  steam  on  red-hot  iron,  should  serve  as 
a  static  method  for  determining  chemical  energy.  For  the  equilibrium 
is  between  two  chemical  affinities,  the  one  tending  to  produce  the 
positive  change,  the  other  tending  to  produce  the  negative  change ;  and 
the  amount  of  each  change  must  be  proportional  to  the  affinity  which 
produces  it ;  so  that  by  analytically  determining  the  quantities  of  sub- 
stances present,  and,  therefore,  the  extent  of  the  reaction,  at  the 
equilibrium  stage,  it  should  be  possible  to  form  a  comparison  between 
these  affinities. 

The  action  of  steam  on  red-hot  iron  does  not  lend  itself  to  the  application  of 
this  method  as  the  system  is  heterogeneous.  But  a  number  of  double  decomposi- 
tions has  been  studied  from  this  point  of  view  ;  they  are  reversible  reactions  and 
are  mostly  between  organic  compounds,  so  that  in  this  place  it  will  be  useful  to 
express  them  by  the  general  form  AB  +  CD^AC  +  BD.  The  opposing  forces  which 
bring  about  the  equilibrium  of  such  a  change  are  the  sum  of  the  affinities  of  A  for 
C  and  B  for  D  (say  /<•)  against  the  sum  of  the  affinities  of  A  for  B  and  C  for  D 
(say  It1).  The  amount  of  chemical  change  which  has  occurred  at  the  equilibrium 
stage  is  proportional  to  the  active  masses  of  the  reacting  substances,  and,  pre- 
sumably, also  to  these  coefficients  of  affinity,  It  and  kl.  The  amount  of  chemical 
change  can  be  measured  by  chemical  analysis.  Suppose  AB  and  CD  be  mixed  in 
the  proportion  of  one  gram-molecule  of  each  ;  then,  when  equilibrium  has  been 
attained,  there  will  be  present  a  fraction  of  a  gram-molecule  of  AC,  BD,  AB,  and 
CD  respectively  :  and  the  fraction  will  be  the  same  for  AC  and  for  BD,  and  also 
the  same  for  AB  and  CD.  Let  this  fraction  of  AC  and  BD  be  a;  then  that  of  AB 
and  CD  must  be  i  -x,  for  one  gram-molecule  was  originally  taken. 

The  active  masses  of  AC  and  BD,  tending  to  produce  the  negative  change,  are  x 
and  x,  and  their  total  effect  maybe  represented  as  xx  or  a?2.  The  affinity  tending  to 
produce  the  negative  change  is'  &1,  so  that  the  total  force  producing  the  negative 
change  is  ft1  •/•-. 

The  active  masses  of  AB  and  CD  are  i-x  and  i-aj,  and  the  affinity  is  k; 
therefore  the  total  force  tending  to  produce  the  positive  change  is  h(i  -a?)'2. 

When  the  equilibrium  stage  is  reached  these  two  forces  are  equal  to  each  other, 
whence  A-(i  -  ./•)-  =  kl,r2  or  It/It1  =  #2/(  I  -  a?)2.  Thus  the  ratio  It  jit1  can  be  determined, 
for  x  is  determinable  by  analysis.  For  example,  when  acetic  acid  and  ethyl 
alcohol  are  heated  together,  ethyl  acetate  and  water  are  produced,  the  reaction 
being  reversible.  When  x  is  determined  (after  no  more  change  appears  to  occur), 
it  is  found  to  be  §,  whence,  by  the  above  formula,  k/kl  =  4. 

By  this  static  method  the  relative  affinity,  or  avidity,  of  acids  for  bases  has  been 
determined.  The  principle  of  the  method  is  to  mix  equivalent  quantities  of  two 
acids  with  a  quantity  of  base  insufficient  to  saturate  both,  and  to  determine  what 
proportion  of  the  base  each  acid  will  acquire.  Thus,  when  NaOH  is  mixed  with 
HNO3  and  £  H2S04  (equal  equivalents)  two-thirds  of  the  soda  combines  with  the 
nitric  acid  and  one-third  with  the  sulphuric  acid,  showing  that  the  avidity  of  the 


312  DISSOCIATION. 

nitric  acid  is  twice  as  great  as  that  of  the  sulphuric  acid.     If  the  avidity  of  nitric 
acid  be  taken  as  I.  that  of  sulphuric  acid  is  0.5. 

The  avidity  of  an  acid  may  be  denned  as  the  proportion  of  base  which 
that  acid  will  appropriate  when  equivalent  quantities  of  the  acid,  a  base  and 
HN03  are  mixed  in  aqueous  solution.  It  is  independent  of  the  nature  of  the 
base.  The  following  order  of  avidities  is  probably  correct  :  HN03=i  ;  HCl  =  i; 


Thus,  in  solutions  of  equivalent  concentration,  HN03  and  HC1  must  be 
accounted  stronger  acids  than  H2S04  ;  but  the  greater  volatility  of  the  two 
first  will  enable  H2S04  to  expel  them  when  heated  with  their  salts. 

Kinetic  method  of  measuring  chemical  affinity.  —  This  method  of  measuring 
chemical  affinity  consists  in  determining  the  amount  of  chemical  change  which 
occurs  in  unit  time,  not  waiting  for  equilibrium  to  occur.  This  value  is  termed  the 
coefficient  of  velocity  of  the  change,  and  the  greater  this  coefficient  of  velocity  the 
greater  the  force  inducing  the  change. 

Most  changes  are  too  rapid  for  any  determination  of  the  coefficient  of  velocity, 
but  in  the  class  of  changes  known  as  hydrolysis  (p.  265),  such  a  measure- 
ment is  possible  because  the  change  only  occurs  with  moderate  rapidity  in  the 
presence  of  an  acid.  Thus,  when  cane  sugar  is  boiled  with  water  it  is  very  slowly 
converted  into  invert  sugar  ;  C^H^Ojj  +  HOH^aCgH^Oe  ;  but  in  the  presence  of  a 
dilute  acid  the  change  is  much  more  rapid,  and  can  be  measured  by  determining 
the  amount  of  invert  sugar  produced.  The  action  of  the  acid  is  not  understood, 
but  is  generally  ascribed  to  a  predisposing  affinity  of  the  acid  for  the  invert  sugar  ; 
this  means  that  the  invert  sugar  is  the  more  readily  produced  because  of  the 
tendency  which  the  acid  has  to  form  an  unstable  compound  with  it  ;  such  a  com- 
pound must  be  soon  decomposed  again,  because  to  all  appearances  the  same  amount 
of  free  acid  remains  in  the  solution  after  the  hydrolysis  as  was  there  before. 

Different  acids  have  a  different  influence  on  the  rate  of  the  hydrolysis  of  cane- 
sugar,  &c.,  and  it  is  reasonable  to  suppose  that  this  rapidity  of  action  is  in  some 
way  proportional  to  the  affinity,  or  avidity,  of  the  acid.  By  determining  the 
velocity  of  hydrolysis  —  that  is,  the  amount  of  cane-sugar  which  has  been  hydro- 
lysed  per  minute  —  when  different  acids  are  present,  the  avidities  of  the  acids  may 
be  compared.  The  mathematical  calculations  involved  are  somewhat  complex, 
and  cannot  be  discuseed  here.  The  method  yields  values  for  the  avidities  of 
acids  which  are  in  the  same  order  of  magnitude  as  those  determined  by  the  static 
method. 

A  little  consideration  of  the  definition  of  dissociation  (p.  86)  will 
show  that  the  phenomenon  belongs  to  the  same  class  as  the  reversible 
reactions,  such  as  the  action  of  steam  on  red-hot  iron  discussed  above.* 
The  contemplation  of  the  case  of  phosphorus  pentachloride  will  render 
this  more  evident.  When  this  compound  is  heated  above  300  °C.  it 
dissociates  to  a  very  large  extent  into  PC13  +  C12,  a  fact  discovered  by 
attempting  to  determine  the  vapour  density  of  PC15.  The  amount  of 
dissociation  depends  on  the  temperature  and  on  the  active  masses  of 
the  substances  present.  The  equilibrium  between  the  positive  and 
negative  changes  of  the  reversible  reaction  PC15^PC13  +  C12,  occurs 
when  the  same  quantity  of  PCJ3  is  dissociated  and  associated  in  unit 
time,  and  this  will  vary  for  every  temperature. 

Since  PC13,  PC13,  C12  each  represents  2  vols.,  the  total  active  mass 
tending  to  produce  the  negative  change  is  twice  as  greafc  as  the  active 
mass  tending  to  produce  the  positive  change.  If  the  vessel  containing 
the  three  substances  at  the  equilibrium  stage  be  diminished  in  size,  that 
is,  if  the  pressure  be  increased,  the  active  masses  of  all  three  will  be 
increased  ;  for  there  will  now  be  more  of  each  in  unit  volume.  Suppose 
the  pressure  to  have  been  trebled,  the  active  mass  of  each  will  have 

*  Recently,  certain  phenomena  have  been  noted,  which  seem  to  indicate  that  dissociation 
of  a  compound  can  occur  in  the  reverse  sense  to  that  usually  observed,  namely,  as  the  com- 
pound cools.  The  behaviour  of  ruthenium  tetroxide  (q.v.)  may  be  cited  as  an  example. 
Further  search  for  phenomena  of  this  kind  is  needed. 


INFLUENCE   OF  PRESSURE  ON  EVAPORATION.  313. 

been  trebled ;  but  the  negative  change  is  proportional  to  the  active 
masses  of  PCI3  and  CI2  so  that  it  will  have  become  nine-fold,  whilst  the 
positive  change  is  only  dependent  on  the  active  mass  of  the  PC15  and 
will  therefore  have  only  been  trebled.  Consequently  the  negative 
change  will  predominate  over  the  positive  change,  and  a  new  equili- 
brium will  be  established — in  other  words,  the  dissociation  will  be 
diminished.  Similar  reasoning  may  be  applied  to  all  cases  of  the  dis- 
sociation of  gases,  when  it  will  be  found  that  if  the  products  of  dis- 
sociation have  a  larger  total  volume  than  the  volume  of  the  substance 
undergoing  dissociation,  an  increase  of  pressure  will  diminish  the  dis- 
sociation, whilst  a  diminution  of  pressure  icill  increase  it. 

The  effect  of  introducing  one  of  the  products  of  the  dissociation  into 
the  vessel  at  the  equilibrium  stage  would  be  to  increase  the  active  mass 
of  that  product  and  to  increase  the  negative  change,  that  is,  to  cause 
association.  Thus,  if  PC13  were  introduced  there  would  immediately  be 
a  reproduction  of  PCL.  Advantage  may  be  taken  of  this  to  prevent 
dissociation  from  occurring  at  all ;  for  instance,  if  PC15  be  heated  in  a 
vessel  containing  PC13,  it  will  not  undergo  dissociation  until  a  much 
higher  temperature  than  that  at  which  it  dissociates  when  heated  alone. 

The  extent  to  which  PC15  has  undergone  dissociation  is  calculated  from  the 
observed  vapour  density.  Let  x  be  the  percentage  of  molecules  which  have  under- 
gone dissociation  ;  then  100-  tr  is  the  percentage  still  associated.  But  the  ,r  mole- 
cules have  become  2-1-  molecules  when  dissociated.  Therefore  100  molecules  have 
become  ioo-x  +  2.z'=  100  +  2-  molecules  after  partial  dissociation,  so  that  the 
volume  is  increased  in  the  ratio  100  :  ioo  +  ./-.  The  vapour  density,  however,  has 
decreased  inversely  to  the  volume.  If  d  be  the  vapour  density  before,  and  D  that 

after,  partial  dissociation,  then  100  :  100  + x  :  :  D  :  d  or  je= ^=r -. 

The  similarity  between  changes  which  are  generally  distinguished 
as  physical  and  chemical  is  well  seen  by  a  comparison  of  certain  cases  of 
dissociation  with  the  phenomenon  of  evaporation.  It  has  been  already 
stated  that  when  evaporation  occurs  in  a  confined  space,  it  apparently 
ceases  when  as  many  particles  leave  the  space  and  attach  themselves  to 
the  surface  of  the  liquid,  as  leave  the  surface  and  move  about  in  the 
space,  in  unit  time.  Thus,  evaporation  is  a  reversible  change  capable 
of  attaining  an  equilibrium  stage.  The  number  of  particles  of  vapour 
which  attach  themselves  to  the  surface  of  the  liquid  in  unit  time 
depends  on  the  number  which  strikes  the  surface;  according  to  the 
kinetic  theory  of  gases,  this  number  is  measured  by  the  pressure  of  the 
vapour,  so  that  the  evaporation  ceases  when  the  pressure  of  the  vapour 
has  reached  a  certain  value.  The  number  of  particles  of  liquid  which 
enter  the  space  in  unit  time  depends  on  the  temperature  of  the  liquid; 
the  higher  this  is,  the  greater  the  number  of  particles  which  leave  the 
liquid  in  unit  time,  and,  therefore,  the  greater  will  have  to  be  the 
number  of  vapour  particles  striking  the  surface  of  the  liquid,  per  unit 
time,  in  order  to  bring  about  equilibrium.  In  other  words,  the  higher 
the  temperature  of  the  liquid,  the  greater  will  be  its  vapour  pressure 
when  evaporation  has  apparently  ceased. 

It  will  be  obvious  from  these  remarks  that  the  evaporation  of  a 
liquid  is  increased  by  raising  its  temperature,  and  is  decreased  by 
raising  the  pressure  of  its  vapour  above  it.  Thus,  if  the  evaporation 
be  considered  as  a  reversible  change,  it  is  analogous  to  the  dissociation 
of  PC15  in  that  temperature  and  pressure  are  at  war  with  each  other  in 


314  THE   LAW   OF   PAKTIAL  PRESSURES. 

their  effect  on  the  extent  of  the  change.  It  is  interesting  to  note  that 
temperature  eventually  prevails,  and  that  for  every  liquid  there  is  a 
temperature  above  which  no  amount  of  pressure  will  prevent  it  from 
becoming  vaporised;  this  is  its  absolute  boiling-point  (p.  29). 

For  a  right  understanding  of  the  influence  of  pressure  on  evaporation 
(and  dissociation)  it  is  necessary  to  realise  the  principle  of  partial  pres- 
sure. When  two  gases  are  mixed  the  resulting  pressure  on  the  sides  of 
the  containing  vessel  is  the  sum  of  the  pressure  which  each  gas  exerted 
before  the  two  were  mixed ;  so  that  a  law  of  partial  pressures  may  be 
stated  in  this  way :  In  a  mixture  of  gases  the  pressure  exerted  by 
each  gas  is  exactly  the  same  as  the  pressure  which  that  gas  would  exert 
did  it  alone  occupy  the  volume  filled  by  (he  mixture.  Thus,  in  air, 
where  the  proportion  of  N  :  O  is  approximately  4:1,  ith  of  the  pres- 
sure is  exerted  by  the  O  and  ith  by  the  N. 

From  this  it  follows  that  in  a  mixture  of  vapour  and  air  the  vapour 
exerts  the  same  pressure  as  it  would  exert  did  it  alone  occupy  the  space 
filled  by  the  mixture,  and  that,  since  the  extent  to  which  a  liquid  will 
evaporate  depends,  when  the  temperature  is  constant,  solely  on  the 
pressure  of  its  vapour,  evaporation  must  proceed  to  the  same  extent  in 
a  vacuum  and  in  air.  Thus,  at  15.3°  0.  water  and  its  vapour  are  in 
equilibrium  when  the  pressure  of  the  latter  is  equal  to  12.9  mm.  of 
mercury,  so  that  water  will  continue  to  evaporate  until  it  has  parted 
with  sufficient  vapour  to  create  this  pressure  in  the  space  above  it.  If 
that  space  originally  contained  a  vacuum,  a  pressure-gauge  will  show  a 
pressure  of  12.9  mm.  when  the  evaporation  has  apparently  ceased  ;  if 
the  space  originally  contained  air  at  760  mm.  pressure,  the  gauge  will 
show  a  pressure  of  760+  12.9  mm. 

The  hastening  of  evaporation  by  a  draught  of  air  is  simply  due  to 
the  prevention  of  the  accumulation  of  vapour  over  the  surface  of  the 
liquid ;  in  this  way  the  vapour  pressure  may  be  hindered  from  rising  to 
that  which  causes  equilibrium. 

From  the  foregoing  it  will  be  seen  that  the  temperature  and  pressure  of  a  vapour 
in  presence  of  its  liquid  are  interdependent  ;  a  given  pressure  of  the  vapour  can 
only  be  attained  at  a  certain  temperature,  and  for  a  given  temperature  the  pressure 
must  have  a  certain  value.  In  the  case  of  unsaturated  vapour  and  gases,  pressure 
and  temperature  can  be  varied  independently,  and  by  an  alteration  of  volume 
either  temperature  or  pressure  is  varied.  The  sole  effect  of  varying  the  volume  of 
a  vapour  in  presence  of  its  liquid  is  to  cause  more  liquid  to  become  vapour,  or  vice 
versa,  and  the  temperature  and  pressure  remain  constant. 

Water  is  one  individual,  capable  of  existing  in  three  2}llase**  ice»  water,  and 
vapour.  A  system  comprising  water  and  its  vapour  alone,  is  a  two-phase  system 
and  the  phases  can  be  in  equilibrium  at  many  different  temperatures,  a  definite 
pressure  corresponding  with  each  temperature.  When  the  pressure  of  the  water 
vapour  is  reduced  to  4.6  mm.,  the  water  passes  into  ice  owing  to  the  heat  lost  by  its 
own  evaporation,  and  the  temperature  is  then  0.007°  C.  ;  any  further  reduction  of 
temperature  or  pressure  will  convert  all  the  water  into  ice  and  the  system  again 
becomes  two-phase,  consisting  of  ice  and  its  vapour.  But  so  long  as  the  tempera- 
ture and  pressure  are  those  named,  the  three-phase  system — ice,  water,  vapour — 
is  in  equilibrium.  Thus,  while  a  two-phase  system  is  in  equilibrium  under  different 
conditions,  there  is  only  one  condition  of  equilibrium  for  a  three-phase  system. 

Water  is  one  individual  ;  where  there  are  two  individuals  in  a  system,  three 
phases  may  be  in  equilibrium  at  different  temperatures,  but  when  the  two  indi- 
viduals are  in  four  phases,  only  one  condition  of  equilibrium  is  possible.  Such  a 
case  is  presented  by  the  two  individuals  chlorine  and  water.  Chlorine  hydrate 

*  The  word  "  phase  "  is  applied  to  any  constituent  of  a  system  which  is  capable  of  differ- 
entiation from  the  other  constituents. 


INFLUENCE  OF  PRESSURE  ON  THE  SOLUBILITY  OF  GASES.  315 

separates  at  9.6°  C.  if  the  pressure  of  the  chlorine  is  that  of  the  atmosphere  ;  by 
raising  the  pressure,  the  temperature  at  which  the  hydrate  separates  is  raised,  and  a 
new  temperature  is  established  at  each  pressure  ;  this  is  an  interdependence  similar 
to  that  in  the  case  of  evaporation,  that  is  to  say,  the  three-phase  system 
Cl,  C1.4H.20,H20  is  in  equilibrium  at  different  temperatures.  As  soon,  however,  as 
ice  begins  to  separate  (at  0.24°  C.)  a  fourth  phase  is  introduced,  and  equilibrium 
between  the  four  is  only  possible  at  this  temperature,  the  pressure  being  244  mm. 

When  there  is  only  one  condition  of  equilibrium,  this  is  called  the  transition- 
point^  for  if  the  pressure  or  temperature  be  varied,  one  of  the  phases  must  pass  into 
one  of  the  others  and  disappear  from  the  system. 

The  phase  rule,  which  is  believed  to  govern  the  equilibrium  of  heterogeneous 
systems,  states  that  a  transition-point  for  a  system  of  n  individuals  is  only  possible 
when  the  number  of  phases  is  n  +  I . 

Allotropic  changes  may  also  be  brought  under  the  phase  rule.  When  the  allo- 
tropes  are  enantiotropes  (that  is,  when  the  change  from  one  to  the  other  is  rever- 
sible, as  in  the  case  of  octahedral  and  prismatic  sulphur  and  red  and  yellow 
phosphorus),  there  is  a  transition-point  for  the  phases  consisting  of  the  two  forms 
the  liquid  element  and  the  vapour. 

The  case  of  the  dissociation  of  calcium  carbonate  by  heat  is  closely 
analogous  to  that  of  evaporation.  The  reversible  change,  CaC03^CaQ 
+  C02,  reaches  equilibrium  when  the  pressure  of  the  C02  has  attained  a 
certain  value  depending  on  the  temperature.  Since  the  pressure  of  the 
C02  is  a  measure  of  the  weight  of  it  in  unit  volume,  the  equilibrium  is 
reached  when  the  product,  CO2,  has  a  certain  active  mass  dependent  on 
the  temperature.  Thus,  at  740°  C.  the  equilibrium  pressure  is  255  mm., 
and  when  this  has  been  attained  no  further  dissociation  can  occur ;  if 
the  calcium  carbonate  be  heated  in  a  vessel  exposed  to  the  open  air,  the 
C02  will  gradually  diffuse  away  and  its  partial  pressure  will  be  reduced 
below  255  mm.,  so  that  the  change  will  continue.  By  exposing  the 
heated  mass  to  a  draught  of  air,  the  admixture  of  the  C02  with  the 
surrounding  atmosphere,  and  therefore  the  completion  of  the  dissocia- 
tion, will  be  more  rapid.  If  the  pressure  of  the  C02  be  not  allowed  to 
rise  to  255  mm.,  the  complete  conversion  of  CaC03  to  OaO  can  be  effected 
at  a  correspondingly  lower  temperature. 

A  precisely  similar  influence  is  exerted  by  temperature  and  pressure 
on  the  solubility  of  a  gas  in  water.  The  solubility  decreases  with  rise 
of  temperature  and  increases  with  rise  of  pressure.  For  perfect  gases 
the  following  generalisation  is  true  : — The  solubility  of  a  gas  in  a  liquid 
is  directly  proportional  to  the  pressure  exerted  by  the  gas.  Since  the 
volume  of  the  gas  varies  inversely  with  the  pressure,  this  statement  may 
be  varied  thus  :  a  given  volume  of  liquid  will  always  dissolve  the  same 
volume  of  a  given  gas,  whatever  the  pressure.  Thus,  if  a  litre  of  water 
dissolve  100  c.c.  of  a  gas  at  760  mm.,  it  will  dissolve  twice  this  quantity 
at  1520  mm.;  but  200  c.c.  measured  at  760  mm.  will  be  100  c.c.  at 
1520  mm.,  so  that  the  litre  of  water  will  still  dissolve  only  100  c.c.  at 
the  higher  pressure. 

Since  the  coefficient  of  solubility  of  a  gas  (p.  54)  is  the  volume  of  the  gas 
which  unit  volume  of  water  will  dissolve  at  760  mm.,  it  follows  that  the  quantity 
of  gas  soluble  in  the  same  volume  of  water,  at  the  same  temperature,  and  at  any 
other  pressure,  is  found  by  multiplying  the  coefficient  of  solubility  by  the  pressure 
divided  by  760.  In  a  mixture  of  gases  the  pressure  of  each  gas  is  only  a  part  of 
the  whole,  being  the  same  fraction  of  the  total  pressure  as  the  volume  of  the  gas 
is  of  the  total  volume.  The  method  of  calculating  the  solubility  of  the  N  and  O 
when  air  is  shaken  with  water  (p.  54)  will  now  be  easily  understood,  and,  as  a 
further  example,  the  volume  of  C02  which  100  c.c.  of  water  will  dissolve  from 
the  air  at  o°  C.  and  720  mm.  may  be  calculated.  Taking  the  percentage  of  C02 
in  the  air  at  0.035,  its  partial  pressure,  when  the  total  pressure  is  720  mm.,  will 


3l6  OSMOTIC   PRESSURE. 

be        35  x  720  =  0.25  mm.       The  coefficient  of  solubility  of  CO.,  at  o°C.  and  760 
100 

mm.  is  1.8  ;  therefore  at  0.25  mm.  and  o°  C.  it  will  be  1.8  x  °±^>.     This,  therefore, 

will  be  the  volume  of  C02  dissolved  by  i  vol.  of  water  under  the  conditions  named  ; 
when  multiplied  by  100,  the  value  will  express  the  number  of  c.c.  dissolved  by 
100  c.c  of  water. 

It  must  be  remarked  that  gases  which  are  easily  liquefied,  and  thus  deviate 
from  true  gases,  fail  to  obey  with  accuracy  the  law  of  solubility  stated  above. 

When  the  space  above  the  solution  of  a  gas  contains  the  same  gas  as  that  which 
is  dissolved,  equilibrium  is  established  when  the  same  quantity  of  gas  passes  from 
the  space  into  the  liquid,  and  from  the  liquid  into  the  space,  in  unit  time.  If  for 
the  gas  in  this  space  there  be  substituted  another,  the  dissolved  gas  will  go  on 
escaping  from  solution  until  its  partial  pressure  in  the  space  is  the  same  as  its  pres- 
sure was  iwhen  it  alone  filled  the  space.  It  will  be  obvious,  therefore,  that  a  few 
such  displacements  of  the  gas  in  the  space  should  cause  the  liquid  to  part  with 
practically  all  its  dissolved  gas. 

Solution. — In  the  case  of  most  gases  it  is  impossible  to  regard  their 
solutions  in  water  as  mere  physical  mixtures.  Reference  has  been  already 
made  to  this  difficulty  and  to  the  companion  one  concerning  the  solu- 
bility of  solids  (p.  50).  Besides  the  thermal  changes  there  mentioned, 
there  are  such  facts  as  the  constant  boiling-point  of  solutions  containing 
gas  and  water  in  definite  proportions — e.g.,  HC1.8H2O  (p.  179),  and  the 
separation  of  salts  containing  water  of  crystallisation — to  compel  the 
conclusion  that  in  many  cases  the  dissolved  substance  enters  into 
combination  with  the  solvent. 

It  is  a  fact,  however,  that  many  dilute  solutions  behave  as  would  be 
anticipated  if  the  dissolved  substance  were  present  in  a  condition 
independent  of  the  solvent.  Thus,  it  has  been  discovered  that  the  mole- 
cules of  a  dissolved  substance  exert  a  pressure  on  the  solvent  identical 
with  the  pressure  which  they  would  exert  on  the  sides  of  a  vessel,  of  the 
same  volume  as  that  of  the  solution,  if  they  were  in  the  gaseous  state. 

This  discovery  has  given  rise  to  a  "physical  theory"  of  dilute  solutions, 
which  may  be  stated  thus :  The  molecules  of  the  dissolved  substance 
pervade  the  solvent  without  being  influenced  thereby,  and  possess  the 
same  properties  as  they  would  possess  did  they  alone,  in  the  state  of 
gas,  occupy  the  volume  filled  by  the  solution. 

The  pressure  which  a  substance  in  solution  exerts  on  the  solvent  is 
called  the  osmotic  pressure  of  the  solution,  because  it  is  only  by  taking 
advantage  of  the  phenomenon  of  osmosis  that  it  can  be  rendered 
apparent  and  directly  measured.  It  has  been  already  shown  (pp.  70, 
277)  that  certain  structureless  substances  (india-rubber,  parchment 
paper,  &c.)  will  allow  of  a  much  more  rapid  passage  through  them 
of  some  kinds  of  molecules  than  of  other  kinds.  Several  such  substances 
exist  which  allow  water  molecules  to  pass  through  them  almost  infinitely 
faster  than  they  allow  many  other  kinds  of  molecules  to  pass.  When 
a  membrane  made  of  one  of  these  substances  is  immersed  in  an  aqueous 
solution,  it  will  generally  happen  that  the  water  molecules  will  pass 
through  the  membrane  very  much  faster  than  the  molecules  of  the 
dissolved  substance.  This  transition  of  molecules  differs  from  that 
called  diffusion,  in  that  it  appears  to  depend  rather  upon  the  specific 
nature  of  the  membrane  than  upon  its  porosity  (compare  p.  22).  The 
term  osmosis  is  introduced  to  indicate  this  difference. 

The  method  employed  for  studying  the  pressure  exerted  by  a  dissolved 
substance  on  the  solvent,  can  now  be  easily  understood.  A  vessel  is 


OSMOTIC  PRESSURE   AND   GASEOUS   PRESSURE.  317 

constructed  of  a  material  which  allows  of  the  osmosis  of  the  solvent 
molecules,  but  not  of  the  dissolved  molecules.  The  solution  whose 
osmotic  pressure  is  to  be  studied,  is  introduced  into  this  vessel,  which  is 
then  immersed  in  a  bath  of  the  pure  solvent.  The  solvent  molecules 
will  pass  into  the  vessel  and  out  of  the  vessel ;  but  since  there  are  more 
of  these  molecules  in  unit  volume  outside  the  vessel  than  there  are 
inside  (on  account  of  the  presence  of  the  dissolved  molecules),  more  of 
the  solvent  will  pass  into  the  vessel  in  unit  time  than  will  pass  out, 
and  equilibrium  will  only  be  established  when  a  certain  pressure,  com- 
pensating for  this  difference  between  the  number  of  solvent  molecules 
in  unit  volume,  has  been  established  inside  the  vessel.  This  pressure  is 
termed  the  osmotic  pressure  of  the  solution,  and  is  attributed  to  the 
dissolved  molecules  ;  it  can  be  measured  by  closing  the  vessel  by  an 
ordinary  pressure-gauge. 

In  practice  it  is  found  necessary  to  support  the  "  osmotic  membrane  "  which  is 
to  form  the  walls  of  the  vessel,  by  depositing  it  on  the  surface  of  a  porous  pot. 
The  most  successful  method  consists  in  depositing  copper  ferrocyanide  (a  material 
which  behaves  as  an  osmotic  membrane  to  aqueous  solutions)  within  the  pores  of 
a  biscuit- porcelain  battery  cell  (3"  x  i")  ;  for  this  purpose  the  cell  is  filled  with  a 
solution  of  copper  sulphate  (3  per  cent.)  and  immersed  in  a  solution  of  potassium 
ferrocyanide  (3  per  cent.).  The  two  solutions  meet  in  the  wall  of  the  cell,  and  a 
continuous  sheet  of  copper  ferrocyanide  is  deposited  therein.  An  inverted  funnel 
is  cemented  in  the  mouth  of  the  cell,  and  a  U-shaped  mercury  gauge  is  sealed  to 
the  stem  of  the  funnel.  The  cell  is  nearly  filled  with  the  aqueous  solution  whose 
osmotic  pressure  is  to  be  measured,  and  is  immersed  in  a  bath  of  distilled  water. 
The  pressure  of  the  air  trapped  between  the  gauge  and  the  solution  is  measured 
by  the  variation  in  the  height  of  the  mercury  in  the  gauge.* 

It  is  found  that  the  same  relationship  exists  between  the  osmotic 
pressure  and  the  concentration  of  a  solution  as  exists  between  the 
pressure  and  the  concentration  of  a  gas.  That  is  to  say,  the  osmotic 
pressure  is  directly  proportional  to  the  weight  of  dissolved  substance 
in  unit  volume  of  the  solution,  just  as  the  pressure  of  a  gas  is  directly 
proportional  to  the  weight  of  the  gas  in  unit  volume  (Boyle's  law). 
Thus,  a  one  per  cent,  sugar  solution  exerts  an  osmotic  pressure  equal  to 
535  mm.  of  mercury,  whilst  the  osmotic  pressure  of  a  two  per  cent, 
solution  is  equal  to  1070  mm.,  provided  the  temperature  is  the  same  in 
each  case. 

Again,  the  osmotic  pressure  of  a  solution  varies  directly  as  the 
absolute  temperature  (thermometric  temperature  +  273)  of  the  solution, 
just  as  the  pressure  of  a  gas  varies  directly  with  its  absolute  tempera- 
ture (Charles'  law).  Thus  the  one  per  cent,  solution  of  sugar  shows  an 
osmotic  pressure  of  544  mm.  of  mercury  at  32°  C.,  and  of  512  mm.  at 
14.15°  (305  :  287.15  =  544  :  512). 

It  seems,  then,  that  the  variations  which  occur  in  the  osmotic  pressure 
of  a  dilute  solution  when  the  concentration  of  the  solution  is  varied, 
are  controlled  by  the  same  laws  as  those  which  govern  the  variations  in 
the  pressure  of  a  gas  when  the  concentration  of  the  gas  is  varied.  But 
the  analogy  between  the  osmotic  pressure  and  the  gaseous  pressure  is 
still  closer  than  this ;  for  it  is  found  that  the  osmotic  pressure  is  identical 
with  the  gaseous  pressure  which  the  weight  of  dissolved  substance  would 

*  A  description  and  drawing  of  the  apparatus  will  be  found  in  Jour.  Chem.  Soc.  Trans. 
1891,  p.  344,  and  directions  for  preparing  the  membrane  by  electrolysis  are  given  in  the 
Amer.  Chem.  Jour.,  1901,  vol.  26,  p.  80. 


3l8  ISOTONIC   SOLUTIONS. 

exert  at  the  same  temperature,  if  it  were  in  the  state  of  gas  and  occupied 
the  volume  filled  by  the  solution. 

It  is  considered  reasonable  to  deduce  from  this  that  the  number  of 
molecules  of  dissolved  substance  in  a  volume  v  of  a  solution,  having  an 
osmotic  pressure  p  and  a  temperature  t,  is  the  same  as  the  number  of 
molecules  in  a  volume  v  of  a  gas  at  the  pressure  p  and  the  temperature  t. 

Thus,  a  I  per  cent,  solution  of  cane  sugar  (C^H^On)  at  o°  C.  exerts  an  osmotic 
pressure  of  493  mm.  Now  the  molecular  weight  corresponding  with  the  formula 
C^H^Oj!  is  342.  and,  could  the  sugar  be  gasified,  342  grams  of  it  would  occupy 
22.22  litres  |at  o°  C.  and  760  mm.  (p.  47)  ;  that  is  to  say,  342  grams  of  gaseous 
sugar  in  a  volume  of  22.22  litres  at  o°  C.  would  exert  a  pressure  of  760  mm.  The 
concentration  of  342  grams  in  22.22  litres  is  the  same  as  a  concentration  of  15.4 
grams  in  one  litre  ;  therefore  15.4  grams  of  gaseous  sugar  in  I  litre  at  o°  C.  should 
exert  a  pressure  of  760  mm.  It  follows  that  10  grams  in  i  litre  at  o°  C.  should 
exert  a  pressure  of  493  mm.  This  is  practically  identical  with  the  osmotic  pres- 
sure of  a  (i  per  cent.)  sugar  solution  containing  10  grams  per  litre. 

Gases  at  high  concentration — that  is,  at  high  pressure — cease  to  obey 
the  laws  of  Boyle  and  Charles.  The  same  is  true  for  solutions  at  high 
concentration. 

Since  Avogadro's  law  is  deducible  mathematically  from  those  of  Boyle 
and  Charles,  and  since  dilute  solutions  appear  to  be  controlled  by  the 
last-named  laws,  it  seemed  probable  that  an  Avogadro's  law  should 
exist  for  dilute  solutions.  This  was  first  pointed  out  by  Van't  Hoff, 
whose  law  of  osmotic  pressure  is  thus  stated  :  Equal  volumes  of  different 
solutions,  at  the  same  temperature  and  osmotic  pressure,  contain  equal 
numbers  of  molecules  of  dissolved  substance. 

The  similarity  between  this  statement  and  that  expressing  Avogadro's 
law  (p.  289)  will  be  at  once  evident. 

Solutions  which  exert  equal  osmotic  pressure  are  said  to  be  isotonic. 

Just  as  the  relation  between  the  weights  of  the  molecules  of  two  gases 
can  be  deduced  from  Avogadro's  law  (p.  289),  so  can  the  relation  between 
the  weights  of  the  molecules  of  two  dissolved  solids  be  deduced  from 
Yan't  Hoff's  law.  For  it  follows  from  this  law,  that  when  equal  volumes 
of  two  solutions  are  isotonic,  and  at  the  same  temperature,  the  weight 
of  dissolved  solid  in  the  one  is  as  much  heavier  than  the  weight  of  the 
dissolved  solid  in  the  other,  as  the  molecular  weight  of  the  first  solid  is 
heavier  than  the  molecular  weight  of  the  second  (cf.  footnote,  p.  47). 

Determination  of  molecular  weights  of  non- volatile  sub- 
stances.— The  applicability  of  the  measurement  of  osmotic  pressure  to 
the  determination  of  molecular  weights  will  now  be  easily  understood. 
A  solution  of  the  solid  whose  molecular  weight  is  unknown  may  be  diluted, 
or  strengthened,  until  its  osmotic  pressure  is  identical  with  that  of  a  solu- 
tion containing  a  known  weight  of  a  solid  whose  molecular  weight  is 
known.  The  ratio  between  the  weights  of  the  solids  in  one  litre  of  each 
solution  is  then  the  ratio  between  the  molecular  weights  of  the  solids. 

Example. — A  solution  of  a  substance  of  unknown  molecular  weight  was  diluted 
until  its  osmotic  pressure  was  found  to  be  identical  with  that  of  a  solution  of 
sugar  in  water  (at  the  same  temperature).  The  weight  of  solid  in  i  litre  of  each 
solution  was  then  determined  ;  that  in  the  sugar  solution  was  i  gram  ;  that  in 
the  other  solution  was  1.5  gram.  By  Van't  Hoff's  law  these  weights  must  have 
the  same  ratio  to  each  other  as  have  the  molecular  weights  of  the  substances. 
Let  x  be  the  unknown  mol.  wt.  ;  the  mol.  wt.  of  sugar  is  342,  therefore  : 
342  :  x  :  :  i  :  1.5  or  x  =  342  x  1.5. 

The  measurement  of  osmotic  pressure  is  neither  easy  nor  capable  of 


METHODS  FOE  DETERMINING  MOLECULAR  WEIGHT.  319 

very  great  accuracy  ;  it  is  not,  therefore,  well  adapted  for  the  determina- 
tion of  molecular  weights. 

There  are,  however,  other  methods  of  determining  whether  solutions 
contain  the  same  number  of  dissolved  molecules  in  equal  volumes,  which, 
owing  to  the  ease  and  accuracy  of  making  the  required  measurements, 
are  much  adopted  for  checking,  and  even  determining,  the  molecular 
weights  of  substances  which  cannot  be  volatilised,  and  are  therefore 
excluded  from  the  method  depending  on  the  determination  of  the  vapour 
density  of  the  substance  (p.  292). 

The  methods  in  question  depend  upon  the  influence  which  the  mole- 
cules of  the  dissolved  substance  have  on  many  of  the  physical  properties 
of  the  solvent.  Thus,  the  more  numerous  the  dissolved  molecules  in  a 
solution  the  lower  will  be  its  freezing- point  and  its  vapour  pressure,  so 
that  a  measurement  of  the  temperature  at  which  the  solution  freezes, 
or  of  the  pressure  exerted  by  its  vapour,  will  serve  as  a  measurement  of 
the  molecular  concentration  of  the  substance  in  solution. 

The  method  of  determining  molecular  weights  which  depends  upon 
the  measurement  of  the  freezing-point  of  a  solution  is  known  as  the 
cryoscopic  method,  or  the  method  of  depression  of  the  freezing-point,  as 
Kaoulfs  method. 

Raoult  discovered,  empirically,  that  the  freezing-point  of  a  solution  is 
always  lower  than  that  of  the  solvent,  and  that  the  depression  is  directly 
proportional  to  the  weight  of  substance  in  solution.  Thus,  if  one  gram 
of  a  solid  in  a  litre  of  water  lowers  the  freezing-point  by  0.1°,  two  grams 
will  lower  it  0.2°.  Collation  of  his  results  showed  that  when  molecular 
quantities  of  different  substances  are  dissolved  in  the  same  amount  of  a 
solvent,  they  lower  the  freezing-point  of  the  solvent  to  the  same  extent.  This 
may  now  be  expressed  by  saying  that  isotonic  solutions  in  the  same 
solvent  have  the  same  freezing-point. 

If  Raoult's  generalisation  (italicised  above)  be  true,  there  will  be  a 
certain  constant  (T)  for  every  solvent,  representing  the  amount  of 
depression  in  the  freezing-point  of  that  solvent  caused  by  the  presence 
of  one  gram-molecule  of  any  substance  in  100  grams  of  the  solvent. 
Thus,  it  is  found  that  in  the  case  of  many  salts,  a  solution  of  one  gram- 
molecule  of  the  salt  in  1000  grams  of  water  freezes  at  -  1.9°  C.  ;  con- 
sequently a  solution  of  one  gram-molecule  in  100  grams  of  water  should 
freeze  at  -  19°  C.,  and  the  constant,  T,  for  water  is  19.  This  value  does 
not  hold  good  for  all  classes  of  salts  for  a  reason  to  be  explained  later. 

A  little  consideration  will  show  that  when  T  is  known  for  a  solvent, 
it  should  be  possible  to  determine  the  molecular  weight  of  a  substance 
by  ascertaining  the  depression  of  the  freezing  point  of  a  solution  of  the 
substance  in  that  solvent. 

Suppose  the  constant  T  to  have  been  ascertained  for  a  solvent.  This  would  be 
effected  by  determining  what  depression  is  caused  in  the  freezing-point  of  the  sol- 
vent by  dissolving  I  gram-molecule  of  any  substance  of  well-known  molecular 
weight  in  100  grains  of  it.  Let  it  be  desired  to  determine  the  molecular  weight  (M) 
of  some  other  substance.  One  gram  of  the  substance  is  dissolved  in  100  grams 
of  the  solvent,  and  the  freezing-point  of  the  solution  is  determined  ;  suppose  this  to 
be  k  degrees  lower  than  the  freezing-point  of  the  pure  solvent.  Then,  if  one  gram 
cause  depression  A,  M  grams  (one  gram-molecule)  will  cause  depression  M.k;  but 
this  depression  is  the  value  T,  whence,  Wt  =  T  or  M  =  T/k.  Since  T  and  k  are  known, 
M  is  thus  determined. 

The  depression  caused  by  one  gram  in  100  grams  of  solvent  is  generally  too  small 
to  measure,  so  a  stronger  solution,  say  P  grams  in  100  grams  of  solvent,  is  used. 


320 


VAPOUR  PPvESSUKE   OF   SOLUTIONS. 


If   P  grams  cause  depression  It,  one  gram  will  cause  depression  Jf/P.  and  M  grams 

will  cause  depression  M&/P,     Therefore  M#/P  =  T  or  M  =  TP/k. 

The  value  of  T  for  water  is  19   for  several  classes  of  salts  ;  for  benzene  it  is  49  ; 

for  glacial  acetic  acid  it  is  39. 

The  method  is  conducted  as  follows  :  A  known  weight  of  the  solvent  is  intro- 

•duced  into  a  long  test- tube  (Fig.  202)  which  has  a  side  neck  closed  by  a  cork  ;  a. 

cork  in  the  mouth  of  the  test-tube  carries  a  ther- 
mometer, graduated  to  0.01°,  and  a  stirrer.  The 
test-tube  is  passed  through  the  cork  of  a  -wider 
test-tube  (to  serve  as  an  air  jacket,  which  shall 
prevent  too  rapid  a  change  of  temperature),  which  is 
immersed  in  a  bath  also  provided  with  a  stirrer  and 
at  a  temperature  several  degrees  'below  the  freezing- 
point  of  the  solvent.  The  bulb  of  the  thermometer 
being  immersed  in  the  solvent,  the  stirrer  is  con- 
tinually agitated  until  the  solvent  begins  to  freeze, 
whereupon  the  temperature  is  noted.  The  tube  is 
then  withdrawn  from  the  bath,  the  solvent  allowed 
to  melt,  and  the  weighed  quantity  of  substance 
added  through  the  side  neck.  When  this  has  dis- 
solved, the  freezing-point  of  the  solutio'n  is  deter- 
mined as  before.  Since  superf usion  of  the  solution 
is  liable  to  occur  it  is  sometimes  necessary  to  add 
a  crystal  of  a  previously  frozen  solution  (of  the 
same  strength)  in  order  to  induce  solidification. 

Example. — The  freezing-point  of  120  grams  of 
benzene  was  found  to  be  6°  C.  ;  6  grams  of  sulphur 
were  dissolved  in  the  benzene  and  the  freezing- 
point  was  again  determined  ;  it  was  found  to  be 
4.68°  C.  In  this  case  120  grams  of  benzene  con- 
tained 6  grams  of  sulphur,  so  that  P,  the  quantity 


present  in   100  grams,  is    — 


6-4.68  =  1.32. 


M    = 


.32 


=  5  grams.     It  = 
T  for  benzene  =  49.     Therefore 
Thus  the  molecular  weight 


of  solid  sulphur  is  185.6,  a  number  sufficiently  close 
Fig.  202. — Beckmann's  apparatus,   to  192  to  warrant  the  conclusion  that  the  molecule 

of  solid  sulphur  is  S6.* 

The  lowering  of  the  vapour  pressure  of  a  solvent  by  the  presence  of  a 
substance  in  solution,  is  controlled  by  laws  which  are  wholly  similar  to 
those  which  apply  to  the  lowering  of  the  freezing-point  of  a  solvent  by 
the  presence  of  a  dissolved  substance.  Since  the  vapour  pressure  varies 
with  the  temperature,  it  is  necessary  to  add  that  the  lowering  is  always 
the  same  fraction  of  the  vapour  pressure  of  the  pure  solvent,  whatever 
the  temperature. 

Inasmuch  as  the  boiling-point  of  a  liquid  is  that  temperature  at 
which  the  pressure  of  its  vapour  is  equal  to  the  pressure  of  the  atmo- 
sphere, the  presence  of  a  dissolved  substance  must  raise  the  boiling-point 
of  a  solution  pari  passu  with  lowering  its  vapour  pressure. 

The  apparatus  shown  in  Fig.  203  is  used  for  determining  the  rise  of  the  boiling- 
point  of  a  solvent  by  the  presence  of  a  dissolved  substance.  To  avoid  heating 
the  solvent  to  a  temperature  above  its  boiling-point,  which  would  vitiate  the  result, 
the  tube  containing  the  solvent  is  surrounded  by  a  jacket  filled  with  an  atmosphere 
of  the  vapour  of  the  solvent  at  its  boiling-point.  This  vapour  is  generated  in  the 
flask  A  and  is  passed  through  the  tube  B,  provided  with  distributing  holes  at  its  lower 
end,  into  the  inner  tube  N  which  contains  another  portion  of  the  solvent.  When 

*  Determinations  of  the  vapour  pressure  of  CS2  when  sulphur  is  dissolved  in  it,  show  a 
value  of  S3  for  the  molecule  of  solid  sulphur. 


SALINE  SOLUTIONS. 


321 


the  latter  has  been  heated  by  the  vapour  to  its  boiling-point,  the  vapour  passes  un~ 
condensed  through  the  solvent  and  through  the  hole  H,  thus  surrounding  the  tube 
N  and  passing  into  the  condenser  C.  The  temperature  is  now  noted  by  the  ther- 
mometer T,  the  tube  N  is  emptied  and  the  operation  repeated  with  the  addition  to 
the  solvent  (about  5  to  7  c.c.)  of  a  weighed  quantity  of  the  substance  (about  4  per 
cent,  of  the  weight  of  the  solvent),  the  molecular  weight  of  which  is  to  be  deter- 
mined. The  tube  N,  whose  weight  when  empty  is  known,  is  now  weighed  to- 
ascertain  the  weight  of  solvent  used.  The  molecular  elevation  of  the  solvent  having 
been  determined  by  the  use  of  a  substance  of  known  molecular  weight,  the  molecular 
weight  of  the  substance  is  calculated  as  in  the  freezing-point  method  described  above. 


Fig.  203. — Landsberger's  apparatus. 

It  must  here  be  noted  that  there  are  many  cases  in  which  the  mole- 
cular weight  of  a  compound,  determined  by  the  osmotic  pressure  of  a 
solution  of  it,  or  by  the  cryoscopic  method,  is  only  a  fraction  of  the 
molecular  weight  which  must  be  assigned  to  the  substance  on  account 
of  the  other  considerations  which  serve  to  settle  molecular  weights.  A 
flagrant  case  is  that  of  potassium  chloride.  The  osmotic  pressure  of  a 
dilute  aqueous  solution  of  this  salt  is  nearly  twice  as  great  as  it  should 
be  if  the  molecular  weight  of  the  salt  be  74.5  ;  again,  the  depression  of 
the  freezing-point  of  a  dilute  solution  is  nearly  twice  as  great  as  it 
should  be  if  the  molecular  weight  of  the  salt  were  74.5.  Both  these 
facts  indicate  that  potassium  chloride,  in  solution,  has  a  molecular  weight 


322  ELECTEOLYSIS. 

about  one  half  of  74.5,  and  yet  a  quantitative  analysis  of  KC1  shows 
that  74.5  parts  by  weight  of  it  contain  35.5  parts  by  weight  of  chlorine, 
so  that  the  salt  cannot  well  have  a  smaller  molecular  weight  than  74.5. 
This  anomalous  behaviour  of  KC1  is  shared  by  a  large  number  of  salts, 
acids  and  bases,  all  of  which  show  a  lower  molecular  weight  when  in 
solution  than  that  which  is  generally  attributed  to  them. 

This  phenomenon  is  so  analogous  to  that  of  the  dissociation  of  a  com- 
pound (e.<7.,NH4Cl,  PC15)  by  heat,  which  causes  the  molecular  weight 
determined  by  the  vapour  density  to  be  lower  than  that  inferred  from 
other  considerations,  that  these  salts,  acids  and  bases  are  supposed  to 
have  been  more  or  less  dissociated  by  the  water  which  has  dissolved 
them.  Thus,  potassium  chloride — which  gives  an  osmotic  pressure  nearly 
twice  that  which  it  should  give  if  its  molecule,  in  dilute  solution,  were 
represented  by  KC1 — is  supposed  to  be  nearly  completely  dissociated 
into  K  and  01 ;  so  that  there  are  twice  as  many  ultimate  particles  in  the 
solution  as  there  would  be  if  the  dissociation  did  not  occur — just  as 
there  are  twice  as  many  molecules,  causing  twice  as  great  a  pressure, 
in  the  vapour  of  PC15  above  300°  C.  as  there  would  be  if  no  dissociation 
occurred. 

The  realisation  of  the  existence  of  osmotic  pressure  renders  it  possible 
to  regard  the  process  of  dissolution  of  a  solid  as  belonging  to  the  same 
type  of  changes  as  that  to  which  dissociation  and  evaporation  have  been 
assigned.  When  a  salt  is  immersed  in  water  particles  of  salt  leave  the 
mass  and  pervade  the  water,  this  process  continuing  until  as  many 
particles  leave  the  mass  of  salt  as  attach  themselves  to  it.  in  unit  time. 
This  equilibrium  stage  is  the  saturation  of  the  water  with  the  salt,  and 
for  every  temperature  there  is  an  appropriate  pressure — the  osmotic 
pressure — at  which  equilibrium  will  occur,  just  as  there  is  an  appro- 
priate vapour  pressure  for  every  temperature  at  which  evaporation  will 
cease. 

Electrolysis. — The  theory  that  many  molecules  are  dissociated  by 
being  dissolved,  finds  its  chief  support  in  a  study  of  the  phenomena 
which  accompany  the  conversion  of  chemical  energy  into  electrical 
energy  and  vice  versd. 

The  chemical  action  which  is  most  frequently  employed  to  develop 
chemical  energy  for  conversion  into  electrical  energy,  is  that  involved  in 
the  dissolution  of  zinc  in  an  acid,  generally  dilute  sulphuric  acid.  If 
a  piece  of  commercial  zinc  be  immersed  in  dilute  sulphuric  acid,  it  dis- 
solves, and  a  quantity  of  heat  is  developed  equivalent  to  the  chemical 
energy  of  the  dissolution  of  the  zinc.  If  the  zinc  and  acid  be  perfectly 
pure  no  action  will  occur  ;  but  if  a  piece  of  platinum  be  immersed  in  the 
acid  and  be  made  to  touch  the  zinc,  whether  beneath  or  above  the 
surface  of  the  acid,  action  will  begin  and  heat  will  be  developed  ;  the 
hydrogen  will  no  longer  appear  to  be  evolved  from  the  zinc,  but  will 
rise  from  the  surface  of  the  platinum.  In  the  case  of  both  the  impure 
zinc  and  the  zinc  +  platinum,  the  chemical  energy  has  to  a  great  extent 
passed  through  the  stage  of  electrical  energy  before  it  has  become  heat 
energy.* 

If  the  platinum  and  zinc  be  connected  with  a  wire  outside  the  acid, 

*  The  impure  zinc  contains  foreign  metals  which,  by  contact  with  the  zinc,  enable  the 
latter  to  dissolve,  with  generation  of  electrical  energy,  just  as  the  platinum  enables  the  pure 
zinc  to  dissolve. 


THE   GALVANIC   CELL.  323 

the  electrical  energy  will  "  flow  "  through  the  wire  and  may  be  utilised 
before  it  becomes  converted  into  heat  energy. 

When  such  a  "galvanic  cell"  is  left  to  itself,  the  rapidity  of  the  dissolution  of 
the  zinc  soon  diminishes  (and  with  it  the  intensity  of  the  electrical  energy)  be- 
cause the  cell  becomes  polarised. ;  this  is  chiefly  due  to  the  coating  of  the  platinum 
plate  with  hydrogen  so  that  it  virtually  becomes  a  plate  of  hydrogen,  which  is  much 
less  effective  than  is  platinum  in  aiding  the  dissolution  of  zinc  by  contact.  It 
is  for  this  reason  that  all  cells  which  have  any  practical  value  contain  an  oxidising 
agent  or  depolarizer  (e.g..  nitric  acid  in  a  Grove  cell)  around  the  platinum  plate  ; 
such  an  agent,  by  oxidising  the  hydrogen,  diminishes  the  polarisation,  and  at  the 
same  time  develops  a  greater  amount  of  chemical  energy,  and  therefore  of 
electrical  energy,  in  the  cell. 

The  total  amount  of  electrical  energy  developed  by  a  galvanic  cell  in  unit  time, 
depends  on  the  amount  of  chemical  energy  occurring  in  the  cell  in  that  time,  and 
upon  the  nature  of  the  plates  which  are  used  in  the  cell.  The  first  of  these  con- 
ditions is  measured  (in  the  zinc  cell)  by  the  amount  of  zinc  which  dissolves,  and  is 
therefore  related  to  the  size  of  the  zinc  plate.*  The  influence  of  the  nature  of  the 
plates  may  be  summed  up  by  saying  that  the  greater  the  antithesis  between  the 
plates,  in  respect  of  the  ease  with  which  they  are  attacked  by  the  exciting  medium 
of  the  cell,  the  greater  will  be  the  total  amount  of  electrical  energy  obtained  from 
the  cell.  Thus,  when  dilute  sulphuric  acid  is  the  exciting  medium,  the  plates 
should  consist  of  a  metal  which  is,  in  a  high  degree,  attackable  by  this  acid,  and 
one  which  is  highly  resistant  ;  zinc  and  platinum  are  the  metals,  among  those 
which  are  sufficiently  cheap  for  use,  which  best  fulfil  these  conditions  ;  zinc  and 
copper  are  frequently  used,  but  since  copper  has  a  greater  tendency  to  dissolve  in 
sulphuric  acid  than  platinum  has,  this  "  couple  "  is  not  capable  of  giving  so  great  a 
total  of  electrical  energy  as  that  yielded  by  a  zinc-platinum  couple.  It  will  be 
obvious,  however,  that  in  the  event  of  an  exciting  medium  which  has  more  action 
on  platinum  than  on  copper  being  used,  the  zinc-copper  couple  may  transcend  the 
•zinc-platinum  couple. 

Since  it  is  a  sine  qua  mm  that  the  plates  used  in  a  battery  should  be  conductors 
of  electricity,  the  non-metals  with  a  few  exceptions  (the  most  notable  of  which  is 
€arbon)  are  put  out  of  court  for  this  purpose. 

It  is  necessary  to  add  that  the  total  amount  of  electrical  energy  is  made  up  of 
two  factors  ;  one  of  these  is  analogous  to  the  factor  expressed  by  the  specific  heat 
of  the  hot  body,  in  heat  energy,  and  is  generally  called  intensity  of  current; 
whilst  the  other  is  analogous  to  the  temperature  of  heat  energy,  and  is  generally 
•called  electromotive  force  or  pressure.  It  is  the  second  factor,  the  pressure, 
which  varies  with  the  nature  of  the  plates.  The  first  factor  is  dependent  upon 
the  amount  of  chemical  action,  just  as  the  number  of  units  of  heat  evolved  in  a 
•chemical  reaction  is  dependent  upon  the  amount  of  chemical  action. 

,  The  word  electrolysis  is  used  to  signify  the  decomposition  of  a  com- 
pound by  the  passage  through  it,  or  its  solution,  of  the  electric  current. 
Any  compound  which  can  be  thus  decomposed  is  termed  an  electrolyte, 
and  the  portions  into  which  it  is  decomposed  are  termed  ions.  An 
-electrolyte  must  be  a  compound,  but  all  compounds  are  not  electrolytes. 
Compounds  may  be  classified  with  regard  to  their  relation  to  the 
electric  current  into  (i)  conductors  which  are  not  electrolytes,  (2)  con- 
ductors which  are  electrolytes,  and  (3)  non-conductors. 

Electrolysis  is  effected  by  passing  the  current  through  the  electrolyte, 
most  conveniently  from  two  plates,  made  of  some  conductors  and  called 
electrodes.  The  plate  connected  with  the  less  attacked  metal  of  the 
battery  (e.g.,  Pt.)  is  regarded  as  the  one  by  which  the  electric  current 
enters  the  electrolyte,  and  is  called  the  anode  or  the  positive  electrode. 
The  other  plate,  attached  to  the  more  attacked  plate  of  the  battery,  is 

*  If  the  zinc  plate  be  badly  amalgamated  (p.  14)  the  impurities  in  it  will  develop  minor 
electric  currents,  causing  evolution  of  hydrogen  "  from  the  zinc,"  and  the  amount  of  electri- 
cal energy  thus  developed  will  be  unavailable  for  external  use,  and  will  be  directly  converted 
auto  heat. 


324  IONS. 

supposed  to  afford  an  exit  for  the  current,  and  is  called  the  cathode  or 
the  negative  electrode. 

The  electrolyte  is  always  split  up  into  two  chemically  equivalent  ions ; 
these  are  either  liberated  at  the  electrodes,  or  there  enter  into  reaction 
with  the  electrolytic  medium,  as  will  be  explained  below.  Ions  which 
are  liberated  at  the  anode  are  anions,  whilst  those  liberated  at  the 
cathode  are  cations.  Since  unlike  electricities  attract  each  other,  and 
the  anode  is  supposed  to  contain  positive  electricity,  the  anions  are 
electro-negative  elements  or  radicles ;  the  cations  are  the  electro-positive 
elements  or  radicles  (p.  15).  Attempts  are  made  to  catalogue  the 
elements  in  the  order  of  their  decreasing  electro-positiveness  ;  that  is,  in 
such  an  order,  that  if  a  compound  of  any  two  elements  be  submitted  to 
electrolysis,  the  one  which  comes  first  in  the  list  will  behave  as  the 
cation.  It  is  obvious  that  such  an  electro-chemical  list  must  differ 
according  to  the  conditions  of  the  electrolysis  (such  as  whether  the 
compound  be  present  in  an  acid  or  an  alkaline  electrolytic  medium,  &c.). 

In  nearly  all  cases,  however,  the  metals  precede  the  non-metals  in  these  lists,. 
and  when  the  list  is  drawn  up  with  reference  to  electrolysis  in  neutral  or  acid 
solution,  the  metals  follow  each  other  in  the  order  of  their  affinity  for  oxygen. 
From  what  was  stated  with  regard  to  the  use  of  metals  as  battery  plates,  it 
will  be  obvious  that  that  metal  which  has  least  affinity  for  oxygen,  and  is, 
therefore,  least  readily  attacked  by  acids,  will  generally  be  best  suited  for  the- 
resistant  plate  in  a  cell. 

The  ions  of  an  electrolyte  are  either  atoms  or  radicles  ;  thus,  when  an 
aqueous  solution  of  HC1  is  electrolysed,  the  ions  are  H  and  01,  these 
being  chemically  equivalent ;  the  H  atoms  move  towards  the  cathode, 
each  carrying  its  charge  of  positive  electricity,  the  Cl  atoms  move 
towards  the  anode,  each  carrying  its  negative  charge.  In  the  case  of 
an  aqueous  solution  of  K2SO4,  the  ions  are  K2  and  SO4,  these  being 
chemically  equivalent ;  each  K  atom  carries  one  positive  charge,  whilst 
the  SO4  radical  carries  two  negative  charges.  When  the  ions  reach 
the  electrodes  the  charges  (electrons)  are  neutralised,  and  the  ions  either 
appear  in  the  free  state  (when  the  atoms  immediately  combine  to- 
form  molecules),  or  they  react  with  the  water  or  with  the  electrode ;  in 
the  latter  case  the  final  products  of  the  electrolysis  will  be  the  products- 
of  these  reactions.  In  the  case  of  hydrochloric  acid  electrolysed  by 
carbon  electrodes,  molecules  of  hydrogen  and  chlorine  are  evolved.  In 
the  case  of  potassium  sulphate  electrolysed  with  carbon  or  platinum 
electrodes,  the  final  products  are  hydrogen  at  the  cathode  and  oxygen 
at  the  anode  ;  for  the  potassium  atoms,  so  soon  as  they  are  discharged 
at  the  cathode,  react  with  the  water  in  the  well-known  manner  pro- 
ducing 2KOH  and  H2,  whilst  the  S04,  when  it  is  discharged,  reacts 
with  the  water,  producing  H2SO4  and  O.  The  2KOH  and  H2S04  left 
in  solution  speedily  neutralise  each  other,  re-forming  potassium  sul- 
phate, the  total  quantity  of  which  thus  suffers  no  diminution  during 
the  electrolysis. 

It  will  now  be  realised  that  the  electrolysis  of  water  described  on 
p.  13  is  the  electrolysis  of  dilute  sulphuric  acid.  Water,  so  far  as'  i& 
known,  is  not  an  electrolyte  ;  when  dilute  sulphuric  acid  is  electrolysed, 
hydrogen  is  liberated  at  the  cathode  and  SO4  at  the  anode,  where  it  at 
once  reacts  with  the  water  to  form  H2S04  and  0. 

When  copper  sulphate  solution  is  electrolysed  with  platinum  elec- 


FARADAY'S   LAW.  325 

trodes,  the  ions  are  Cu"  and  SO4.  The  copper  is  deposited  on  the 
cathode  and  oxygen  is  evolved  at  the  anode,  owing  to  the  reaction 
between  discharged  SO4  and  water.  If  the  anode  be  made  of  some 
material  which  is  more  easily  attacked  by  S04  than  is  water,  this  will 
react  with  S04,  Thus,  a  copper  anode  will  be  dissolved  by  com- 
bining with  the  SO4,  and  the  quantity  of  copper  which  will  pass  into 
solution  will  be  exactly  equal  to  that  deposited  on  the  cathode ;  this 
fact  is  applied  in  the  process  of  electro-plating  (see  Silver). 

Faraday's  law  of  electrolysis  states  that  the  same  intensity  of  electric 
current  will  liberate  all  ions  in  the  proportion  of  their  chemical  equiva- 
lents. For  example,  if  the  same  current  of  electricity  be  passed 
through  electrolytic  cells  containing  sulphuric  acid  and  silver  nitrate 
respectively,  there  will  be  108  grams  of  silver  deposited  on  the  cathode 
of  the  one  cell  for  every  i  gram  of  hydrogen  liberated  at  the  cathode 
of  the  other  cell,  these  quantities  of  silver  and  hydrogen  being  chemi- 
cally equivalent.  So  also  there  will  be  48  grams  of  S04  discharged  at  the 
anode  of  the  one  cell,  and  62  grams  of  N03  at  the  anode  of  the  other 
cell. 

Since  some  elements  have  two  chemical  equivalents,  ions  composed 
of  them  will  have  two  electro-chemical  equivalents.  Thus,  copper  in 
cupric  chloride  has  an  electro-chemical  equivalent  of  31.5,  this  propor- 
tion being  deposited  for  every  i  part  of  hydrogen  evolved  in  a  sulphuric 
acid  cell ;  but  copper  in  cuprous  chloride  has  an  electro-chemical  equiva*- 
lent  of  63. 

The  converse  of  Faraday's  law  is  equally  true ;  that  is  to  say,  the 
chemical  change  of  chemically  equivalent  quantities  of  ions  gives  rise  to 
the  same  intensity  of  electric  current.  Thus,  in  a  galvanic  cell  the 
same  intensity  of  current  will  be  generated,  whether  32.5  parts  of  zinc 
or  28  parts  of  iron  be  dissolved  in  acid. 

The  intensity  of  electric  current  necessary  to  decompose  i  grain -equivalent  of 
any  electrolyte  is  96,540  units  (coitloinb*').  But  this  is  only  one  factor  of  the 
electrical  energy  required,  for  the  latter  is  the  product  of  the  intensity  of  current 
x  the  pressure  at  which  it  is  delivered.  The  pressure  necessary  for  electrolysing 
any  particular  electrolyte  depends  on  the  chemical  affinity  of  the  ions  for  each 
other.  If  now  the  heat  equivalent  to  this  chemical  affinity  be  known,  the  electrical 
energy  can  be  calculated,  because  i  unit  of  electrical  energy  (Joule)  is  equal  to  0.24 
gram-unit  of  heat.  The  joule  =  i  coulomb  x  i  volt  (the  unit  of  pressure).  Let  a 
be  the  heat  equivalent  to  the  affinity  between  i  gram  equivalent  of  each  of  the 
ions  ;  this  will  be  equal  to  a/o.24  joules.  But  the  intensity  of  current  necessary  to 
effect  the  electrolysis  is  96,540  coulombs,  so  that  the  electrical  energy  must  be  made 
up  of  96,540  coulombs  x  x  volts  ;  thus  the  equation  a  jo.  24  =  96540  x  a?  is  obtained, 
from  which  the  value  of  a1,  the  voltage  necessary  for  the  electrolysis,  may  be  calcu- 
lated. The  value  ascertained  in  this  manner  is,  of  course,  open  to  the  same 
uncertainty  as  that  which  surrounds  the  value  for  the  heat  equivalent  to  the 
affinity  (p.'  308). 

The  best  electrolytes  are  aqueous  solutions  of  powerful  acids  and 
bases,  and  of  salts.  Feeble  acids  are  poor  electrolytes.  Fused  salts  are 
generally  electrolytes.  It  is  necessary  to  refer  to  the  question  as  to 
what  constitutes  an  electrolyte. 

It  is  generally  stated  that  the  transmission  of  the  electrical  energy, 
commonly  called  the  electric  current,  can  occur  in  two  ways,  either  along 
matter  or  with  matter.  The  first  method  of  transference  happens  when 
electricity  is  conducted  by  a  metal ;  substances  which  are  able  to  effect 
such  a  transference  are  called  conductors  of  the  first  class.  The  second 


326  DEGREE   OF   IONISATION. 

method  is  that  which  obtains  in  electrolytes,  which  are  called  con- 
ductors of  the  second  class. 

These  facts  were  early  recognised,  but  it  was  at  first  thought  that 
the  electricity  obtained  the  matter  with  which  it  was  to  move  in  the 
electrolyte  by  tearing  asunder  the  molecules.  This,  however,  would  be 
inconsistent  with  the  fact  that  even  the  smallest  electrical  pressure  will 
exert  some  electrolysis.  It  has  only  recently  been  realised  that  the 
molecules  in  an  electrolyte  must  be  regarded  as  being  already  ionised, 
nearly  completely  in  dilute  solutions,  and  to  a  certain  extent  in  all 
electrolytes.  The  free  ions  exist  in  the  electrolytic  medium,  each  bear- 
ing its  charge  of  electricity.  It  is  this  charge  that  prevents  the  ion 
from  behaving  chemically  like  the  free  element  or  radicle,  and  it  is  only 
when  the  ion  has  been  conducted  to  the  electrode  by  the  electric  current, 
and  is  discharged,  that  it  exhibits  the  chemical  properties  expected  of  the 
free  element  or  radicle. 

That  this  view  of  the  constitution  of  an  electrolyte  is  correct  is 
evidenced  by  the  facts  concerning  the  conductivity  of  saline  solutions. 
If  the  passage  of  an  electric  current  through  an  electrolyte  depends 
upon  the  presence  of  ions,  a  saline  solution  should  offer  a  lower  resist- 
ance to  this  passage  the  more  perfect  the  ionisation  of  the  dissolved 
salt.  Hence  the  conductivity  of  a  dilute  solution,  in  which  ionisation 
is  more  perfect,  should  be  proportionally  better  than  that  of  one  which 
is  stronger,  and  therefore  less  ionised.  This  is  found  to  be  the  case  ;  as 
the  dilution  of  a  saline  solution  is  increased  the  conductivity  tends  to 
become  constant,  the  more  perfect  ionisation  compensating  for  the 
smaller  number  of  ultimate  particles  in  unit  volume. 

Judging  by  conductivity,  ionisation  appears  to  be  practically  complete  when 
one  gram-equivalent  of  a  salt  is  dissolved  in  1000  litres  of  water  ;  the  degree 
of  ionisation  at  any  other  dilution  is  equal  to  the  ratio  of  the  molecular  conduc- 
tivity (the  conductivity  calculated,  from  the  observed  value,  for  a  solution  con- 
taining i  gram-molecule  per  litre)  at  this  dilution  to  the  molecular  conductivity 
at  a  dilution  of  1000  litres.  This  statement  only  applies  to  good  electrolytes  ; 
poor  electrolytes  do  not  reach  a  constant  conductivity  at  any  dilution  at  which 
it  is  practicable  to  make  the  necessary  measurements. 

The  degree  of  ionisation  may  also  be  calculated  from  measurements  of  osmotic 
pressure,  for  this  is  proportional  to  the  ionisation.  If  N  be  the  number  of  ulti- 
mate particles  present  when  the  osmotic  pressure  is  P,  and  N1  the  number  when 
it  is  P1,  then  P:P1  =  N:N1.  The  number  of  ultimate  particles  present  at  any 
degree  of  ionisation  depends  on  the  nature  of  the  dissolved  substance  :  for  this 
may  split  up  into  n  ions  ;  in  the  case  of  H2S04,%  =  3  ;  in  the  case  of  K4FeCy6,fl  =  5. 
If  ionisation  were  complete,  the  original  number  of  molecules,  N,  would  become 
riN.  Let  a?  be  the  fraction  of  the  total  number  of  molecules  ionised,  then  i  -  x  will 
be  the  fraction  left  unionised.  The  total  number  of  unionised  molecules  will  be 
N(i  -  a?),  and  Na?  will  be  ionised.  But  N  x  molecules  become  riSsc  ions,  so  that  the 
total  number  of  ultimate  particles  in  the  ionised  solution  will  be  N(i  —  a?)  +  wNa?, 
and  this  is  the  value  of  N1  in  the  above  equation.  Therefore  P  :  P1  =  N:N(i  -  x)  + 

Whence  x  = 


It  is  found  in  many  cases  that  during  electrolysis  the  concentration  of  the  electro- 
lyte at  the  anode  (or  cathode)  becomes  greater  than  that  at  the  cathode  (or  anode). 
This  can  only  be  explained  by  assuming  that  the  anions  (or  cations)  move  faster 
through  the  liquid  than  the  cations  (or  anions)  do.  This  difference  in  the  rate  of 
migration  of  the  ions  is  also  indicated  by  the  fact  that  the  conductivity  of  solutions 
containing  equivalent  quantities  of  various  salts  which  are  ionised  in  the  same 
degree,  is  different.  When  a  solution  of  KC1  is  electrolysed,  the  concentration  at 
the  electrodes  remains  practically  the  same,  so  that  the  ions  of  K  and  Cl  move  at 
nearly  the  same  rate  ;  but  the  equivalent  conductivity  of  NaCl  solution  of  equiva- 


ELECTROLYTIC   DISSOCIATION.  327 

lent  strength  is  only  about  65  per  cent,  of  that  of  KC1  solution  ;  hence  the  sodium 
ion  must  migrate  at  only  65  per  cent,  of  the  speed  of  the  potassium  ion. 

It  is  supposed  that  those  solutions  which  are  not  electrolytes  contain 
no  ionised  molecules ;  thus,  sugar,  a  solution  of  which  is  not  an 
electrolyte,  does  not  suffer  ionisation  when  dissolved. 

The  solutions  of  all  substances  which  are  electrolytes  show  abnormal 
osmotic  pressures,  abnormal  depressions  of  the  freezing-point,  &c. ;  this 
supports  the  theory  that  many  salts,  acids  and  bases  are  dissociated 
when  they  are  dissolved.  It  must  be  remembered,  however,  that  the 
dissociation  is  always  into  ions,  and  not  necessarily  of  the  same  character 
as  the  dissociation  effected  by  heat. 

At  the  present  day  the  theory  of  ionisation  is  being  extensively 
adopted  as  affording  the  best  explanation  of  chemical  reactions  in 
solution.  The  analytical  tests  for  metals  and  acid  radicles  are  the 
reactions  of  the  ions ;  if  a  reaction  occurs  in  a  dilute  solution  which  will 
not  occur  in  a  strong  one  it  is  because  there  are  no  ions  in  the  strong 
solution,  the  salt  not  having  been  ionised  therein. 

From  what  has  been  said  above  on  the  physical  theory  of  solution  and  the 
evidence  in  support  of  it,  it  will  be  seen  that  a  solvent  has  an  effect  upon  a 
soluble  substance  which  may  be  well  compared  with  the  effect  of  heat  on  a 
volatile  substance.  Just  as  there  are  many  substances  which  resist  in  a  high 
degree  the  disgregating  action  of  heat,  so  there  are  many  which  resist  that  of 
solvents.  Equally  noteworthy  is  the  similarity  which  exists  between  the  influence 
of  solvents  and  of  heat  on  chemical  change  :  reactions  occur  between  substances 
in  solution  which  have  no  tendency  to  happen  between  the  solid  substances,  how- 
ever finely  these  may  be  divided,  and  however  intimately  they  may  be  mixed  ; 
so  also,  reactions  occur  at  an  elevated  temperature  which  are  impossible  at  low 
temperatures.  It  is  also  worth  while  to  call  attention  to  the  fact  that  the  presence 
of  the  best  solvent,  water,  will  enable  a  smaller  stress  to  convert  the  potential 
energy  of  a  mixture  into  the  kinetic  energy  represented  by  the  combination  of  its 
constituents  than  would  otherwise  be  the  case  ;  thus,  as  has  been  already  stated, 
a  mixture  of  carbon  monoxide  and  oxygen  requires  a  far  greater  stress  in  the 
form  of  high-pressure  heat  (high  temperature)  to  start  combination,  when  it  is 
perfectly  dry  than  when  moisture  is  present.  Many  cases  have  been  cited  in  which 
the  presence  of  water  enables  a  chemical  change  to  be  brought  about  by  heat  of 
moderate  temperature — e.g.,  the  combustion  of  carbon  (p.  32) ;  there  is  not  sufficient 
evidence  to  show  whether  or  not  the  stress  of  a  much  higher  temperature  will 
render  these  changes,  also,  independent  of  moisture. 

There  are,  however,  many  changes,  which  are  capable  of  occurring  at  the 
ordinary  temperature,  that  are  dependent  on  the  presence  of  water.  It  is  also  a 
fact  that  many  substances  which  are  excellent  electrolytes  when  dissolved  in 
water,  have  an  almost  infinite  electrical  resistance  when  anhydrous  ;  in  other 
words,  these  substances  require  the  presence  of  water  in  order  that  they  may 
become  partially  ionised.  On  the  basis  of  this  latter  observation  it  has  been 
suggested  that  an  electrolytic  medium,  that  is,  one  which  will  enable  ionisation 
to  occur,  is  essential  for  chemical  change  ;  on  this  hypothesis  the  fact  that  an- 
hydrous HC1  will  not  attack  calcium  oxide,  would  be  explained  by  stating  that  it 
is  only  the  ions  of  HC1  which  can  enter  into  reaction  with  CaO.  A  very  little 
water  should  suffice  for  the  reaction,  since  when  the  first  formed  ions  have  been 
removed  by  reaction  with  the  CaO,  further  ionisation  could  occur.  The  dis- 
covery of  some  other  third  substance  which  shall  have  a  similar  influence  to  that 
of  water  is  the  present  business  of  the  chemist.* 

As  a  final  word  on  this  subject,  attention  must  be  called  to  the  fact  that  high 
heat  pressure  and  high  electrical  pressure  are  not  alone  in  inducing  chemical 

*  A  tendency  to  return  to  the  old  view  that  chemical  energy  is  to  be  regarded  as  due  to  a 
difference  of  electrical  potential  between  elements,  seems  at  present  prevalent,  and  it  must 
be  admitted  that  support  for  such  a  view  is  derived  from  the  recent  observations  of  Baker, 
who  shows  that  when  electrodes,  carrying  high  pressure  electricity,  are  introduced  into  a 
mixture  of  hydrogen  and  oxygen,  sufficiently  dry  to  hinder  combination,  the  gas  around  the 
"  positive  "  electrode  is  richer  in  oxygen  than  that  around  the  opposite  electrode. 


328 


THE  SPECTROSCOPE. 


change  ;  it  has  been  shown  that  high  mechanical  pressure  is  in  many  cases  effec- 
tive (such  as  in  decomposing  moist  silver  chloride),  and  the  influence  of  another 
form  of  energy,  the  shorter  wave  lengths  of  light,  in  inducing  the  numerous 
changes  on  which  the  art  of  photography  depends,  is  well  known. 

Spectroscopy. — Heated  solids  have  their  molecules  vibrating  in  so 
many  phases  that  they  give  rise  to  waves  in  the  luminiferous  ether 
which  are  of  every  possible  wave  length  ;  consequently  a  heated  solid 
gives  a  continuous  spectrum  in  which  the  red  is  more  prominent  at 
lower  temperatures.  Heated  gases,  on  the  other  hand,  have  their 
molecules  vibrating  in  such  a  way  that  they  give  out  waves  of  com- 
paratively few  wave  lengths. 

By  passing  the  light  emitted  from  a  hot  gas  through  a  prism  the 
wave  lengths  are  separated  and  take  up  their  proper  positions  in  the 
spectrum — i.e.,  somewhere  in  the  violet,  indigo,  blue,  green,  yellow, 


Fig'.  204. — Spectroscope. 

orange,  red — in  accordance  with  the  length  of  the  wave  between  the 
limits  766  millionths  of  a  millimetre  for  red,  and  396  millionths  of  a 
millimetre  for  violet.  Of  all  the  wave  lengths  from  a  given  gas  a  few 
will  be  more  visible  than  the  rest ;  so  that  there  are  characteristic  lines 
in  the  spectrum  for  the  gas  of  each  element.  Thus,  heated  sodium 
vapour  gives  rise  to  two  very  prominent  wave  lengths  (589.5  and  588.9 
millionths  of  a  millimetre)  which  give  the  sensation  of  yellow  light. 

When  the  white  light  emanating  from  an  ordinary  flame  is  allowed 
to  pass  through  the  narrow  slit,  or  collimator,  of  a  spectroscope  (Fig.  204),* 

*  This  form  of  instrument  has  been  found  to  be  well  suited  to  the  general  work  required 
of  a  spectroscope  in  a  chemical  laboratory.  Either  one  or  two  prisms  can  be  used,  and  the 
central  table  is  arranged  so  as  to  take  the  levelling1  screws  of  a  reflection  grating.  The 
instrument  is  well  adapted  for  determination  of  refractive  indices  and  dispersive  powers. 


SPECTEUM   ANALYSIS. 


329 


.and  is  transmitted  through  a  prism  of  flint  glass,  a  continuous  spectrum 
composed  of  overlapping  images  of  the  slit  in  all  the  colours  which  make 
up  white  light  will  be  perceived  through  the  telescope ;  but  if  a  Bunsen 
flame  be  employed,  a  single  image  will  be  seen,  forming  a  bright  yellow 
line  in  the  place  where  the  brightest  yellow  was  seen  in  the  continuous 
spectrum  ;  this  line  is  due  to  the  presence  of  a  little  sodium  in  the 
flame,  from  the  dust  in  the  air,  and  it  becomes  very  intense  if  a  little 
sodium  chloride  be  held  in  the  flame  on  a  loop  of  platinum  wire.  By 
comparing  the  spectra  of  the  flames  containing  vapours  of  the  metals 
with  a  map  of  the  wave  lengths  in  the  solar  spectrum  (Fig.  205),  the 
exact  position  of  the  various  colours  may  be  noted,  and  thus,  if  several 
metals  are  present  in  the  same  flame,  they  may  still  be  distinguished  by 
the  colours  and  positions  of  their  bright  lines.  Thus,  if  a  mixture  of 
the  chlorides  of  potassium,  sodium,  and  lithium  be  taken  upon  a  loop  of 


Violet.       Indigo.          .Blue 


Green.  Yellnw.    Oranae.    Recb. 


Spectrum  furnished  by  a  solar  light  decomposed  by  a  prism. 


K           .        g  S 

«                                g                              S  A-          ,-  .R   1       1 

S                         B  §  £•*§ 

s                         f  'ji    \S    c            (5! 

g                    e  B       ^         ^ 

Slran/li 

s 

•li 

« 

K> 

s 

•i 
t» 

Pot  as  si 
Jluttdi 

Xct 


Coloured  bands  in  the  spectrum. 
Fig'.  205. 

platinum  wire  and  held  in  the  flame,  the  dull  red  line  of  potassium  (K, 
Fig.  205)  is  seen  close  to  one  end  of  the  spectrum ;  at  some  distance 
from  it  the  bright  red  band  (L)  of  lithium ;  at  about  the  same  distance 
from  this,  the  pale  yellow  lithium  line ;  and  close  to  this  the  bright 
yellow  sodium  lines  (Na) ;  whilst  near  the  other  end  of  the  spectrum  is 
the  feeble  violet  line  of  potassium  (k).  The  chlorides  of  the  metals  are 
most  suitable  for  this  experiment  on  account  of  their  volatility.  Since 
a  very  little  vapour  (for  instance,  Towo~o  mgm-)  can  be  detected  by  its 
characteristic  wave  lengths,  the  use  of  the  spectroscope  furnishes  an 
extremely  delicate  test  for  many  elements. 

The  character  of  the  spectrum  of  a  gas  differs  with  the  temperature 
and  pressure.  Increased  temperature  increases  its  complexity,  the 
bright  lines  becoming  more  numerous  and  broader.  The  same  effect 
is  produced  by  increased  pressure,  which  probably  increases  the 
collisions  between  the  molecules,  and  thus  gives  rise  to  a  larger  number 


330 


SPECTRA  OF  GASES. 


of  phases  of  vibration, 
continuous  spectrum. 


Thus,  H2  +  O  fired  in  a  closed  space  gives  a 


Hence  arises  the  custom  of  examining  the  spectrum  of  a  gas  at 
much  diminished  pressure  in  a  Geissler  tube  (Fig.  206).  This  consists 
of  a  tube  very  much  constricted  at  the  middle  part  of  its  length  and 
having  electrodes  of  aluminium  sealed  through  the  glass.  The  tube 
is  first  exhausted  by  the  air-pump,  and  then  a  small  quantity  of  the 
gas  to  be  examined,  sufficient  to  create  a  pressure  of  a  few  milli- 
metres, is  admitted.  The  electrodes  are  connected  with  the 
terminals  of  a  powerful  induction  coil,  and  the  spectroscope  is 
directed  to  the  constricted  part  of  the  tube  for  examination  of  the 
spectrum  of  the  gas. 

When  the  vapour  whose  spectrum  is  to  be  examined  is 
heated  by  contact  with  a  flame  (as  in  the  method  for 
obtaining  the  spectra  of  metallic  vapours  described  above), 
chemical  reactions  will  frequently  render  the  spectrum 


Fig.  206. 
Geissler  tube. 


Fig.  207. — Radiant  matter  bulb. 


different  from  that  observed  by  volatilising  the  substance  and  heating 
the  vapour  by  electric  sparks  (spark  spectrum).  Thus,  when  cupric 
chloride  is  introduced  into  the  Bunsen  flame,  the  reducing  action  of 


Fig.  208. — Air-pump. 


the  gases  causes  the  spectrum  to  contain  a  blue  line  due  to  cuprous 
chloride,  a  green  line  due  to  cuprous  oxide,  and  a  red  line  due  to 
copper,  together  with  the  other,  fainter  lines  characteristic  of  these 
vapours. 


ABSOKPTION  SPECTEA.  331 

A  gas  will  absorb  those  wave  lengths  from  the  spectrum  which  it  will 
itself  emit  when  heated.  Thus,  if  white  light  be  passed  through  sodium 
vapour  and  then  through  a  prism,  black  lines  in  the  position  of  wave 
lengths  589.5  and  588.9  millionths  of  a  millimetre  will  appear  in  the 
spectrum. 

The  black  lines  in  the  solar  spectrum  are  presumed  to  be  due  to  the 
light  passing  through  gaseous  elements  surrounding  the  sun.t  Such 
absorption  spectra  are  also  exhibited  by  some  solutions,  such  as  solutions 
of  didymium  salts,  of  blood  and  of  many  dyes.  Analytical  use  may  be 
made  of  these  for  identifying  the  substance  in  solution. 

Another  method  for  obtaining  a  characteristic  spectrum  is  to  expose 
the  substance  in  a  vacuous  glass  bulb  (Fig.  207)  to  a  high  pressure 
electrical  discharge  (from  an  induction  coil)  delivered  from  two  platinum 
electrodes,  attached  to  wires  of  the  same  metal  sealed  through  the  glass. 
Many  substances  phosphoresce  under  this  treatment,  and  when  the 
light  thus  emitted  is  viewed  through  a  spectroscope  it  exhibits  bright 
bands  which  serve  to  identify  the  substance.  A  pump  capable  of  cre- 
ating, in  a  very  short  time,  a  sufficiently  high  vacuum  for  the  observa- 
tion of  such  phosphorescence  is  shown  in  Fig.  208. 


CHEMISTRY  OF  THE  METALS. 


178.  The  definition  of  a  metal  has  already  been  given  at  p,  38,  as  an 
element  capable  of  forming  a  base  by  union  with  oxygen.     It  will  also  be 
noticed  that  the  metals  are  but  little  disposed  to  form  combinations  with 
hydrogen  ;  but  that  they  evince  very  powerful  attraction  for  the  chlorine 
group  of  elements,  with  which  they  form,  as  a  rule,  compounds  soluble, 
without  apparent  decomposition,  in  water. 

With  a  few  exceptions  the  metals  will  be  considered  in  the  same 
order  as  they  occur  in  the  families  of  the  periodic  grouping  of  the 
elements,  to  the  table  of  which  the  reader  must  refer  for  a  true  classifi- 
cation of  the  metals. 

POTASSIUM. 

K'  =  39.i  parts  by  weight. 

179.  Potassium   is  found  in  abundance,  as  potassium  chloride  and 
sulphate,  in  certain  salt-mines  (see  below),  and  is  contained  in  granite, 
of  which  it  forms  about   5   or   6   per  cent.     The  indispensable  alkali, 
potash,  appears  to  have  been  originally  derived  from  the  granite  rocks, 
where  it  exists,  in  combination  with  silica  and  alumina,  in  the  well- 
known  minerals  felspar  and  mica.     These  rocks  having,  in   course  of 
time,  disintegrated  to  form  soils  for  the  support  of  plants,  the  potash 
has  been  converted  into  a  soluble  state,  and  has  passed  into  the  plants 
as  a  necessary  portion  of  their  food. 

In  the  plant,  the  potash  is  found  to  have  entered  into  various  forms 
of  combination  ;  thus,  most  plants  contain  sulphate  and  chloride  of 
potassium  ;  but  the  greater  portion  of  the  potassium  exists  in  the  form 
of  salts  of  certain  vegetable  acids  formed  in  the  plant,  and  when  the 
latter  is  burnt,  these  salts  are  decomposed  by  the  heat,  leaving  the 
potassium  in  the  form  of  carbonate. 

Potassium  carbonate,  or  carbonate  of  potash,  K.,C03. — When  the 
ashes  of  plants  are  treated  with  water,  the  salts  of  potassium  are  dissolved, 
those  of  calcium  and  magnesium  being  left.  On  separating  the  aqueous 
solution  and  evaporating  it  to  a  certain  point,  a  great  deal  of  the 
potassium  sulphate,  being  much  less  soluble,  is  deposited,  and  the 
carbonate  remains  in  the  solution  ;  this  is  evaporated  to.  dryness,  when 
the  carbonate  is  left,  mixed  with  much  potassium  chloride,  and  some 
sulphate  ;  this  mixture  constitutes  the  substances  imported  from  America 
and  other  countries  where  wood  (containing  about  0.5  per  cent,  of 
K20)  is  abundant,  under  the  name  of  potashes,  which  are  much  in 
demand  for  the  manufacture  of  soap  and  glass.  When  further  purified, 


pOTAgIL 
OF 


3  are  sold;utUra*^e  name  of  pearlash,  but  this  is  still  far  from  being 
potassium  carbonate. 


these ; 
pure 

During  the  fermentation  of  the  grape-juice,  in  the  preparation  of  wine,  a  hard 
crystalline  substance  is  deposited,  which  is  known  in  commerce  by  the  name  of 
argol,  or,  when  purified,  as  cream  of  tartar.  The  chemical  name  of  this  salt  is 
bitartrate  of  potash  or  hydropotassium  tartrate,  for  it  is  derived  from  potash  and 
tartaric  acid,  a  vegetable  acid  having  the  composition  H2C4H406.  When  this  salt 
(KHC4H406)  is  heated,  it  leaves  potassium  carbonate  mixed  with  carbon ;  but  if 
the  heat  be  continued,  and  free  access  of  air  permitted,  the  carbon  will  be  entirely 
burnt  away,  and  potassium  carbonate  will  be  left  (salt  of  tartar). 

The  residue  left  after  the  sugar  has  been  extracted  from  the  sugar  beet  is  worked 
up  for  the  potassium  carbonate  it  contains  by  first  charring  it,  extracting  it  with 
water,  and  fractionally  crystallising  the  solution  obtained ;  the  sulphate  and 
chloride  of  potassium  crystallise  first,  leaving  the  K2C03  in  the  mother  liquor. 

The  fleeces  of  sheep  contain  about  50  per  cent,  of  fatty  matter  (suint  or  yolJt),  rich 
in  potassium  combined  with  an  organic  acid  ;  when  the  fleece  is  washed  with  waterr 
this  salt  is  dissolved  out,  and  on  evaporating  the  liquid  and  burning  the  residue 
this  is  converted  into  potassium  carbonate. 

Potassium  carbonate  is  also  made  from  potassium  sulphate  by  a  process  similar 
to  that  by  which  sodium  sulphate  is  converted  into  carbonate  (see  Alkali  Manu- 
facture). Potassium  chloride  is  converted  into  potassium  carbonate  by  heating 
it  under  pressure  with  magnesium  carbonate  and  CO2,  whereby  "the  salt 
KHMg(C03)24H2O  is  obtained  ;  when  this  is  heated  with  water  at  120°  C.  it  yields 
insoluble  MgC03  and  a  solution  of  K2C03  which  is  evaporated. 

Potassium  carbonate  is  deliquescent  and  soluble  in  its  own  weight  of 
cold  water,  yielding  a  strongly  alkaline  solution.  It  may  be  crystallised 
in  prisms  of  the  formula  2K2C03.3H20,  which  become  K2C03.H20  at 
1 00°  C.  It  is  insoluble  in  alcohol.  It  melts  at  830°  C. 

Bicarbonate  of  potash,  or  hydropotassium  carbonate,  KHC03,  often 
sold  as  the  carbonate  and  used  in  medicine,  is  made  by  saturating  moist 
K2C03  with  C02,  or  by  passing  C02  through  a  strong  solution  of  K2C03 
(in  three  parts  of  water).  It  forms  prismatic  crystals  which  are  much 
less  alkaline  and  less  soluble  in  water  (30.4  per  cent,  at  15°  C.)  than  is 
the  normal  carbonate,  into  which  they  are  converted  by  heat ;  2KHC03  = 
K2C03  +  H20  +  C02.  The  aqueous  solution  of  KHCO3  gradually  loses 
CO2  when  boiled. 

Caustic  potash,  or  potassium  hydroxide,  KOH. — Potassium  car- 
bonate was  formerly  called  potash,  and  was  supposed  to  be  an  elementary 
substance.  It  was  known  that  its  alkaline  qualities  were  rendered  far 
more  powerful  by  treating  it  with  lime,  which  caused  it  to  be  termed  mild 
alkali,  in  order  to  distinguish  it  from  the  caustic  alkali  obtained  by  means 
of  lime,  and  possessed  of  very  powerful  corrosive  properties. 

The  caustic  potash,  so  largely  employed  by  the  soap-maker,  is  obtained 
by  adding  slaked  lime  (Ca(OH)2)  to  a  boiling  solution  of  the  potassium 
carbonate,  in  not  less  than  12  parts  of  water,  when  calcium  carbonate  is 
deposited  at  the  bottom  of  the  vessel,  whilst  potassium  hydrate  remains 
in  the  clear  solution  ;  K2C03  +  Ca(OH)2  =  CaC03  +  2KOH. 

If  the  solution  be  too  strong,  the  lime  will  not  decompose  the  carbon- 
ate, for  the  reaction  is  reversible  (p.  309). 

When  the  solution  is  evaporated,  the  potassium  hydroxide  remains  as 
a  clear  oily  liquid,  which  solidifies  to  a  white  mass  as  it  cools,  and  forms 
the  fused  potash  of  commerce,  which  is  often  cast  into  cylindrical  sticks 
for  more  convenient  use.*  Potassium  hydroxide  is  vapourised  at  high 

*  These  have  sometimes  a  greenish  colour,  due  to  the  presence  of  some  potassium 
manganate. 


334  POTASSIUM. 

temperatures  without  decomposition.  It  readily  absorbs  water  and  C02 
from  the  air.  Half  its  weight  of  water  suffices  to  dissolve  it,  with  great 
evolution  of  heat.  A  strong  solution  deposits  crystals  of  KOH.2Aq. 
Alcohol  dissolves  it  easily.  The  potassium  hydroxide  is  the  most 
powerful  alkaline  substance  in  ordinary  use,  and  is  much  used  by  the 
chemist,  generally  in  the  state  of  solution,  the  strength  of  which  is 
inferred  from  its  specific  gravity,  which  increases  with  the  amount  of 
potash  contained  in  the  solution. 

Potassium.  —  Of  the  composition  of  potassium  hydroxide  nothing 
was  known  till  the  year  1807,  when  Davy  succeeded  in  decomposing  it  by 
the  galvanic  battery  ;  this  experiment,  which  deserves  particular  notice 
as  being  the  first  of  a  series  resulting  in  the  discovery  of  so  many 
important  metals,  was  made  in  the  following  manner  :  A  fragment  of 
potassium  hydroxide,  which,  in  its  dry  state,  does  not  conduct  elec- 
tricity, was  allowed  to  become  slightly  moist  by  exposure  to  the  air,  and 
placed  upon  a  plate  of  platinum  attached  to  the  copper  end  of  a  very 
powerful  galvanic  battery  ;  when  the  wire  connected  with  the  zinc  end 
was  made  to  touch  the  surface  of  the  hydrate,  some  small  metallic 
globules  resembling  mercury  made  their  appearance  at  the  extremity  of 
this  (negative)  wire,  at  which  the  hydrogen  contained  in  the  hydroxide 
was  also  eliminated,  whilst  bubbles  of  oxygen  were  separated  on  the 
surface  of  the  platinum  plate  connected  with  the  positive  wire  (see 
p.  324).  By  allowing  the  negative  wire  to  dip  into  a  little  mercury 
contained  in  a  cavity  at  the  surface  of  the  potash,  a  combination  of 
potassium  with  mercury  was  obtained,  and  the  mercury  was  afterwards 
separated  by  distillation.  This  process,  however,  furnished  the  metal  in 
very  small  quantities,  and,  though  it  was  obtained  with  greater  facility 
a  year  or  two  afterwards  by  decomposing  potassium  hydroxide  with 
white-hot  iron,  some  years  elapsed  before  any  considerable  quantity  of 
potassium  was  prepared  by  the  present  method  of  distilling  in  an  iron 
retort  an  intimate  mixture  of  potassium  carbonate  and  carbon,  obtained 
by  calcining  cream  of  tartar  ;  in  this  process  the  oxygen  of  the  carbonate 
is  removed  by  the  carbon  in  the  form  of  carbonic  oxide  (K2C03  +  C2  = 


The  metal  thus  prepared  requires  re-distillation  in  order  to  decompose 
the  explosive  compound  of  potassium  with  carbon  monoxide,  K6(CO)6, 
which  it  always  contains. 

Some  of  the  most  striking  properties  of  this  metal  have  already  been 
referred  to  (p.  16);  its  softness,  causing  it  to  be  easily  cut  like  wax,  the 
rapidity  with  which  its  silvery  surface  tarnishes  when  exposed  to  the 
air,  its  great  lightness  (sp.  gr.  0.865),  causing  it  to  float  upon  water, 
and  its  taking  fire  when  in  contact  with  that  liquid,  sufficiently  distin- 
guish it  from  other  metals.  It  fuses  at  62°.  5  C.  and  boils  at  a  low  red 
heat  (667°  C.),  yielding  a  green  vapour;  if  air  be  present,  it  burns  with 
a  violet-coloured  flame,  the  oxide  K204  being  the  chief  product.  In 
dry  air  or  oxygen  the  metal  may  be  distilled  unchanged. 

The  property  of  burning  with  this  peculiar  violet-coloured  flame  is 
characteristic  of  potassium,  and  allows  it  to  be  recognised  in  its  com- 
pounds. 

If  a  solution  of  potassium  nitrate  (saltpetre)  in  water  be  mixed  with  enough 
spirit  of  wine  to  allow  of  its  being  inflamed,  the  flame  will  have  a  peculiar  lilac 
colour.  This  colour  may  also  be  developed  by  exposing  a  very  minute  particle  of 


POTASSIUM  SALTS.  335 

saltpetre,  taken  on  the  end  of  a  heated  platinum  wire,  to  the  reducing  (inner) 
blowpipe  flame  (Fig.  209),  when  the  potassium,  being  reduced  to  the  metallic 
state  and  passing  into  the  oxidising  (outer)  flame  in  the  state  of  vapour,  imparts 
to  that  flame  a  lilac  tinge. 

The  difficulty  and  expense  attending  the  preparation  of  potassium 
have  prevented  its  receiving  any  application  except  in  purely  chemical 


Fig.  209. — Coloured  flame  test. 

operations,  where  its  attraction  for  oxygen,  chlorine,  and  other  electro- 
negative elements  is  often  turned  to  account. 

Potassium  hydride,  K2H,  is  formed  when  potassium  is  heated  in  hydrogen  to 
about  350°  C.  It  forms  a  silvery  brittle  mass,  which  takes  fire  in  air  and  is 
dissociated  in  a  vacuum  at  200°  C. 

Oxides  of  Potassium. — K20,  is  alleged  to  be  formed  when  K  is  heated  with  KOH, 
H  being  expelled,  but  the  evidence  as  to  the  existence  of  this  oxide  is  very  poor. 
Potassium  tetroxide,  K204,  is  the  yellow  powder  obtained  when  the  metal  is  heated 
in  air  or  oxygen.  It  is  decomposed  by  water  yielding  the  dioxide,  K202,  and 
•evolving  0.  By  heating  potassium  in  a  limited  supply  of  nitrous  oxide,  the 
trioxide,  K203,  is  formed  as  a  buff  powder. 

Potassium  chloride  (KC1)  is  an  important  natural  source  of  this 
metal,  occurring  in  combination  with  magnesium  chloride  as  the  mineral 
carnallite  (KCl.MgCl2.6H2O),  an  immense  saline  deposit  overlying  the 
rock-salt  in  the  salt-mines  of  Stassfurt,  in  Saxony.  Carnallite  re- 
sembles rock-salt  in  appearance,  but  is  very  deliquescent.  It  yields  a 
magma  of  KC1  crystals  when  treated  with  water  ;  this  is  re-crystallised. 
Potassium  chloride  crystallises  in  anhydrous  cubes ;  it  is  very  soluble  in 
water  and  insoluble  in  alcohol ;  it  melts  at  734°  C.  By  melting  KC1 
with  potassium  a  blue  subchloride  K,C1  is  alleged  to  be  obtained  ;  it 
decomposes  water  evolving  H. 

Potassium  chlorate,  KC103,  is  prepared  as  described  at  page  185. 
It  is  also  made  by  electrolysing  a  solution  of  KC1,  but  the  methods  are 
kept  secret ;  the  principle  underlying  them  is  noticed  in  the  section  on 
soda.  It  crystallises  in  four-sided  tables,  soluble  in  16  parts  of  cold  and 
2  parts  of  boiling  water.  It  fuses  at  360°  C.,  and  is  decomposed  at  400°, 
when  it  gives  off  oxygen,  and  leaves,  at  first,  a  mixture  of  chloride  and 
perchlorate,  and  lastly  chloride  only  ;  2KC103  =  KC104  +  KC1  +  O2.  Its 
action  on  combustible  bodies  and  consequent  useful  applications  have 
been  described  at  p.  186. 

Potassium  perchlorate,  KC104,  is  remarkable  for  its  sparing  solubility,  for  it 
requires  70  parts  of  cold  water  to  dissolve  it.  It  is  prepared  by  heating  KC1O3 
until  1 2  grams  have  evolved  a  litre  of  oxygen,  as  shown  in  the  above  equation ;  the 
mass  is  boiled  with  just  enough  water  to  dissolve  it,  and  the  solution,  on  cooling, 


POTASSIUM   SALTS. 

deposits  crystals  of  KC104,  leaving  the  KC1  in  solution.     The  perchlorate  is  decom- 
posed above  400°  C.  into  KC1  and  04. 

Potassium  bromide,  KBr  (in.  p.  699°  C.),  forms  cubical  crystals  very  soluble  in 
water. 

Potassium  iodide,  KI,  is  prepared  by  adding  iodine  in  small  quanti- 
ties to  solution  of  potash  till  it  is  coloured  slightly  brown,  when  a 
mixture  of  potassium  iodide  and  iodate  is  obtained ;  6KOH  + 16  = 
KIO3  +  5KI  +  3H20.  The  solution  is  evaporated  to  dryness,  the  residue 
mixed  with  one-tenth  of  its  weight  of  powdered  charcoal,  thrown  in 
small  quantities  into  a  red-hot  iron  crucible  and  fused ;  KIO3  +  C3  = 
KI  +  3CO.  The  fused  mass  is  dissolved  in  hot  water,  filtered,  evapor- 
ated till  a  film  appears  upon  the  surface,  and  set  aside  to  crystallise. 
It  is  also  made  by  digesting  iron  filings  with  iodine  and  water,  and 
decomposing  the  solution  of  ferrous  iodide,  which  is  formed,  with  potas- 
sium ca,rbonate. 

Potassium  iodide  forms  cubical  crystals  very  soluble  in  water,  but 
sparingly  soluble  in  alcohol.  It  is  of  the  greatest  importance  in 
medicine,  in  chemical  analysis,  and  in  photography.  It  melts  at 
634°  C. 

Potassium  tri-iodide,  KI3,  obtained  by  saturating  potassium  iodide  with  iodine 
and  evaporating  over  sulphuric  acid,  forms  dark  brown  needles  with  a  metallic 
lustre,  very  deliquescent,  and  easily  decomposed  into  KI  and  I2. 

Potassium  iodate,  KIO8,  is  useful  in  testing  for  S02,  and  may  be  prepared  for 
that  purpose  by  mixing  50  grains  of  iodine  with  an  equal  weight  of  potassium 
chlorate  in  fine  powder,  adding,  in  a  flask,  about  half  a  measured  ounce  of  nitric 
acid,  and  digesting  till  the  colour  disappears.  The  liquid  is  then  boiled  for  a 
minute,  poured  into  a  dish,  evaporated  to  dryness,  and  moderately  heated,  when 
it  leaves  a  mixture  of  potassium  iodate  and  a  little  potassium  chloride  which 
may  be  dissolved  in  water.  S02  at  once  liberates  iodine  from  it,  which  gives  a 
blue  colour  to  starch. 

Potassium  fluoride,  KF  (m.  p.  789°  C.),  is  prepared  by  neutralising  HF  with 
K2C03.  Crystallised  by  slow  evaporation  of  a  cold  solution,  it  gives  KF.2H2Or 
but  above  35°  C.  it  yields  cubes  of  KF.  It  is  deliquescent  and  easily  soluble  ;  the 
solution  corrodes  glass.  It  combines  with  HF,  forming  KF.FH,  which  is  employed 
for  the  preparation  of  pure  HF. 

Potassium  sulphide,  K2S,  is  obtained  as  a  red  crystalline  mass  by  heating  K2S04 
in  hydrogen.  Solution  of  K2S  is  prepared  by  saturating  solution  of  KOH  with 
H2S,  and  adding  an  equal  quantity  of  KOH.  From  the  solution,  colourless 
crystals  of  K2S.5H20  may  be  obtained  ;  they  deliquesce  in  air  and  are  decomposed 
by  the  C02  therein  with  evolution  of  H2S. 

Potassium  hydrogen  sulphide,  KSH,  maybe  formed  by  saturating  a  strong  solution 
of  KOH  with  H2S  and  evaporating  in  vacuo,  when  colourless  deliquescent  crystals, 
2KSH.H20,  separate.  On  exposure  to  air  the  solution  of  KHS  evolves  H2S  owing 
to  the  action  of  C02  ;  if  the  air  be  free  from  C02  the  solution  is  oxidised  to  potas- 
sium thiosulphate,  K2S203. 

Potassium  sulphate,  K2S04,  is  found  in  certain  salt-mines,  in  the 
mineral  kainit,  K2S04.MgSO4.MgCl2.6Aq.  This  is  decomposed  by  adding 
KC1,  whereupon  all  the  MgS04  becomes  Mg012,  and  crystallising  from 
water  when  the  K2S04  crystallises,  on  cooling,  in  rhombic  prisms  which 
are  rather  sparingly  soluble  in  cold  water  (10  parts),  but  easily  in 
boiling  water  (4  parts).  It  is  also  obtained  as  a  by-product  in  some 
chemical  manufactures,  and  is  used  in  making  alum.  It  melts  at  1066°  C. 
Kainit  is  largely  used  as  an  artificial  manure. 

Bisulphate  of  potash,  or  hydrogen-potassium  sulphate,  KHSO4,  is 
obtained  as  the  residue  in  the  preparation  of  nitric  acid  from  saltpetre. 
It  is  more  fusible  and  more  soluble  in  water  than  the  normal  sulphate 


SALTPETRE. 


337 


is.  Its  solution  is  strongly  acid.  Much  water  decomposes  it  into  sul- 
phuric acid  and  K2S04.  When  heated,  it  undergoes  decomposition  in 
two  stages:  (i)  2KHS04--H20  +  K2S207  (pyrosulphate  or  anhydro- 
sulphate);  (2)  K2S2O7  =  K2SO4  +  S03.  This  evolution  of  SO3  makes  the 
bisulphate  very  useful  in  chemical  operations  for  decomposing  minerals 
at  high  temperatures. 

Potassium  nitrate  (KN03),  or  saltpetre,  is  found  in  India,  especially 
in  Bengal  and  Oude,  and  other  hot  climates,  where  it  sometimes  appears 
in  the  dry  season  as  a  white  incrustation  on  the  surface  of  the  soil,  and 
is  sometimes  mixed  with  the  soil  to  some  depth.  The  nitre  is  extracted 
from  the  earth  by  treating  it  with  water,  and  the  solution  is  evaporated, 
at  first  by  the  heat  of  the  sun,  and  afterwards  by  artificial  heat,  when 
the  impure  crystals  are  obtained,  which  are  packed  in  bags  and  sent  to 
this  country  as  grough  (or  impure)  saltpetre.  It  contains  a  quantity  of 
extraneous  matter  varying  from  i  to  10  per  cent.,  and  consisting  of  the 
chlorides  of  potassium  and  sodium,  sulphates  of  potassium,  sodium,  and 
calcium,  vegetable  matter  from  the  soil,  sand,  and  moisture.  The 
number  representing  the  percentage  of  impurity  present  is  usually 
termed  the  refraction  of  the  nitre,  in  allusion  to  the  old  method  of 
estimating  it  by  casting  the  melted  nitre  into  a  cake  and  examining  its 
fracture,  the  appearance  of  which  varies  according  to  the  amount  of 
foreign  matter  present. 

Potassium  nitrate  is  also  made  by  decomposing  sodium  nitrate  with 
potassium  chloride. 

In  order  to  understand  this  decomposition,  it  is  necessary  to  be  acquainted  with 
the  solubility  of  these  salts  and  of  those  produced  by  exchange  of  their  elements. 


TOO  parts  of  boiling  water  dissolve 

1 80  parts  of  sodium  nitrate 
57         „       potassium  chloride 

240         „       potassium  nitrate 
37         „       sodium  chloride 


100  parts  of  cold  water  dissolve 

80  parts  of  sodium  nitrate 
28        ,,       potassium  chloride 
30        „       potassium  nitrate 
36         ,,       sodium  chloride 


It  is  a  general  rule  that  when  two  salts  in  solution  are  mixed,  which  are  capable 
of  forming,  by  exchange  of  their  metals,  a  salt  which  is  less  soluble  in  the  liquid, 
that  salt  will  be  produced  and  separated. 

Thus,  when  sodium  nitrate  and  potassium  chloride  are  mixed,  and  the  solution 
boiled  down,  sodium  chloride  is  deposited,  and  potassium  nitrate  remains  in  the 
boiling  liquid  ;  NaN03  +  KCl  =  KNO3  +  NaCl.  When  this  is  allowed  to  cool,  the 
greater  part  of  the  potassium  nitrate  crystallises,  leaving  the  remainder  of  the 
sodium  chloride  in  solution. 

The  method  usually  adopted  is  to  add  the  potassium  chloride  by  degrees  to  the 
boiling  solution  of  sodium  nitrate,  to  remove  the  sodium  chloride  with  a  perforated 
ladle  in  proportion  as  it  is  deposited,  and  after  allowing  the  liquid  to  rest  for  some 
time  to  deposit  suspended  impurities,  to  run  it  out  into  the  crystallising  pans. 

Potassium  nitrate  was  at  one  time  prepared  from  the  nitrates  obtained  in  nitre- 
heaps,  which  consist  of  accumulations  of  vegetable  and  animal  refuse,  with 
limestone,  old  mortar,  ashes,  &c.  These  heaps  are  constructed  upon  an  imper- 
meable clay  floor  under  a  shed  to  protect  them  from  rain.  One  side  of  the  heap 
is  usually  vertical  and  exposed  to  the  prevailing  wind,  the  other  side  being  cut 
into  steps  or  terraces.  They  are  occasionally  moistened  with  stable  drainings, 
which  are  allowed  to  run  into  grooves  cut  in  the  steps  at  the  back  of  the  heap. 
In  such  a  mass,  at  an  atmospheric  temperature  between  60°  and  70°  F.,  nitrates 
of  the  various  metals  present  in  the  heap  are  slowly  formed,  and,  being  dissolved 
by  the  moisture,  are  left  by  it,  as  it  evaporates  on  the  vertical  side,  in  the  form  of 
an  efflorescence.  When  this  has  accumulated  in  sufficient  quantity,  it  is  scraped 
off,  together  with  a  few  inches  of  the  nitrified  earth,  and  extracted  with  water, 
which  dissolves  the  nitrates,  whilst  the  undissolved  earth  is  built  up  again  on 


338 


PUEIFICATION   OF   NITRE. 


the  terraced  back  of  the  heap.  After  two  or  three  years  the  heap  is  entirely 
broken  up  and  reconstructed.  The  principal  nitrates  which  are  found  dissolved 
in  the  water  are  those  of  potassium,  calcium,  magnesium  and  ammonium,  the- 
three  last  of  which  may  be  converted  into  potassium  nitrate  by  decomposing  them 
with  potassium  carbonate. 

The  formation  of  nitrates  in  these  heaps  is  probably  the  result  of  chemical 
changes  similar  to  those  which  occur  in  the  soils  in  which  nitre  is  naturally  formed, 
the  nitrates  being  produced  by  the  oxidation,  under  the  influence  of  the  nitrifying 
organism  (p.  88),  of  ammonia  (page  88)  evolved  by  the  putrefaction  of  the  nitro- 
genised  matters  which  the  heaps  contain.  The  oxidation  is  much  promoted  by 
the  presence  of  the  strongly  alkaline  lime  and  of  the  porous  materials  capable  of 
absorbing  ammonia  and  presenting  it  under  circumstances  favourable  to  oxidation. 

In  refining  saltpetre  for  the  manufacture  of  gunpowder,  the  impure 
(grough)  salt  is  dissolved  in  about  an  equal  weight  of  boiling  water  in  a 
copper  boiler,  the  solution  run  through  cloth  niters 
to  remove  insoluble  matter,  and  allowed  to  crystal- 
lise in  a  shallow  wooden  trough  lined  with  copper,, 
the  bottom  of  which  is  formed  of  two  inclined  planes- 
(Fig.  210).  Whilst  cooling,  the  solution  is  kept  in 
continual  agitation  with  wooden  stirrers,  in  order 
that  the  saltpetre  may  be  deposited  in  the  minute 
crystals  known  as  saltpetre  flour,  and  not  in  the 
large  prisms  which  are  formed  when  the  solution  is 
allowed  to  crystallise  tranquilly,  and  which  contain 
within  them  cavities  enclosing  some  of  the  impure 
liquor  from  which  the  saltpetre  has  been  crystallised. 

The  saltpetre,  being  so  much  less  soluble  in  cold  than  in. 
hot  water,  is,  in  great  part,  deposited  as  the  liquid  cools,, 
whilst  the  chlorides  and  other  impurities,  being  present  in 


Fig-.  210. 


small  proportion,  and  not  presenting  the  same  disparity  in  their  solubility  at 
different  temperatures,  are  retained  in  the  liquid.  The  saltpetre  flour  is  drained 
and  washed  with  two  or  three  successive  small  quantities  of  water  ;  it  is  then 
allowed  to  drain  thoroughly,  and  in  that  state,  containing  from  3  to  6  per  cent,  of 
water,  according  to  the  season,  is  ready  to  be  transferred  to  the  incorporating  mill 
or  to  a  hot-air  oven,  wrhere  it  is  dried  if  not  required  for  immediate  use. 

The  impurities  most  objectionable  in  saltpetre  for  gunpowder  are 
KC1  and  NaCl,  which  absorb  moisture  from  the  air.  Potassium  per- 
chlorate,  KC104,  is  also  liable  to  be  present  in  the  saltpetre,  and  is  said 
to  have  led  to  spontaneous  explosion  of  powder  made  with  such  salt- 
petre. 

Potassium  nitrate  is  usually  distinguishable  by  the  long  striated  or 
grooved  six-sided  prismatic  form  in  which  it  crystallises  (though  it  may 
also  be  obtained  in  rhoinbohedral  crystals  like  those  of  sodium  nitrate), 
and  by  the  deflagration  which  it  produces  when  thrown  on  red-hot 
coals.  Its  solubility  in  water  has  been  given  at  p.  337.  It  is  insoluble 
in  alcohol.  It  fuses  at  339°  C.  to  a  colourless  liquid,  which  solidifies  on 
cooling  to  a  translucent  brittle  crystalline  mass.  The  sal  prunelle  of 
the  shops  consists  of  nitre  which  has  been  fused  and  cast  into  balls. 
At  a  red  heat  it  effervesces  from  the  escape  of  bubbles  of  oxygen,  and 
is  converted  into  potassium  nitrite  (KN02),  which  is  itself  decomposed 
by  a  higher  temperature,  evolving  nitrogen  and  oxygen,  and  leaving  a 
mixture  of  potassium  oxides.  The  fused  salt  attacks  all  oxidisable 
bodies  and  the  potassium  oxide  attacks  siliceous  bodies,  so  that  it  is 
difficult  to  find  a  vessel  capable  of  resisting  it  at  a  high  temperature. 
Platinum  gives  way,  but  gold  is  less  corroded.  In  contact  with  any 


COMPOSITION  OF  GUNPOWDER.  339 

combustible  body,  it  undergoes  decomposition  with  great  rapidity,  five- 
sixths  of  its  oxygen  being  available  for  the  oxidation  of  the  combustible 
substance,  and  the  nitrogen  being  evolved  in  a  free  state  ;  thus,  in  con- 
tact with  carbon,  the  complete  decomposition  of  the  nitre  may  be  repre- 
sented by  the  equation  2KNO3  +  03  =  K2C03  +  C02  +  CO  +  N2.  Since 
the  combustion  of  a  large  quantity  of  material  may  be  thus  effected  in 
a  very  small  space  and  in  a  short  time,  the  temperature  produced  is 
much  higher  than  that  obtained  by  burning  the  combustible  in  the 
ordinary  way. 

The  specific  gravity  of  saltpetre  is  2.07,  so  that  i  c.c.  weighs  2.07  grams.  Since 
202  grams  (2  molecules)  of  nitre  contain  80  grams  (5  atoms)  of  oxygen  available 
for  the  oxidation  of  combustible  bodies,  2.07  grams'(or  I  c.c.  of  nitre)  would  contain 
0.8  gram  (or  555  c.c.)  of  available  oxygen,  a  volume  which  would  be  contained  in 
about  2700  c.c.  of  air  ;  hence,  i  volume  of  saltpetre  represents,  in  its  power  of 
supporting  combustion,  2700  volumes  of  atmospheric  air.  It  also  enables  some 
combustible  substances  to  burn  without  actual  flame,  as  is  exemplified  by  its  use  in 
touchpaper  or  slow  portfire,  which  consists  of  paper  soaked  in  a  weak  solution  of 
saltpetre  and  dried,  the  combustion  taking  place  between  the  solid  combustible 
and  the  solid  oxygen  in  the  nitre  instead  of  between  gases  as  in  the  case  of 
flame. 

If  a  continuous  design  be  traced  on  foolscap  paper  with  a  brush  dipped  in  a 
solution  of  30  grams  of  saltpetre  in  100  grams  of  water,  and  allowed  to  dry,  it 
will  be  found  that  when  one  part  of  the  pattern  is  touched  with  a  red-hot  iron  it 
will  gradually  burn  its  way  out,  the  other  portion  of  the  paper  remaining 
unaffected.  A  mixture  of  6  grams  of  KN03,  2  of  sulphur,  and  2  of  moderately 
fine  dried  sawdust  (Baum&sflua;)  will  deflagrate  with  sufficient  intensity  to  fuse  a 
small  silver  coin  into  a  globule  ;  the  mixture  may  be  pressed  down  in  a  walnut- 
shell  or  a  small  porcelain  crucible,  and  the  coin  buried  in  it,  the  flame  of  a  lamp 
being  applied  outside  until  deflagration  commences. 

Pulvis  fulminam  (white  gunpowder)  is  a  mixture  of  3  parts  of  KN03,  i  part  of 
sulphur,  and  2  of  K2C03,  all  carefully  dried  ;  when  it  is  heated  on  an  iron  plate 
no  action  occurs  till  it  melts,  when  it  explodes  very  violently.* 

Gunpowder  is  a  very  intimate  mixture  of  saltpetre,  sulphur,  and 
charcoal,  which  do  not  act  upon  each  other  at  the  ordinary  temperature, 
but,  when  heated  together,  arrange  themselves  into  new  forms,  evolving 
a  very  large  amount  of  gas. 

The  great  attention  that  has  been  paid  to  the  manufacture  of  gun- 
powder is  due  to  the  fact  that  until  recently  it  was  the  sole  explosive 
available  for  warfare.  Now,  however,  it  may  be  said  to  be  displaced 
by  the  various  forms  of  "smokeless  powders"  which  are  all  products  of 
nitration  (p.  94)  of  organic  substances.  Gunpowder  is  now  made  almost 
solely  for  use  as  a  blasting  explosive  for  mining. 

The  proportions  of  the  ingredients  of  gunpowder  have  been  varied 
somewhat  in  different  countries,  the  saltpetre  ranging  from  74  to  77 
per  cent.,  the  charcoal  from  12  to  16  per  cent.,  and  the  sulphur  from 
9  to  12.5  per  cent.  English  military  powder  contains  75  per  cent,  of 
nitre,  15  per  cent,  of  charcoal,  and  10  per  cent,  of  sulphur.  Mining 
powder  contains  about  67  per  cent,  of  nitre,  19  per  cent,  of  charcoal, 
and  14  per  cent,  of  sulphur. 

The  powdered  ingredients  f  are  first  roughly  mixed  in  a  revolving  gun-metal 
drum,  with  mixing  arms  turning  in  an  opposite  direction,  and  the  mixture  is 
subjected,  in  quantities  of  about  50  Ibs  at  a  time,  to  the  action  of  the  incorporating  mill 


*  Probably  2KNO3  +  K2CO3  +  S2=K2SO4  +  K2S  +  CO2  +  NO  +  NO2.  The  XO  and  NO2 
would  probably  be  decomposed  into  their  elements  by  the  high  temperature  attained. 

t  The  amount  of  water  in  the  moist  saltpetre  (p.  338)  is  ascertained  by  drying  and  melt- 
ing a  weighed  sample  before  the  proportions  are  weighed  out. 


340  MANUFACTURE  OF  GUNPOWDER. 

(Fig.  21 1),  where  it  is  sprinkled  with  water,  poured  through  the  funnel  (F),  or  from 
a  can  with  a  fine  rose,  and  exposed  to  trituration  and  pressure  under  two  cast-iron 
edge-runners  (B),  rolling  in  different  circular  paths  upon  a  cast-iron  bed,  a  very 
intimate  mixture  being  thus  effected  by  the  same  kind  of  movement  as  in  a 
-Common  pestle  and  mortar,  the  distribution  of  the  nitre  through  the  mass  being 
"also  assisted  by  its  solubility  in  water.  A  wooden  scraper  (C)  tipped  with  copper- 
prevents  the  roller  from  getting  clogged,  and  a  plough  (D)  keeps  the  mixture  in 
the  path.  Of  course,  the  water  employed  to  moisten  the  powder  must  be  as  free 
from  deliquescent  salts  (especially  chlorides,  see  page  338)  as  possible  ;  at  Waltham, 
•condensed  steam  is  employed  :  the  quantity  required  varies  with  the  state  of  the 

atmosphere.  The  duration  of  the  incor- 
porating process  is  varied  according  to  the 
kind  of  powder  required,  the  slow-burning 
powder  employed  for  cannon  being  suffi- 
ciently incorporated  in  about  three  hours, 
whilst  rifle-powder  requires  five  hours. 

The  dark  grey  mass  of  mill-cake  which 
is  thus  produced  contains  2  or  3  per  cent, 
of  water.  It  is  broken  up  by  passing 
between  grooved  1'ollers  of  gun-metal,  and 
is  then  placed,  in  layers  of  about  half  an 
inch  thick,  between  copper  plates  packed 
in  a  stout  gun-metal  box  lined  inside  and 
outside  with  wood,  in  which  it  is  subjected 
for  a  quarter  of  an  hour  to  a  pressure  of 
about  70  tons  on  the  square  foot,  in  a 
hydraulic  press,  which  has  the  effect  of 
condensing  a  larger  quantity  of  explosive 
Fig.  2ii.— Incorporating  mill.  material  into  a  given  volume,  and  of  di- 

minishing the  tendency  of  the  powder  to 

absorb  moisture  from  the  air,  and  to  disintegrate  or  dust  after  granulation.  The 
press-cake  thus  obtained  is  very  hard -and  compact,  resembling  slate  in  appearance. 
As  far  as  its  chemical  nature  is  concerned  it  is  finished  gunpowder,  but  if  it  be 
reduced  to  powder  and  a  gun  loaded  with  it,  the  combustion  of  the  charge  is  found 
to  occur  too  slowly  to  produce  its  full  effect,  since  the  pulverulent  form  offers 
so  great  an  obstacle  to  the  passage  of  the  flame  by  which  the  combustion  is  com- 
municated from  one  end  of  the  charge  to  the  other.  The  press-cake  must,  there- 
fore, be  granulated  (corned)  or  broken  up  into  grains  of  sufficient  size  to  allow  the 
rapid  passage  of  the  flame  between  them,  and  the  consequent  rapid  firing  of  the 
whole  charge.  The  granulation  is  effected  by  crushing  the  press-cake  between 
successive  pairs  of  toothed  gun-metal  rollers,  from  which  it  falls  on  to  sieves, 
which  separate  it  'into  grains  of  different  sizes,  the  dust,  or  meal  powder,  passing 
through  the  last  sieve.  The  granulated  powders  are  freed  from  dust  by  passing 
them  through  revolving  cylinders  of  wooden  framework  covered  with  canvas  or 
wire  cloth,  and  the  fine-grain  powder  is  glazed  by  the  friction  of  its  own  grains 
against  each  other  in  revolving  barrels.  The  large-grain  powders  are  sometimes 
glazed  or  faced  with  graphite,  by  introducing  a  little  of  that  substance  into  the 
glazing-barrels  with  the  powder.  The  powder  is  dried  in  a  chamber  heated  by 
steam,  very  gradually,  so  as  not  to  injure  the  grain,  and  is  once  more  dusted  in 
canvas  cylinders  before  being  packed. 

When  it  is  required  that  the  powder  shall  burn  rapidly  the  grains  are  made 
small,  but  where  a  slower  combustion  is  required,  as  was  the  case  with  heavy 
ordnance  which  were  too  much  strained  by  the  rapid  combustion  of  fine  grain 
powder,  the  size  of  grain  is  much  increased,  being  from  f  to  i^  inch  or  more  in 
diameter.  To  the  same  end  the  percentage  of  sulphur,  on  which  the  inflammability 
of  the  powder  depends,  is  reduced,  and  a  charcoal  carbonised  at  a  low  temperature, 
and  therefore  comparatively  inflammable,  is  used.  Thus  cocoa-poioder,  or  'brown- 
powder,  is  made  with  79  per  cent,  nitre,  2  per  cent,  sulphur,  and  18  per  cent,  of 
lightly  burnt  charcoal.  In  mining  powders,  rapidity  of  combustion  is  desirable, 
so  that  the  proportion  of  sulphur  and  charcoal  is  increased,  as  shown  in  the  com- 
position given  above. 

1 80.  Good  gunpowder  is  composed  of  hard  angular  grains,  which  do 
not  soil  the  fingers,  and  have  a  perfectly  uniform  dark  grey  colour. 


EXPLOSION  OF   GUNPOWDER.  341 

Its  specific  gravity  (absolute  density),  as  determined  by  the  densimeter* 
varies  between  1.67  and  1.84,  and  its  apparent  density  (obtained  by 
weighing  a  given  measure  of  the  grain  against  an  equal  measure  of 
water)  varies  from  0.89  to  0.94,  so  that  a  cubic  foot  will  weigh  from  55 
to  58  Ibs.  When  exposed  to  air  of  average  dry  ness,  gunpowder  absorbs 
from  0.5  to  i  per  cent,  of  water.  In  damp  air  it  absorbs  a  much  larger 
proportion,  and  becomes  deteriorated  in  consequence  of  the  saltpetre 
being  dissolved,  and  crystallising  upon  the  surface  of  the  grains. 
Actual  contact  with  water  dissolves  the  saltpetre  and  disintegrates  the 
grains.  When  very  gradually  heated  in  air,  gunpowder  begins  to  lose 
sulphur,  even  at  100°  C.,  this  ingredient  passing  off  rapidly  as  the  tem- 
perature rises,  so  that  the  greater  part  of  it  may  be  expelled  without 
inflaming  the  powder,  especially  if  the  powder  be  heated  in  carbonic 
acid  gas  or  hydrogen,  to  prevent  contact  with  air.  If  gunpowder  be 
suddenly  heated  to  600°  F.  (315°  C.)  in  air,  it  explodes,  the  sulphur 
probably  inflaming  first;  but  out  of  contact  with  air  a  higher  tempera- 
ture is  required  to  inflame  it.  The  ignition  of  gunpowder  by  flame  is 
not  ensured  unless  the  flame  be  flashed  among  the  grains  of  powder ;  it 
often  takes  some  time  to  ignite  powder  with  the  flame  of  a  piece  of 
burning  paper  or  stick,  but  contact  with  a  red-hot  solid  body  inflames 
it  at  once.  A  heap  of  good  powder,  when  fired  on  a  sheet  of  white 
paper,  burns  without  sparks  and  without  scorching  or  kindling  the 
paper,  which  should  exhibit  only  scanty  black  marks  of  charcoal  after 
the  explosion.  If  the  powder  has  not  been  thoroughly  incorporated,  it 
will  leave  minute  globules  of  fused  nitre  upon  the  paper.  Two  ounces 
of  the  powder  should  be  capable  of  throwing  a  68-lb.  shot  to  a  distance 
of  260  to  300  feet  from  an  8o-inch  mortar  at  45°  elevation. 

Very  fortunately,  it  is  difficult  to  explode  gunpowder  by  concussion,  though  it 
has  been  found  possible  to  do  so,  especially  on  iron,  and  accidents  appear  to  have 
been  caused  in  this  way  by  the  iron  edge-runners  in  the  incorporating  mill,  when 
the  workmen  have  neglected  the  special  precautions  which  are  laid  down  for  them. 
The  use  of  stone  upon  iron  in  the  incorporation  is  avoided,  because  of  the  great 
risk  of  producing  sparks,  and  copper  is  employed  in  the  various  fittings  of  a 
powder-mill  wherever  it  is  possible. 

The  electric  spark  is,  of  course,  capable  of  firing  gunpowder,  though  it  is  not 
easy  to  ensure  the  inflammation  of  a  charge  by  a  spark  unless  its  conducting  power 
is  slightly  improved  by  mixing  it  with  a  little  graphite,  or  by  keeping  it  a  little 
moist,  which  may  be  effected  by  introducing  a  minute  quantity  of  calcium  chloride. 

181.  PRODUCTS  OP  EXPLOSION  OF  GUNPOWDER. — In  the  explosion  of  gun- 
powder, the  oxygen  of  the  nitre  converts  the  carbon  of  the  charcoal  chiefly  into 
carbon  dioxide  (C02),  part  of  which  assumes  the  gaseous  state,  whilst  the 
remainder  is  converted  into  potassium  carbonate  (K2C03).  The  greater  part  of  the 
sulphur  is  converted  into  potassium  sulphate  (K2S04).  The  chief  part  of  the 
nitrogen  contained  in  the  nitre  is  evolved  in  the  uncombined  state.  The  rough 
chemical  account  of  the  explosion  of  gunpowder,  therefore,  is  that  the  mixture  of 
nitre,  sulphur,  and  charcoal  is  resolved  into  a  mixture  of  potassium  carbonate, 
potassium  sulphate,  carbon  dioxide,  and  nitrogen,  the  two  last  being  gases,  the 
elastic  force  of  which,  when  expanded  by  the  heat  of  the  combustion,  accounts  for 
the  mechanical  effect  of  the  explosion. 

But  in  addition  to  these,  several  other  substances  are  found  among  the  products 
of  the  explosion.  Thus,  the  presence  of  potassium  sulphide  (K2S)  may  be  recog- 
nised by  the  smell  of  hydrogen  sulphide  produced  on  moistening  the  solid  residue 
in  the  barrel  of  a  gun,  and  hydrogen  sulphide  (H2S)  itself  may  often  be  perceived 
in  the  gases  produced  by  the  explosion,  the  hydrogen  being  derived  from  the 
charcoal.  A  little  marsh  gas  (CH4)  is  also  found  among  the  gases,  being  produced 

*  This  is  a  simple  apparatus  for  determining-  the  weight  of  mercury  displaced  by  a  given 
weight  of  gunpowder,  from  which  all  the  air  has  been  exhausted. 


342  EXPLOSION   OF  GUNPOWDER. 

by  the  decomposition  of  the  charcoal,  a  portion  of  the  hydrogen  of  which  is  also 
disengaged  in  the  free  state.  Carbonic  oxide  (CO)  is  always  detected  among  the 
products.  It  is  evident  that  the  collection  for  analysis  of  the  products  of  explo- 
sion must  be  attended  with  some  trouble,  and  that  considerable  differences  are  to 
be  expected  between  the  results  obtained  by  different  operators,  from  the  variation 
of  the  circumstances  under  which  the  powder  is  fired  and  the  products  collected. 
When  the  powder  is  slowly  fired,  a  considerable  proportion  of  the  nitrogen  in  the 
saltpetre  is  evolved  in  the  form  of  nitric  oxide  gas  .(NO),  which  is  not  found 
among  the  products  of  the  rapid  explosion  of  powder. 

The  period  over  which  the  combustion  of  a  given  weight  of  powder  extends  will, 
of  course,  depend  upon  the  area  of  surface  over  which  it  can  be  kindled  ;  thus  a 
single  fragment  of  powder  weighing  10  grains,  even  if  it  were  instantaneously 
kindled  over  its  entire  surface,  could  not  evolve  so  much  gas  in  a  given  time 
as  if  it  had  been  broken  into  10  separate  grains,  each  of  which  was  kindled  at 
the  same  instant,  since  the  inside  of  the  large  fragment  can  only  be  kindled  from 
the  outside.  Upon  this  principle  a  given  weight  of  powder  in  large  grains  will 
occupy  a  longer  period  in  its  explosion  than  the  same  weight  in  small  grains,  so 
that  the  large  grain  powder  is  best  fitted  for  ordnance,  where  the  ball  is  very  heavy, 
and  the  time  occupied  in  moving  it  will  permit  the  whole  of  the  charge  to  be  fired 
before  the  ball  has  left  the  muzzle,  whilst  in  small  arms  with  light  projectiles,  a 
finer-grained  and  more  quickly  burning  charge  is  required.  If  the  fine-grain 
powder  were  used  in  cannon,  the  whole  of  the  gas  might  be  evolved  before  the 
containing  space  had  been  sensibly  enlarged  by  the  movement  of  the  heavy  pro- 
jectile, and  the  gun  would  be  subjected  to  an  unnecessary  strain  ;  on  the  other 
hand,  a  large  grain  powder  in  a  musket  would  evolve  its  gas  so  slowly  that  the 
ball  might  be  expelled  with  little  velocity  by  the  first  half  of  it,  and  the  remainder 
would  be  wasted.  There  is  good  reason  to  believe  that  even  under  the  most 
favourable  circumstances  a  large  proportion  of  every  charge  of  powder  is  discharged 
unexploded  from  the  muzzle  of  the  gun  and  is  therefore  wasted.  In  blasting 
rocks  and  other  mining  operations,  the  space  within  which  the  powder  is  confined 
is  absolutely  incapable  of  enlargement  until  the  gas  evolved  by  the  combustion  has 
attained  sufficient  pressure  to  do  the  whole  work,  that  is,  to  rend  the  rock,  for 
example,  asunder.  Accordingly,  a  slowly  burning  charge  will  produce  the  effect, 
since  the  rock  must  give  way  when  the  gas  attains  a  certain  pressure,  whether  that 
happen  in  one  second  or  in  ten.  Indeed,  a  slowly  burning  charge  is  advantageous, 
as  being  less  liable  to  shatter  the  rock  or  coal,  and  bringing  it  away  in  larger  masses 
with  less  danger.  Barium  nitrate  and  sodium  nitrate  are  sometimes  substituted  for 
a  part  of  the  potassium  nitrate  in  mining  powder,  its  combustion  being  thus 
retarded. 

The  same  charge  of  the  same  powder  produces  very  different  results  when 
heated  in  different  ways.  If  5  grains  of  gunpowder  be  placed  in  a  wide  test-tube 
and  fired  by  passing  a  heated  wire  into  the  tube,  a  slight  puff  only  is  perceived  ; 
but  if  the  same  amount  of  powder  be  heated  in  the  tube  by  a  spirit  lamp,  it  will 
explode  with  a  loud  report,  and  perhaps  shatter  the  tube  (a  copper  or  brass  tube 
is  safer).  In  the  first  place,  the  combustion  is  propagated  slowly  from  the  par- 
ticle first  touched  by  the  wire  ;  in  the  second,  all  the  particles  are  raised  at  once 
to  pretty  nearly  the  same  temperature,  and  as  soon  as  one  explodes,  all  the  rest 
follow  instantaneously. 

When  gunpowder  is  slowly  fired,  the  products  of  its  decomposition  are  different 
from  those  mentioned  above  ;  thus,  nitric  oxide  (NO),  arising  from  incomplete  de- 
composition of  the  nitre,  is  perceived  in  considerable  quantity,  and  may  be  recog- 
nised by  the  red  colour  produced  when  it  is  brought  in  contact  with  air. 

The  white  smoke  arising  from  the  explosion  of  gunpowder  consists  chiefly  of 
the  sulphate  and  carbonate  of  potassium  in  a  very  finely  divided  state  :  it  seems 
probable  that  at  the  instant  of  explosion  they  are  converted  into  vapour,  and  are 
afterwards  deposited  in  a  state  of  minute  division  as  the  temperatute  falls.  From 
this  it  will  be  obvious  that  a  powder  that  is  required  to  be  smokeless  must  be  free 
from  such  saline  products  of  explosion  (see  Nitro-glycerine).  The  fouling  or  actual 
solid  residue  in  the  gun  is  very  trifling  when  the  powder  is  dry  and  has  been  well 
incorporated  ;  a  damp  or  slowly  burning  powder  leaves,  as  might  be  expected,  a 
large  residue.  The  residue  always  becomes  wet  on  exposure  to  air,  from  the  great 
attraction  for  moisture  possessed  by  the  carbonate  and  sulphide  of  potassium. 

From  the  circumstance  that  the  combustion  of  gunpowder  is  independent  of 
any  supply  of  oxygen  from  the  air,  it  might  be  supposed  that  it  would  be  as  easily 


COMMON  SALT.  343 

inflamed  in  vacuo  as  under  ordinary  atmospheric  pressure.  This  is  not  found  to  be 
the  case,  however,  for  a  mechanical  reason,  viz.,  that  the  flame  from  the  particles 
which  are  first  ignited  escapes  so  rapidly  into  the  vacuous  space  that  it  does  not 
inflame  the  more  remote  particles.  For  a  similar  reason,  charges  of  powder  in 
fuses  are  found  to  burn  more  slowly  under  diminished  atmospheric  pressure,  the 
flame  (or  heating  gas)  escaping  more  rapidly  and  igniting  less  of  the  remaining 
charge  in  a  given  time.  It  has  been  determined  that  if  a  fuse  be  charged  so  as  to 
burn  for  thirty  seconds  under  ordinary  atmospheric  pressure  (30  inches  barometer), 
each  diminution  of  I  inch  in  barometric  pressure  will  cause  a  delay  of  I  second  in 
the  combustion  of  the  charge,  so  that  the  fuze  will  burn  for  thirty-one  seconds 
when  the  barometer  stands  at  29  inches. 

SODIUM. 

Na'  =  23  parts  by  weight. 

182.  Sodium  is  often  found,  in  place  of  potassium,  in  the  felspars  and 
other  minerals,  but  we  are  far  more  abundantly  supplied  with  it  in  the 
form  of  common  salt  (sodium  chloride,  NaCl),  occurring  not  only  in  the 
solid  state,  but  dissolved  in  sea  water,  and  in  smaller  quantity  in  the 
waters  derived  from  most  lakes,  rivers,  and  springs. 

Rock-salt  forms  very  considerable  deposits  in  many  regions ;  in  this 
country  the  most  important  is  situated  at  Northwich,  in  Cheshire,  where 
very  large  quantities  are  extracted  by  mining.  Wielitzka,  in  Poland,  is 
celebrated  for  an  extensive  salt-mine,  in  which  there  are  a  chapel  and 
dwelling-rooms,  with  furniture  made  of  this  rock.  Extensive  beds  of 
rock-salt  also  occur  in  France,  Germany,  Hungary,  Spain,  Abyssinia, 
and  Mexico.  Perfectly  pure  specimens  form  beautiful  colourless  cubes, 
and  are  styled  sal  gemme ;  but  ordinary  rock-salt  is  only  parcially  trans- 
parent, and  exhibits  a  rusty  colour,  due  to  the  presence  of  iron.  In 
some  places  the  salt  is  extracted  by  boring  a  hole  into  the  rock  and 
filling  it  with  water,  which  is  pumped  up  when  saturated  with  salt,  and 
evaporated  in  boilers,  the  minute  crystals  of  salt  being  removed  as  they 
are  deposited. 

At  Droitwich,  in  Worcestershire,  the  salt  is  obtained  by  evaporation 
from  the  waters  of  certain  salt  springs.  In  some  parts  of  France  and 
Germany  the  water  from  the  salt  springs  contains  so  little  salt  that  it 
would  not  pay  for  the  fuel  necessary  to  evaporate  the  water,  and  a  very 
ingenious  plan  is  adopted  by  which  the  proportion  of  water  is  greatly 
reduced  without  the  application  of  artificial  heat.  For  this  purpose  a 
lofty  scaffolding  is  erected  and  filled  with  bundles  of  brushwood,  over 
which  the  salt  water  is  allowed  to  flow,  having  been  raised  to  the  top 
of  the  scaffolding  by  pumps.  In  trickling  over  the  brushwood  this 
water  exposes  a  large  surface  to  the  action  of  the  wind,  and  a  consider- 
able evaporation  occurs,  so  that  a  much  stronger  brine  is  collected  in 
the  reservoir  beneath  the  scaffolding ;  by  several  repetitions  of  the 
operation,  the  proportion  of  water  is  so  far  diminished  that  the  rest  may 
be  economically  evaporated  by  artificial  heat.  In  England  the  brine 
(containing  about  22  per  cent,  of  salt)  is  run  into  large  pans  and 
rapidly  boiled  for  about  thirty  hours,  fresh  brine  being  allowed  to  flow 
in  continually,  so  as  to  maintain  the  liquid  at  the  same  level  in  the 
boiler.  During  this  ebullition  a  considerable  deposit,  composed  of  the 
sulphates  of  calcium  and  sodium,  is  formed,  and  raked  out  by  the  work- 
men. When  a  film  of  crystals  of  salt  begins  to  form  upon  the  surface 
the  fire  is  lowered,  and  the  temperature  of  the  brine  allowed  to  fall  to 


344  SALT  FKOM   SEA  WATER. 

about  82°  C.,  at  which  temperature  it  is  maintained  for  several  days 
whilst  the  salt  is  crystallising.  The  crystals  are  afterwards  drained, 
and  dried  by  exposure  to  air.  The  grain  of  the  salt  is  regulated  by  the 
temperature  at  which  it  crystallises,  the  size  of  the  crystals  increasing 
as  the  temperature  falls.  The  coarsest  crystals  thus  obtained  are  known 
in  commerce  as  bay-salt.  It  is  not  possible  to  extract  the  whole  of  the 
salt  in  this  way,  since  the  last  portions  which  crystallise  will  always  be 
contaminated  with  other  salts  present  in  the  brine  ;  but  the  mother-liquor 
is  not  wasted,  for  after  as  much  salt  as  possible  has  been  obtained,  it  is 
made  to  yield  sodium  sulphate  (Glauber's  salt),  magnesium  sulphate 
(Epsom  salts),  bromine,  and  iodine. 

The  process  adopted  for  extracting  the  salt  from  sea  water  depends  upon  the 
climate.  In  Kussia,  shallow  pits  are  dug  upon  the  shore,  in  which  the  sea  water  is 
allowed  to  freeze,  when  a  great  portion  of  the  water  separates  in  the  form  of  pure 
ice,  leaving  a  solution  of  salt  sufficiently  strong  to  pay  for  evaporation. 

Where  the  climate  is  sufficiently  warm,  the  sea  water  is  allowed  to  run  very 
slowly  through  a  series  of  shallow  pits  upon  the  shore,  where  it  becomes  concentrated 
by  spontaneous  evaporation,  and  is  afterwards  allowed  to  remain  for  some  time  in 
reservoirs  in  which  the  salt  is  deposited.  Before  being  sent  into  the  market,  it  is 
allowed  to  drain  for  a  long  time,  in  a  sheltered  situation,  when  the  magnesium  chlo- 
ride with  which  it  is  contaminated  deliquesces  in  the  moisture  of  the  air  and  drains 
away.  The  bittern,  or  liquor  remaining  after  the  salt  has  been  extracted,  is  employed 
to  furnish  magnesia  and  bromine. 

1000  parts  of  sea  water  contain  about  29  parts  of  NaCl,  0.5  of  KC1,  2  of  MgCl2, 
2.5  of  MgS04,  1.5  of  CaS04,  &c. 

In  a  warm  climate,  that  of  Marseilles,  for  example,  the  water  is  allowed  to  evapo- 
rate spontaneously  until  it  has  a  specific  gravity  of  1.24.  During  this  operation  it 
deposits  about  four-fifths  of  its  sodium  chloride.  It  is  then  mixed  with  one-tenth 
of  its  volume  of  water,  and  artificially  cooled  to  O°  F.  (see  p.  82),  when  it  deposits 
a  quantity  of  sodium  sulphate,  resulting  from  the  decomposition  of  part  of  the 
remaining  sodium  chloride  by  the  magnesium  sulphate.  The  mother-liquor  is 
evaporated  till  its  specific  gravity  is  1.33,  a  fresh  quantity  of  sodium  chloride  being 
deposited  during  the  evaporation.  When  the  liquid  cools,  it  deposits  a  double  salt 
composed  of  chlorides  of  potassium  and  magnesium,  from  which  the  latter  chloride 
may  be  extracted  by  washing  with  a  very  little  water,  leaving  the  potassium  chlo- 
ride fit  for  the  market. 

This  process  is  instructive  as  illustrating  the  influence  exerted  upon  the  nature  of 
the  salts  which  will  be  deposited  from  a  solution  by  the  temperature  to  which  this 
is  exposed,  the  general  rule  being  that  that  salt  separates  which  is  least  soluble  in 
the  liquid  at  the  particular  temperature. 

The  great  tendency  observed  in  ordinary  table  salt  to  become  damp 
when  exposed  to  the  air  is  due  chiefly  to  the  presence  of  small  quan- 
tities of  chlorides  of  magnesium  and  calcium,  for  pure  sodium  chloride 
has  a  very  much  smaller  disposition  to  attract  atmospheric  moisture, 
although  it  is  very  easily  dissolved  by  water,  2^  parts  being  able  to  dis- 
solve i  part  (by  weight)  of  salt.  The  saturated  solution  boils  at  107.5°  V. 

In  the  history  of  the  useful  applications  of  common  salt  is  to  be  found 
one  of  the  best  illustrations  of  the  influence  of  chemical  research  upon 
the  development  of  the  resources  of  a  country,  and  a  capital  example  of 
a  manufacturing  process  not  based,  as  such  processes  usually  are,  upon 
mere  experience,  independent  of  any  knowledge  of  chemical  principles, 
but  upon  a  direct  and  intentional  application  of  these  to  the  attainment 
of  a  particular  object. 

Until  the  last  quarter  of  the  eighteenth  century,  the  uses  of  common 
salt  were  limited  to  culinary  and  agricultural  purposes,  and  to  the 
glazing  of  the  coarser  kinds  of  earthenware,  whilst  a  substance  far  more 
useful  in  the  arts,  carbonate  of  soda,  was  imported  chiefly  from  Spain 


LEBLANC  ALKALI  PROCESS. 


345 


under  the  name  of  barilla,  which  was  the  ash  obtained  by  burning  a 
marine  plant  known  as  the  salsola  soda.  But  this  ash  only  contained 
about  one-fourth  of  its  weight  of  carbonate  of  soda,  so  that  this  latter 
substance  was  thus  imported  at  a  great  expense,  and  the  manufacturer 
of  soap  and  glass,  to  which  it  is  indispensable,  were  proportionately 
fettered. 

During  the  wars  of  the  French  Revolution  the  price  of  barilla  had 
risen  so  considerably  that  it  was  deemed  advisable  by  Napoleon  to  offer 
a  premium  for  the  discovery  of  a  process  by  which  the  carbonate  of 
soda  could  be  manufactured  at  home,  and  to  this  circumstance  we  are 
indebted  for  the  discovery,  by  Leblanc,  of  the  process,  which  is  only 
now  being  superseded,  for  the  manui'acture  of  carbonate  of  soda  from 
common  salt,  a  discovery  which  placed  this  substance  at  once  among 
the  most  important  raw  materials  with  which  a  country  could  be 
furnished. 

183.  Manufacture  of  sodium  carbonate  from  common  salt  by  the  Leblanc 
jjrocess. — This  process  consists  in  heating  salt  with  sulphuric  acid, 


Fig'.  212.  —  Furnace  for  converting  common  salt  into  sulphate  of  soda. 

whereby  sodium  sulphate  and  hydrogen  chloride  are  produced  (seep.  177). 
Tho  sodium  sulphate,  technically  called  salt  cake,  is  then  mixed  with 
small  coal  and  limestone,  and  again  heated  in  order  to  convert  it  into 
sodium  carbonate,  a  change  which  may  be  represented  by  the  two 
equations  : 

(i)  Na.2S04  +  C.2         =  Na2S       +  2C02 
Sodium  sulphate.  Sodium  sulphide. 


(2)  Na2S 


CaC0    =  Na.C0 


CaS 


Calcium  sulphide. 

The  resulting  mixture  of  sodium  carbonate  and  calcium  sulphide,  technically 
called  Mack  ash  —  being  black  from  the  presence  of  coal  —  is  leached  with  water  to 
dissolve  the  sodium  carbonate  and  leave  the  calcium  sulphide  (tank-watte).*  The 
liquor  is  evaporated  to  crystallise  the  sodium  carbonate  (soda  crystals). 

In  the  first  part  of  the  process  {salt  cake  process}  the  salt  is  introduced  into  the 
iron  pan,  A,  of  a  salt  cake  furnace  (Fig.  212),  where  it  is  mixed  with  an  equal  weight 
of  H2S04  (sp.  gr.  1.72)  and  heated  by  the  fire  in  the  grate,  C.  Much  HC1  is  expelled 
and  escapes  through  the  flue  B,  whence  it  passes  to  the  bottom  of  a  brick  tower 

*  The  CaS  in  the  waste  is  insoluble  because  combined  with  lime. 


34^  AMMONIA-SODA  ALKALI  PROCESS. 

packed  with  coke  down  which  water  is  trickled  ;  the  water  absorbs  the  HC1  from 
the  gases  as  they  ascend  the  tower,  forming  the  muriatic  acid  of  commerce  (p.  178). 
The  door  F  is  then  raised,  and  the  partly  decomposed  salt  raked  from  the  pan  into 
the  brick  roaster  D  :  this  is  virtually  a  muffle  heated  by  the  flames  from  a  furnace, 
which  circulate  in  the  flues  surrounding  it.  The  conversion  of  the  salt  into  sodium 
sulphate  is  here  completed,  the  remaining  HC1  escaping  through  the  flue  E  to  con- 
densing towers  similar  to  that  described  above. 

In  the  second  part  of  the  process  the  mixture  of  ground  salt  cake  (10  parts),  lime- 
stone (10  parts),  and  small  coal  (4-6  parts)  is  heated  in  a  black  ash  furnace,  which 
is  essentially  a  reverberator}"  furnace,  such  as  is  shown  in  Fig.  109. 

When  the  black  ash  is  treated  with  water,  the  sodium  carbonate  is  dissolved, 
leaving  the  calcium  sulphide,*  and  by  evaporating  the  solution,  and  calcining  the 
residue,  ordinary  soda  ash  is  obtained,  f  But  this  is  by  no  means  pure  sodium  car- 
bonate, for  it  contains,  in  addition  to  a  considerable  quantity  of  common  salt  and 
sodium  sulphate,  a  certain  amount  of  caustic  soda,  formed  by  the  action  of  lime 
(formed  from  the  heating  of  the  excess  of  limestone  used)  upon  the  carbonate.  In 
order  to  purify  it,  the  crude  soda  ash  is  mixed  with  small  coal  or  sawdust  and  again 
heated,  when  the  carbonic  acid  gas  formed  from  the  carbonaceous  matter  converts 
the  caustic  soda  into  carbonate,  and  on  dissolving  the  mass  in  water  and  evaporating 
the  solution,  it  deposits  oblique  rhombic  prisms  of  common  washing  soda,  having 
the  composition  Na-jCOg. I oAq  (soda  crystals). 

Hargreare's  process  dispenses  with  the  use  of  sulphuric  acid,  and  converts  the 
sodium  chloride  into  sulphate  by  the  action  of  sulphurous  acid  gas  (obtained  by 
burning  pyrites),  steam,  and  air,  at  a  dull  red  heat;  2NaCl  +  H20  +  S02  +  0  = 
Na2S04  +  2HCl.  The  hydrochloric  acid  is  absorbed  by  water,  as  usual,  and  the 
sodium  sulphate  converted  into  carbonate  as  described  above. 

A  little  reflection  will  show  the  important  influence  which  this  pro- 
cess has  exerted  upon  the  progress  of  the  useful  arts  in  this  country. 
The  three  raw  materials,  salt,  coal,  and  limestone,  we  possess  in 
abundance.  The  sulphuric  acid,  when  the  process  was  first  introduced, 
bore  a  high  price,  but  the  resulting  demand  for  this  acid  gave  rise  to 
so  many  improvements  in  its  manufacture  that  its  price  has  been  very 
greatly  diminished — a  circumstance  which  has  of  course  produced  a 
most  beneficial  effect  upon  all  branches  of  manufacture  in  which  the 
acid  is  employed. 

The  large  quantity  of  hydrochloric  acid  obtained  as  a  secondary  pro- 
duct has  been  employed  for  the  preparation  of  bleaching-powder,  and 
the  important  arts  of  bleaching  and  calico-printing  have  thence  received 
a  considerable  impulse.  These  arts  have  also  derived  a  more  direct 
benefit  from  the  increased  supply  of  sodium  carbonate,  which  is  so 
largely  used  for  cleansing  all  kinds  of  textile  fabrics.  The  manufactures 
of  soap  and  glass,  which  probably  create  the  greatest  demand  for  sodium 
carbonate,  have  been  increased  and  improved  beyond  all  precedent  by 
the  production  of  this  salt  from  native  sources. 

Ammonia -soda  process,  or  ftolvays  process.  — This  process  for  convert- 
ting  NaCl  into  Na,,C03,  which  has  almost  completely  superseded  the 
Leblanc  process,  depends  upon  the  reaction  between  sodium  chloride, 
carbon  dioxide,  ammonia  and  water,  NaCl  +  NH3  +  C02  +  H2O  = 
NaHC03  +  NH4C1.  A  solution  of  salt  is  saturated,  first  with  ammonia 
and  then  with  carbon  dioxide,  whereupon  sodium  hydrogen  carbonate 
is  precipitated.  This  is  collected  and  calcined  in  order  to  convert  it  into 
soda,  ash;  2NaHC03  =  Na2CO3  +  H20  +  C02.  The  solution  containing 
NH4C1  is  heated  with  lime  to  recover  the  ammonia — 
2NH4C1  +  CaO  =  2NH3  +  H20  +  CaCl2. 

*  The  CaS  in  the  waste  is  insoluble  because  combined  with  lime. 

f  Before  evaporation,  air  is  generally  blown  through  the  liquor  to  oxidise  the  sodium 
sulphide  which  may  remain  unaltered  (see  p.  348,  Sodium  hydroxide). 


CHANCE'S   SULPHUR   RECOVERY  PROCESS.  347 

The  brine  pumped  from  the  wells  contains  magnesium  salts  and  other  salts  ;  lime 
is  added  to  remove  these,  and  the  excess  of  lime  is  precipitated  by  ammonium  car- 
bonate. The  liquor  is  then  saturated  with  salt  by  addition  of  pure  salt,  and  with 
NH3  by  passing  in  this  gas  from  the  ammonia  stills  ;  it  is  then  made  to  flow  down  a 
vertical  iron  cylinder  containing  perforated  shelves  and  kept  cool  by  water.  C0.2  is 
pumped  up  this  cylinder  and  meets  the  descending  liquor,  from  which  NaHC03  is 
deposited  and  collected  on  the  shelves,  whence  it  falls  as  a  sludge  to  the  bottom  of  the 
•cylinder.  The  liquor  from  which  the  NaHC03  has  separated  is  run  into  the  ammonia 
stills  where  it  is  heated  with  lime  in  order  to  recover  the  NH3.  The  CO2  used  in  the 
process  is  derived  partly  from  the  limekilns  in  which  the  lime  for  the  ammonia  stills 
is  burnt,  and  partly  from  the  calcining  of  the  NaHC03  to  get 


Recovery  of  waste  in  alkali  manufacture.  —  It  is  obvious  that  it  should 
be  the  object  of  every  chemical  manufacturer  to  utilise  his  raw  materials 
in  such  a  manner  that  none  of  the  elements  in  them  shall  ultimately 
remain  in  an  unmarketable  form.  A  little  reflection  will  show  that  in  an 
ideal  process  for  making  alkali,  the  only  component  of  the  raw  materials 
which  should  be  finally  rejected  is  the  atmospheric  nitrogen.  In 
practice,  however,  there  has  been,  until  lately,  a  large  source  of  waste 
in  both  the  above  processes.  It  will  have  been  seen  that  in  the  Leblanc 
process  the  whole  of  the  sulphur  of  the  H2SO4  which  is  used  makes  its 
appearance  as  CaS  in  the  tank  waste  ;  whilst  in  the  ammonia-soda 
process  all.  the  chlorine  in  the  salt  makes  its  appearance  as  CaCl2  in  the 
ammonia-still  liquor.  The  tank  waste  and  still  liquor  were  originally 
rejected,  so  that  whilst  the  ammonia-soda  process  had  the  advantage 
over  the  Leblanc  process  that  it  did  not  pay  for  sulphur  which  was 
finally  wasted,  it  had  the  accompanying  disadvantage  that  it  did  not 
recover  the  chlorine  of  the  salt,  which  is  a  source  of  profit  to  the  Leblanc 
process.  Whilst,  therefore,  CaS  is  the  alkali  ivaste  of  the  older  process, 
CaCl.,  is  that  of  the  newer  process,  although  since  the  sulphur  is  now 
recovered  from  the  CaS,  and  the  Cl  from  the  still  liquor,*  this  term  has 
become  a  misnomer.  It  must  be  added  that  much  of  the  soda  in  black 
ash  being  in  the  form  of  caustic  soda  (see  above),  this  product  is  more 
easily  made  by  the  Leblanc  process  than  by  the  ammonia-soda  process  ; 
so  that  in  many  cases  the  Leblanc  makers  have  ceased  to  produce 
sodium  carbonate,  and  are  now  manufacturers  of  caustic  alkali,  bleach- 
ing-powder,  and  pure  sulphur.  The  manufacture  of  chlorine  and  bleach 
have  been  sketched  on  pp.  170  and  183,  and  the  recovery  of  manganese 
from  the  chlorine-still  liquor  on  p.  170. 

Recovery  of  sulphur  from  tank  ivaste.  —  This  is  now  effected  by  Chance's 
Access,  which  depends  upon  the  fact  that  when  carbon  dioxide  (lime-kiln 
gases)  is  passed  into  alkali  waste  (CaS),  made  into  a  cream  with  water, 
H2Sis  evolved  and  CaC03  remains  ;  CaS  +  H2O  +  C02  =  CaC03  +  H2S.t 
The  sulphuretted  hydrogen  is  mixed  with  a  carefully  regulated  supply 
of  air  and  passed  through  a  kiln  (Claus  kiln)  containing  some  porous 
material,  when  the  hydrogen  alone  is  burnt,  the  sulphur  being  subse- 
quently deposited  in  condensing-chambers  ;  H2S  +  0  =  H,O  +  S.  The 
CaC03  from  this  process  is  used  again  in  making  black  ash. 

Recovery  of  chlorine  from  ammonia-still  liquor.  —  When  lime  is  used 
in  the  ammonia  stills  calcium  chloride  remains  in  the  liquor;  it  is 
difficult  to  recover  chlorine  from  this  compound.  If  magnesia  be 

*  Exact  information  as  to  the  recovery  of  chlorine  is  not  divulged,  by  the  ammonia-soda 
makers,  but  it  is  believed  to  have  been  successfully  effected. 

f  An  elaborate,  systematically  worked  plant  is  essential  in  order  that  the  evolved  gas  ir,ay 
be  as  rich  as  possible  in  H2S. 


CAEBONATE   OF  SODA. 

substituted  for  lime,  magnesium  chloride  is  left  (2NH4Cl  +  MgO  = 
2NH3  +  H20  +  MgCl2),  from  which  chlorine  may  be  recovered  by  the 
Weldon-Pechiney  process.  This  consists  in  mixing  MgQ  with  the 
concentrated  MgCl2  solution,  whereby  magnesium  oxy  chloride 
(5MgO.4MgCl2)  is  produced.  This  can  be  dried  without  .  losing  HC1, 
which  is  not  possible  with  MgCl.,  itself  ;  and  when  the  dried  mass  is 
heated  in  air  at  1000°  C.,  it  gives  up  its  chlorine  in  exchange  for  oxygen. 
The  MgO  thus  left  is  used  again. 

Mond  seeks  to  prepare  the  MgCl2  in  a  nearly  anhydrous  state  by  volatilising  the 
NH4C1  and  passing  the  vapour  over  heated  MgO,  whereby  NH3,  H.20,  and  MgCl2  are 
produced  ;  the  first  is  used  in  the  ammonia-soda  plant,  whilst  the  MgCl2  may  be 
heated  in  air  to  yield  MgO  and  Cl,  as  described  above.  The  NH4C1  is  obtained  in 
crystals  by  cooling  the  mother-liquor  from  the  towers  in  which  the  NaHC03  is  pre- 
cipitated (see  above). 

Sodium  carbonate,  washing  soda,  Na2C03.ioAq.  —  The  crystals  of 
sodium  carbonate  are  easily  distinguished  by  their  property  of  efflor- 
escing in  dry  air  (p.  52),  and  by  their  alkaline  taste,  which  is  much 
milder  than  that  of  potassium  carbonate,  this  being,  moreover,  a 
deliquescent  salt.  The  crystals  are  very  soluble  in  water,  requiring 
only  2  parts  of  cold,  and  less  than  their  own  weight  of  boiling  water  ; 
the  solution  is  strongly  alkaline  to  test-papers.  The  crystals  fuse  at 
50°  C.,  evolve  steam,  and  deposit  a  granular  powder  of  the  composition 
Na2C03.Aq  (crystal  carbonate).  At  a  higher  temperature  it  becomes 
Na2CO3,  and  fuses  at  850°  C.  If  a  solution  of  sodium  carbonate  be 
crystallised  between  30°  and  50°  C.,  the  crystals  are  Na2C03.7Aq.  The 
mineral  natron  found  at  the  soda  lakes  of  Egypt  is  Na2CO3.io  Aq.  The 
chief  impurities  in  soda  crystals  are  NaCl  and  Na2S04  ;  soda  ash  may 
contain  in  addition  NaOH  and  lsTa2S. 

Bicarbonate  of  soda,  or  hydrogen  sodium  carbonate,  NaHC03,  is 
the  substance  commonly  used  in  medicine  as  carbonate  of  soda.  It  is 
prepared  either  by  saturating  the  crystallised  carbonate  with  CO2,  or 
by  passing  C02  through  a  strong  solution  of  common  salt  mixed 
with  ammonia  (see  p.  346).*  It  forms  small  prismatic  crystals  much 
less  easily  dissolved  by  water  (8.85  per  cent,  at  15°  C.)  than  the 
carbonate.  The  solution  is  much  less  alkaline.  When  the  solution 
is  heated  it  evolves  CO2,  and  crystals  of  the  sesquicarbonate 
Na2C03.NaHCO3.2Aq,  may  be  obtained  from  it.  A  similar  salt  is  the 
mineral  Trona.  It  has  been  seen  that,  when  strongly  heated,  2NaHC03  = 


23          2        2. 

Potassium  sodium  carbonate,  KNaC03.6Aq,  may  be  crystallised  from 
a  mixture  of  solutions  of  the  carbonates. 

Soda  lye,  employed  in  the  manufacture  of  hard  soap,  is  a  solution  of 
sodium  hydroxide  (NaOH),  obtained  by  decomposing  the  carbonate 
with  calcium  hydroxide  (slaked  lime);  Na2C03  +  Ca(OH)2  =  2NaOH  + 
CaCO3.  The  solid  NaOH  of  commerce,  caustic  soda,  is  prepared  in  the 
Leblanc  alkali  process  ;  the  solution  obtained  by  treating  the  black  ash 
with  water  is  causticised  with  lime,  as  represented  in  the  above  equation, 
and  concentrated  by  evaporation  until  it  solidifies  on  cooling,  at  which 
stage  it  is  poured  out  into  iron  moulds.  In  properties  it  closely 

*  A  saturated  solution  of  NaCl  mixed  with  one-third  of  its  volume  of  NH3  (sp.  yr.  0.88) 
and  saturated  with  CO2  £>ives  a  copious  precipitate  of  NaHCO3. 


ELECTEOLYSIS   OF   SALT. 


349 


resembles  KOH  ;   its  common  impurities  are  carbonate,  chloride,  sul- 
phate, and  nitrite  of  sodium,  sometimes  accompanied  by  zinc  oxide. 

In  practice,  the  tank  liquor  (from  the  black  ash)  is  purified  from  sulphides  before 
it  is  causticised,  partly  by  blowing  air  through  it  which  oxidises  the  sulphides, 
and  partly  by  addition  of  zinc  oxide  which  precipitates  the  sulphur  as  zinc 
sulphide.  The  removal  of  the  other  salts  (sulphate  and  chloride)  occurs  when  the 
caustic  liquor  is  concentrated,  for  they  then  crystallise  and  may  be  fished  out ;  the 
last  traces  of  sulphide  are  oxidised  by  the  addition  of  a  little  NaN03  to  the  melted 
NaOH  before  it  is  cast. 

Electrolytic  production  of  alkali  and  chlorine. — Since  these  main 
products  of  the  alkali  industry  contain  much  more  chemical  energy 
than  that  of  the  salt  from  which  they  are  derived,  it  is  obvious  that 
they  can  only  be  obtained  by  transferring  the  chemical  energy  of  other 
substances,  or  by  transforming  some  other  kind  of  energy  into  chemical 
energy.  In  the  foregoing  processes  both  these  methods  of  procuring 
the  necessary  energy  are  applied.  There  is  an  increasing  tendency, 
however,  to  apply  electrical  energy  directly  to  the  salt  and  thus  to 
convert  it  into  the  chemical  energy  of  alkali  and  chlorine.  There  are 
certain  conveniences  in  converting  heat  energy  first  into  electrical 
energy,  by  means  of  a  steam-engine  and  dynamo,  and  then  applying 
this  electrical  energy  directly  instead  of  the  heat  energy.  But  the  use 
of  electrical  energy  has  most  to  recommend  it  in  places  where  dynamos 
can  be  driven  by  the  energy  of  running  water. 

Two  methods  of  using  the  electrical  energy  present  themselves  : 
(i)  The  current  may  be  passed  through  fused  salt,  in  which  case  the 
sodium  chloride  will  be  electrolysed  with  separation  of  the  sodium  at 
the  cathode  and  chlorine  at  the  anode.  Since  the  heat  of  formation  of 
salt  is  Na,Cl  =  97,7oo  (p.  306),  the  electrical  energy  supplied  must  be 
the  equivalent  of  this  heat  energy.  (2)  The  current  may  be  used  to 
electrolyse  a  solution  of  salt,  in  which  case  hydrogen  will  appear  at  the 
cathode  instead  of  sodium  (p.  324)  while  chlorine  will  be  evolved  at  the 
anode,  as  before.  The  reason  why  hydrogen  is  evolved  from  the  cathode 
may  be  said  to  be  that  the  sodium  at  first  liberated  by  the  electrolysis 
attacks  the  water  forming  NaOH  and  liberating  hydrogen.  As  this 
reaction  is  exothermic,  viz.,  Na+  HOH  =  NaOH  + 11  +  43,500,  the 
amount  of  electrical  energy  necessary  to  electrolyse  the  aqueous  solution 
is  less  than  that  required  for  the  fused  salt  by  the  equivalent  of  this 
amount  of  heat.  Caustic  soda  being  the  product  required,  not  sodium, 
which  when  obtained  must  be  treated  with  water  to  make  the  caustic, 
it  would  seem  preferable  to  electrolyse  a  solution  of  salt  rather  than 
the  fused  material. 

When  fused  salt  is  electrolysed  the  sodium  must  be  collected  in  some  solvent  for 
it,  such  as  metallic  lead,  which  is  heavier  than  the  liquid  salt ;  otherwise  the 
sodium  would  float  to  the  surface  and  burn  in  the  air  or  chlorine  there  present. 
The  cathode,  therefore,  consists  of  melted  lead  at  the  bottom  of  the  crucible  (of 
iron  lined  with  magnesia)  containing  the  melted  salt,  and  the  anode  is  a  carbon 
rod  immersed  in  the  molten  mass.  Sodium  is  liberated  at  the  cathode  and  dis- 
solves in  the  melted  lead,  whilst  chlorine  is  evolved  at  the  anode  and  is  led  away 
from  the  top  of  the  crucible  to  a  bleaching-powder  chamber  (p.  183).  The  alloy  of 
sodium  and  lead  is  treated  with  water  to  convert  the  Na  into  NaOH. 

Instead  of  using  a  lead  cathode  the  fused  salt  may  contain  lead  chloride,  so  that 
the  alloy  of  lead  and  sodium  is  separated  electrolytically  at  the  carbon  cathode  and 
sinks  in  the  liquid  salt. 

When  a  solution  of  salt  is  electrolysed,  the  caustic  soda  collecting  in  solution 
around  the  cathode  is  liable  to  mix  with  the  saturated  solution  of  chlorine  collect- 


350  SODIUM. 

ing  around  the  anode,  forming  a  solution  of  sodium  of  hypochlorite  and  chloride- 
(p.  182),  which  has  powerful  bleaching  properties  (electrolytic  bleacli).  When  the 
anode  and  cathode  are  separated  by  a  porous  diaphragm  the  caustic  soda  liquor 
may  be  drawn  off  and  evaporated,  whilst  the  chlorine  may  be  conducted  into  lime 
chambers.  The  diaphragm  constitutes  a  serious  difficulty  in  the  process,  as  a 
material  which  will  satisfactorily  resist  the  disintegrating  effect  of  the  electrolysis 
does  not  exist.  In  the  Castner-Kellner  process  the  anode  and  cathode  are  separated 
by  a  non-porous  (and  therefore  less  easily  attacked)  partition,  which  dips  into  a 
layer  of  mercury  ;  in  the  anode  compartment  the  mercury  dissolves  sodium,  and 
by  rocking  the  vessel  is  made  to  flow  to  the  cathode  compartment  where  its  sodium 
is  dissolved  as  caustic  soda.  Thus  the  vessel  being  continually  rocked,  the  mercury 
serves  to  convey  the  sodium  from  anode  to  cathode  without  allowing  the  liquids  in 
the  compartments  to  mix. 

184.  Sodium. — Potash  and  soda  exhibit  so  much  similarity  in  their 
properties  that  we  cannot  be  surprised  at  their  having  been  confounded 
together  by  the  earlier  chemists,  and  it  was  not  till  17 36  that  Du  Hamel 
pointed  out  the  difference  between  them.  The  discovery  of  potassium 
naturally  led  Davy  to  that  of  sodium,  which  can  be  obtained  by  processes- 
exactly  similar  to  those  adopted  for  procuring  potassium,  to  which  it 
will  be  remembered  sodium  presents  very  great  similarity  in  properties 
(p.  20).  Sodium,  however,  is  readily  distinguished  from  potassium  by 
its  burning  with  a  yellow  flame,  which  serves  even  to  characterise  it 
when  in  combination. 

This  yellow  flame  is  well  seen  by  dissolving  salt  in  water  in  a  plate,  and  adding 
enough  alcohol  to  render  it  inflammable,  the  mixture  being  well  stirred  while 
burning.  A  little  piece  of  sodium  burnt  in  an  iron  spoon  held  in  a  flame  tinges- 
yellow  all  the  flames  in  the  room,  even  at  a  remote  distance.  The  blowpipe  flame 
may  also  be  employed  to  detect  sodium  by  this  colour,  as  in  the  case  of  potassium 
(p.  335).  In  fireworks,  sodium  nitrate  is  used  for  producing  yellow  flames.  A 
very  good  yellow  fire  may  be  made  by  carefully  and  intimately  mixing,  in  a  mortar, 
74  grains  of  nitrate  of  soda,  20  grains  of  sulphur,  6  grains  of  sulphide  of  antimony,, 
and  2  grains  of  charcoal,  all  carefully  dried,  and  very  finely  powdered. 

Sodium  is  manufactured  by  electrolysing  fused  caustic  soda  in  an 
iron  vessel  kept  hot  by  a  suitable  furnace.  Sodium  and  hydrogen  are 
separated  at  the  cathode  and  oxygen  at  the  anode. 

The  iron  cathode  is  surrounded  by  iron  wire  gauze  terminating  at  the  surface  of 
the  liquid  in  an  inverted  pot  in  which  the  sodium  and  hydrogen  collect  as  they  rise 
through  the  liquid.  The  anode  is  an  iron  cylinder  surrounding  the  gauze.  The 
object  of  the  latter  is  really  that  of  a  porous  diaphragm  to  keep  the  cathode  and 
anode  products  apart ;  the  reason  why  a  material  with  such  large  pores  can  be  used 
is  because  the  fused  sodium  has  a  high  surface  tension  and  will  not  pass  through 
the  gauze.  When  sufficient  sodium  has  collected  in  the  inverted  pot,  the  bottom 
of  this  is  removed  and  the  metal  ladled  out. 

Sodium  is  a  whiter  metal  than  potassium  ;  its  sp.  gr.  is  0.973  '•>  & 
melte  at  95°. 6  0.,  and  boils  at  742°  C.  When  heated  in  air,  it  gives 
a  mixture  of  Na2O  and  Na202,  which  is  converted  into  NaOH  by 
water,  0  being  evolved  from  the  Na202.  If  water  be  gradually  added 
to  Na2O2,  it  dissolves,  and  the  solution  yields  crystals  of  Na202.8H2O. 

Sodium  is  not  attacked  by  perfectly  dry  chlorine,  dry  bromine,  or  dry 
oxygen,  but  if  a  trace  of  aqueous  vapour  be  present,  combination  occurs 
with  violence.  When  mixed  with  10  to  30  per  cent,  of  its  weight  of 
potassium,  sodium  yields  an  alloy  which  is  liquid  at  temperatures  above 
o°  0.  and  is  used  for  filling  thermometers. 

Sodium  is  far  less  costly  than  potassium,  and  is  used  on  the  large 
scale  for  making  sodium  peroxide.  An  amalgam  of  sodium  (p.  85)  is 


GLAUBER'S  SALT.  351 

also  employed  with  advantage  in  extracting  gold  and  silver  from  their 
ores. 

Sodium  hydride  is  similar  to  the  potassium  compound  (p.  335). 

Sodium  peroxide,  Na202,  is  manufactured  by  causing  slices  of  sodium,  disposed 
on  trays  of  aluminium  (which  is  not  attacked),  to  pass  through  a  hot  (400°  C.) 
tunnel  which  is  traversed  in  the  contrary  direction  by  a  current  of  dry  air,  freed 
from  C0.2.  It  is  a  yellowish- white  powder  much  used  as  an  oxidising  and  bleaching 
agent. 

Sodium  chloride,  NaCl,  forms  rock  salt  and  table  salt,  the  latter 
consisting  of  minute  crystals  formed  by  boiling  down  the  water  of  brine 
springs  (see  p.  343).  It  forms  cubical,  anhydrous  crystals  of  sp.  gr, 
2.15,  and  is  almost  equally  soluble  in  hot  and  cold  water ;  100  parts  of 
water  at  15°  C.  dissolve  36  parts  of  salt,  at  100°  39  parts.  It  is  in- 
soluble in  alcohol.  It  melts  at  772°  C.,  and  is  afterwards  vaporised. 
It  forms  two  cryohydrates,  NaC1.2Aq,  deposited  from  a  saturated  solu- 
tion cooled  to  -  10°  C.,  and  NaCl.ioAq,  deposited  at  -  22°  C.  They 
are  decomposed  at  higher  temperatures.  Needles  of  Na01.2Aq  are 
obtained  from  a  solution  of  salt  in  hot  HC1. 

Sodium  fluoride,  NaF,  made  by  fusing  fluor  spar  (CaF2)  with  Na.,00^ 
is  used  for  softening  boiler  feed  waters. 

The  sulphides  of  sodium  are  similar  to  those  of  potassium. 

Sodium  sulphate  is  found  anhydrous  as  Thenardite.  Glauber's  salt, 
Na2S04.ioAq,  is  made  by  crystallising  salt  cake.  It  forms  prismatic 
crystals  which  effloresce  in  air,  fuse  at  33°  C.,  and  becomes  anhydrous  at 
100°.  It  is  more  soluble  in  water  at  33°  C.  than  at  any  other  tempera- 
ture, 100  parts  of  water  dissolving  115  parts  of  the  crystals.  When 
this  solution  is  heated,  it  deposits  anhydrous,  Na2S04,  the  temperature, 
33°  C.,  being  the  transition-point  (p.  315)  between  the  hydrate  and  the 
anhydrous  salt.  When  cooled  quietly  in  a  covered  vessel,  the  solution 
exhibits,  in  a  high  degree,  the  phenomenon  of  super  saturation  (p.  50), 
and  when  the  supersaturated  solution  is  cooled  to  5°  C.  crystals  of 
Na2S04.7Aq  may  be  obtained.  The  crystals  of  Na2S04.ioAq,  with  half 
their  weight  of  strong  HC1,  form  an  excellent  freezing-mixture,  giving 
the  same  temperature  as  ice  and  salt  (—18°  C.,  o°  F.) — 
Na2S04.ioAq  +  HC1  =  NaHS04  +  NaCl  +  loAq. 

Anhydrous  Na2S04  melts  at  865°  C.  ;  the  double  salt  Na2S04K2S04 
crystallises  in  plates  (plate  sulphate)  from  hot  water,  a  flash  of  light 
accompanying  the  separation  of  each  crystal. 

Glauberite  is  Na2Ca(S04)2,  and  is  nearly  insoluble  in  water. 

Hydrogen  sodium  sulphate,  NaHS04,  or  bisulphate  of  soda,  crystallises 
in  prisms  with  lAq.  It  is  more  fusible  and  more  easily  decomposed  by 
heat  than  is  KHS04.  It  is  decomposed  by  alcohol  into  H2S04,  and 
Na2S04,  which  remains  undissolved.  When  moderately  heated, 
2NaHSO4  =  H2O  +  Na2S207  (pyrosulphate},  decomposed  by  a  red  heat 
into  Na.,S04  and  S03.  Sodium  pyrosulphate  is  also  formed  when  NaCl 
is  heated  with  S03 ;  2NaCl  +  380,  =  Na2S2O7  +  S02C12. 

Sodium  sulphite  crystallises  in  prisms,  Na2S03<7Aq,  which  are  very 
soluble  in  water,  yielding  an  alkaline  solution.  It  is  prepared  by  satu- 
rating one-half  of  a  solution  of  Na2C03  with  SO2  gas,  and  adding  the 
other  half— 


(1)  Na^COg  +  2S02  +  H20  =  2NaHS03  +  C00 ; 

(2)  2NaHS03  +  Na^CO-j  =  2Na,jS03  +  H20  +  C02. 


352  BOEAX. 

The  sodium  sulphite  is  useful  in  the  laboratory  as  a  reducing-agent 
(p.  221),  and  the  hydrogen  sodium  sulphite  (bisulphite),  NaHS03,  is  used  in 
organic  chemistry  and  by  the  brewer. 

Sodium,  thiosulphate,  Na2S2O3,  or  hyposulphite  of  soda,  crystallises 
in  glassy  prisms,  Na2S203.5Aq,  the  preparation  and  properties  of  which 
have  been  described  at  p.  235. 

Sodium  thiosulphate  is  much  used  in  photography  for  fixing  prints 
by  dissolving  the  unaltered  portion  of  the  sensitive  film  of  silver  chloride, 
bromide,  or  iodide.  It  is  also  used  by  bleachers  as  an  antichlore. 

Phosphate  of  soda,  or  hydrogen  disodium  phosphate,  HNa2P04, 
crystallises  in  prisms,  Na2HP04.  12  Aq,  which  effloresce  in  air  and  dis- 
solve easily  in  water,  giving  an  alkaline  solution.  When  heated,  they 
fuse  easily,  and  lose  the  i2Aq  at  45°  C.  ;  at  a  red  heat,  2Na2HP04  = 
H20  +  Na4P2O7  (pyrophosphate). 

Na.,HPO4  occurs  in  the  blood  and  in  urine.  It  is  prepared  by  de- 
composing a  mineral  phosphate,  which  contains  Ca3(P04)2,  with  H2S04, 
so  as  to  obtain  the  insoluble  CaS04  and  a  solution  of  impure  H3PO4. 
This  is  decomposed  by  Na2C03,  the  solution  filtered  from  the  small 
•quantity  of  CaC03,  evaporated  and  crystallised  — 

H3P04  +  NaaCOg  =  Na^HP04  +  H20  +  C02. 

Arsenate  of  soda,  or  hydrogen  disodium  arsenate,  HNa2As04,  forms 
crystals  with  i2Aq,  resembling  those  of  the  phosphate,  but  the  salt  as 
commonly  sold  contains  yAq.  There  exists  also  the  salt  Na2HP04>7Aq, 
but  this  is  not  that  commonly  sold. 

Sodium  arsenate  is  made  by  dissolving  white  arsenic  in  caustic  soda, 
adding  sodium  nitrate,  evaporating  to  dryness,  heating  the  residue  to 
iredness  and  dissolving  in  water  — 


(1)  As406  +  !2NaOH  =  4Na3As03  +  6H20  ; 

(2)  Na3As03  +  NaN03  =  Na3As04  +  NaNOo 

(3)  Na3As04  +  H20  =  Na^HAsC^  +  NaOH. 


185.  Borax,  biborate  of  soda  (Na20.2B203),  or  sodium  pyroborate 
;(Na2B407).  —  It  has  already  been  stated  that  borax  is  deposited  during 
the  evaporation  of  the  waters  of  certain  lakes  in  Thibet,  whence  it  is 
imported  into  this  country  in  impure  crystals  (tincal),  which  are  covered 
with  a  peculiar  greasy  coating.  Borax  has  also  been  found  abundantly 
in  Southern  California. 

The  refiner  of  tincal  powders  the  crystals  and  washes  them,  upon  a  strainer, 
with  a  weak  solution  of  soda,  which  converts  the  greasy  matter  into  a  soap  and 
dissolves  it.  The  borax  is  then  dissolved  in  water,  a  quantity  of  sodium  carbonate 
is  added  to  separate  some  lime  which  the  borax  usually  contains,  and,  after 
filtering  off  the  carbonate  of  lime,  the  solution  is  evaporated  to  the  crystallising 
point  and  allowed  to  cool,  in  order  that  it  may  deposit  the  pure  crystals  of  borax. 
Boracite,  2Ca0.3B203,  from  Asia  Minor,  is  frequently  used  as  a  raw  material  for 
making  borax  ;  the  mineral  is  boiled  with  Na^COg,  the  CaC03  filtered,  and  the 
solution  crystallised. 

Borax  is  manufactured  in  this  country  by  heating  sodium  carbonate  with  boric 
acid,  when  the  latter  expels  the  carbonic  acid.*  The  mass  is  then  dissolved  in 
water,  and  the  borax  crystallised,  an  operation  upon  which  much  care  is  bestowed, 
since  the  product  does  not  meet  with  a  ready  sale  unless  in  large  crystals.  The 
solution  of  borax,  having  been  evaporated  to  the  requisite  degree  of  concentration, 
is  allowed  to  crystallise  in  covered  wooden  boxes,  which  are  lined  with  lead  and 

*  The  ammonia  which  is  evolved  from  the  Tuscan  boracic  acid  employed  in  this  process 
is  known  in  commerce  as  Volcanic  ammonia,  and  is  free  from  the  empyreumatic  odour  which 
generally  accompanies  that  from  coal  and  bones. 


CHILI  SALTPETEE.  353 

enclosed  in  an  outer  case  of  wood,  the  space  between  the  sides  of  the  case  and 
the  box  being  stuffed  with  some  bad  conductor  of  heat,  so  that  the  solution  of 
borax  may  cool  very  slowly,  and  large  crystals  may  be  deposited.  In  about  thirty 
hours  the  crystallisation  is  completed,  when  the  liquid  is  drawn  off  as  rapidly  as 
possible,  the  last  portion  being  carefully  soaked  up  with  sponges,  so  that  no  small 
crystals  may  be  afterwards  formed  upon  the  surface  of  the  large  ones  ;  the  case  is 
then  again  covered  up,  so  that  the  crystals  may  cool  slowly  without  cracking. 
When  a  solution  of  borax  is  crystallised  above  56°  C.,  it  yields  octahedral  borax, 
Na2B407.5Aq.  which  is  also  deposited  when  solution  of  prismatic  borax  is  evaporated 
in  vacua. 

The  ordinary  prismatic  crystals  of  borax  are  represented  by  the 
formula  Na2B4Or.ioAq.  They  soon  effloresce  and  become  opaque  when 
exposed  to  air,  and  may  readily  be  distinguished  by  their  alkaline  taste 
and  action  upon  test-papers,  and  especially  by  their  behaviour  when 
heated,  for  they  fuse  easily  and  intumesce  most  violently,  swelling  up  to 
a  white  spongy  mass  of  many  times  their  original  bulk  ;  this  mass 
afterwards  fuses  down  to  a  clear  liquid  which  forms  a  transparent 
glassy  mass  on  cooling  (vitrejied  borax),  and  since  this  glass  is  capable  of 
dissolving  many  metallic  oxides  with  great  readiness  (borax  being,  by 
constitution,  an  acid  salt,  and  therefore  ready  to  combine  with  more 
base),  it  is  much  used  in  the  metallurgic  arts.  Large  quantities  of  borax 
are  also  employed  in  glazing  stoneware. 

A  dilute  solution  of  borax  dissolves  iodine  to  a  colourless  solution,  but  on  con- 
centration the  iodine  is  precipitated  ;  probably  the  borax  is  decomposed  in  the 
dilute  solution  into  boric  acid  and  soda,  which  converts  the  iodine  into  iodide  and 
iodate  ;  on  concentrating,  the  boric  acid  liberates  hydriodic  and  iodic  acids,  which 
react  with  each  other,  separating  iodine  (p.  200). 

Sodium  nitrate  or  nitrate  of  soda,  NaN03,  also  known  as  Peruvian 
Chili  saltpetre,  is  found  in  Peru  and  Chili  in  beds  beneath  the  surface 
soil,  where  it  is  dug  out  and  crystallised  from  water.  It  is  often  spoken 
of  as  cubical  saltpetre,  since  it  crystallises  in  rhombohedra,  easily  mis- 
taken for  cubes,  whilst  prismatic  saltpetre,  nitrate  of  potassium,  crystal- 
lises in  six-sided  prisms.  Sodium  nitrate  cannot  be  substituted  for 
potassium  nitrate  as  an  ingredient  of  gunpowder,  since  it  attracts 
moisture  from  the  air,  becoming  damp,  and  is  less  powerful  in  its 
oxidising  action  upon  combustible  bodies  at  a  high  temperature.  It  is, 
however,  used  for  making  potassium  nitrate  for  gunpowder  (p.  337), 
A  much  more  extended  application  is  its  use  as  a  manure,  for  supplying 
nitrogen  ;  large  quantities  are  also  used  for  making  nitric  acid.  It 
melts  at  320°  C.  and  dissolves  in  water  to  the  extent  of  87  per  cent,  at 
20°  C.  and  180  per  cent,  at  100°  C. 

Sodium  nitrite,  NaN02,  is  much  used  for  diazotising  organic  amides  (p.  106).  It 
is  made  by  heating  NaN03  to  420°  C.  in  an  iron  vessel  and  stirring  the  molten 
mass  with  metallic  lead  ;  NaN03  +  Pb  =  NaN02  +  PbO.  It  crystallises  in 
colourless  deliquescent  prisms  very  soluble  in  water  ;  the  solution  of  the  commercial 
salt  is  generally  alkaline  owing  to  the  presence  of  a  small  quantity  of  caustic  soda, 
but  the  pure  salt  is  neutral. 

Sodium  silicate. — A  combination  of  soda  with  silica  has  long  been 
used,  under  the  name  of  soluble  glass,  for  imparting  a  fire-proof  character 
to  wood  and  other  materials,  and,  more  recently,  for  producing  artificial 
stone  for  building  purposes,  and  for  a  peculiar  kind  of  permanent  fresco- 
painting  (stereochromy),  the  results  of  which  are  intended  to  withstand 
exposure  to  the  weather. 

Sodium  metasllicate  has  been  obtained  in  prismatic  crystals,  Na^SiOg-SAq,  by 

z 


354  AMMONIUM   SALTS. 

dissolving  amorphous  silica  in  NaOH.  It  is  soluble  in  water,  and  the  solution  is 
decomposed  by  C02.  A  solution  of  amorphous  Si02  in  hot  aqueous  Na2C03 
gelatinises,  on  cooling. 

Soluble  glass  is  usually  prepared  by  fusing  15  parts  of  sand  with  8  parts  of 
•carbonate  of  soda  and  I  part  of  charcoal.  The  silicic  acid,  combining  with  the 
«oda,  disengages  the  carbonic  acid  gas,  the  expulsion  of  which  is  facilitated  by  the 
presence  of  charcoal,  which  converts  it  into  carbonic  oxide.  The  mass  thus  formed 
is  scarcely  affected  by  cold  water,  but  dissolves  when  boiled  with  water,  yielding  a 
strongly  alkaline  liquid. 

In  using  this  substance  for  rendering  wood  fire-proof,  a  rather  weak  solution  is 
first  applied  to  the  wood,  and  over  this  a  coating  of  lime-wash  is  laid  ;  a  second 
coating  of  soluble  glass  (in  a  more  concentrated  solution)  is  then  applied.  The 
wood  so  prepared  is,  of  course,  charred,  as  usual,  by  the  application  of  heat,  but 
its  inflammability  is  remarkably  diminished. 

For  the  manufacture  of  Ransome's  artificial  stone,  the  soluble  glass  is  prepared  by 
heating  flints,  under  pressure,  with  a  strong  solution  of  caustic  soda,  to  a  tempera- 
ture between  300°  and  400°  F.  (149°  and  204°  C.),  when  the  silica  constituting  the 
flint  enters  into  combination  with  the  soda.  Finely  divided  sand  is  moistened 
with  this  solution,  pressed  into  moulds,  dried,  and  exposed  to  a  high  temperature, 
when  the  silicate  of  soda  fuses  and  cements  the  grains  of  sand  together  into  a  mass 
of  artificial  sandstone,  to  which  any  required  colour  may  be  imparted  by  mixing 
metallic  oxides  with  the  sand  before  it  is  moulded. 

Silicate  of  soda  is  also  sometimes  used  as  a  dung  substitute  in  calico-printing  (q.v.). 

Sodium  chlorate,  NaC103,  resembles  the  potassium  salt,  but  is  very  soluble,  and  is 
on  this  account  preferred  for  some  purposes.  It  is  made  by  substituting  Na2S04  for 
KC1  in  the  method  described  on  p.  184  for  making  KC103. 

SALTS  OF  AMMONIUM. 

1 86.  The  great  chemical  resemblance  between  some  of  the  salts  formed 
by  neutralising  acids  with  ammonia,  and  the  salts  of  potassium  and 
sodium,  has  been  already  pointed  out  as  affording  a  reason  for  the 
hypothesis  of  the  existence  of  a  compound  metal,  ammonium  (NH4), 
equivalent  in  its  functions  to  potassium  and  sodium  (p.  85). 

The  compounds  which  are  formed  when  ammonia  (NH3)  combines 
with  the  anhydrides,  such  as  carbonic  (CO,)  and  sulphuric  (SO3),  do  not 
exhibit  the  resemblance  to  the  salts  of  potassium  and  sodium  until  water 
is  added.  Thus,  by  the  action  of  dry  ammonia  gas  upon  sulphuric 
anhydride,  a  compound  called  sulphuric  ammonide  is  formed,  having  the 
composition  (NH3)2S03.  This  substance  dissolves  in  water  and  crystal- 
lises in  octahedra,  but  its  solution  is  not  precipitated  by  barium  chloride, 
which  always  precipitates  the  true  sulphates,  nor  by  platinic  chloride, 
which  precipitates  the  true  ammonium  salts.  By  long  boiling  with 
water,  however,  it  becomes  ammonium  sulphate,  (NH4)2S04,  which 
yields  precipitates  with  both  the  above  tests.*  The  phosphoric,  carbonic, 
and  sulphurous  anhydrides  also  combine  with  nearly  dry  ammonia  to 
form  ammonides,  which  do  not  respond  to  the  ordinary  tests  for  the 
corresponding  salts  of  ammonium  until  after  water  has  been  assimilated. 
The  true  salts  of  ammonium  are  produced  either  by  the  combination  of 
an  acid  with  ammonia,  or  by  double  decomposition. 

Ammonium  nitrate,  NH4N03,  is  prepared  by  neutralising  ordinary 
nitric  acid  with  lumps  of  ammonium  carbonate,  when  the  nitrate 
crystallises  on  cooling  in  six-sided  prisms  like  those  of  KN03,  but  they 
are  deliquescent  and  very  soluble  in  water ;  it  absorbs  one-third  of  its 

1  » *  Representing  sulphuric  acid  as  sulphuryl  hydroxide,  SO2.OH.OH,  ammonium  sulphate  is 
SO2.ONH4.ONH4,  and  sulphuric  ammonide  is  SO2.XB2.ONH4,  the  amidogen  group,  NH2, 
being  substituted  for  the  ammon-oxyl  group,  O(NH4). 


AMMONIUM   CARBONATE. 


355 


weight  of  ammonia  and  becomes  liquid,  the  ammonia  being  expelled 
again  at  25°  C.  When  gently  heated,  it  melts  at  150°  C.,  and  is  de- 
composed at  210°  0.,  when  it  boils  and  passes  off  entirely  as  water  and 
nitrous  oxide  ;  N H4NO?  =  2  H20  +  N20.  If  sharply  heated,  as  by  throw- 
ing it  on  a  red-hot  surface,  it  deflagrates.  If  very  carefully  heated,  it 
may  be  sublimed.  It  is  largely  used  for  making  nitrous  oxide,  and  is 
a  constituent  of  some  explosives.* 

Ammonium  nitrite,  NH4N02,  is  interesting  on  account  of  its  easy  decomposition 
by  heat  ;  NH4N02  =  N2  +  2H20.  This  occurs  even  on  boiling  the  solution,  so  that 
a  mixture  of  solutions  of  potassium  nitrite  and  ammonium  chloride  is  used  for 
preparing  nitrogen,  Ammonium  nitrite  is  found,  in  very  small  quantity,  in  rain 
water  ;  it  can  also  be  detected  in  the  water  condensed  from  hydrogen  burning  in 
air.  Ammonia  is  partly  converted  into  this  salt  when  oxidised  by  ozone  or  even 
by  air  in  presence  of  heated  platinum  ;  2NH3  +  03  =  NH4N02  +  H20. 

187.  Ammonium  sulphate,  (NH4)2S04,  is  largely  employed  in  the 
preparation  of  ammonia  alum,  and  as  an  artificial  manure,  for  which 
purposes  it  is  generally  obtained  from  the  ammoniacal  liquor  of  the 
gas-works  by  distillation  with  lime  and  absorption  of   the   liberated 
ammonia  in   H2SO4.     The  rough  crystals  are  gently  heated  to  expel 
tarry  substances,  and  purified  by  recrystallisation.     The  crystals  have 
the  same  shape  as  those  of  potassium  sulphate,  and  are  easily  soluble  in 
water,   but    not   in   alcohol.       When   heated   to   about    260°    C.,   the 
(NH4)2S04  is  decomposed,  yielding  vapour  of  ammonium  sulphite,  water, 
ammonia,  nitrogen,  and  sulphur  dioxide.     If  muslin  be  dipped  into  a 
solution  of  ammonium  sulphate  in  ten  parts  of  water  and  dried,  it  will 
no  longer  burn  with   flame   when   ignited.     The  mineral  mascagnine 
consists  of   ammonium    sulphate.     This   salt  is  occasionally  found  in 
needle-like  crystals  upon  the  windows  of  rooms  in  which  coal  gas  is 
burnt, 

1 88.  Ammonium  carbonate,  also  called  smelling  salts,  or  Preston 
salts,  is  largely  used  in  medicine,  and  by  bakers  and  confectioners,  for  im- 
parting lightness  or  porosity  to  cakes,  &c.     It  is  commonly  prepared  by 
mixing  ammonium  sulphate  with  twice  its  weight  of  chalk,  and  distilling 
the  mixture  in  an  earthern  or  iron  retort,  communicating,  through  an 
iron  pipe,  with  a  leaden  chamber  or  receiver,  in  which  the  ammonium 
carbonate  collects  as  a  transparent  fibrous  mass,  which  is  extracted  by 
taking  the  receiver  to  pieces,  and  purified  by  resubliming  it  in  iron 
vessels  surmounted  by  leaden  domes.     The  action  of  calcium  carbonate 
upon  ammonium   sulphate  would   be  expected  to  furnish  the  normal 
carbonate,  (NH4)2C03,  but  this  salt  (even  if  produced)  is  decomposed  by 
the  heat  employed  in  the  process  into  hydrogen  ammonium  carbonate, 
OO(ONH4)(ONH4)  =  CO(ONH4)(OH)  +  NH3,   and   ammonium   car- 
bamate,  CO(ONH4)(ONH4)  =  CO(ONH4)(NHS)  +  H20. 

The  commercial  carbonate  is  usually  a  mixture  of  2  mols.  of  the 
former  to  one  of  the  latter.  By  treating  it  with  strong  alcohol,  the 
carbamate  is  dissolved  and  the  hydrogen  ammonium  carbonate  left. 

When  exposed  to  the  air  it  smells  of  ammonia,  and  gradually  be- 
comes NH4HC03  or  CO(ONH4)(OH),  the  carbamate  being  decomposed 
and  volatilised;  CO(ONH4)(NH2)  =  C03  +  2NH3.  On  treating  the 
commercial  carbonate  with  a  little  water,  the  NH4HC03  is  left  un- 

*  The  explosive  Bellite  consists  of  5  parts  of  ammonium  nitrate  and  i  part  of  di-uitro- 
bcnzene  (q.v.)  ;  it  is  said  to  be  30  per  cent,  stronger  than  dynamite,  and  to  explode  only  by 
detonation. 


SAL  AMMONIAC, 

dissolved,  whilst  the  car  bam  ate  is  converted  into  normal  carbonate  and 
dissolved  ;  CO(ONH4)(NH2)  +  H2O  =  (NH4)2C03/ 

Sal  volatile  is  an  alcoholic  solution  of  ammonium  carbonate  and  car- 
bamate. 

By  saturating  ammonia  solution  with  C02,  crystals  of  ammonium 
sesquicarbonate,  (NH4)2CO3.2NH4HC03  are  obtained. 

Ammonium  carbonate,  (NH4)2C03,  is  obtained  in  crystals  by  treating  the  com- 
mercial carbonate  with  strong  ammonia.  The  crystals  contain  lAq.  They  are 
deliquescent  in  air,  and  evolve  NH3,  becoming  converted  into  the  bicarbonate  ; 
(NH4)2C03  =  NH3  +  NH4HC03. 

Ammonium  bicarbonate,  NH4HC03  or  hydrogen  ammonium  carbonate,  is  the  most 
stable,  and  is  obtained  by  dissolving  the  commercial  carbonate  in  a  little  boiling 
water,  when  it  crystallises  on  cooling. 

The  ammonium  carbamate  is  deposited  as  a  white  solid  when  ammonia  gas  is. 
mixed  with  carbonic  acid  gas,  unless  both  be  quite  dry.  It  may  be  obtained  in 
crystals  by  passing  C02  and  NH3  into  the  strongest  solution  of  ammonia. 

Ammonium  carbamate  is  easily  soluble  in  water,  which  soon  converts  it  into 
ammonium  carbonate.  The  aqueous  solution,  when  freshly  prepared,  is  not  pre- 
cipitated by  calcium  chloride,  but  the  calcium  carbonate  is  deposited  on  standing 
or  heating.  When  ammonium  carbamate  is  heated  in  a  sealed  tube  at  130°  C.  it 
is  decomposed  into  ammonium  carbonate  and  urea;  2NH4C02NH2=(JSTH4)2C03  + 
CON2H4.  Carbamic  acid,  HC02NH2,  has  not  been  isolated  ;  its  relation  to  carbonic 
acid  is  seen  by  a  comparison  of  their  formulae  ;  carbonic  acid,  CO.  OH.  OH  ; 
carbamic  acid,  CO.OH.NH2.  Other  carbamates  have  been  obtained  by  passing 
C02  through  strongly  ammoniacal  solutions  of  different  bases,  and  precipitating 
the  carbamates  by  alcohol.  When  potassium  carbamate  is  heated,  it  yields  water 
and  potassium  cyanate ;  KC02NH2=  KCNO  +  H20. 

Carbamates  are  remarkable  for  evolving  nitrogen  when  treated  with  a  mixture  of 
soda  and  sodium  hypobromite,  but  not  with  the  hypochlorite  ;  thus — 

2(CO.NH2.ONa)  +  sNaOBr  +  2NaOH  =  2CO(ONa)2  +  sNaBr  +  sH20  +N2. 
If  solution  of  sodium  carbamate  be  mixed  with  sodium  hypochlorite  and"  soda,  no 
nitrogen  is  evolved  until  a  soluble  bromide  is  added,  a  reaction  which  will  indicate 
bromides  even  in  dilute  solutions.  The  solution  of  sodium  carbamate  may  be  pre- 
pared by  dissolving  ammonium  carbamate  in  a  strong  solution  of  soda,  and 
evaporating  over  strong  sulphuric  acid. 

189.  Ammonium  chloride  (NH4C1),  also  called  muriate  of  ammonia 
and  sal  ammoniac. — When  ordinarily  dry  NH3  is  brought  in  contact 
with  an  equal  volume  of  dry  HC1,  it  has  been  seen  (p.  84)  that  they 
combine  directly  to  produce  this  salt,  the  preparation  of  which  on  the 
large  scale  has  been  noticed  at  p.  78.  Its  commercial  form  is  that  of 
a  very  tough  translucent  fibrous  mass,  generally  of  the  dome -like 
shape  of  the  receivers  in  which  it  has  been  condensed,  and  often 
striped  with  brown,  from  the  presence  of  a  little  iron.  It  has  not  the 
least  smell  of  ammonia,  and  is  very  soluble  in  water,  requiring  about 
three  parts  of  cold  water,  and  little  more  than  its  own  weight  of  boiling 
water.  As  the  hot  solution  cools,  it  deposits  beautiful  fern-like 
crystallisations  composed  of  minute  cubes  and  octahedra.  The  dis- 
solution of  sal  ammoniac  in  water  lowers  the  temperature  very  con- 
siderably, which  renders  the  salt  very  useful  in  freezing-mixtures.  A 
mixture  of  equal  weights  of  sal  ammoniac  and  nitre,  dissolved  in  its 
own  weight  of  water,  lowers  the  temperature  of  the  latter  from  10° 
to  -  12°  C.  In  this  case  partial  decomposition  occurs,  resulting  in  the 
production  of  potassium  chloride  and  ammonium  nitrite,  both  of  which 
absorb  much  heat  whilst  being  dissolved  by  water.  The  solution  of 
ammonium  chloride  in  water  is  slightly  acid  to  blue  litmus-paper. 
When  sal  ammoniac  is  heated,  it  vaporises,  at  a  temperature  below 
redness,  without  fusing  ;  the  vapour  forms  thick  white  clouds  in  the 


SULPHIDES   OF  AMMONIUM.  357 

air,  and  may  be  condensed  as  a  white  crust  upon  a  cold  surface  ;  but  it 
is  said  that  it  cannot  be  sublimed  without  some  loss,  a  portion  being 
decomposed  into  HC1,  H  and  N. 

As  already  stated  (p.  85),  ammonium  chloride  dissociates  when 
heated,  so  that  the  heat  which  becomes  latent  or  is  absorbed  in  vapor- 
ising the  NH4C1,  is  almost  exactly  that  which  is  produced  by  the  com- 
bination of  the  hydrochloric  acid  and  ammonia,  viz.,  NH3,  HC1  =  42,000. 

When  ammonium  chloride  is  heated  with  metallic  oxides,  the  hydro- 
chloric acid  often  converts  the  oxide  into  a  chloride  which  is  either 
fusible  or  volatile,  so  that  sal  ammoniac  is  often  employed  for  cleansing 
the  surfaces  of  metals  previously  to  soldering  them.  Even  those  metallic 
oxides  which  are  destitute  of  basic  properties,  such  as  antimonic  and 
stannic  oxides,  are  convertible  into  chlorides  by  the  action  of  sal  am- 
moniac at  a  high  temperature. 

Ammonium  chloride  is  found  in  volcanic  districts,  and  is  present  in 
very  small  quantity  in  sea  water. 

190.  Hydrosulphate  of  ammonia,  2NH3.H2S,  or  ammonium  sul- 
phide, (NH4)2S,  has  been  obtained  in  colourless  crystals  by  mixing 
hydrosulphuric  acid  gas  with  twice  its  volume  of  ammonia  gas  in  a 
vessel  cooled  by  a  mixture  of  ice  and  salt.*  It  is  a  very  unstable  com- 
pound, decomposing  in  solution  into  free  ammonia  and  ammonium 
hydrosulphide,  NH4HS,  which  may  also  be  obtained  in  solution  by 
saturating  with  H2S  at  o°  C.  strong  ammonia  diluted  with  four  times 
its  volume  of  water. 

Solution  of  ammonium  sulphide,  prepared  by  mixing  the  "  hydrosulphide  " 
(made  by  saturating  ammonia  solution  with  H2S)  with  an  equal  volume  of 
ammonia,  is  much  used  in  analytical  chemistry,  and  is  supposed  to  contain 
(NH4)2S.  The  solution  has  a  very  disagreeable  odour. 

When  a  strong  solution  of  ammonia  is  saturated  with  hydrogen  sulphide  at  o°  C., 
a  colourless  solution  is  formed,  from  which  colourless  crystals  separate,  the  com- 
position of  which  varies  with  the  strength  of  the  ammonia,  but  may  be  expressed  by 
the  general  formula,  (NH4)2S.a;-NH4HS.  The  solution  soon  becomes  yellow  in  con- 
tact with  the  air,  from  the  formation  of  ammonium  poly  sulphides  of  the  form 
(NH^Stf  ;  eventually  the  solution  deposits  sulphur  and  becomes  colourless,  thio- 
sulphate,  sulphite,  and  sulphate  of  ammonium  being  formed.  When  the  freshly 
prepared  colourless  solution  is  mixed  with  an  acid,  the  solution  remains  clear,  H2S 
being  evolved  with  effervescence  ;  NH4HS  +  HC1  =  NH4C1  +  H2S  and  (NH4)2S  + 
2HC1  =  2NH4C1  +  H2S  ;  but  if  the  solution  be  yellow,  a  milky  precipitate  of  sulphur 
is  produced,  from  the  decomposition  of  the  polysulphides  ;  (NH4)2Sa! 


The  fresh  solution  gives  a  black  precipitate  of  lead  sulphide  when  solution  of 
lead  acetate  is  added  to  it,  but  after  it  has  been  kept  till  it  is  of  a  dark  yellow  or 
red  colour,  it  gives  a  red  precipitate  of  the  persulphide  of  lead. 

Ammonium  polysulphides  are  the  chief  constituents  of  Boyle's  fuming  liquor,  a 
fetid  yellow  liquid  obtained  by  distilling  sal  ammoniac  with  sulphur  and  lime. 
They  are  sometimes  deposited  in  yellow  crystals  from  this  liquid.  By  dissolving 
sulphur  in  ammonium  disulphide,  orange-yellow  prismatic  crystals  of  ammonium 
pentasulphlde,  (NH4)2S5,  maybe  obtained. 

Ammonium  bromide  (NH4Br)  and  ammonium  iodide  (NH4I)  are  useful  in  pho- 
tography. They  are  both  colourless  crystalline  salts,  but  the  iodide  is  very  liable 
to  become  yellow  or  brown,  from  the  separation  of  iodine,  unless  kept  dry  and  in 
the  dark.  Both  salts  are  extremely  soluble  in  water. 

Microcosmic  salt,  phosphorus  salt,  or  hydrogen  sodium  ammonium  phosphate, 
HNaNH4P04.4Aq,  is  found  in  putrid  urine  and  in  guano.  It  is  prepared  by  mixing 
hot  strong  solutions  of  ammonium  chloride  and  sodium  phosphate  — 

NH4C1  =  HNaNH4P04  +  NaCl. 


*  When  the  NH3  is  in  large  excess  a  volatile  liquid,  (NH4)2S.2NH3,  is  formed,  the  vapour 
of  which  is  very  poisonous. 


RUBIDIUM  AND   CAESIUM. 

It  forms  prismatic  crystals  which  are  very  soluble  and  fusible,  boiling  violently 
when  further  heated,  and  finally  leaving  a  transparent  glass  of  sodium  meta- 
phosphate,  which  is  valuable  in  blowpipe  work  for  dissolving  metallic  oxides  ; 
NaNH4HP04  =  NH3  +  H20  +  NaP03. 

LITHIUM. 

Li  =  7  parts  by  weight. 

191.  This  comparatively  rare  metal  is  obtained  chiefly  from  the  minerals  lepido- 
lite  (\eirls,  a  scale)   or  lithia-mica,  containing  silicate  of  alumina  with  fluorides  of 
potassium  and  lithium  ;   petallte  (-rr6Ta\ov,  a  leaf),   silicate  of   soda,  lithia,    and 
alumina  ;  and  triphane  or  spodumene  (crTroSds,   aslies),  which  has  a  similar  composi- 
tion.    Its   name  (from  \ldos,   a  stone]  was  bestowed   in  the  belief  that  it  existed 
only  in  the  mineral  kingdom,  but  recent  investigation  has  detected  it  in  minute 
proportion  in  the  ashes  of  tobacco  and  other  plants.     The  water  of  a  hot  spring  in 
Clifford  United  Mines,  in  Cornwall,  contains  26  grains  of  lithium   chloride  per 
gallon. 

Metallic  lithium  is  obtained  by  decomposing  fused  lithium  chloride  by  a  gal- 
vanic current.  It  is  remarkable  as  the  lightest  solid  known  (sp.  gr.  0.59).  It 
bears  a  general  resemblance  to  potassium  and  sodium,  but  it  is  harder  and  less 
easily  oxidised  than  those  metals.  It  decomposes  water  rapidly  at  the  ordinary 
temperature,  but  does  not  inflame  upon  it.  It  melts  at  186°  C.,  but  cannot  be 
distilled. 

Lithium  bears  some  resemblance  to  calcium  as  well  as  to  potassium  and  sodium. 
Thus  it  forms  an  oxide,  L120,  when  it  burns,  which  is  earthy,  and  dissolves  only 
gradually  in  water,  unlike  oxides  of  K  and  Na.  The  hydroxide  LiOH,  obtained 
by  causticising  the  carbonate  with  lime,  is  less  soluble  than  KOH  and  NaOH  and 
a  less  powerful  alkali.  Another  leaning  towards  the  calcium  group  of  metals  is 
seen  in  the  sparing  solubility  of  lithium  phosphate,  Li3P04  (i  in  2500),  and  car- 
bonate, Li2C03  (i  in  100).  The  latter,  however,  is  not  decomposed  by  heat  as 
calcium  carbonate  is  ;  it  is  made  from  lepidolite  by  fusing  the  mineral,  powdering 
it,  boiling  with  HC1  and  HN03  and  precipitating  the  iron  lime,  &c.,  by  Na^COg ; 
the  filtrate  contains  NaCl,  KC1,  and  LiCl ;  it  is  concentrated  and  mixed  with 
Na2C03  to  precipitate  the  Li2C03. 

The  "lithia"  used  as  a  remedy  for  gout  is  a  mixture  of  lithium  carbonate  and 
citric  acid,  the  latter  dissolving  the  former  as  lithium  citrate  with  effervescence 
when  the  mixture  is  put  in  water. 

The  compounds  of  lithium  impart  a  red  colour  to  a  flame. 

RUBIDIUM  AND  CAESIUM. 
Rb'  =  84.8  parts  by  weight,  Cs'  =  i32  parts  by  weight. 

192.  These  elements  were  discovered  in  1860,  by  Bunsen  and  Kirchhoff,  during  the 
analysis  of  a  certain  spring  water  which  contained  these  metals  in  so  minute  quantity 
(2  or  3  grains  in  a  ton)  that  they  would  certainly  have  escaped  observation  if  the 
analysis  had  been  conducted  in  the  ordinary  way.     The  discovery  of  these  metals, 
as  well  as  of  three  others  (thallium,  indium,  gallium),  to  be  mentioned  hereafter, 
was  the  result  of  the  application  of  the  method  of  spectrum  analysis  (see  p.  329). 

When  examining,  with  the  spectroscope,  the  alkali  chlorides  extracted  from  the 
spring  water,  Bunsen  and  Kirchhoff  observed  two  red  and  two  blue  bands  in  the 
spectrum,  which  they  could  not  ascribe  to  any  known  substance,  and  which  they 
ultimately  traced  to  the  two  new  metals,  rubidium  (rubidus,  I  dark-red)  and  CEesium 
(ccesius,  sky-blue),  which  may  be  isolated  by  the  electrolysis  of  their  fused  salts,  or 
by  distilling  them  from  a  mixture  of  their  hydroxides  with  magnesium. 

Rubidium  (m.  p.  38° ;  sp.  gr.  1.52)  has  since  been  found  in  small  quantity  in 
carnallite,  in  lepidolite,  and  in  the  ashes  of  many  plants.  This  metal  is  closely 
related  in  properties  to  potassium,  but  is  more  easily  fusible  and  convertible  into 
vapour,  and  actually  surpasses  that  metal  in  its  attraction  for  oxygen,  rubidium 
taking  fire  spontaneously  in  air,  forming  Rb02.  It  burns  on  water  with  exactly 
the  same  flame  as  potassium.  Its  hydroxide  is  a  powerful  alkali,  like  potash,  and 
its  salts  are  isomorphous  with,  and  more  soluble  than,  those  of  potassium.  The 
double  chloride  of  platinum  and  potassium  is  eight  times  as  soluble  in  boiling  water 
as  the  corresponding  salt  of  rubidium,  which  is  taken  advantage  of  in  separating 
these  two 'allied  metals.  Rubidium  forms  stable  and  sparingly  soluble  double  salts 


REVIEW   OF   THE  ALKALI   METALS.  359 

with  many  halides  ;  thus  the  borofluoride,  RbBF4,  requires  100  parts  of  boiling 
water  to  dissolve  it. 

Caesium  (m.  p.  27° ;  sp.  gr.  1.88)  appears  to  be  even  more  highly  electro-positive 
than  rubidium,  forming  a  strong  alkali,  caesium  hydroxide,  and  salts  which  are 
isomorphous  with  those  of  potassium.  Caesium  carbonate,  however,  is  soluble  in 
alcohol,  which  does  not  dissolve  the  carbonates  of  potassium  and  rubidium. 
Moreover,  the  caesium  bitartrate  is  nine  times  as  soluble  in  water  as  the  rubidium 
bitartrate  is. 

Caesium  has  been  found  in  lepidolite  ;  and  the  rare  mineral  pollux,  found  in 
Elba,  and  resembling  felspar  in  composition,  is  said  to  contain  a  very  large  quantity 
of  this  metal.  The  alum  of  the  island  of  Vulcano  is  mentioned  as  a  rich  source  of 
caesium  and  rubidium. 

Metallic  caesium  cannot  be  obtained  by  reduction  with  carbon,  but  it  has 
been  extracted  by  decomposing  its  cyanide  by  the  galvanic  current. 

Both  rubidium  and  caesium  show  a  remarkable  tendency  to  combine  with  halo- 
gens as  though  they  were  trivalent  or  pentavalent,  forming  such  compounds  as 
EbICl4,  CsI5,  and  KbIBr3. 

193.  General  review  of  the  group  of  alkali  metals. — Caesium, 
rubidium,  potassium,  sodium,  and  lithium  constitute  a  group  of  elements 
conspicuous  for  their  highly  electro-positive  character,  the  powerfully 
alkaline  nature  of  their  hydroxides,  and  the  general  solubility  of  their 
salts.  Their  chemical  characters  and  functions  are  directly  opposite  to 
those  of  the  electro-negative  group  containing  fluorine,  chlorine,  bromine, 
and  iodine,  and,  like  those  elements,  they  exhibit  a  gradation  of  pro- 
perties. Thus,  caesium  appears  to  be  the  most  highly  electro-positive 
member,  rubidium  the  next,  then  potassium  and  sodium,  whilst  lithium 
is  the  least  electro-positive ;  and  just  as  iodine,  the  least  electro-negative 
of  the  halogens,  possesses  the  highest  atomic  number,  so  caesium,  the  least 
electro-negative  (or  most  electro-positive)  of  the  alkali-metals,  has  a 
higher  atomic  weight  than  any  other  member  of  this  group,  their 
atomic  weights  being  represented  by  the  numbers,  caesium,  132  ;  rubi- 
dium, 85  ;  potassium,  39  ;  sodium,  23  ;  lithium,  7.  As  in  the  case  of 
the  halogens,  also,  these  are  all  monovalent  elements.  Just  as  chlorine 
is  accepted  as  the  representative  of  chlorous  radicles,  so  potassium  is  com- 
monly regarded  as  the  type  of  basylous  radicles,  the  term  radicle  being 
applied  to  all  substances,  whether  elementary  or  compound,  which  are 
capable  of  being  transferred,  like  chlorine  or  potassium,  from  one  com- 
pound to  another  without  suffering  decomposition. 

Attention  has  been  called  (p.  304)  to  the  gradation  exhibited  in  some 
of  the  physical  properties  of  these  elements. 

In  some  of  their  salts  a  similar  gradational  relation  is  observed ;  the 
carbonates,  for  example,  of  caesium,  rubidium,  and  potassium  are  highly 
deliquescent,  absorbing  water  greedily  from  the  air,  while  carbonate  of 
sodium  is  not  deliquescent,  and  carbonate  of  lithium  is  sparingly  soluble 
in  water.  The  difficult  solubility  of  the  carbonate  and  phosphate  of 
lithium  constitutes  the  connecting  link  between  this  and  the  succeeding 
group  of  metals,  the  carbonates  and  phosphates  of  which  are  insoluble 
in  water. 

BARIUM. 

Ba"=  136.4  parts  by  weight. 

194.  Barium,  so  named  from  the  great  weight  of  its  compounds 
(ftapvs,  heavy),  is  found  in  considerable  abundance  in  the  north  of 
England,  in  two  minerals  known  as  Witherite  (barium  carbonate,  BaC03) 


360  BARIUM  SULPHATE. 

and  heavy  spar  or  barytes  (barium  sulphate,  BaS04).  Witherite  is 
found  in  large  masses  in  the  lead  mines  at  Alston  Moor,  and  at  Angle- 
sark  in  Lancashire.  It  is  said  to  be  used  for  poisoning  rats,  and  was 
originally  mistaken,  on  account  of  its  great  weight  (sp.  gr.  4.5),  for  an 
ore  of  lead.  All  salts  of  barium  are  poisonous. 

The  metal  itself  is  obtained  by  electrolysing  fused  barium  chloride  or 
heating  it  with  sodium.  It  is  a  pale  yellow  malleable  metal  of  sp.  gr. 
3.6  ;  it  is  easily  oxidised  by  air,  and  rapidly  decomposes  water  at  common 
temperatures.  It  requires  a  high  temperature  to  fuse  it.  Barium  and 
its  salts  impart  a  green  colour  to  a  flame. 

Such  compounds  of  barium  as  are  used  in  the  arts  are  chiefly  prepared 
from  heavy  spar  or  barium  sulphate,  which  is  remarkable  for  its  in- 
solubility in  water  and  acids.  In  order  to  prepare  other  compounds  of 
barium  from  this  refractory  mineral,  it  is  ground  to  powder  and  strongly 
heated  in  contact  with  charcoal  or  some  other  carbonaceous  substance, 
which  removes  the  oxygen  from  the  mineral  in  the  form  of  carbonic 
oxide,  thus  converting  the  barium  sulphate  into  barium  sulphide; 
BaS04  +  C4  =  400  +  BaS.  This  latter  compound,  being  soluble  in  water, 
can  be  readily  converted  into  other  barium  compounds. 

The  artificial  barium  sulphate,  which  is  used  by  painters,  instead  of 
white  lead,  under  the  name  of  permanent  white  (blanc  fixe),  and  is 
employed  for  glazing  cards,  is  prepared  by  mixing  the  solution  of  barium 
sulphide  with  dilute  sulphuric  acid,  when  the  barium  sulphate  separates 
as  a  white  precipitate,  which  is  collected,  washed,  and  dried — 
BaS  +  H2S04  =  H2S  +  BaS04. 

The  artificial  barium  carbonate,  which  is  used  in  the  manufacture  of 
some  kinds  of  glass,  is  prepared  by  passing  carbonic  acid  gas  through  a 
solution  of  barium  sulphide,  when  the  carbonate  is  precipitated  ;  BaS  + 
H20  +  C02  =  H2S  +  BaC03. 

In  preparing  compounds  of  barium  from  heavy  spar  on  the  small  scale  it  is 
better  to  convert  the  sulphate  into  barium  carbonate.  50  parts  of  the  finely 
powdered  sulphate  are  mixed  with  100  of  dried  sodium  carbonate,  600  of  pow- 
dered nitre,  and  100  of  very  finely  powdered  charcoal.  The  mixture  is  placed  in  a 
heap  upon  a  brick  or  iron  plate,  and  kindled  with  a  match,  when  the  heat  evolved 
by  the  combustion  of  the  charcoal  in  the  oxygen  of  the  nitre  fuses  the  barium 
sulphate  with  the  sodium  carbonate,  whereupon  they  react  to  form  barium  carbonate 
and  sodium  sulphate;  BaS04  +  Na2C03  =  Na2S04  +  BaC03.  The  mass  is  thrown 
into  boiling  water,  which  dissolves  the  sodium  sulphate  and  leaves  the  barium 
carbonate.  The  latter  may  be  allowed  to  settle,  and  washed  several  times,  by 
decantation,  with  distilled  water,  until  the  washings  no  longer  yield  a  precipitate 
with  barium  chloride,  showing  that  the  whole  of  the  sodium  sulphate  has  been 
washed  away  and  pure  barium  carbonate  remains. 

Barium  oxide  or  baryta,  BaO,  may  be  obtained  by  strongly  heating  a 
mixture  of  barium  carbonate  and  charcoal,  BaC03  +  C  =  BaO  +  2 CO,  but 
is  now  generally  prepared  by  heating  the  nitrate,  Ba(N03)2  = 
BaO  +  2N02  +  O.  It  is  a  heavy  grey  solid  which  combines  with  water 
with  great  evolution  of  heat  to  form  barium  hydroxide. 

Barium  dioxide  or  peroxide,  Ba02,  has  been  noticed  under  hydrogen 
dioxide  (p.  63)  and  under  Erin's  oxygen  process  (p.  39). 

Barium  hydroxide,  Ba(OH)2,  may  be  prepared  by  passing  C02  and 
steam  over  barium  sulphide  at  a  red  heat,  and  decomposing  the 
carbonate  thus  produced  by  a  current  of  superheated  steam  :  (i) 
BaS  +  CO,  +  H20  =  BaC03  +  H2S ;  (2)  BaC03  +  H20  ±  Ba(OH)2  +  C02.  It 
dissolves  in  boiling  water,  and  crystallises  in  prisms,  Ba(OH)2.8Aq. 


BAEIUM  NITRATE,  361 

Crystallised  barium  hydroxide  may  be  produced  by  adding  113  grams  of  powdered 
barium  nitrate  to  340  c.c.  of  a  boiling  solution  of  NaOH,  containing  85  grams  of 
commercial  caustic  soda  in  567  c.c.  of  water  ;  the  solution  becomes  turbid  from  the 
separation  of  barium  carbonate  produced  from  the  sodium  carbonate  in  the 
hydroxide  ;  it  is  boiled  for  some  minutes  and  then  filtered  ;  on  partial  cooling, 
some  crystals  of  undecomposed  barium  nitrate  are  deposited,  and  if  the  clear  liquid 
be  poured  off  into  another  vessel  and  stirred,  it  deposits  abundant  crystals  of 
barium  hydroxide  having  the  composition  Ba(OH)2.8Aq  ;  these  effloresce  and 
become  opaque  when  exposed  to  air,  becoming  Ba(OH)2.Aq  ;  when  heated  to  red- 
ness they  become  pure,  Ba(OH)2,  which  fuses,  but  is  not  decomposed  when  further 
heated.  The  hydroxide  is  moderately  soluble  in  water  (baryta  water),  100  parts 
•of  water  dissolving  3  parts  at  the  ordinary  temperature  ;  the  solution  is  strongly 
alkaline  and  absorbs  carbonic  acid  gas  from  the  air,  depositing  barium  carbonate. 

Barium  carbonate,  BaC03,  or  Witherite,  has  the  sp.  gr.  4.3.  It  may 
be  prepared  by  precipitating  barium  chloride  with  sodium  carbonate. 
It  is  very  insoluble  in  water,  and  is  not  decomposed  by  a  red  heat. 

Barium  chloride,  which  is  the  barium  compound  most  commonly 
employed  in  the  laboratory,  may  be  obtained  by  dissolving  the  carbonate 
in  diluted  hydrochloric  acid,  and  evaporating  the  solution  ;  on  cooling, 
the  chloride  is  deposited  in  tabular  crystals,  BaCl2.2Aq. 

On  the  large  scale,  it  is  generally  manufactured  by  fusing  heavy  spar  with 
calcium  chloride  (the  residue  from  the  preparation  of  ammonia,  see  p.  79)  in  a 
reverberatory  furnace,  BaS04  +  CaCL2  =  CaS04  +  BaCl2.  The  mass  is  rapidly 
extracted  with  hot  water,  which  leaves  the  calcium  sulphate  undissolved,  and  the 
clear  solution  of  barium  chloride  is  decanted  and  evaporated.  If  the  calcium 
sulphate  and  barium  chloride  were  allowed  to  remain  long  together  in  contact 
with  the  water,  barium  sulphate  and  calcium  chloride  would  be  reproduced. 
This  process  has  been  improved  by  adding  chalk  and  coal-dust  to  the  mixture, 
when  (i)  BaS04+C4  =  BaS  +  4CO  ;  (2)  BaS  +  CaCl2  =  BaCl2  +  CaS.  The  calcium 
sulphide  forms  an  insoluble  compound  with  the  lime  from  the  chalk. 

Barium  chloride  is  easily  soluble  in  water,  but  insoluble  in  alcohol 
and  in  strong  acids.  Barium  bromide  is  soluble  in  alcohol. 

Barium  nitrate,  Ba(N03)2,  is  obtained  by  dissolving  the  carbonate  in 
dilute  nitric  acid,  and  evaporating  the  solution,  when  octahedral  crystals 
of  the  nitrate  are  deposited.  It  is  an  ingredient  in  some  kinds  of 
blasting  powder  used  by  miners.  When  heated,  it  fuses  and  is  decom- 
posed, leaving  a  grey  porous  mass  of  baryta. 

Barium  chlorate,  Ba(C103)2,  is  employed  in  the  manufacture  of  fireworks,  being 
prepared  for  that  purpose  by  dissolving  the  artificial  barium  carbonate  in  solution 
of  chloric  acid  ;  it  forms  beautiful  shining  tabular  crystals.  When  mixed  with 
combustible  substances,  such  as  charcoal  and  sulphur,  it  imparts  a  brilliant  green 
colour  to  the  flame  of  the  burning  mixture  (see  p.  186). 

Barium  sulphate,  BaS04,  found  as  heavy  spar  or  eawlt,,  has  the  sp.  gr.  4.5.  It  is 
precipitated  whenever  sulphates  and  barium  salts  meet  in  solution.  It  is  remark- 
able for  its  insolubility  in  water  and  acids,  and  is  the  form  in  which  either  barium 
or  sulphur  is  determined  in  quantitative  analysis.  It  dissolves  in  hot  strong  H2S04, 
and  the  solution,  on  cooling,  deposits  crystals  of  acid  barium  sulphate,  BaH2(S04)2. 

Barium  sulphide,  BaS,  prepared  as  described  above,  dissolves  in  water  with 
decomposition,  yielding  barium  hydroxide  and  sulphydrate  ;  2BaS  +  2H20  = 
Ba(OH)2  +  Ba(SH)2.  It  has  the  property  of  shining  in  the  dark  after  it  has  been 
exposed  to  the  action  of  light. 

Barium  carbide,  BaC2,  is  a  grey  amorphous  substance  made  by  heating  BaC03 
(26  parts)  with  magnesium  powder  (10.5  parts)  and  powdered  coke  (4  parts)  in  an 


iron  flask;  BaC03  +  Mg.,  +  C  =  BaC2  +  3MgO.     It  evolves    acetylene  when  treated 
with  water,  BaC2  +  2H2O  =  C2H2  +  Ba(OH)2. 


362  STRONTIUM   MINERALS. 

STKONTIUM. 

Sr"  =  87  parts  by  weight. 

195.  Strontium  is  less  abundant  than  barium,  and  occurs  in  nature 
in  similar  forms  of  combination.  /Strontianite,  the  strontium  carbonate 
(SrC03),  was  first  discovered  in  the  lead-mines  of  Strontian  in  Argyle- 
shire,  and  has  since  been  found  in  small  quantity  in  some  mineral 
waters.  Sr003  is  more  easily  dissociated  by  heat  than  is  BaC03,  but 
less  easily  than  is  CaC03. 

Celestine  (so  called  from  the  blue  tint  of  many  specimens*)  is  the 
strontium  sulphate  (SrS04),  and  is  found  in  beautiful  crystals  associated 
with  the  native  sulphur  in  Sicily.  It  is  also  met  with  in  this  country,, 
and  is  the  source  from  which  the  strontium  nitrate  employed  in  firework 
compositions  is  derived.  The  strontium  sulphate  resembles  barium 
sulphate  with  respect  to  its  insolubility,  and  is  converted  into  the 
soluble  strontium  sulphide  (SrS)  by  calcination  with  carbonaceous 
matter.  The  solution  of  strontium  sulphide  so  obtained  is  decomposed 
by  nitric  acid,  and  the  strontium  nitrate  crystallised  from  the  solution. 
It  has  the  property  of  imparting  a  magnificent  crimson  colour  to  flames, 
and  is  hence  largely  used  for  the  preparation  of  red  theatrical  fire  (see 
p.  186). 

The  metal  itself  is  prepared  in  a  similar  manner  to  metallic  barium. t 
which  it  much  resembles,  but  is  lighter  (sp.  gr.  2.54)  and  more  fusible. 
It  burns,  when  heated  in  air,  with  a  crimson  flame. 

Strontia,  SrO,  resembles  BaO,  but  does  not  absorb  0  when  heated. 

/Strontium  dioxide,  SrO2,  is  precipitated,  in  combination  with  8H20? 
when  a  solution  of  strontia  in  water  is  mixed  with  hydrogen  peroxide. 

/Strontium  hydroxide,  Sr(OH)2,  is  made  on  the  large  scale  by  heating 
the  native  strontium  sulphate  with  brown  iron  ore  (hydrated  ferric 
oxide)  and  coal-dust.  On  treating  the  product  with  water,  ferrous 
sulphide  remains  undissolved,  and  Sr(HO)2  passes  into  solution.  It  is- 
used  in  sugar  refining.  It  is  less  soluble  than  barium  hydroxide,  and 
is  converted  into  SrO  by  heat. 

Strontium  nitrate,  Sr(N03)2,  may  be  prepared  by  dissolving  stron- 
tianite  in  nitric  acid.  It  crystallises  from  hot  strong  solutions  in 
anhydrous  octahedra.  Cold  solutions  deposit  prisms  of  Sr(NO3)2.4Aq. 
(Barium  nitrate  is  always  anhydrous.)  Strontium  nitrate  is  easily 
soluble  in  water,  but  insoluble  in  alcohol. 

/Strontium  chloride,  SrCl2,  differs  from  BaCl2  in  being  deliquescent  and 
soluble  in  alcohol.  It  crystallises  in  prisms,  SrCl9.6Aq. 

Strontium  sulphate,  SrSO4,  is  not  so  heavy  as  BaS04 ;  sp.  gr.  3.  It 
is  slightly  soluble  in  water,  and  is  easily  converted  into  SrC03  by  alka- 
line carbonates,  in  the  cold,  which  is  not  the  case  with  BaS04. 

*  Said  to  be  due  to  the  presence  of  ferroso-ferric  phosphate. 

f  Strontium  has  been  made  in  quantity  by  distilling  strontium  amalgam  in  hydrogen. 
The  amalgam  was  prepared  by  the  action  of  sodium-amalgam  on  a  saturated  solution  of 
strontium  chloride. 


VAEIETIES   OF   CALCIUM   CARBONATE.  363 

CALCIUM. 

Ca"  =  40  parts  by  weight. 

196.  No  other  metal  is  so  largely  employed  in  a  state  of  combination 
as  is  calcium,  for  its  oxide,  lime  (CaO),  occupies  among  bases  much  the 
same  position  as  that  which  sulphuric  acid  holds  among  the  acids,  and 
is  used,  directly  or  indirectly,  in  most  of  the  arts  and  manufactures. 

Like  barium  and  strontium,  calcium  is  found,  though  far  more  abun- 
dantly than  these,  in  the  mineral  kingdom,  in  the  forms  of  carbonate 
and  sulphate,  but  it  also  occurs  in  large  quantity  as  calcium  fluoride 
(p.  202),  and  less  frequently  in  the  form  of  phosphate  (p.  256).  Calcium, 
moreover,  is  found  in  all  animals  and  vegetables,  and  its  presence  in 
their  food,  in  one  form  or  other,  is  an  essential  condition  of  their 
existence. 

Metallic  calcium  may  be  obtained  by  decomposing  fused  calcium  iodide 
with  metallic  sodium.  It  crystallises  from  the  excess  of  sodium  as  the 
mass  cools  and  may  be  isolated  by  dissolving  the  sodium  in  alcohol.  It 
has  a  silvery  appearance  and  is  as  hard  as  Iceland  spar,  very  ductile 
and  malleable.  It  melts  at  760°  C.  and  is  lighter  than  barium  and 
strontium,  its  sp.  gr.  being  1.56.  It  oxidises  slowly  in  air  at  the 
ordinary  temperature,  but,  when  heated  to  redness,  it  fuses  and  burns 
with  a  very  brilliant  white  light,  being  converted  into  lime  (calx).  It 
decomposes  water  at  the  ordinary  temperature.  Its  salts  impart  a  red 
colour  to  a  colourless  flame. 

Carbonate  of  lime,  or  Calcium  carbonate  (CaO.C02  or  CaC03), 
from  which  all  the  manufactured  compounds  of  lime  are  derived,  con- 
stitutes the  different  varieties  of  limestone  which  are  met  with  in  such 
abundance. 

Chalk  is  simply  calcium  carbonate  in  an  amorphous  or  uncrystallised 
state ;  it  is  known  to  the  agriculturist  as  mild  lime.  Limestone  consists 
of  minute  crystals  of  calc  spar  (see  below).  The  oolite  limestone,  of 
which  the  Bath  and  Portland  building-stones  are  composed,  is  so-called 
from  its  resemblance  to  the  roe  of  fish  (o>oi>,  an  egg).  Marble,  in  its 
different  varieties,  is  also  an  assemblage  of  minute  crystals  of  calc  spar, 
sometimes  variegated  by  the  presence  of  oxides  of  iron  and  manganese, 
or  of  bituminous  matter.  This  last  constituent  gives  the  colour  to  black 
niurble.  Calcium  carbonate  is  also  found  in  large  transparent  rhombo- 
hedral  crystals,  which  are  known  to  mineralogists  as  calcareous  spar, 
calc  spar,  or  Iceland  spar,  and  calcite  (sp.  gr.  2.7).  When  the  crystals 
have  the  form  of  a  six-sided  prism,  the  mineral  is  termed  aragonite 
(sp.  gr.  2.94). 

The  attention  of  the  crystallographer  has  long  been  directed  to  these  two 
crystalline  forms  of  calcium  carbonate,  on  account  of  the  circumstance  that  if  a 
prism  of  aragonite  be  heated,  it  breaks  .up  into  a  number  of  minute  rhombohedra 
of  calc  spar.  Satin  spar  is  a  variety  of  calcium  carbonate.  When  slowly  deposited 
from  its  solution  in  carbonic  acid,  calcium  carbonate  gives  six-sided  prisms  of 
CaC03.5Aq.  Precipitated  calcium  carbonate  is  amorphous,  and  is  the  least  stable 
of  the  three  forms  and  hence  the  most  soluble  (20  mgrns.  per  litre).  When  heated 
to  a  high  temperature  it  becomes  aragonite,  but  when  kept  at  moderate  tempera- 
tures, in  contact  with  the  liquid  from  which  it  was  precipitated,  it  becomes  calcite. 

Calcium  carbonate  is  a  chief  constituent  of  the  shells  of  fishes  and  of  egg-shells, 
so  that,  except  calcium  phosphate,  no  mineral  compound  has  so  large  a  share  in 
the  composition  of  animal  frames.  Corals  also  consist  chiefly  of  calcium  carbonate 


LIME-BURNING. 


derived  from  the  skeletons  of  innumerable  minute  insects.  The  mineral  gaylussite 
is  a  double  carbonate  of  calcium  and  sodium  (CaCO3.Na2C03.5Aq),  and  is  scarcely 
affected  by  water  unless  previously  heated,  when  water  dissolves  out  the  sodium 
carbonate.  Baryta-calcite  is  a  double  carbonate  of  barium  and  calcium 
(BaC03.CaC03). 

The  presence  of  calcium  carbonate  in  spring  waters  and  the  solubility 
of  this  compound  in  a  solution  of  carbon  dioxide  have  already  been 
considered  (p.  56). 

Lime  (CaO). — The  process  by  which  lime  is  obtained  from  the  car- 
bonate has  been  already  alluded  to  under  the  name  of  lime-burning. 
At  a  red  heat  calcium  carbonate  begins  to  decompose  into  CaO  and  C02 ; 
but  unless  the  C02  be  removed,  it  prevents  further  decomposition,  so 
that  marble  or  chalk  cannot  be  completely  decomposed  in  a  covered 
crucible,  and  a  lime-kiln  must  have  a  good  draught  to  carry  off  the  C02. 
At  812°  C.  the  dissociation-pressure  (p.  315)  of  CaC03  is  753  mm.,  and 
this  is  the  best  temperature  for  lime-burning.* 

Accordingly,  a  kiln  is  commonly  employed  of  the  form  of  an  inverted 
cone  of  brickwork  (Fig.  213),  and  into  this  limestone  and  fuel  are  thrown 
in  alternate  layers.  The  former,  losing  its  C02  before  it  reaches  the 


Fig.  213. — Limekiln. 


Fig.  214. — Limekiln. 


bottom  of  the  furnace,  is  raked  out  in  the  form  of  burnt  or  quick  lime 
(CaO),  whilst  its  place  is  supplied  by  a  fresh  layer  of  limestone  thrown 
in  at  the  top  of  the  kiln.  Fig.  214  represents  another  form  of  kiln,  in 
which  the  limestone  is  supported  upon  an  arch  built  with  large  lumps 
of  the  stone  above  the  fire,  which  is  kept  burning  for  about  three  days 
and  nights,  until  the  whole  of  the  limestone  is  decomposed. 

The  usual  test  of  the  quality  of  the  lime  thus  obtained  consists  in 
sprinkling  it  with  water,  with  which  it  should  eagerly  combine,  evolving 
much  heat,t  swelling  to  about  z\  times  its  bulk,  and  crumbling  to  a  light 
white  powder  of  calcium  hydrate  (slaked  lime),  Ca(OH)2.  Lime  which 
behaves  in  this  manner  is  termed  fat  lime  ;  whereas,  if  it  be  found  to 

*  When  precipitated  CaC03  is  heated  to  about  1000°  C.  under  such  conditions  that  none 
of  its  CO2  can  escape,  it  is  converted  into  marble. 

|  The  sudden  slaking  of  a  large  quantity  of  lime  may  be  a  cause  of  fire.  A  rise  of  tem- 
perature to  150°  C.  frequently  occurs.  56  grams  of  CaO  evolve  15,540  gram  units  of  heat 
when  slaked. 


BUILDING  MATERIALS,  365 

slake  feebly,  it  is  pronounced  a  poor  lime,  and  is  known  to  contain  a 
considerable  proportion  of  foreign  substances,  such  as  silica,  aluminia, 
magnesia,  &c.  Lime  is  said  to  be  overburnt  when  it  contains  hard 
cinder-like  masses  of  silicate  of  lime,  formed  by  the  combination  of  the 
silica,  which  is  generally  found  in  limestone,  with  a  portion  of  the  lime, 
under  the  influence  of  excessive  heat  in  the  kiln.  Air-slaked  lime  has 
slaked  by  simple  exposure  to  air  ;  it  has  absorbed  C02  as  well  as  H20, 
and  contains  5  7  per  cent.  CaC03  and  43  per  cent.  Ca(OH)2. 

Calcium  hydroxide,  Ca(OH)2,  is  much  less  soluble  in  water  than  is 
barium  or  strontium  hydroxide.  It  requires  700  parts  of  cold  water  to 
dissolve  it,  and  twice  as  much  hot  water,  so  that  lime-water  always  gives 
a  precipitate  when  boiled.  The  solution  is  strongly  alkaline,  and 
readily  absorbs  C02  from  the  air,  which  precipitates  CaCO3.  When 
lime  water  is  evaporated  in  vacua  over  H2S04,  it  deposits  small  crystals 
of  Ca(OH)2. 

Ca(OH)2  is  easily  converted  into  CaO  by  heat.  It  is  used  in  manu- 
facturing chemistry  as  the  cheapest  alkaline  substance. 

197.  Closely  connected  with  limestone  and  lime  is  the  chemistry  of 
building  materials. 

Chemical  principles  would  lead  to  the  selection  of  pure  silica  (quartz, 
rock-crystal)  as  the  most  durable  of  building  materials,  since  it  is  not 
attacked  by  any  of  the  substances  likely  to  be  present  in  the  atmosphere; 
but  even  if  it  could  be  obtained  in  sufficiently  large  masses  for  the 
purpose,  its  great  hardness  presents  an  obstacle  to  its  being  hewn  into 
the  required  forms.  Of  the  building  stones  actually  employed,  granite, 
basalt,  and  porphyry  are  the  most  lasting,  on  account  of  their  capability 
of  resisting  for  a  great  length  of  time  the  action  of  water  and  of  atmo- 
spheric carbonic  acid ;  but  their  hardness  makes  them  so  difficult  to 
work,  as  to  prevent  their  employment  except  for  the  construction  of 
pavements,  bridges,  &c.,  where  the  work  is  massive  and  straightforward, 
and  much  resistance  to  wear  and  tear  is  required.  The  millstone  grit 
is  also  a  very  durable  stone,  consisting  chiefly  of  silica,  and  employed 
for  the  foundations  of  houses.  Freestone  is  a  term  applied  to  any  stone 
which  is  soft  enough  to  be  wrought  with  hammer  and  chisel,  or  cut 
with  a  saw ;  it  includes  the  different  varieties  of  sandstone  and  lime- 
stone. The  Yorkshire  flags  employed  for  paving  are  siliceous  stones  of 
this  description.  The  Craigleith  sandstone,  which  is  one  of  the  free- 
stones used  in  London,  contains  about  98  per  cent,  of  silica,  together 
with  some  calcium  carbonate. 

The  building  stones  in  most  general  use  are  the  different  varieties  of 
calcium  carbonate.  The  durability  of  these  is  in  proportion  to  their 
compact  structure  ;  thus  marble,  being  the  most  compact,  has  been  found 
to  resist  for  many  centuries  the  action  of  the  atmosphere,  whilst  the 
more  porous  limestones  are  corroded  at  the  surface  in  a  very  short  time. 
Portland  stone,  of  which  St.  Paul's  and  Somerset  House  are  built,  and 
Bath  stone,  are  among  the  most  durable  of  these ;  but  they  are  all  slowly 
corroded  by  exposure  to  the  atmosphere.  The  chief  cause  of  this 
corrosion  appears  to  be  the  mechanical  disintegration  caused  by  the 
expansion  in  freezing,  of  the  water  absorbed  in  the  pores  of  the  stone. 
In  order  to  determine  the  relative  extent  to  which  different  stones  are 
liable  to  be  disintegrated  by  frost,  a  piece  of  the  stone  may  be  saturated 
with  water  and  alternately  frozen  and  thawed.  Magnesian  limestones 


366  MOETAR  AND   CEMENT. 

(carbonate  of  calcium  with  carbonate  of  magnesium)  are  much  valued 
for  ornamental  architecture,  on  account  of  the  ease  with  which  they 
may  be  carved,  and  are  said  to  be  more  durable  in  proportion  as  they 
approach  the  composition  expressed  by  the  formula  CaC03.MgCO3.* 
The  magnesian  limestone  from  Bolsover  Moor,  of  which  the  Houses  of 
Parliament  are  built,  contains  50  per  cent,  of  calcium  carbonate,  40  of 
magnesium  carbonate,  with  some  silica  and  alumina. 

It  is  probable  that  a  slow  corrosion  of  the  surface  of  limestone  is 
effected  by  the  carbonic  acid  continually  deposited  in  aqueous  solution 
from  the  air ;  and  it  is  certain  that  in  the  atmosphere  of  towns  the 
limestone  is  attacked  by  the  sulphuric  acid  which  results  from  the  com- 
bustion of  coal  and  the  operations  of  chemical  works.  The  Houses  of 
Parliament  have  suffered  severely,  probably  from  this  cause.  Many 
processes  have  been  recommended  for  the  preservation  of  building 
stones,  such  as  waterproofing  them  by  the  application  of  oily  and 
resinous  substances,  and  coating  or  impregnating  them  with  solution  of 
soluble  glass  and  similar  matters;  but  none  seems  yet  to  have  been 
thoroughly  tested  by  practical  experience. 

Purbeck,  Ancaster,  and  Caen  stones  are  well-known  limestones  employed 
for  building. 

The  mortar  employed  for  building  is  composed  of  i  part  of  freshly 
slaked  lime  and  2  or  3  parts  of  sand  intimately  mixed  with  enough 
water  to  form  a  uniform  paste.  The  hardening  of  such  a  composition 
appears  to  be  due,  in  the  first  instance,  to  the  absorption  of  carbon 
dioxide  from  the  air,  by  which  a  portion  of  the  lime  is  converted  into 
calcium  carbonate,  and  this,  uniting  with  the  unaltered  calcium  hydrate, 
forms  a  solid  layer,  adhering  closely  to  the  two  surfaces  of  brick  or 
stone,  which  it  cements  together.  In  the  course  of  time  the  lime  would 
act  upon  the  silica,  producing  calcium  silicate,  and  this  chemical  action 
would  render  the  adhesion  more  perfect.  The  chief  use  of  the  sand 
here,  as  in  the  manufacture  of  pottery  (q.v.)  is  to  prevent  excessive 
shrinking  during  the  drying  of  the  mortar. 

In  constructions  which  are  exposed  to  the  action  of  water,  mortars  of 
peculiar  composition  are  employed.  These  hydraulic  mortars,  or  cements, 
as  they  are  termed,  are  prepared  by  calcining  mixtures  of  calcium  car- 
bonate with  from  10  to  30  per  cent,  of  clay,  when  carbonic  acid  gas  is 
expelled,  and  the  lime  combines  with  a  portion  of  the  silica  and  alumina 
from  the  clay,  producing  tricalcium  silicate,  3CaO.Si02,  and  tricalcium 
aluminate,  30aO.Al203.  When  the  calcined  mass  is  ground  to  powder 
and  mixed  with  water  these  silicates  combine  with  water  to  form 
hydrated  silicates  (with  liberation  of  free  lime),  which  dissolve  in  the 
water  and  immediately  crystallise  again  (in  the  manner  described  for 
the  setting  of  plaster  of  Paris),  thus  causing  the  cement  to  set.  Roman 
cement  is  prepared  by  calcining  a  limestone  containing  about  25  per 
cent,  of  clay,  and  hardens  in  a  very  short  time  after  mixing  with  water. 
For  Portland  cement  (so-called  from  its  resembling  Portland  stone)  a 
mixture  of  river-mud  (chiefly  clay)  and  limestone  is  calcined  at  a  very 
high  temperature. 

Hydraulic  cements  are  mixed  for  use  with  sand  before  they  are 
wetted  with  water.  Concrete  is  a  mixture  of  hydraulic  cement  (i  vol.) 

*  Any  excess  of  calcium  carbonate  above  that  required  by  this  formula  may  be  dissolved 
out  by  treating-  the  powdered  magnesium  limestone  with  weak  acetic  acid. 


PLASTEE  OF  PAEIS.  367 

with  sand  (2  vols.)  and  small  gravel  (4  vols.),  the  last  being  known  as 
the  "  aggregate." 

Scott's  cement  is  a  mixture  of  quick-lime  with  a  small  proportion  of 
calcium  sulphate. 

Calcium  dioxide,  Ca02,  is  precipitated  in  combination  with  8H20, 
when  solution  of  sodium  peroxide  is  added  to  one  of  a  calcium  salt. 

Calcium  nitrate,  Ca(IS"03)2.4Aq,  differs  from  those  of  Ba  and  Sr  by 
being  deliquescent,  much  more  soluble  in  water,  and  soluble  in  alcohol. 
It  occurs  in  well-waters  and  in  soils,  the  NO3  having  been  formed  by 
oxidation  of  NH3. 

198.  Sulphate  of  lime,  or  Calcium  sulphate,  in  combination  with 
water  (CaS04.2H20),  is  met  with  in  nature,  both  in  the  form  of  trans- 
parent prisms  of  selenite,  and  in  opaque  and  semi-opaque  masses  known 
as  alabaster  and  gypsum.  It  is  this  latter  form  which  yields  plaster  of 
Paris,  for  when  heated  to  between  150°  and  2oo°C.  it  loses  j-  of 
its  water,  becoming  2CaS04.H20,  and  if  the  mass  be  then  powdered, 
and  mixed  with  water,  the  powder  recombines  with  the  water  to 
form  a  mass,  the  hardness  of  which  nearly  equals  that  of  the  original 
gypsum. 

In  the  preparation  of  plaster  of  Paris,  a  number  of  large  lumps  of 
gypsum  are  built  up  into  a  series  of  arches,  upon  which  the  rest  of  the 

fypsum  is  supported;  under  these  arches  the  fuel  is  burnt,  and  its 
ame  is  allowed  to  traverse  the  gypsum,  care  being  taken  that  the  tem- 
perature does  not  rise  too  high,  lest  the  gypsum  be  overburnt  and  set 
very  slowly  with  water.  When  the  operation  is  supposed  to  be  com- 
pleted, the  lumps  are  carefully  sorted,  and  those  which  appear  to  have 
been  properly  calcined  are  ground  to  a  very  fine  powder.  When  this 
powder  is  mixed  with  water  to  a  cream,  and  poured  into  a  mould,  the 
minute  particles  of  calcium  sulphate  combine  with  water  to  reproduce 
the  original  gypsum  (CaSO4.2H20),  and  this  act  of  combination  is 
attended  with  a  slight  expansion  which  forces  the  plaster  into  the  finest 
lines  of  the  mould. 

The  setting  is  due  to  the  fact  that  a  small  portion  of  the  plaster  (2CaS04.H20) 
dissolves  in  the  water,  crystallising  again  immediately  as  CaSO4.2H20,  thus  leaving 
the  water  free  to  dissolve  another  portion  of  2CaS04.H20,  which  crystallises  in  its 
turn  as  CaS04.2H20.  Thus  the  mass  soon  becomes  one  of  interlaced  crystals  of 
CaS04.2H20.  An  addition  of  one-tenth  of  lime  to  the  plaster  hardens  it  and  accele- 
rates the  setting. 

It  is  not  known  why  overburnt  gypsum  does  not  set,  or  sets  only  very  slowly,  but 
it  is  supposed  to  be  due  to  the  fact  that  there  is  no  nucleus  of  undecomposed  gypsum 
in  it.  This  view  is  supported  by  the  behaviour  of  anhydrous  Na2S04,  which  remains 
as  a  powder  underwater  until  a  crystal  of  the  hydrated  salt  is  added,  when  the  whole 
mass  solidifies. 

The  transition -point  from  CaS04.2H2O  to  2CaS04.H2O  is  107°  C.,  at  which  tem- 
perature the  pressure  of  the  water  vapour  from  the  gypsum  is  higher  than  that  of 
the  vapour  from  water  itself  at  this  temperature.  It  follows  that  when  gypsum  is 
heated  in  a  sealed  tube  the  water  vapour  condenses,  and  the  gypsum  becomes  a 
magma  of  plaster  of  Paris  in  water.  The  change  at  107°  C.  is  exceedingly  slow,  so 
that  the  gypsum-burner  is  obliged  to  use  a  considerably  higher  temperature  than 
this. 

Stucco  consists  of  plaster  of  Paris  (occasionally  coloured)  mixed  with  a  solution 
of  size  ;  certain  cements  used  for  building  purposes  are  prepared  from  burnt  gypsum, 
which  has  been  soaked  in  a  solution  of  alum  and  again  burnt  ;  and  although  the 
plaster  thus  obtained  takes  much  longer  to  set  than  the  ordinary  kind,  it  is  much 
harder,  and  therefore  takes  a  good  polish.  A  similar  hardening  of  objects  cast  from 
plaster  of  Paris  is  effected  by  soaking  them  in  solution  of  KHS03,  probably  owing 


368  CALCIUM  CHLORIDE. 

to  the  slow  formation  of  a  double  salt  of  CaS04  and  K0S04  ;  this  is  applied  in  the 
making  of  artificial  marble.  Plaster  of  Paris  is  much  damaged  by  long  exposure  to 
moist  air,  from  which  it  regains  a  portion  of  its  water,  and  its  property  of  setting 
is  so  far  diminished.  Precipitated  calcium  sulphate  is  used  by  paper-makers  under 
the  name  of  pearl  hardener.  Calcium  sulphate  is  useful  in  the  farmyard  and  stables 
for  absorbing  the  ammonia  of  the  decomposing  excrements,  which  would  otherwise 
be  lost  to  the  manure. 

CaS04  forms  the  mineral  anhydrite,  a  bed  of  which,  when  exposed  to 
the  air  in  a  railway  cutting,  has  been  known  to  increase  in  bulk  by 
absorbing  water  to  such  an  extent  as  to  disturb  the  stability  of  the 
sides  of  the  cutting.  Calcium  sulphate  is  contained  in  most  natural 
waters,  and  is  one  of  the  chief  causes  of  the  permanent  hardness  which 
is  not  removed  by  boiling.  It  is  much  more  soluble  in  water  than  is 
strontium  sulphate,  so  that  sulphates  will  precipitate  calcium  only  from 
strong  solutions.  The  aqueous  solution  of  CaS04  precipitates  barium 
salts  immediately,  but  strontium  salts  only  after  an  interval,  on  account 
of  the  greater  solubility  of  SrS04.  The  calcium  sulphate  is  more 
soluble  in  water  at  35°  C.  than  at  any  other  temperature,  i  part  of 
CaSO4  then  dissolving  in  about  400  parts  of  water.  It  is  insoluble  in 
alcohol.  Boiling  HC1  dissolves  it,  and  deposits  it  in  needles  on  cooling. 

Calcium  chloride  (CaCl2)  has  been  mentioned  as  the  residue  left  in 
the  preparation  of  ammonia.  The  pure  salt  may  be  obtained  by  dis- 
solving pure  calcium  carbonate  (Iceland  spar)  in  hydrochloric  acid,  and 
evaporating  the  solution,  when  prismatic  crystals  of  the  composition 
CaCl2.6Aq  are  obtained,  which  dissolve  in  one-fourth  of  their  weight  of 
cold  water.  When  these  are  heated  they  melt  at  29°  0.,  and  at  about 
200°  C.  are  converted  into  a  white  porous  mass  of  CaCl2.2Aq,  which  is 
much  used  for  drying  gases.  At  a  higher  temperature,  fused  calcium 
chloride,  free  from  water,  is  left;  this  is  very  useful  for  removing 
water  from  some  liquids.  When  heated  in  air,  it  evolves  chlorine  and 
becomes  alkaline.  A  saturated  (325  per  cent.)  solution  of  calcium 
chloride  boils  at  355°  F.  (180°  C.),  and  is  sometimes  used  as  a  con- 
venient bath  for  obtaining  a  temperature  above  the  boiling-point  of 
water.  When  mixed  with  snow  the  crystals  CaCl2.6H20  form  a  cryo- 
hydrate,  reducing  the  temperature  to -48°  C.  In  consequence  of  the 
attraction  of  calcium  chloride  for  water,  surfaces  wetted  with  a  solution 
of  the  salt  never  get  dry.  Rope  mantlets,  for  the  protection  of  gunners^ 
are  saturated  with  it  to  prevent  their  taking  fire.  Calcium  chloride  is 
easily  soluble  in  alcohol. 

When  Ca(OH)2  is  boiled  with  a  strong  solution  of  calcium  chloride, 
it  is  dissolved,  and  the  filtered  solution  deposits  prismatic  crystals  of 
calcium  oxychloride,  CaCl2.3CaO.i5Aq,  which  are  decomposed  by  water. 

Chloride  of  lime  ;  seep.  183. 

Calcium  fluoride,  CaF2,  already  described  asfluor  spar  (p.  202),  occurs 
in  the  bones  and  teeth.  Many  specimens  of  it  decrepitate  and  emit  a 
phosphorescent  light  when  heated.  It  fuses  at  a  red  heat,  and  is  used 
in  metallurgy  as  a  flux,  since  it  attacks  silicates  at  a  high  temperature. 
Calcium  fluoride  is  slightly  soluble  in  hot  HC1,  and  is  reprecipitated  by 
NH3.  It  is  obtained  as  a  gelatinous  precipitate  insoluble  in  acetic  acid 
when  CaCl2  is  added  to  an  alkali  fluoride.  Artificial  teeth  are  made  of 
calcium  fluoride. 

Calcium  sulphide  (CaS)  is  present  in  Balmairis  luminous  paint.  Its  property  of 
shining  in  the  dark  after  exposure  to  a  bright  light  was  observed  by  Canton  in  1761  ; 


PHOSPHATE   OF  LIME,  369 

his  so-called  phosphorus  was  obtained  by  strongly  heating  oyster-shells  with  sulphur. 
The  phosphorescence  is  not  due  to  slow  oxidation,  since  a  specimen  which  has  been 
kept  for  more  than  a  century  in  a  sealed  tube  still  exhibits  it ;  it  does  not  appear  to 
be  a  property  of  the  pure  sulphide. 

When  Cab  is  acted  on  by  H2S  it  yields  a  crystalline  calcium  hydrosulphidef 
Ca(SH)2.  When  this  is  heated  in  H2S  it  is  decomposed  ;  Ca(SH)2  =  CaS  +  H2S. 
The  CaS  is  a  white  solid,  soluble  in  water.  When  Ca(SH)2  is  exposed  to  air  it 
deliquesces,  evolves  H2S,  and  becomes  Ca(SH)(OH)  ;  Ca(SH)2  +  H20  =  H2S  +  Ca 
(SH)(OH).  Calcium  sulphide  occurs,  combined  with  CaO,  in  the  tank-waste  of  the 
alkali  works.  A  solution  of  Ca(SH)2  is  used  as  a  depilatory. 

Calcium  phosphate,  Ca3(PO4)2,  occurs  in  the  minerals  apatite,  phos- 
phorite, sombrerite,  and  coprolite  ;  in  the  two  first  it  is  combined  with 
calcium  fluoride,  forming  3Ca3(P04)2,CaF2,  and  this  is  also  contained  in 
bone  ash,  of  which  Ca3(P04)2  forms  the  larger  proportion  (80  per  cent.). 
This  is  sold  as  a  non-mercurial  plate  powder,  under  the  name  of  white 
rouge.  Calcium  phosphate  is  nearly  insoluble  in  water,  but  it  is  dis- 
solved by  HC1  or  HNO3,  and  is  precipitated  again  by  ammonia.  When 
CaCl2  is  added  to  Na2HP04,  a  gelatinous  precipitate  is  obtained,  which 
becomes  crystalline  after  a  short  time.  The  gelatinous  precipitate  dis- 
solves easily  in  acetic  acid,  but  the  crystalline  precipitate  does  not,  and 
if  the  solution  of  the  gelatinous  precipitate  in  very  little  acetic  acid  be 
allowed  to  stand,  or  briskly  stirred,  it  deposits  crystals  of  CaHP04.2Aq. 
This  salt  is  found  in  calculi  in  the  sturgeon. 

Tetra-hydrogen  calcium  phosphate,  CaH4(PO4)2,  commonly  called  super- 
phosphate of  lime,  is  made  by  decomposing  Ca3(P04)2  with  sulphuric 
acid;  Ca3(P04)2  + 2H2S04  =  CaH4(P04)2+ 2CaSO4;  the  calcium  sulphate 
is  filtered  off,  and  the  superphosphate  is  left  in  solution.  The  pure  super- 
phosphate may  be  prepared  by  dissolving  bone-ash  in  HC1,  precipitating 
with  ammonia,  and  digesting  the  washed  precipitate  of  Ca3(P04)2  with 
H3PO4;  Ca3(P04)2  +  4H3P04  =  3CaH4(P04)2.  On  allowing  the  solution 
to  evaporate  spontaneously,  the  salt  crystallises  in  rhomboidal  plates 
containing  a  molecule  of  water.  It  is  dissolved  by  a  small  quantity  of 
water,  but  it  is  decomposed  and  precipitated  by  much  water,  or  by 
boiling ;  CaH4(P04)2  =  H3P04  +  CaHPO4. 

The  commercial  superphosphate  manure  is  a  damp  mixture  of  CaH4  (P04)2,  and 
CaS04,  prepared  by  mixing  ground  mineral  phosphates  with  sulphuric  acid.  It  is 
valued  by  the  agriculturist  for  the  large  amount  of  soluble  phosphate  which  it 
contains  ;  in  course  of  time,  the  proportion  of  this  decreases,  and  the  phosphate  is 
said  to  have  reverted  to  the  insoluble  form,  owing  to  the  action  of  the  superphos- 
phate upon  some  undecomposed  Ca3(P04)2  remaining  in  the  compound,  resulting  in 
the  formation  of  the  insoluble  hydrocalcium  phosphate— CaH4(P04)2  +  Ca3(PO4)2= 
4CaHP04.  Another  cause  for  this  retrogression  of  the  superphosphate  which  has 
been  prepared  from  mineral  phosphates,  is  the  presence  of  the  sulphates  of  alu- 
minium, magnesium,  and  iron,  which  gradually  convert  the  phosphoric  acid  into 
insoluble  forms. 

Calcium  jiyrapliasithate,  Ca2P207,  when  exposed  for  several  hours  to  a  dull  red 
heat,  forms  a  perfectly  transparent  glass  of  sp.  gr.  2.6,  which  may  be  worked  into 
prisms  and  lenses  like  ordinary  glass,  its  refractive  power  being  equal  to  that  of 
crown  glass.  It  is  not  acted  on  by  acids  in  the  cold,  and  even  resists  HF. 

Calcium  aniniii/i/iiiii  arse-note,  CaNH4As04-7Aq,  is  obtained  as  a  white  precipitate 
by  mixing  CaCl2  with  excess  of  NH3,  and  adding  arsenic  acid.  The  precipitate  is 
gelatinous  at  first,  but  changes  rapidly  into  fine  needles,  especially  if  stirred.  It  is 
slightly  soluble  in  water,  but  almost  insoluble  in  ammonia.  Dried  in  vacua,  over 
sulphuric  acid,  it  becomes  Ca3NH4H2(As04)3.3Aq.  Dried  at  ico°  C.,  it  has  the  formula 
Ca6NH4H5(As04)6.3Aq.  Heated  to  redness,  it  becomes  calcium  pyro-arscnate,Ca<zA.&207. 
Calcium  urtho-arxenate,  Ca3(As04)2,  and  metar senate,  Ca(As03)2,  have  also  been 
obtained, 

2  A 


37°  WINDOW  GLASS. 

Calcium  carbide,  CaC2.  Some  of  the  properties  of  this  substance  have  been 
described  at  p.  137.  Its  manufacture  is  conducted  by  feeding  a  mixture  of  100  parts 
of  powdered  quicklime  with  80  parts  of  powdered  coke  between  the  poles  of 
an  electric  arc,  when  the  materials  fuse,  having  reacted  to  form  calcium  carbide  ; 
CaO  +  C3  =  CaC2  +  CO.  Several  forms  of  electric  furnace  have  been  devised  for  this 
manufacture  ;  one  of  them  consists  of  an  iron  truck  contained  in  a  brickwork 
•chamber,  and  having  suspended  in  it  a  bundle  of  carbon  rods.  The  latter  are  con- 
nected with  one  pole  of  the  dynamo,  the  truck  being  connected  with  the  other  pole, 
•and  thus  conducting  the  current  to  the  charge  it  contains,  which  forms  the  actual 
•electrode  and  protects  the  truck  from  the  heat.  The  truck  is  run  out  of  the  furnace 
and  another  substituted  for  it  as  soon  as  it  is  full  of  the  carbide. 

Pure  calcium  carbide  forms  colourless  transparent  crystals,  but  the  commercial 
product  is  a  grey  opaque  crystalline  substance  of  sp.  gr.  2.2,  which  is  decomposed  by 
aqueous  vapour  so  that  it  smells  of  impure  acetylene  when  exposed  to  the  atmo- 
sphere (p.  137). 

Calcium  silicates  are  found  associated  with  other  silicates  in  many  materials.  They 
are  also  constituents  of  most  forms  of  glass,  which  will  therefore  receive  attention 
here. 

199.  Grlass  is  defined  chemically  to  be  an  amorphous  mixture  of  two 
or  more  silicates,  one  of  which  is  a  silicate  of  an  alkali-metal,  the  other 
being  a  silicate  of  calcium,  barium,  iron,  lead,  or  zinc.  Typical  glass 
may  be  said  to  correspond  with  the  formula  M2CaSi6014,  where  M  is  an 
alkali  metal.  The  different  kinds  of  glass  may,  however,  vary  consider- 
ably from  this  formula. 

If  silica  be  fused  with  an  equal  weight  of  carbonate  of  potassium  or 
sodium,  a  transparent  glassy  mass  is  obtained,  but  this  is  slowly  dissolved 
by  water,  and  would  therefore  be  incapable  of  resisting  the  action  of  the 
weather  ;  if  a  small  proportion  of  lime  or  baryta,  or  of  the  oxides  of  iron, 
lead,  or  zinc,  be  added,  the  glass  becomes  far  less  easily  affected  by  atmo- 
spheric influences. 

The  most  valuable  property  of  glass,  after  its  transparency  and  per- 
manence, is  that  of  assuming  a  viscid  or  plastic  consistence  when  fused, 
which  allows  it  to  be  so  easily  fashioned  into  the  various  shapes  required 
for  use  or  ornament. 

The  composition  of  glass  is  varied  according  to  the  particular  purpose 
for  which  it  is  intended,  the  materials  selected  being  fused  in  large  clay 
crucibles  placed  in  reverberatory  furnaces,  and  heated  by  a  coal  fire  or 
in  a  gas-furnace. 

Ordinary  window  glass  is  a  soda  glass,  essentially  composed  of  sodium 
silicate  and  calcium  silicate,  containing  one  molecule  (13.3  %)  of  soda, 
one  molecule  (12.9  %)  of  lime,  and  five  molecules  (69.1  %)  of  silica;  it 
also  usually  contains  a  little  alumina.  This  variety  of  glass  is  manu- 
factured by  fusing  sand  (100  parts)  with  chalk  (35)  and  soda-ash  (35) : 
a  considerable  quantity  of  broken  window  glass  is  always  fused  up  at 
the  same  time.  Of  course,  C02  is  expelled  from  the  chalk  and  the 
Na,C03  in  the  gaseous  state ;  and  in  order  that  this  may  not  cause  the 
contents  of  the  crucible  to  froth  over  during  the  fusion,  the  materials 
are  fast,  fritted  together,  as  it  is  termed,  at  a  temperature  insufficient  to 
liquefy  them,  when  the  C02  is  evolved  gradually,  and  the  fusion  after- 
wards occurs  without  effervescence. 

Occasionally,  sodium  sulphate  is  employed  instead  of  the  carbonate,  when  it  is  usual 
to  add  a  small  proportion  of  charcoal  in  order  to  facilitate  the  decomposition  of  the 
sulphate  by  removing  part  of  its  oxygen  (Na2S04  +  SiO2  +  C  =  ]Sra2Si03  +  S02  +  CO). 
Before  the  glass  is  worked  into  sheets,  it  is  allowed  to  remain  at  rest  for  some  time 
in  the  fused  state,  so  that  the  air-bubbles  may  escape,  and  the  glass-gall  or  scum 


FLINT   GLASS.  371 

(consisting  chiefly  of  sodium  sulphate  and  sodium  chloride),  which  rises  to  the 
surface,  is  removed. 

Plate  glass  is  also  chiefly  a  silicate  of  sodium  and  calcium,  but  it  con- 
tains, in  addition,  a  considerable  quantity  of  silicate  of  potassium  (74 
per  cent,  of  Si02,  12  of  Na20,  5.5  of  K20,  and  5.5  of  CaO).  The  purest 
white  sand  is  selected,  and  great  care  is  taken  to  exclude  impurities. 

Crown  glass,  used  for  optical  purposes,  contains  no  sodium,  since  that 
metal  has  the  property  of  imparting  a  greenish  tint  to  glass,  which  is 
nofc  the  case  with  potassium.  This  variety  of  glass,  therefore,  is  pre- 
pared by  fusing  sand  with  potassium  carbonate  and  chalk  in  such  pro- 
portions that  the  glass  may  contain  i  mol.  (22  %)  of  K20,  i  mol.  (12.5  %) 
of  CaO,  and  4  mols.  (62  %)  of  SiO2. 

Bohemian  glass,  also  a  potash  glass  (silicate  of  K20  and  CaO),  is  less 
fusible  than  soda  glass,  and  less  easily  attacked  by  acids  ;  hence  its  use 
for  chemical  vessels ;  it  appears  to  owe  its  infusibility  to  its  high  con- 
tent of  silica. 

The  alkali  silicate  in  glass  being  the  more  soluble  in  water  the  richer 
it  is  in  alkali,  a  glass  containing  a  high  percentage  of  silica  is  the  more 
generally  useful  for  chemical  vessels,  particularly  as  it  is  less  fusible 
than  that  poorer  in  this  constituent.  It  is  only  comparatively  recently, 
however,  that  furnaces  attaining  the  high  temperatures  necessary  for 
working  glass  rich  in  silica  have  been  used.  As  stated  at  p.  279  the 
introduction  of  the  electric  furnace  may  enable  pure  silica  to  be  sub- 
stituted for  glass. 

Acid  solutions  attack  glass  less  than  water  does,  while  alkali  pro- 
duces the  most  effect.  By  steaming  the  glass  for  some  time  its  surface 
becomes  more  resistant.  Glass  containing  both  alkalies  is  more  easily 
attacked  than  that  containing  only  one. 

The  glass  of  which  wine  bottles  are  made  is  of  much  cheaper  and 
commoner  description,  consisting  chiefly  of  calcium  silicate,  but  contain- 
ing, in  addition,  small  quantities  of  the  silicates  of  sodium,  of  aluminium, 
and  of  iron,  to  the  last  of  which  it  owes  its  dark  colour. 

Flint  glass,  which  is  used  for  table  glass  and  for  ornamental  purposes, 
is  a  double  silicate  of  potassium  and  lead,  containing  one  mol.  (13.67  %) 
of  K20,  one  mol.  (33.28  %)  of  PbO,  and  six  mols.  (51.93  %)  of  Si02. 
It  is  prepared  by  fusing  300  parts  of  the  purest  white  sand  with  200 
parts  of  minium  (red  oxide  of  lead),  100  parts  of  refined  pearl-ash,  and 
30  parts  of  nitre.  The  fusion  is  effected  in  crucibles  covered  in  at  the 
top  to  prevent  the  access  of  the  flame,  which  would  reduce  a  portion  of 
the  lead  to  the  metallic  state.  The  nitre  is  added  in  order  to  oxidise 
any  accidental  impurities  which  might  reduce  the  lead. 

The  presence  of  the  lead  in  glass  very  much  increases  its  fusibility, 
and  renders  it  much  softer,  so  that  it  may  be  more  easily  cut  into  orna- 
mental forms  ;  it  also  greatly  increases  its  lustre  and  beauty. 

Barium  has  also  the  effect  of  increasing  the  fusibility  of  glass,  and 
zinc,  like  lead,  increases  its  brilliancy  and  refracting  power,  on  which 
account  it  is  employed  in  some  kinds  of  glass  for  optical  purposes.  Glass 
of  this  description  is  also  made  by  substituting  boric  oxide  for  a  portion 
of  the  silica. 

All  glass  articles  must  be  annealed  by  being  slowly  cooled,  otherwise 
they  are  liable  to  spontaneous  fracture,  due  to  the  excessive  strains  pro- 
duced in  the  structure  of  the  glass. 


372  COLOURED   GLASS. 

Some  varieties  of  glass,  if  heated  nearly  to  their  melting-point,  and 
allowed  to  cool  slowly,  become  converted  into  an  opaque  very  hard  mass 
resembling  porcelain  (Reaumur's  porcelain).  This  change;  which  is  known 
as  devitrification,  is  due  to  the  crystallisation  of  the  silicates  contained  in 
the  mass,  and,  by  again  fusing  it,  the  glass  may  be  restored  to  its  original 
transparent  condition. 

Toughened  glass  is  made  by  heating  the  glass  vessel  to  its  softening 
point,  immersing  it  in  a  bath  of  oil  or  steam  at  200°  0.,  and  cooling  it 
quickly.  This  treatment  hardens  it,  increases  its  specific  gravity,  and 
renders  it  less  brittle  externally,  but  puts  the  inner  portion  in  a  state  of 
tension,  so  that  it  sometimes  breaks  up  spontaneously. 

In  producing  coloured  glass,  advantage  is  taken  of  its  property  of  dis- 
solving many  metallic  oxides  with  production  of  peculiar  colours.  It  has 
been  mentioned  above  that  bottle  glass  owes  its  green  colour  to  the 
presence  of  iron;  and  since  this  metal  is  generally  found  in  small 
quantity  in  sand,  and  even  in  chalk,  it  occasionally  happens  that  a  glass 
which  is  required  to  be  perfectly  colourless  turns  out  to  have  a  slight 
green  tinge. 

In  order  to  remove  this,  a  small  quantity  of  some  oxidising  agent  is  usually 
added,  in  order  to  convert  the  ferrous  oxide  into  ferric  oxide,  which  does  not 
impart  any  colour  when  present  in  minute  proportion.  A  little  nitre  is  sometimes 
added  for  this  purpose,  or  some  white  arsenic,  which  yields  its  oxygen  to  the  ferrous 
oxide,  and  escapes  in  the  form  of  vapour  of  arsenic  ;  red  oxide  of  lead  (Pb.}04)  may 
also  be  employed,  and  is  reduced  to  oxide  of  lead  (PbO),  which  remains  in  the 
glass.  Manganese  dioxide  (ylassm  alters  soap)  is  often  added  as  an  oxidising  agent, 
being  reduced  to  the  state  of  manganous  oxide  (MnO),  which  does  not  colour  the 
glass  ;  but  care  is  then  taken  not  to  add  too  much  of  the  dioxide,  for  a  very  minute 
quantity  of  this  substance  imparts  a  beautiful  amethyst-purple  colour  to  glass. 

Suboxide  of  copper  is  used  to  produce  a  red  glass,  and  the  finest  ruby  glass  is 
obtained  by  the  addition  of  a  little  gold.  The  oxides  of  antimony  impart  a  yellow 
colour  to  glass  ;  a  peculiar  brown-yellow  shade  is  given  by  charcoal  in  a  fine  state 
of  division,  and  sesquioxide  of  uranium  produces  a  fine  greenish-yellow  glass. 
Green  glass  is  coloured  either  by  oxide  of  copper  or  sesquioxide  of  chromium, 
whilst  oxide  of  cobalt  gives  a  magnificent  blue  colour.  For  black  glass  a  mixture 
of  the  oxides  of  cobalt  and  manganese  is  employed.  The  white  enamel  glass  is 
a  flint  glass,  containing  about  10  per  cent,  of  binoxide  of  tin.  Bone-ash  is  also 
used  to  impart  this  appearance  to  glass.  The  irisatlon  of  glass,  giving  it  the  tints 
of  mother-of-pearl,  is  effected  by  corroding  its  surface  with  hydrochloric  acid  of 
15  per  cent,  strength,  under  heat  and  pressure. 

Kryolite  is  employed  in  making  opal-glass  containing  64  per  cent,  of  silica,  17  of 
alumina,  16  of  lead  oxide,  and  3  of  potash. 

200.  General  review  of  the  metals  of  the  alkaline  earths. — 
Barium,  strontium,  and  calcium  form  a  highly  interesting  natural  group 
of  metals  related  to  each  other  in  a  most  remarkable  manner.  They 
exhibit  a  marked  gradation  in  their  attraction  for  oxygen  :  barium  is 
more  readily  tarnished  or  oxidised,  even  in  dry  air,  than  strontium,  and 
strontium  more  readily  than  calcium.  The  hydroxides  of  the  metals 
exhibit  a  similar  gradation  in  properties;  barium  hydroxide  does  not  lose 
water,  however  strongly  it  may  be  heated,  whereas  the  hydroxides  of 
strontium  and  calcium  are  decomposed  at  a  red  heat.  Then  barium 
hydroxide  and  strontium  hydroxide  are  far  more  soluble  in  water  than 
is  calcium  hydroxide,  and  all  these  three  exhibit  a  very  decided  alkaline 
reaction  which  entitles  them  to  the  name  of  alkaline  earths. 

Among  the  other  compounds  of  these  metals,  the  sulphates  may  be 
named  as  presenting  a  gradation  of  a  similar  description  ;  for  barium 
sulphate  may  be  said  to  be  insoluble  in  water,  strontium  sulphate 


SOUECES   OF  MAGNESIUM.  373 

dissolves  to  a  very  slight  extent,  and  calcium  sulphate  is  much  more 
soluble. 

The  manner  in  which  these  metals  are  associated  in  nature  is  also  not 
without  its  significance :  for  if  two  of  them  are  found  in  the  same 
mineral  they  will  usually  be  those  which  stand  next  to  each  other  in 
the  group ;  thus  strontium  carbonate  is  found  together  with  barium 
carbonate  in  witherite,  whilst  calcium  carbonate  is  associated  with 
strontium  sulphate  in  celestine.  Again,  strontium  carbonate  is  often 
found  with  calcium  carbonate  in  aragonite.  Such  facts  lend  support  to 
the  hypotheses  of  Crookes  and  others  as  to  the  possible  evolution  of  the 
elements. 

MAGNESIUM. 

Mg"  =  24.2  parts  by  weight. 

201.  Magnesium  is  found,  like  calcium,  though  less  abundantly,  in 
each  of  the  three  natural  kingdoms.  Among  minerals  containing  this 
metal,  those  with  which  we  are  most  familiar  are  certain  combinations 
of  silica  and  magnesia  (silicates  of  magnesium)  known  by  the  names  of 
talc,  steatite  or  French  chalk,  asbestos,  and  meerschaum,  which  always 
contains  water.  Magnesite  is  a  carbonate  of  magnesium.  Most  of  the 
minerals  containing  magnesium  have  a  remarkably  soapy  feel.  The 
compounds  of  magnesium,  which  are  employed  in  medicine,  are  derived 
either  from  the  mineral  dolomite,  or  magnesian  limestone,  which  contains 
the  carbonates  of  magnesium  and  calcium,  or  from  the  magnesium 
sulphate  which  is  obtained  from  sea  water  and  from  the  waters  of  many 
mineral  springs. 

Metallic  magnesium  is  important  as  a  source  of  light.  When  the 
extremity  of  a  wire  of  this  metal  is  heated  in  a  flame,  it  takes  fire,  and 
burns  with  a  dazzling  white  light,*  becoming  magnesia  (MgO).  If  the 
burning  wire  be  plunged  into  a  bottle  of  oxygen,  the  combustion  is  still 
more  brilliant.  The  light  emitted  by  burning  magnesium  induces 
chemical  changes  similar  to  those  caused  by  sunlight,  a  circumstance 
turned  to  advantage  for  the  production  of  photographic  pictures,  for 
which  purpose  the  powdered  metal  is  blown  through  a  flame  producing 
a  flash  of  very  short  duration  but  intense  luminosity.  Attempts  have 
been  made  to  introduce  magnesium  as  an  illuminating  agent  for  general 
purposes,  but  the  large  quantity  of  solid  magnesia  produced  in  its  com- 
bustion forms  a  very  serious  obstacle  to  its  use.  The  metal  is  obtained 
by  electrolysing  fused  carnallite  (p.  335),  which,  when  melted,  loses  its 
water  and  becomes  KCl.MgCl2.  The  liquid  is  contained  in  an  iron 
vessel  externally  heated  and  serving  as  the  cathode.  The  anode  is  a 
carbon  rod  surrounded  by  a  porous  cylinder  and  partly  immersed  in  the 
fused  mass.  The  metal  separates  at  the  cathode  and  floats  on  the  top 
of  the  liquid,  while  the  chlorine  escapes  at  the  anode  and  is  kept  from 
the  metal  by  the  porous  cylinder.  To  prevent  the  Mg  from  burning 
the  atmosphere  in  the  vessel  must  be  nitrogen.  This  electrolysis  has 
displaced  the  older  method  of  reducing  MgCl2  by  fusing  it  with 
sodium. 

*  A  wire  of  0.33  millimetre  diameter  gives  a  light  of  74  candle-power.  Although  the 
illuminatiu"  power  of  the  sun's  rays  is  524  times  that  of  burning  Mg,  their  chemical  activity 
is  only  5  times  as  great.  The  heat  of  combustion  is  Mg,O  =  143,400  calories. 


374  MAGNESIA. 

In  most  of  its  physical  and  chemical  characters,  magnesium  resembles 
zinc,  though  its  colour  more  nearly  approaches  that  of  silver  ;  in  ductility 
and  malleability,  it  also  surpasses  zinc.  It  is  nearly  as  light,  however, 
as  calcium,  its  specific  gravity  being  1.74.  It  fuses  about  750°  C.,  and 
may  be  distilled  like  zinc.  Cold  water  has  scarcely  any  action  upon 
magnesium;  even  when  boiled,  it  oxidises  the  metal  very  slowly. 
In  the  presence  of  acids,  however,  it  is  rapidly  oxidised  by  water. 
Solution  of  ammonium  chloride  also  dissolves  it,  owing  to  the  tendency 
of  the  magnesium  salts  to  form  double  salts  with  those  of  ammonium  ; 
4NH4C1  +  Mg  =  (NH4)2MgCl4  +  H2  +  2NH3.  Magnesium  is  one  of  the 
few  elements  which  unite  directly  with  nitrogen  at  a  high  temperature. 
The  magnesium  nitride,  Mg3N2,  has  been  obtained  in  transparent 
crystals,  and  is  evidently  composed  after  the  type  2NH3,  so  that  it  is 
not  surprising  that  the  action  of  water  upon  it  gives  rise  to  magnesia 
and  ammonia  ;  Mg3N2  +  3H2O  =  2NH3  +  3MgO.  If  a  foot  of  Mg  tape 
be  burnt  in  air,  the  residue  evolves  much  NH3  when  boiled  with  water. 

Magnesia,  MgO,  occurs,  crystallised  in  octahedra,  as  the  mineral 
periclase.  It  is  prepared  by  decomposing  magnesium  carbonate  by  heat, 
and  is  a  light  white  powder,  very  infusible  (so  that  it  is  used  for  making 
basic  fire-bricks)  and  scarcely  affected  by  water.  It  dissolves  easily  in 
acids.  Magnesium  hydroxide,  Mg(OH)2,  also  occurs  crystallised  as 
brucite.  When  MgO  is  mixed  with  water,  combination  occurs,  but  not 
with  much  evolution  of  heat,  as  with  BaO,  SrO,  and  CaO.  If  excess 
of  water  be  avoided,  the  mass  sets  like  plaster  of  Paris.  Mg(OH)2  is 
precipitated  when  an  alkali  is  added  to  a  magnesium  salt.  The 
hydroxide  slowly  absorbs  CO2  from  the  air,  and  is  easily  decomposed  by 
heat  into  MgO  and  H2O.  It  is  used  in  extracting  sugar  from  the  beet. 

Magnesium  carbonate,  MgC03,  is  found  as  magnesite,  which  is 
imported  from  Greece.  It  is  unaffected  by  water,  and  does  not  effervesce 
so  briskly  with  acids  as  do  the  other  carbonates.  It  is  easily  decomposed 
by  heat  into  MgO  and  C02.  When  a  salt  of  magnesium  is  precipitated 
by  an  alkali  carbonate,  the  precipitate  is  not  the  normal  carbonate,  as 
in  the  cases  of  Ba,  Sr,  and  Ca,  but  a  basic  carbonate,  or  a  compound  of 
the  carbonate  and  hydroxide.  Ordinary  magnesia  alba,  or  light  carbo- 
nate of  magnesia,  is  prepared  by  precipitating  magnesium  sulphate  with 
sodium  carbonate,  and  boiling ;  it  generally  has  the  composition 
5MgC03.2Mg(OH)2.7Aq.  In  preparing  the  heavy  carbonate,  the  mixed 
solutions  are  evaporated  to  dryness,  and  the  sodium  sulphate  washed 
out  of  the  residue  by  water.  These  light  and  heavy  carbonates,  when 
calcined,  yield  light  and  heavy  magnesia,  the  former  having  3^  times 
the  bulk  of  the  latter. 

Magnesium  carbonate,  like  CaC03,  is  soluble  in  carbonic  acid,  and  is 
present  in  most  natural  waters,  causing  temporary  hardness,  the  MgCO3 
being  precipitated  by  boiling.  When  magnesia  alba  is  dissolved  in 
carbonic  acid  water,  and  the  solution  exposed  to  air,  needles  of 
MgC03-3Aq  are  deposited.  If  this  be  boiled  with  water,  it  loses  C02 
and  becomes  a  basic  carbonate. 

Dolomite  or  magnesium  limestone,  is  a  mixture  of  magnesium  carbonate 
and  calcium  carbonate  in  variable  proportions.  Magnesium  carbonate 
is  prepared  from  it  by  heating  it  sufficiently  to  decompose  the  MgCO3, 
and  exposing  it,  under  pressure,  to  the  action  of  water  and  C02,  when 
the  MgO  is  dissolved  and  the  CaC03  is  left.  By  passing  steam  through 


EPSOM   SALTS.  375 

the  solution,  the  basic  magnesium  carbonate  is  precipitated.    Pearl  spar 
is  a  crystalline  form  of  the  double  carbonate,  MgCa(CO3)2. 

The  sulphate  of  magnesia  or  magnesium  sulphate,  so  well 
known  as  Epsom  salts,  is  sometimes  prepared  by  calcining  dolomite  to 
expel  the  CO,,  washing  the  residual  mixture  of  lime  and  magnesia  with 
water  to  remove  part  of  the  lime,  and  treating  it  with  sulphuric  acid, 
which  converts  the  calcium  and  magnesium  into  sulphates ;  and  since 
calcium  sulphate  is  almost  insoluble  in  water,  it  is  readily  separated  from 
the  magnesium  sulphate  which  passes  into  the  solution,  and  is  obtained  by 
evaporation  in  prismatic  crystals,  having  the  composition  MgSO4.H20.6Aq, 
Epsom  salts  are  now  made  from  Kieserite,  MgS04.H20,  found  in  the 
Stassfurt  salt  beds.  This  is  almost  insoluble  in  water,  but,  when  kept 
in  contact  with  it,  is  slowly  converted  into  MgS04.7H20.  The  prepara- 
tion of  Epsom  salts  from  sea  water  has  already  been  alluded  to  (p.  344). 

In  some  parts  of  Spain,  magnesium  sulphate  is  found  in  large  quantities  (like 
nitre  in  hot  climates)  as  an  efflorescence  upon  the  surface  of  the  soil.  This  sulphate, 
as  well  as  that  contained  in  well-waters,  appears  to  have  been  produced  by  the 
action  of  the  calcium  sulphate,  originally  present  in  the  water,  upon  magnesian 
limestone  rocks  ;  MgC03  +  CaS04  =  MgS04  +  CaC03. 

The  crystals  MgS04.7H20  fuse  easily,  and  become  MgS04.H2Oat  150°  C.  The 
last  H20,  can  only  be  expelled  at  above  200°,  and  is  termed  the  water  of  constitu- 
tion. 

The  water  of  constitution  in  the  magnesium  sulphate  may  be  displaced  by  the 
sulphate  of  an  alkali-metal  without  alteration  in  its  crystalline  form  ;  a  double 
sulphate  of  magnesium  and  potassium  (MgS04.K2SO4.6Aq),  and  a  similar  salt  of 
ammonium  may  be  thus  obtained.  The  mineral  polyhaUte  (TTO\I/S,  many,  #Xs,  salt) 
is  a  remarkable  salt,  containing  MgS04.K2S04.2CaS64.2H20.*  Water  decomposes 
it  into  its  constituent  salts. 

Epsom  salts  dissolve  very  easily  in  water,  but  not  in  alcohol.  If  the  aqueous 
solution  be  mixed  with  enough  alcohol  to  render  it  turbid,  small  oily  drops 
separate,  from  which  small  crystals  presently  shoot  out,  and  the  liquid  becomes, 
by  degrees,  a  pasty  mass  of  very  light  needles  closely  interlaced.  These  contain 
7H20.  An  aqueous  solution  crystallised  at  above  70°  C.  deposits  MgS04.H20.5Aq  ; 
at  6°,  crystals  of  MgS04.H20.  iiAq  are  formed. 

Phosphates  of  magnesium. — Mg3(PO4)2  is  contained  in  bones  and  in  some  seeds. 
MgHP04.7Aq  is  the  precipitate  produced  by  Na2HP04  in  magnesium  salts  ;  it  is  de- 
composed by  boiling  with  water  ;  3MgHP04  =  H3P04  +  MggCPO^o.  MgNH4P04. 6Aq 
is  deposited  in  crystals  from  alkaline  urine,  and  forms  triple  phosphate  calculi. 
It  is  precipitated  by  Na2HP04  from  a  magnesium  salt  to  which  NH3  has  been 
added;  MgS04  +  NH3  +  Na2HP04  =  Na2S04  +  MgNH4P04.  Ammonium  chloride 
should  be  added  first  to  prevent  the  separation  of  Mg(OH)2.  The  precipitation 
is  much  promoted  by  stirring  ;  the  MgNH4P04  is  sparingly  soluble  in  water, 
and  almost  insoluble  in  ammonia  ;  when  it  is  heated  to  redness,  2MgNH4P04  = 
Mg2P207  +  NH3  +  H20.  In  quantitative  analysis,  Mg  and  P  are  generally  deter- 
mined in  this  form. 

Magnesium-ammonium  arsenate,  MgNH4As04.6H20,  is  very  similar,  and  is  used 
in  determining  arsenic. 

Magnesium  .bo-rate  and  chloride  compose  the  mineral  stassfurtite ;  hydroboracite 
is  a  hydrated  borate  of  calcium  and  magnesium. 

Serpentine,  2SiO2>3(Mg,Fe)0,  and  olivine,  Si02.3(Mg,Fe)0,  are  silicates 
of  magnesia  and  ferrous  oxide.  Some  of  the  varieties  of  serpentine  are 
used  for  preparing  the  compounds  of  magnesium,  being  easily  decom- 
posed by  acids  with  separation  of  silica.  The  minerals,  asbestos,  meer- 
schaum, steatite,  and  talc  consist  chiefly  of  magnesium  silicates. 

Magnesium  chloride  occurs  in  sea-water,  in  brine-springs,  in  many 
natural  waters  and  in  the  minerals  carnallite  (p.  335)  and  bischqfite, 

*  Polyhalite  is  found  in  the  salt-beds  of  Stassfurt.  Kainite,  from  the  same  locality,  is 
K2S04.MgS04.MgCl2.6Aq. 


376  USES   OF  ZINC. 

MgCl2.6Aq.  It  is  easily  obtained  in  solution  by  neutralising  hydro- 
chloric acid  with  magnesia  or  its  carbonate  ;  but  if  this  solution  be 
evaporated  in  order  to  obtain  the  dry  chloride,  a  considerable  quantity 
of  the  salt  is  decomposed  by  the  water  at  the  close  of  the  evaporation, 
leaving  much  magnesia  mixed  with  the  chloride  (MgCl2  +  H2O  = 
2HCl  +  MgO).  This  decomposition  may  be  prevented  by  mixing  the 
solution  with  three  parts  of  chloride  of  ammonium  for  every  part  of 
magnesia,  when  a  double  salt,  MgCl2.2NH4Cl,  is  formed,  which  may  be 
evaporated  to  dry  ness  without  decomposition,  and  leaves  fused  magne- 
sium chloride  when  further  heated,  the  ammonium  chloride  being 
volatilised.  The  magnesium  chloride  absorbs  moisture  very  rapidly 
from  the  air,  and  is  very  soluble  in  water.  Like  all  the  soluble  salts  of 
magnesium,  it  has  a  decidedly  bitter  taste.  When  magnesia  is  moist- 
ened with  a  strong  solution  of  magnesium  chloride,  it  sets  into  a  hard 
mass  like  plaster  of  Paris,  apparently  from  the  formation  of  an  oxy- 
chloride.  It  may  be  mixed  with  several  times  its  weight  of  sand,  and 
will  bind  the  sand  firmly  together. 

The  ammonium  magnesium  chloride,  NH4Cl.MgCl2.Aq,  is  not  decom- 
posed by  ammonia,  which  therefore  gives  no  precipitate  in  solutions  of 
magnesium  to  which  NH4C1  has  been  added  in  sufficient  quantity. 

Magnesium  stands  apart  from  other  metals,  on  the  one  hand,  by  the 
non-precipitation  of  its  sulphide,  and,  on  the  other,  by  the  tendency  of 
all  its  salts,  except  the  phosphate  and  arsenate,  to  form  soluble  com- 
pounds with  the  salts  of  ammonium. 

ZINC. 

Zn"  =  65  parts  by  weight  =  2  vols. 

2 02.  Zinc  occupies  a  high  position  among  useful  metals,  being  pecu- 
liarly fitted,  on  account  of  its  lightness,  for  the  construction  of  gutters, 
water-pipes,  and  roofs  of  buildings,  and  possessing  for  these  purposes  a 
great  advantage  over  lead,  since  the  specific  gravity  of  the  latter  metal 
is  about  11.5,  whilst  that  of  zinc  is  only  7.  For  such  applications  as 
these,  where  great  strength  is  not  required,  zinc  is  preferable  to  iron,  on 
account  of  its  superior  malleability;  for  although  a  bar  of  zinc  breaks 
under  the  hammer  at  the  ordinary  temperature,  it  becomes  so  malleable 
at  250°  F.  (121°  C.)  as  to  admit  of  being  rolled  into  thin  sheets.  This 
malleability  of  zinc  when  heated  was  discovered  only  in  the  commence- 
ment of  the  last  century,  until  which  time  the  sole  use  of  the  metal  was 
in  the  manufacture  of  brass.  When  zinc  is  heated  to  400°  F.  (204°  C.), 
it  again  becomes  brittle,  and  may  be  powdered  in  a  mortar.  The  easy 
fusibility  of  zinc  also  gives  it  a  great  advantage  over  iron,  as  rendering 
it  easy  to  be  cast  into  any  desired  form  ;  indeed,  zinc  is  surpassed  in 
fusibility  (among  the  metals  in  ordinary  use)  only  by  tin  and  lead,  its 
melting-point  being  below  a  red  heat,  and  usually  estimated  at  786°  F. 
(410°  C.).  Zinc  is  also  less  liable  than  iron  to  corrosion  under  the  in- 
fluence of  moist  air,  for  although  a  bright  surface  of  zinc  soon  tarnishes 
when  exposed  to  the  air,  it  merely  becomes  covered  with  a  thin  film  of 
zinc  oxide  (passing  gradually  into  basic  carbonate,  by  absorption  of  CO2 
from  the  air)  which  protects  the  metal  from  further  action. 

The  great  strength  of  iron  has  been  ingeniously  combined  with  the 
durability  of  zinc,  in  the  so-called  galvanised  iron,  which  is  made  by 


EXTRACTION  OF  ZINC.  377 

coating  clean  iron  with  melted  zinc,  thus  affording  a  protection  much 
needed  in  and  around  large  towns,  where  the  sulphurous  and  sulphuric 
acids  arising  from  the  combustion  of  coal,  and  the  acid  emanations  from 
various  factories,  greatly  accelerate  the  corrosion  of  unprotected  iron. 
The  iron  plates  to  be  coated  are  first  thoroughly  cleansed  by  a  process 
which  will  be  more  particularly  noticed  in  the  manufacture  of  tin-plate, 
and  are  then  dipped  into  a  vessel  of  melted  zinc,  the  surface  of  which  is 
coated  with  sal  ammoniac  (ammonium  chloride)  in  order  to  dissolve  the 
zinc  oxide  which  forms  upon  the  surface  of  the  metal,  and  might 
adhere  to  the  iron  plate  so  as  to  prevent  its  becoming  uniformly  coated 
with  the  zinc.*  A  more  firmly  adherent  coating  of  zinc  is  obtained  by 
first  depositing  a  thin  film  of  tin  upon  the  surface  of  the  iron  plate  by 
galvanic  action,  and  hence  the  name  galvanised  iron. 

The  ores  of  zinc  are  found  pretty  abundantly  in  England,  chiefly  in 
the  Mendip  Hills  in  Somersetshire,  at  Alston  Moor  in  Cumberland,  in 
Cornwall  and  Derbyshire,  but  the  greater  part  of  the  zinc  used  in  this 
country  is  imported  from  Belgium  and  Germany,  being  derived  from 
the  ores  of  Transylvania,  Hungary,  and  Silesia. 

Metallic  zinc  is  never  met  with  in  nature.  Its  chief  ores  are  cola- 
mine  or  zinc  carbonate  (ZnC03),  blende  or  zinc  sulphide  (ZnS),  and  red 
zinc  ore,  in  which  zinc  oxide  (ZnO)  is  associated  with  the  oxides  of  iron 
and  manganese. 

Calamine  is  so  called  from  its  tendency  to  form  masses  resembling  a  bundle  of 
reeds  (calamus,  a  reed).  It  is  found  in  considerable  quantities  in  Somersetshire, 
Cumberland,  and  Derbyshire.  A  compound  of  zinc  carbonate  with  zinc  hydroxide 
ZnC03.2Zn(OH)2,  is  found  abundantly  in  Spain.  The  mineral  known  as  electric 
calamine  (hemimorphite)  is  a  silicate  of  zinc  (2ZnO.Si02.H20),  which  becomes 
electrified  when  heated.  Blende  derives  its  name  from  the  German  blenden,  to 
dazzle,  in  allusion  to  the  brilliancy  of  its  crystals,  which  are  generally  almost  black 
from  the  presence  of  iron  sulphide,  the  true  colour  of  pure  zinc  sulphide  being 
white.  Blende  is  found  in  Cornwall,  Cumberland,  Derbyshire,  Wales,  and  the  Isle 
of  Man,  and  is  generally  associated  with  galena  or  lead  sulphide,  which  is  always 
carefully  picked  out  of  the  ore  before  smelting  it,  since  it  would  become  converted 
into  lead  oxide,  which  corrodes  the  earthern  retorts  employed  in  the  process. 

Before  extracting  the  metal  from  these  ores,  they  are  subjected  to  a 
preliminary  treatment  which  brings  them  both  to  the  condition  of  zinc 
oxide.  For  this  purpose  the  calamine  is  simply  calcined  in  a  reverbera- 
tory  furnace,  in  order  to  expel  carbonic  acid  gas;  but  the  blende  is 
roasted  for  ten  or  twelve  hours,  with  constant  stirring,  so  as  to  expose 
fresh  surfaces  to  the  air,  when  the  sulphur  passes  off  in  the  form  of 
S02,  and  its  place  is  taken  by  the  oxygen,  the  ZnS  becoming  ZnO.  The 
extraction  of  the  metal  from  this  zinc  oxide  depends  upon  the  circum- 
stance that  zinc  is  capable  of  being  distilled  at  a  bright  red  heat,  its 
boiling-point  being  about  930°  C. 

The  facility  with  which  this  metal  passes  oft'  in  the  form  of  vapour  is 
seen  wThen  it  is  melted  in  a  ladle  over  a  brisk  fire,  for  at  a  bright  red 
heat  abundance  of  vapour  rises  from  it,  which,  taking  fire  in  the  air, 
burns  with  a  brilliant  greenish-white  light,  throwing  off  into  the  air, 
numerous  white  flakes  of  light  zinc  oxide  (the philosophers  wool,  or  nil 
album  of  the  old  chemists). 

*  The  sal  ammoniac  acts  upon  the  heated  zinc  according  to  the  equation,  Zn  +  2XH4Cl=: 
ZnCl2  +  2XH3  +  H2,  and  the  zinc  chloride  which  is  formed  dissolves  the  oxide  from  the 
surface  of  the  metal,  producing'  zinc  oxychloride. 


378 


EXTRACTION   OF   ZINC. 


The  distillation  of  zinc  may  be  effected  on  the  small  scale  in  a  black-lead  crucible 
(A,  Fig.  215)  about  5  inches'high  and  3  in  diameter.  A  hole  is  drilled  through  the 
bottom  with  a  round  file,  and  into  this  is  fitted  a  piece  of  wrought-iron  gas-pipe 
(B)  about  nine  inches  long  and  I  inch  wide,  so  as  to  reach  nearly  to  the  top  of  the 
inside  of  the  crucible.  Any  crevices  between  the  pipe  and  the  sides  of  the  hole 
are  carefully  stopped  up  with  fireclay  moistened  with  solution  of  borax.  A  few 
ounces  of  zinc  are  introduced  into  the  crucible,  the  cover  of  which  is  then  carefully 
cemented  on  with  fireclay  (a  little  borax  being  added  to  bind  it  together  at  a  high 
temperature),  and  the  hole  in  the  cover  is  stopped  up  with  fireclay.  The  crucible 
having  been  kept  for  several  hours  in  a  warm  place,  so  that  the  clay  may  dry,  it  is 
placed  in  a  cylindrical  furnace  with  a  hole  at  the  bottom,  through  which  the  iron 
pipe  may  pass,  and  a  lateral  opening,  into  which  is  inserted  an  iron  tube  (C)  con- 
nected with  a  forge  bellows.  Some  lighted  charcoal  is  thrown  into  the  furnace, 
and  when  this  has  been  blown  into  a  blaze,  the  furnace  is  filled  up  with  coke 
broken  into  small  pieces.  The  fire  is  then  blown  till  the  zinc  distils  freely  into  a 
vessel  of  water  placed  for  its  reception.  Four  ounces  of  zinc  may  be  easily  distilled 
in  half  an  hour. 

The  original  English  method  for  extracting  zinc  from  the  roasted  ore& 
consisted  in  mixing  the  ground  ore  with  about  half  its  weight  of  coker 

and  strongly  heating  the 
mixture  in  crucibles  pro- 
vided with  tubes,  like 
that  shown  in  Fig.  215; 
the  zinc  was  thus  distilled 
per  descensum  in  the 
manner  described  in  the 
preceding  paragraph. 
The  reduction  of  zinc 
oxide  by  carbon  is  repre- 
sented by  the  equation 


Fig.  215. 
Distillation  of  zinc. 


Fig.  216. 
Belgian  zinc  furnace. 


This  reaction  is  found  to  be 
endothermic  when  its  thermal 
value  is  calculated  from 
ordinary  data  (see  p.  307),. 
which  will  account  for  the 
very  high  temperature  (1300° 
C.)  required  to  effect  the 

reduction  ;  this  is  probably  aided  by  the  volatility  of  zinc,  which  escapes  from  the 
sphere  of  action  as  soon  as  it  is  liberated,  and  allows  a  mass  action  of  the  carbon  to 
come  into  play  (see  p.  310). 

At  the  present  day  the  reduction  and  distillation  of  zinc  is  effected 
in  retorts,  which  are  either  of  the  Belgian  or  the  Silesian  type  ;  the 
construction  of  each  will  be  understood  from  the  accompanying  figures. 

At  Liege,  in  Belgium,  calamine  is  exposed  to  the  rain  for  several  months  in 
order  -to  wash  out  the  clay  ;  it  is  then  calcined  and  mixed  with  half  its  weight  of 
coal-dust,  and  distilled  in  cylindrical  fireclay  retorts  (C,  Fig.  216),  holding  about 
40  Ibs.  each,  and  set  in  seven  tiers  of  six  each  in  the  same  furnace,  the  vapour  of 
zinc  being  conveyed  by  a;  short  conical  iron  pipe  (B)  into  a  conical  iron  receiver 
(D),  which  is  emptied  every  two  hours  into  a  large  ladle,  from  which  the  zinc  is 
poured  into  ingot  moulds.  Each  distillation  occupies  about  twelve  hours.  The 
advantage  of  this  particular  mode  of  arranging  the  cylinders  is,  that  it  economises 
fuel  by  allowing  the  poorer  ores,  which  require  less  heat  to  distil  all  the  zinc  from 
them,  to  be  introduced  into  the  upper  rows  of  cylinders  farthest  from  the  fire  (A). 
There  are  two  varieties  of  Belgian  ore,  one  containing  33  and  the  other  46  per 
cent,  of  zinc,  but  a  large  proportion  of  this  is  in  the  form  of  silicate,  which  is  not 
extracted  by  the  distillation. 

In  Silesia  the  zinc  oxide  is  mixed  with  fine  cinders,  and  distilled  in  arched 


EXTRACTION   OF  ZINC. 


379 


earthen  retorts  (A,  Fig.  217),  into  which  the  charge  is  introduced  through  a  small 
door  (B),  which  is  then  cemented  up.  The  retorts  are  arranged  in  a  double  row 
in  the  same  furnace  (Fig.  218),  and  the  vapour  of  zinc  is  condensed  in  a  bent 
earthenware  pipe  attached  to  each  retort,  and  having  an  opening  (C)  near  the 
bend,  which  is  kept  closed,  unless  it  is  necessary  to  clear  out  the  pipe. 

The  Silesian  zinc  is  remelted,  before  casting  into  ingots,  in  clay  in- 
stead of  iron  pots,  since  melted  zinc  always  dissolves  iron,  and  a  very 
small  quantity  of  that 
metal  is  found  to  injure 
zinc  when  required  for 
rolling  into  sheets. 

A  small  quantity  of 
lead  always  distils  over 
together  with  the  zinc, 
and  since  this  metal  also 
interferes  with  the  roll- 
ing of  zinc  into  sheets, 
a  portion  of  it  is  sepa- 
rated from  zinc  intended 
for  this  purpose,  by 
melting  the  spelter,  in 
large  quantity,  upon  the 
hearth  of  a  reverberatory 
furnace,  the  bed  of  which 
is  inclined  so  as  to  form 
a  deep  cavity  at  the  end 
nearest  the  chimney. 
The  specific  gravity  of 
lead  being  11.4,  whilst  that  of  zinc  is  7,  the  former  accumulates  chiefly 
at  the  bottom  of  the  cavity,  and  the  ingots  cast  from  the  upper  part  of 
the  melted  zinc  will  contain  but  little  lead,  since  zinc  is  not  able  to 
dissolve  more  than  1.5  per  cent,  of  that  metal  at  400°  C. 

The  electrolytic  extraction  of  zinc  is  said  to  be  practised  at  some  places.  By  one 
process  the  roasted  ore  is  leached  with  dilute  sulphuric  acid  which  dissolves  the 
zinc  oxide  as  sulphate  ;  the  solution  is  passed  over  metallic  zinc  to  deposit  other 
metals  electro- negative  to  zinc,  and  electrolysed  with  zinc  cathodes  and  carbon 
anodes.  The  zinc  is  deposited  on  the  former,  and  oxygen  evolved  at  the  latter, 
dilute  H2S04  being  left  in  the  liquid  to  be  used  to  leach  more  ore. 

Ingots  of  zinc,  when  broken  across,  exhibit  a  beautiful  crystalline 
fracture,  which,  taken  in  conjunction  with  'the  bluish  colour  of  the 
metal,  enables  it  to  be  easily  identified.  The  spelter  of  commerce  is 
liable  to  contain  lead,  iron,  tin,  antimony,  arsenic,  copper,  cadmium, 
magnesium,  and  aluminium.  Belgian  zinc  is  usually  purer  than  the 
English  metal. 

Zinc  being  easily  dissolved  by  diluted  acids,  it  is  necessary  to  be 
careful  in  employing  this  metal  for  culinary  purposes,  since  its  soluble 
salts  are  poisonous. 

It  will  be  remembered  that  the  action  of  diluted  sulphuric  acid  upon  zinc  is 
employed  for  the  preparation  of  hydrogen.  Pure  zinc,  however,  evolves  hydrogen 
very  slowly,  since  it  becomes  covered  with  a  number  of  hydrogen  bubbles  which 
protect  it  from  further  action  ;  but  if  a  piece  of  copper  or  platinum  be  made  to 
touch  the  zinc  beneath  the  acid,  these  metals,  being  electro-negative  towards  the 
zinc,  will  attract  the  electro-positive  hydrogen,  leaving  the  zinc  free  from  bubbles, 
and  exposed  on  all  points  to  the  action  of  the  acid,  so  that  a  continuous  dis- 


Fig.  218. — Silesian  zinc  furnace. 


380  ZINC   WHITE. 

engagement  of  hydrogen  is  maintained.  As  a  curious  illustration  of  this,  a  thin 
sheet  of  platinum  or  silver  foil  may  be  shown  to  sink  in  diluted  sulphuric  acid, 
until  it  comes  in  contact  with  a  piece  of  zinc,  when  the  bubbles  of  hydrogen  bring 
it  up  to  the  surface.  The  lead,  iron,  &c..  met  with  in  commercial  zinc,  are  electro- 
negative to  the  zinc,  and  thus  serve  to  maintain  a  constant  evolution  of  hydrogen. 

Zinc  also  dissolves  in  boiling  solutions  of  potash  arid  soda,  evolving 
hydrogen;  2KOH +  Zn  =  Zn(OK)2  + H2.  Even  solution  of  ammonia 
dissolves  it  slowly.  When  heated  with  Ca(OH)2  it  evolves  hydrogen. 

A  coating  of  metallic  zinc  may  be  deposited  upon  copper  by  slow 
galvanic  action,  if  the  copper  be  immersed  in  a  concentrated  solution  of 
potash,  at  the  boiling-point  of  water,  in  contact  with  metallic  zinc, 
when  a  portion  of  the  latter  is  dissolved  in  the  form  of  oxide,  with 
evolution  of  hydrogen,  and  is  afterwards  precipitated,  on  the  surface  of 
the  copper. 

Zinc-dust  is  metallic  zinc  which  has  condensed  in  a  fine  powder  in 
smelting  the  ores.  It  is  very  useful  in  the  laboratory  as  a  reducing-agent. 

Zinc  oxide  (ZnO). — Zinc  forms  but  one  oxide,  which  is  known  in 
commerce  as  zinc-white  or  Chinese  white,  and  is  prepared  by  allowing 
the  vapour  of  the  metal  to  burn  in  earthen  chambers  through  which  a 
current  of  air  is  maintained.  It  is  practically  insoluble  in  water,  and 
is  sometimes  used  for  painting  in  place  of  white  lead  (basic  lead  car- 
bonate), over  which  it  has  the  advantages  of  not  injuring  the  health  of 
the  persons  using  it,  and  of  being  unaffected  by  sulphuretted  hydrogen, 
an  important  consideration  in  manufacturing  towns  where  tnat  sub- 
stance is  so  abundantly  supplied  to  the  atmosphere.  Unfortunately, 
however,  the  zinc  oxide  paint  has  less  covering  power  and  is  more  liable 
to  peel  off  than  white  lead  paint.  The  zinc  oxide  has  the  character- 
istic property  of  becoming  yellow  when  heated,  and  white  again  as  it 
cools.  Its  sp.  gr.  is  5.6.  It  is  sometimes  used  in  the  manufacture  of 
glass  for  optical  purposes.  At  the  temperature  of  the  electric  arc  it  is 
volatile. 

Zinc  hydroxide,  Zn(OH)2,  is  precipitated  in  a  gelatinous  state  when  caustic 
alkalies  are  added  to  solutions  containing  zinc ;  the  precipitate  dissolves  in  the 
excess  of  alkali,  and,  if  this  be  not  too  great,  is  reprecipitated  by  boiling.  The 
alkaline  solution  is  said  to  contain  an  alkali  zincate,  e.g.,  K2Zn02.  Ammonia  does 
not  precipitate  zinc  hydroxide  from  solutions  containing  ammonium  salts,  since 
zinc  resembles  magnesium  in  forming  double  salts  containing  ammonium.  Zinc 
hydroxide  is  easily  decomposed  by  heat  ;  Zn(OH)2  =  ZnO  +  H20. 

Zinc  nitride,  Zn3N2. — When  zinc  ethide  (see  Org a  no-mineral  Compounds)  is  acted 
on  by  ammonia,  it  is  converted  into  zinc-diamine ;  Zn(C2Hg)2  +  2NH3  =  Zn(NH2)0  + 
2C2H6  (ethyl  hydride).  When  zinc-diamine  is  heated,  out  of  contact  with  air,  it 
gives  zinc  nitride;  3Zn(NH2)2  =  Zn3N2  +  4NH3.  The  nitride  decomposes  with 
water,  evolving  much  heat ;  Zn3N2  +  3H20  =  2NH3  +  3ZnO. 

Zinc  carbonate,  ZnCO3,  as  found  in  nature  (calamine,  timithsonite) 
forms  rhombohedral  crystals.  The  place  of  part  of  the  zinc  in  the 
mineral  is  often  taken  by  isomorphous  metals,  such  as  cadmium, 
magnesium,  and  ferrous  iron.  ZnC03  is  precipitated  when  ZnS04  is 
boiled  with  KHC03;  ZnS04  +  2KHC03  =  Zn003  +  K2SO4  +  H2O  +  C02. 
The  normal  alkali  carbonates  precipitate  basic  carbonates  of  variable 
composition  (as  is  the  case  with  magnesium).  The  precipitate  produced 
by  ammonium  carbonate  is  soluble  in  excess. 

Zinc  chloride,  ZnCl2  ( =  136.5  =  2  volumes),  is  prepared  by  dissolving 
Zn  or  ZnO  in  HOI,  and  evaporating*.  If  the  solution  contains  a  little 

*  If  iron  be  present,  it  may  be  separated  by  adding-  a  little  chlorine  water  to  peroxidise 
it,  and  precipitating  it  aa  hydrated  Fe2O3  by  adding-  zinc  carbonate. 


ZINC   SULPHATE.  381 

HC1  in  excess,  it  deposits  octahedral  crystals  of  ZnCl2.H2O.  The  solu- 
tion, like  that  of  MgCl,,  undergoes  partial  decomposition  when  evapor- 
ated leaving  an  oxychloride  ;  when  this  residue  is  distilled,  ZnCl2  passes 
over.  It  may  also  be  obtained  by  distilling  a  mixture  of  zinc  sulphate 
and  sodium  chloride.  Zinc  chloride  is  a  deliquescent  solid,  very  soluble 
in  water,  alcohol,  and  ether;  it  melts  at  250°  C.  and  boils  at  730°  C. 
Its  attraction  for  water  renders  it  a  powerful  caustic,  and  it  is  used  as 
such  in  surgery.  A  strong  solution  of  ZnCl2  dissolves  much  ZnO,  and 
if  the  solution  of  oxychloride  thus  formed  be  mixed  with  water,  precipi- 
tates are  obtained  which  contain  Zn(OH)Cl  and  Zn(OH)2.  Solution  of 
ZnCl2  dissolves  paper  and  cotton,  and  the  oxychloride  dissolves  wool  and 
silk.  This  is  sometimes  useful  in  examining  textile  fabrics. 

When  zinc  oxide  is  moistened  with  a  strong  solution  of  zinc  chloride, 
an  oxychloride  is  formed,  which  soon  sets  into  a  hard  mass,  forming  a 
very  useful  stopping  for  teeth. 

Burnett's  disinfecting  fluid  is  a  solution  of  zinc  chloride,  and  is  capable  of 
absorbing  H2S,  NH3,  and  other  offensive  products  of  putrefaction,  as  well  as  of 
arresting  the  decomposition  of  wood  and  animal  substances.  Zinc  chloride  is  also 
used  in  soldering,  to  cleanse  the  metallic  surface,  and  the  careless  use  of  this 
poisonous  salt  in  soldering  tins  of  preserved  food  has  frequently  caused  accidents. 

Zinc  chloride  is  sometimes  made  from  pyrites  containing  blende.  This  is  burnt 
as  usual  to  furnish  S02  for  the  manufacture  of  sulphuric  acid,  when  the  ZnS  is  con- 
verted into  ZnS04  which  is  extracted  from  the  spent  pyrites  by  water,  and  decom- 
posed with  sodium  chloride,  when  Na2SO4  is  deposited  in  crystals,  leaving  ZnCl2  in 
solution. 

Zinc  sulphate,  or  white  vitriol,  ZnS04.H2O.6Aq,  bears  a  dangerous 
resemblance  to  Epsom  salts,  but  it  loses  its  water  of  crystallisation  at 
100°  C.,  and  is  decomposed  at  a  very  high  temperature  into  ZnO, 
sulphur  dioxide,  and  oxygen,  whereas  MgS04  bears  fusion  without 
being  decomposed.  Hence  ZnSO4,  when  heated  to  redness,  leaves  a 
residue  which  is  yellow  when  hot  and  white  wThen  cold. 

At  temperatures  above  40°  C.  zinc  sulphate  crystallises  as  ZnS04 
H20.5Aq.  which  is  isomorphous  with  the  corresponding  salt  of  mag- 
nesium. Like  the  magnesium  sulphate,  it  forms  double  sulphates,  in 
which  the  H2O  is  exchanged  for  alkali  sulphates.  ZnSO4.K2S04.6Aq 
and  ZnS04.(NH4)2S04.6Aq  are  isomorphous  with  the  Mg  double  salts. 
Like  all  other  truly  isomorphous  salts,  the  sulphates  of  magnesium  and 
zinc  crystallise  together  from  their  mixed  solutions. 

It  is  made  on  the  large  scale  by  roasting  blende  (zinc  sulphide,  ZnS) 
at  a  low  red  heat,  when  it  combines  with  O  from  the  air  to  form 
ZnS04,  which  is  dissolved  out  by  water  and  crystallised.  It  has  a 
metallic,  nauseous  taste,  and  is  used  medicinally  and  in  dyeing. 

Zinc  sulphide,  ZnS,  as  found  native,  is  usually  crystallised  in  octa- 
hedra  or  dodecahedra,  coloured  black  by  ferrous  sulphide  (black  Jack"). 
Pale  yellow  specimens  are  sometimes  found.  When  precipitated  by  a 
soluble  sulphide  from  a  solution  of  a  zinc  salt  it  is  perfectly  white,  but 
it  darkens  somewhat  when  exposed  to  air  and  light. 

An  intimate  mixture  of  zinc-dust  with  half  its  weight  of  flowers 
of  sulphur  burns  like  gunpowder  when  kindled  with  a  match, 
leaving  a  bulky  mass  of  ZnS,  which  is  primrose-yellow  while  hot,  and 
white  on  cooling.  Zinc  sulphide  is  insoluble  in  water,  in  alkalies, 
and  in  acetic  acid,  but  dissolves  in  HC1  and  in  HN03.  It  may  be 
sublimed  in  colourless  crystals  by  strongly  heating  in  a  current  of  H2S. 


382  PROPERTIES   OF   CADMIUM. 

Zinc  silicate  is  found  as  electric  calamine,  Zn2Si04.Aq,  in  rhombic 
crystals.  Zinc  phosphate  forms  the  mineral  hopeite,  Zn3(P04)2.4Aq. 

Zinc  differs  from  all  the  other  common  metals  in  being  precipitated 
as  a  white  sulphide. 

CADMIUM. 

Cd"=m.6  parts  by  weight  =  2  vols. 

203.  This  metal  is  found  in  small  quantities  in  the  ores  of  zinc,  its 
presence  being  indicated  during  the  extraction  of  that  metal  (p.  378)  by 
the  appearance  of  a  brown  flame  (brown  blaze)  at  the  commencement  of 
the  distillation,  before  the  characteristic  zinc  flame  is  seen  at  the  orifice 
of  the  receiver.  Cadmium  is  more  easily  vaporised  than  zinc,  boiling 
at  778°  C.,  so  that  the  bulk  of  it  is  found  in  the  first  portions  of  the 
distilled  metal,  If  the  mixture  of  cadmium  and  zinc  be  dissolved  in 
diluted  sulphuric  acid,  and  the  solution  treated  with  hydrosulphuric 
acid  gas,  a  bright  yellow  precipitate  of  cadmium  sulphide  (CdS)  is 
obtained,  which  is  employed  in  painting  under  the  name  of  cadmia  or 
cadmium  yellow*  By  dissolving  this  in  strong  hydrochloric  acid  and 
adding  ammonium  carbonate,  cadmium  carbonate  (CdC03)  is  precipi- 
tated from  which  metallic  cadmium  may  be  extracted  by  distillation 
with  charcoal. 

Although  resembling  zinc  in  its  volatility  and  its  chemical  relations, 
in  appearance  it  is  much  more  similar  to  tin,  and  emits  a  crackling 
sound  like  that  metal  when  bent.  Like  tin,  also,  it  is  malleable  and 
ductile  at  the  ordinary  temperature,  and  becomes  brittle  at  about 
82°  C.  Cadmium  is  slightly  heavier  than  zinc,  sp.  gr.  8.6,  and  has  a 
lower  melting-point,  320°  C.,  so  that  it  is  useful  for  making  fusible 
alloys.  An  alloy  of  3  parts  of  cadmium  with  16  of  bismuth,  8  of  lead, 
and  4  of  tin,  fuses  at  60°  C.  In  its  behaviour  with  acids  and  alkalies 
cadmium  is  similar  to  zinc,  but  the  metal  is  easily  distinguished  from 
all  others  by  its  yielding  a  characteristic  chestnut-brown  oxide  when 
heated  in  air.  This  oxide  (CdO)  is  the  only  oxide  of  cadmium. 

An  amalgam  of  cadmium  and  mercury  is  used  by  dentists  for  stopping 
teeth,  for  while  it  is  plastic  when  freshly  made  it  rapidly  hardens.  It 
is  also  electro-deposited  as  an  alloy  with  silver  instead  of  ordinary 
electro-plating. 

Cadmium  chloride,  CdCl2.2Aq,  effloresces  in  air,  whilst  zinc  chloride  deliquesces. 
Moreover,  it  may  be  dried  without  undergoing  partial  decomposition.  It  is  fusible 
and  volatile  like  zinc  chloride.  Cadmium  bromide,  CdBr2.4Aq,  and  the  iodide,  CdI2, 
are  used  in  photography.  Cadmium  sulphate,  3CdS04.8Aq  is  much  less  soluble 
than  zinc  sulphate. 

Cadmium  differs  from  all  the  other  metals  in  forming  a  yellow  sulphide 
insoluble  in  alkalies,  so  that  its  salts,  mixed  with  excess  of  ammonia, 
and  treated  with  H2S,  give  a  yellow  precipitate. 

BERYLLIUM,  OR  GLUCINUM. 
Be"  or  Gr  =  9  parts  by  weight. 

204.  This  comparatively  rare  metal  (which  derives  its  name  from  the  sweet 
taste  of  its  salts,  yXvicts,  sweet)  is  found  associated  with  silica  and  alumina  in 
the  emerald,  which  is  a  double  silicate  of  A1203  and  BeO  (Al203.3Be0.6Si02),  and 

*  The  darker  varieties  of  this  pigment  contain  thallium. 


OCCURRENCE   OF  ALUMINIUM.  383 

appears  to  owe  its  colour  to  the  presence  of  a  minute  quantity  of  chromium  oxide. 
The  more  common  mineral  beryl  or  aquamarine,  has  a  similar  composition,  but  is 
of  a  paler  green  colour,  apparently  caused  by  iron.  Chrysoben/l  consists  of 
Al203.BeO,  also  coloured  by  iron.  The  earlier  analysts  of  these  minerals  mistook 
the  beryllium  oxide  for  alumina,  which  it  resembles  in  forming  a  gelatinous  pre- 
cipitate on  adding  ammonia  to  its  solutions,  but  it  is  a  stronger  base  than  alumina, 
and  is  therefore  capable  of  displacing  ammonia  from  its  salts,  and  of  being  dissolved 
by  them.  Ammonium  carbonate  is  employed  to  separate  the  beryllium  oxide  from 
alumina,  since  it  dissolves  the  former  in  the  cold,  forming  a  double  carbonate  of 
beryllium  and  ammonium,  from  which  the  beryllium  carbonate  is  precipitated  on 
boiling.  Beryllium  oxide,  BeO,  is  intermediate  in  properties  between  alumina  and 
magnesia,  resembling  the  latter  in  its  tendency  to  absorb  carbonic  acid  from  the  air, 
and  to  form  soluble  double  salts  with  the  salts  of  ammonium,  and  so  much  re- 
sembling alumina  in  the  gelatinous  form  of  its  hydrate,  its  solubility  in  alkalies,  and 
the  sweet  astringent  taste  of  its  salts,  that  it  was  formerly  regarded  as  a  sesquioxide 
like  alumina.  By  the  radiant  matter  test  (p.  330),  beryllium  oxide  phosphoresces  of 
a  bright  blue  colour. 

The  metal  itself  is  very  similar  to  aluminium  ;  it  is  prepared  by  passing  the 
vapour  of  its  chloride,  BeCl2,  over  melted  sodium.  Its  sp.  gr.  is  1.6.  and  it  melts  at 
about  1000°  C.  It  is  not  seriously  oxidised  by  air  and  decomposes  hot  water  very 
slowly. 

General  review  of  the  magnesium  group  of  metals. — This  group 
includes  Be,  Mg,  Zn,  Cd  and  Hg.  As  in  the  case  of  the  preceding  groups 
of  metals,  the  melting-point  falls  with  the  rise  of  atomic  weight  (Hg  =  200 
melts  at -36°  C.),  whilst  the  specific  gravity  and  atomic  volume 
(p.  304)  rise  with  the  atomic  weight  (sp.  gr.  Hg=  13.5).*  Their  order 
of  chemical  energy,  on  the  other  hand,  is  the  reverse  of  that  of  the 
metals  of  the  preceding  groups,  falling  with  rise  of  atomic  weight. 
Their  oxides  are  practically  insoluble  in  water,  and  are  less  basic  as  the 
molecular  weight  increases.  The  carbonates  are  easily  decomposed  by 
heat ;  the  sulphates  are  more  easily  decomposed  than  those  of  the 
metals  of  the  preceding  groups  and  appear  to  decrease  in  stability  with 
rise  of  molecular  weight.  The  vapours  of  these  metals  contain  mon- 
atomic  molecules  (p.  300). 

Mercury  will  be  considered  later. 

ALUMINIUM. 

Al'"  =  27  parts  by  weight. 

205.  Aluminium  is  distinguished  among  metals,  as  silicon  is  among 
non-metallic  bodies,  for  its  immense  abundance  in  the  solid  mineral 
portion  of  the  earth,  to  which,  indeed,  it  is  almost  entirely  confined,  for 
it  is  present  in  vegetables  and  animals  in  so  small  a  quantity  that  it  can 
scarcely  be  regarded  as  forming  one  of  their  necessary  components. 
Church  has,  however,  found  it  in  certain  cryptogamous  plants,  especially 
in  the  Lycopodiums ;  the  ash  of  Lycopodium  alpinum  yielding  one-third 
of  its  weight  of  alumina. 

One  of  the  oldest  rocks,  which  appears  to  have  originally  formed  the 
basis  of  the  solid  structure  of  the  globe,  is  that  known  as  granite.  This 
mineral,  which  derives  its  name  from  its  conspicuous  granular  structure, 
is  a  mixture,  in  variable  proportions,  of  quartz,  felspar,  and  mica,  tinged 
of  various  colours  by  the  presence  of  small  quantities  of  the  oxides  of 
iron  and  manganese. 

Quartz,   which  forms  the  translucent  or  transparent  grains  in  the 

*  The  atomic  volume  of  Mg  is  greater  than  that  of  Zn. 


384  CLAY. 

granite,  consists  simply  of  silica;  felspar,  the  dull,  cream-coloured,, 
opaque  part,  is  a  combination  of  silica  with  oxides  of  aluminium  and 
potassium,  of  the  composition  K2O.3SiO2.Al203.Si02. 

Mica,  so  named  from  the  glittering   scales  which   it  forms  in  the 

franite,  is  also  a  double  silicate  of  alumina  and  potash,  K90.3Al203<4Si02, 
ut  the  A1203  is  very  frequently  displaced  by  Fe203  and  the  K  0  by 
MgO. 

By  the  long-continued  action  of  air  and  water,  the  granite  is  gradually 
crumbled  down  or  disintegrated,  an  effect  which  must  be  ascribed  to  a 
concurrence  of  mechanical  and  chemical  causes.  Mechanically,  the  rock 
is  continually  worn  down  by  variations  of  temperature,  and  by  the 
congelation  of  water  within  its  minute  pores,  the  rock  being  gradually 
split  by  the  expansion  attendant  upon  such  congelation.  Chemically, 
the  action  of  water  containing  carbonic  acid  would  tend  to  remove 
the  potash  from  the  felspar  and  mica  in  the  form  of  carbonate  of 
potash,  whilst  the  silicate  of  alumina  and  the  quartz  would  subsequently 
be  separated  by  the  action  of  water  ;  the  former  being  so  much  lighter, 
would  be  soon  washed  away  from  the  heavy  quartz,  and,  when  again 
deposited,  would  constitute  clay,  the  purest  form  of  which  is  kaolin 
(Al203.2Si02.2H20). 

Although  clay,  therefore,  always  consists  mainly  of  silicate  of  alumina, 
it  generally  contains  some  uncombined  silicic  acid,  together  with 
variable  proportions  of  lime,  of  oxide  of  iron,  &c.,  which  give  rise  to  the 
numerous  varieties  of  clay.  Thus  a  pure  Chinese  kaolin  will  contain, 
per  cent. — 

Si02        A1203        H20         Fe203        MgO         Alkalies 
5°-5         33-7         *  i  "2  1.8  0.8  1.9 

whilst  Stourbridge  fireclay  will  contain  about  85  per  cent,  of  this  clay- 
substance  and  some  15  per  cent,  of  silica  as  quartz. 

The  silicate  of  alumina  also  constitutes  the  chief  portion  of  several 
other  very  important  mineral  substances,  among  which  may  be  mentioned 
slate,  fuller  s  earth,  and  pumice-stone.  Marl  is  clay  containing  a  con- 
siderable quantity  of  carbonate  of  lime.  Loam  is  also  an  impure  variety 
of  clay.  The  different  varieties  of  ochre,  as  well  as  umber  and  sienna, 
are  simply  clays  coloured  by  the  oxides  of  iron  and  manganese. 

Notwithstanding  the  abundance  of  aluminium  in  the  form  of  clay,  it 
is  only  comparatively  recently  that  the  metal  has  been  extracted  in 
quantity  sufficient  to  make  it  of  practical  importance.  Originally  the 
metal  was  prepared  by  fusing  the  chloride,  preferably  in  the  form  of 
the  double  chloride,  Al2Cl6.2NaCl,  with  sodium,  which  abstracted  the 
chlorine.  Now,  however,  aluminium  is  prepared  by  the  electrolysis  of 
a  bath  of  fused  cryolite  (the  double  fluoride  of  aluminium  and  sodium, 
Na3AlF6),  containing  aluminium  oxide  (alumina,  A18O3),  dissolved  in  it ; 
the  metal  is  deposited  around  the  cathode,  oxygen,  and  probably  also 
fluorine,  being  evolved  at  the  anode. 

An  iron  box  with  double  walls  between  which  water  is  circulated  has  a  steel  plug 
protruding  through  its  bottom  ;  this  plug  serves  as  the  cathode,  the  anode  being  a 
bundle  of  carbon  rods  suspended  a  short  distance  above  the  plug.  At  first  an  arc  is 
struck  between  these  electrodes  and  cryolite  is  fed  into  the  vessel.  As  the  cryolite 
melts  the  anode  is  drawn  up  and  electrolysis  begins,  the  bath  being  kept  melted,  by 
the  heat  generated  by  its  electrical  resistance,  except  the  layer  next  the  cooled  walls 
of  the  vessel  which  are  thus  protected  from  the  heat.  Alumina  is  now  fed  into  the 


PROPERTIES   OF  ALUMINIUM.  385. 

vessel  in  proportion   as  the  aluminium    separates  around   the   cathode   and    is 
tapped  off. 

The  alumina  for  this  process  is  obtained  from  bauxite,  a  mineral  found  at  Baux, 
near  Aries  in  the  South  of  France,  and  in  Antrim,  Ireland.  It  contains  alumina 
56  per  cent,  ferric  oxide  3,  silica  12,  titanic  acid  3,  and  water  26.  To  obtain  alumina, 
from  it,  it  is  roasted  to  oxidise  any  organic  matter  and  ferrous  oxide,  and  heated 
under  pressure  with  caustic  soda  solution  whereby  the  alumina  is  dissolved  a» 
sodium  aluminate,  3Na20.Al2O3.  After  nitration  a  small  proportion  of  alumina  is 
added  to  the  liquid  and  the  whole  is  agitated.  In  the  course  of  some  hours  the 
greater  part  of  the  alumina  is  deposited  from  the  solution,  recalling  the  separation 
of  a  salt  from  a  supersaturated  solution  by  addition  of  a  nucleus.  The  liquor  from 
which  the  alumina  has  been  separated  is  used  for  extracting  another  portion  of  the 
ignited  bauxite.  The  deposited  alumina  is  filtered,  washed,  and  heated  to  expel 
water. 

Aluminium  is  less  fusible  than  tin  and  zinc,  but  more  so  than  silver,, 
its  fusing-point  being  655°  0.*  It  requires  a  very  high  temperature  to- 
vaporise  it.  Like  zinc,  it  is  most  easily  rolled  and  bent  between  100° 
and  150°  C.  It  is  much  more  sonorous  than  most  other  metals.  A  bar 
of  it  suspended  from  a  string,  and  struck  with  a  hammer,  emits  a  clear 
musical  sound.  It  is  remarkable  as  being  the  lightest  metal  (sp.  gr.  2.7) 
capable  of  resisting  the  action  of  air  even  in  the  presence  of  moisture. 
This  lightness  renders  it  valuable  for  the  manufacture  of  small  weights, 
such  as  the  grain  and  its  fractions,  since  these,  when  made  of  aluminium, 
are  more  than  three  times  as  large  as  when  made  of  brass,  and  nearly 
nine  times  as  large  as  platinum  weights  of  the  same  denomination  ;  and 
for  canteen  vessels,  for  which  purpose  it  is  applicable  since  it  is  suffi- 
ciently resistant  to  the  attack  of  vegetable  and  animal  juices. t  It  is 
also  employed  for  ornamental  purposes,  for,  though  not  so  brilliant  as 
silver,  it  is  not  blackened  by  sulphuretted  hydrogen,  which  so  easily 
affects  that  metal  (see  p.  215).  Aluminium  leaf  has  largely  displaced 
silver  leaf  as  a  decorative  material,  and  is  capable  of  being  printed  on 
fabrics.  Iron  and  silicon  are  the  chief  impurities  in  commercial 
aluminium. 

Another  characteristic  feature  of  aluminium  is  its  comparative  resist- 
ance to  the  action  of  nitric  acid  even  at  a  boiling  heat.  No  other  metal 
commonly  met  with,  except  platinum  and  gold,  is  capable  of  resisting 
the  action  of  nitric  acid  to  the  same  extent.  Hydrochloric  acid,  how- 
ever, which  will  not  attack  gold  and  platinum,  dissolves  aluminium 
with  facility,  converting  it  into  aluminium  chloride,  with  disengage- 
ment of  hydrogen  ;  A12  +  6HC1  =  A12C16  +  H6.  Solutions  of  potash  and 
soda  also  easily  dissolve  it,  forming  the  so-called  aluminates  of 
those  alkalies ;  thus,  6NaOH  +  AJ3  =  Al2(ONa)6  +  H6.  Even  when  very 
strongly  heated  in  air,  aluminium  is  oxidised  to  a  very  slight  extent, 
probably  because  the  coating  of  alumina  which  is  formed  remains 
infusible  and  protects  the  metal  beneath  it.  For  a  similar  reason, 
apparently,  aluminium  decomposes  steam  but  slowly,  even  at  a  high 
temperature. 

When  aluminium  is  rubbed  with  a  solution  of  mercuric  chloride  it 
becomes  amalgamated  with  mercury  on  the  surface  and  is  then  remark- 
ably active,  decomposing  water  at  the  ordinary  temperature  with 
violence,  and  serving  as  a  useful  neutral  reducing-agent. 

»  It  is  not  easily  fused  before  the  blowpipe,  as  its  surface  becomes  covered  with  infusible- 
oxide. 

f  The  metal  is  not  easily  soldered  and  many  alloys  have  been  suggested  for  the  purpose;, 
of  late  one  containing  i  of  Al,  o.i  of  P,  8  of  Zn  and  30  of  Sn  has  been  used. 

2  B 


386  ALLOYS   OF  ALUMINIUM. 

Although  massive  aluminium  does  not  oxidise  more  than  superficially 
when  heated,  the  powdered  metal  burns  with  ease  like  powdered 
magnesium.  The  heat  of  combustion  is  A12,O3  =  360,000  cals.,  and  the 
temperature  produced  is  very  high.  Indeed,  it'  the  oxygen  be  supplied 
by  an  admixture  of  a  metallic  oxide  the  temperature  becomes  compar- 
able with  that  of  the  electric  arc,  and  even  highly  refractory  metals  are 
both  reduced  and  melted  when  their  oxides  are  mixed  with  powdered 
aluminium  and  the  mixture  is  ignited.* 

Metallic  chromium  has  been  produced  in  this  manner.  A  mixture  of  ferric  oxide 
and  aluminium  powder  has  been  used  under  the  name  "  thermite,"  for  the  produc- 
tion of  local  high  temperatures  ;  the  mixture  is  ignited  in  a  crucible  by  a  fuse  com- 
posed of  a  mixture  of  barium  peroxide  and  aluminium  powder  and  when  the 
combustion  is  over  the  white  hot  molten  iron  with  its  superincumbent  layer  of 
molten  aluminium  is  poured  on-to  the  surface  to  be  heated,  such  as  two  rails  which 
are  to  be  butt- jointed  by  fusing  the  ends  together.  When  the  mixture  is  ignited 
on  an  iron  plate  it  fuses  its  way  through  the  metal. 

When  aluminium  is  fused  with  nine  times  its  weight  of  copper,  it 
forms  an  alloy  [aluminium  bronze)  very  similar  to  gold  in  appearance, 
but  almost  as  strong  as  iron.  This  alloy  was  strongly  recommended  as 
a  substitute  for  gold  for  ornamental  purposes,  but  it  does  not  retain  its 
brilliancy  so  completely  as  that  metal.  Aluminium  does  not  dissolve 
in  cold  mercury  nor  in  melted  lead,  both  of  which  are  capable  of  dis- 
solving nearly  all  other  metals. 

An  alloy  of  aluminium  with  from  TO  to  25  per  cent,  of  magnesium  is 
sold  as  "  magnalium  "  ;  it  is  of  lower  specific  gravity  than  aluminium  and 
is  more  easily  worked. 

Aluminium  is  also  used  for  reducing  any  oxide  which  may  be  present 
in  molten  steel  when  it  is  being  cast,  a  small  amount  being  added  to  the 
steel  just  before  it  is  poured. 

206.  Alum,  which  is  the  chief  compound  of  aluminium  employed  in 
the  arts,  is  always  obtained  either  from  clay  or  slate,  but  there  are 
several  processes  by  which  it  may  be  manufactured. 

The  simplest  process  is  that  in  which  pipe-clay,  or  some  other  clay 
containing  very  little  iron,  is  calcined,  ground  to  powder,  and  heated  on 
the  hearth  of  a  reverberatory  furnace  with  half  its  weight  of  sulphuric 
acid,  until  it  becomes  a  stiff  paste,  which  is  then  exposed  to  air  for 
several  weeks.  During  this  time  the  alumina  of  the  clay  is  attacked  by 
the  sulphuric  acid  to  form  aluminium  sulphate,  which  may  be  obtained 
by  washing  the  mass  with  water,  when  the  sulphate  dissolves,  and  the 
undissolved  silica  (still  retaining  a  portion  of  the  alumina)  is  left. 
When  the  solution  containing  the  aluminium  sulphate  is  evaporated 
to  a  syrupy  consistence  and  allowed  to  cool,  it  solidifies  into  a  white 
crystalline  mass,  which  is  used  by  dyers  under  the  erroneous  name  of 
concentrated  alum  or  cake-alum,  and  contains  about  47.5  per  cent,  of 
the  dry  salt.  The  aluminium  sulphate  can  be  obtained  in  crystals 
containing  Al2(S04)3.i8Aq,f  but  there  is  considerable  difficulty  in 
obtaining  these  crystals  on  account  of  the  extreme  solubility  of  the  salt. 
It  is  on  account  of  this  circumstance  that  the  aluminium  sulphate  is 
usually  converted  into  alum,  which  admits  of  very  easy  crystallisation 

*  A  mixture  of  aluminium  powder  and  sodium  peroxide  ignites  spontaneously  when 
moistened. 

t  The  mineral  alunogen  found  in  New  South  Wales  has  this  composition  (Liversidge).  It 
forms  fibrous  masses  like  satin-spar,  and  occurs  in  sandstone  rocks. 


MANUFACTUKE   OF  ALUM.  387 

and  purification.  In  order  to  transfer  the  sulphate  into  alum,  its 
solution  is  mixed  with  potassium  sulphate,  when,  by  suitable  evapora- 
tion, beautiful  octahedral  crystals  are  obtained,  having  the  composition 
AlK(S04),.i2Aq.» 

Alum  is  more  commonly  prepared  from  the  mineral  termed  alum  shale,  which 
contains  silicate  of  alumina,  together  with  a  considerable  quantity  of  finely  divided 
iron  pyrites  and  some  bituminous  matter.  This  shale  is  coarsely  broken  up,  and 
built  into  long  pyramidal  heaps,  together  with  alternate  layers  of  coal,  unless  the 
shale  should  happen  to  contain  a  sufficient  amount  of  bitumen.  These  heaps  are 
kindled  in  several  places,  and  are  partly  smothered  with  spent  ore  in  order  to  prevent 
too  great  a  rise  of  temperature.  During  this  slow  roasting  of  the  heap,  the  iron  pyrites 
(FeS2)  loses  half  its  sulphur,  which  is  converted  by  burning  into  sulphurous  acid  gas 
(S02),  and  this,  in  contact  with  the  porous  shale  and  the  atmospheric  oxygen,  be- 
comes converted  into  S03  (p.  222).  This  latter  combines  with  the  alumina  to 
produce  sulphate  of  alumina.  The  roasted  heap  is  then  allowed  to  remain  for  some 
months  exposed  to  the  air,  and  moistened  from  time  to  time,  in  order  to  promote 
the  absorption  of  oxygen  by  the  sulphide  of  iron  (FeS),  and  its  conversion  into  sul- 
phate of  iron  (FeSO4).  This  heap  is  afterwards  lixiviated  with  water,  which 
dissolves  out  the  sulphates  of  aluminium  and  iron,  together  with  some  magnesium 
sulphate,  which  has  also  been  formed  in  the  process.  When  this  crude  alum  liquor 
is  evaporated  to  a  certain  extent,  a  large  quantity  of  ferrous  sulphate  (green  vitriol) 
crystallises  out,  and  the  liquid  from  which  these  crystals  have  separated  is  then 
mixed  with  so  much  solution  of  potassium  chloride  as  a  preliminary  experiment 
has  showTn  to  be  necessary  to  yield  the  largest  amount  of  alum.  The  potassium 
chloride  is  obtained  either  from  Stassfurt,  or  as  soap-boiler's  waste,  or  as  the  refuse 
from  saltpetre  refineries  and  glass-houses.  The  ferrous  sulphate  still  left  in  the 
solution  is  decomposed  by  the  potassium  chloride,  yielding  ferrous  chloride,  and 
potassium  sulphate,  which  combines  with  the  aluminium  sulphate  to  form  alum  ; 
(T)  FeS04  +  2KCl  =  K2S04  +  FeCl2;  (2)  K2S04  +  A]2(S04)3  =  2KA1(S04)2.  The  hot 
liquor  is  stirred  while  cooling,  when  alum  meal  is  deposited  in  small  crystals,  and 
the  FeCl2  remains  in  solution.  The  alum  is  redissolved  in  boiling  water,  and 
•crystallised  in  barrels,  which  are  taken  to  pieces  to  get  out  the  large  crystals.  If 
there  be  much  magnesium  sulphate  in  the  liquor,  it  is  subsequently  obtained  in 
crystals  and  sent  into  the  market. 

Where  ammonium  sulphate  can  be  obtained  at  a  cheap  rate  (as  in  the 
neighbourhood  of  gasworks),  it  is  very  commonly  substituted  for  the 
potassium  sulphate,  when  ammonia-alum  is  obtained  instead  of  potash- 
alum.  The  former  is  similar  in  all  respects  to  the  latter  salt,  except 
that  it  contains  the  hypothetical  metal  ammonium  (NH4)  in  place  of 
potassium,  and  its  formula  is  therefore  AlNH4(S04)2.i2  Aq. 

For  all  the  uses  of  alum,  in  dyeing  and  calico-printing,  in  paper- 
making,  and  in  the  manufacture  of  colours,  ammonia-alum  answers 
quite  as  well  as  potash-alum,  and  hence  both  these  salts  are  sold  under 
the  common  name  of  alum. 

These  alums  are  the  representatives  of  an  important  class  of  double 
sulphates,  containing  a  monatomic  and  a  triatoinic  metal.  They  all  con- 
tain 1 2  molecules  of  water  of  crystallisation,  and  their  crystalline  form 
is  that  of  the  cube  or  octahedron.  Alum  dissolves  in  one-third  of  its 
weight  of  boiling  water,  and  in  seven  parts  of  cold  water ;  it  is  insoluble 
in  alcohol.  When  heated,  it  fuses  and  swells  up  to  a  light  porous  mass 
of  burnt  alum,  having  lost  its  water. 

The  solution  of    alum    is    acid    to  test-papers.      When  solution  of 

*  When  a  supersaturated  solution  (p.  51)  of  these  crystals  is  concentrated  in  a  flask,  stop- 
pered with  cotton-wool,  until  a  film  of  solid  appears  on  the  surface  of  the  liquor,  the  solution 
sets,  on  cooling,  to  a  mass  of  prismatic  crystals.  By  carefully  removing-  the  cotton-wool  and 
introducing-  a  crystal  of  the  ordinary,  octahedral  alum,  the  whole  of  the  already  solidified 
substance  may  be  made  to  break  up,  the  prismatic  crystals  being-  transformed  into  the  octa- 
hedral variety,  with  much  evolution  of  heat. 


388  ALUMINA. 

sodium  carbonate  is  added  to  it  by  degrees,  a  precipitate  of  aluminium 
hydroxide  is  formed,  which,  at  first,  is  redissolved  on  stirring.  The 
solution,  to  which  sodium  carbonate  has  been  added  as  long  as  the 
precipitate  redissolves,  is  used  under  the  name  of  basic  alum  in  dyeing, 
because  stuffs  immersed  in  it  become  impregnated  with  alumina,  which 
serves  as  a  mordant  to  attract  and  fix  the  colouring-matter  when  the 
stuff  is  transferred  to  a  dye-bath. 

Aluminium  sulphate  is  superseding  alum  in  many  applications ;  being 
prepared  by  treating  clay  or  bauxite  (see  p.  385)  with  sulphuric  acid, 
and  precipitating  the  iron  either  as  ferric  arsenate  or  as  Prussian  blue. 

Alumina. — When  ammonia-alum  is  strongly  heated  it  leaves  a  white 
insoluble  earthy  substance  which  is  alumina  itself  (A12O3),  and  differs- 
widely  from  the  metallic  oxides  which  have  been  hitherto  considered, 
by  the  feebly  basic  character  which  it  exhibits.*  Not  only  is  alumina 
destitute  of  alkaline  properties,  but  it  is  not  even  capable  of  entirely 
neutralising  the  acids,  and  hence  both  aluminium  sulphate  and  alum 
are  exceedingly  acid  salts.  Indeed,  alumina  has  feebly  acid  properties 
towards  the  powerful  bases,  forming  aluminates  such  as  sodium  alu- 
minate,  3Na2O.Al2O3. 

Pure  crystallised  alumina  is  found  in  nature  as  the  mineral  corundum, 
distinguished  by  its  extreme  hardness,  in  which  it  ranks  next  to  the 
diamond.  An  opaque  and  impure  variety  of  corundum  constitutes  the 
very  useful  substance  emery.  The  ruby,  oriental  amethyst,  and  sapphire^ 
consist  of  nearly  pure  alumina ;  spinelle  is  a  compound  of  magnesia 
with  alumina,  MgO.Al203 ;  whilst  in  the  topaz  the  alumina  is  associated 
with  silica  and  aluminium  fluoride.  In  these  forms  the  alumina  is  in- 
soluble in  acids,  but  it  may  be  rendered  soluble  by  fusion  with  acid 
potassium  sulphate,  or  with  alkali  hydroxides.  The  sp.  gr.  of  alumina 
varies  from  3.7  to  4.2. 

The  mineral  diaspore  is  a  hydrate  of  alumina  (A1203.2H2O),  so  named  from  its 
falling  to  powder  when  heated  (5ta<r7ro/?d,  dispersion). 

Artificial  corundum  has  been  made  by  fusing  alumina  either  in  the  electric 
furnace  or  by  the  combustion  of  aluminium  (p.  386)  and  allowing  the  fused  mass  to- 
cool. 

Aluminium  hydroxide,  A12(OH)6,  is  found  crystallised  as  kydrargillite,  or  Gibbsite. 
Artificially  prepared  aluminium  hydroxide  is  characterised  by  its  gelatinous  appear- 
ance. If  a  little  alum  be  dissolved  in  warm  water,  and  some  ammonia  added  to  the 
solution,  the  alumina  will  precipitate  as  a  semi-transparent  gelatinous  mass  of  the 
hydrate  A12(OH)6.2H20.  It  is  nearly  insoluble  in  ammonia,  but  dissolves  in  potash 
and  soda.  Aluminium  hydroxide  may  be  obtained  in  solution  in  water  by  dis- 
solving it  in  solution  of  A12C16,  and  dialysing  (see  p.  278).  It  resembles  solution  of 
silicic  acid  in  being  very  easily  gelatinised.  When  washed  and  dried,  the  gelatinous 
hydroxide  shrinks  very  much,  and  forms  a  mass  resembling  gum.  The  hydroxide 
has  a  great  attraction  for  most  colouring-matters,  with  which  it  forms  insoluble 
compounds  called  lakes.  Thus,  if  a  solution  of  alum  be  mixed  with  infusion  of 
logwood,  and  a  little  ammonia  added,  the  aluminium  hydroxide  will  form,  with  the 
colouring-matter,  a  purplish-red  lake,  which  may  be  filtered  off,  leaving  the  solution 
colourless.  This  property  is  turned  to  advantage  in  calico-printing,  where  the 
compounds  of  alumina  are  largely  used  as  mordants. 

By  the  radiant  matter  test  (p.  330)  alumina  phosphoresces  crimson. 

*  The  great  absorption  and  disappearance  of  heat  during  the  evaporation  of  the  water  and 
ammonia  from  this  alum,  has  led  to  its  employment  for  filling-  the  space  between  the  double 
walls  of  fire-proof  safes,  which  may  become  red-hot  outside^  whilst  the  inside  is  kept  below 
the  scorching-  point  of  paper. 

f  Small  crystals  of  alumina  resembling  natural  sapphire  have  been  obtained  by  the  action 
of  vapour  of  aluminium  fluoride  upon  boric  anhydride  at  a  high  temperature.  By  adding-  a 
little  chromium  fluoride,  crystals  similar  to  rubies  and  emeralds  have  been  produced. 


SILICATES   OF  ALUMINA.  389 

Aluminium  chloride,  A1C13. — If  the  alumina  obtained  by  calcining 
ammonia-alum  be  intimately  mixed  with  charcoal,  and  strongly  heated 
in  an  earthen  tube  or  retort  through  which  a  stream  of  well-dried 
chlorine  is  passed,  the  oxygen  of  the  alumina  is  abstracted  by  the 
charcoal,  to  form  carbonic  oxide,  whilst  the  chlorine  combines  with  the 
aluminium,  yielding  aluminium  chloride,  which  passes  off  in  vapour, 
and  may  be  condensed,  in  an  appropriate  receiver,  as  a  white  crystalline 
solid;  A1203  +  C3  +  C16=2A1C13  +  3CO. 

A1C13  absorbs  moisture  from  the  air,  and  becomes  partly  decomposed 
into  Al,03  and  HC1.  By  dissolving  alumina  in  HC1  and  evaporating, 
needles  of  A1C13.6H20  are  obtained,  but  they  are  decomposed,  when 
heated,  into  A1203,  6HC1,  and  9H20.  An  impure  solution  of  aluminium 
chloride  is  sold  as  a  disinfectant  under  the  name  of  chloralum. 

Aluminium  fluoride,  A1F3,  occurs  in  kryolite,  3NaF.AlF3. 

207.  Mineral  silicates  of  alumina. — Many  of  the  chemical  formulae 
of  minerals  which  contain  silicates  of  alumina  associated  with  the  silicates 
of  other  metallic  oxides,  are  complicated,  from  the  circumstance  that 
iron  often  takes  the  place  of  a  part  of  the  aluminium,  which  is  possible 
because  Fe2Os  is  isomorphous  with  A1203,  and  therefore  capable  of  taking 
its  place  without  altering  the  crystalline  form  and  general  character 
of  the  mineral.  In  a  similar  manner,  the  other  metals  present  in  the 
mineral  may  be  exchanged  for  isomorphous  representatives  ;  thus,  there 
are  two  well-known  felspars,  potash-felspar  (orthoclase)  and  soda-felspar 
(albite),  having  the  formula?  K2O.Al203.6Si02  and  Na2O.Al2O3.6SiO2. 
These  minerals  are  sometimes  mingled  in  one  and  the  same  crystal 
(potash-albite  or  pericline)  without  bearing  any  definite  equivalent  pro- 
portion to  each  other  ;  the  formula  of  such  a  mineral  would  be  written 
(KNa)2O.Al2O3.6Si09.  Porphyry  has  the  same  chemical  composition  as 
felspar. 

Mica  includes  the  two  minerals  muscorite,  K20.3A]203.4Si02,  and  biotite, 
3MgO.Al203.3Si02. 

Garnet  is  essentially  a  double  silicate  of  alumina  and  lime,  but  often  contains 
magnesium,  iron,  or  manganese,  in  place  of  part  of  the  calcium,  and  iron  in  place  of 
part  of  the  aluminium,  being  written  3[CaMgFeMn]0.[AlFe]203.3Si02.  This 
mineral  is  sometimes  formed  artificially  in  the  slag  of  the  iron  blast-furnaces. 
Chlorite  has  the  composition  ;  [6MgFe]0.[AlFe]203.3Si02.4H20. 

Basalt  is  a  felspathic  rock  containing  crystals  of  augite  ([Fe,Mg]O.Si02)  and 
magnetic  oxide  of  iron.  Cyanite,  Jtyanite,  or  disthene  is  Al203.Si02;  a  crystal  of 
this  is  said  to  point  north  and  south  when  freely  suspended. 

Gneiss  is  chemically  composed  like  granite,  but  the  mica  is  arranged  in  regular 
layers.  Trap  rock  contains  felspar  together  with  hornblende,  (£Fe0.fMgO)Si02. 
Hornblende  is  sometimes  found  in  the  place  of  mica  in  syenitic  granite.  Lava, 
from  volcanoes,  consists  essentially  of  ferrous,  calcium,  and  aluminium  silicates  ; 
the  presence  of  a  considerable  proportion  of  potassium  and  of  phosphoric  acid 
renders  the  soil  formed  by  the  weathering  of  lava  very  fertile. 

Lapis  lazuli,  the  valuable  mineral  which  furnishes  the  natural  ultra- 
marine used  in  painting,  consists  chiefly  of  silica  and  alumina,  which  con- 
stitute respectively  45  and  25  per  cent,  of  it,  but  there  are  also  present 
10  per  cent,  of  soda,  6  per  cent,  of  sulphuric  acid,  about  3  per  cent,  of  sul- 
phur, and  a  somewhat  smaller  quantity  of  iron,  together  with  a  variable 
proportion  of  lime.  The  cause  of  its  blue  colour  is  not  understood,  since 
neither  of  its  predominant  constituents  is  concerned  in  the  production  of 
such  a  colour  in  other  cases.  In  consequence  of  the  rarity  of  the  mineral, 
the  natural  ultramarine  has  a  very  high  price,  but  the  artificial  ultra- 


39°  ULTRAMARINE. 

marine  is  manufactured  in  very  large  quantities  at  a  low  cost,  and  forms 
a  very  good  imitation. 

One  of  the  processes  for  preparing  it  consists  in  heating  to  bright  redness  in  a 
covered  crucible,  for  three  or  four  hours,  an  intimate  mixture  of  100  parts  of  pure 
white  clay  (kaolin),  100  of  dried  carbonate  of  soda,  60  of  sulphur,  and  12  of  charcoal. 
This  would  be  expected  to  yield  a  mixture  of  silicate  of  soda,  aluminate  of  soda,  and 
sulphide  of  sodium,  the  two  first  being  white,  and  the  last  yellow  or  brown,  but  the 
mass  is  found  to  have  a  green  colour  (green  ultramarine).  It  is  finely  powdered, 
washed  with  water,  dried,  mixed  with  a  fifth  of  its  weight  of  sulphur,  and  gently 
roasted  in  a  thin  layer  till  the  sulphur  has  burnt  off,  this  operation  being  repeated, 
with  fresh  additions  of  sulphur,  until  the  residue  has  a  fine  blue  colour.  In  the 
opinion  of  some  chemists,  the  presence  of  a  small  proportion  of  iron  is  essential  to 
the  blue  colour,  whilst  others  believe  the  colour  to  be  due  to  sodium  sulphide  or 
thio-sulphate,  or  both.  * 

Ultramarine  is  a  very  permanent  colour  under  ordinary  conditions 
of  exposure  to  the  air  and  light,  but  acids  bleach  it  at  once,  with 
separation  of  gelatinous  silica  and  evolution  of  sulphuretted  hydrogen. 
Blue  writing  paper  is  often  coloured  with  ultramarine,  so  that  its 
colour  is  discharged  by  acids  falling  upon  it  in  the  laboratory.  Chlorine 
also  bleaches  ultramarine.  Starch  is  often  coloured  blue  with  this 
substance. 

Phosphate  of  alumina,  or  aluminium,  phosphate,  AlPOj,  is  found  naturally  in 
several  forms.  It  occurs  in  large  quantities  in  the  West  India  Islands.  Turquoise 
is  a  hydrated  aluminium  phosphate,  owing  its  colour  to  the  presence  of  oxide  of 
copper.f  Wavellite  has  the  composition  3A1203.2P205.I2H20.  None  of  the  earlier 
analysts  detected  the  phosphoric  acid  in  this  mineral,  on  account  of  the  difficulty  in 
separating  it  from  the  alumina,  so  that  even  in  comparatively  modern  chemical 
works  it  is  described  as  a  hydrate  of  alumina. 

A  gelatinous  precipitate  of  A1P04  is  formed  when  Na2HP04  is  added  to  solution 
of  alum.  It  is  soluble  in  HC1  and  in  potash,  but  insoluble  in  acetic  acid,  which 
distinguishes  it  from  aluminium  hydroxide. 

208.  Pottery,  Porcelain  and  Bricks. — The  manufacture  of  these 
articles  is  frequently  termed  the  clay  industries,  since  clay  of  one  kind 
or  another  is  the  basis  of  the  industry  in  each  case ;  the  subject  is 
therefore  conveniently  considered  as  an  appendix  to  the  chemistry  of 
aluminium  compounds. 

The  manufacture  of  pottery  obviously  belongs  to  an  earlier  period  of 
civilisation  than  that  of  glass,  since  the  raw  material,  clay,  would  at 
once  suggest,  by  its  plastic  properties,  the  possibility  of  working  it  into 
useful  vessels,  and  the  application  of  heat  would  naturally  be  had  re- 
course to  in  order  to  dry  and  harden  it.  Indeed,  at  the  first  glance,  it 
would  appear  that  this  manufacture,  unlike  that  of  glass,  did  not  involve 
the  application  of  chemical  principles,  but  consisted  simply  in  fashioning 
the  clay  by  mere  mechanical  dexterity  into  the  required  form.  It  is 
found,  however,  at  the  outset  that  the  name  of  clay  is  applied  to  a  large 
class  of  minerals,  differing  very  considerably  in  composition,  and  pos- 
sessing in  common  the  two  characteristic  features  of  plasticity  and  a 
predominance  of  aluminium  silicate. 

It  has  already  been  stated  (page  384)  that  kaolin  is  a  hydrated  alu- 
minium silicate,  and  it  is  from  this  material  that  the  best  variety  of 

*  Heumann  assigns  to  ultramarine  the  formula  2Na2AJ2Si2O8.Na2S2.  Knapp  attributes 
the  blue  colour  to  the  presence  of  a  modification  of  sulphur  which  is  only  blue  when  spread 
over  a  large  surface  ;  in  this  case  acids  would  bleach  the  colour  by  destroying-  the  surface. 
Potassium  ultramarine,  in  which  K  takes  the  place  of  Na,  is  also  blue,  whilst  silver  ultra- 
marine, in  which  Ag  is  substituted  for  the  Na,  is  yellow. 

f  False  or  bone  turquoise  is  fossil  ivory,  owing  its  colour  to  the  presence  of  the  natural 
blue  phosphate  of  iron.  Redonda  phosphate  consists  chiefly  of  A1PO4. 


PORCELAIN.  391 

porcelain  is  made.  This  clay  is  eminently  plastic,  and  can  therefore  be 
readily  moulded,  but  when  baked  it  shrinks  very  much,  so  that  the 
vessels  made  from  it  lose  their  shape  and  often  crack  in  the  kiln.  In 
order  to  prevent  this,  the  clay  is  mixed  with  a  certain  proportion  of 
sand,  chalk,  bone-ash,  or  heavy-spar;  but  another  difficulty  is  thus 
introduced,  for  these  substances  diminish  the  tenacity  of  the  clay,  and 
would  thus  render  the  vessels  brittle.  A  further  addition  must  there- 
fore be  made  of  some  substance  which  fuses  at  the  temperature  employed 
in  baking  the  ware,  and  thus  serves  as  a  cement  to  bind  the  unfused 
particles  of  clay,  &c.,  into  a  compact  mass.  Felspar  (silicate  of  alumi- 
nium and  potassium)  answers  this  purpose ;  or  carbonate  of  potassium 
or  of  sodium  is  sometimes  added,  to  convert  a  portion  of  the  silica  into 
a  fusible  alkaline  silicate.  With  a  mixture  of  clay  with  sand  and  fel- 
spar (or  some  substitutes),  a  vessel  may  be  moulded  which  will  preserve 
its  shape  and  tenacity  when  baked,  and  will  be  impervious  to  water  if  it 
have  been  "  fired  "  at  a  temperature  sufficiently  high  to  fuse  the  felspar 
and  clinker  the  ware  throughout.  This  is  the  case  with  porcelain  and 
stoneware ;  earthenware,  on  the  other  hand,  is  not  clinkered  throughout 
and  must  be  waterproofed  by  the  application  of  some  easily-fusible 
material  which  shall  form  a  glaze  over  the  surface  of  the  ware.  Porce- 
lain is  generally  glazed  in  order  to  present  a  perfectly  smooth  surface, 
unless  biscuit  ware  is  to  be  manufactured.  A  distinction  is  drawn 
between  hard  porcelain,  the  constituents  of  which  are  such  that  the 
ware  is  exceedingly  infusible,  and  soft  porcelain,  which  is  far  more  easily 
fused.  Berlin  hard  porcelain  is  made  from  a  mixture  of  some  55  parts 
of  kaolin,  22.5  of  quartz,  and  22.5  of  felspar. 

These  materials  are  ground  up  with  water  before  being  mixed,  and 
the  coarser  particles  are  allowed  to  subside  ;  the  creamy  fluids  containing 
the  finer  particles  in  suspension  are  then  mixed  in  the  proper  proportions 
and  allowed  to  settle ;  the  paste  deposited  at  the  bottom  is  drained, 
thoroughly  kneaded,  and  stored  away  for  some  months  in  a  damp  place, 
by  which  its  texture  is  considerably  improved,  and  any  organic  matter 
which  it  contains  becomes  oxidised  and  removed,  the  oxidation  being 
effected  partly  by  the  sulphates  present,  which  become  reduced  to 
sulphides.  It  is  then  moulded  into  the  required  forms,  and  dried  by 
simple  exposure  to  the  air.  The  vessels  are  packed  in  cylindrical  cases 
(saggers)  of  very  refractory  clay,  which  are  arranged  in  a  furnace  or  kiln 
of  peculiar  construction,  and  very  gradually  heated  at  about  800°  0. 
When  sufficiently  baked,  the  biscuit  porcelain  has  to  be  glazed,  and  great 
care  is  taken  that  the  glaze  may  possess  the  same  expansibility  by  heat  as 
the  ware  itself,  for  otherwise  it  would  crack  in  all  directions  as  the 
glaze  ware  cooled.  The  glaze  employed  is  a  mixture  of  felspar,  quartz, 
kaolin,  marble,  and  broken  porcelain  very  finely  ground,  and  suspended 
in  water.  When  the  porous  ware  is  dipped  into  this  mixture,  it  absorbs 
the  water,  and  retains  a  thin  coating  of  the  mixture  of  quartz  and  felspar 
upon  its  surface.  It  is  now  again  fired,  this  time  at  1700°  C.,  when 
the  glaze  fuses,  partly  penetrating  the  ware,  partly  remaining  as  a  varnish 
upon  the  surface. 

When  the  ware  is  required  to  have  some  uniform  colour,  a  mineral  pigment 
capable  of  resisting  very  high  temperatures  is  mixed  with  the  glaze  ;  but  coloured 
designs  are  painted  upon  the  ware  after  glazing,  the  ware  being  then  baked  a  third 
time,  in  order  to  fix  the  colours.  These  colours  are  glasses  coloured  with  metallic 


392  BEICKS. 

oxides,  and  ground  up  with  oil  of  turpentine,  so  that  they  may  be  painted  in  the 
ordinary  way  upon  the  surface  of  the  ware  ;  when  the  latter  is  again  heated  in  the 
kiln  the  coloured  glass  fuses,  and  thus  contracts  firm  adhesion  with  the  ware. 

Gold  is  applied  either  in  the  form  of  precipitated  metallic  gold,  or  of  f ulminating 
gold,  being  ground  up  in  either  case  with  oil  of  turpentine  burnt  in,  and  burnished. 

English  soft  porcelain  is  made  from  Cornish  clay  mixed  with  ground 
flints,  burnt  bones,  and  sometimes  a  little  sodium  carbonate,  borax,  and 
binoxide  of  tin,  the  last  improving  the  colour  of  the  ware.  It  is  glazed 
with  a  mixture  of  Cornish  stone  (consisting  of  quartz  and  felspar),  flint, 
chalk,  borax,  and  sometimes  white  lead  to  increase  its  fusibility. 

Stone-ware  is  made  from  less  pure  materials,  and  is  covered  with  a  glaze 
of  sodium  silicate,  in  a  very  simple  manner,  by  a  process  known  as  salt- 
glazing.  The  ware  is  coated  with  a  thin  iilm  of  sand  by  dipping  it  in  a 
mixture  of  fine  sand  and  water,  and  is  then  intensely  heated  in  a  kiln 
into  which  a  quantity  of  damp  salt  is  presently  thrown.  The  water  is 
decomposed,  its  hydrogen  taking  the  chlorine  of  the  salt  to  form  hydro- 
chloric acid,  and  its  oxygen  converting  the  sodium  into  soda,  which  com- 
bines with  the  sand  to  form  sodium  silicate ;  this  fuses  into  a  glass  upon 
the  surface  of  the  ware. 

Pipkins,  and  similar  earthenware  vessels,  are  made  of  common  clay 
mixed  with  a  certain  proportion  of  marl  and  of  sand.  They  are  glazed 
with  a  mixture  of  4  or  5  parts  of  clay  with  6  or  7  parts  of  litharge. 
The  colour  of  this  ware  is  due  to  the  presence  of  ferric  oxide. 

Bricks  and  tiles  are  also  made  from  common  clay  mixed,  if  necessary, 
with  sand  ;  such  common  clay  contains  sufficient  fusible  material  to  sinter 
the  bricks.  These  are  very  often  grey,  or  blue,  or  yellow,  before 
baking,  and  become  red  under  the  action  of  heat,  since  the  iron,  which 
is  originally  present  as  carbonate  (FeC03),  becomes  converted  into  the 
red  peroxide  (Fe203)  by  the  atmospheric  oxygen.* 

For  the  manufacture  of  the  refractory  bricks  for  lining  furnaces,  of 
glass-pots,  crucibles  for  making  cast-steel,  &c.,  a  pure,  and  therefore 
infusible,  clay  is  employed,  to  which  a  certain  quantity  of  broken  pots  of 
the  same  material  is  added,  to  prevent  the  articles  from  shrinking  whilst 
being  dried. 

Dinas  firebricks  are  made  from  a  peculiar  siliceous  material  found  in  the  Vale 
of  Neath,  and  containing  alumina  with  about  98  per  cent,  of  silica.  The  ground 
rock  is  mixed  with  i  per  cent,  of  lime  and  a  little  water  before  moulding.  These 
bricks  are  expanded  by  heat,  whilst  ordinary  firebricks,  contract. 

Blue  bricks  are  glazed  by  sprinkling  with  iron  scurf,  a  mixture  of  particles  of 
stone  and  iron  produced  by  the  wear  of  the  siliceous  grindstones  employed  in 
grinding  gun-barrels,  &c.  When  the  bricks  are  fired,  a  glaze  of  silicate  of  iron  is 
formed  upon  them. 

GALLIUM. 
Ga'"  =  69.5. 

209.  This  metal  is  found  in  very  small  quantities  in  certain  ores  of  zinc,  particu- 
larly in  the  blende  from  Bensberg,  in  the  Pyrenees. 

The  powdered  ore  is  treated  with  aqua  regia,  care  being  taken  that  the  blende  is 
in  excess,  so  that  the  nitric  acid  may  be  destroyed  as  far  as  possible.  Lumps  of 
zinc  are  immersed  in  the  cooled  filtrate  from  the  undissolved  ore,  whereupon  all 
metals  appreciably  electro-negative  to  zinc  are  precipitated  ;  the  filtrate  from  these 
is  mixed  with  more  zinc  and  boiled  for  some  hours  so  that  the  acid  may  be  com- 
pletely neutralised  by  the  zinc  and  basic  salts  of  Al,  Zn  and  Ga  precipitated.  They 

*  The  efflorescence  frequently  noticed  on  bricks  consists  mainly  of  sulphate  and  chloride 
of  sodium,  which  existed  in  the  original  clay  ;  the  former  salt  is  frequently  formed  when 
iron  pyrites  is  a  constituent  of  the  clay. 


INDIUM.  393 

are  dissolved  in  HC1,  ammonium  acetate  is  added  and  the  Ga  and  Zn  are  pre- 
cipitated by  H2S.  The  sulphides  are  dissolved  in  HC1,  H2S  is  boiled  off  and  a 
deficiency  of  Na2C03  added  to  precipitate  Ga  (which  is  less  basic  than  Zn)  as 
•carbonate.  The  carbonate  is  dissolved  in  H2S04  and  excess  of  NH3  is  added  ;  Ga^Og 
is  precipitated,  any  ZnO  present  being  soluble  in  NH3.  The  precipitate  is  dissolved 
in  KHO  and  the  solution  electrolysed  to  deposit  Ga  on  the  cathode. 

Gallium  is  a  hard  white  metal  of  sp.  gr.  6  remarkable  for  its  low  fusing-point 
(30°  C.),  so  that  it  melts  with  the  heat  of  the  hand.  It  will  remain  liquid  when 
cooled  far  below  this  temperature,  but  solidifies  when  touched  with  a  piece  of  the 
solid  metal.  It  is  not  oxidised  by  dry  air  until  heated  nearly  to  redness,  and  the 
oxidation  is  then  only  superficial.  Nitric  acid  scarcely  attacks  it  in  the  cold,  but 
•dissolves  it  on  heating.  Hydrochloric  acid  dissolves  it,  with  evolution  of  hydrogen. 
Potash  has  a  similar  action. 

Gallium  xcxyulojeide,  Ga203,  left  on  igniting  the  nitrate,  is  white.  When  heated 
in  hydrogen,  a  part  sublimes,  and  the  rest  is  converted  into  a  bluish  grey 
substance,  which  appears  to  be  gallium,  oj-lde,  GaO.  Two  chlorides,  GaCl2  and 
GaCl3,  exist  ;  they  are  very  fusible,  and  deliquescent ;  they  boil  at  535°  C.  and 
:220°0.  respectively.  GaCl2  is  oxidised  to  GaCl3  by  potassium  permanganate 
solution. 

Gallium  sulphate,  Ga2(S04)3,  is  very  soluble  in  water ;  the  solution  deposits  a 
basic  salt  when  boiled.  It  combines  with  ammonium  sulphate  to  form  an  alum, 
the  solution  of  which  is  also  precipitated  by  boiling. 

Ammonia  precipitates  solutions  of  gallium,  but  the  precipitate  is  more  easily 
soluble  in  excess  than  in  the  case  of  aluminium.  Ammonium  sulphide  precipi- 
tates Ga^Sg  only  if  zinc  be  present,  when  ZnS  is  precipitated  at  the  same  time. 
Potash  gives  a  precipitate  which  dissolves  easily  in  excess.  Potassium  f errocyanide 
produces  a  white  precipitate,  similar  to  that  yielded  by  zinc. 

The  most  delicate  test  for  gallium  (which  led  to  its  discovery  in  1875)  is  the 
production  of  two  violet  bands  in  the  spectrum,  when  an  induction  spark 
passes  from  the  positive  terminal  of  a  secondary  coil  to  the  surface  of  the 
solution  under  examination,  into  which  the  negative  terminal  of  the  coil  is 
made  to  dip. 

From  the  description  of  its  properties,  it  will  be  seen  that  gallium  bears 
considerable  resemblance  to  aluminium. 

INDIUM. 
IN'"  =  113.  i. 

210.  Indium  was  discovered  (1863)  with  the  help  of  the  spectroscope,  in   a 
specimen  of  blende  from  Freiberg,  and  in  some  calamines.     Its  name  refers  to  an 
indigo-blue  line  in  the  spectrum.     It  is  a  white  malleable  metal,  and  dissolves  in 
hydrochloric  acid.     Its  specific  gravity  is  7.42.     Fusing-point,  176°  C.     Less  easily 
vaporised  than  zinc  or  cadmium.     Indium  dissolves  in  HC1,  forming  InCl3  ;  in 
HN03,  forming  In(NO3)3  ;  and  in  H2S04,  forming  In2(S04)3,  which  crystallises  with 
9H20,  and  forms  an  alum. 

Ammonia  produces,  in  solutions  of  indium,  a  white  precipitate,  In(OH)3 ; 
insoluble  in  excess.  Ammonium  carbonate  gives  a  precipitate  soluble  in  excess 
and  reprecipitated  by  boiling.  When  ignited,  In(OH)3  yields  the  sesquioxide, 
In.20o,  which  is  brown  when  hot  but  yellow  when  cold.  When  this  is  heated  in 
hydrogen,  InO  is  produced.  The  chlorides,  InCl,  InCl2,  and  InCl3  have  been 
prepared  ;  they  have  all  been  volatilised.  In2S3  is  a  yellowish  precipitate  thrown 
down  by  H2S  from  feebly  acid  solutions  of  indium. 

To  extract  indium  from  the  Freiberg  zinc,  the  metal  is  boiled  with  dilute 
sulphuric  acid,  employed  in  such  quantity  as  to  leave  part  of  the  zinc  undissolved, 
together  with  indium  and  lead.  The  residue  is  dissolved  in  nitric  acid,  the  lead 
and  cadmium  precipitated  by  hydrosulphuric  acid,  the  latter  expelled  by  boiling, 
and  the  oxide  of  indium  precipitated  from  the  solution  by  barium  carbonate. 
When  this  precipitate  is  dissolved  in  hydrochloric  acid,  and  excess  of  ammonia 
added,  the  white  indium  hydroxide  is  precipitated,  and  may  be  reduced  by  heating 
in  hydrogen.  At  a  bright  red  heat  it  burns  with  a  violet  blue  flame,  yielding 
In203. 

211.  Review  of  the  aluminium  group  of  metals. — This  group  comprises  Al,  Ga, 
In,  and  Tl  (thallium  =  204).     The  last-named   bears  the  same  relation  to  the  other 
metals  of  the  group  as    mercury  bears  to    the    other    metals   of  the   magnesium 


394  RAKE  EAETHS. 

group  (p.  381).  The  melting-points  of  the  metals  of  the  Al  group  do  not  descend 
with  the  rise  of  atomic  weight  ;  it  is  true  that  Al,  which  has  the  lowest  atomic 
weight,  has  the  highest  melting-point,  but  the  remaining  metals  show  a  rise  of 
melting-point  for  increase  of  atomic  weight  (Tl  melts  at  290°  C.).  The  sp.  gr. 
rises  with  the  atomic  weight  (Tl  has  sp.  gr.  11.9).  As  the  atomic  weight  increases 
there  is  a  tendency  for  the  formation  of  stable  oxides  lower  than  that  typical  of 
the  group  (E203),  and  this  typical  oxide  becomes  less  stable  ;  this  will  be  evident 
when  the  properties  of  thallium  have  been  considered,  a  matter  best  postponed 
until  lead  has  been  treated  of. 

The  metals  in  the  odd  series  of  this  group  (see  table,  p.  302)  are  the  rare 
elements  scandium,  yttrium  lanthanum,  and  ytterbium. 

212.  Scandium  (80  =  43.8)  is  the  metal  existing  in  the  basic  oxide  scandia,  Sc203? 
found  in  the  mineral  gadolinite,  a  mixture    of   silicates    occurring  at  Ytterby,  in 
Sweden.     The  oxide  is  infusible  and   insoluble   in  alkalies.     The    metal   has  not 
been  isolated,  but  the  atomic  weight  is  deduced  from  the  equivalent  of  the  oxide. 
Mendeleeff  prophesied  the  existence  of  a  metal  (ekaboron)   whose    oxide  would 
have  the  properties  since  discovered  for  scandia  (see  p.  304). 

213.  Yttrium  (Yt  =  88.3)  is  the  metal  ofi  the  oxide  yttria,  Yt203,  which  is  extracted 
from  gadolinite  and  a  similar  mineral,  samarsMte.       Its    properties   are  not  yet 
known.     Yttria   is    a   white    oxide   insoluble   in    alkalies   and    soluble   in    alkali 
carbonates.     It  has  been  recently  shown  to  contain  five  or  six  oxides  of  basicity 
differing    very  slightly  from  its  own,  and   separable  by  fractional  precipitation  ; 
these  may  be  identified  by  the  difference  between  their  radiant  spectra  (p.  330), 
though  their  spark-spectra  are  identical  with  that  formerly  ascribed  to  yttrium. 

214.  Lanthanum  (La  =137)  also  occurs  in  gadolinite,  but  is  more  abundant  in 
cerite,  a  mineral  of  the  same  type,  also  containing  the  metal  cerium.     The  mixture 
of  lanthana,  La203,  and  ceria  obtained  from  this  mineral  is  converted  into  nitrates 
which   are  fractionally  crystallised,    when   the  lanthanum  nitrate  separates  first. 
When  this  is  ignited  it  is  converted  into  oxide  which  may  be  dissolved  in  HC1, 
and  the  chloride  thus  prepared  majr  be  fused  with  potassium  to  yield  the  metal 
lanthanum.     It  is  a  white  malleable  metal  (sp.  gr.  6.16),  decomposes  hot  water, 
and  oxidises  rapidly  in  air. 

215.  Ytterbium  (Yb  =  i72). — This  metal  is  only  known  as  its  oxide,  Yb.203,  at 
present ;  this  is  extracted  from  gadolinite. 

216.  Besides  the  above  oxides,  several  others  have  been  described  as  obtainable 
from    the    gadolinite    minerals — e.g.,  terbia,  erbia,    holmia,    thulia,    samaria,   and 
didymia.     These   rare  earths   have   received    much    attention  from    the    spectro- 
scopist,  to   whom  the  evidence  of  their    existence  is  due,  and    who  is    gradually 
arriving  at  the  conclusion  that  they  are  of  more  complex  composition  than  was 
at  first  supposed.     They  have  also  received  much  attention  from  those  interested  in 
incandescence  gas  lighting  (p.  155). 

For  example,  the  metal  didymium,  which  was  originally  regarded  as  a  chemical 
unit  yielding  the  oxides  DiO,  Di203,  and  Di205,  has  been  shown  to  contain  two 
constituents,  praseodymium  and  neodymium.  When  the  red-coloured  didymium 
nitrate  is  fractionally  crystallised,  it  yields  two  salts,  one  of  which,  the  praseo- 
salt,  is  green,  whilst  the  other,  the  neo-salt,  is  red.  Solutions  of  these  give  different 
absorption  spectra  (p.  331),  but  when  they  are  mixed  the  absorption  spectrum 
characteristic  of  didymium  nitrate  is  obtained. 

217.  For  a  detailed  account  of  the  rare  earths  the  reader  must  consult  a  more 
exhaustive  treatise  than  the  present  one.     It  is  possible  that  when  the  elements 
contained  in  them  have  been  isolated,  these  will  be  found  to  occupy  the  ninth 
series  of  the  periodic  table  (p.  302). 

IRON. 

Fe"  =  56  parts  by  weight.  (Fe^1  =112. 

2 1 8.  This  most  useful  of  all  metals  is  one  of  those  most  widely  and 
abundantly  diffused  in  nature.  It  is  to  be  found  in  nearly  all  forms  of 
rock,  clay,  sand  and  earth,  its  presence  in  these  being  commonly  indi- 
cated by  their  colours,  for  iron  is  the  commonest  of  natural  mineral 
colouring  ingredients.  It  is  also  found,  though  in  small  proportion,  in 
plants,  and  in  larger  quantity  in  the  bodies  of  animals,  especially  in  the 


IRON  ORES. 


395 


blood,  which  contains  about  0*5  per  cent,  of  iron  in  very  intimate  asso- 
ciation with  its  colouring-matter. 

But  iron  is  very  rarely  found  in  the  metallic  state  in  nature,  being 
almost  invariably  combined  either  with  oxygen  or  sulphur. 

Metallic  iron  is  met  with,  however,  in  the  meteorites  or  metallic 
masses,  sometimes  of  enormous  size,  and  of  unknown  origin,  which 
occasionally  fall  upon  the  earth.  Of  these,  iron  is  the  chief  component, 
but  there  are  also  generally  present  cobalt,  nickel,  chromium,  man- 
ganese, copper,  tin,  magnesium,  carbon,  phosphorus,  and  sulphur. 

The  chief  forms  of  combination  in  which  iron  is  found  in  sufficient 
abundance  to  render  them  available  as  sources  of  the  metal,  are  shown 
in  the  following  table  : 

Ores  of  Iron. 


Common  Name. 

Chemical  Name. 

Composition. 

Magnetic  iron  ore  . 

Ferroso-ferric  oxide     . 

FeA 

Red  haematite  ) 
Specular  iron    } 

Ferric  oxide         .... 

Fe203 

Brown  hsematite     . 

Ferric  hydrate      .... 

2Fe203.3H20 

Spathic  iron  ore 

Ferrous  carbonate 

FeC03 

Clay  ironstone 

Ferrous  carbonate  with  clay 

Blackband 

Ferrous  carbonate  with  clay  and 

bituminous  matter 

Iron  pyrites     . 

Bisulphide  of  iron 

FeS2 

These  ores  are  frequently  associated  with  extraneous  minerals,  some 
of  the  constituents  of  which  are  productive  of  injury  to  the  quality  of 
the  iron.  It  is  worthy  of  notice  that  scarcely  one  of  the  ores  of  iron  is 
entirely  free  from  sulphur  and  phosphorus,  substances  which  will  be 
seen  to  have  a  very  serious  influence  on  the  quality  of  the  iron  extracted 
from  the  ores,  and  the  presence  of  which  increases  the  difficulty  of 
obtaining  the  metal  in  a  marketable  condition. 

The  following  table  illustrates  the  general  composition  of  the  most 
important  English  ores  of  iron,  with  reference  to  the  proportions  of  iron, 
and  of  those  substances  which  materially  influence  the  character  of  the 
iron  extracted  from  the  ore — viz.,  manganese  (present  as  oxide  or  car- 
bonate), phosphorus  (present  as  phosphates),  and  sulphur  (present  as 
bisulphide  of  iron).  The  maximum  and  minimum  quantities  found  in 
each  ore  are  specified. 

British  Iron  Ores. 


In  ioo  Parts. 

Iron. 

Oxide  of 
Manganese, 
MnO. 

Phosphoric 
Anhydride, 
P205. 

Bisulphide 
of  Iron 
(Pyrites). 

No.  of 
Samples 
Analysed. 

Clay  ironstone  from  coal-measures 
Clay  ironstone  from  the  lias  . 
Brown  haematite    .... 
Red  haematite         .... 
Spathic  ore     
Magnetic  ore  . 

Max. 

43-30 
49.17 
63.04 
69.10 
49.78 
57 

Min. 

20.95 
J7-34 
11.98 
47-47 
13.98 

OI 

Max. 

3-3° 
1.30 
i.  60 

"3 

12.64 

o 

Min. 

0.46 

trace 
trace 
i-93 
J4 

Max. 

1.42 
5-05 
3-i7 
trace 

O.22 
O 

Min. 

0.07 

trace 

IO 

Max. 

I.  21 

1.  60 
0.30 
0.06 
O.  II 
O 

Min. 

07 

77 

12 
23 

I 

I 

From  this  table  it  will  be  gathered  that,  among  the  most  abundant  of 
the  iron  ores  of  this  country,  red  haematite  is  the  richest  and  purest, 


IRON   OEES. 

whilst  the  brown  haematite  often  contains  considerable  proportions  of 
sulphur  and  phosphorus,  and  the  spathic  ore,  though  containing  little 
sulphur  and  phosphorus,  often  contains  much  manganese. 

The  argillaceous  ores,  or  clay  iron-stones  found  in  the  lias,  contain 
more  phosphorus  than  those  from  the  coal-measures ;  and  these  latter, 
a,s  a  general  rule,  contain  more  sulphur  (pyrites)  than  the  former, 
although  the  maximum  in  the  table  does  not  show  this. 

Clay  iron-stone  is  the  ore  from  which  the  largest  quantity  of  iron  is  extracted 
in  England,  since  it  is  found  abundantly  in  the  coal-measures  of  Staffordshire, 
Shropshire  and  South  Wales  ;  and  it  is  a  circumstance  of  great  importance  in  the 
economy  of  English  iron-smelting  that  the  coal  and  limestone  required  in  the 
smelting  process,  and  even  the  fireclay  employed  in  the  construction  of  the 
furnace,  are  found  in  the  immediate  vicinity  of  the  ore. 

Blacltband  is  the  clay -iron-stone  found  in  the  coalfields  of  Scotland,  and  often 
contains  between  20  and  30  per  cent,  of  bituminous  matter,  which  contributes  to 
the  economy  of  fuel  in  smelting  it. 

Red  haematite  (Fe203)  is  the  most  characteristic  of  the  ores  of  iron,  occurring  in 
hard,  shining,  rounded  masses,  with  a  peculiar  fibrous  structure  and  a  dark  red- 
brown  colour,  whence  the  ore  derives  its  name  (afyca,  blood).  It  is  found  in  con- 
siderable quantities  in  Lancashire,  Cornwall,  the  Spanish  Peninsula,  Algiers,  and 
North  America. 

Red  ochre  is  a  soft  variety  of  this  ore,  containing  a  little  clay. 

Brown  hcematite  (2Fe203.3H20)  is  found  at  Alston  Moor  (Cumberland)  and  in 
Durham,  but  it  is  more  abundant  on  the  Continent,  and  is  the  source  of  most  of 
the  Belgian  and  French  irons.  Pea  iron  ore  and  yellow  ochre  are  varieties  of  brown 
haematite.  The  Scotch  ore,  called  kidney-form  clay  iron-stone,  is  really  an  ore  of 
this  class. 

The  red  and  brown  haematites  of  Lancashire,  Cumberland,  and  Spain  are  the 
chief  ores  used  in  the  manufacture  of  the  variety  of  pig-iron  known  as  "  Bessemer 
or  haematite  pig." 

Specular  iron  ore  (Fe203)  (oligist  ore  or  iron-glance),  although  of  the  same 
composition  as  red  haematite,  is  very  different  from  it  in  appearance,  having  a 
steel-grey  colour  and  a  brilliant  metallic  lustre.  The  island  of  Elba  is  the  chief 
locality  where  this  ore  is  found,  but  it  also  occurs  in  Germany,  France,  and 
Russia.  The  excellent  quality  of  the  iron  smelted  from  this  ore  is  due  partly  to 
the  purity  of  the  ore,  and  partly  to  the  circumstance  that  charcoal,  and  not  coal, 
is  employed  in  smelting  it. 

Magnetic  iron  ore  (Fe304),of  which  the  loadstone  is  a  variety,  has  a  more  granular 
structure  and  a  dark  iron-grey  colour.  It  forms  mountainous  masses  in  Sweden, 
and  is  also  found  in  Russia  and  North  America.  It  is  generally  smelted  with 
charcoal  and  yields  Jin  excellent  iron.  Iron  sand,  a  peculiar  heavy  black  sand 
of  metallic  lustre,  consists  in  great  measure  of  the  magnetic  ore,  but  contains  a 
very  large  proportion  of  titanium.  It  is  found  abundantly  in  India,  Nova  Scotia, 
and  New  Zealand  ;  but  its  fine  state  of  division  prevents  it  from  being  largely 
available  as  a  source  of  iron. 

Spathic  iron  ore  (FeC03)  is  found  in  abundance  in  Saxony,  and  often  contains 
a  considerable  quantity  of  manganese  carbonate,  which  influences  the  character 
of  the  metal  extracted  from  it. 

The  oolitic  iron  ore,  occurring  in  the  Northampton  oolite,  contains  both  hydrated 
sesquioxide  and  carbonate  of  iron,  together  with  clay. 

Iron  pyrites  (FeS2)  is  remarkable  for  its  yellow  colour,  its  brilliant  metallic 
lustre  and  crystalline  structure,  being  generally  found  either  in  distinct  cubical 
or  dodecahedral  crystals,  or  in  rounded  nodules  of  radiated  structure.  It  was 
formerly  disregarded  as  a  source  of  iron,  on  account  of  the  difficulty  of  separating 
the  sulphur  ;  but  an  inferior  quality  of  the  metal  has  been  extracted  from  the 
residue  left  after  burning  the  pyrites  in  the  manufacture  of  oil  of  vitriol  (p.  226). 
the  residue  being  first  well  roasted  in  a  lime-kiln  to  remove  as  much  as  possible 
of  the  remaining  sulphur. 

219.  Metallurgy  of  iron. — Iron  owes  the  high  position  which  it  occupies 
among  useful  metals  to  a  combination  of  valuable  qualities  not  met  with 
in  any  other  metal.  Although  possessing  nearly  twice  as  great  tenacity 


THE   BLAST-FURNACE.  397 

or  strength  as  the  strongest  of  the  other  metals  commonly  used  in  the 
metallic  state,  it  is  yet  one  of  the  lightest,  its  specific  gravity  being  only 
7-7,  and  is  therefore  particularly  well  adapted  for  the  construction  of 
bridges  and  large  edifices,  as  well  as  for  ships  and  carriages.  It  is  the 
least  yielding  or  malleable  of  the  metals  in  common  use,  and  can  there- 
fore be  relied  upon  for  affording  a  rigid  support ;  and  yet  its  ductility  is 
such  that  it  admits  of  being  rolled  into  the  thinnest  sheets  and  drawn 
into  the  finest  wire,  the  strength  of  which  is  so  great  that  a  wire  of  y^th 
inch  in  diameter  is  able  to  sustain  705  pounds,  while  a  similar  wire  of 
copper  will  not  support  more  than  385  pounds. 

Being,  with  the  exception  of  platinum,  the  least  fusible  of  useful  metals, 
iron  is  applicable  to  the  construction  of  fire-grates  and  furnaces.  Nor 
are  its  qualifications  all  dependent  upon  its  physical  properties,  for  it  not 
only  enters  into  a  great  number  of  compounds  which  are  of  the  utmost 
use  in  the  arts,  but  its  chemical  relations  to  one  of  the  non-metallic 
elements,  carbon,  are  such,  that  the  addition  of  a  small  quantity  of  this 
element  converts  it  into  steel,  far  surpassing  iron  in  the  valuable  proper- 
ties of  hardness  and  elasticity  ;  whilst  a  larger  quantity  of  carbon  gives 
rise  to  cast-iron,  the  greater  fusibility  of  which  permits  it  to  be  moulded 
into  vessels  and 'shapes  which  could  not  be  produced  by  forging. 

220.  English  process  of  smelting  clay  iron-stone.— -The  first  step  towards 
the  extraction  of  the  metal  consists  in  calcining  (or  roasting)  the  ore,  in 
order  to  expel  water  and  carbonic  acid  gas.  To  effect  this  the  ore  is 
sometimes  built  up,  together  with  a  certain  amount  of  small  coal,  into 
long  pyramidal  heaps,  resting  upon  a  foundation  of  large  lumps  of  coal ; 
blackband  often  contains  so  much  bituminous  matter  that  any  other  fuel 
is  unnecessary.  These  heaps  are  kindled  in  several  places,  and  allowed 
to  burn  slowly  until  all  the  fuel  is  consumed.  This  calcination  has  the 
effect  of  rendering  the  ore  more  porous,  and  better  fitted  for  the  smelting 
process.  If  the  ore  contained  much  sulphur,  a  part  of  it  would  be  ex- 
pelled by  the  roasting  in  the  form  of  sulphurous  acid  gas.  The  FeCO3  is 
converted  into  Fe2O3,  which,  being  a  feebler  base  than  FeO,  is  less  likely 
to  combine  with  silica  and  form  a  fusible  slag. 

More  commonly  the  calcination  is  effected  in  kilns  resembling  lime- 
kilns, and  it  is  often  altogether  omitted  as  a  separate  process,  the  expul- 
sion of  the  water  and  carbonic  acid  gas  being  then  effected  in  the 
smelting-furnace  itself  as  the  ore  descends. 

The  calcined  ore  is  smelted  in  a  huge  blast-furnace  A  (Fig.  219)  from 
fifty  to  eighty  feet  high,  built  of  massive  masonry,  and  lined  internally 
with  firebrick.  Since  it  would  be  impossible  to  obtain  a  sufficiently  high 
temperature  with  the  natural  draught  of  this  furnace,  air  is  forced  into  it 
at  the  bottom,  under  a  pressure  of  three  to  seven  pounds  upon  the  square 
inch,  through  tuyere  or  twyer  pipes  H,  the  nozzles  G  of  which  pass  through 
apertures  in  three  sides  of  the  furnace.  As  the  nitrogen  of  the  air  thus 
forced  through  the  furnace  carries  away  much  heat  with  it,  a  hot-blast 
is  found  to  economise  fuel.  To  heat  the  blast  the  air  is  passed  over 
firebricks  which  have  been  raised  to  a  high  temperature  by  the  com- 
bustion of  the  gases  which  escape  from  the  furnace  (see  over).  In 
this  way  the  temperature  of  the  blast  is  frequently  raised  to  800°  C.  and 
that  of  the  furnace  when  the  combustion  is  most  vigorous  to  1930°  C. 

It  would  be  very  easy  to  reduce  to  the  metallic  state  the  oxide  of  iron 
contained  in  the  calcined  ore,  by  simply  throwing  it  into  this  furnace, 


398 


SMELTING  IRON  ORES. 


together  with  a  proper  quantity  of  coal,  coke,  or  charcoal;  but  the 
metallic  iron  fuses  with  so  great  difficulty,  that  it  is  impossible  to  sepa- 
rate it  from  the  clay  or  gangue,  as  it  is  called,  unless  this  latter  is 
brought  into  a  liquid  state ;  and  even  then  the  fusion  of  the  iron,  which 
is  necessary  for  complete  separation,  is  only  effected  after  it  has  formed 
a  more  easily  fusible  compound  with  a  small  proportion  of  carbon 
derived  from  the  fuel. 


Fig.  219. — Blast-furnace  for  smelting  iron  ores. 

Now,  clay  is  even  more  difficult  to  fuse  than  iron,  so  that  it  is  neces- 
sary to  add,  in  the  smelting  of  the  ore,  some  substance  capable  of  form- 
ing with  the  clay  a  combination  which  is  fusible  at  the  temperature  of 
the  furnace.  If  clay  (aluminium  silicate)  be  mixed  with  limestone 
(CaC03),  and  exposed  to  a  high  temperature,  C02  is  expelled  from  the 
limestone,  and  the  lime  unites  with  the  clay,  forming  a  double  silicate 
of  alumina  and  lime,  which  melts  completely,  and,  when  cool,  solidifies 
to  a  glass  or  slag.  The  limestone  acts  as  a  flux,  inducing  the  clay  to 
flow  in  the  liquid  state.  In  order,  therefore,  that  the  clay  may  be 
readily  separated  from  the  metallic  iron,  the  calcined  ore  is  mixed  with 
a  certain  proportion  of  limestone  before  being  introduced  into  the 
furnace. 


KEACTrONS   IN  THE  BLAST-FUKNACE,  399 

Great  care  is  necessary  in  first  lighting  the  blast-furnace  lest  the  new 
masonry  should  be  cracked  by  too  sudden  a  rise  of  temperature,  and, 
when  once  lighted,  the  furnace  is  kept  in  constant  work  for  years  until 
in  want  of  repair.  When  the  fire  has  been  lighted,  the  furnace  is 
filled  up  with  coke,  and  as  soon  as  this  has  burnt  down  to  some  distance 
below  the  top  opening  or  throat,  a  layer  of  the  mixture  of  calcined  ore 
with  the  requisite  proportion  of  limestone  is  thrown  upon  it ;  over  this 
there  is  placed  another  layer  of  coke,  then  a  second  layer  of  the  mixture 
of  ore  and  flux,  and  so  on,  in  alternate  layers,  until  the  furnace  has 
been  filled  up;  when  the  layers  sink  down,  fresh  quantities  of  fuel,  ore, 
and  flux  are  added,  so  that  the  furnace  is  kept  constantly  full.  As  the 
air  passes  from  the  tuyere  pipes  into  the  bottom  of  the  furnace  it  parts 
with  its  oxygen  to  the  carbon  of  the  fuel  which  it  converts  into  C02 ; 
the  latter,  passing  over  the  red-hot  fuel  in  the  widest  part  or  boshes  B  of 
the  furnace,  becomes  CO  (see  p.  132).  It  is  this  carbonic  oxide,  amount- 
ing to  some  33  per  cent,  of  the  gases,  which  reduces  the  calcined  ore  to 
the  metallic  state  when  it  comes  in  contact  with  it  at  that  part  of  the 
throat  of  the  furnace  where  the  ore  has  already  attained  a  red-heat.  In 
effecting  this  reduction,  the  CO  is  of  course  oxidised  to  C02.  The 
metallic  iron  being  infusible  at  the  temperatures  at  which  it  is  reduced, 
remains  disseminated  through  the  gangue  of  the  ore  and  as  it  descends 
into  a  hotter  region  of  the  furnace  some  of  it  reduces  CO  liberating  carbon 
with  which  the  rest  of  the  iron  combines  to  form  cast-iron.  At  this 
stage,  the  clay  or  gangue  of  the  ore  is  attacked  by  the  lime  which  has 
been  produced  from  the  calcination  of  the  limestone  flux  at  a  somewhat 
higher  point  in  the  furnace  and  a  fusible  slag  of  silicate  of  lime  and 
alumina  is  formed.  This  melts  and  liberates  the  disseminated  cast-iron 
at  the  hottest  portion  C  of  the  furnace,  just  above  the  tuyeres.  The  cast- 
iron  now  melts  and  runs  together,  collecting  in  the  crucible  or  cavity  D  for 
its  reception  at  the  bottom  of  the  furnace.  The  slag,  which  has  five  or 
six  times  the  bulk  of  the  iron,  is  allowed  to  accumulate  in  the  crucible, 
and  to  run  over  its  edge  down  the  incline  upon  which  the  blast-furnace 
is  built ;  but  when  a  sufficient  quantity  of  cast-iron  has  collected  at  the 
bottom  of  the  crucible,  it  is  run  out  through  a  hole  provided  for  the 
purpose,  either  into  .channels  made  in  a  bed  of  sand,  or  into  iron 
moulds,  where  it  is  cast  into  rough  semi-cylindrical  masses  called  pigs, 
whence  cast-iron  is  also  spoken  of  as  pig-iron. 

A  furnace  consumes,  in  the  course  of  twenty-four  hours,  about  50  tons  of  coal, 
30  tons  of  ore,  6  tons  of  limestone,  and  100  tons  of  air.  The  cast-iron  is  run  off 
from  the  crucible  once  or  twice  in  twelve  hours,  in  quantities  of  five  or  six  tons 
at  a  time.  The  average  yield  of  calcined  clay  ironstone  is  35  per  cent,  of  iron. 

The  gases  escaping  from  the  blast-furnace  are  highly  inflammable, 
for  they  contain  as  much  as  25  per  cent,  of  carbon  monoxide ;  *  in 
modern  furnaces  the  throat  is  closed  when  the  furnace  has  been  charged, 
by  a  bell  E,  and  the  gases  are  made  to  pass  through  a  flue  into  the 
stoves  L,  where  they  are  burnt  in  flues  M  in  order  to  heat  the  brickwork 
N  which  is  subsequently  to  raise  the  temperature  of  the  blast.  When 
one  stove  has  been  heated  the  combustible  gases  are  turned  into  another 
stove  and  an  air  blast  is  passed  through  the  first  one  from  pipe  R 
in  a  direction  contrary  to  that  of  the  combustible  gases.  The  pipe  P 

*  If  coal  be  used  as  fuel  hydrogen  and  hydrocarbons  will  also  be  present.  The  gases  from 
a  coke-fed  furnace  contain  in  100  vols.  :  N,  55  ;  CO2,  18.5  ;  CO,  26.4 ;  H,  o.i  vols. 


400  BLAST-FUENACE   SLAG. 

conducts  the  blast  to  the  tuyeres,  and  the  products  of  combustion  leave 
the  stove  by  flue  0.  As  there  is  generally  more  than  sufficient  com- 
bustible gas  for  this  purpose,  in  some  works  a  portion  is  burnt  in  gas- 
engines  to  supply  power  for  the  blowing  engines,  &c. 

When  coal  is  used  as  fuel  it  is  sometimes  profitable  to  pass  the  gases  through 
cooling  apparatus  before  they  are  burnt,  in  order  to  condense  the  tar  and 
ammonia  which  they  contain. 

Although  the  bulk  of  the  nitrogen  present  in  the  air  escapes  unchanged  from 
the  furnace,  it  is  not  improbable  that  a  portion  of  it  contributes  to  the  formation 
of  the  cyanide  of  potassium  (KCN),  which  is  produced  in  the  lower  part  of  the 
furnace,  the  potassium  being  furnished  by  the  ashes  of  the  fuel.  Cyanogen  is 
generally  found  in  the  escaping  gases. 

The  slag  from  the  blast-furnace  is  essentially  a  glass  composed  of  a 
double  silicate  of  aluminium  and  calcium,  the  composition  of  which  varies 
much  according  to  the  nature  of  the  earthy  matters  in  the  ore  and  the 
composition  of  the  flux.  Its  colour  is  generally  grey,  streaked  with 
blue,  green,  or  brown. 

The  nature  of  the  flux  employed  must,  of  course,  be  modified  according 
to  the  composition  of  the  gangue  present  in  the  ore.  Where  this  con- 
sists of  clay  (silicate  of  alumina),  that  is,  is  acid  in  character,  the 
addition  of  lime  (which  is  sometimes  added  in  the  form  of  limestone 
and  sometimes  as  quicklime)  will  provide  for  the  formation  of  the 
double  silicate  of  alumina  and  lime.  But  if  the  iron-ore  happened 
already  to  contain  limestone,  a  basic  gangue,  an  addition  of  clay  would 
be  necessary,  or  if  quartz  were  present,  consisting  of  silica  only,  both 
lime  and  alumina  (in  the  form  of  clay)  will  be  necessary  as  a  flux.  It 
is  sometimes  found  economical  to  employ  a  mixture  of  ores  containing 
different  kinds  of  gangue,  so  that  one  may  serve  as  a  flux  to  the  other. 
If  a  proper  proportion  of  lime  were  not  added,  a  portion  of  the  oxide  of 
iron  would  serve  as  the  base  to  combine  with  the  silica  and  be  carried 
off  in  the  slag ;  but  if  too  large  a  quantity  of  lime  be  employed,  it  will 
diminish  the  fusibility  of  the  slag,  and  prevent  the  complete  separation 
of  the  iron  from  the  earthy  matter. 

The  most  easily  fusible  slag  which  can  be  formed  by  the  action  of  lime  upon 
clay  has  the  composition  6CaO.Al203.9Si02  ;  but  in  English  furnaces,  where  coal 
and  coke  are  employed,  it  is  found  necessary  to  use  a  larger  proportion  of  lime  to 
convert  the  sulphur  of  the  fuel  into  calcium  sulphide,  so  that  the  slag  commonly 
has  a  composition  more  nearly  represented  by  the  formula  i2Ca0.2Al203.9Si02r 
which  would  express  a  compound  of  6  molecules  of  normal  calcium  silicate  with 
I  molecule  of  normal  aluminium  silicate  ;  6Ca,2Si04.Al4(Si04)3. 

Since  iron,  manganese,  and  magnesium  are  commonly  found  occupying  the  place 
of  a  portion  of  the  calcium,  a  more  general  formula  for  the  slag  from  English 
blast-furnaces  would  be  6(CaFeMnMg)2Si04.Al4(Si04)3. 

A  fair  impression  of  the  ordinary  composition  of  the  slag  from  blast-furnaces  is 
conveyed  by  the  following  table  : 

Slag  from  Blast- Furnace  ;  in  100  parts. 


Silica 43-07 

Alumina        .        .        •        -14-85 

Lime 28.92 

Magnesia 


Oxide  of  manganese  (MnO)  .     1.37 

Potash  (K20)  .         .  .1.84 

Sulphide  of  calcium         .  .     1.90 

Phosphoric  oxide  (P205)  .  trace 


Oxide  of  iron  (FeO)       .         .         2.35 

From  i o  to  30  cwt.  of  slag  are  produced  per  ton  of  cast-iron  smelted. 

These  slags  are  sometimes  run  from  the  blast-furnace  into  iron  moulds, 
in  which  they  are  cast  into  blocks  for  rough  building  purposes.     The 


CAST  IRON.  401 

presence  of  a  considerable  proportion  of  potash  has  led  to  experiments- 
upon  their  employment  as  a  manure,  for  which  purpose  they  have  been 
blown  out,  when  liquid,  into  a  finely  divided  frothy  condition  fit  for 
grinding  and  applying  to  the  soil.  They  are  also  used  for  making 
cement.  By  blowing  air  through  the  slag,  it  is  converted  into  a  sub- 
stance resembling  spun  glass,  and  used,  under  the  name  of  slag  wool  or 
mineral  cotton,  for  packing  round  steam-pipes,  &c. 

220.  CAST  IRON  is,  essentially,  composed  of  iron  with  from  2  to  5  per 
cent,  of  carbon,  but  always  contains  other  substances  derived  either  from 
the  ore  or  from  the  fuel  employed  in  smelting  it.  On  taking  into  con- 
sideration the  energetic  deoxidising  action  in  the  blast-furnace,  it  is  not 
surprising  that  portions  of  the  various  oxygen  compounds  exposed  to  it 
should  part  with  their  oxygen,  and  that  the  elements  thus  liberated  should 
find  their  way  into  the  cast  iron.  In  this  way  the  silica  is  reduced,  and 
its  silicon  is  found  in  cast  iron  in  quantity  sometimes  amounting  to  3  or 
4  per  cent.  Haematite  pig  is  usually  rich  in  silicon,  from  the  presence 
of  silica  in  an  easily  reducible  condition  in  the  ore.  Sulphur  and  phos- 
phorus are  also  generally  present  in  cast  iron,  but  in  very  much  smaller 
proportion;  their  presence  diminishes  its  tenacity,  and  the  smelter 
endeavours  to  exclude  them  as  far  as  possible,  though  a  small  quantity 
of  phosphorus  appears  to  be  rather  advantageous  for  some  castings, 
since  it  augments  the  fusibility  and  fluidity  of  the  cast-iron.  The 
sulphur  is  chiefly  derived  from  the  coal  or  coke  employed  in  smelting, 
and  for  this  reason  charcoal  would  be  preferable  to  any  other  fuel  if  it 
could  be  obtained  at  a  sufficiently  cheap  rate.  The  ironworks  of  some 
parts  of  Europe  enjoy  a  great  advantage  in  this  respect  over  those  of 
England.  The  phosphorus  is  derived  chiefly  from  the  phosphates 
existing  in  the  ore  or  in  the  flux.*  The  proportion  of  phosphorus  taken 
up  by  the  cast  iron  increases  with  the  temperature  of  the  blast-furnace. 
Manganese,  amounting  to  i  or  2  per  cent.,  is  often  met  with  in  cast 
iron,  having  been  reduced  from  the  oxide  of  manganese,  which  is 
usually  found  in  iron  ores ;  its  presence  generally  enables  the  iron  to 
hold  more  carbon  and  less  sulphur.  Other  metals,  such  as  chromium, 
cobalt,  &c.,  are  also  occasionally  present,  though  in  such  small  quantities 
as  to  be  of  no  importance  in  practice. 

The  following  table  exhibits  the  largest  and  smallest  proportion  of  the 
various  elements  determined  in  the  analysis  of  upwards  of  a  hundred 
specimens  of  cast  iron  : 


Composition  of  Cast  Iron. 

Maximum.  Minimum. 


Carbon 

Silicon 

Sulphur 

Phosphorus 

Manganese 

Iron 


4.81 

4-77 
i. 06 
1.87 
6.08 


1.04  per  cent. 
0.08 


trace 
trace 


In  order  to  understand  the  difference  observed  in  the  several  varieties 
of  cast  iron,  it  is  necessary  to  consider  the  peculiar  relations  between 
iron  and  carbon.  Iron  fused  in  contact  with  carbon  is  capable  of  com- 
bining with  nearly  6  per  cent,  of  that  element,  to  form  a  white,  brilliant, 

*  It  appears  to  exist  in  the  iron,  at  least  in  some  cases,  as  Fe4P. 

2  C 


402 


VARIETIES  OF   CAST   IEON, 


and  brittle  compound,  which  may  be  represented  pretty  nearly  as  com- 
posed of  Fe4G.  Under  certain  circumstances,  as  this  compound  of  iron 
and  carbon  cools,  a  portion  of  the  carbon  separates  from  the  iron,  and 
remains  disseminated  throughout  the  mass  in  the  form  of  minute 
crystalline  particles  very  much  resembling  natural  graphite.  If  a  broken 
piece  of  iron  containing  these  scales  be  examined,  the  fracture  will  be 
found  to  exhibit  a  more  or  less  dark  grey  colour,  due  to  the  presence  of 
the  uncombined  carbon,  and  for  this  reason  a  cast  iron  in  which  a  por- 
tion of  the  carbon  has  thus  separated  is  commonly  spoken  of  as  grey 
iron,  whilst  that  in  which  the  whole  of  the  carbon  has  remained  in  com- 
bination with  the  metal  exhibits  a  white  fracture,  and  is  termed  white 
iron  or  bright  iron.  Intermediate  between  these  is  the  variety  known 
as  mottled  iron,  which  has  the  appearance  of  a  mixture  of  the  grey  and 
white  varieties. 

The  different  condition  of  the  carbon  in  the  two  varieties  of  cast  iron 
is  rendered  apparent  when  the  metal  is  dissolved  in  diluted  sulphuric  or 
hydrochloric  acid,  for  any  carbon  which  exists  in  the  uncombined  state 
will  then  be  left,  whilst  that  which  had  been  in  combination  with  the 
iron  passes  off  in  the  form  of  peculiar  compounds  of  carbon  and  hydro- 
gen, which  impart  the  disagreeable  odour  perceived  in  the  gas  evolved 
when  the  metal  is  dissolved  in  an  acid. 

The  properties  of  these  two  varieties  of  cast  iron  are  widely  different, 
grey  iron  being  so  soft  that  it  may  be  turned  in  a  lathe,  whilst  the 
white  iron  is  extremely  hard,  and  of  higher  specific  gravity,  7.5,  that  of 
grey  iron  being  7.1.  Again,  although  white  iron  fuses  at  a  lower  tem- 
perature (1100°  C.)  than  grey  iron  (1200°  C.),  the  latter  is  far  more 
liquid  when  fused,  and  is  therefore  much  better  fitted  for  casting. 

Although  the  presence  of  uncombined  carbon  is  the  chief  point  which 
distinguishes  grey  from  white  iron,  other  differences  are  commonly 
observed  in  the  composition  of  the  two  varieties.  The  white  iron 
usually  contains  less  silicon  than  grey  iron,  but  a  larger  proportion  of 
sulphur. 

The  difference  in  the  composition  of  these  three  varieties  of  cast  iron 
is  shown  in  the  following  table  : 


Grey. 

Mottled. 

White. 

Iron 

92.00 

92-75 

94.04 

Combined  carbon   . 

0.30 

0-75 

3.20 

Graphitic  carbon     . 

3-70 

2.90 

Silicon     . 

2.50 

I.OO 

0.64 

Sulphur  . 

0.04 

0.15 

0.20 

Phosphorus 

1.50 

i.  60 

1.32 

Manganese 

0.72 

0.47 

O.6O 

As  might  be  expected,  it  is  not  easy  to  tell  where  a  cast  iron  ceases  to  be  grey  and 
begins  to  be  mottled,  or  where  the  mottled  iron  ends  and  white  iron  begins.  There 
are,  in  fact,  eight  varieties  or  grades  of  cast  iron  in  commerce,  distinguished  by  the 
numbers  one  to  eight,  of  which  No.  I  is  dark  grey  and  contains  the  largest  propor- 
tion of  graphite,  which  diminishes  in  the  succeeding  numbers  up  to  No.  8,  which  is 
the  whitest  iron,  the  intermediate  numbers  being  more  or  less  mottled. 

The  particular  variety  of  cast  iron  produced  is  to  some  extent  under  the  control  of 
the  smelter.  A  furnace  working  with  siliceous  ores  and  a  high  percentage  of  fuel, 
at  a  high  temperature,  yields  an  iron  containing  much  silicon,  and  therefore  a  grey 
pig,  for  the  presence  of  silicon  determines  the  separation  of  carbon  as  graphite. 


PIG-IRON,  403 

When  the  furnace  is  working  with  a  minimum  of  fuel  the  iron  will  contain  but  little 
silicon,  and  will  consequently  retain  all  its  carbon  in  combination,  giving  a  white 
pig.  But  the  metal  sometimes  varies  considerably  at  different  levels  in  the  crucible 
of  the  furnace,  so  that  pigs  of  different  degrees  of  greyness  are  obtained  at 
the  same  tapping.  Mottled  cast  iron  surpasses  both  the  other  varieties  in 
tenacity,  and  is  therefore  preferred  where  this  quality  is  particularly  desirable. 

The  extra  consumption  of  fuel,  of  course,  renders  the  grey  iron  more  expen- 
sive. When  a  furnace  is  worked  with  a  low  charge  of  fuel  to  produce  a  white 
iron,  a  larger  quantity  of  iron  is  lost  in  the  slag,  sometimes  amounting  to  5  per 
cent,  of  the  metal,  whilst  the  average  loss  in  producing  grey  iron  does  not  ex- 
ceed 2  per  cent.  Ores  containing  a  large  proportion  of  manganese  are  generally 
found  to  yield  a  white  iron. 

White  iron  is  usually  used  as  forge-iron  (that  is  for  conversion  into 
malleable  iron),  whilst  grey  iron  is  used  as  foundry-iron  (for  making 
castings)  and  for  conversion  into  steel. 

When  grey  iron  is  melted,  the  particles  of  graphite  to  which  its  grey 
colour  is  due  are  dissolved  by  the  liquid  iron,  and  if  it  be  poured  into  a 
cold  iron  mould  so  as  to  solidify  it  as  rapidly  as  possible,  the  external 
portion  of  the  casting  will  present  much  of  the  hardness  and  appearance 
of  white  iron,  the  sudden  cooling  having  prevented  the  separation  of 
the  graphite.  This  affords  the  explanation  of  the  process  of  chill-casting 
by  which  shot,  &c.,  made  of  the  soft  fusible  grey  iron,  are  made  to 
acquire,  externally,  a  hardness  approaching  that  of  steel.  It  is  a  com- 
mon practice  to  produce  compound  castings,  that  portion  of  the  mould 
where  chilling  and  consequent  hardness  is  required  being  made  of  thick 
cast  iron,  and  the  other  part,  which  is  to  give  a  tougher  and  a  softer 
casting,  of  sand.  When  white  pig-iron  is  melted  at  an  extremely  high 
temperature  (in  a  Siemens  furnace)  and  slowly  cooled,  it  becomes  grey. 

When  grey  iron  is  re-melted  in  the  foundry  for  casting  it  becomes  harder,  both 
because  some  of  the  silicon  is  eliminated  by  oxidation,  causing  a  corresponding 
amount  of  the  graphite  to  pass  into  combination,  and  because  sulphur  is  absorbed 
from  the  fuel  with  which  the  iron  is  melted. 

By  the  use  of  ores  containing  an  unusually  large  proportion  of  any  of  the 
foreign  constituents  which  enter  into  the  reduced  iron,  the  blast-furnace  may  be 
made  to  produce  special  irons,  which  have  particular  applications.  Thus,  ferro- 
silicon  (iron  rich  in  silicon)  used  for  converting  white  iron  into  grey  iron,  ferro- 
manganese  (iron  containing  68-80  per  cent,  of  Mn  ;  spiegel-eisen  contains  about 
10  per  cent  of  Mn),  and  ferro-chromiutn  (containing  60-70  per  cent,  of  Cr)  are 
made  ;  the  last  two  are  used  in  steel-making. 

Pig-iron  has  a  very  limited  application  as  a  building  material  on 
account  of  its  low  tensile  strength  (8  tons  per  sq.  in.)  and  its  lack  of 
malleability.  For  constructional  use  it  must  be  converted  into  malleable 
iron  which  possesses  a  high  tensile  strength  and  is  capable  of  being 
forged.  In  order  to  effect  this  conversion  the  silicon,  phosphorus  and 
.sulphur  of  the  pig-iron  must  be  removed,  and  the  content  of  carbon 
must  be  reduced  to  below  2  per  cent.  The  attainment  of  these  ends  is 
rendered  possible  by  the  fact  that  the  impurities  are  more  readily 
oxidised  than  is  the  iron,  and  this  oxidation  may  be  effected  either  by 
mixing  the  hot  iron  with  iron  oxide,  or  by  blowing  air  through  the 
molten  metal.  The  carbon  is  thus  evolved  in  the  form  of  CO,  whilst 
the  silicon  and  phosphorus  are  oxidised  to  Si0.2  and  P2O5,  both  of  which 
oxides  are  capable  of  uniting  with  a  base  (FeO  or  CaO)  and  of  being 
removed  as  slag. 

Before  the  production  and  maintenance  of  very  high  temperatures 
was  understood,  it  was  customary  to  heat  the  iron  until  it  became  pasty 


404 


KEFINING   CAST   IKON. 


and  to  mix  it  with  iron  oxide  whilst  in  this  condition  (a  process  known 
as  puddling) ;  the  impurities,  oxidised  at  the  expense  of  the  ferric  oxide, 
were  then  squeezed  out  of  the  iron  by  working  the  pasty  mass  under 
the  hammer.  The  product  was  known  as  wrought  iron,  and,  since  it 
was  not  necessary  to  fuse  the  iron  at  any  stage  of  the  process,  it  was 
possible  to  reduce  the  carbon  to  a  very  low  percentage,  for  it  will  be 
remembered  that  it  is  the  presence  of  this  element  which  lowers  the 
fusing-point  of  iron.  At  the  present  day  it  is  possible  to  keep  iron  con- 
taining very  little  carbon  in  a  state  of  fusion,  so  that  the  iron  oxide  can 
be  mixed  with  it  in  this  condition  and  the  decarburised  iron  can  be  cast 
into  ingots  prior  to  being  rolled  into  plates  or  bars  (Siemens- Martin  pro- 
cess). Instead  of  iron  oxide,  air  is  frequently  used  as  the  oxidant,  in 
which  case  it  is  blown  through  the  molten  iron,  the  heat  generated  by 
the  oxidation  of  the  impurities  serving  to  keep  the  metal  in  fusion 
(Bessemer  process).  By  this  method  also  the  metal  is  obtained  in  the 
form  of  cast  ingots. 

The  original  distinction  between  cast  iron,  wrought  iron  and  steel  lay 
in  their  content  of  carbon.  Cast  iron  contains  3-5  per  cent,  of  C ; 
wrought  iron  under  o.i  per  cent.,  and  steel  0.5-2.0  per  cent.  The 
term  ingot  iron  is  now  employed  to  signify  all  iron  made  by  methods 
involving  fusion,  and  includes  all  grades  of  refined  iron  except  the  very 
softest  and  the  very  hardest  (hard  steel) ;  the  expression  mild  steel  is 
nearly  synonymous  with  ingot  iron. 

Conversion  of  cast  iron  into  bar  or  wrought  iron. — Puddling.  With 
pig-iron  containing  much  graphite  and  silicon,  namely  grey  iron,  the 
puddling  process  is  preceded  by  the  process  of  refining,  which  will  there- 
fore be  first  described. 

Refining  cast  iron. — This  process  consists  essentially  in  exposing  the 

metal,  in  the  fused 
state,  to  the  action  of  a 
blast  of  air  in  which 
part  of  the  oxygen  has 
been  converted  into 
carbonic  oxide  by  pass- 
ing over  red-hot  coke 
or  charcoal. 

The  refinery  (Fig.  220)  is 
a  rectangular  trough  with 
double  walls  of  cast  iron, 
between  which  cold  water 
is  kept  circulating  to  pre- 
vent their  fusion.  This 
trough  is  about  3^  feet 
long  by  2\  feet  wide,  and 
usually  lined  with  fireclay  ; 
on  each  side  of  it  are  ar- 
ranged three  tuyere  pipes 
for  the  supply  of  air,  in- 
clined at  an  angle  of  25°  to- 

30°  to  the  bottom  of  the  furnace,  which  is  fed  with  coke,  unless  the  very  best  iron 
is  required,  as  for  the  manufacture  of  tin-plate,  when  charcoal  is  generally  used  in 
the  refinery. 

This  furnace  having  been  filled  to  a  certain  height  with  fuel,  five  or  six  pigs  of 
iron  (from  20  to  30  cwt.)  are  arranged  symmetrically  upon  it,  and  covered  with 
coke,  a  blast  of  air  being  forced  in  through  the  tuyeres,  under  a  pressure  of  about 


Fig.  220. — Hearth  for  refining  pig-iron. 


PUDDLING,  405 

3  Ibs.  upon  the  square  inch.  In  about  a  quarter  of  an  hour  the  metal  begins  to  fuse 
gradually,  and  to  trickle  down  through  the  fuel  to  the  bottom  of  the  refinery,  a 
portion  of  the  iron  being  converted  into  oxide  in  its  descent,  by  the  air  issuing  from 
the  tuyere  pipes.  When  the  whole  of  the  metal  has  been  fused,  the  air  is  still 
allowed  to  play  for  some  time  upon  its  surface,  when  the  fused  metal  appears  to 
boil  in  consequence  of  the  escape  of  bubbles  of  carbonic  oxide. 

After  about  two  hours  the  tap-hole  is  opened,  and  the  molten  metal  run  out  into 
a  flat  cast-iron  mould  kept  cold  by  water,  in  order  to  chill  the  metal  and  render  it 
brittle.  The  plate  of  refined  iron  thus  obtained  is  usually  about  2  inches  thick. 
The  slag  (or  finery  chide;-)  is  generally  received  in  a  separate  mould  ;  its  compo- 
sition may  be  generally  expressed  by  the  formula  2FeO.Si02,  the  silica  having  been 
derived  from  the  silicon  contained  in  the  cast  iron. 

The  change  effected  in  the  composition  of  the  iron  by  the  process  of 
refining  will  be  apparent  from  the  following  percentage  composition  of 
refined  iron  :  Fe,  95.14  ;  C,  3.07  ;  Si,  0.63;  S,  0.16;  P,  0.73  ;  Mn,  trace  ; 
slag,  0.44.  The  carbon,  therefore,  is  not  nearly  so  much  diminished  as 
the  silicon,  which  is  in  some  cases  reduced  to  T\j-  of  its  former  propor- 
tion by  the  refining  process.  The  main  effect  of  the  refining  is  to  con- 
vert the  graphite  into  combined  carbon,  that  is,  to  make  the  grey  iron 
white  iron ;  no  doubt  this  conversion  is  connected  with  the  removal  of 
the  silicon  ;  its  practical  advantage  resides  in  the  fact  that  the  white 
iron  passes  through  a  pasty  stage  before  it  melts,  so  that  it  is  better 
fitted  than  grey  iron  for  puddling.  Half  of  the  sulphur  is  also  some- 
times removed  by  the  refining,  being  found  in  the  slag  as  sulphide  of 
iron.  The  phosphorus  is  not  removed  to  the  same  extent,  though  some 
of  it  is  converted  into  ferrous  phosphate,  which  may  be  found  in  the 
finery  cinder. 

It  will  be  seen  that  the  term  "  refining  "  is  somewhat  misapplied  to 
the  process  of  the  refinery  hearth,  as  but  iittle  of  the  carbon  which 
must  be  removed  in  order  to  obtain  a  malleable  iron  is  separated  by  the 
operation.  The  purification  proper  could  not  be  effected  in  the  refinery, 
since  the  fusibility  of  the  iron  is  so  greatly  diminished,  as  it  approaches 
to  a  pure  state,  that  it  could  not  be  kept  fluid  at  the  temperature  attain- 
able in  this  furnace,  and  a  more  spacious  hearth  is  required  upon  which 
the  pasty  metal  may  be  kneaded  into  close  contact  with  the  oxide  of 
iron  which  is  to  complete  the  oxidation  and  separation  of  the  carbon. 
For  this  reason  the  metal  is  transferred  to  the  puddling  furnace. 

The  puddling  process  is  carried  out  in  a  reverberatory  furnace 
(Figs.  221,  222)  connected  with  a  tall  chimney  provided  with  a  damper, 
so  as  to  admit  of  a  very  perfect  regulation  oi  the  draught.  A  bridge  of 
firebrick  between  the  grate  and  the  hearth  prevents  the  contact  of  the 
coal  with  the  iron  to  be  puddled.  The  hearth  is  composed  either  of 
fire-brick  or  of  cast-iron  plates,  covered  with  a  layer  of  very  infusible 
slag,  and  cooled  by  a  free  circulation  of  air  between  them.  This  hearth 
is  about  6  feet  in  length  by  4  feet  in  the  widest  part  near  the  grate, 
and  2  feet  at  the  opposite  end ;  it  is  slightly  inclined  towards  the  end 
farthest  from  the  grate,  and  finishes  in  a  very  considerable  slope,  at  the 
lowest  point  of  which  is  the  floss-hole  for  the  removal  of  the  slag. 
Since  the  metal  is  to  attain  a  very  high  temperature  in  this  furnace 
(estimated  at  i3oo°C.),  the  latter  is  usually  covered  with  an  iron  casing, 
so  as  to  prevent  any  entrance  of  cold  air  through  chinks  in  the  brick- 
work. 

About  5  cwt.  of  the  fine  metal  is  broken  up  and  heaped  upon  the 
hearth  of  this  furnace,  together  with  about  i  cwt.  of  iron  scales  (black 


406 


PUDDLING. 


oxide  of  iron,  Fe304),  and  of  hammer-slag  (basic  silicate  of  iron,  obtained 
in  subsequent  operations),  which  are  added  in  order  to  assist  in  oxidising 
the  impurities.  When  the  metal  has  fused,  the  mass  is  well  stirred  or 
puddled,  so  that  the  oxide  of  iron  may  be  brought  into  contact  with 
every  part  of  the  metal,  to  effect  the  oxidation  of  the  impurities.  The 
metal  now  appears  to  boil,  in  consequence  of  the  escape  of  carbonic 
oxide,  and  in  about  an  hour  from  the  commencement  of  the  puddling, 


Fig-.  221. — Puddliug-furuace  (elevation). 


Fig.  222. — Puddling-furnace  (section). 

so  much  of  the  carbon  has  been  removed  that  the  fusibility  of  the  metal 
is  considerably  diminished,  and  instead  of  retaining  a  fused  condition 
at  the  temperature  prevailing  in  the  furnace,  it  assumes  a  granular 
sandy  or  dry  state,  spongy  masses  of  pure  iron  separating  or  coming  to 
nature  in  the  fused  mass.  The  puddling  of  the  iron  is  continued  until 
the  whole  has  assumed  this  granular  appearance,  when  the  evolution  of 
carbonic  oxide  ceases  almost  entirely,  showing  that  the  removal  of  the 
carbon  is  nearly  completed.  The  damper  is  now  gradually  raised  so  as 
to  increase  the  temperature  and  soften  the  particles  of  iron,  in  order 
that  they  may  be  collected  into  a  mass ;  and,  the  more  easily  to  effect 
this,  a  part  of  the  slag  is  run  off  through  the  floss-hole.  The  workman 
then  collects  some  of  the  iron  upon  the  end  of  the  paddle,  and  rolls  it 


BAR-IRON. 


407 


about  on  the  hearth  until  he  has  collected  a  sort  of  rough  ball  of  iron, 
weighing  about  half  a  hundredweight.     When  all   the  iron  has  been 
collected  into  balls  in  this  way,  they  are  placed  in  the  hottest  part  of 
the  furnace,  and  pressed  occasionally  with  the  paddle,  so  as  to  squeeze 
out  a  portion  of  the  slag  with  which  their  interstices  are  filled.     The 
doors  are  then  closed  to  raise  the  interior  of  the  furnace  to  a  very  high 
temperature,  and  after  a  short  time,  when  the  balls  are  sufficiently 
heated,  they  are  removed  from  the  furnace,  and  placed  under  a  steam 
hammer,  which  squeezes  out  the  liquid  slag,  and  forces  the  softened 
particles  of  iron  to  cohere  into  a  continuous  oblong  mass  or  bloom,  which 
is  then  passed  between  rollers,  by  which  it  is  extended  into  bars.     These 
bars,  however  (Rough  or  Puddled,  or  No.  i  Bar),  are  always  hard  and 
brittle,  and  are  not  fit  for  use.     In  order  to  improve  the  tenacity  of  the 
iron,  the  rough  bars  are  cut  up  into  short  lengths,  which  are  made  into 
bundles,  and,  after  being  raised  to  a  high  temperature  in  the  mill- furnace, 
are  passed  through  rollers,  which  weld  the  several  bars  into  one  com- 
pound bar,  to  be  subsequently  passed  through  other  rollers  until  it  has 
acquired  the  desired  dimensions.     By  thus  fagoting  or  piling  the  bars, 
their  texture  is  rendered  far  more  unifurm,  and  they  are  made  to 
assume  a   fibrous   structure,    which    greatly  increases   their   strength 
(Merchant  Bar,  or  No.  2  Bar).     To  obtain  the  best,  or  No.  3  Bar,  or  wire- 
iron,  these  bars  are  doubled  upon  themselves,  raised  to  a  welding-heat, 
and  again  passed   between  rollers.     These  repeated  rollings  have  the 
effect  of   thoroughly  squeezing   out  the    slag  which   is   mechanically 
entangled  among  the  particles  of  iron  in  the  rough  bar,  and  would 
produce  flaws  if  allowed  to  remain  in  the  metal.     A  slight  improvement 
appears  also  to  be  effected    in  the  chemical  composition  of  the  iron 
during  the  rolling,  some  of  the  carbon,  silicon,  phosphorus,  and  sulphur, 
still  retained  by  the  puddled  iron,  becoming  oxidised,  and  passing  away 
as  gas  and  slag. 

The  following  table  exhibits  the  change  in  chemical  composition 
which  occurs  in  pig-iron  when  puddled  (without  previous  refining)  and 
rolled  into  wire-iron  : 

Effect  of  Puddling  and  Forging  on  Cast  Iron. 


In  100  parts. 

Carbon. 

Silicon. 

Sulphur. 

Phosphorus. 

0.645 
0.139 
0.117 

Grey  pig-iron 
Puddled  bar  . 
Wire-iron 

2.275 
0.296 

O.I  1  1 

2.720 

0.120 

0.088 

0.301 
0.134 
0.094 

About  90  parts  of  bar-iron  are  obtained  from  100  of  refined  iron  by  the  puddling 
process,  the  difference  representing  the  carbon  which  has  passed  off  as  carbonic 
oxide,  and  the  silicon,  sulphur,  phosphorus,  and  iron  which  have  been  removed  in 
the  slag  or  tap-cinder,  this  being  essentially  a  mixture  of  ferrous  and  ferric  sili- 
cates, varying  much  in  composition  according  to  the  character  of  the  iron  employed 
for  puddling,  and  the  proportions  of  iron-scale  and  hammer-slag  introduced  into 
the  furnace.  Of  course,  also,  the  material  of  which  the  hearth  is  composed  (the 
fettling}  will  influence  the  composition  of  the  slag.  The  following  table  affords  an 
illustration  of  its  percentage  composition  : 


Tap-cinder  from  Puddling -Furnace. 


Ferrous  oxide  (FeO)  .         .  57.67 

Ferric  oxide  (Fe2O3) .         .  13.53 

Silica 8.32 

Phosphoric  oxide  (P205)     .  7.29 


Ferrous  Sulphide  . 

Lime 

Oxide  of  manganese 

Magnesia 


7.07 
4.70 
0.78 
0.26 


408  BAR-IRON. 

The  lime  in  the  above  cinder  was  probably  derived  from  the  hearth  of  the  furnace, 
which  is  sometimes  lined  with  that  material  to  assist  in  removing  the  sulphur. 

When  grey  pig-iron  is  puddled  without  undergoing  the  refining  process,  it  becomes 
much  more  liquid  than  white  pig  or  refined  iron,  and  the  process  is  sometimes 
described  as  the  pig-boiling  process,  whilst  refined  iron  undergoes  dry  puddling.  In 
the  latter,  the  oxygen  of  the  air  has  more  share  in  the  de-carburising  of  the  iron 
than  it  has  in  the  former. 

Formerly  it  was  sometimes  the  custom  to  make  a  puddled-steel,  by  arresting  the 
puddling  process  at  an  earlier  stage  than  usual,  so  as  to  leave  a  proportion  of  carbon 
varying  from  0.3  to  I  per  cent. 

It  will  be  observed  that  this  process  of  puddling  is  attended  with  some 
important  disadvantages ;  it  involves  a  great  expenditure  of  manual 
labour,  and  of  a  most  exhausting  kind ;  the  wear  and  tear  of  the  pudd- 
ling furnace  is  very  considerable,  and  since  it  receives  only  ten  or  eleven 
charges  of  about  5  cwts.  each  in  the  course  of  twenty-four  hours,  it  is 
necessary  to  work  five  or  six  puddling- furnaces  at  once,  in  order  to 
convert  into  bar-iron  the  whole  of  the  cast  iron  turned  out  from  a 
single  blast-furnace.  These  considerations  have  led  to  several  attempts 
to  improve  the  puddling  process  by  employing  revolving  furnaces  and 
other  mechanical  arrangements  to  supersede  the  heavy  manual  labour. 
In  Dankes'  rotating  puddling -furnace  the  pig-iron  is  run  into  a  cylindrical 
chamber  lined  with  a  mixture  of  haematite  and  lime.  Air  is  supplied 
by  a  fan,  and  the  cylinder  is  revolved  so  as  to  bring  the  metal  thoroughly 
into  contact  with  the  oxides  of  iron,  which  form  part  of  the  charge,  as 
in  the  ordinary  puddling  process.  The  charge  of  about  600  Ibs.  is 
turned  out  in  a  single  ball,  which  is  further  treated  as  usual. 

Properties  of  bar -iron. — Even  the  best  bar-iron  contains  from  o.i  to 
0.2  per  cent,  of  carbon,  together  with  minute  proportions  of  silicon, 
sulphur,  and  phosphorus.  Perfectly  pure  iron  is  inferior  in  hardness 
and  tenacity  to  that  which  contains  a  small  proportion  of  carbon. 

Bar-iron  is  liable  to  two  important  defects,  which  are  technically 
known  as  cold- shortness  and  red- shortness.  Cold-short  iron  is  brittle  at 
ordinary  temperatures,  and  appears  to  owe  this  to  the  presence  of 
phosphorus,  of  which  element  0.5  per  cent,  is  sufficient  materially  to 
dimmish  the  tenacity  of  the  iron.  When  the  iron  is  liable  to  brittleness 
at  a  red  heat,  it  is  termed  red-short  iron,  and  a  very  little  sulphur  is 
sufficient  to  affect  the  quality  of  the  iron  in  this  respect. 

Not  only  may  the  proportions  of  carbon,  silicon,  sulphur,  phosphorus, 
and  manganese  be  supposed  to  affect  the  quality  of  the  iron,  but  the 
state  of  combination  in  which  these  elements  exist  in  the  mass  is  not 
unlikely  to  cause  a  difference.  It  also  appears  certain  that  the  mechani- 
cal structure,  dependent  upon  the  arrangement  of  the  particles  compos- 
ing the  mass  of  metal,  has  at  least  as  much  influence  upon  the  tenacity 
of  the  iron  as  has  its  chemical  composition. 

The  best  bar-iron,  if  broken  slowly,  always  exhibits  a  fibrous  structure, 
the  particles  of  iron  being  arranged  in  parallel  lines.  This  appears  to 
contribute  greatty  to  the  strength  of  the  iron,  for  when  it-  is  wanting, 
and  the  bar  is  composed  of  a  fused  mass  of  crystals,  it  is  weaker  in 
proportion  to  the  size  of  the  crystals.  The  presence  of  phosphorus  is 
said  to  favour  the  formation  of  large  crystals,  and  hence  to  produce 
cold-shortness.  There  is  some  reason  to  believe  that  the  fibrous  is  some- 
times exchanged  for  the  crystalline  texture  under  the  influence  of 
frequent  vibrations,  as  in  the  case  of  railway  axles,  girders  of  suspension- 
bridges,  &c. 


THE   SIEMENS-MARTIN  PROCESS.  409 

Considering  the  difficult  fusibility  of  bar-iron,  it  is  fortunate  that  it 
possesses  the  property  of  being  welded  ;  that  is,  of  being  united  by 
hammering  when  softened  by  heat.  It  is  customary  first  to  sprinkle  the 
heated  bars  with  sand  or  clay  in  order  to  convert  the  superficial  oxide 
of  iron  into  a  liquid  silicate,  which  will  be  forced  out  from  between  them 
by  hammering  or  rolling,  leaving  the  clean  metallic  surfaces  to  adhere. 

221.  Production  of  ingot-iron  (mild  steel). —  In  the  Siemens- Martin  or 
•open-hearth  process  the  pig-iron  is  melted  in  a  saucer-shaped  depression 
made  of  iron  plates  lined  with  ganister,  a  fairly  pure  sand  ;  this  hearth 
is  built  in  a  furnace  which  is  so  constructed  that  a  flame  of  carbon 
monoxide  (producer  gas),  raised  to  a  very  high  temperature  by  the  sys- 
tem of  regenerative  firing  (see  Chemistry  of  Fuel),  plays  across  the 
hearth.  When  the  pigs  have  been  thoroughly  melted,  scraps  of  iron 
plate,  which,  since  they  are  of  no  other  value,  may  be  used  to  dilute  the 
impure  iron,  are  stirred  in,  and  these  are  followed  by  an  appropriate 
quantity  of  iron  oxide,  generally  haematite.  The  oxidation  of  the  im- 
purities in  the  iron  is  effected  in  part  by  the  oxygen  of  the  haematite 
and  in  part  by  the  excess  of  oxygen  in  the  flame  used  to  heat  the  hearth, 
the  temperature  of  which  is  about  1500°  C.  When  the  aspect  of  a  test 
piece  withdrawn  and  hammered  by  the  furnace-man  indicates  that  the 
process  is  complete  (in  8-10  hours),  the  tamping-hole  of  the  hearth  is 
unstopped,  the  metal  run  into  a  ladle,  and  thence  into  ingot-moulds. 

In  this  process  the  silicon  and  phosphorus  are  removed,  chiefly  in  the 
form  of  iron  silicate  and  phosphate,  as  slag,  which  floats  on  the  surface 
of  the  metal,  and  in  order  that  the  complete  removal  of  the  phos- 
phorus may  be  effected  the  oxidation  must  be  carried  sufficiently  far 
to  oxidise  nearly  the  whole  of  the  carbon  in  the  iron,  producing  a 
very  soft  metal.  Since  for  most  purposes  this  product  would  be 
too  soft,  it  is  customary  to  bring  up  the  carbon  content  of  the  metal 
in  the  ladle  by  the  addition  of  a  small  quantity  of  ferro-manganese, 
which  immediately  melts  and  mixes  with  the  charge.  Eerro-manganese 
is  an  alloy  of  iron  and  manganese  (74  per  cent.),  the  presence  of  which 
enables  the  alloy  to  hold  much  carbon  (5  per  cent.).  The  yield  by  this 
process  is  about  95  per  cent,  of  the  iron  charged  into  the  furnace. 

In  the  Bessemer  process  the  molten 
pig-iron  is  run  into  a  converter,  which 
is  a  large  vessel  of  the  shape  shown 
in  Fig.  223.  It  is  made  of  iron  plates 
and  is  lined  with  ganister.  At  the 
bottom  of  the  vessel  there  is  a  number 
of  openings  of  about  ^-inch  in  diameter 
'(A)  through  which  air  is  blown  at  a 
pressure  of  15  or  20  Ibs.  to  the 
square  inch.  The  charge  (about  10 
tons)  having  been  melted  in  a  separate  F1  22 

furnace  is  run  into  the  converter  which  Bessemer's  converting-  vessel, 

is  suspended  on  trunnions  so  that  it 

may  be  turned  into  a  horizontal  position  for  this  purpose,  and  then  erected 
again  into  the  vertical  position.  The  converter  is  previously  heated  by 
a  little  burning  coke,  and  the  blast  is  turned  on  before  the  iron  is 
charged  in  so  that  the  liquid  iron  may  not  run  into  the  air  tubes.  The 
silicon  and  manganese  burn  first  in  the  stream  of  air,  producing  a  very 


410  THE   BESSEMER  PEOCESS. 

high  temperature,  then  the  carbon  is  converted  into  carbon  monoxide,, 
which  burns  with  a  long  name  at  the  mouth  of  the  converter,  and  a 
little  of  the  iron  is  burnt  to  oxide,  which  forms  a  slag  with  the  silica, 
and  is  carried  up  as  a  froth  to  the  surface  of  the  liquid  iron.  The  blast 
of  air,  or  blow,  is  continued  for  about  twenty  minutes,  when  the  dis- 
appearance of  the  flame  of  CO  indicates  the  completion  of  the  process  ;. 
but  the  remaining  purified  iron  is  not  pasty  as  in  the  puddling-furnace, 
being  retained  in  a  perfectly  liquid  condition  by  the  high  temperature 
(1580°  C.)  resulting  from  the  combustion  of  the  silicon  and  manganese, 
so  that  the  metal  may  be  run  out  into  ingot-moulds  by  tilting  the  con- 
verter. As  in  the  case  of  the  Siemens- Martin  process,  the  desired 
hardness  is  imparted  to  the  metal  by  the  addition  of  ferro-manganese 
to  the  converter  just  before  the  iron  is  poured.  The  yield  is  about  85 
per  cent. 

In  the  original  Bessemer  process  the  converter  was  lined,  as  described 
above,  with  ganister  (sand) ;  this  rendered  the  method  applicable  only 
to  such  grades  of  pig-iron  as  were  fairly  free  from  phosphorus,  because 
the  most  efficient  means  of  removing  this  element,  namely,  the  admix- 
ture of  the  strong  base  lime  with  the  charge,  was  impossible,  on  account 
of  the  ease  with  which  lime  combines  with  silica,  destroying  the  lining 
of  the  furnace.  It  is  now  customary  to  line  converters  which  are  to  be 
used  for  phosphoric  pig  with  a  basic  material,  namely,  a  mixture  of 
magnesia  and  lime,  made  by  calcining  dolomite.  This  basic  Bessemer- 
process  is  conducted  as  described  above,  save  that  lime  to  the  extent  of 
15-20  per  cent,  of  the  charge  of  iron  is  thrown  into  the  converter 
before  the  iron  is  run  in.  This  lime  combines  with  the  P2O5  produced 
by  the  oxidation  of  the  phosphorus,  as  well  as  with  the  silica  produced 
by  the  oxidation  of  the  silicon^  The  basic  slag  formed  in  this  way  is 
useful  as  a  manure,  for  the  sake  of  its  phosphorus  (see  Chemistry  of 
Vegetation).  The  following  percentage  compositions  illustrate  the  effect 
of  the  two  processes  : — 

C.  Si.  Mn.  S.  P. 


Acid  Bessemer  pig 

After  blow  . 

After  ferro-manganese 

Basic  Bessemer  pig     . 

After  blow  . 

After  ferro-manganese 


3.57  2.26  0.04  o.io  0.07 

0.19  trace  trace  o.io  0.07 

0.37  trace  0.54  0.09  0.05 

3.57  1.70  0.71  0.06  1.57 

trace  —  trace  0.05  0.08 

o.i  2  0.03  0.27  0.04  0.02 


Properties  of  ingot  iron  (mild  steel). — Owing  to  the  fact  that  bar-iron 
is  not  fused  whilst  ingot  iron  is  completely  fused  in  the  process  of  its 
manufacture,  the  main  difference  between  these  two  forms  of  iron  is  that 
ingot  iron  does  not  show  the  fibrous  structure  of  bar-iron,  and  is,  more- 
over, free  from  particles  of  intermixed  slag.  Ingot  iron  is  liable  to  the 
same  defects  as  bar-iron,  and  these  are  due  to  the  same  causes. 

222.  Manufacture  of  tool-steel  (hard  steel).— Steel  differs  from  bar- 
iron  in  possessing  the  property  of  becoming  much  harder  when  heated 
to  redness,  and  then  suddenly  cooled  by  being  plunged  into  water. 
Perfectly  pure  iron  obtained  by  the  electrotype  process  is  not  hardened 
by  sudden  cooling ;  but  all  bar-iron  which  contains  carbon  exhibits 
this  property  in  a  greater  or  smaller  degree  according  to  the  proportion 
of  carbon  present.  It  does  not  become  decidedly  steely,  however,  until  the 


CEMENTATION.  411 

carbon  amounts  to  0.25  per  cent.  The  term  steel  was  formerly  applied 
only  to  iron  containing  enough  carbon  (not  less  than  0.75  per  cent.)  to 
harden  it  sufficiently  for  cutting  implements,  but  all  iron  containing 
more  than  0.2  per  cent,  of  carbon  is  now  referred  to  as  (mild)  steel.  The 
hardest  steel  contains  about  1.2  per  cent,  of  carbon,  and  when  the  pro- 
portion reaches  1.5  per  cent,  the  metal  begins  to  assume  the  properties 
of  white  cast  iron.  Bar-iron  may,  therefore,  be  converted  into  hard  steel 
by  the  addition  of  about  i  per  cent,  of  carbon,  and,  conversely,  cast 
iron  is  converted  into  mild  steel  when  the  quantity  of  carbon  contained 
in  it  is  reduced  to  from  0.2  to  0.5  per  cent.* 

Since  the  presence  of  even  the  small  quantities  of  impurities,  other 
than  carbon,  which  cannot  be  eliminated  by  the  above  processes  for 
making  ingot  iron  are  fatal  to  the  best  hard  steel,  this  material  must 
be  made  from  the  best  bar-iron. 

The  process  is  known  as  cementation,  the  bars  of  iron  being  imbedded 
in  charcoal  and  exposed  for  several  days  to  a  high  temperature. 

The  operation  is  effected  in  large  chests  of  firebrick  or  stone,  about 
10  or  12  feet  long  by  3  feet  wide  and  3  feet  deep. 


Fig.  224. — Furnace  for  converting  bar-iron  into  steel. 

Two  of  these  chests  are  built  into  a  dome-shaped  furnace  (converting  - 
furnace,  Fig.  224),  so  that  the  flame  may  circulate  round  them,  and  the 
furnace  is  surrounded  with  a  conical  jacket  of  brickwork  in  order  to 
allow  a  steady  temperature  to  be  maintained  in  it  for  some  days.  The 
charcoal  is  ground  so  as  to  pass  through  a  sieve  of  J-inch  mesh,  and 
spread  in  an  even  layer  upon  the  bottom  of  the  chests.  Upon  this  the 
bars  of  iron,  which  must  be  of  the  best  quality,  are  laid  in  regular 
order,  a  small  interval  being  left  between  them,  which  is  afterwards 
filled  in  with  the  charcoal  powder,  with  a  layer  of  which  the  bars  are 
now  covered  ;  over  this  more  bars  are  laid,  then  another  layer  of  char- 
coal, and  so  on  until  the  chest  is  filled.  Each  chest  holds  5  or  6  tons 
of  bars.  One  of  the  bars  is  allowed  to  project  through  an  opening  in 
the  end  of  the  chest,  so  that  the  workmen  may  withdraw  it  from  time 
to  time  and  judge  of  the  progress  of  the  operation.  The  whole  is 
covered  in  with  a  layer  of  about  6  inches  of  damp  clay  or  sand,  or 
grinders  waste  (silica  and  oxide  of  iron). 

*  Many  metallurgists  are  of  opinion  that  manganese  has  an  influence  similar  to  that  of 
carbon  in  converting  iron  into  steel. 


412  CEMENTATION, 

The  fire  is  carefully  and  gradually  lighted,  lest  the  chests  should  be 
split  by  too  sudden  application  of  heat,  and  the  temperature  is  eventually 
raised  to  about  the  fusing-point  of  copper  (2000°  F.,  1090°  C.),  at 
which  it  is  maintained  for  a  period  varying  with  the  quality  of  steel 
which  it  is  desired  to  obtain.  Six  or  eight  days  suffice  to  produce 
steel  of  moderate  hardness ;  but  the  process  is  continued  for  three 
or  four  days  longer  if  very  hard  steel  be  required.  The  fire  is 
gradually  extinguished,  so  that  the  chests  are  about  ten  days  in  cooling 
down. 

On  opening  the  chests  the  bars  are  found  to  have  suffered  a  remark- 
able change  both  in  their  external  appearance  and  internal  structure. 
They  are  covered  with  large  blisters,  obviously  produced  by  some  gaseous 
substance  raising  the  softened  surface  of  the  metal  in  its  attempt  to 
escape.  It  is  conjectured  that  the  blisters  are  caused  by  carbonic  oxide 
produced  by  the  action  of  the  carbon  upon  particles  of  slag  accidentally 
present  in  the  bar.  On  breaking  the  bars  across,  the  fracture  is  found 
to  have  a  finely  granular  structure,  instead  of  the  fibrous  appearance 
exhibited  by  bar-iron.  Chemical  analysis  shows  that  the  iron  has  com- 
bined with  about  j  per  cent,  of  carbon,  and  the  most  remarkable  part 
of  the  result  is  that  this  carbon  is  not  only  found  in  the  external  layer 
of  iron,  which  has  been  in  direct  contact  with  the  heated  charcoal,  but 
is  also  present  in  the  very  centre  of  the  bar.  It  is  this  transmission  of 
the  solid  carbon  through  the  solid  mass  of  iron  which  is  implied  by  the 
term  cementation.  The  chemistry  of  the  process  probably  consists  in  the 
formation  of  carbonic  oxide  from  the  small  quantity  of  atmospheric  oxy- 
gen in  the  chest,  and  the  removal  of  one-half  of  the  carbon  from  this 
carbonic  oxide,  by  the  iron,  which  it  converts  into  steel,  leaving  carbonic 
acid  gas  (200  —  C  =  C02)  to  be  re-converted  into  carbonic  oxide  by  taking 
up  more  carbon  from  the  charcoal  (C02  +  C  =  200),  which  it  transfers 
again  to  the  iron.  Experiment  has  shown  that  soft  iron  is  capable  of 
absorbing  mechanically  4.15  volumes  of  carbonic  oxide  at  a  low  red 
heat,  so  that  the  action  of  the  gas  upon  the  metal  may  occur  through- 
out the  substance  of  the  bar.  The  carbonic  oxide  is  retained  unaltered 
by  the  iron  after  cooling,  unless  the  bar  is  raised  to  the  temperature 
required  for  the  production  of  steel. 

The  blistered  steel  obtained  by  this  process  is,  as  would  be  expected, 
far  from  uniform  either  in  composition  or  in  texture  ;  some  portions  of 
the  bar  contain  more  carbon  than  others,  and  the  interior  contains 
numerous  cavities.  In  order  to  improve  its  quality  it  is  subjected  to  a 
process  of  fagoting  similar  to  that  mentioned  in  the  case  of  bar-iron ; 
the  bars  of  blistered  steel,  being  cut  into  short  lengths,  are  made  up 
into  bundles,  which  are  raised  to  a  welding  heat,  and  placed  under  a 
tilt-hammer  weighing  about  2  cwt.,  which  strikes  two  or  three  hundred 
blows  in  a  minute ;  in  this  way  the  several  bars  are  consolidated  into 
one  compound  bar,  which  is  then  extended  under  the  hammer  till  of  the 
required  dimensions.  The  bars,  before  being  hammered,  are  sprinkled 
with  sand,  which  combines  with  the  oxide  of  iron  upon  the  surface,  and 
forms  a  vitreous  layer  which  protects  the  bar  from  further  oxidation. 
The  steel  which  has  been  thus  hammered  is  much  denser  and  more 
uniform  in  composition  ;  its  tenacity,  malleability,  and  ductility  are 
greatly  increased,  and  it  is  fitted  for  the  manufacture  of  shears,  files, 
and  other  tools.  It  is  commonlv  known  as  shear  steel.  Double  shear 


PROPERTIES   OF   STEEL, 


413 


steel  is  obtained  by  breaking  the  tilted  bars  in  two,  and  welding  these 
into  a  compound  bar. 

The  best  variety  of  steel,  however,  which  is  perfectly  homogeneous  in 
composition,  is  that  known  as  cast  steel  or  crucible  steel,  to  obtain  which 
about  50  Ibs.  of  blistered  steel  are  broken  into  fragments,  and  fused  in 
a  fireclay  or  plumbago  crucible,  heated  in  a  wind-furnace,  the  surface  of 
the  metal  being  protected  from  oxidation  by  a  little  glass  melted  upon 
it.  The  fused  steel  is  cast  into  ingots,  several  crucibles  being  emptied 
simultaneously  into  the  same  mould. 

Cast  steel  is  far  superior  in  density  and  hardness  to  shear  steel,  but  since  it  is 
exceedingly  brittle  at  a  red  heat,  great  care  is  necessary  in  forging  it.  It  has  been 
found  that  the  addition,  to  100  parts  of  the  cast  steel,  of  I  part  of  a  mixture  of 
charcoal  and  oxide  of  manganese,  produces  a  fine-grained  steel  which  admits  of 
being  cast  on  to  a  bar  of  wrought  iron  in  the  ingot-mould,  so  that  the  tenacity  of 
the  latter  may  compensate  for  the  brittleness  of  the  steel  when  the  compound  bar 
is  forged,  the  wrought  iron  forming  the  back  of  the  implement,  and  the  steel  its 
cutting  edge.  Manganese  has  a  stronger  attraction  than  iron  has  for  oxygen  and 
sulphur  ;  hence  it  would  decompose  any  sulphide  or  oxide  of  iron  present  in  the 
metal,  and  carry  those  elements  into  the  slag.  The  soundness  of  steel  ingots  is  often 
impaired  by  minute  bubbles  or  blow-holes,  formed  by  CO  or  H,  the  former  produced 
by  the  action  of  the  carburised  iron  on  a  portion  of  oxidised  iron,  the  latter  by  the 
decomposition  of  moisture  in  the  air.  To  obviate  this,  the  steel  is  sometimes  sub- 
jected to  a  pressure  of  several  tons  on  the  square  inch,  while  it  is  solidifyin^ 
(WhitwortVs  steel). 

Some  small  instruments,  such  as  keys,  gun-locks,  &c.,  which  are  exposed  to  con- 
siderable wear  and  tear  by  friction,  and  require  the  external  hardness  of  steel  without 
its  brittleness,  are  forged  from  bar-iron,  and  converted  externally  into  steel  by  the 
process  of  case-hardening,  which  consists  in  heating  them  in  contact  with  some 
substance  containing  carbon  (such  as  bone-dust,  yellow  prussiate  of  potash,  &c. ),  and 
afterwards  chilling  in  water.  A  process  which  is  the  reverse  of  this  is  adopted  in 
order  to  increase  the  tenacity  of  stirrups,  bits,  and  similar  articles  made  of  cast  iron  ; 
by  heating  them  for  some  hours  in  contact  with  oxide  of  iron  or  manganese,  their 
carbon  and  silicon  are  removed  in  the  forms  of  carbonic  oxide  and  silica,  and  they 
become  converted  into  malleable  cast  iron.  A  similar  effect  is  produced  by  heating 
in  sand,  the  air  between  its  grains  affording  the  required  oxygen. 

Properties  of  steel. — After  the  steel  has  been  forged  into  the  shape  of 
any  implement,  it  is  hardened  by  being  heated  to  redness,  and  suddenly 
chilled  in  cold  water,  or  oil,*  or  mercury.  It  can  thus  be  rendered 
nearly  as  hard  as  diamond,  at  the  same  time  increasing  slightly  in 
volume  (sp.  gr.  of  cast-steel  7.93  ;  after  hardening,  7.66),  and  consider- 
ably in  tensile  strength,  but  diminishing  in  ductility.  If  the  hardened 
steel  be  heated  to  redness  and  allowed  to  cool  slowly,  it  is  again  con- 
verted into  soft  steel,  but  by  heating  it  to  a  temperature  short  of  a  red 
heat,  its  hardness  may  be  proportionally  reduced.  This  is  taken  advan- 
tage of  in  annealing  the  steel  or  "  letting  it  down  "  to  the  proper 
temper.  The  very  hardest  steel  is  almost  as  brittle  as  glass,  and  totally 
unfit  for  any  ordinary  use  ;  but  by  heating  it  to  a  given  temperature 
and  allowing  it  to  cool,  its  elasticity  may  be  increased  to  the  desired 
extent,  without  reducing  its  hardness  below  that  required  for  the  im- 
plement in  hand.  On  heating  a  steel  blade  gradually  over  a  flame,  it 
will  acquire  a  light  yellow  colour  when  its  temperature  reaches  430°  F., 
from  the  formation  of  a  thin  film  of  oxide ;  as  the  temperature  rises, 
the  thickness  of  the  film  increases,  and  at  470°  a  decided  yellow  colour 
is  seen,  which  assumes  a  brown  shade  at  490°,  becomes  purple  at  520°, 

*  Chilling  in  oil  cools  the  steel  less  suddenly,  on  account  of  the  lower  specific  heat  of  oil, 
and  therefore  does  not  render  it  so  hard  and  brittle.  It  is  often  spoken  of  as  toughening. 


414 


THE   TEMPEE   OF   STEEL, 


and  blue  at  550°.  At  a  still  higher  temperature  the  film  of  oxide 
becomes  so  thick  as  to  be  black  and  opaque.  Steel  which  has  been 
heated  to  430°,  and  allowed  to  cool  slowly,  is  said  to  be  tempered  to  the 
yellow,  and  is  hard  enough  to  take  a  very  fine  cutting  edge ;  whilst,  if 
tempered  to  the  blue,  at  550°,  it  is  too  soft  to  take  a  very  keen  edge,  but 
has  a  very  high  degree  of  elasticity.  The  following  table  indicates  the 
tempering  heats  for  various  implements : 

Tempering  of  Steel. 


Temperature,  F. 

Colour. 

Implements  thus  Tempered. 

430°  to  450° 
470°  •         . 
490°  . 
510°  .          . 
520°  . 
530°  to  570° 

Straw-yellow 
Yellow. 
Brown-yellow  ' 
Brown-purple 
Purple  . 
Blue     . 

Kazors,  lancets. 
Penknives. 
Large  shears  for  cutting  metal. 
Clasp-knives. 
Table-knives. 
Watch-springs,  sword-blades. 

If  a  knife-blade  be  heated  to  redness  its  temper  is  spoilt,  for  it  is  con- 
verted into  soft  steel.  In  general  the  steel  implements  are  ground 
after  being  tempered,  so  that  they  are  not  seen  of  the  colours  mentioned 
above,  except  in  the  case  of  watch-springs.  A  steel  blade  may  be  easily 
distinguished  from  iron  by  placing  a  drop  of  diluted  nitric  acid  upon  it, 
when  a  dark  stain  is  produced  upon  the  steel,  from  the  separation  of 
the  carbon. 

According  to  modern  views  the  change  which  occurs  in  the  character 
of  steel  during  the  process  of  hardening,  is  primarily  due  to  the  exist- 
ence of  two  allotropic  forms  of  iron,  which  are  distinguished  as  a-iron 
and  /3-iron,  the  former  being  present  in  soft  iron,  the  latter  in  hard 
iron. 

When  pure  iron  is  allowed  to  cool  slowly  from  a  temperature  near  its  melting- 
point,  it  is  noticed  that  at  864°  C.  the  rate  at  which  the  iron  cools  undergoes  a 
change,  and  that  the  temperature  is  four-fold  as  long  a  time  in  falling  from 
864°  C.  to  852°  C.,  as  it  is  in  falling  through  an  equal  number  of  degrees  during  the 
whole  of  the  rest  of  its  cooling.  The  mean  of  these  temperatures,  858°  C.,  is  called 
the  critical  temperature  or  transition-point  of  iron.  It  will  be  obvious  that  this 
delay  in  cooling  can  only  be  due  to  an  evolution  of  heat  by  the  iron,  which  must 
indicate  some  profound  change  in  the  nature  of  the  metal  at  this  temperature. 
Thus,  iron  below  858°  C.  must  be  different  in  nature  from  the  metal  above  this 
temperature.  Iron  below  852°  C.  is  said  to  be  in  the  ft-condition  (a-ferrite),  whilst 
above  864°  C.  it  is  in  the  /3-condition  (j3-ferrite). 

When  the  polished  surface  of  a  sample  of  iron  or  steel  is  etched  with  a  solution  of 
iodine  in  potassium  iodide  or  of  hydrochloric  acid  in  alcohol  and  viewed  by  reflected 
light  through  the  microscope,  it  is  possible  to  obtain  some  idea  of  the  structure  of 
the  metal.  Examination  in  this  manner  of  many  specimens  of  different  grades  has 
led  to  the  conclusion  that  there  are  three  distinct  forms  in  which  the  carbon  in  iron 
exists,  namely,  the  compound  Fe3C,  called  cementite,  the  solid  solution  of  carbon  in 
iron,  called  martensite,  and  pet-lite,  a  mixture  of  cementite  and  iron  in  constant 
proportion.  Of  these  forms  martensite  is  that  characteristic  of  steel  which  has  been 
hardened  by  quenching  from  a  temperature  of  about  1000°  C.  ;  the  structure  of  such 
metal  is  homogeneous  and  crystalline,  and  as  the  same  appearance  is  to  be  noted  in 
hardened  steels  of  different  carbon  content  no  compound  of  carbon  and  iron  can  well 
be  supposed  to  exist  in  this  case. 

When  a  steel  containing  0.8  per  cent,  of  carbon  is  slowly  cooled,  there  is  an  arrest 
in  the  temperature  at  670°  C.  similar  to  that  occurring  at  858°  C.  in  pure  iron. 


DIRECT  EXTRACTION   OF   IRON.  415 

This  arrest  corresponds  with  the  transformation  of  the  mass  into  perlite,  showing 
under  the  microscope  an  etched  surface  different  from  that  of  hardened  steel,  con- 
stituting, in  fact,  unhardened  steel.  Thus  the  hardening  of  steel  may  be  supposed 
to  consist  in  cooling  /3-iron,  which  has  carbon  dissolved  in  it,  so  quickly  that  the 
mass  remains  in  this  form  (martensite)  and  is  not  transformed  into  perlite. 

When  iron  containing  more  than  0.8  per  cent,  of  carbon  is  cooled  there  are  two 
arrests  noticed,  the  one  above  670°  C.  and  varying  with  the  percentage  of  carbon, 
and  the  other  at  670°  C.  The  first  corresponds  with  the  separation  of  cementite, 
Fe3C,  from  the  solution  of  carbon  in  iron,  until  the  solution  contains  0.8  per  cent, 
of  carbon,  whereupon  perlite  separates  at  670°  C.  The  etched  surface  appears  as  a 
mass  of  perlite  with  flakes  of  cementite  embedded  therein. 

When  less  than  0.8  per  cent,  of  carbon  is  present  there  are  also  two  arrests  in  the 
cooling,  the  first  corresponding  with  the  separation  of  ct-iron  while  the  second  is  at 
670°  C.,  as  before,  and  is  due  to  the  separation  of  perlite.  The  a-iron  is  malleable 
iron. 

The  following  chemical  observations,  which  are  much  older  than  the  foregoing 
physical  demonstration,  fully  conform  with  the  theory  at  present  held.  If  hardened 
steel  be  dissolved  in  dilute  HC1  or  H2S04,  nearly  the  whole  of  the  carbon  is  evolved 
as  hydrocarbons,  but  when  the  temper  has  been  let  down,  so  that  the  steel  is  com- 
pletely softened,  the  carbon  is  left,  on  dissolution  of  the  metal  in  acid,  as  a  dark 
powder  consisting  of  a  carbide  of  iron,  Fe3C.  Steel  which  has  been  partially  tempered 
in  the  manner  described  above,  is  found  to  contain  the  carbon  both  in  the  invisible 
form,  which  yields  hydrocarbons  when  the  metal  is  dissolved  in  acids,  and  in  the 
form  of  carbide  disseminated  as  grey  scales  throughout  the  mass. 

Manganese,  nickel,  chromium,  and  tungsten,  respectively,  in  steel  appear  to  make 
it  hard  however  it  is  cooled,  and  are  used  for  making  specially  hard  steel.  Man- 
ganese steel  containing  12  per  cent,  of  that  metal  is  non-magnetic,  until  it  has  been 
heated  for  some  hours  at  500-600°  C.,  when  it  becomes  magnetic  ;  if  it  then  be 
heated  above  800°  C.  and  quickly  cooled  it  again  becomes  non-magnetic.  Steel 
containing  25  per  cent,  of  nickel  is  magnetic  when  heated  above  500°  C.  and  cooled 
slowly. 

223.  Direct  extraction  of  wrought  iron  from  the  ore. — Where  very  rich 
and  pure  ores  of  iron,  such  as  haematite  and  magnetic  iron  ore,  are 
obtainable,  and  fuel  is  abundant,  the  metal  is  sometimes  extracted  with- 
out being  converted  into  cast  iron.  It  is  probable  that  the  iron  of  anti- 
quity was  extracted  in  this  way,  for  it  is  doubtful  whether  cast  iron  was 
known  to  the  ancients,  and  the  slag  left  from  old  ironworks  does  not 
indicate  the  use  of  any  flux.  For  such  direct  extraction  the  ore  is 
heated  in  a  crucible  with  charcoal,  the  combustion  being  urged  by  a 
blast  of  air  from  a  tuyere  pipe.  The  spongy  mass  of  bar  iron  thus 
obtained  is  hammered  as  in  the  puddling  process. 

The  wrought  iron  produced 
by  this  process  always  contains 
a  larger  proportion  of  carbon 
than  puddled  iron,  and  is  there- 
fore somewhat  steely  in  charac- 
ter. In  India  the  native 
smelters  produce  iron  or  steel 
at  will  by  this  process. 

224.  Extraction  of  iron  on  the 
small  scale. — In  the  laboratory,  iron  Fi8"-  225- — Fletcher's  injector  furnace, 

may  be  extracted  from  hcematite  in 

the  following  manner  :  A  fireclay  crucible,  about  3  inches  high,  is  filled  with  char- 
coal powder,  rammed  down  in  successive  layers  ;  a  smooth  conical  cavity  is  scooped 
in  the  charcoal,  and  a  mixture  of  8  grams  red  haematite,  2  grams  chalk,  and  2  grams 
pipeclay,  is  introduced  into  it ;  the  mixture  is  covered  with  a  layer  of  charcoal,  and 
a  lid  placed  on  the  crucible,  which  is  heated  in  a  Fletcher's  furnace  (Fig.  225)  for 
about  half  an  hour.  On  breaking  the  cold  crucible  a  button  of  cast  iron  will  be 
obtained. 


41 6  CEfEMICAL  PROPERTIES   OF   IRON, 

Nearly  pure  iron  may  be  prepared  by  fusing  the  best  wire-iron  with  about  one- 
fifth  of  its  weight  of  pure  ferric  oxide,  to  oxidise  the  carbon  >  and  silicon  which  it 
contains.  Some  powdered  green  glass,  perfectly  free  from  lead,  must  be  employed 
as  a  flux,  and  the  crucible  (with  its  cover  well  cemented  on  with  fireclay)  exposed 
for  an  hour  to  a  very  high  temperature.  A  silvery  button  of  iron  will  then  be 
obtained. 

225.  Chemical  properties  of  iron. — Pure  iron  is  prepared  by  electro- 
lysis.    Its  sp.  gr.  is  7.9  and  it  melts  at   1600°  C.     In  its  ordinary  con- 
dition iron  is  unaffected  by  perfectly  dry  air,  but  in  the   presence  of 
moisture  and  carbonic  acid  gas  it  is  gradually  converted  into  hydrated 
ferric  oxide  (2Fe2O3.3H20)  or  rust*     The  water  is  decomposed,  and 
ferrous  carbonate  formed  (Fe  +  H20  +  002  =  FeC03  +  H2) ;  this  is  dis- 
solved  by  the  carbonic  acid  present,  and  the  solution  rapidly  absorbs 
oxygen  from  the  air,  depositing  the  ferric  oxide  in  a  hydrated  state  ; 
2FeCO3  +  0  =  Fe203  +  2CO2.     When  iron  nails  are  driven  into  a  new 
oaken  fence,  a  black  streak  will  soon  be  observed  descending  from  each 
nail,  caused  by  the  formation  of  tannate  of  iron  (ink)  by  the  action  of 
the  tannic  acid  in  the  wood  upon  the  solution  of   carbonate  of  iron 
formed  from  the  nails.     The  diffusion  of  iron-mould  stains  through  the 
fibre  of  wet  linen  by  contact  with  a  nail,  is  also  caused  by  the  formation 
of  solution  of  carbonate  of  iron.     The  iron  in  chalybeate  waters  is  also 
generally  present  in  the  form  of  carbonate  dissolved  in  carbonic  acid,, 
and  hence  the  rusty  deposit  which  is  formed  when  they  are  exposed  to 
the  air.    Iron  does  not  rust  in  water  containing  a  free  alkali,  or  alkaline 
earth,  or  an  alkaline  carbonate. 

Concentrated  H2S04  and  HN03  do  not  act  upon  iron  at  the  ordinary 
temperature,  though  they  dissolve  it  rapidly  when  diluted.  Even  when 
boiling,  strong  sulphuric  acid  acts  upon  it  but  slowly.  When  iron  has- 
been  immersed  in  strong  nitric  acid  (sp.  gr.  1.45),  it  is  found  to  be 
unattackedf  when  subsequently  placed  in  HN03  of  sp.  gr.  1.35,  unless- 
previously  wiped  ;  it  is  then  said  to  have  assumed  the  passive  state.  If 
iron  wire  be  placed  in  HNO3  of  sp.  gr.  1.35,  it  is  attacked  immediately  ; 
but  if  a  piece  of  gold  or  platinum  be  made  to  touch  it  beneath  the  acid, 
the  iron  assumes  the  passive  state,  and  the  action  ceases  at  once.  A 
state  similar  to  this,  the  cause  of  which  has  not  yet  been  satisfactorily 
explained,  is  sometimes  assumed  by  the  other  metals,  though  in  a  less 
marked  degree.  In  the  case  of  iron  it  has  been  attributed  to  the  forma- 
tion of  a  coating  of  the  magnetic  oxide,  which  is  sparingly  soluble  in 
strong  HN03. 

Ferrum  redactum  is  iron  in  powder  obtained  by  reducing  Fe203  with 
hydrogen  at  a  red  heat  in  an  iron  tube.  It  always  contains  some 
Fe304. 

226.  Oxides  of  iron.. — Three  compounds  of  iron  with  oxygen  are 
known  in  the  separate  state  ;  FeO,  Fe3O4,  Fe2O3. 

Ferrous  oxide,  or  protoxide  of  iron,  FeO,  is  obtained  by  heating  ferric  oxide  to 
500°  C.  in  dry  hydrogen;  Fe203  +  H2  =  H20  +  2FeO.  It  is  obtained  as  a  grey 
powder,  which  readily  absorbs  O  from  the  air,  taking  fire  and  becoming  Fe304.  It 
is  a  basic  oxide,  yielding  ferrous  salts.  In  the  finely  divided  state  it  decomposes 
water. 

Ferrous  hydroxide,  Fe(OH)2,  is  precipitated  by  alkalies  from  the  ferrous  salts. 
When  pure  it  forms  a  white  precipitate,  but  if  air  be  present  it  becomes  green  from 

*  Most  samples  of  rust  are  magnetic,  indicating  the  presence  of  the  magnetic  oxide, 
f  It  is  doubtful  whether  the  iron  ever  remains  quite  unattacked,  although  no  gas  is 
evolved. 


OXIDES   OF   IRON. 


417 


the  production  of  ferroso-ferric  oxide,  and  ultimately  brown  ferric  hydroxide. 
These  changes  are  best  seen  when  potash  or  ammonia  is  added  to  the  ferrous 
salt  obtained  by  shaking  iron  turnings  or  filings  with  a  strong  solution  of 
sulphurous  acid.  This  disposition  of  the  ferrous  hydroxide  to  absorb  oxygen  is 
turned  to  advantage  when  a  mixture  of  ferrous  sulphate  with  lime  or  potash 
is  employed  for  converting  blue  into  white  indigo. 

Ferric  oxide,  or  peroxide  of  iron,  Fe203,  occurs  as  specular  iron  ore  in 
six-sided  crystals,  and  in  haematite,  as  already  noticed  among  the  ores  of 
iron,  and  has  also  been  referred  to  as  occurring  in  commerce  under  the 
names  of  colcothar,  jewellers  rouge,  and  Venetian  red,  which  are  ob- 
tained by  the  calcination  of  the  green  sulphate  of  iron;  2Fe!304  — 
Fe203  +  SO.,  +  S03.  The  ferric  hydroxide  obtained  by  decomposing  a 
solution  of  ferric  chloride  with  an  alkali,  forms  a  brown  gelatinous  pre- 
cipitate, which  is  easily  dissolved  by  acids.  When  freshly  precipitated 
and  well  washed  it  dissolves  in  a  solution  of  ferric  chloride,  forming  a 
basic  chloride  which  by  dialysis  is  slowly  decomposed,  HC1  passing 
through  the  dialyser  and  a  blood-red  colloidal  solution  of  Fe(OH)3  being 
left  in  the  dialyser.  When  dried  at  100°  C.,  the  hydroxide  becomes 
2Fe203.H2O.  If  a  hot  solution  of  a  ferric  salt  be  precipitated  by  an  alkali, 
and  the  precipitate  dried  over  sulphuric  acid,  it  becomes  Fe2(OH)6.Fe203, 
which  is  the  composition  of  iron-rust  and  of  some  brown  haematites. 
When  either  of  the  hydroxides  is  heated  to  dull  redness,  it  exhibits  a 
sudden  glow,  and  is  converted  into  a  modification  of  Fe2O3,  which  is 
dissolved  with  great  difficulty  by  acids,  although  it  has  the  same  com- 
position as  the  soluble  form  which  has  not  been  strongly  heated. 
When  the  ferric  oxide  is  heated  to  whiteness,  it  loses  oxygen,  and  is 
converted  into  magnetic  oxide  of  iron;  3Fe203=  2Fe3O4  +  O.  Existing 
as  it  does  in  all  soils,  ferric  oxide  is  believed  to  fulfil  the  purpose  of 
oxidising  the  organic  matter  in  the  soil,  and  converting  its  carbon  into 
carbon  dioxide,  to  be  absorbed  by  the  plant :  the  ferric  oxide  being  thus 
reduced  to  ferrous  oxide,  which  is  oxidised  by  the  air,  and  fitted  to 
perform  again  the  same  office.  Ferric  oxide,  like  alumina,  is  a  weak 
base,  and  even  exhibits  some  tendency  to  play  the  part  of  an  acid 
towards  strong  bases,  though  not  in  so  marked  a  degree  as  alumina. 
When  heated  in  a  stream  of  H  or  CO,  it  yields  Fe304  at  350°  C.,  pyro- 
phoric  FeO  at  500°  C.,  and  metallic  iron  at  from  700°  to  800°  C. 

Magnetic  or  black  oxide  of  iron,  or  magnetite,  Fe3O4,  is  generally 
regarded  as  a  compound  of  ferrous  oxide  with  ferric  oxide  (FeO.Fe803), 
a  view  which  is  confirmed  by  the  occurrence  of  a  number  of  minerals 
having  the  same  crystalline  form  as  the  native  magnetic  oxide  of  iron,  in 
which  the  iron,  or  part  of  it,  is  displaced  by  other  metals.  Thus, 
spinelle  is  MgO.Al203;  FranJdinite,  ZnO,Fe203;  chrome-iron  ore, 
FeO.Cr,03 ;  pleonaste,  MgO.Fe203 ;  Gahnite,  ZnO.Al203.  The  natural 
magnetic  oxide  was  mentioned  among  the  ores  of  iron,  and  this  oxide 
has  been  seen  to  be  the  result  of  the  action  of  air  or  steam  upon  iron  at 
a  high  temperature.  The  hydrated  magnetic  oxide  of  iron  (F3e04.H20) 
is  obtained  as  a  black  crystalline  powder  by  mixing  i  molecule  of  ferrous 
sulphate  with  i  molecule  of  ferric  sulphate,  and  pouring  the  mixture 
into  a  slight  excess  of  solution  of  ammonia,  which  is  afterwards  boiled 
with  it.  Magnetic  oxide  of  iron,  when  acted  upon  by  acids,  yields 
mixtures  of  ferrous  and  ferric  salts,  so  that  it  is  not  an  independent 
basic  oxide. 

The  very  stable   character   of  Fe304  has   led  to  its  application  for 

2  D 


4l8  GEEEN  VITEIOL. 

protecting  iron  from  rust.  When  superheated  steam  is  passed  over  the 
red-hot  metal,  a  very  dense  strongly  adherent  film  of  Fe3O4  is  produced, 
which  effectually  protects  the  metal  (Barff's  process).  A  similar  coat- 
ing is  produced  by  the  action  of  a  mixture  of  air  and  carbonic  acid  gas 
(Bower's  process}. 

Ferric  acid,  H2Fe04,  has  not  been  obtained  in  the  free  state,  but  some 
of  its  salts  are  known.* 

When  iron  filings  are  strongly  heated  with  nitre,  and  the  mass  treated  with  a 
little  water,  a  fine  purple  solution  of  potassium  ferrate  is  obtained.  A  better 
method  of  preparing  this  salt  consists  in  suspending  I  part  of  freshly  precipitated 
ferric  hydrate  in  50  parts  of  water,  adding  30  parts  of  solid  potassium  hydrate 
and  passing  chlorine  till  a  slight  effervescence  commences  ;  Fe203  +  C]6  +  ioKOH  = 
6KCl  +  2(K2Fe04)-t-5H20  ;  the  ferrate  forms  a  black  precipitate,  being  insoluble 
in  the  strongly  alkaline  solution,  though  it  dissolves  in  pure  water  to  form  a 
purple  solution,  which  is  decomposed  even  by  dilution,  oxygen  escaping,  and 
hydrated  ferric  oxide  being  precipitated.  A  similar  decomposition  happens 
on  boiling  a  strong  solution,  or  on  adding  an  acid  with  a  view  to  liberate  the 
ferric  acid.  The  ferrates  of  barium,  strontium,  and  calcium  are  obtained  as  fine 
red  precipitates  when  solutions  of  their  salts  are  mixed  with  potassium  ferrate. 

As  a  lecture  experiment,  the  ferrate  is  readily  prepared  by  dissolving  a  frag- 
ment of  KOH  in  a  little  solution  of  Fe2Cl6,  adding  a  few  drops  of  bromine,  and 
gently  heating.  On  dissolving  the  cold  mass  in  water,  a  fine  red  solution  is 
obtained,  which  gives  a  red  granular  precipitate  with  Ba012. 

The  pink  solution  obtained  by  boiling  some  samples  of  chloride  of  lime  with 
water  contains  calcium  ferrate,  and  gives  a  pink  precipitate  with  BaCl2.  By 
boiling  Fe2Cl6  with  excess  of  chloride  of  lime,  a  fine  pink  solution  of  calcium 
ferrate  is  obtained. 

Ferrous  carbonate,  FeC03,  or  spat/tic  iron  ore,  or  siderite,  is  found  in  rhombo- 
hedral  crystals  associated  with  the  carbonates  of  Ca,  Mg,  and  Mn,  which  are 
isomorphous  with  it.  It  occurs  in  chalybeate  waters,  dissolved  in  carbonic  acid, 
and  deposits  as  ferric  hydrate  when  the  water  is  exposed  to  air.  If  powdered 
iron  which  has  been  reduced  from  the  oxide  by  hydrogen  (ferrum  redactuni)  be 
suspended  in  water,  and  a  stream  of  C02  be  passed  for  some  time,  a  solution  of 
FeC03  in  carbonic  acid  is  obtained,  which,  when  filtered,  is  colourless,  becomes 
rusty  when  exposed  to  air,  and  gives,  when  boiled,  an  abundant  precipitate  of 
FeC03,  which  is  nearly  white,  and  becomes  green  when  exposed  to  air.  Sodium 
carbonate  added  to  a  ferrous  salt  gives  a  white  precipitate  if  all  air  be  excluded  ; 
otherwise  oxygen  is  absorbed,  and  a  dingy  green  precipitate  containing  Fe304  is 
formed. 

The  substance  sold  as  ferric  carbonate,  obtained  by  precipitating  a  ferric  salt 
with  sodium  carbonate,  is  mainly  ferric  hydrate,  since  weak  bases  like  Fe203  do  not 
form  carbonates. 

227.  Ferrous  sulphate,  copperas,  green  vitriol,  or  sulphate  of  iron, 
is  easily  obtained  by  heating  i  part  of  iron  wire  with  i  J  part  of  strong 
sulphuric  acid,  mixed  with  4  times  its  weight  of  water,  until  the  whole 
of  the  metal  is  dissolved,  when  the  solution  is  allowed  to  crystallise. 
Its  manufacture  on  the  large  scale  by  the  oxidation  of  iron  pyrites  has 
been  already  referred  to.  It  forms  fine  green  monoclinic  crystals,  having 
the  composition  FeS04.H2O.6Aq.  Rhombic  crystals,  isomorphous  with 
the  sulphates  Zn  and  Mg,  can  also  be  obtained. 

The  colour  of  the  crystals  varies  somewhat,  from  the  occasional  pre- 
sence of  small  quantities  of  ferric  sulphate,  Fe2(S04)3.  It  dissolves  very 
easily  in  twice  its  weight  of  cold  water,  yielding  a  pale  green  solution. 
One  part  of  boiling  water  dissolves  about  3  parts  of  the  crystals.  When 
the  commercial  sulphate  of  iron  is  boiled  with  water  it  yields  a  brown 

*  The  common  ferrates  correspond  with  an  anhydride,  FeO3.  Lately  a  barium  perferrate 
corresponding-  with  FeO4  has  been  prepared,  a  fact  important  from  the  point  of  view  of  the 
periodic  law  (p.  302). 


SALTS  OF  IEON.  419 

muddy  solution,  in  consequence  of  the  decomposition  of  the  ferric  sul- 
phate contained  in  it,  with  precipitation  of  a  basic  sulphate.  Ferrous 
sulphate  has  a  great  tendency  to  absorb  oxygen,  and  to  become  con- 
verted into  ferric  sulphate,  and  is  thus  useful  as  a  reducing-agent.  For 
example,  it  is  employed  for  precipitating  gold  in  the  metallic  state  from 
its  solutions.  But  its  chief  use  is  for  the  manufacture  of  ink  and  black 
dyes  by  its  action  upon  vegetable  infusions  containing  tannic  acid,  such 
as  that  of  nut-galls. 

Crystals  of  FeS04.H20.4Aq,  isomorphous  with  CuS04.H20.4Aq,  may  be  obtained 
by  dropping  a  crystal  of  cupric  sulphate  into  a  supersaturated  solution  of  ferrous 
sulphate.  As  in  the  case  of  MgS04.7H20  (p.  375)  one  molecule  of  the  H20  in 
FeS04.7H00  may  be  exchanged  for  other  sulphates  ;  thus,  ammonium  ferrous  sul- 
phate, FeS"04.(NH4)2S04.6H20,  is  well  known. 

The  salt  FeS04.S03  is  obtained  in  minute  prismatic  crystals  when  a  saturated 
solution  of  ferrous  sulphate  is  added  to  an  excess  of  strong  sulphuric  acid. 

Ferric  sulphate,  Fe2(S04)3,  is  found  in  Chili  as  a  white  silky  crystalline  mineral, 
coquimbite,  having  the  composition  Feo(S04)3.9Aq.  Iron  alums,  constructed  on  the 
type  of  the  common  alums  (p.  387),  with  Fe'"  in  place  of  Al"'  (e.g.,  NH4.Fe'" 
(S04)2. 12H20),  are  commercial  salts. 

Ferrous  phosphate,  Fe3(P04)2,  and  arsenate,  Fe3(As04)2,  are  used  in  medicine, 
being  prepared  by  precipitating  ferrous  sulphate  with  a  mixture  of  sodium 
acetate  and  sodium  phosphate  or  arsenate.  The  acetate  is  used  so  that  the  resulting 
liquid  may  contain  free  acetic  acid  instead  of  the  free  sulphuric  formed  by  the  H  in 
the  sodium  salt;  3FeSO4+2NaaHP04=Fei(P04)ft+2NaaS04+HaSO4.  Both  the 
phosphate  and  arsenate  are  white  when  perfectly  pure,  but  they  become  blue  when 
exposed  to  air,  from  the  production  of  a  little  ferroso-ferric  salt.  The  precipitated 
ferric  phosphate  is  2FeP04-5A.q.  Ferrous  phosphate  is  found  in  the  mineral 
Virianite  or  native  Prussian  blue,  Fe3(P04)2.8Aq. 

Ferrous  silicate,  Fe2Si04,  is  found  crystallised  in  finer y  cinder  of  the  ironworks. 

Ferrous  chloride,  FeCl2,  sublimes  in  colourless  six-sided  scales  when  iron  is  heated 
in  HC1  gas.  It  is  deliquescent,  and  crystallises  from  water  in  pale  green  crystals, 
FeCl24Aq,  which  are  oxidised  by  air. 

Ferrous  iodide,  FeI2,  is  prepared  by  digesting  fine  iron  wire  with  twice  its  weight 
of  iodine  and  about  eight  parts  of  water  for  some  time,  afterwards  boiling  till  the 
red  colour  has  disappeared,  filtering,  and  evaporating  in  contact  with  clean  iron. 
It  forms  green  crystals,  FeI2.5Aq,  which  are  deliquescent  and  very  soluble  in  water. 
The  solution  absorbs  oxygen  from  the  air,  and  deposits  a  brown  precipitate  unless 
kept  in  contact  with  clean  iron  or  mixed  with  strong  syrup. 

228.  Ferric  chloride,  or  perchloride  of  iron  (FeCl3),  is  obtained  in 
beautiful  dark  green  crystalline  scales  when  iron  wire  is  heated  in  a 
glass  tube  through  which  a  current  of  dry  chlorine  is  passed,  the  ferric 
chloride  passing  off  in  vapour,  and  condensing  in  the  cool  part  of  the 
tube.  The  crystals  almost  instantly  become  wet  when  exposed  to  air 
on  account  of  their  great  attraction  for  water.  Ferric  chloride  may  be 
obtained  in  solution  by  dissolving  iron  in  hydrochloric  acid,  and  con- 
verting the  ferrous  chloride  (FeCl2)  thus  formed  into  ferric  chloride  by 
the  action  of  nitric  and  hydrochloric  acids  (p.  191).  A  strong  solution 
yields  crystals  of  FeCl3.6Aq.  The  aqueous  solution  reddens  litmus. 
The  crystals  are  decomposed  by  heat,  leaving  an  oxychloride.  The 
solution  of  ferric  chloride  has  been  recommended  in  some  cases  as  a 
disinfectant,  being  easily  reduced  to  ferrous  chloride,  and  thus  affording 
chlorine  to  oxidise  unstable  organic  matters  (p.  175).  In  contact  with 
paper,  FeCl3  becomes  reduced  to  Fe012  when  exposed  to  light.  A 
solution  of  perchloride  of  iron  in  alcohol  is  used  in  medicine  under  the 
name  of  tincture  of  iron.  It  is  also  soluble  in  ether  and  benzene. 

Solution  of  ferric  chloride  dissolves  a  very  large  quantity  of  pure  freshly  precipi- 
tated ferric  oxide  (p.  417),  nine  molecules  of  Fe203  being  dissolved  by  one  molecule 


420  SULPHIDES   OF  IRON. 

of  ferric  chloride.  The  solution  of  ferric  oxy chloride  thus  obtained  has  a  very  dark- 
red  colour,  and  yields  a  very  copious  brown  precipitate  with  common  water,  or  any 
solution  containing  even  a  trace  of  a  sulphate.  When  the  aqueous  solution  of  FeCl3 
is  heated,  it  dissociates  into  a  similar  soluble  hydroxide  and  HC1. 

Ferrous  sulphide,  FeS,  is  formed  when  a  red-hot  bar  of  iron  is  rubbed  with  a 
stick  of  sulphur,  the  fused  FeS  running  off  in  globules,  and  is  prepared  as  described 
at  p.  214.  It  is  obtained  as  a  black  precipitate  when  an  alkaline  sulphide  is  added 
to  a  ferrous  salt.  It  is  easily  oxidised  iwhen  exposed  to  air  in  a  moist  state,  and 
dissolves  readily  in  HC1,  being  indeed  the  only  black  sulphide  which  dissolves  easily 
in  dilute  HC1.  It  is  used  in  the  laboratory  for  making  H2S. 

Magnetic  pyrites,  Fe7S8,  is  found  in  yellow  six-sided  crystals. 

Iron  pyrites,  or  mundic,  FeS2,  forms  yellow  cubes  or  octahedra  of  sp.  gr.  5.2.  It 
is  formed  by  the  slow  reduction  of  ferrous  sulphate  by  organic  matter,  and  its 
presence  in  coal  appears  to  be  accounted  for  in  this  way.  Minute  crystals  of  iron 
pyrites  are  sometimes  found  as  rough  casts  of  organic  substances.  It  burns 
when  heated,  yielding  Fe203  and  S02,  and  is  largely  used  as  a  source  of  the 
latter  by  the  vitriol  manufacturer.  Sulphur  itself  may  be  obtained  from  it  by 
distillation  at  a  high  temperature,  Fe3S4  being  left.  FeS2  is  insoluble  in  HC1, 
which  distinguishes  it  from  FeS.  It  may  be  dissolved  by  nitric  acid.  Radiated 
pyrites,  or  white  pyrites,  or  marcasite,  has  the  same  composition,  but  its  sp.  gr.  is 
only  4. 8. 

Some  kinds  of  pyrites  explode  with  considerable  violence  when  heated,  and 
create  much  alarm  when  they  occur  in  household  coal ;  these  have  been  found 
to  contain  small  cavities  filled  with  highly  compressed  (probably  liquid)  COg, 
which  expands  suddenly  when  heated. 

Compact  yellow  iron  pyrites  is  not  oxidised  by  exposure  to  air,  but  white 
pyrites  is  easily  converted  into  ferrous  sulphate  and  sulphuric  acid.  Even  yellow, 
pyrites  in  minute  crystals  diffused  through  clay  will  behave  in  the  same  way. 

The  FeS2  may  be  obtained  artificially  by  heating  iron  with  excess  of  sulphur  to 
a  temperature  below  redness,  or  by  heating  ferric  oxide  or  hydrate  moderately  in 
a  stream  of  H2S  as  long  as  it  increases  in  weight. 

Iron  nitride,  a  compound  of  iron  with  about  9  per  cent,  of  nitrogen,  has  been 
found  as  a  silvery  deposit  on  the  lavas  of  Etna.  It  yields  ammonia  when  heated 
in  hydrogen. 

Iron  carbonyls. — When  finely  divided  iron,  prepared  by  igniting  ferrous  oxalate 
and  reducing  the  resulting  oxide  in  a  current  of  hydrogen,  is  allowed  to  remain 
in  the  cold  in  contact  with  CO,  a  compound  Fe(CO)5,  iron  pentacarbonyl,  is  formed 
and  can  be  distilled  from  the  unaltered  iron  at  120°  C.  and  condensed  in  a  receiver 
surrounded  by  ice  and  salt.  It  is  an  amber-coloured  liquid  of  sp.  gr.  1.46  ;  it 
boils  at  103°  C.  and  crystallises  below  -  21°  C. ;  at  180°  C.  it  is  decomposed  into 
Fe  and  CO.  It  dissolves  in  many  organic  solvents,  and  is  slowly  decomposed 
with  precipitation  of  Fe2(OH)6  on  exposure  to  air.  When  exposed  to  sunlight  it 
deposits  golden  scales  which  appear  to  have  the  composition  Fe(CO)7,  iron  hepta- 
car'bonyl.  The  properties  of  these  compounds  should  be  compared  with  those  of 
nickel  carbonyl  (p.  425).  Iron  carbonyl  has  been  detected  in  coal  gas  which  has 
been  compressed  in  iron  cylinders. 

229.  Atomic  weight  of  iron. — When  iron  is  dissolved  in  hydrochloric 
acid,  28  parts  by  weight  of  iron  combine  with  35.5  parts  of  chlorine, 
displacing  i  part  of  hydrogen.  The  specific  heat  of  iron,  and  its  iso- 
morphism with  magnesium,  zinc,  and  cadmium,  show  that  its  atomic 
weight  must  be  represented  by  56,  so  that  iron  is  a  diad  or  divalent 
element,  one  atom  of  iron  being  exchangeable  for  two  atoms  of 
hydrogen. 

The  molecular  formula  of  ferric  chloride  has  been  confirmed  by  the 
determination  of  the  vapour  density  at  400°  C.,  which  has  been  found 
to  be  165,  corresponding  with  the  formula  Fe2016.  But  at  higher  tem- 
peratures the  vapour  density  approaches  81.25,  corresponding  with  the 
formula  FeCl3,  although  it  does  not  quite  reach  this  value,  since  a 
certain  amount  of  dissociation  into  FeCl2  and  C12  occurs. 

It  will  be  remarked  that  iron  possesses  a  different  valency  accordingly 


OXIDES   OF  COBALT.  421 

as  it  exists  in  ferrous  or  ferric  compounds.  Thus,  in  ferrous  oxide  (FeO) 
and  ferrous  chloride  (FeCl2)  it  occupies  the  place  of  two  atoms  of  hydro- 
gen, and  is  divalent ;  but  in  ferric  oxide  (Fe,03)  and  ferric  chloride 
(Fed 3)  each  atom  of  iron  occupies  the  place  of  three  atoms  of  hydrogen, 
and  is  trivalent. 

Iron  is  remarkable  for  its  two  series  of  fairly  stable  salts,  the  ferrous 
and  ferric,  the  former  acting  as  reducing-agents,  and  the  latter  as 
oxidising  agents.  Ferrous  iron  resembles  magnesium  and  zinc  in  its 
disposition  to  form  double  salts  with  salts  of  ammonium,  hence  its 
solutions  are  imperfectly  precipitated  by  ammonia ;  but  ferric  iron 
resembles  aluminium,  and  is  completely  precipitated.  Nitric  acid, 
chloric  acid,  and  chlorine  will  always  convert  ferrous  into  ferric  salts, 
and  ensure  complete  precipitation  by  ammonia. 

Some  chemists  designate  the  divalent  iron  existing  in  ferrous  compounds  by 
the  name  ferrosum  (Fe"),  and  the  trivalent  iron  of  the  ferric  compounds  by 
ferricum  (Fe'").  Others  regard  iron  as  a  tetravalent  metal  Feiv,  existing  in  the 
ferrous  salts  as  a  group  of  two  atoms  united  by  two  bonds,  and  in  the  ferric  salts 
as  a  group  of  two  atoms  united  by  one  bond.  On  this  view,  ferrous  chloride 
would  be  Fe.2Cl4,  or  Cl2=Fe=Fe=Cl2,  and  ferric  chloride  would  be  Fe2Cl6,  or 
Cl3=Fe— Fe=Cl3. 

COBALT. 

Co'' =  58. 5  parts  by  weight. 

230.  Some  of  the  compounds  of  cobalt  are  of  considerable  importance 
in  the  arts,  on  account  of  their  brilliant  and  permanent  colours.  It  is 
generally  found  in  combination  with  arsenic  and  sulphur,  forming  tin- 
white  cobalt,  CoAs2,  and  cobalt  glance,  CoAs2.CoS2,  but  its  ores  also 
generally  contain  nickel,  copper,  iron,  manganese,  and  bismuth. 

The  metal  itself  is  obtained  by  strongly  heating  cobalt  oxide  with 
charcoal,  in  the  manner  to  be  described  for  preparing  nickel  from  its 
oxide,  or  by  heating  the  oxide  with  aluminium  powder  (p.  386).  In  its 
properties  it  closely  resembles  iron,  but  it  is  said  to  surpass  iron  in 
tenacity.  It  is  magnetic.  It  is  heavier  than  iron,  sp.  gr.  8.5,  and  rather 
more  easily  fusible  (1500°  C.).  It  has  been  substituted  for  nickel  in 
plating  goods  which  are  usually  nickel-plated. 

Three  oxides  of  cobalt,  corresponding  with  those  of  iron,  are  known  : 
cobaltous  oxide,  CoO ;  cobaltic  oxide,  Co203 ;  and  cobalto-cobaltic  oxide, 
Co304  or  CoO.Co203.  The  first  of  these,  CoO,  is  a  brown  powder  left 
when  Co(OH)2  is  ignited  in  absence  of  air ;  it  is  a  basic  oxide,  dissolv- 
ing in  acids  to  form  cobaltous  salts.  When  heated  in  air,  it  oxidises  to 
CoO.Co203.  When  heated  in  the  electric  furnace,  it  melts  and  forms 
rose-coloured  crystals. 

Cobaltic  oxide  is  left  as  a  black  powder  when  cobaltous  nitrate  is 
gently  heated.  It  is  a  feeble  base,  and  the  cobaltic  salts  are  very  un- 
stable ;  thus  the  oxide  dissolves  in  cold  HC1,  yielding  a  brown  solution 
of  cobaltic  chloride,  Co2Cl6,  which  is  easily  decomposed  when  heated, 
evolving  C12  and  leaving  2CoCl.,.  When  Co203  is  heated  it  becomes 
CoO.Co203.  It  is  doubtful  whether  a  cobalt  dioxide,  Co02,  exists,  but 
when  Co203  is  fused  with  MgO  in  the  electric  furnace,  red  crystals  of 
MgCoO3  are  obtained. 

Cobalto-cobaltic  oxide  is  the  commercial  oxide  of  cobalt  employed 
for  painting  on  porcelain,  and  for  preparing  other  commercial  cobalt 


422  COBALT   SALTS. 

products.  It  is  a  black  powder,  which  evolves  chlorine  when  boiled  with 
HC1,  yielding  a  solution  of  CoCl2.  It  is  generally  prepared  as  a  by- 
product in  the  manufacture  of  nickel  from  its  arsenical  ores  (see  Nickel). 
Co304  is  not  an  independent  base,  but  gives  cobaltous  and  cobaltic 
salts  when  dissolved  in  acids. 

Cobaltous  hydroxide,  Co(OH)2,  is  obtained  by  adding  potash  in  excess 
to  a  solution  of  a  cobaltous  salt,  and  boiling.  The  blue  precipitate  pro- 
duced at  first  is  a  basic  salt  which  becomes  converted  into  the  red 
hydroxide  on  boiling  with  excess  of  potash.  If  air  be  allowed  access  it 
oxidises  the  red  precipitate,  converting  it  into  brown  cobaltic  hydroxide. 
Co(OH)9  dissolves  in  ammonia,  giving  a  fine  red  solution,  which  absorbs 
oxygen  from  the  air  and  becomes  brown.  Cobaltic  hydroxide,  Co2(OH)6, 
forms  the  black  precipitate  when  the  solution  of  a  hypochlorite  or  hypo- 
bromite  is  added  to  one  of  a  cobaltous  salt. 

Cobaltous  nitrate,  Co(N03)2.6Aq,  obtained  by  dissolving  cobalt  oxide 
in  HN03  and  crystallising,  forms  red  prisms,  which  become  blue  when 
their  water  is  expelled,  and  black  Co2O3  on  further  heating. 

Cobalt-yellow  or  potassium- cobaltic  nitrite,  K6CO///2(NO2)12,  is  obtained 
as  a  yellow  precipitate  when  cobaltous  nitrate  is  acidified  with  acetic 
acid,  and  potassium  nitrite  added  ;  the  acetic  acid  liberates  nitrous  acid, 
which  oxidises  the  cobaltous  salt;  2Co"(N03)2  +  ioKNO2  +  4HN02  = 
K6Co'//2(N02)1?  +  4KN03  +  2NO+ 2H20.  It  forms  a  yellow  crystalline 
precipitate,  slighly  soluble  in  water,  and  not  decomposed  by  cold  HC1 
or  HN03.  Caustic  alkalies  decompose  it,  separating  C02(OH)6. 

Cobaltous  chloride  (CoCl2),  obtained  by  dissolving  any  of  the  oxides 
in  hydrochloric  acid,  forms  red  prisms,  CoCl9.6Aq,  which  become  blue 
CoCl2.2Aq  at  120°  C.,  and  at  140°  C.,  CoCl2,  which  may  be  sublimed 
in  dark  blue  scales  in  a  current  of  chlorine.  If  strong  hydrochloric 
acid  be  added  to  a  red  solution  of  this  salt,  it  becomes  blue  ;  if  enough 
water  be  now  added  to  render  it  pink,  the  blue  colour  may  be  produced 
at  pleasure  by  boiling,  the  solution  first  passing  through  a  neutral  tint.* 
Chloride  (muriate)  of  cobalt  is  employed  as  a  sympathetic  ink,  for  charac- 
ters written  with  its  pink  solution  are  nearly  invisible  until  they  are 
held  before  the  fire,  when  they  become  blue  and  resume  their  original 
pink  colour  if  exposed  to  the  air  ;  a  little  chloride  of  iron  causes  a  green 
colour. 

The  cobaltous  sulphide  (CoS)  is  obtained  as  a  black  precipitate  when  an  alkaline 
sulphide  is  added  to  a  solution  of  a  salt  of  cobalt.  It  differs  from  FeS  by  being 
insoluble  in  HC1.  A  cobaltic  sulphide  (Co2S3)  is  found  in  grey  octahedra,  forming 
cobalt  pyrites.  The  disulphide  (CoS2)  has  been  obtained  artificially. 

Cobaltous  sulphate,  CoSO4.7H20,  is  found  as  cobalt  'vitriol.  It  forms  red  prisms 
isomorphous  with  ferrous  sulphate.  It  does  not  become  blue  when  dried,  and 
bears  a  high  temperature  without  decomposing.  Cobaltic  sulphate  and  cobaltic 
alums  have  been  prepared. 

Cobaltous  arsenate,  or  cobalt  bloom,  Co3(As04)2.8Aq,  is  found  in  pink  needles. 

Cobalt  di-arsenide,  CoAs2  is  found  crystallised  as  tin-wliite  cobalt  and  speiss 
cobalt,  in  which  it  is  associated  with  the  isomorphous  arsenides  of  nickel  and 
iron,  so  that  it  is  written  [CoNiFe]As2.  CoAs3  is  also  found  in  nature. 

The  cobaltous  silicate  associated  with  potassium  silicate  forms  the 
blue  colour  known  as  smalt,  which  is  prepared  by  roasting  the  cobalt  ore, 
so  as  to  convert  the  bulk  of  the  cobalt  into  oxide,  leaving,  however,  a 

*  A  solution  containing-  so  small  a  quantity  as  0.015  per  cent,  of  cobalt  will  give  a  distinct 
blue  colour  when  boiled  with  an  equal  bulk  of  strong  hydrochloric  acid. 


COBALT  AMMONIA  COMPOUNDS.  423 

considerable  quantity  of  arsenic  and  sulphur  still  in  the  ore,  The  residue 
is  then  fused  in  a  crucible  with  ground  quartz  and  carbonate  of  potash, 
when  a  blue  glass  is  formed,  containing  cobalt  silicate  and  potassium 
silicate ;  whilst  the  iron,  nickel,  and  copper,  combined  with  arsenic  and 
sulphur,  collect  at  the  bottom  of  the  crucible  and  form  a  fused  mass  of 
metallic  appearance  known  as  speiss,  which  is  employed  as  a  source  of 
nickel.  The  blue  glass  is  poured  into  cold  water,  so  that  it  may  be 
more  easily  reduced  to  the  fine  powder  in  which  the  smalt  is  sold.  If 
the  cobalt  ore  destined  for  smalt  be  over- roasted,  so  as  to  convert  the 
iron  into  oxide,  this  will  pass  into  the  smalt  as  a  silicate,  injuring  its 
colour.  Smalt  much  resembles  ultramarine,  but  is  not  bleached  by 
acids.  Zaffre  is  prepared  by  roasting  a  mixture  of  cobalt  ore  with  two 
or  three  parts  of  sand. 

Thenard's  blue,  or  cobalt  ultramarine,  consists  of  cobalt  phosphate  and 
aluminium  phosphate,  and  is  prepared  by  mixing  precipitated  alumina 
with  cobalt  phosphate  and  calcining  in  a  covered  crucible.  The  phos- 
phate is  obtained  by  precipitating  a  solution  of  cobalt  nitrate  with 
phosphate  of  potassium  or  sodium. 

Rinmanris  green  is  prepared  by  calcining  the  precipitate  produced  by 
sodium  carbonate  in  a  mixture  of  cobalt  sulphate  with  zinc  sulphate. 
It  is  a  compound  of  the  oxides  of  cobalt  and  zinc. 

The  relations  of  ammonia  to  the  cobalt  salts  are  very  remarkable  and 
characteristic,  the  NH3  combining  both  with  cobaltous  and  cobaltic  salts 
to  form  compounds  which  behave  like  salts  of  new  bases  containing 
cobalt,  nitrogen,  and  hydrogen,  known  as  cobaltosamines  and  cobalta- 
mines. 

When  NH3  is  added  to  the  solution  of  a  cobaltous  salt,  air  being  excluded,  a 
cdboltosamine  salt  of  the  general  type  CoX2.6NH3,  where  X  is  an  acid  radicle,  is 
formed.  When  these  are  exposed  to  the  air  they  undergo  oxidation,  yielding 
oxy  cobaltamine  salts  of  the  type  CoOX2. 5NH3,  in  which  the  cobalt  may  be  regarded 
as  tetrad,  corresponding  with  the  oxide  Co02  ;  these  salts  lose  oxygen,  becoming 
cobaltamine  salts,  when  their  solutions  are  heated.  If  the  cobaltosainine  solution 
be  fairly  dilute  when  it  is  exposed  to  the  air,  the  oxy-salt  will  not  be  formed,  and 
on  addition  of  an  acid  a  cobaltamine  salt  will  be  separated.  These  are  of  six 
types,  represented  by  CoX3.wNH3,  where  n=  I,  2,  3,  4,  5  or  6  ;  they  are  all  coloured 
salts  and  distinguished  by  prefixes  signifying  the  colour  characteristic  of  the  series 
— for  example,  xantko-  (yellow),  luteo-  (yellow),  roseo-,  purpureo-,  croceo-  (saffron), 
and.fu.sco-  (brown). 

Cobalt  is  seen  to  resemble  iron  in  many  respects,  but  the  cobaltic 
compounds  are  much  less  stable  than  the  ferric  compounds.  Cobaltous 
compounds  become  oxidised  to  cobaltic  compounds  only  in  solutions 
which  are  neutral  or  alkaline,  while  ferrous  compounds  are  easily 
oxidised  in  acid  solutions.  Both  iron  and  cobalt  form  remarkable 
compounds  with  potassium  and  cyanogen,  iron  forming  the  ferro- 
cyanide,  K4Fe"Cy6,  and  ferricyanide,  K3F'"Cy6,  while  cobalt  forms  the 
cobalticyanide,  K3Co"'Cy6  (see  Cyanides).  No  carbonyl  of  cobalt  has 
yet  been  obtained. 

NICKEL. 

Ni"  =  58-3  parts  by  weight. 

231.  Nickel  owes  its  value  in  the  useful  arts  chiefly  to  its  property  of 
imparting  a  white  colour  to  the  alloys  of  copper  and  zinc,  with  which  it 
forms  the  alloy  known  as  German  silver,  and  to  the  ease  with  which  it 


424  METALLURGY  OF  NICKEL. 

can  be  deposited  by  electrolysis  on  other  metals  (electro-plating),  as  a 
lustrous  and  coherent  film,  which  is  only  slowly  tarnished  by  the  atmo- 
sphere. Dishes  and  crucibles  of  this  metal  .are  used  in  the  laboratory 
in  many  cases  as  substitutes  for  those  of  platinum  and  silver,  though 
they  are,  of  course,  more  ea.sily  oxidised.  It  has  been  found  possible 
to  weld  sheet  nickel  upon  iron  and  steel  plates,  and  culinary  vessels,  &c., 
have  been  made  of  such  plates,  which  are  not  liable  to  rust.  Steel  con- 
taining nickel  is  exceptionally  hard.  Alloys  of  copper  and  nickel  are 
used  in  coinage.  Nickel  is  very  nearly  allied  to  cobalt,  and  generally 
occurs  associated  with  that  metal  in  its  ores. 

Recently  a  nickel  ore  has  been  discovered  in  Canada,  which  consists 
of  magnetic  iron  pyrites  (Fe.^)  in  which  nickel  takes  the  place  of  some 
3-8  per  cent,  of  the  iron.  This  promises  to  become  the  most  important 
ore  of  nickel,  though  at  present  the  mineral  garnierile,  a  silicate  of 
nickel  and  magnesium  found  in  New  Caledonia,  furnishes  the  largest 
supply  of  the  metal.  The  first  of  these  ores  contains  a  little  cobalt,  but 
the  second  is  free  from  that  metal.  The  Saxon  and  Bohemian  ores  of 
nickel  contain  cobalt,  arsenic,  sulphur,  and  iron  ;  the  chief  are  kupfer- 
nickel,  NiAs,  nickel  glance,  NiAs2.NiS2,  and  nickel  blende,  NiS. 

In  the  extraction  of  metals  from  ores  which  contain  much  iron  sul- 
phide, as  is  always  the  case  with  sulphureous  nickel  ores,  advantage  is 
taken  of  the  ease  with  which  iron  sulphide  can  be  roasted  to  oxide,* 
and  the  oxide  fluxed  as  ferrous  silicate  by  fusion  with  silica.  This 
method  of  removing  iron  may  be  extended  to  those  nickel  ores  which 
contain  no  sulphur,  by  heating  them  with  gypsum  and  coke,  when  the 
iron  becomes  converted  into  sulphide.  When  the  iron  has  been  removed, 
a  mixture  (matte}  of  the  sulphides  of  nickel  and  copper  (when  this  is 
present  in  the  ores)  remains.  This  is  completely  oxidised  by  roasting 
in  air,t  and  the  mixture  of  oxides  of  nickel  and  copper  is  treated  with 
dilute  sulphuric  acid,  which  dissolves  the  copper  oxide;  the  nickel  oxide 
is  made  into  a  paste  with  charcoal,  the  paste  is  cut  into  cubes  and 
heated  to  reduce  the  nickel,  which  retains  the  shape  of  the  cubes.  The 
commercial  metal  contains  carbon,  iron,  silicon,  and  sulphur.  The 
furnace  operations  necessary  for  the  above  process  will  be  understood  by 
reference  to  the  metallurgy  of  copper. 

The  arsenical  nickel  ores  are  treated  as  described  above  for  the  removal  of  iron, 
and  the  speiss  thus  obtained,  consisting  essentially  of  nickel  and  arsenic,  but  con- 
taining a  little  cobalt  and  copper,  is  treated  by  a  wet  method  for  the  separation  of 
the  cobalt.  This  is  effected  by  roasting  the  speiss  to  expel  most  of  the  arsenic, 
dissolving  in  HC1,  peroxidising  the  solution  by  bleaching-powder,  and  neutralising 
with  chalk  ;  in  this  way  the  iron  is  precipitated  as  basic  ferric  carbonate,  and  the 
remaining  arsenic  as  ferric  arsenate.  H2S  is  passed  through  the  solution  to 
precipitate  bismuth  and  copper  as  sulphides,  leaving  cobalt  and  nickel  in  solution. 
The  latter,  having  been  boiled  to  expel  the  excess  of  H2S,  is  neutralised  with  lime 
and  mixed  with  bleaching-powder,  which  precipitates  the  cobalt  as  Co203,  leaving 
NiO  in  solution,  from  which  it  may  be  precipitated  by  adding  lime  ;  it  is  reduced 
as  described  above.  The  Co203  becomes  Co3O4  when  ignited. 

Mond's  process  for  extracting  nickel  depends  on  the  fact  that  when 
the  finely  divided  metal  is  heated  in  a  current  of  CO  at  50°— 100  C.  it  is 
volatilised  in  the  form  of  nickel  carbonyl  (see  below),  and  thus  separated 
from  any  other  metals,  &c.,  which  may  accompany  it.  The  nickel 


-  OXIDES   OF  NICKEL.  425 

carbonyl  vapour  is  then  heated  in  another  vessel,  whereby  it  is  decom- 
posed and  deposits  its  nickel. 

In  practice  the  finely  divided  roasted  matte  or  speiss  is  caused  to  descend  a  tower 
containing  hollow  shelves  heated  internally  by  hot  gas  to  250°  C.,  where  it  meets 
.an  ascending  stream  of  water-gas.  The  oxides  are  thus  reduced  to  metal,  and  the 
material  is  next  conveyed  to  the  top  of  a  second  tower,  not  heated,  in  descending 
which  it  meets  a  current  of  gas  rich  in  CO  and  at  a  temperature  of  50°  C.  Nickel 
-carbonyl  is  produced  and  carried  forward  as  vapour  by  the  gas  into  an  apparatus 
in  which  a  mass  of  granules  of  nickel  is  kept  in  motion  so  that  the  granules 
perpetually  roll  over  each  other  and  are  prevented  from  cohering.  The  tempera- 
ture of  this  apparatus  being  about  200°  C.,  the  carbonyl  deposits  its  nickel  on  the 
granules  while  its  CO  passes  on  to  be  used  again  in  the  second  tower  for  volatilising 
more  'nickel.  By  keeping  the  temperature  of  the  volatilising  tower  as  low  as 
possible,  the  production  of  iron  carbonyl  (p.  420)  is  avoided. 

Nickel  closely  resembles  iron,  but  is  less  attacked  by  air  and  water ; 
its  sp.  gr.  is  8.8,  and  it  melts  at  1600°  C.  At  ordinary  temperatures  it 
is  magnetic,  but  it  loses  this  property  at  250°  C. 

The  oxides  of  nickel  correspond  in  composition  with  those  of  cobalt. 
The  salts  formed  by  nickelous  oxide  (NiO)  are  usually  green,  and  give 
bright  green  solutions.  The  hydroxide  has  a  characteristic  apple-green 
•colour,  and  does  not  absorb  oxygen  from  the  air  like  the  cobaltous 
hydroxide.  It  dissolves  in  ammonia  with  a  blue  colour  unchanged  by 
air.  The  greater  facility  with  which  the  cobalt  is  converted  into 
sesquioxide  has  been  applied  (as  above  described)  to  effect  the  separation 
of  the  two  metals.  NiO  has  been  found  native  in  octahedral  crystals, 
which  have  also  been  obtained  accidentally  in  a  copper-smelting  furnace  ; 
it  melts  and  crystallises  in  the  electric  arc. 

Ni3O4  is  obtained  by  passing  moist  oxygen  over  NiCl2  at  about  400°  C. 
It  has  a  metallic  appearance,  and  is  seen  in  octahedral  crystals  under 
the  microscope.  It  is  converted  into  NiO  when  heated,  and  dissolves 
in  hydrochloric  acid  with  evolution  of  chlorine. 

Nickel  sulphate  (NiS04.H20.6Aq)  forms  fine  green  prismatic 
crystals,  the  water  of  constitution  in  which  may  be  displaced  by  K2S04 
or  (NH4)9S04.  Nickel  ammonium  sulphate,  NiS04.(NH4)2S04.6H20,  is 
used  in  electro-plating  with  nickel.  It  is  almost  insoluble  in  ammonium 
sulphate  solution. 

Nickel  sulphate  maybe  obtained  by  dissolving  nickel  in  dilute  sul- 
phuric acid.  It  is  isoinorphous  with  the  sulphates  of  Mg,  Zn,  Fe,  and 
Co.  When  ammonia  is  added  to  its  solution,  it  produces  a  green  pre- 
cipitate of  a  basic  salt,  which  dissolves  in  excess  of  ammonia  to  a  violet 
solution,  depositing  violet  crystals  of  NiS04.4NH3.2H20. 

Four  sulphides  of  nickel  are  known — Ni2S,  FiS,  Ni3S4  and  NiS2.  NiS 
is  found  native  as  capillary  pyrites,  and  is  obtained  as  a  black  precipitate 
by  the  action  of  an  alkaline  sulphide  on  a  salt  of  nickel ;  like  cobalt 
sulphide,  it  is  insoluble  in  HC1 ;  but  ammonium  disulphide  dissolves  it 
to  a  dark  brown  liquid. 

Nickel  carbonyl,  Ni(CO)4,  is  a  colourless  liquid  (sp.  gr.  1.3)  which 
boils  at  43°  C.  and  crystallises  at-  25°  C.  It  is  prepared  by  passing 
dry  CO  through  a  tube  containing  finely  divided  nickel  which  has  been 
reduced  from  NiO  by  heating  it  in  hydrogen  at  400°  C.  The  Ni(CO)4 
is  condensed  from  the  excess  of  CO  used  by  passing  the  gas  through  a 
tube  surrounded  by  ice  and  salt.  It  is  insoluble  in  water,  but  dissolves 
in  alcohol,  benzene,  and  chloroform.  Its  vapour  is  decomposed  at 


426  OXIDES   OF  MANGANESE. 

150°  C.  into  CO  and  Ni,  which  is  deposited  in  the  form  of  a  mirror  on 
the  sides  of  the  vessel ;  it  is  a  powerful  reducing-agent.  Theoretically,, 
it  is  of  great  importance  as  furnishing  a  volatile  compound,  by  means 
of  which  the  atomic  weight  of  nickel  can  be  determined. 

Nickel  is  farther  removed  from  iron  than  cobalt  is  ;  its  peroxide, 
Ni203,  shows  no  disposition  to  form  salts,  and  it  does  not  form  any  com- 
pound corresponding  with  ferro-  or  cobalti-cyanides.  It  has  far  less 
colouring  power  than  cobalt,  and  its  salts  are  commonly  green.  In 
many  respects  nickel  more  nearly  resembles  copper  than  iron. 

Nickel  salts  are  poisonous. 

MANGANESE. 

Mn"  =  54.6  parts  by  weight. 

232.  Manganese  much  resembles  iron  in  several  particulars  relating 
both  to  its  physical  and  chemical  characters,  and  is  often  found  asso- 
ciated, in  small  quantities,  with  the  compounds  of  that  metal.  It  is 
found  chiefly  as  pyrolusite,  Mn02,  braunite,  Mn203,  and  manganese  spar, 
MnC03.  The  metal  itself  has  not  been  applied  to  any  useful  purpose. 
It  is  obtained  either  by  reducing  one  of  the  oxides  with  charcoal  at  a 
very  high  temperature— when  a  fused  mass,  composed  of  manganese 
combined  with  a  little  carbon  (corresponding  with  cast  iron),  is  obtained, 
and  may  be  freed  from  carbon  by  a  second  fusion  in  contact  with  man- 
ganous  oxide — by  reducing  Mn012  with  magnesium,  or  by  igniting  a 
mixture  of  aluminium  powder  and  manganese  oxide  (p.  386). 

Manganese  is  grey  with  a  red  tinge,  hard  and  brittle,  sp.  gr.  8,  very 
difficult  to  fuse  (1900°  C.),  and  more  easily  oxidised  than  iron,  so  that 
it  decomposes  water  when  slightly  warmed.  It  is  not  magnetic  unless 
cooled  to  -  20°  C.  It  appears  to  be  more  volatile  than  iron. 

Manganese  dissolves  easily  in  diluted  hydrochloric  or  sulphuric  acid, 
Mn  displacing  H2,  like  Fe  and  Or.  It  resembles  iron  in  its  tendency 
to  combine  with  carbon  at  a  high  temperature  to  form  a  compound 
corresponding  with  cast  iron,  and  in  this  form  the  manganese  is  not 
oxidised  by  air.  It  decomposes  water  gradually  at  ordinary  tempera- 
tures, and  boiling  water  more  quickly. 

Spiegel-eisen  and  ferro-manganese  are  alloys  containing  iron,  manga- 
nese, and  carbon,  which  are  largely  used  in  the  production  of  steel. 

233.  Oxides  of  manganese,  MnO,  Mn203,  Mn304,  Mn02,  Mn03, 
Mn2O7 ;  the  first  two  are  bases,  the  last  two  anhydrides. 

Manganese  dioxide  or  peroxide,  Mn02,  is  the  chief  form  in  which 
this  metal  is  found  in  nature,  and  is  the  source  from  which  all  other 
compounds  of  manganese  are  obtained.  Its  chief  mineral  form  is 
pyrolusite,  which  forms  steel-grey  prismatic  crystals  of  sp.  gr.  4.9  ;  but 
it  is  also  found  amorphous,  as  psilomelane,  and  in  the  hydra  ted  state  as 
wad.  In  commerce,  pyrolusite  is  known  as  black  manganese,  or  simply 
manganese,  and  is  largely  imported  from  Germany,  Spain,  &c.,  for  the 
use  of  the  manufacturer  of  bleaching-powder  and  the  glass-maker.  It 
is  also  used  as  a  cheap  source  of  oxygen,  which  it  evolves  when  heated 
to  redness,  without  fusing,  leaving  the  red  oxide  of  manganese,  Mn3O4. 
The  manganese  dioxide  is  an  indifferent  oxide,  and  does  not  combine 
with  acids.  Strong  HC1,  however,  dissolves  it,  giving  a  brown  solution 
from  which  water  precipitates  a  brown  oxychloride.  If  the  brown 


OXIDES   OF  MANGANESE.  427 

solution,  which  probably  contains  Mn2016  and  MnCl4,  be  heated,  it  evolves 
C12  and  becomes  colourless  MnCl2.  Nitric  acid  is  almost  without  action 
on'Mn02.  Strong  sulphuric  acid  evolves  oxygen  from  it ;  MnO2  +  H2S04  = 
MnS04  +  H20  +  0.  Even  dilute  sulphuric  acid  effects  the  same  change 
if  some  substance  ready  to  combine  with  oxygen  is  added,  such  as 
ferrous  sulphate  or  oxalic  acid.  Hence  a  mixture  of  Mn02  and  H2S04 
is  much  used  as  an  oxidising  agent,  and  it  will  be  seen  from  the  above 
equation  that  only  half  the  oxygen  in  the  Mn02  is  available  for  purposes 
of  oxidation.  It  becomes  necessary,  therefore,  to  value  the  commercial 
black  oxide  by  ascertaining  how  much  FeS04  a  given  weight  of  it  will 
oxidise  in  the  presence  of  dilute  acid,  H2S04. 

2(FeO.S03)  +  Mn02  +  2(H2O.S03)  =  Fe203.(S03)3  +  MnO.S03  +  2H20. 

When  heated  in  hydrogen,  the  oxides  of  manganese  are  not  reduced 
to  the  motal,  like  those  of  iron,  but  are  converted  into  MnO. 

Manganous  oxide,  MnO,  obtained  in  this  way,  is  a  greenish  powder.  It  has  been 
obtained  in  transparent  emerald-green  crystals.  It  easily  absorbs  oxygen  from 
the  air.  It  is  a  basic  oxide,  dissolving  in  acids  to  form  the  manganous  salts.  It 
has  been  found  native  in  a  manganiferous  dolomite. 

Manganic  oxide,  or  manganese  sesquioxide,  Mn203,  is  found  in  the  mineral 
braunite  in  octahedral  crystals.  By  its  general  appearance  it  might  be  mistaken 
for  Mn02,  but  it  dissolves  in  moderately  strong  sulphuric  acid,  forming  a  red 
solution  of  manganic  sulphate,  Mn2(S04)3. 

Mn203  is  a  feebly  basic  oxide."  It  may  be  obtained  by  heating  any  of  the 
oxides  of  manganese  to  redness  in  a  current  of  oxygen,  while  Mn304  is  formed 
when  any  one  of  the  oxides  is  heated  in  air.  When  Mn02  in  very  small  quantity 
is  added  to  melted  glass,  it  imparts  a  purple  colour,  which  is  probably  due  to  the 
formation  of  a  manganic  silicate.  The  amethyst  is  believed  by  some  to  owe  its 
colour  to  the  same  cause. 

Red  oxide  of  manganese  (Mn304)  is  the  most  stable  of  the  oxides  of  this  metal, 
and  is  formed  when  any  of  the  others  is  heated  in  air.  Thus  obtained,  it  has  a 
brown  or  reddish  colour  ;  but  it  is  found  in  nature  as  the  black  mineral  hausmannite. 
In  composition  it  resembles  the  magnetic  oxide  of  iron,  but  it  seems  probable  that 
the  true  formula  is  2MnO.Mn02,  for  when  treated  with  diluted  nitric  acid  it  leaves 
the  black  hydrated  dioxide.  Strong  sulphuric  acid  dissolves  it  to  a  red  liquid 
containing  manganous  and  manganic  sulphates.  Dilute  sulphuric  acid  leaves 
Mn02  undissolved.  HC1  dissolves  it  when  heated,  evolving  Cl  and  leaving  MnClg. 

Mn03  or  manganic  anhydride,  is  formed  in  small  quantity  by  dropping  a  solution 
of  potassium  permanganate  in  concentrated  H2S04  upon  dry  Na2C03,  and  con- 
densing the  pink  cloud  which  arises,  in  a  tube  cooled  by  ice  and  salt.  It  is  a  red 
amorphous  mass,  yielding  manganic  acid  in  contact  with  water. 

Permanganic  anhydride,  Mi^O^,  is  a  red  oily  liquid  formed  when  potassium 
permanganate  is  decomposed  by  strong  sulphuric  acid;  K2Mn208  +  2H2S04  = 
2KHS04  +  Mn207  +  H20.  It  decomposes  slowly,  even  at  common  temperatures, 
evolving  oxygen,  together  with  violet  vapour  of  Mn207.  When  heated,  it  decom- 
poses with  explosion.  It  is  a  most  powerful  oxidising  agent,  setting  fire  to  most 
combustible  bodies.  In  contact  with  water,  it  yields  permanganic  acid,  H2Mn208. 

Manganous  hydroxide,  Mn(OH)2,  is  obtained  as  a  white  precipitate  when  an 
alkali  is  added  to  a  manganous  salt,  out  of  contact  with  air.  When  exposed  to 
air  it  rapidly  becomes  brown,  forming  manganic  hydroxide. 

Manganic  hydroxide,  Mn202(OH)2,  may  be  regarded,  as  Mn203,  in  which  0  has 
been  exchanged  for  (OH)2,  or  as  Mn203.H20,  hydrated  manganese  sesquioxide.  It 
is  found  in  dark  grey  prismatic  crystals,  as  manganite,  associated  with  Mn02,  from 
which  it  differs  by  giving  a  brown  instead  of  a  black  streak  on  unglazed  earthen- 
ware. Moreover,  on  boiling  it  with  dilute  nitric  acid,  part  of  it  is  dissolved  as 
manganous  nitrate,  leaving  a  hydrated  manganese  dioxide,  which  dissolves  to  a 
brown  solution  when  thoroughly  washed.  A  hydrated  manganese  dioxide  is  also 
precipitated  when  chloride  of  lime  is  added  to  a  manganese  salt. 

Manganic  acid,   H2MnO4,    has  not  been  isolated,    but  several  man- 


428  PERMANGANATES. 

ganates  are  known,  which  are  isomorphous  with  the  chromates  and 
sulphates. 

Potassium  manganate,  K2MnO4,  is  formed  when  MnO2  is  fused  with 
potash;  3Mn02  + 2KOH  =  K2Mn04  + Mn203  +  H2O.  If  an  oxidising 
agent,  such  as  air  or  nitre,  be  present,  the  Mn2O3  is  also  converted  into 
K2MnO4 ;  Mn2O3  +  4KOH  +  O3  =  2K2Mn04  +  2H2O.  The  extraction  of 
oxygen  from  air  upon  this  principle  has  been  described  at  p.  39. 

Sodium  manganate  (Na2MnO4),  obtained  by  heating  manganese 
dioxide  with  sodium  hydroxide  under  free  exposure  to  air,  is  employed 
in  a  state  of  solution  in  water,  as  Condy's  green  disinfecting  fluid.  It  is 
also  used  as  a  bleaching-agent,  and  in  the  preparation  of  oxygen  at  a 
cheap  rate.  The  manganates  of  potassium  and  sodium  dissolve  in  water 
containing  potash  or  soda,  forming  green  liquids,  but  when  dissolved  in 
pure  water  they  are  decomposed,  yielding  the  red  permanganates — 

3Na2Mn04  +  2H20  =  Na2Mn208  +  Mn02  +  4NaOH. 
Barium  manganate  forms  the  pigment  known  as  Cassel  green. 

Manganous  acid,  of  which  Mn02  would  be  the  anhydride,  might  be  expected  to 
exist,  but  is  not  known.  When  Mn(OH)2  is  oxidised  in  presence  of  an  alkali,  the 
resulting  brown  substance  contains  more  or  less  of  the  alkali  combined  with 
Mn02.  These  compounds  are  known  as  manganites — e.g.,  CaO.Mn02. 

Permanganic  acid,  H2Mn208,  has  been  obtained  in  a  hydrated  crystalline  state 
by  decomposing  the  barium  permanganate  with  sulphuric  acid,  and  evaporating 
the  solution  in  vacua.  It  is  a  brown  substance,  easily  dissolving  in  water  to  a  red 
liquid,  which  is  decomposed  at  about  90°  F.  (32°  C.),  evolving  oxygen,  and 
depositing  manganese  dioxide. 

Potassium  permanganate,  K2Mn208,  forms  rhombic  prisms  isomor- 
phous with  the  perchlorate,  KC104,  on  which  account  it  is  sometimes 
written  KMnO4.  It  dissolves  in  20  parts  of  cold  water,  forming  a 
purple  solution,  which  becomes  green  K2MnO4  by  contact  with  many 
substances  capable  of  taking  up  oxygen.  When  crystallised  perman- 
ganate is  heated  to  240°  C.  it  gives  manganate — 

K2Mn208  —  K2Mn04  +  Mn02  +  02. 

It  is  largely  used  in  many  chemical  operations.  In  order  to  prepare  it,  4  parts  of 
finely  powdered  manganese  dioxide  are  intimately  mixed  with  3^  parts  of  KC103, 
and  5  parts  of  KOH  dissolved  in  a  very  little  water.  The  pasty  mass  is  dried,  and 
heated  to  dull  redness  for  some  time  in  an  iron  tray  or  earthen  crucible.  The 
potassium  chlorate  imparts  the  required  oxygen.  On  treating  the  cool  mass  with 
water,  potassium  manganate  is  dissolved,  forming  a  dark  green  solution.  This  is 
diluted  with  water,  and  a  stream  of  C02  passed  through  it  so  long  as  any  change  of 
colour  is  observed;  3K2Mn04  +  2C02  =  K2Mn208  +  Mn02  +  2K2C03.  The  precipi- 
tated Mn02  is  allowed  to  settle,  and  the  clear  red  solution  poured  off  and  evapo- 
rated to  a  small  bulk.  On  cooling,  it  deposits  prismatic  crystals  of  the  per- 
manganate (K2Mn208),  which  are  red  by  transmitted  light,  but  reflect  a  dark  green 
colour.  The  K2C03,  being  much  more  soluble  in  water,  is  left  in  the  solution. 

Potassium  permanganate  is  remarkable  for  its  great  colouring  power, 
a  very  small  quantity  of  the  salt  producing  an  intense  purplish-red 
colour  in  a  large  quantity  of  water.  Its  solution  in  water  is  very  easily 
decomposed  and  bleached  by  substances  having  an  attraction  for  oxygen, 
such  as  sulphurous  acid  or  a  ferrous  salt.  If  a  very  small  piece  of  iron 
wire  be  dissolved  in  diluted  sulphuric  acid,  the  solution  of  ferrous  sul- 
phate so  produced  will  decolorise  a  large  volume  of  weak  solution  of  the 
permanganate,  being  converted  into  ferric  sulphate — 

K2Mn208  +  ioFeS04  +  8H2S04  =  K2S04  +  2MnS04  +  5Fe2(S04)3  +  8H20. 


CHLORIDES   OF  MANGANESE.  429 

or  K2O.Mn207  +  io(FeO.S03)  +  8(H0O.S03)  = 

K2O.S03  +  2(MnO.S03)  +  5(Fe2O3.3S03)  =  8H20, 

which  shows  that  the  molecule  of  K,Mu208  has  5  atoms  of  oxygen  avail- 
able for  purposes  of  oxidation. 

This  decomposition  forms  the  basis  of  a  valuable  method  for  deter- 
mining the  proportion  of  iron  in  its  ores. 

Many  organic  substances  are  easily  oxidised  by  potassium  perman- 
ganate, and  this  is  the  case  especially  with  the  offensive  emanations 
from  putrescent  organic  matter.  Hence  it  is  extensively  used,  under 
the  name  of  Condys  red  disinfecting  Jluicl,  in  cases  where  a  solid  or 
liquid  substance  is  to  be  deodorised. 

The  oxidising  power  of  potassium  permanganate  is  effectively  illus- 
trated by  pouring  a  little  glycerine  into  a  cavity  made  in  a  small  heap  of 
the  powdered  crystals  on  a  porcelain  crucible  lid ;  the  glycerine  slowly 
sinks  into  the  permanganate,  and  after  a  minute  or  two  bursts  into 
vivid  combustion. 

An  alkaline  solution  of  the  permanganate  is  sometimes  used  as  an 
oxidising  agent,  since  it  parts  with  oxygen  when  boiled  with  oxidisable 
substances,  becoming  green  from  the  production  of  manganate — 

K2Mn208  +  2KOH  =  2K2Mn04  +  H20  +  0. 

/Sodium  permanganate,  Na2Mn208,  is  often  used  as  a  disinfectant,  being 
cheaper  than  the  potassium  salt.  It  is  made  by  heating  Mn02  with 
NaOH,  in  a  flat  vessel,  exposed  to  air,  for  48  hours,  to  dull  redness  ;  the 
mass  is  boiled  with  water  to  convert  the  manganate  into  permanganate ; 
3Na2MnO4  +  2H20  =  Na2Mn2O8  +  Mn02  f  4NaOH. 

234.  There  appear  to  be  three  chlorides  of  manganese  corresponding 
with  three  of  the  oxides,  viz.,  MnCl2,  Mn2Cl6,  and  MnCl4;  but  only  the 
first  is  obtainable  in  the  pure  state,  the  others  forming  solutions  which 
are  easily  decomposed  with  evolution  of  chlorine.  There  is  also  some 
evidence  of  the  existence  of  a  chloride  MnClr 

By  dissolving  potassium  permanganate  in  oil  of  vitriol,  and  adding  fragments 
of  fused  sodium  chloride,  a  remarkable  greenish-yellow  gas  is  obtained,  which 
gives  purple  fumes  with  moist  air.  and  is  decomposed  by  water,  yielding  a  red 
solution  which  contains  hydrochloric  and  permanganic  acids.  It,  therefore, 
must  contain  manganese  and  chlorine,  and  is  sometimes  regarded  as  the  per- 
chloride  (MnCl7)  ;  but  it  is  more  probably  an  oxychloride  of  manganese  (see 
Chlorochromic  acid).  Care  is  required  in  its  preparation,  which  is  sometimes 
attended  with  explosion. 

The  manga  nous  chloride  (MnCl2)  is  obtained  in  large  quantity  as  a  waste  pro- 
duct in  the  preparation  of  chlorine  for  the  manufacture  of  bleaching-powder. 
Since  there  is  no  useful  application  for  it,  the  manufacturer  sometimes  reconverts 
it  into  the  black  oxide  by  Weldon's  process  (see  p.  170).  As  the  native  binoxide 
always  contains  iron,  the  liquor  obtained  by  treating  it  with  HC1  contains  ferric 
chloride  (Fe2Cl6)  mixed  with  MnCl2.  In  order  to  separate  the  iron,  advantage  is 
taken  of  the  circumstance  that  sesquioxides  are  weaker  bases  than  the  protoxides, 
so  that  if  a  small  proportion  of  lime  or  chalk  be  added  to  the  solution,  the  iron 
may  be  precipitated  as  ferric  oxide,  without  decomposing  the  chloride  of  man- 
ganese ;  Fe2Cl6  +  3CaO  =  Fe203  +  3CaCl2. 

After  separating  the  Fe2O3,  an  excess  of  lime  is  added  and  air  blown  through 
the  mixture  at  about  150°  F.,  when  the  white  precipitate  of  MnO,  formed  at  first, 
absorbs  the  oxygen,  and  becomes  a  black  compound  of  Mn02  with  lime,  which  is 
used  over  again  for  the  preparation  of  chlorine.  Unless  the  lime  is  added  in 
excess,  only  MnO.Mn02  is  formed,  so  that  the  excess  of  lime  displaces  the  MnO 
and  allows  it  to  be  converted  into  Mn02.  In  another  process  Weldon  employs 
magnesia  instead  of  lime,  with  the  view  of  afterwards  recovering  the  chlorine 


430  POTASSIUM  BICHROMATE. 

from  the  chloride  of  magnesium,  in  the  form  of  hydrochloric  acid  (see  p.  348),  and 
using  the  magnesia  over  again. 

Manganous  sulphate,  MnS04.H20.6Aq.  isomorphous  with  green  vitriol,  forms 
faintly  pink  crystals  easily  soluble  in  water.  It  is  prepared  by  adding  strong  H2SO4 
to  Mn02,  heating  the  paste  to  redness  to  decompose  any  ferric  sulphate,  extracting 
with  water,  precipitating  the  last  traces  of  iron  by  adding  manganous  carbonate, 
filtering,  and  crystallising.  Manganous  sulphate  is  employed  by  the  dyer  and 
calico-printer  in  the  production  of  black  and  brown  colours.  Crystals  have  been 
obtained  of  MnS04.H20.4Aq.,  isomorphous  with  copper  sulphate. 

Manganous  sulphide,  MnS,  occurs  as  manganese  blende  in  steel-grey  masses.  It 
may  be  obtained  as  a  greenish  powder  by  heating  any  of  the  oxides  of  manganese 
in  a  current  of  H2S.  When  precipitated  by  alkaline  sulphides  from  manganese 
salts,  it  has  a  pink  colour  and  contains  water.  When  the  pink  precipitate  is 
boiled  with  an  excess  of  alkali  sulphide,  it  becomes  a  green  crystalline  powder, 
3MnS.H20.  The  manganous  sulphide  has  a  tendency  to  form  soluble  compounds 
with  the  alkali  sulphides,  so  that  a  solution  of  manganese  often  requires  boiling 
with  ammonium  sulphide  before  a  precipitate  is  formed.  It  dissolves  easily  in 
HC1.  Manganese  disulpTiide,  MnS2,  is  found,  in  crystals  belonging  to  the  regular 
system,  as  Hauerite,  in  Hungary. 

Manganese,  though  more  nearly  allied  to  iron  than  to  any  other 
metal,  is  parted  from  it  by  the  greater  stability  of  the  manganous  salts, 
which  are  less  easily  oxidised  than  the  ferrous  'salts,  as  well  as  by  the 
far  greater  stability  of  the  manganates  than  of  the  ferrates,  and  by  the 
existence  of  permanganates,  which  have  no  parallel  in  the  iron  series. 

The  chlorides  of  manganese  give  a  green  colour  to  a  colourless  flame. 

CHROMIUM. 

0  =  51.7  parts  by  weight. 

235.  This  metal  derives  its  name  from  xpw/*a,  colour,  in  allusion  to 
the  varied  colours  of  its  compounds,  upon  which  their  uses  in  the  arts 
chiefly  depend.  It  is  comparatively  seldom  met  with,  its  principal  ore 
being  the  chrome-iron  ore  ( FeO.Cr203),  which  is  remarkable  for  its  re- 
sistance to  the  action  of  acids  and  other  chemical  agents.*  It  is  chiefly 
found  in  the  Shetland  Islands,  Sweden,  Russia,  Hungary,  and  the 
United  States,  and  is  imported  for  the  manufacture  of  bichromate  of 
potash  (K20.2Cr03),  which  is  one  of  the  chief  commercial  compounds  of 
chromium.  The  ore  is  first  heated  to  redness  and  thrown  into  water, 
in  order  that  it  may  be  easily  ground  to  a  fine  powder,  which  is  mixed 
with  carbonate  of  potash,  chalk  being  added  to  prevent  the  fusion  of 
the  mass,  and  strongly  heated  in  a  current  of  air  on  the  hearth  of  a 
reverberatory  furnace,  the  mass  being  occasionally  stirred  to  expose 
a  fresh  surface  to  the  air.  The  ferrous  oxide  is  thus  converted  into 
ferric  oxide,  and  the  oxide  of  chromium  (O203)  into  potassium  chromate 
(K2Cr04) ;  2(FeO.O2O3)  +  4K2C03  +  O7  =  Fe2O3  +  4K,Cr04  +  4C02.  Nitre 
is  sometimes  added  to  hasten  the  oxidation.  On  treating  the  mass  with 
water,  a  yellow  solution  of  potassium  chromate  is  obtained,  which  is 
drawn  off  from  the  insoluble  residue  of  ferric  oxide  and  lime,  and  mixed 
with  a  slight  excess  of  acid,  e.g.,  nitric  acid — 

2(K2Cr04)  +  2HN03  =  K2Cr207  +  2KN03  +  H20. 

The  solution,  when  evaporated,  deposits  anhydrous,  red,  tabular  crystals 
of  bichromate  of  potash  (potassium  dichromate),  which  dissolve  in 

*  There  appear  to   be   four    types  of   chrome-iron    ore,    viz.,    FeO.Cr2O3,   2FeO.Cr2O«, 
3FeO.2Cr2O3,  and  2FeO.3Cr2O3. 


CHROMIC  ANHYDRIDE.  431 

10  parts  of  cold  water,  forming  an  acid  solution.     It  is  from  this  salt 
that  the  other  compounds  of  chromium  are  immediately  derived. 

Metallic  chromium  has  received  no  useful  application.  It  is  obtained 
by  reducing  chromic  chloride  with  zinc  (or  magnesium)  at  a  high  tem- 
perature, and  removing  the  excess  of  zinc  with  dilute  nitric  acid.  Or 
Cr,03  may  be  reduced  by  aluminium  at  a  high  temperature  (p.  386).  It 
has  a  grey  colour,  is  about  as  heavy  as  iron  (sp.  gr.  6.8),  is  extremely 
hard,  and  less  fusible  (about  3000°  C.)  than  platinum.  It  resembles 
aluminium  in  not  being  attacked  by  nitric  acid,  very  readily  becoming 
passive  (p.  416)  therein,  but  HOI  dissolves  it,  yielding  chromous  chloride, 
CrCl2,  a  property  which  connects  chromium  with  iron.  Chromium,  like 
aluminium,  is  attacked  by  the  alkali  hydroxides  at  high  temperatures, 
evolving  hydrogen  and  producing  chromates.  By  the  action  of  sodium 
on  chromic  chloride  the  metal  has  been  obtained  in  octahedral  crystals, 
which  are  not  dissolved  even  by  nitro-hydrochloric  acid. 

236.  Oxides  of  chromium.  —  Three  oxides  of  chromium  are  known 
in  the  separate  state  —  chromic  oxide,  Cr203,  chromium  dioxide,  Cr02,  and 
chromic  anhydride,  Cr03.  Monoxide  of  chromium  or  chromous  oxide  (CrO) 
is  known  in  the  hydrated  state,  and  perchromic  acid  (H2Cr208)  is  believed 
to  exist  in  solution.  The  chromous  salts  correspond  with  the  ferrous 
salts,  but  are  much  more  susceptible  of  oxidation. 

Chromic  anhydride  (often  called  chromic  acid),  the  most  important  of 
these,  is  obtained  by  adding  to  one  measure  of  a  solution  of  potassium 
dichromate,  saturated  at  54°  C.,  one  measure  and  a  half  of  concentrated 
sulphuric  acid,  by  small  portions  at  a  time,  and  allowing  the  solution 
to  cool,  when  chromic  anhydride  crystallises  out  in  fine  crimson  needles, 
which  are  deliquescent,  very  soluble  in  water,  fusing  easily,  and  decom- 
posed at  250°  C.  into  oxygen  and  chromic  oxide.  Chromic  anhydride 
is  a  powerful  oxidising  agent  ;  most  organic  substances,  even  paper,  will 
reduce  it  to  the  green  chromic  oxide.  A  mixture  of  potassium  dichro- 
mate  and  sulphuric  acid  is  employed  for  bleaching  some  oils,  the 
colouring-matter  being  oxidised  at  the  expense  of  the  chromic  acid,  and 
chromic  sulphate  being  produced  — 


K2Cr207  +  4H2S04  =  K2S04  +  Cr2(S04)3  +  03 

The  dichromate  itself  evolves  oxygen  when  heated  to  bright  red- 
ness, being  first  fused  (about  400°  C.),  and  afterwards  decomposed; 
2K2Cr207  =  2K,CrO4  +  Cr2O3  +  Os.  Heated  with  strong  HC1,  it  evolves 
01;  K,Cr,O7+i4HCl  =  2KCl  +  CrgCl6  +  7H8q  +  016.  The  oxidising  effect 
of  the  potassium  dichromate,  under  the  action  of  light,  upon  gelatine 
and  albumin,  receives  very  important  applications  in  photography. 

Sodium  dichromate,  Na,2Cr2O7.2H3O,  is  much  more  soluble  than  the 
potassium  salt,  requiring  only  an  equal  weight  of  water  ;  it  is  now  often 
substituted  for  K2Cr207,  being  similarly  prepared,  and  containing,  of 
course,  a  higher  percentage  of  available  oxygen  owing  to  the  lower 
atomic  weight  of  sodium. 

Chromic  acid,  H2Cr04,  is  not  known  in  the  pure  form.  Its  salts, 
the  chromates,  are  isomorphous  with  the  sulphates. 

Chromate  of  potash,  or  normal  potassium  chr  ornate  (K2O.Cr03  or 
K2Cr04),  is  formed  by  adding  potassium  carbonate  to  the  red  solution 
of  potassium  dichromate  until  its  red  colour  is  changed  to  a  fine  yellow, 
when  it  is  evaporated  and  allowed  to  crystallise.  It  forms  yellow 


432  CHROMIC   OXIDE. 

prismatic  crystals,  having  the  same  form  as  those  of  potassium  sul- 
phate, and  is  five  times  as  soluble  in  water  as  the  dichromate  is,  yielding 
an  alkaline  solution,  which  is  partly  decomposed  by  evaporation,  with 
formation  of  the  dichromate.  Acids,  even  carbonic,  change  its  solution 
from  yellow  to  red,  from  production  of  dichromate.  It  becomes  red 
when  heated,  and  yellow  again  on  cooling,  and  fuses  without  decompo- 
sition. Potassium  chromate  has  been  found  in  some  yellow  samples 
of  saltpetre  from  Chili.  No  compound  corresponding  with  KHSO4  is 
known. 

Trichromate  of  potash  (K20.3Cr03)  has  been  obtained  in  red  crystals  by  adding 
nitric  acid  to  the  dichromate. 

It  will  be  observed  that  the  chromates  of  potassium  are  rather  exceptional  salts. 
The  yellow  or  normal  chromate,  K2CrO4,  is  formed  upon  the  model  of  imaginary 
chromic  acid,  H2Cr04.  The  red  chromate,  or  potassium  dichromate,  is  not  a  true 
acid  salt,  for  it  contains  no  hydrogen  ;  it  is  sometimes  called  anhydro-chromatet 
and  written  K2Cr04.Cr03.  The  trichromate  would  be  K2Cr04.2Cr03. 

Barium  chromate,  BaCr04.  is  used  in  painting,  as  yellow  ultra-marine,,  being  pre- 
cipitated by  potassium  chromate  from  barium  chloride  ;  it  is  insoluble  in  acetic 
acid  ;  i  million  parts  of  H20  dissolve  15  parts  of  BaCr04  at  18°  C. 

Chrome  yellow  is  the  chromate  of  lead  (PbCr04),  prepared  by  mixing  dilute  solu- 
tions of  lead  acetate  and  potassium  chromate.  The  precipitate  is  insoluble  in  acetic 
acid.  It  is  largely  used  in  painting  and  calico-printing,  and  by  the  chemist  as  a 
source  of  oxygen  for  the  analysis  of  organic  substances,  since,  when  heated,  it  fuses 
to  a  brown  mass,  which  evolves  oxygen  at  a  red  heat.  Chrome  yellow  being  a 
poisonous  salt,  its  occasional  use  for  colouring  confectionery  is  very  objectionable. 
Chromate  of  lead  in  prismatic  crystals  forms  the  rather  rare  red  lead  ore  of  Siberia, 
in  which  chromium  was  first  discovered. 

Orange  chrome  is  a  basic  chromate  of  lead  (PbCr04.PbO),  and  maybe  obtained  by 
boiling  the  yellow  chromate  with  lime  ;  2(PbCr04)  +  CaO  =  PbCr04.PbO  +  CaCr04. 
The  calico-printer  dyes  the  stuff  with  yellow  chromate  of  lead,  and  converts  it  into 
orange  chromate  by  a  bath  of  lime-water.  Chrome-orange  is  also  made  by  precipi- 
tating a  lead  salt  with  a  weak  alkaline  solution  of  potassium  chromate,  which  gives- 
a  mixture  of  the  two  chromates  of  lead. 

Silver  chromate,  Ag2Cr04,  is  obtained  as  a  red  crystalline  precipitate  when  silver 
nitrate  is  added  to  potassium  chromate.  When  K2Cro07  is  added  gradually  to 
AgN03,  a  scarlet  precipitate  of  silver  dichromate,  Ag2Cr267,  is  obtained  ;  and  if  this- 
be  boiled  with  water,  it  leaves  Ag2Cr04  in  dark  green  crystals,  which  become  red 
when  powdered. 

The  colour  of  the  ruby  (crystallised  alumina)  appears  to  be  due  to  the  presence 
of  a  small  proportion  of  chromic  anhydride. 

Sesquioxide  of  chromium,  or  chromic  oxide  (Cr203),  is  valuable  as  a 
green  colour,  especially  for  glass  and  porcelain,  since  it  is  not  decomposed 
by  heat.  Being  extremely  hard,  it  is  used  in  making  razor-strops.  It  is 
prepared  by  heating  potassium  dichromate  with  one-fourth  of  its  weight 
of  starch,  the  carbon  of  which  removes  oxygen,  leaving  a  mixture  of 
chromic  oxide  with  potassium  carbonate,  which  may  be  removed  by 
washing  with  water.  If  sulphur  be  substituted  for  the  starch,  potas- 
sium sulphate  will  be  formed,  which  may  also  be  removed  by  water. 
"When  hydrated  chromic  oxide  is  strongly  heated,  it  loses  its  water  and 
exhibits  a  sudden  glow,  becoming  'darker  in  colour,  and  insoluble  in 
acids  which  previously  dissolved  it  easily ;  in  this  respect  it  resembles 
aluminia  and  ferric  oxide.  Like  these  oxides,  the  chromic  oxide  is  a 
feeble  base ;  it  is  remarkable  for  forming  two  classes  of  salts,  having  the 
same  composition,  but  differing  in  the  colour  of  their  solutions,  and  in 
some  other  properties.  Thus,  there  are  two  modifications  of  the  chromic 
sulphate — the  green  sulphate,  O2(S04)3.6Aq,  and  the  violet  sulphate, 
Cr2(S04)3.9Aq.  The  solution  of  the  latter  conducts  electricity  well  and 


CHROMIUM  CHLORIDES. 


433 


gives  the  reactions  of  a  sulphate,  but  when  boiled  ifc  becomes  greeny 
conducts  badly,  and  gives  no  precipitate  with  BaCl2.  Chrome  alum 
forms  dark  purple  octahedra  (KCr"'(S04)2.i2Aq)  which  contain  the 
violet  modification  of  the  sulphate ;  and  if  its  solution  in  water  be 
boiled,  its  purple  colour  changes  to  green,  and  the  solution  refuses  to 
crystallise.*  It  is  obtained  as  a  secondary  product  in  certain  chemical 
manufactures,  and  may  be  prepared  by  the  action  of  sulphurous  acid 
gas  on  a  mixture  of  potassium  dichromate  and  sulphuric  acid ;  K2O307 
+  H2S04  +  3S02  =  2KCr(S04)2  +  H3O.  The  anhydrous  chromic  sul- 
phate forms  red  crystals,  which  are  insoluble  in  water  and  acids. 
Guignet's  green,  used  in  painting  and  calico-printing,  is  hydrated  Cr2O3 
prepared  by  heating  K2Cr2O7  with  3  parts  of  boric  acid  (when  oxygen 
is  evolved)  and  washing  the  product  until  it  is  free  from  potassium 
borate ;  it  generally  retains  a  little  boric  acid,  perhaps  as  chromic 
borate.  Cr2O3  combines  with  the  oxides  of  the  magnesium  group  of 
metals  to  form  very  insoluble  and  infusible  compounds,  crystallising  in 
octahedra,  e.g.,  ZnO.Cr,O3,  MnO.Cr203,  FeO.O2O3,  which  have  been 
termed  chromites,  and  are  isomorphous  with  the  spinelles  (p.  388). 

Crystallised  Cr2O3,  prepared  by  passing  chromyl  chloride  (p.  434) 
through  a  red-hot  tube,  is  isomorphous  with  A1203  and  Fe203. 

Chromic  hydroxide.  Cr.2(OH)6,  is  thrown  down  by  alkalies  from  solutions  of 
chromic  salts,  such  as  chrome  alum,  as  a  greenish-blue  precipitate.  It  dissolves 
sparingly  in  ammonia  to  a  pink  solution,  from  which  chromic  oxide  is  precipitated 
by  boiling.  Potash  dissolves  it  to  a  fine  green  solution,  which  becomes  gelatinous 
when  boiled,  from  precipitation  of  chromic  oxide.  It  yields  a  hydrosol  by  the 
dialysis  of  its  solution  in  CrCl3. 

Chromium  dioxide,  Cr02. — When  potassium  dichromate  is  reduced  by  nitric 
oxide  or  sodium  thiosulphate,  a  brown  precipitate  is  obtained  ;  this  is  a  compound 
of  water  with  Cr02,  which  is  left,  on  heating  to  250°  C. ,  as  a  black  powder,  which 
evolves  oxygen  at  300°  C.,  becoming  Cr203.  It  may  be  regarded  as  chromic 
cht'omate,  Cr203.Cr03. 

Chro mous  oxide  (CrO)  is  not  known  in  the  pure  state,  but  is  precipitated  as  a  brown 
hydrate  when  chromous  chloride  is  decomposed  by  potash.  It  absorbs  oxygen 
even  more  readily  than  ferrous  oxide  does,  becoming  converted  into  CrO.Cr203, 
corresponding  in  composition  with  the  magnetic  oxide  of  iron.  Chromous  oxide 
is  a  feeble  base  ;  a  double  sulphate,  K2Cr"(S04)2.6Aq,  is  known,  isomorphous 
with  the  corresponding  iron  salt,  K2Fe"(S04)2.6Aq  ;  it  has  a  blue  colour,  and  gives 
a  blue  solution,  which  becomes  green  when  exposed  to  air. 

Perchromlc  acid.  (H2Cr208)  is  believed  to  exist  as  the  blue  solution  obtained  by 
the  action  of  H202  upon  solution  of  chromic  acid,  but  neither  the  acid  nor  its 
salts  have  been  obtained  in  a  separate  state  (p.  64).  A  sodium  perchramnte, 
Na6Cr2015.28H20,  crystallises  from  a  solution  made  by  adding  Na/)2  to  a  thin 
paste  of  Cr2(OH)6  in  water.  Acids  decompose  it,  the  blue  colour  of  perchromic 
acid  being  first  produced. 

237.  Chlorides  of  chromium. — The  chromic  chloride  (CrCl3)  obtained  by  passing 
dry  chlorine  over  a  mixture  of  chromic  oxide  with  charcoal,  heated  to  redness 
in  a  glass  tube,  is  converted  into  vapour,  and  condenses  upon  the  cooler  part 
of  the  tube  in  shining  leaflets,  having  a  fine  violet  colour.  When  heated  in  air, 
it  is  decomposed,  evolving  01,  and  leaving  Cr2O3.  Very  soluble  green  crystals 
of  CrCl3.6Aq  may  be  obtained,  but  the  water  cannot  be  expelled  without  decom- 
posing the  chloride.  Cold  water  does  not  affect  CrCl3,  but  boiling  water  slowly 
dissolves  it  to  a  green  solution  resembling  that  obtained  by  dissolving  Cr203  in 
HC1.  If  a  little  chromous  chloride  be  added  to  water  in  which  CrCl3  is  suspended, 
the  latter  dissolves  quickly  and  with  evolution  of  heat,  yielding  the  green  solution, 
which  becomes  violet  after  some  time.  Only  two-thirds  of  the  Cl  is  precipitated 
from  the  green  solution  by  AgN03  when  this  is  first  added. 

Chromous  chloride  (CrCl2)  is  obtained  by  heating  CrCl3  in  hydrogen.     It  is  white, 

*  Exposure  to  cold,  it  is  said,  again  converts  it  into  the  crystallisable  violet  form. 

2  E 


434  REVIEW  OF  THE  IRON  GROUP. 

and  dissolves  in  water  to  form  a  blue  solution,  which  absorbs  oxygen  from  the  air, 
becoming  green.  CrCl2  is  also  formed  when  chromium  is  dissolved  in  HC1.  A 
solution  of  chromic  chloride  or  sulphate,  mixed  with  HC1,  is  reduced  to  chromous 
chloride  by  metallic  zinc,  the  liquid  becoming  greenish  blue  and  giving  a  pink 
precipitate  of  chromous  acetate  on  addition  of  ammonium  acetate,  becoming 
blue  when  shaken  with  air.  Chromous  chloride  resembles  ferrous  chloride  in 
absorbing  NO  to  form  a  brown  compound. 

Chromyl  chloride,  Cr02Cl2  ( =  2  vols.),  or  chromic  oxychloride.  formerly  called 
vhlorochromic  acid,  bears  the  same  relation  to  Cr03  that  sulphuryl  chloride,  S02C12, 
bears  to  S03.  It  is  a  brown-red  liquid,  obtained  by  distilling  10  parts  of  NaCl  and 
17  of  K2Cr20.7,  previously  fused  together  and  broken  into  fragments,  with  40  parts 
of  oil  of  vitriol — 

K2Cr207  +  4NaCl  +  3H2S04  =  K2S04  +  2Na2S04  +  3H20  +  2Cr02Cl2. 
It  much  resembles  bromine  in  appearance,  and  fumes  very  strongly  in  air,  the 
moisture  of  which  decomposes  its  red  vapour,  forming  chromic  and  hydrochloric 
acids  ;  Cr02Cl2  +  2H20  =  H2CrO4  +  2HCl.  Its  sp.  gr.  is  1.92,  and  it  boils  at  118°  C. 
It  is  a  very  powerful  oxidising  and  chlorinating  agent,  and  inflames  ammonia  and 
alcohol  when  brought  in  contact  with  them. 

It  is  occasionally  used  to  illustrate  the  nature  of  illuminating  flames  ;  for  if 
hydrogen  be  passed  through  a  bottle  containing  a  few  drops  of  it,  the  gas  becomes 
charged  with  its  vapour,  and,  if  kindled,  burns  with  a  brilliant  white  flame,  which 
deposits  a  beautiful  green  film  of  chromic  oxide  upon  a  cold  surface.  When  heated, 
in  a  sealed  tube,  to  190°  C.,  it  is  converted  into  a  black  solid  body,  according  to 
the  equation  3Cr02Cl2  =  Cl4+CrCl2.2Cr03.  When  K2Cr207  is  gently  warmed  with 
HC1,  the  solution  deposits  red  prisms  of  KClCr03,  formerly  known  as  potassium 
chlorochromate,  which  may  be  regarded  as  Cr02Cl(OK),  being  derived  from  the  at 
present  unknown  Cr02Cl(OH),  corresponding  with  S02C1(OH). 

Cliromyl  fluoride,  Cr02F2,  is  another  volatile  compound  of  chromium  obtained 
by  distilling  lead  chromate  with  fluor  spar  and  sulphuric  acid  ;  it  is  a  red  gas, 
condensible  to  a  red  liquid  at  a  low  temperature.  Water  decomposes  it,  yielding 
chromic  and  hydrofluoric  acids.  Chromic  fluoride,  CrF34H20,  is  a  green  crystalline 
powder  used  as  a  mordant. 

Chromic  sulphide  (Cr2S3)  is  formed  when  H2S  is  passed  over  chromic  oxide  heated 
to  redness.  It  forms  black  lustrous  scales  resembling  graphite. 

By  fusing  chromic  hydroxide  with  sodium  carbonate  and  sulphur,  sodium  thio- 
chromite,  Na2Cr2S4,  is  obtained  as  a  dark  red  body  insoluble  in  water,  and  not 
easily  attacked  "by  hydrochloric  or  sulphuric  acid.  Thiochromites  of  other 
metals  have  also  been  obtained. 

Chromium  nitride,  ON,  has  been  obtained  by  heating  chromium  to  redness  in 
nitrogen. 

Chromium  salts  form  a  series  of  amines  analogous  to  the  cobalt- 
amines  (p.  423). 

Chromium  is  nearly  allied  to  iron  by  its  property  of  forming 
chromous  and  chromic  salts,  and  to  manganese  through  the  chromates 
which  correspond  and  are  isomorphous  with  the  manganates,  and  rival 
them  in  colour.  Soluble  chromium  compounds  are  very  poisonous. 

238.  Review  of  iron,  cobalt,  nickel,  manganese,  and  chromium. 
— Many  points  of  resemblance  will  have  been  noticed  in  the  chemical 
history  of  these  metals.  They  are  all  capable  of  decomposing  water  at 
a  red  heat,  and  easily  displace  hydrogen  from  hydrochloric  acid.  Each 
of  them  forms  a  base  by  combining  with  one  atom  of  oxygen,  and  these 
oxides  produce  salts  which  have  the  same  crystalline  form.  All  these 
oxides,  except  that  of  nickel,  easily  absorb  oxygen  from  the  air,  and 
are  converted  into  sesquioxides.  The  sesquioxide  of  nickel  is  very 
feebly  basic,  whilst  that  of  cobalt  is  slightly  more  basic  ;  the  sesquioxide 
of  manganese  is  a  stronger  base,  and  the  basic  properties  of  the  sesqui- 
oxides of  chromium  and  iron  are  very  decided.  Nickel  does  not  exhibit 
any  tendency  to  form  a  well-marked  acid  oxide,  but  the  existence  of  an 
acid  oxide  of  cobalt  is  suspected ;  and  iron,  manganese,  and  chromium 


MOLYBDENUM. 


435 


form  undoubted  acid  oxides  with  three  atoms  of  oxygen.  Nickel  is  only 
known  to  form  one  compound  with  chlorine  ;  cobalt  and  manganese 
form,  in  addition  to  their  protochlorides,  very  unstable  perchlorides 
known  only  in  solution,  but  iron  and  chromium  form  very  stable 
volatile  perchlorides.  The  metals  composing  this  group  are  all  divalent 
in  their  protoxides  and  the  corresponding  salts,  and  are  found  associated 
in  natural  minerals ;  this  is  especially  the  case  with  iron,  manganese, 
cobalt,  and  nickel.  They  all  require  a  very  high  temperature  for  their 
fusion.  Iron  and  chromium  connect  this  group  with  aluminium,  their 
sesquioxides  being  isomorphous  with  alumina,  and  their  perchlorides 
volatile  like  aluminium  chloride.  In  the  periodic  table  (p.  302)  Cr  falls 
in  group  vi.,  since  its  highest  salt-forming  oxide  is  Cr03 ;  Mn  forms  salts 
corresponding  with  Mn207  (permanganates),  and  is  therefore  in  group  vii. 
Fe,  Co,  and  Ni  are  placed  in  group  viii.,  although  oxides  of  the  type  R04 
have  yet  to  be  discovered. 

MOLYBDENUM,  Mo  =  95. 3. 

239.  This  metal  derives  its  name  from  //,oAt}/35cuj>a,  lead,  on  account  of  the 
resemblance  of  its  chief  ore,  molybdenite,  to  black  lead.  Molybdenite,  or  molyb- 
denum glance,  is  the  disulphide  (MoS2),  and  is  found  chiefly  in  Bohemia  and 
Sweden  ;  it  may  be  recognised  by  its  remarkable  similarity  to  plumbago,  and  by 
its  giving  a  blue  solution  when  boiled  with  strong  sulphuric  acid.  It  is  chiefly 
employed  for  the  preparation  of  ammonium  molybdate,  which  is  used  in  testing  for 
phosphoric  acid.  For  this  purpose  the  disulphide  is  roasted  in  air  at  a  dull  red- 
heat,  when  S02  is  evolved,  and  molybdic  anhydride  (Mo03)  mixed  with  oxide  of 
iron  is  left.  The  residue  is  digested  with  strong  ammonia,  which  dissolves  the 
former  as  ammonium  molybdate,  obtainable  in  prismatic  crystals  (NH4HMo04)  on 
evaporation.  When  a  solution  of  ammonium  molybdate  is  added  to  a  phosphate 
dissolved  in  dilute  nitric  acid,  a  yellow  precipitate  of  ammonium  phosplio-molyb- 
date  *  is  produced,  containing  molybdic  and  phosphoric  acids  combined  with 
ammonia,  by  the  formation  of  which  very  minute  quantities  of  phosphoric  acid  can 
be  detected.  If  hydrochloric  acid  be  added  in  small  quantity  to  a  strong  solution 
of  molybdate  of  ammonium,  the  molybdic  acid  is  precipitated,  but  it  is  dissolved  by 
an  excess  of  hydrochloric  acid,  and  if  the  solution  be  dialysed,  the  molybdic  acid, 
H2Mo04,  is  obtained  in  the  form  of  an  aqueous  solution  which  reddens  blue  litmus, 
has  an  astringent  taste,  and  leaves  a  soluble  gum-like  residue  when  evaporated.  Be- 
sides this  simple  acid,  salts  of  many  complex  acids  are  known,  recalling  the  poly- 
silicates.  Molybdic  anhydride  fuses  at  a  red  heat  to  a  yellow  glass,  and  may  be 
sublimed  in  a  current  of  air  in  shining  needles.  In  contact  with  dilute  hydro- 
chloric acid  and  metallic  zinc,  it  is  converted  into  a  blue  compound  of  the  com- 
position Mo02.2Mo03  (molybdenum  molybdate')  which  is  soluble  in  water,  but  is 
precipitated  on  adding  a  saline  solution.  Molybdate  of  lead  (PbMo04)  is  found  as  a 
yellow  crystalline  mineral  ( Wulfenite).  When  Mo03  is  heated  in  hydrogen  it  is 
successively  reduced  to  Mo02  arid  Mo2O3  and  finally  to  metal.  The  molybdic  oxide 
(Mo02)  is  basic,  and  forms  dark  red-brown  salts.  Molybdous  oxide  (MoO)  is  ob- 
tained by  adding  an  alkali  to  the  solution  resulting  from  the  prolonged  action  of 
zinc  upon  a  hydrochloric  solution  of  molybdic  acid.  It  is  a  black,  basic  oxide  which 
absorbs  oxygen  from  the  air. 

Metallic  molybdenum  is  obtained  by  heating  a  mixture  of  an  excess  of  Mo03  with 
charcoal  in  the  electric  furnace.  The  pure  metal  is  like  the  best  wrought  iron.  It 
is  of  about  the  same  colour  and  malleability,  easily  polished  and  capable  of  being 
forged.  Its  sp.  gr.  is  9.01  and  its  melting-point  very  high.  At  600°  C.  it  oxidises 
slowly  in  air  and  volatilises  as  Mo03  ;  it  is  also  attacked  by  halogens  at  this 
temperature  but  not  violently.  It  decomposes  steam  when  hot  and  is  oxidised  by 
hot  strong  H2S04,  by  nitric  acid  and  by  fused  alkalies  from  which  it  evolves  H, 
but  it  is  not  attacked  by  HC1.  The  resemblance  to  iron  extends  to  its  relation  to 
carbon,  with  which  it  maybe  combined  by  cementation  (p.  411)  to  form  a  metal  of 
.steely  properties,  hard  enough  to  scratch  glass,  and  capable  of  being  tempered  by 

*  Its  composition  varies  with  the  conditions  ;  it  is  commonly  6NH4.P2O8.24MoO3. 


436  TUNGSTEN. 

quenching  from  300°  C.  With  a  larger  proportion  of  carbon  it  forms  a  metal 
capable  of  being  cast  and  containing  the  carbide  Mo2C  ;  the  sp.  gr.  of  such  metal 
is  about  8.7. 

When  heated  in  chlorine  Mo  yields  molybdenum  pentachloride  (MoCl5),  which 
forms  a  red  vapour,  and  condenses  in  crystals  resembling  iodine,  soluble  in  water. 
A  subchloride  (Mo3Cl6),  trichloride  (MoCl3),  tetrachloride  (MoCl4),  and  several  oxy- 
chlorides  are  also  known.  The  trisulphide  (MoS3)  and  tetrasulpMde  (MoS4)  of 
molybdenum  are  soluble  in  alkali  sulphides. 

In  addition  to  the  natural  sources  of  molybdenum  above  mentioned,  there  may 
be  noticed  molybdic  ochre  (an  impure  rnolybdic  anhydride),  and  the  difficultly 
fusible  masses  called  bear,  from  the  copper  works  in  Saxony,  which  contain  a 
large  amount  of  molybdenum  combined  with  iron,  copper,  cobalt,  and  nickel. 
Molybdenum  has  been  detected  in  the  mud  deposited  by  the  Buxton  thermal 
water. 

TUNGSTEN,  W  =  182.6. 

240.  Tungsten  is  chiefly  found  in  the  mineral  wolfram,  which  occurs,  often 
associated  with  tin-stone,  in  large  brown  shining  prismatic  crystals,  which  are 
even  heavier  than  tin-stone  (sp.  gr.  7.3),  from  which  circumstance  the  metal 
derives  its  name,  tungsten,  in  Swedish,  meaning  heavy  stone.  The  symbol  (W) 
used  for  tungsten  is  derived  from  the  Latin  name  wolfratiiium.  Wolfram  contains 
the  tungstates  of  iron  and  manganese  in  variable  proportions,  and  may  be  regarded 
as  an  isomorphous  mixture  of  tungstates  of  iron  and  manganese  (MnFe)W04r 
Scheelite,  tungstate  of  calcium  (CaW04),  and  a  tungstate  of  copper  are  also  found. 

Tungstate  of  sodium,  Na2W04.2H2O,  is  employed  by  calico-printers  as  a  mordant, 
and  is  sometimes  applied  to  muslin,  in  order  to  render  it  uninflammable.  It  is  ob- 
tained by  fusing  wolfram  with  Na2C03,  an  operation  to  which  tin  ores  containing 
this  mineral  in  large  quantity  are  sometimes  submitted  previously  to  smelting 
them.  Water  extracts  the  sodium  tungstate,  which  may  be  crystallised  in 
rhomboidal  plates.  When  a  solution  of  this  salt  is  mixed  with  an  excess  of  hydro- 
chloric acid,  white  hydrated  tungstic  acid  (H2W04.Aq)  is  precipitated,  while  hot 
solutions  give  a  yellow  precipitate  of  H2W04  ;  but  if  dilute  HC1  be  carefully  added 
to  a  5  per  cent,  solution  of  sodium  tungstate  in  sufficient  proportion  to  neutralise 
the  alkali,  and  the  solution  be  then  dialysed  (p.  278),  the  sodium  chloride  passes 
through,  and  a  pure  aqueous  solution  of  tungstic  acid  is  left  in  the  dialyser.  This 
solution  is  unchanged  by  boiling,  and  when  evaporated  to  dryness,  vitreous  scales,, 
like  gelatine,  are  left,  which  adhere  very  strongly  to  the  dish,  and  redissolve  in  one- 
fourth  of  their  weight  of  water,  forming  a  solution  of  the  very  high  specific  gravity 
3.2,  which  is,  therefore,  able  to  float  glass.  The  solution  has  a  bitter  and  astringent- 
taste,  and  decomposes  Na^COg  with  effervescence.  It  becomes  green  when  exposed 
to  air,  from  the  de-oxidising  action  of  organic  dust.  When  tungstic  acid  is  heated,. 
it  loses  water,  and  becomes  of  a  straw-yellow  colour,  and  insoluble  in  acids.  There 
are  at  least  two  modifications  of  tungstic  acid,  which  bear  to  each  other  a  relation 
similar  to  that  between  stannic  and  metastannic  acids  (q.v.). 

Barium  tungstate  has  been  employed  as  a  substitute  for  white  lead  in  painting. 

The  most  characteristic  property  of  tungstic  acid  is  that  of  yielding  a  blue  oxide 
(W02.2W03),  when  placed  in  contact  with  HC1  and  metallic  zinc. 

A  very  remarkable  compound  containing  tungstic  acid  and  soda  is  obtained  when 
sodium  ditung  state  (Na2W207.4H20)  is  fused  with  tin.  If  the  fused  mass  be  treated 
with  strong  KOH,  to  remove  free  tungstic  acid,  washed  with  water,  and  treated 
with  HC1,  yellow,  lustrous,  cubical  crystals,  probably iNa2O.W02. 2 W03,  are  obtained, 
which  are  remarkable,  among  sodium  compounds,  for  their  resistance  to  the  action 
of  water,  of  alkalies,  and  of  all  acids  except  HF.  This  salt  is  called  gold-  or  saffron- 
bronze.  The  corresponding  potassium  salt  is  violet-  or  magenta-bronze. 

The  tungstob  orates  are  remarkable  salts,  containing  W03  and  B203,  combined 
with  metallic  oxides.  Their  solutions  have  a  very  high  specific  gravity  ;  that  of 
cadmium  tungstoborate  has  the  sp.  gr.  3.6,  and  is  used  to  effect  the  mechanical 
separation  of  minerals  of  different  specific  gravities.  Thus,  a  diamond  (sp.  gr.  3.5) 
would  float  ;  whilst  a  white  sapphire  (sp.  gr.  4.0)  would  sink  in  the  solution. 
Tungstosilicates  also  exist. 

Tungsten  trioxide,  W03,  is  obtained  by  decomposing  metallic  tungstates  with 
nitric  acid,  and  heating  the  tungstic  acid  thus  precipitated.  It  is  a  canary  yellow 
powder,  becoming  orange  when  heated  and  yellow  again  on  cooling. 

The  tungsten  dioxide  (W02)  appears  to  be  an  indifferent  oxide,  and  is  obtained 


URANIUM.  437 

by  reducing  tungstic  anhydride  with  hydrogen  at  a  low  red  heat,  when  it  forms 
a  brown  powder,  which  is  dissolved  by  boiling  in  solution  of  potash,  hydrogen 
being  evolved,  and  potassium  tungstate  formed. 

Metallic  tungsten  is  obtained  by  reducing  tungstic  anhydride  with  charcoal  (or 
hydrogen)  at  a  white  heat.  It  may  also  be  obtained  by  igniting  a  mixture  of 
W03  and  aluminium  powder,  but  in  order  to  obtain  the  necessarily  high  tempera- 
ture the  mixture  must  be  moistened  with  about  £  of  its  volume  of  liquid  air.  It 
is  an  iron-grey  infusible  metal  of  sp.  gr.  18.7,  very  hard,  very  infusible,  not  affected 
by  hydrochloric  or  diluted  sulphuric  acid,  but  converted  into  tungstic  acid  by  the 
action  of  nitric  acid.  Tungsten  dissolved  in  about  20  times  its  weight  of  fused 
steel  increases  the  hardness  of  the  steel  without  diminishing  its  tenacity. 

When  tungsten  is  heated  in  chlorine,  the  tungstic  chloride  (WC12)  sublimes  in 
bronze-coloured  needles.  When  gently  heated  in  hydrogen,  it  is  converted  into 
the  tetrachloride  (WC14),  but  if  its  vapour  be  mixed  with  hydrogen  and  passed 
through  a  glass  tube  heated  to  redness,  metallic  tungsten  is  obtained  in  a  form 
in  which  it  is  not  dissolved  even  by  aqua  regia,  though  it  may  be  converted  into 
potassium  tungstate  by  potassium  hypochlorite  mixed  with  potash  in  excess. 
WC16  is  also  obtained  in  steel-blue  needles,  together  with  WOC14  and  W02C12  by 
the  action  of  PC15  on  W03. 

Tungsten  disulphide  (WS2)  is  a  black  crystalline  substance  resembling  plum- 
bago, obtained  by  heating  a  mixture  of  potassium  ditungstate  with  sulphur,  and 
washing  with  hot  water.  Tungsten  tri  sulphide  (WS3)  is  a  sulphur-acid,  obtainable 
as  a  brown  precipitate  by  dissolving  tungstic  acid  in  an  alkaline  sulphide,  and 
precipitating  by  an  acid. 

Both  Mo03  and  W03  form  a  number  of  complex  salts  with  the  alkali  oxides  and 
the  pentoxides  of  As,  P,  and  V.  These  are  the  tungsto-  and  molybdo-  arsenates, 
phosphates,  and  vanadates. 

URANIUM,  U  =  237.y. 

241.  This  metal  occurs  in  the  pitchblende  (U0.2.2U03)  of  Cornwall,  It  is  not 
used  in  the  metallic  state,  but  in  the  form  of  the  black  oxide,  U02.U03,  and  of 
will nin  uranate,  Na2U207.6H20  (uranium  yellow),  for  imparting  black  and  yellow 
colours  respectively  to  glass"  and  porcelain.*  The  latter  compound  is  prepared 
from  pitchblende  by  roasting  the  mineral  with  lime,  decomposing  the  calcium 
uranate  thus  formed  with  sulphuric  acid,  and  treating  the  solution  of  uranyl 
sulphate  with  sodium  carbonate.  This  precipitates  the  foreign  metals  and  the 
Na.2U207,  which  redissolves  in  the  excess  of  sodium  carbonate,  and  is  precipitated 
by  neutralisation  with  sulphuric  acid  and  boiling. 

Uranium  forms  two  oxides,  U02,  a  basic  oxide  known  as  uranyl,  and  U03,  an  acid 
oxide.  Pitchblende  (the  green  oxide)  and  the  black  oxide  may  be  regarded  as 
uranyl  diuranate  and  uranyl  uranate  respectively.  Of  the  uranyl  (also  called 
uranic)  salts,  the  nitrate,  UO2(N03)2.6H20,  and  acetate,  U02Ac2.2H20,  are  used  as 
laboratory  reagents,  and  in  photographic  printing,  for  which  they  are  fitted  by 
the  fact  that  they  are  reduced  by  light  in  contact  with  organic  matter  to  uranous 
salts,  corresponding  with  the  base,  UO.  These  latter  salts  have  been  but  little 
studied,  but  they  give  a  brown  precipitate  with  potassium  ferricyanide,  by  which 
means  the  photographic  print  may  be  developed.  Some  organic  salts  of  uranyl 
are  decomposed  by  light  without  reduction  ;  thus  the  oxalate  in  water  evolves 
CO  and  C02,  leaving  a  precipitate  of  uranylhydroxide,  U02(OH)2. 

Sodium  perura-nate,  Na4U08.ioH20,  is  obtained  by  the  addition  of  sodium  per- 
oxide to  a  solution  of  a  uranyl  salt.  Uranium  tetrachloride,  UC14  (which  is  volatile, 
so  that  its  vapour  density  is  known),  and  uranyl  chloride,  U02C12,  have  been  pre- 
pared. UC13  and  UC15  are  also  known. 

Metallic  iirn /iium  is  prepared  by  reducing  UC14  with  sodium.  It  is  white  and 
malleable  ;  sp.  gr.  18.7  ;  dissolves  in  acids  evolving  hydrogen.  When  reduced 
from  the  oxide  by  carbon  it  contains  5-13  per  cent,  of  C,  is  very  hard,  melts  at  a 
temperature  higher  than  the  melting-point  of  platinum,  and  decomposes  water  at 
the  ordinary  temperature. 

There  must  here  be  noticed  a  curious  phenomenon  first  observed  in  uranium 
salts,  namely,  the  power  possessed  by  certain  substances  of  emitting  radiations 
which  produce  the  same  effect  as  that  of  light  on  a  photographic  plate  and  also  so 
influence  the  air  that  its  conductivity  for  electricity  is  increased.  Thus  if  a  crystal 

*  "  Urauiuui  glass  "  exhibits  a  strong-  greenish-yellow  fluorescence. 


43$  REVIEW  OF  THE   CHROMIUM   GROUP. 

of  an  ordinary  uranium  salt  be  placed  on  a  material  opaque  to  light,  such  as  black 
paper,  or  to  electricity  such  as  glass  or  aluminium,  and  the  material  be  laid  upon 
a  photographic  plate,  the  position  and  shape  of  the  crystal  will  be  faithfully 
recorded  as  an  invisible  image  capable  of  development,  in  the  course  of  a  short 
time  varying  with  the  degree  of  activity.  Again,  if  the  crystal  be  held  at  a  short 
distance  from  a  charged  electroscope  this  will  lose  its  charge  more  quickly  than  it 
would  normally. 

It  has  been  shown  that  uranium  nitrate  recrystallised  from  ether  is  free  from 
this  property,  indicating  that  the  activity  is  due  to  some  other  substance. 

Certain  specimens  of  pitchblende  containing  bismuth  are  particularly  active,  and 
when  the  bismuth  is  extracted  the  activity  is  found  to  have  accompanied  it,  but 
the  radiations  differ  from  those  of  uranium  salts  in  that  they  are  not  deviated  by 
an  electro-magnet.  It  has  been  supposed  that  such  bismuth  contains  an  element, 
polonium,  which  is  the  source  of  the  activity.  A  second  supposed  element,  radium, 
having  great  "  radio-activity "  and  closely  resembling  barium  in  character,  has 
been  detected  in  pitchblende.  The  rays  from  the  compounds  of  this  substance 
colour  glass,  ozonise  oxygen  and  convert  yellow  phosphorus  into  red.  besides 
having  the  properties  already  cited  for  such  radiations.  The  effect  of  radium 
radiation  on  the  skin  is  remarkable,  creating  painful  sores  which  are  slow  to  heal. 
This  effect  has  been  shown  to  occur  even  through  the  clothing  and  when  the  absolute 
quantity  of  radium  is  very  small. 

Thorium  compounds  also  possess  radio-activity,  and  it  has  been  shown  that  both 
in  this  case  and  that  of  radium  part  of  the  radiation  is  an  emanation  of  material 
particles  which  may  be  deposited  on  other  substances,  especially  if  they  be 
negatively  electrified,  rendering  them  also  radio-active  temporarily.  '  A  negatively 
electrified  platinum  wire  becomes  radio-active  when  it  has  been  exposed  to  the  air 
for  some  time.  At  present  these  phenomena  must  be  regarded  as  inexplicable,  and 
the  existence  of  new  elements  cannot  be  safely  deduced  from  the  observation  of 
such  properties. 

Review  of  the  chromium  family  of  metals. — The  members  of  this 
family,  chromium,  molybdenum,  tungsten,  and  uranium,  exhibit  great 
similarity  in  their  tendency  to  form  acid  oxides  of  the  type  R03,  and 
oxychlorides  of  the  type  R02CJ2.  They  also  enter  into  the  composition 
of  many  complex  salts  analogous  to  the  phospho-molybdates  and  the 
boro-tungstates.  Sulphur,  selenium,  and  tellurium  belong  to  the  same 
group,  and  form  oxyacids  of  the  same  type. 

BISMUTH. 

Bi'"  =  206.9  parts  by  weight. 

242.  Bismuth,  though  useful  in  various  forms  of  combination,  is  too 
brittle  to  be  employed  in  the  pure  metallic  state.  It  is  readily  distin- 
guished from  other  metals  by  its  peculiar  reddish  lustre  and  its  highly 
crystalline  structure,  which  is  very  perceptible  upon  a  freshly  broken 
surface  ;  large  crystals  (apparently  cubes)  of  bismuth  are  easily  obtained 
by  melting  a  few  ounces  in  a  crucible,  allowing  it  to  cool  till  a  crust 
has  formed  upon  the  surface,  and  pouring  out  the  portion  which  has 
not  yet  solidified,  when  the  crystals  are  found  lining  the  interior  of  the 
crucible.  It  is  isomorphous  with  antimony.  It  is  somewhat  lighter 
than  lead  (sp.  gr.  9.8),  and  volatilises  more  readily  at  high  tempera- 
tures. It  is  less  volatile  than  antimony,  and  burns  like  it  in  air. 

Unlike  most  other  metals,  bismuth  is  found  chiefly  in  the  metallic 
state,  disseminated  in  veins,  through  gneiss  and  clay-slate.  The  chief 
supply  is  derived  from  the  mines  of  Schneeberg,  in  Saxony,  where  it  is 
associated  with  the  ores  of  cobalt.  Native  bismuth,  together  with  the 
oxides  and  sulphides,  is  found  abundantly  in  Bolivia  and  Australia, 
accompanied  by  tin-stone  and  sometimes  by  silver  and  gold. 


EXTRACTION  OF  BISMUTH.  439 

In  order  to  extract  the  metal  from  the  masses  of  earthy  matter 
through  which  it  is  distributed,  advantage  is  taken  of  its  very  low 
fusing-point  (268°  C.).  The  ore  is  broken  into  small  pieces,  and  in- 
troduced into  iron  cylinders  which  are  fixed  in  an  inclined  position  over 
a  furnace  (Fig.  226).  The  upper  opening  of  the  cylinders,  through  which 
the  ore  is  introduced,  is 
provided  with  an  iron  door, 
and  the  lower  opening  is 
closed  with  a  plate  of  fire- 
brick perforated  for  the 
escape  of  the  metal,  which 
flows  out,  when  the  cylin- 
ders are  heated,  into  iron 
receiving  pots,  which  are 
kept  hot  by  a  charcoal  fire. 

Commercial        bismuth 
generally  contains  arsenic, 

copper,     Sulphur,     and    Sll-  Fig.  226.— Extraction  of  bismuth. 

ver  ;      it      is     sometimes 

cupelled  in  the  same  manner  as  lead,  in  order  to  extract  the  silver,  the 
oxide  of  bismuth  being  afterwards  again  reduced  to  the  metallic  state 
by  heating  it  with  charcoal.  Pure  bismuth  dissolves  entirely  and 
easily  in  diluted  nitric  acid  (sp.  gr.  1.2);  but  if  it  contains  arsenic,  a 
white  deposit  of  bismuth  arsenate  is  obtained.  Hydrochloric  and 
diluted  sulphuric  acids  will  not  attack  bismuth. 

The  chief  use  of  bismuth  is  in  the  preparation  of  certain  alloys  with 
other  metals.  Some  kinds  of  type  metal  and  stereotype  metal  contain 
bismuth,  which  confers  upon  them  the  property  of  expanding  in  the 
mould  during  solidification,  so  that  they  are  forced  into  the  finest  lines 
of  the  impression. 

This  metal  is  also  remarkable  for  its  tendency  to  lower  the  fusing- 
point  of  alloys,  which  cannot  be  accounted  for  merely  by  referring  to 
the  low  fusing-point  of  the  metal  itself.  Thus,  an  alloy  of  2  parts  bis- 
muth, i  part  lead,  and  i  part  tin,  fuses  below  the  temperature  of  boiling 
water,  although  the  most  fusible  of  the  three  metals,  tin,  requires  a 
temperature  of  227°  C.  An  alloy  of  this  kind  is  used  for  soldering 
pewter.  Wood's  fusible  alloy  consists  of  4  of  Bi,  2  of  Pb,  i  of  Sn,  and 
i  of  Cd  ;  it  melts  at  60.5°  C.  Bismuth  is  also  employed,  together  with 
antimony,  in  the  construction  of  thermo-electric  piles. 

243.  Oxides  of  bismuth. — There  are  four  oxides,  BiO,  Bi203,  Bi2O4, 
and  Bi205. 

Bismuth  mboxlde,  BiO,  is  a  black  powder  obtained  by  heating  bismuth  oxalate 
in  C02.  When  bismuthic  chloride  mixed  with  stannous  chloride  is  added  to  an 
excess  of  potash,  a  black  precipitate  is  obtained,  alleged  by  some  to  be  the  suboxide, 
by  others  metallic  bismuth. 

Bismuthous  oxide,  Bi203,  is  the  basic  and  most  important  oxide.  It 
is  formed  when  bismuth  is  heated  in  air,  or  when  bismuth  nitrate  is 
decomposed  by  heat,  and  is  a  yellow  powder  becoming  brown  when 
heated,  and  fuses  easily.  Bismuthous  oxide  forms  the  rare  mineral 
bismuth-ochre.  This  oxide  of  bismuth  is  obtained  in  tine  needles  by 
precipitating  a  boiling  solution  of  a  bismuth  salt  with  potash. 


440  SALTS   OF   BISMUTH. 

Bismuthic  anhydride,  Bi205,  is  formed  when  Bi203  is  suspended  in  a  strong 
solution  of  potash  through  which  chlorine  is  passed,  when  a  brown  substance  is 
formed  which,  when  treated  with  warm  strong  HN03,  yields  bismuthic  acid 
(HBi03)  as  a  red  powder,  which  becomes  brown  at  120°  C..  losing  H20  and 
becoming  Bi205.  When  further  heated,  it  loses  0  and  becomes  Bi204  or 
Bi2O3.Bi005.  When  heated  with  acids  it  also  evolves  O,  and  forms  salts  of 
Bi203. 

Bismuth  hydroxide,  Bi(OH)3,  is  obtained  as  a  white  precipitate  when  a  caustic 
alkali  is  added  to  a  bismuth  salt ;  it  does  not  dissolve  in  excess  of  alkali.  Acted 
on  by  chlorine  in  the  alkaline  liquid,  it  becomes  dark  brown  HBi03. 

Bismuthic  acid,  HBi03,  the  analogue  of  HN03,  is  formed  when  basic  bismuth 
nitrate  is  fused  with  potash,  in  contact  with  air,  until  it  has  become  dark  brown. 
On  dissolving  in  dilute  nitric  acid,  HBi03  is  left  as  a  red  powder.  The  bismuthates 
of  the  alkali  metals  are  very  unstable,  being  decomposed  by  water.  Pyrolismuthic 
acid,  H4Bi207,  is  said  to  have  been  obtained. 

244.  The  only  two  salts  of  bismuth  which  are  known  in  the  arts  are 
the  basic  nitrate  (trisnitrate  of  bismuth,  or  flake-white)  and  the  oxy- 
chloride  of  bismuth  (pearl-white).  The  preparation  of  these  com- 
pounds illustrates  one  of  the  characteristic  properties  of  the  salts  of 
bismuth,  viz.,  the  facility  with  which  they  are  decomposed  by  water 
with  the  production  of  insoluble  basic  salts. 

If  bismuth  be  dissolved  in  nitric  acid,  it  becomes  bismuth  nitrate, 
Bi(NO3)3,  and  this  may  be  obtained  in  prismatic  crystals  containing 
5Aq.  If  the  solution  be  mixed  with  a  large  quantity  of  water,  it  de- 
posits a  precipitate  of  flake-white,  Bi(NO3)3.2Bi(OH)3,  or  Bi(OH)2N03, 
the  remainder  of  the  nitric  acid  being  left  in  the  solution — 

Bi(N03)3  +  2H20  =  Bi(OH)2N03  +  2HN03. 

The  basic  nitrate,  when  long  washed,  becomes  Bi(OH)3.  It  is  a  crystal- 
line powder,  which  is  acid  to  moist  test-paper.  It  is  used  as  a  paint 
and  cosmetic,  and  in  enamelling  porcelain. 

Pearl-white  has  the  composition  6BiOCl.Aq,  and  is  obtained  by  dis- 
solving bismuth  in  nitric  acid,  and  pouring  the  solution  into  water  in 
which  common  salt  has  been  dissolved. 

Bismuthite,  which  is,  next  to  native  bismuth,  the  most  important  of  the  bismuth 
ores,  is  composed  of  3Bi203.C02.H20. 

Bismuthic  chloride,  BiCl3  (  =  2  vols.),  may  be  distilled  over  when  bismuth  is 
heated  in  a  current  of  dry  chlorine  ;  it  is  a  deliquescent,  fusible,  volatile,  crystalline 
solid,  easily  dissolved  by  a  small  quantity  of  water,  but  decomposed  by  much  water, 
with  formation  of  the  above-mentioned  o,rychloride  of  bismuth;  BiCl3  +  H20=: 
BiOCl  +  2HCl.  This  compound  is  so  insoluble  in  water  that  nearly  every  trace  of 
bismuth  may  be  precipitated  from  a  moderately  acid  solution  of  the  trichloride  by 
adding  much  water. 

Bismuth  tri-iodide,  BiI3.  is  obtained  as  a  dark  brown  precipitate  when  potassium 
iodide  is  added  to  a  solution  of  a  bismuthic  salt.  If  the  solution  be  dilute  or  very 
acid,  a  red  or  yellow  colour  is  produced,  without  precipitation,  and  if  a  solution  of 
a  lead  salt  be  added  to  this,  a  brown  or  red  precipitate  of  a  double  iodide  of  bismuth 
and  lead  is  produced,  which  dissolves  in  hot  dilute  HC1,  and  separates  in  minute 
crystals,  like  bronze  powder,  on  cooling. 

Sismuthous  sulphide  (Bi2S2)  is  sometimes  found  in  nature,  but  more  frequently 
bi-smuthic  sulphide  (Bi2S3)  or  bismuth  glance,  which  occurs  in  dark  grey  lustrous 
prisms  isomorphous  with  native  sulphide  of  antimony.  Bi2S3  is  also  obtained  as  a 
brown  precipitate  by  the  action  of  hydrosulphuric  acid  upon  bismuthic  salts.  Bis- 
muthic sulphide  is  not  soluble  in  diluted  sulphuric  or  hydrochloric  acid,  but  dis- 
solves easily  in  nitric  acid.  Bolirite  is  an  oxysulphide,  Bi2S3.Bi203. 


METALLURGY   OF  ANTIMONY.  441 

ANTIMONY. 

Sb"'  =  119  parts  by  weight. 

245.  Antimony  is  nearly  allied  to  bismuth  in  its  physical  and 
chemical  characters.  It  is  even  harder  and  more  brittle  than  that 
metal,  being  easily  reduced  to  powder.  Its  highly  crystalline  structure 
is  another  very  well-marked  feature,  and  is  at  once  perceived  upon  the 
surface  of  an  ingot  of  antimony,  where  it  is  exhibited  in  beautiful  fern- 
like  markings  (star  antimony).  Its  crystals  belong  to  the  same  system 
(the  rhombohedral)  as  those  of  bismuth  and  arsenic.  It  is  much  lighter 
than  bismuth  (sp.  gr.  6.715),  and  requires  a  higher  temperature  (630°  C.) 
to  fuse  it,  though  it  is  more  easily  converted  into  vapour,  so  that,  when 
strongly  heated  in  air,  it  emits  a  thick  white  smoke,  the  vapour  being 
oxidised.  Like  bismuth,  it  is  but  little  affected  by  hydrochloric  or 
dilute  sulphuric  acid,  but  nitric  acid  oxidises  it,  though  it  dissolves  very 
little  of  the  metal,  the  greater  part  being  left  in  the  form  of  antimonic 
acid.  The  best  method  of  dissolving  antimony  is  to  boil  it  with  hydro- 
chloric acid  and  to  add  nitric  acid,  or  some  other  oxidising  agent,  by 
degrees.  The  metal  decomposes  steam  at  a  red  heat. 

Antimony  is  chiefly  found  in  nature  as  grey  antimony  ore,  stibnite, 
which  is  a  sulphide  of  antimony  (Sb2S3),  occurring  in  Cornwall,  but 
much  more  abundantly  in  Hungary,  in  veins  associated  with  galena, 
iron  pyrites,  quartz,  and  heavy  spar.  To  purify  it  from  these,  advan- 
tage is  taken  of  its  fusibility,  the  ore  being  heated  upon  the  hearth  of 
a  reverberatory  furnace,  with  some  charcoal  to  prevent  oxidation,  when 
the  sulphide  of  antimony  melts  and  collects  below  the  impurities,  whence 
it  is  run  off  and  cast  into  moulds.  The  product  is  known  in  commerce 
as  crude  antimony,  and  contains  sulphides  of  arsenic,  iron,  and  lead. 

To  obtain  regulus  of  antimony,  or  metallic  antimony,  the  sulphide  is 
fused  in  contact  with  refuse  iron  (such  as  tin-plate  clippings),  when 
sulphide  of  iron  is  formed,  and  collects  as  a  fused  slag  upon  the  surface 
of  the  melted  antimony  ;  Sb2S3  +  Fe3  =  3FeS  +  Sb2.  The  antimony  always 
contains  a  considerable  proportion  of  iron. 

To  refine  it  the  metal  is  melted  again  with  sufficient  Sb2S3  to  convert  the  iron 
into  sulphide.  To  eliminate  sulphur  and  obtain  star  antimony,  the  product  must 
be  fused  with  an  alkali  sulphide  which  dissolves  the  Sb2S3,  producing  a  slag  con- 
sisting mainly  of  3Na2S.Sb2S3,  and  called  crocus  vf  antimony. 

In  some  places  the  antimony  ore  is  roasted  to  convert  the  bulk  of  it  into  oxide, 
which  is  then  heated  with  fresh  ore,  in  order  that  the  mixture  may  undergo  "  self- 
reduction"  ;  2Sb2S3  +  3Sb204  =  Sb10  +  6S02. 

Antimony  is  now  obtained  by  leaching  the  ore  with  a  solution  of  sodium  sul- 
phide, whereby  the  Sb2S3  is  dissolved.  The  solution  is  then  electrolysed,  Sb  being 
deposited  on  the  cathode,  leaving  a  solution  of  sodium  sulphide  to  be  used  for 
leaching  more  ore. 

On  the  small  scale,  antimony  may  be  extracted  from  the  sulphide  by  fusing  it  in 
an  earthen  crucible  with  4  parts  of  commercial  potassium  cyanide,  at  a  moderate 
heat ;  or  by  mixing  4  parts  of  the  sulphide  with  3  of  bitartrate  of  potash  and  i^  of 
nitre,  and  throwing  the  mixture,  by  small  portions,  into  a  red-hot  crucible,  when 
the  sulphur  is  oxidised,  and  converted  into  potassium  sulphate,  by  the  nitre,  which 
is  not  present  in  sufficient  quantity  to  oxidise  the  antimony,  so  that  the  metal 
collects  at  the  bottom  of  the  crucible. 

When  tartar-emetic  is  strongly  heated  in  a  closed  crucible,  an  alloy  of  antimony 
and  potassium  is  obtained  which  decomposes  water  rapidly,  and  becomes  hot  when 
exposed  to  air. 

The  brittleness  of  antimony  renders  it  useless  in  the  metallic  state, 


442  ANTIMONY   OXIDES. 

except  for  the  construction  of  thermo-electric  piles,  where  it  is  in  con- 
junction with  bismuth.  Antimony  is  employed,  however,  to  harden 
several  useful  alloys,  such  as  type-metal,  shrapnel-shell  bullets,  Britannia 
metal,  and  pewter. 

Amorphous  antimony. — The  ordinary  crystalline  form  of  antimony  may  be  ob- 
tained, like  copper  and  other  metals,  by  electrolysing  a  solution  containing  about  7 
per  cent,  of  antimonious  chloride  ;  but  in  some  cases  the  antimony  is  deposited  from 
very  strong  solutions  in  an  amorphous  condition,  having  properties  very  different  from 
those  of  ordinary  antimony.  One  part  of  tartar-emetic  is  dissolved  in  4  parts  of  a 
strong  solution  of  antimony  trichloride  and  the  solution  is  slowly  electrolysed.  The 
deposit  of  antimony  which  forms  upon  the  cathode  has  a  brilliant  metallic  appear- 
ance, but  is  amorphous,  and  not  crystalline,  like  the  ordinary  metal.  Its  specific 
gravity  is  5.78.  If  it  be  gently  heated,  scratched  or  sharply  struck,  its  temperature 
rises  suddenly  to  about  200°  C.,  and  it  becomes  converted  into  a  form  more  nearly 
resembling  crystalline  antimony.  At  the  same  time,  however,  thick  fumes  of 
antimony  trichloride  are  evolved,  for  this  substance  is  always  present  in  the  amor- 
phous antimony  to  the  amount  of  5  or  6  per  cent.  ;  *  so  that,  as  yet,  there  is  not 
sufficient  evidence  to  establish  beyond  a  doubt  the  existence  of  a  pure  amorphous 
form  of  antimony  corresponding  with  amorphous  phosphorus,  however  probable 
this  may  appear  from  the  chemical  resemblance  between  these  elements. 

246.  Oxides  of  antimony,  Sb4O6,t  Sb2O4,  Sb205. — Antimonious  oxide, 
Sb406,  is  formed  when  antimony  burns  in  air  (flowers  of  antimony),  and 
is  prepared  on  a  large  scale  by  roasting  either  the  metal  or  the  sulphide 
in  air,  for  use  in  painting  as  a  substitute  for  white  lead.  It  is  also 
found  in  nature  as  white  antimony  ore,  or  valentinite.  Antimonious 
oxide  forms  a  crystalline  powder  (sp.  gr.  5.56),  usually  composed  of 
minute  prisms  having  the  shape  of  the  rarer  form  of  arsenious  oxide 
(page  268),  whilst  occasionally  it  is  obtained  in  crystals  similar  to  those 
of  the  common  octahedral  arsenious  oxide,  with  which,  therefore,  anti- 
monious oxide  is  isodimorphous.  The  octahedral  form  appears  to  be 
produced  only  when  the  prismatic  form  is  slowly  sublimed  in  a  non- 
oxidising  atmosphere.  The  mineral  exitele  is  prismatic  oxide  of  anti- 
mony, and  senarmontite  is  the  octahedral  form  of  that  oxide.  When 
heated  in  air  the  oxide  assumes  a  yellow  colour,  afterwards  takes  fire, 
smoulders,  and  becomes  converted  into  the  antimonious  antimonate 
(Sb2O3.Sb205  =  2Sb204),  which  was  formerly  regarded  as  an  independent 
oxide.  Sb406  may  be  obtained  by  oxidising  antimony  with  very  weak 
nitric  acid,  or  better,  by  dissolving  antimony  sulphide  in  strong  HC1, 
boiling  off  all  H2S,  diluting  largely  with  water,  washing  the  precipitated 
oxy chloride  by  decantation  till  it  is  no  longer  acid,  and  boiling  it;  with  a 
strong  solution  of  sodium  carbonate;  4SbOCl  +  2Na2C03  =  Sb4O6-f 
4NaCl  +  2C02.  The  oxide  is  insoluble  in  water,  but  acids  dissolve  it, 
forming  salts,  though  its  basic  properties  are  feeble,  and  its  salts  rather 
ill-defined.  A  hot  solution  of  hydropotassium  tartrate,  HKC4H406, 
dissolves  it,  forming  tartar-emetic,  SbO.KC4H406.  Potash  and  soda  are 
also  capable  of  dissolving  it,  whence  it  is  sometimes  called  antimonious 
anhydride,  corresponding  with  nitrous  anhydride.  Two  crystallised 
antimonites  of  sodium  have  been  obtained,  the  neutral  antimonite 
NaSb02.6Aq,  and  the  triantimonite  NaSbO2.Sb203.Aq  ;  the  former  is 
sparingly  soluble,  the  latter  almost  insoluble  in  water. 

*  It  has  been  plausibly  suggested  that  the  sudden  rise  of  temperature  may  be  due  to  the 
presence  of  an  endothermic  antimony  compound  analogous  to  the  so-called  chloride  of  nitro- 
gen, the  latter  element  being  connected  with  antimony  by  several  chemical  analogies. 

f  The  vapour  density  of  this  oxide  shows  that  its  formula  cannot  be  .Sb2O3,  as  formerly 
supposed. 


ANTIMONATES.  443 

Antimony  tetroxide,  Sb204,  is  important  because  it  is  the  product  of 
the  action  of  heat  upon  either  of  the  other  oxides  in  contact  with  air, 
so  that  antimony  is  often  weighed  in  this  form  in  quantitative  analysis. 
It  is  readily  obtained  by  boiling  antimony  with  nitric  acid,  evaporating 
to  dryness,  and  heating  the  residue  to  redness.  It  is  yellow  while  hot, 
and  becomes  white  on  cooling. 

Antimony  ash,  obtained  by  roasting  the  grey  sulphide  in  air,  consists 
chiefly  of  Sb204,  and  is  used  for  preparing  other  antimony  compounds. 

Thus,  tartar-emetic  may  be  obtained  by  boiling  Bb.,04  with  hydro- 
potassium  tartrate;  Sb2O4  +  HKC4H406  =  SbO.KC4H406  (tartar-emetic) 
+  HSb03  (antimonic  acid).  This  leads  to  the  belief  that  Sb204  is  really 
antimonyl  antimonate,  SbO.SbO3,  in  which  case  this  formation  of  tartar- 
emetic  would  merely  consist  in  the  exchange  of  SbO  for  H. 

The  presence  of  Sb204  in  Sb4O6  can  be  detected  by  dissolving  in  HC1 
and  adding  KI,  when  iodine  will  be  liberated  — 
Sb204  +  2KI  +  8HC1  =  2SbCl3 


Antimonic  oxide,  Sb2O5,  is  formed  when  antimony  is  oxidised  by  nitric 
acid,  and  the  product  well  washed  and  dried  at  280°  C.  It  is  a  yellow 
powder  (sp.  gr.  6.5).  It  will  be  remembered  that  As2O5may  be  obtained 
in  a  similar  way,  but  not  P203.  Sb205  is  a  pale  yellow  amorphous 
powder,  insoluble  in  water,  and  decomposed  at  300°  C.,  leaving  Sb2O4. 
It  is  dissolved  by  potash,  forming  the  antimonate,  KSbO3. 

Antimoniwts  acid*  HSb02,  corresponding  with  nitrous  acid,  is  said  to  have  been 
obtained  as  2HSb02.3Aq,  in  the  form  of  a  white  precipitate,  by  decomposing 
sodium  antinionite  with  nitric  acid. 

Antimonic  acid,  HSb03,  corresponding  with  nitric  acid,  is  precipitated  as 
HSb03.2Aq  by  adding  nitric  acid  to  solution  of  potassium  antimonate.  It  is  a 
white  powder,  slightly  soluble  in  water,  and  easily  so  in  potash. 

Potassium  antimonate,  KSb03,  is  made  by  gradually  adding  I  part  of  powdered 
antimony  to  4  parts  of  nitre  fused  in  a  clay  crucible.  The  mass  is  powdered  and 
washed  with  warm  water  to  remove  the  excess  of  nitre  and  the  potassium  nitrite, 
when  the  anhydrous  potassium  antimonate  is  left  ;  and  on  boiling  this  for  an 
hour  or  two  with  water,  it  becomes  hydrated,  and  dissolves.  The  solution,  when 
evaporated,  leaves  a  gummy  mass  of  potassium  antimonate,  having  the  composition 
2KSb03-5Aq.  This  dissolves  in  warm  water,  and  is  decomposed  by  boiling  for 
some  time,  yielding  an  acid  antimonate,  K4H2(Sb03)6.9Aq. 

Sodium  antimonate,  2NaSb03.yAq,  is  prepared  like  the  potassium  salt. 

Ammonium  antimonate,  NH4SbO3,  is  obtained  as  a  crystalline  powder,  insoluble 
in  water,  by  dissolving  HSb03  in  warm  ammonia. 

A  basic  lead  antimonate  is  used  in  oil-painting  as  Naples  yellow. 

Metantimonic  acid,  H4Sb2O7,  should  really  be  called  pyro-antimonic  acid,  since 
it  corresponds  with  pyrophosphoric  acid,  H4P207.  It  is  obtained  as  a  white  precipi- 
tate by  decomposing  antimonic  chloride  with  water  ;  2SbCl5  +  7H20  =  H4Sb207  + 
loHCl.  It  is  rather  more  soluble  in  water  than  is  antimonic  acid,  and  dissolves  in 
cold  ammonia.  When  heated  to  200°  C.,  it  is  converted  into  antimonic  acid  ; 
H4Sb2O7  =  2HSb03  +  H20.  This  resembles  the  conversion  of  pyrophosphoric  into 
metaphosphoric  acid  by  the  action  of  the  heat.  It  is  said  that  orthantimonic  acid, 
H3Sb04,  has  been  isolated. 

Potassium,  met  ant  intonate.  K4Sb207,  is  made  by  fusing  the  antimonate  with 
potash,  in  a  silver  crucible  ;  2KSb03  +  2KOH  =  K4Sb2O7  +  H20.  On  dissolving  in 
water  and  evaporating,  crystals  of  the  metantimonate  are  obtained,  but  water 
decomposes  these  into  potash  and  potassium  dimetantimonate,  K2H2Sb207,  which 
forms  a  crystalline  powder  containing  6Aq.  It  is  sparingly  soluble  in  cold  water, 
but  dissolves  in  warm  water.  The  solution  forms  a  valuable  test  for  sodium, 
which  it  precipitates  in  the  form  of  Na2H2Sb207.6Aq.  When  long  kept,  the  solu- 
tion of  potassium  dimetantimonate  becomes  converted  into  antimonate,  which 

*  Strictly  metantimonious  acid  ;  orthantimonfous  acid,  Sb(OH)3,  lias  not  been  prepared. 


444  TESTING  FOR  ANTIMONY. 


does  not  precipitate  sodium  ;  K2Sb2Ol7  +  H20  =  2KSbO3  +  2KOH.  Acids  precipitate 
metantiinonic  acid,  which  dissolves  in  HC1.  Nearly  all  metallic  solutions  yield 
precipitates  with  the  potassium  dimetantimonate,  so  that  all  other  metals  must 
be  removed  from  the  solution  before  testing  for  sodium. 

247.  Antimonetted  hydrogen,  or  hydrogen  antimonide,  SbH3,  is  not 
known  in  the  pure  state,  but  is  obtained,  mixed  with  H,  when  an  alloy 
of  antimony  with  zinc  is  attacked  by  dilute  sulphuric  acid,  or  when  a 
solution  of  an  antimony  salt  (tartar-emetic,  for  example)  is  poured  into 
a  hydrogen  apparatus  containing  zinc  and  dilute  sulphuric  acid  (see 
page  272).      Its  production  forms  the  most  delicate  test  for  antimony, 
as  in  the  parallel  case  of  arsenic,  but  the  one  cannot  be  mistaken  for 
the  other,  if  the  following  differences  be  observed.     The  SbH3  burns  to 
Sb406  and  H2O  with  a  greenish  flame,  which  deposits  a  soot-black  spot 
upon  a  porcelain  crucible  lid  (Fig.  192).     This  spot  dissolves  when  a 
drop  of  yellow  ammonium  sulphide  is  placed  on  it  with  a  glass  rod,  and 
on  evaporation  gives  an  orange  film  of  Sb2S3.     When  the  tube  through 
which  the  gas  passes  is  heated  to  150°  C.  (Fig.  193),  metallic  antimony 
is  deposited  at  the  heated  part,  and  not  beyond  it,  like  arsenic.     When 
the  gas  is  passed  into  silver  nitrate,  the  antimony  is  precipitated  as 
black  silver   antimonide;    SbH3  +  3AgN03  =  SbAg3  +  3HN03   (whereas 
arsenic  passes  into  solution  as  arsenious  acid,  and  gives  a  black  precipi- 
tate of  metallic  silver). 

Sulphur  decomposes  SbH3  in  sunlight  or  at  100°  C.,  but  not  in  the  dark  ; 
2SbH3  +  3S2  =  Sb.2S3  +  3H2S.  The  reactions  with  silver  nitrate  and  with  sulphur 
prove  the  composition  of  the  gas  to  be  SbH3,  so  that  it  is  analogous  to  AsH3,  PH3, 
and  NH3. 

If  the  hydrogen  antimonide  be  prepared  by  the  action  of  dilute  sulphuric  acid 
upon  an  alloy  of  2  parts  of  antimony  with  3  parts  of  zinc,  and  the  first  portions 
collected  separately  and  cooled  to  —  91°  C.,  it  solidifies,  but  on  raising  the  tem- 
perature to  about  —60°  it  is  decomposed,  antimony  being  deposited.  This 
explains  why  so  little  of  the  compound  is  obtained  in  the  gas  made  under  ordinary 
conditions. 

248.  Chlorides  of  antimony.  —  Chlorine    and    antimony   combine 
readily  with  evolution  of  heat  and  light  ;  the  chlorides  are  among  the 
most  important  compounds  of  this  metal. 

Trichloride  of  antimony,  or  antimonious  chloride,  SbCl3,  may  be  pre- 
pared by  dissolving  powdered  antimony  sulphide  (100  grams)  in  com- 
mercial hydrochloric  acid  (500  c.c.),  adding  gradually  potassium  chlorate 
(4  grams),  filtering  from  sulphur  and  distilling.  HC1  distils  first,  then 
a  solution  of  SbCl3  and  finally  SbCl3  itself,  which  forms  white  crystals  in 
the  receiver.  The  trichloride  is  a  soft  crystalline  solid,  whence  its  old 
name  of  butter  of  antimony.  It  fuses  at  73°  C.  and  boils  at  223°  C.  It 
may  be  dissolved  in  a  small  quantity  of  water,  but  a  large  quantity 
decomposes  it,  forming  a  bulky  white  precipitate,  which  is  an  oxy  chloride 
of  antimony;  SbCl3  +  H20  =  2HC1  +  SbOCl  ;  this  is  a  decomposition 
similar  to  that  which  occurs  with  PC13,  AsCl3,  and  BiCl3.  By  long 
washing,  4SbOCl  +  2H20  =  4HC1  +  Sb4O6.  When  hot  water  is  added  to 
a  hot  solution  of  trichloride  of  antimony  in  hydrochloric  acid,  minute 
prismatic  needles  are  deposited,  containing  Sb4Cl2O5,  and  formerly  called 
powder  of  Algaroth.  The  same  body  is  formed  when  SbOCl  is  heated; 
5SbOCl  =  SbCl3  +  Sb4Cl205.  Trichloride  of  antimony  is  occasionally  used 
in  surgery  as  a  caustic  ;  it  also  serves  as  a  bronze  for  gun-barrels,  upon 
which  it  deposits  a  film  of  antimony. 


ANTIMONY  SULPHIDES,  445 

Pentachloride  of  antimony,  or  antimonic  chloride  (SbCl5),  is  prepared 
by  heating  coarsely  powdered  antimony  in  a  retort,  through  which  a 
stream  of  dry  chlorine  is  passed  (Fig.  182),  the  neck  of  the  retort  being 
fitted  into  an  adapter,  which  serves  to  condense  the  pentachloride.  One 
ounce  of  antimony  will  require  the  chlorine  from  about  6  oz.  of  common 
manganese  and  18  oz.  (measured)  of  hydrochloric  acid.  The  pure 
pentachloride  is  a  colourless  fuming  liquid  of  a  very  suffocating  odour ; 
it  combines  energetically  with  a  small  quantity  of  water,  forming  a 
crystalline  hydrate,  SbCl5.4Aq,  but  an  excess  of  water  decomposes  it 
into  hydrochloric  and  metantimonic  acids,  the  latter  forming  a  white 
precipitate ;  2SbCl5  +  7H2O  =  loHCl  +  H4Sb207. 

If  it  be  dropped  into  water  kept  cool  by  ice,  it  yields  antimony  oxytrichloride  as  a 
deliquescent  crystalline  body;  SbCl5  +  H20  =  SbOCl3  +  2HCl.  Pentachloride  of 
antimony  is  employed  by  the  chemist  as  a  chlorinating  agent ;  thus,  olefiant  gas 
(C2H4),  when  passed  through  it,  is  converted  into  Dutch  liquid  (C2H4C12),  and 
carbonic  oxide  into  phosgene  gas,  the  pentachloride  of  antimony  being  converted 
into  trichloride.  ^SbClg  is  partially  dissociated  into  SbCl3  and  C12  at  140°  C.  and 
completely  at  200°  C.,  and  can  only  be  distilled  in  chlorine. 

The  pentachloride  of  antimony  is  the  analogue  of  pentachloride  of  phosphorus, 
and  a  chlorosulpliide  of  antimony  (SbCl3S),  corresponding  with  chlorosulphide  of 
phosphorus,  is  obtained  as  a  white  crystalline  solid  by  the  action  of  hydrosulphuric 
acid  upon  pentachloride  of  antimony. 

249.  Sulphides  of  antimony. — Antimonious  sulphide,  or  sesquisul- 
of  antimony  (Sb2S3),  has  been  noticed  as  the  chief  ore  of  antimony. 
It  is  abundant  in  Borneo.  It  is  a  heavy  mineral  (sp.  gr.  4.63),  of  a  dark 
grey  colour  and  metallic  lustre,  occurring  in  masses  which  are  made  up 
of  long  prismatic  needles.  It  fuses  easily,  and  may  be  sublimed  un- 
changed out  of  contact  with  air.  When  melted  and  suddenly  cooled 
it  forms  a  dark  brown  amorphous  mass  of  sp.  gr.  4.15,  which  is  not  a 
conductor  of  electricity,  whereas  the  grey  form  conducts.  It  is  easily 
recognised  by  heating  it,  in  powder,  with  hydrochloric  acid,  when  it 
evolves  the  odour  of  hydrosulphuric  acid,  and  if  the  solution  be  poured 
into  water,  it  deposits  an  orange  precipitate  (page  214).  This  orange 
sulphide,  which  is  a  compound  of  Sb2S3  with  water,  is  also  obtained  by 
adding  hydrosulphuric  acid  to  a  solution  of  a  salt  of  antimony  (for 
example,  tartar-emetic)  acidified  with  HC1.  It  may  be  converted  into 
the  grey  sulphide  at  210°  C.,  and  becomes  black  when  boiled  with  HC1 
in  a  current  of  C02.  The  orange  variety  constitutes  the  antimony  ver- 
milion, the  preparation  of  which  has  been  described  at  p.  232.  Native 
sulphide  of  antimony  is  employed,  in  conjunction  with  potassium 
chlorate,  in  the  friction-tube  for  firing  cannon  ;  it  is  also  used  in  per- 
cussion caps,  together  with  potassium  chlorate  and  mercuric  fulminate. 
Its  property  of  deflagrating  with  a  bluish-white  flame,  when  heated  with 
nitre,  renders  it  useful  in  compositions  for  coloured  fires. 

Glass  of  antimony  is  a  transparent  red  mass  obtained  by  roasting 
antimonious  sulphide  in  air,  and  fusing  the  product;  it  contains  about 
8  parts  of  oxide  and  i  part  of  sulphide  of  antimony.  It  is  used  for 
colouring  glass  yellow. 

Red  antimony  ore  is  an  oxysulphide  of  antimony,  Sb.,03.2Sb2S3. 

Antimonic  sulphide  (Sb2S5)  is  obtained  as  a  bright  orange-red  precipi- 
tate by  the  rapid  action  of  H2S  upon  a  solution  of  pentachloride  of 
antimony  in  HC1 ;  it  is  decomposed  by  heat  into  Sb2S3  and  S,.  When 
boiled  with  hydrochloric  acid,  Sb2S.  +  6HC1  =  2SbCl3  +  3H2S  +  S8,  show- 


446  VANADIUM. 

ing  the  trivalence  of  antimony  to  be  stronger  than  the  pentavalence. 
It  is  prepared  on  a  large  scale  under  the  name  of  golden  sulphuret  of 
antimony  by  boiling  SbaS3  with  KOH  and  S,  and  adding  acid  to  the 
solution  of  potassium  thioantimonate  (liver  of  antimony)  thus  obtained. 
It  is  used  for  vulcanising  india-rubber. 

When  H2S  acts  slowly  on  SbCl5  a  mixture  of  Sb.2S5,  Sb.2S3  and  S  is  obtained.  In 
presence  of  Cr2Cl6  more  Sb2S3  is  formed.  When  exposed  to  light  under  water  or 
boiled  with  water,  Sb2S5  yields  black  crystalline  Sb2S3  and  S. 

Both  Sb2S3  and  Sb2S5  are  dissolved  by  the  alkali  sulphides,  forming  tliio- 
metantimonites  (from  HSbS2)  and  thwantimonates  (from  H3SbS4)  respectively. 
Thus,  like  the  sulphide  of  arsenic,  they  dissolve  in  alkalies  yielding  the  appropriate 
oxy-salts  and  thio-salts  ;  for  example,  2Sb2S3  +  4KOH  =  3KSbS2+  KSb02  +  2H2O, 
and  4Sb2S5  +  24KOH  =  5K3SbS4  +  3K3Sb04  +  i2H20.  When  the  solutions  are  acidi- 
fied, all  the  Sb  is  precipitated  again  as  sulphide.  Even  metallic  antimony,  in 
powder,  is  dissolved  when  gently  heated  with  solution  of  potassium  sulphide 
in  which  sulphur  has  been  dissolved,  any  lead  or  iron  which  may  be  present 
being  left  in  the  residue,  so  that  the  antimony  may  be  tested  by  this  process  as 
to  its  freedom  from  those  metals. 

Mineral  Itermes  is  a  variable  mixture  of  oxide  and  sulphide  of  antimony,  which 
is  deposited  as  a  reddish-brown  powder  from  the  solution  obtained  by  boiling 
sulphide  of  antimony  with  potash  or  soda.  It  was  formerly  much  valued  for 
medicinal  purposes.  Kermes  was  the  Arabic  name  of  an  insect  used  in  dyeing 
scarlet. 

Schlippe's  salt  is  the  sodium  thioantimonate  (Na3SbS4.9H20),  and  may  be 
obtained  in  fine  transparent  tetrahedral  crystals  by  dissolving  Sb2S3  in  NaOH  and 
adding  sulphur.  This  salt  is  sometimes  used  in  photography. 

Antimonious  sulphate,  Sb2(S04)3,  is  formed  when  antimony  is  boiled  with  strong 
H2S04.  It  crystallises  in  needles,  which  are  decomposed  by  water  into  a  soluble 
sulphate,  and  an  insoluble  basic  sulphate. 

VANADIUM.* 


This  metal  was  originally  discovered  in  certain  Swedish  iron  ores,  but  its 
chief  ore  is  the  vanadate  of  lead,  which  is  found  in  Scotland,  Mexico,  and  Chili. 
Vanadic  acid  has  also  been  found  in  some  clays,  in  the  cupriferous  sandstone  at 
Perm  in  Kussia,  and  Alderley  Edge  in  Cheshire  ;  it  is  contained  in  some  specimens 
of  coal.  By  treating  the  vanadate  of  lead  with  HN03,  expelling  the  excess  of  acid 
by  evaporation,  and  washing  out  the  lead  nitrate  with  water,  impure  vanadic 
anhydride  (V205)  is  obtained,  which  may  be  purified  by  dissolving  in  ammonia, 
crystallising  the  ammonium  metavanadate  NH4V03,  and  decomposing  it  by  heat,  when 
vanadic  anhydride  is  left  as  a  reddish-yellow  fusible  solid,  which  crystallises  on 
cooling,  and  dissolves  sparingly  in  water  to  a  yellow  solution.  It  dissolves  in  HC1, 
and  if  the  solution  be  treated  with  a  reducing-agent  (such  as  H2S)  it  assumes  a 
fine  blue  colour.  If  a  solution  of  ammonium  vanadate  be  mixed  with  tincture  of 
galls,  it  gives  an  intensely  black  fluid,  which  forms  an  excellent  ink,  for  it  is  not 
bleached  by  acids  (which  turn  it  blue),  alkalies,  or  chlorine. 

Vanadium  has  been  obtained  by  heating  its  chloride  in  hydrogen,  or  by  electro- 
lysing a  solution  of  an  alkali  vanadate  in  HC1,  as  a  silver  white  metal  (sp.  gr.  5.5). 
It  is  not  oxidised  by  air,  and  does  not  decompose  water,  but  burns  when  strongly 
heated  in  air.  Its  melting-point  is  not  known.  It  is  insoluble  in  HC1,  but  soluble 
in  HN03.  Fused  NaOH  converts  it  into  sodium  vanadate. 

The  oxides  of  vanadium  correspond  in  composition  with  those  of  nitrogen. 
VO  is  a  basic  oxide  forming  salts  which  give  lavender-  coloured  solutions  ;  these 
absorb  oxygen  rapidly  from  the  air,  and  act  as  powerful  reducing  agents.  V203 
is  a  black  crystalline  body  resembling  plumbago,  and  capable  of  conducting 
electricity,  obtained  by  heating  vanadic  anhydride  in  a  current  of  hydrogen  ;  it 
is  insoluble  in  acids,  and  combines  with  bases  to  form  ranadites  (KV02).  V204  is 
produced  when  V203  is  heated  in  air  ;  it  dissolves  in  acids  forming  salts  of  vanadyl 
(VO),  and  in  alkalies  forming  hypovanadates  (K2V409).  Vanadic  anhydride,  V205, 
forms  purple  and  green  compounds  with  the  above  oxides.  Metavanadic  acid, 

*  Vanadis,  a  Scandinavian  deity. 


THE   BISMUTH   GKOUP. 


447 


crystallises  in  beautiful  golden  scales.  The  yellow  fuming  liquid,  formerly 
called  chloride  of  vanadium,  is  really  an  oxychloride,  vanadyl  trichloride,  VOC13. 
The  oxychlorides,  V202C1,  VOC1,  and  VOC12,  have  also  been  obtained.  There  are 
two  compounds  of  vanadium  with  nitrogen,  VN  and  VN2.  Ammonium  meta- 
vanadate  is  now  used  as  an  oxygen-carrier  for  blacks  in  calico-printing,  in  con- 
junction with  chlorates  and  aniline  hydrochloride.  The  slag  of  the  Creusot  steel 
works  is  now  the  chief  source  of  vanadic  acid,  of  which  it  contains  2  per  cent. 

NIOBIUM,*  Nb  =  93.3,  and  TANTALUM,  Ta  =  i8i.6. 

249^.  These  metals  occur  as  niobates  and  tantalates  respectively  in  several  rare 
minerals,  of  which  columbite  from  Massachusetts  is  most  important.  By  fusing  the 
mineral  with  KHS04,  treating  with  water,  digesting  the  insoluble  residue  with 
(NH4).2S  (to  remove  Sn  and  W),  and  with  HC1  to  remove  FeS,  a  mixture  of  Nb205 
and  Ta.205  is  obtained.  This  is  dissolved  in  HF,  and  KHF2  is  added  ;  on  concen- 
trating K2TaF7  crystallises  first  and  is  followed  by  NbOF3.2KF  ;  each  yields  the 
corresponding  pentoxide  when  boiled  with  much  water. 

To  extract  Nb  from  Nb205  this  is  first  converted  into  NbCl5  (by  ignition  with 
charcoal  and  chlorine),  the  vapour  of  which  is  mixed  with  H  and  passed  through 
a  red-hot  tube.  The  deposited  metal  is  steel-grey  (sp.  gr.  7),  burns  to  Nb205,  and 
is  insoluble  in  all  acids  except  in  a  mixture  of  HF  and  HN03  and  in  H2S04  cone. 

By  heating  a  mixture  of  Nb205  and  C  in  the  electric  furnace  a  button  of  the 
metal  is  obtained,  hard  enough  to  scratch  quartz.  It  melts  above  1800°  C. 

NioMc  anhydride,  Nb205,  is  a  white  powder  soluble  in  alkalies  to  form  meta- 
niobates,  KNb03.  NbO  and  Nb02  are  also  known.  NbCl3  and  NbCl5  have  been 
prepared  as  well  as  oxychlorides  analogous  to  those  of  vanadium. 

A  fused  button  of  tantalum  (containing  0.5  per  cent.  C.)  may  be  obtained  by 
heating  a  mixture  of  Ta205  and  C  in  the  electric  furnace  ;  it  scratches  quartz  and 
has  sp.  gr.  12.79. 

When  heated  at  600°  C.  in  oxygen  both  niobium  and  tantalum  burn  to  the 
pentoxide.  They  are  both  active  reducing-agents  at  moderately  high  temperatures, 
niobium  being  the  more  active  in  this  regard.  Fused  alkalies  or  nitre  oxidise 
them  to  the  corresponding  metaniobate  or  metatantalate. 

lu  its  compounds  tantalum  resembles  niobium. 

The  bismuth  group  of  metals.  —The  metals  JBi,  Sb,  Ta,  Nb,  and 
V  belong  to  the  same  group  of  elements,  which  also  includes  N,  P,  and 
As.  All  these  are  characterised  by  their  acid  pentoxides.  Ta,  Nb,  and 
Y  do  not  form  hydrides  analogous  to  PH3,  nor  is  BiH3  known.  Many 
points  of  resemblance  may  be  noted  between  vanadium  and  chromium, 
whilst  niobium  and  tantalum  recall  tungsten. 

TIN. 

Sn  =  1  1  7.  6  parts  by  weight. 

250.  Tin  is  by  no  means  so  widely  diffused  as  most  of  the  other  metals 
which  are  largely  used,  and  is  scarcely  ever  found  in  the  metallic  state 
in  nature.  Its  only  important  ore  is  that  known  as  tin-stone,  which  is 
a  binoxide  of  tin,  Sn02,  and  is  generally  found  in  veins  traversing 
quartz,  granite,  or  slate.  It  is  generally  associated  with  arsenical  iron 
pyrites,  and  with  a  mineral  called  wolfram,  which  is  a  tungstate  of  iron 
and  manganese. 

Tin-stone  is  sometimes  found  in  alluvial  soils  in  the  form  of  detached 
rounded  masses  ;  it  is  then  called  stream  tin  ore,  and  is  much  purer  than 
that  found  in  veins,  for  it  has  undergone  a  natural  process  of  oxidation 
and  levigation  exactly  similar  to  the  artificial  treatment  of  the  impure 
ore.  These  detached  masses  of  stream  tin  ore  are  not  unfrequently 
rectangular  prisms  with  pyramidal  terminations. 

*  Niobe,  daughter  of  Tantalus. 


448  SMELTING   TIN-STONE. 

The  Cornish  mines,  and  those  of  Malacca  and  Banca,  furnish  the 
largest  supplies  of  tin.  Tin-stone  is  also  found  in  Bohemia,  Saxony, 
California,  and  Australia.  At  the  Cornish  tin-works  the  purer  portions 
of  the  ore  are  picked  out  by  hand,  and  the  residue,  which  contains 
quartz  and  other  earthy  impurities,  together  with  copper  pyrites  and 
arsenical  iron  pyrites,  is  reduced  to  a  coaroe  powder  in  the  stamping- 
mills,  and  washed  in  a  stream  of  water.  The  tin-stone,  being  extremely 
hard,  is  not  reduced  to  so  fine  a  powder  as  the  pyritic  minerals  associated 
with  it,  and  these  latter  are  therefore  more  readily  carried  away  by  the 
stream  of  water  than  is  the  tin-slone.  The  removal  of  the  foreign 
matters  from  the  ore  is  also  much  favoured  by  the  high  specific  gravity 
of  the  binoxide  of  tin,  which  is  6.5,  whilst  that  of  sand  or  quartz  is  only 
2.7,  so  that  the  latter  would  be  carried  off  by  a  stream  which  would  not 
disturb  the  former.  So  easily  and  completely  can  this  separation  be 
effected,  that  a  sand  containing  less  than  i  per  cent,  of  tin-stone  is  found 
capable  of  being  economically  treated. 

In  order  to  expel  any  arsenic  and  sulphur  which  may  still  remain  in 
the  washed  ore,  it  is  roasted  in  quantities  of  8  or  10  cvvts.  in  a  rever- 
beratory  furnace,  when  the  sulphur  is  disengaged  in  the  form  of  sul- 
phurous acid  gas,  and  the  arsenic  in  that  of  arsenious  oxide,  the  iron 
being  left  in  the  state  of  ferric  oxide,  and  the  copper  partly  as  sulphate 
of  copper,  partly  as  unaltered  sulphide.  To  complete  the  oxidation  of 
the  insoluble  sulphide  of  copper,  and  its  conversion  into  the  soluble  sul- 
phate, the  roasted  ore  is  moistened  with  water  and  exposed  to  the  air  for 
some  days,  after  which  the  whole  of  the  copper  may  be  removed  by  again 
washing  with  water. 

A  second  washing  in  a  stream  of  water  also  removes  the  ferric  oxide 
in  a  state  of  suspension,  and  this  is  much  more  easily  effected  than  when 
the  iron  was  in  the  form  of  pyrites,  since  the  difference  between  the 
specific  gravity  of  this  mineral  (5.0)  and  that  of  the  tin-stone  (6.5)  is 
far  less  than  that  between  the  sp.  gr.  of  ferric  oxide  and  tin-stone. 

The  ore  thus  purified  contains  between  60  and  70  per  cent,  of  tin  ;  it 
is  mixed  very  intimately  with  about  Jth  of  powdered  coal,  and  a  little 
lime  or  fluor  spar,  to  form  a  fusible  slag  with  the  siliceous  impurities, 
and  reduced  in  a  reverberatory  furnace,  a  comparatively  easy  task  since 
binoxide  of  tin  readily  parts  with  its  oxygen  to  carbon  at  a  red  heat. 

The  tin-smelting  furnace  is  shown  in  Fig.  227.  The  mixture  of  ore  and  coal  is 
moistened  to  prevent  its  dispersion  by  the  draught  of  air,  and  spread  on  the 
hearth  (A)  in  charges  of  between  20  and  25  cwts. 

The  temperature  is  not  permitted  to  rise  too  high  at  first,  lest  a  portion  of  the 
oxide  of  tin  should  combine  with  the  silica  to  form  a  silicate,  from  which  the  metal 
would  be  reduced  with  difficulty.  During  the  first  six  or  eight  hours  the  doors  of 
the  furnace  are  kept  shut,  so  as  to  exclude  the  air  and  favour  the  reducing  action  of 
the  carbon  upon  the  binoxide  of  tin,  the  oxygen  of  which  it  converts  into  carbonic 
oxide,  leaving  the  tin  in  the  metallic  state  to  accumulate  upon  the  hearth  beneath 
the  layer  of  slag.  When  the  reduction  is  deemed  complete,  the  mass  is  well  stirred 
with  an  iron  paddle  to  separate  the  metal  from  the  slag ;  the  latter  is  run  out 
first,  and  the  tin  is  then  drawn  off  into  an  iron  pan  (B),  where  it  is  allowed 
to  remain  at  rest  for  the  dross  to  rise  to  the  surface,  and  is  ladled  out  into  ingot 
moulds. 

The  slags  drawn  out  of  the  smelting-furnace  are  carefully  sorted,  those  which 
contain  much  oxide  of  tin  being  worked  up  with  the  next  charge  of  ore,  whilst 
those  in  which  globules  of  tin  are  disseminated  are  crushed,  so  that  the  metal  may 
be  separated  by  washing  in  a  stream  of  water. 

The  tin,  when  first  extracted  from  the  ore,  is  far  from  pure,  being  contaminated 


PURIFICATION   OF   TIN. 


449 


with  small  quantities  of  iron,  arsenic,  copper,  and  tungsten.  In  order  to  purify  it 
from  these,  the  metal  is  submitted  to  a  process  of  liquation,  in  which  the  easy 
fusibility  of  tin  is  taken  advantage  of  ;  the  ingots  are  piled  into  a  hollow  heap  near 
the  fire-bridge  of  a  reverberatory  furnace,  and  gradually  heated  to  the  fusing- 
point,  when  the  greater  portion  of  the  tin  flows  into  an  outer  basin,  whilst  the 
remainder  is  converted  into  the  binoxide,  which  remains  as  dross  upon  the  hearth, 
together  with  the  oxides  of  iron,  copper,  and  tungsten,  the  arsenic  having  passed 
off  in  the  form  of  arsenious  oxide.  Fresh  ingots  of  tin  are  introduced  at  intervals, 
until  about  5  tons  of  the  metal  have  collected  in  the  basin,  which  is  commonly 
the  case  in  about  an  hour  after  the  com- 
mencement of  the  operation. 

The  specific  gravity  of  tin  being  very 
low  (7.285),  any  dross  which  may  still 
remain  mingled  with  it  does  not  separate 
very  readily  ;  to  obviate  this,  the  molten 
metal  is  well  agitated  by  stirring  with 
wet  wooden  poles,  or  by  lowering  billets 
of  wet  wood  into  it,?when  the  evolved 
bubbles  of  steam  carry  the  impurities  up 
to  the  surface  in  a  kind  of  froth  ;  the 
stirring  is  continued  for  about  three 
hours,  and  the  metal  is  allowed  to  re- 
main at  rest  for  two  hours,  when  it  is 
skimmed  and  ladled  into  ingot  moulds 
(block  tifi).  It  is  found  that,  in  conse- 
quence of  the  lightness  of  the  metal,  and 
its  tendency  to  separate  from  the  other 
metals  with  which  it  is  contaminated, 
the  ingots  which  are  cast  from  the  metal 
first  ladled  out  of  the  pot  are  purer  than 
those  from  the  bottom  ;  this  is  shown  by 
striking  the  hot  ingots  with  a  hammer, 
when  they  break  up  into  the  irregular 
prismatic  fragments  known  as  dropped 
or  grain  tin,  the  impure  metal  not 
exhibiting  this  extreme  brittleness  at 
a  high  temperature.  The  tin  imported  from  Banca  is  celebrated  for  its  purity 
(Straits  tin). 

When  the  tin  ore  contains  wolfram,  [FeMn]W04,  which  has  sp.  gr.  7.3,  this 
remains  behind  with  the  prepared  tin  ore,  and  must  be  removed  before  smelting  by 
fusion  with  sodium  carbonate  in  a  reverberatory  furnace,  when  the  tungstic  acid  is 
converted  into  sodium  tungstate,  which  is  dissolved  out  by  water,  and  crystallised. 
This  salt  finds  an  application  in  calico-printing. 

On  the  small  scale,  tin  maybe  extracted  from  tin-stone  by  fusing  100  grains  with 
20  grains  of  dried  sodium  carbonate,  and  20  of  dried  borax,  in  a  crucible  lined  with 
charcoal,  exactly  as  in  the  extraction  of  iron  (see  p.  415). 

The  extraction  is  more  easily  effected  by  fusing  100  grains  of  tin-stone  with  500 
grains  of  potassium  cyanide  for  fifteen  minutes  at  a  red  heat. 

251.  Properties  of  Tin. — Tin  is  remarkable  for  its  lustre  and  white- 
ness, in  which  it  rivals  silver,  but  is  at  once  distinguished  from  the  latter 
by  its  greater  fusibility,  and  by  its  oxidising  when  heated  in  air.  It  is  the 
most  fusible  of  the  metals  in  common  use  (233°  C.),  much  lighter  than 
silver,  sp.  gr.  7.28,  and  emits  a  curious  grating  sound  when  bent;  it  is 
harder  than  lead,  but  softer  than  zinc  ;  very  malleable  at  ordinary  tem- 
peratures (tin-foil),  brittle  at  200°  C.  (dropped  or  grain  tin),  not  vapor- 
ised except  at  very  high  temperatures.  It  has  the  lowest  tenacity  of  all 
the  metals  in  common  use,  and  therefore  its  ductility  is  very  low,  only 
one  other  common  metal,  lead,  being  more  difficult  to  draw  into  wire  at 
the  common  temperature.  Tin  may,  however,  be  drawn  at  100°  C. 
Only  gold,  silver,  and  copper  surpass  it  in  malleability. 

Tin  decomposes  steam  at  a  red  heat.     It  is  scarcely  affected  by  air  or 

2  P 


45°  MANUFACTURE   OF  TIN-PLATE. 

water  at  common  temperatures,*  and  is  therefore  used  for  tinning  other 
metals.  Tin  is  easily  soluble  in  strong  hydrochloric  acid,  which  distin- 
guishes it  from  silver,  and  it  is  converted  into  a  white  nearly  insoluble 
powder  by  nitric  acid,  which  distinguishes  it  from  all  other  metals  except 
.antimony. 

Exposure  to  extreme  cold  converts  tin  into  a  modification  which  has 
lost  its  reflecting  surface,  and  has  thus  acquired  a  grey  appearance  (grey 
tin).  A  spontaneous  disintegration  of  the  tin  may  even  occur  from  this 
cause.f  The  sp.  gr.  of  grey  tin  is  5.73. 

The  transition  temperature  of  these  enantiotropic  forms  of  tin  is  20°  C.,  so  that 
the  grey  form  must  become  white  when  heated  above  this  temperature  ;  but  the 
change  from  white  to  grey  below  20°  C.  is  very  slow  until  the  temperature  has 
fallen  considerably  lower.  The  conversion  is  most  rapid  at  -  48°  C.,  and  is  acceler- 
ated by  contact  with  grey  tin  already  formed,  and  with  stannic  chloride. 

Tin-foil  is  made  from  bars  of  the  best  tin,  which  are  hammered  down 
to  a  certain  thinness,  then  cut  up,  laid  upon  each  other,  and  again  beaten 
till  extended  to  the  required  degree. 

Tin-plate  is  made  by  coating  sheets  of  iron  with  a  layer  of  tin  ;  to 
effect  this,  the  sheets,  cleansed  from  oxide,  are  dipped  into  melted  tin,  a 
coating  of  which  adheres  to  the  iron  when  the  sheet  is  withdrawn.  Tin 
being  unaltered  by  exposure  to  air  at  the  ordinary  temperature,  will 
effectually  protect  the  iron  from  rust  as  long  as  the  coating  of  tin  is 
perfect,  but  as  soon  as  a  portion  of  the  tin  is  removed  so  as  to  leave  the 
iron  exposed,  corrosion  occurs  very  rapidly,  because  the  two  metals  form, 
a  galvanic  couple,  which  decomposes  the  water  (charged  with  carbonic 
acid)  deposited  upon  them  from  the  air,  and  the  iron,  having  the  greater 
attraction  for  oxygen,  is  the  metal  attacked.  In  the  case  of  galvanised 
iron  (coated  with  zinc),  on  the  contrary,  the  zinc  would  be  the  metal 
attacked,  and  hence  the  greater  durability  of  this  material  under  certain 
conditions. 

For  the  manufacture  of  tin-plate,  the  best  mild  steel  is  employed,  and  the  most 
important  part  of  the  process  consists  in  cleansing  the  iron  plates  from  every  trace 
of  oxide  which  would  prevent  the  adhesion  of  the  tin.  To  effect  this,  and  to  anneal 
the  iron,  they  are  made  to  undergo  several  processes,  of  which  the  most  important 
are — (i)  immersion  in  diluted  sulphuric  acid  ;  (2)  heating  to  redness  to  anneal  the 
plate  ;  (3)  rolling  to  improve  the  surface  ;  (4)  a  second  annealing  ;  (5)  immersion 
in  diluted  sulphuric  acid  ;  (6)  scouring  with  sand  ;  (7)  washing  with  water  ;  they 
are  then  dried  for  an  hour  in  a  vessel  of  melted  tallow,  which  prevents  contact  of 
air,  and  immersed  for  an  hour  and  a  half  in  melted  tin,  the  surface  of  which  is 
protected  from  oxidation  by  tallow  ;  after  draining,  they  are  dipped  a  second  time 
into  the  tin  to  thicken  the  layer  ;  then  transferred  to  a  bath  of  hot  tallow  to  allow 
the  superfluous  tin  to  run  down  to  the  lower  edge,  whence  it  is  afterwards  removed 
by  passing  the  plate  through  rollers.  About  8  Ibs.  of  tin  are  required  to  cover  225 
plates,  weighing  112  Ibs. 

To  recover  the  tin  from  tin-plate  cuttings  they  are  boiled  with  caustic  soda 
and  litharge;  Sn  +  2NaOH  +  2PbO  =  Na2Sn03  +  Pb24-H20.  The  sodium  stannate, 
Na2SnO3,  is  used  in  dye-works,  and  the  precipitated  lead  is  again  converted  into 
litharge  by  heating  in  air. 

Term-plate  is  iron  coated  with  an  alloy  of  tin  and  lead. 

In  tinning  the  interior  of  copper  vessels,  in  order  to  prevent  the  contamination 

*  Crystalline  tin  (sp.  gr.  7.18),  deposited  upon  zinc  from  neutral  stannous  chloride,  and 
powdered  tin,  made  by  shaking  molten  tin  in  a  wooden  box,  oxidise  to  a  considerable  extent 
at  the  ordinary  temperature ;  when  heated,  the  superficial  oxide  prevents  the  tin  from 
fusing,  and  it  burns  like  tinder. 

f  The  disintegration  of  the  tin  pipes  of  church  organs,  observed  in  cold  climates,  has  been 
attributed  to  the  conversion  of  the  tin  into  the  grey  modification  by  the  cold,  perhaps  aided 
by  the  vibrations  to  which  the  pipes  are  subjected. 


ALLOYS.  451 

of  food  with  the  copper,  the  surface  is  first  thoroughly  cleaned  from  oxide  by  heat- 
ing it  and  rubbing  over  it  a  little  sal-ammoniac,  which  decomposes  any  oxide  of 
copper,  converting  it  into  the  volatile  chloride  of  copper  (CuO  +  2NH4C1  = 
CuCl2  +  H20  +  2NH3).  A  little  resin  is  then  sprinkled  upon  the  metallic  surface,  to 
protect  it  from  oxidation,  and  the  melted  tin  is  spread  over  it  with  tow. 

Pins  (made  of  brass  wire)  are  coated  with  tin  by  boiling  them  with  cream  of 
tartar  (bitartrate  of  potash),  common  salt,  alum,  granulated  tin,  and  water  ;  the  tin 
is  dissolved  by  the  acid  liquid,  from  which  solution  it  is  reduced  by  electrolytic 
action,  for  the  tin  is  more  highly  electro-positive  than  the  brass,  and  the  latter  acts 
as  the  negative  plate. 

252.  Alloys. — The  term  alloy  is  applied  to  any  homogeneous  mass 
consisting  of  two  or  more  metals.  In  the  majority  of  cases,  it  is  not 
possible  to  detect  the  properties  of  the  individual  metals  in  such  a  mass, 
so  that  the  alloy  cannot  be  regarded  as  a  mere  mixture.  In  many  cases, 
on  the  other  hand,  the  alteration  of  properties  induced  in  one  metal  by 
the  addition  of  another  does  not  show  any  definite  relationship  with  the 
mass  of  the  added  metal,  as  would  be  the  case  if  such  alteration  were 
wholly  due  to  chemical  combination.  A  little  consideration  will  show 
that  the  difficulty  thus  experienced  in  assigning  the  phenomenon  of 
alloy-formation  to  its  proper  position  in  the  classes  of  change,  usually 
distinguished  as  physical  and  chemical,  is  parallel  to  that  experienced  in 
assigning  the  phenomenon  of  solution  to  one  of  these  two  classes  (p.  50). 
It  has  thus  become  customary  to  regard  alloys  as  solidified  solutions, 
which  in  some  cases  are  analogous  to  what  has  been  already  termed  a 
simple  solution — that  is,  the  alloy  shows  no  evidence  of  containing  a 
chemical  compound — and  in  other  cases  are  analogous  to  those  solutions 
which  undoubtedly  contain  a  compound  of  the  solvent  with  the  dissolved 
substance  in  a  state  of  simple  solution.  The  majority  of  alloys  belong 
to  the  second  class,  and  consist  of  solutions  of  compounds  of  the  con- 
stituent metals  in  an  excess  of  one  of  the  metals. 

Two  important  pieces  of  evidence  in  favour  of  these  views  must  be  quoted, 
(i)  In  many  instances,  when  one  metal  is  alloyed,  in  small  proportion,  with 
another,  the  freezing-point  of  the  preponderating  metal  is  lowered  to  an  extent 
which  is  in  accord  with  the  laws  controlling  the  lowering  of  the  freezing-point  of 
a  solvent  by  a  dissolved  solid  (p.  319).*  This  indicates  that  the  alloy  is  but  a 
solidified  solution.  (2)  When  a  compound  plate  (of  copper  and  zinc,  for  instance), 
consisting  of  one  metal  closely  attached  to  another,  is  used  as  the  attackable 
plate  of  a  galvanic  cell,  the  electro-motive  force  of  the  cell  is  that  which  would  be 
produced  were  the  more  attackable  of  these  metals  (zinc,  for  instance)  alone  used 
as  the  attackable  plate.  When  an  alloy  is  thus  treated,  the  E.M.F.  is  in  some 
cases  that  which  would  be  produced  by  the  more  attackable  constituent,  and  is 
in  some  cases  different  from  this.  Identity  of  the  E.M.F.  with  that  of  the  more 
attackable  metal  indicates  that  the  alloy  is  a  solidified  simple  solution,  whereas 
a  difference  from  this  value  can  only  be  due  to  the  existence  of  a  compound  in  the 
alloy. 

Alloys  are  industrially  made  by  mixing  the  constituent  metals  in  a 
melted  condition,  although  they  have  been  also  prepared  both  by  strongly 
compressing  a  mixture  of  the  powdered  metals  at  the  ordinary  tempera- 
ture, and  by  electrolysing  a  solution  containing  salts  of  the  constituent 
metals  ;  the  metallic  deposit  obtained  by  the  latter  method  consists,  in 
some  cases,  of  an  alloy. 

2$2a.  Alloys  of  Tin. — Tin  is  the  chief  metal  used  for  making  white 
alloys,  some  of  which  resemble  silver  in  appearance.  Britannia  metal 
•consists  chiefly  of  tin  (about  80  per  cent.)  hardened  by  antimony  (about 

*  It  may  be  remarked  that  evidence  as  to  the  molecular  weight  of  metals  has  been  ob- 
tained from  alloys  by  a  method  analogous  to  that  of  Kaoult  (p.  319). 


452  ALLOYS    OF    TIN. 

10  per  cent.)  and  a  little  copper.  Base  silver  coin  consists  chiefly  of  tin. 
Pewter  consists  of  4  parts  of  tin  and  i  part  of  lead.  Much  inferior  tin- 
foil is  made  of  pewter.  The  fusibility  of  tin  recommends  it  for  solder. 
The  solder  employed  for  tin-wares  is  an  alloy  of  tin  and  lead  in  various 
proportions,  sometimes  containing  2  parts  of  tin  to  i  of  lead  (fine  solder), 
sometimes  equal  weights  of  the  two  metals  (common  solder),  and  some- 
times 2  parts  of  lead  and  i  of  tin  (coarse  solder).  All  these  alloys  melt 
at  a  lower  temperature  than  tin,  and,  therefore,  than  lead.  In  applying 
solder,  it  is  essential  that  the  surfaces  to  be  united  be  quite  free  from 
oxide,  which  would  prevent  adhesion  of  the  solder ;  this  is  insured  by 
the  application  of  sal  ammoniac,  or  of  hydrochloric  acid,*  or  sometimes 
of  powdered  borax,  remarkable  for  its  ready  fusibility  and  its  solvent 
power  for  the  metallic  oxides. 

Gun  metal  is  an  alloy  of  90.5  parts  of  copper  with  9.5  of  tin,  especially 
valuable  for  its  tenacity,  hardness,  and  fusibility. 

In  preparing  this  alloy,  it  is  usual  to  melt  the  tin  in  the  first  place  with  twice  its- 
weight  of  copper,  when  a  white,  hard,  and  extremely  brittle  alloy  (Jiard  metaT)  is 
obtained.  The  remainder  of  the  copper  is  fused  in  a  de-oxidising  flame  on  the 
hearth  of  a  reverberatory  furnace,  and  the  hard  metal  thoroughly  mixed  with  it, 
long  wooden  stirrers  being  employed.  A  quantity  of  old  gun  metal  is  usually 
melted  with  the  copper,  and  facilitates  the  mixing  of  the  metals.  When  the 
metals  are  thoroughly  mixed,  the  oxide  is  removed  from  the  surface  and  the  gun- 
metal  is  run  into  moulds  made  of  loam,  the  stirring  being  continued  during  the 
running,  in  order  to  prevent  the  separation,  to  which  this  alloy  is  very  liable,  of  a 
white  alloy  containing  a  larger  proportion  of  tin,  which  has  a  lower  specific  gravity, 
and  would  chiefly  collect  in  the  upper  part  of  the  casting  (forming  tin-spots).  The 
purest  commercial  qualities  of  copper  and  tin  are  always  employed  in  gun-metal. 

The  brittle  white  alloy  alluded  to  above  as  hard  metal  appears  to  be  a  chemical 
compound  having  the  formula  SnCu4  (which  requires  31.8  per  cent,  of  tin  and  68.2 
per  cent,  of  copper),  though  the  alloy  which  has  the  highest  density,  and  bears 
repeated  fusion  without  alteration  in  its  composition,  corresponds  with  the 
formula  SnCu3  (38.2  per  cent,  of  tin).  It  is  probably  one  of  these  alloys  which 
forms  the  tin-spots  or  flaws  in  gun-metal  castings. 

Bronze  is  essentially  an  alloy  of  copper  and  tin,  containing  more  tin 
than  gun-metal  contains  ;  its  composition  is  varied  according  to  its 
application,  small  quantities  of  zinc  and  lead  being  often  added  to  it. 
Bronze  is  affected  by  changes  of  temperature,  in  a  manner  precisely  the 
reverse  of  that  in  which  steel  is  influenced,  for  it  becomes  hard  and 
brittle  when  allowed  to  cool  slowly,  but  soft  and  malleable  when  quickly 
cooled,  a  property  which  the  ancients  applied  in  the  manufacture  of 
weapons.  Bronze  coin  (substituted  for  the  copper  coinage)  is  composed 
of  95  copper,  4  tin,  and  i  zinc.  Manganese-bronze,  an  alloy  of  ordinary 
bronze  containing  Mn,  is  said  to  rival  bar-iron  in  tenacity  and  extensi- 
bility ;  it  is  used  for  ships'  propellers.  Phosphor-bronze  contains  about 
J  per  cent,  of  phosphorus  added  as  tin  phosphide. 

Bell-metal  is  an  alloy  of  about  4  parts  of  copper  and  i  of  tin,  to  which 
lead  and  zinc  are  sometimes  added.  The  metal  of  which  musical  instru- 
ments are  made  generally  contains  the  same  proportions  of  copper  and 
tin  as  bell-metal.  At  a  little  below  a  dark  red  heat,  this  alloy  may  be 
hammered  into  thin  plates,  imitating  the  celebrated  Chinese  gongs. 

Speculum  metal,  employed  for  reflectors  in  optical  instruments,  con- 
sists of  2  parts  of  copper  and  i  of  tin,  to  which  a  little  Zn,  As,  and 
Ag  are  sometimes  added  to  harden  it  and  render  it  susceptible  to  a  high 

*  It  is  customary  to  kill  the  hydrochloric  acid  by  dissolving  some  zinc  in  it.  The  chloride 
of  zinc  is  probably  useful  in  protecting  the  work  from  oxidation. 


OXIDES   OF  TIN.  453 

polish.  A  superior  kind  of  type-metal  is  composed  of  i  part  of  Sn,  i 
of  Sb,  and  2  of  Pb. 

Tin  is  not  dissolved  by  nitric  acid,  but  is  converted  into  a  white 
powder,  metastannic  acid  ;  hydrochloric  acid  dissolves  it  with  the  aid  of 
heat,  evolving  hydrogen  ;  but  the  best  solvent  for  tin  is  a  mixture  of 
hydrochloric  with  a  little  nitric  acid.  When  the  metal  is  acted  upon  by 
hydrochloric  acid,  it  assumes  a  crystalline  appearance,  which  has  been 
turned  to  account  for  ornamenting  tin-plate.  If  a  piece  of  common 
tin-plate  be  rubbed  over  with  tow  dipped  in  a  warm  mixture  of  hydro- 
chloric and  nitric  acids,  its  surface  is  very  prettily  diversified  (moire 
metallique) ;  it  is  usual  to  cover  the  surface  with  a  coloured  transparent 
varnish. 

A  mixture  of  i  vol.  H2SO4,  2  vols.  HN03,  and  3  vols.  water  dissolves 
tin  in  the  cold,  evolving  nearly  pure  nitrous  oxide.  The  solution  is  pre- 
cipitated when  heated.  Poured  into  boiling  water,  all  the  tin  is  thrown 
down  as  metastannic  acid. 

Commercial  tin  is  liable  to  contain  minute  quantities  of  lead,  iron, 
copper,  arsenic,  antimony,  bismuth,  gold,  molybdenum,  and  tungsten. 
Pure  tin  may  be  precipitated  in  crystals  by  the  feeble  galvanic  current 
excited  by  immersing  a  plate  of  tin  in  a  strong  solution  of  stannous 
chloride,  covered  with  a  layer  of  water,  so  that  the  metal  may  be  in 
contact  with  both  layers  of  liquid. 

253.  Oxides  of  tin. — Two  oxides  of  this  metal  are  known — stannous 
oxide,  SnO,  and  stannic  oxide,  SnO2. 

Protoxide  of  tin  (SnO),  or  stannous  oxide,  is  a  substance  of  little  practical 
importance,  obtained  by  heating  stannous  oxalate  out  of  contact  with  air ; 
SnC204=:SnO  +  C02+CO.  It  is  a  black  powder  which  burns  when  heated  in  air, 
becoming  Sn02.  It  is  a  feebly  basic  oxide,  and  therefore  dissolves  in  the  acids  ; 
it  may  also  be  dissolved  by  a  strong  solution  of  potash,  but  is  then  easily 
decomposed  into  metallic  tin  and  stannic  oxide,  which  combines  with  the  potash. 
By  heating  tin  with  caustic  soda  a  "  stannite "  of  soda  is  obtained  ;  this  is 
substituted  for  stannate  of  soda,  into  which  it  is  converted,  with  precipitation  of 
tin.  by  boiling. 

Binoxide  of  tin  (Sn02)  or  stannic  oxide,  has  been  mentioned  as  the 
chief  ore  of  tin,  and  is  formed  when  tin  is  heated  in  air.  Tin-stone,  or 
cassiterite,  as  the  natural  form  of  this  oxide  is  called,  occurs  in  very  hard 
square  prisms,  usually  coloured  brown  by  ferric  oxide.  In  its  insolu- 
bility in  acids  it  resembles  crystallised  silica,  and,  like  that  substance, 
it  forms,  when  fused  with  alkalies  or  their  carbonates,  compounds  which 
are  soluble  in  water ;  these  are  termed  stannates,  the  binoxide  of  tin 
being  known  as  stannic  anhydride.  The  artificial  Sn02  dissolves  in  hot 
strong  H2S04,  and  is  precipitated  on  adding  water.  It  is  easily  reduced 
when  heated  in  hydrogen,  and  is  converted  into  SnCL  when  heated  in 
HC1  gas. 

Sodium  stannate,  Na2O.Sn02,  is  prepared,  on  the  large  scale,  for 
use  as  a  mordant  by  calico-printers.  The  prepared  tin  ore  (p.  448)  is 
heated  with  solution  of  caustic  soda,  and  boiled  down  till  the  tem- 
perature rises  to  600°  F.  (315°  0.) ;  or  the  tin  ore  is  fused  with  sodium 
nitrate,  when  the  nitric  acid  is  expelled.  It  crystallises  easily  in  hex- 
agonal tables  having  the  composition  Na2Sn03.3Aq,  which  dissolve 
easily  in  cold  water,  and  are  partly  deposited  again  when  the  solution 
is  heated.  Prismatic  crystals  have  been  obtained  of  Na2Sn03.ioAq, 
like  Na2C03.ioAq.  Most  normal  salts  of  the  alkalies  also  cause  a 


454  STANNOUS   CHLOKIDE. 

separation  of  sodium  stannate  from  its  aqueous  solution.  The  solution 
of  sodium  stannate  has,  like  the  silicate,  a  strong  alkaline  reaction,  and 
when  neutralised  by  an  acid  yields  a  precipitate  of  stannic  acid,  H2SnO3, 
or  SnO(OH)2,  which  may  be  obtained  as  a  hydrosol  and  a  hydrogel 
exactly  as  described  for  silicic  acid  (p.  278).  The  great  similarity 
between  stannic  and  silicic  acids  is  here  very  remarkable.  When 
heated,  stannic  acid  is  converted  into  Sn02. 

Stannic  or  metastannic  acid,  H2Sn03  (dried  at  100°  C.),  is  obtained  as  a  white 
crystalline  hydrate  when  tin  is  oxidised  by  nitric  acid.  When  heated,  it  assumes  a 
yellowish  colour,  and  a  hardness  resembling  that  of  powdered  tin-stone.  Putty 
2)owder,  used  for  polishing,  consists  of  metastannic  anhydride  ;  as  found  in 
commerce,  it  generally  contains  much  oxide  of  lead.  Metastannic  acid  is  insoluble 
in  water  and  diluted  acids,  but  when  boiled  with  dilute  HC1  it  combines  with 
some  of  the  acid,  and  when  the  excess  of  HC1  has  been  removed  by  washing,  the 
compound  passes  into  solution,  from  which  it  is  reprecipitated  by  HC1,  or  by 
boiling.  When  fused  with  hydrated  alkalies  it  is  converted  into  a  soluble 
stannate,  but  if  boiled  with  solution  of  potash  it  is  dissolved  in  the  form  of 
potassium  metastannate,  which  will  not  crystallise,  like  the  stannate,  but  is 
obtained  as  a  granular  •  precipitate  by  dissolving  potassium  hydrate  in  its  solu- 
tion. This  precipitate  has  the  composition  K2Sn5Oi;i.4Aq  ;  it  is  very  soluble  in 
water,  and  is  strongly  alkaline.  When  it  is  heated  to  expel  the  water,  it  is 
decomposed,  and  the  potash  may  be  washed  out  with  water,  leaving  metastannic 
anhydride.  The  sodium  metastannate,  Na2Sn50114Aq,  has  also  been  obtained  as  a 
sparingly  soluble  crystalline  powder,  by  the  action  of  cold  sodium  hydroxide  on 
metastannic  acid.  It  is  claimed  that  the  precipitate  formed  by  alkalies  in  stannic 
chloride  is  orthostannic  acid,  Sn(OH)4. 

Stannate  of  tin  is  obtained  as  a  yellowish  hydrate  by  boiling  stannous  chloride 
with  ferric  hydroxide  ;  Fe203  +  2SnCl2  =  SnSn03  +  2FeCl2.  It  is  sometimes  written 
Sn203,  and  called  sesquioxide  of  tin. 

Stannous  nitrate,  Sn(N03)2.  is  formed  when  tin  is  dissolved  in  cold  very  dilute 
nitric  acid  ;  Sn4+  ioHN03  =  4Sn(N03)2  +  NH4N03  +  3H20.  It  forms  a  yellow  solu- 
tion, which  absorbs  oxygen  and  deposits  Sn02.  Stannic  nitrate,  Sn(N03)4,  has 
been  crystallised  from  a  solution  of  stannic  acid  in  nitric  acid. 

254.  Chlorides  of  tin. — The  two  chlorides  of  tin  correspond  in 
composition  with  the  oxides. 

Stannous  chloride,  or  protochloride  of  tin  (SnCl2),  is  much  used  by  dyers 
and  calico-printers,*  and  is  prepared  by  dissolving  tin  in  hydrochloric 
acid,  when  it  is  deposited,  on  cooling,  in  lustrous  prismatic  needles 
(Sn012.2Aq)  known  as  tin  crystals  or  salts  of  tin.  In  vamio,  over  H2S04, 
they  become  SnCl2  (m.  p.  249°  C.).  The  dissolution  of  the  tin  is 
generally  effected  in  a  copper  vessel,  in  order  to  accelerate  the  action  by 
forming  a  voltaic  couple,  of  which  the  tin  is  the  attacked  metal.  When 
gently  heated,  the  crystals  lose  their  water,  and  are  partly  decomposed, 
some  hydrochloric  acid  being  evolved  (SnCl,  -f  H2O  =  SnO  +  2HC1)  ;  at  a 
higher  temperature  (610°  0.)  the  anhydrous  chloride  may  be  distilled. 
The  crystallised  stannous  chloride  dissolves  in  about  one-third  of  its 
weight  of  water,  but  if  much  water  be  added,  a  precipitate  of  stannous 
hydroxy  chloride,  2Sn(OH)Cl.Aq,  is  formed,  which  dissolves  on  adding 
HC1.  A  moderately  dilute  solution  of  stannous  chloride  absorbs  oxygen 
from  the  air,  and  deposits  the  hydroxychloride,  leaving  stannic  chloride 
in  solution ;  3SnCl2  +  H2O  +  0  =  SnCl4  +  2Sn(OH)Cl.  If  the  solution 
contains  much  free  hydrochloric  acid,  it  remains  clear,  being  entirely 
converted  into  stannic  chloride.  A  strong  solution  of  the  chloride  is 
not  oxidised  by  the  air,  and  the  weak  solution  may  be  longer  preserved 
in  contact  with  metallic  tin.  Stannous  chloride  has  a  great  attraction 

*  It  is  sometimes  used  for  imparting  a  fine  golden  colour  to  sugar. 


STANNIC   CHLORIDE.  455 

for  chlorine  as  well  as  for  oxygen,  and  is  frequently  employed  as  a 
de-oxidising  or  de-chlorinating  agent.  Tin  may  be  precipitated  from 
stannous  chloride  by  the  action  of  zinc,  in  the  form  of  minute  crystals. 
A  very  beautiful  tin  tree  is  obtained  by  dissolving  granulated  tin  in 
strong  hydrochloric  acid,  with  the  aid  of  heat,  in  the  proportion  of  8 
measured  oz.  of  acid  to  1000  grs.  of  tin,  diluting  the  solution  with  four 
times  its  bulk  of  water,  and  introducing  a  piece  of  zinc. 

Stannous  chloride  is  also  obtained  by  heating  tin  in  HC1  gas,  or  by 
distilling  tin  with  mercuric  chloride;  Sn  +  HgCl2  =  SnCl2  +  Hg.  The 
mercury  distils  over,  leaving  the  stannous  chloride  as  a  transparent 
vitreous  mass.  Above  880°  C.  the  density  of  its  vapour  is  94.5  (H=  i), 
agreeing  with  the  formula  SnCl2,  but  below  700°  C.  it  is  189,  corre- 
sponding with  Sn2Cl4. 

Stannic  chloride  or  tetrachloride  of  tin  (SnCl4),  is  obtained  in  solution 
when  tin  is  heated  with  hydrochloric  and  nitric  acids  ;  for  the  use  of 
the  dyer,  the  solution  (nitromuriate  of  tin)  is  generally  made  with 
chloride  of  ammonium  (sal-ammoniac)  and  nitric  acid.  The  anhydrous 
tetrachloride  is  obtained  by  heating  tin  in  a  current  of  dry  chlorine, 
when  combination  occurs  with  combustion,  and  the  tetrachloride  distils 
over  as  a  heavy  (sp.  gr.  2.28)  colourless  volatile  liquid  (boiling-point, 
114°  C.),  giving  suffocating  white  fumes  in  the  air.  When  it  is  mixed 
with  a  little  water,  there  is  energetic  combination,  and  three  crystalline 
compounds  may  be  produced,  containing  3,  5,  and  8  molecules  of  water. 
A  large  quantity  of  water  causes  precipitation  of  stannic  acid.  The 
commercial  crystals  are  SnCl^Aq.  The  anhydrous  chloride  is  also 
obtained  by  distilling  tin  with  an  excess  of  mercuric  chloride ; 
Sn-i- 2Hg012  =  SnCl4-l-Hg2 ;  but  here,  the  result  is  opposite  to  that  in 
the  case  of  stannous  chloride,  as  the  stannic  chloride  distils  over  before 
the  mercury.  Stannic  chloride  forms  crystallisable  double  salts  with 
the  alkali  chlorides.  Pink  salt,  used  by  dyers,  is  a  compound  of  stannic 
chloride  with  ammonium  chloride,  2NH4Cl.SnCl4 ;  it  is  colourless,  but 
is  used  in  dying  red  with  madder.  The  compound  2H01.SnCl4.6Aq 
has  been  obtained  in  crystals. 

Stannic  bromide,  SnBr4,  is  crystalline,  fuses  at  30°  C.,  and  boils  at 
201°  C.  It  dissolves  in  water  without  immediate  decomposition. 

255.  Sulphides  of  tin. — The  p)*otosulphide,  or  stannous  sulphide 
(SnS),  may  be  easily  prepared  by  heating  tin  with  sulphur,  when  it 
forms  a  grey  crystalline  mass.  It  is  also  obtained  as  a  dark  brown 
precipitate  by  the  action  of  H2S  upon  a  solution  of  SnCl2.  Stannous 
sulphide  is  not  dissolved  by  alkalies  unless  some  sulphur  be  added, 
which  converts  it  into  stannic  sulphide.  It  dissolves  in  hot  strong 
HC1. 

Bisulphide  of  tin,  or  stannic  sulphide  (SnS2),  is  commonly  known  as 
mosaic  gold  or  bronze  powder,*  and  is  used  for  decorative  purposes.  It 
cannot  be  made  by  heating  tin  with  sulphur,  because  it  is  decomposed 
by  heat  into  SnS  and  S.  It  is  prepared  by  a  curious  process,  which 
was  devised  in  1771,  and  must  have  been  the  result  of  a  number  of 
trials.  1 2  parts  by  weight  of  tin  are  dissolved  in  6  parts  of  mercury  ; 
the  brittle  amalgam  thus  obtained  is  powdered  and  mixed  with  7  parts 
of  sulphur  and  6  of  sal-ammoniac.  The  mixture  is  introduced  into  a 

*  A  bronze  powder  is  also  made  by  powdering  finely  laminated  alloys  of  copper  and  zinc 
a  little  oil  being-  used  to  prevent  oxidation. 


456  TITANIUM. 

Florence  flask,  which  is  gently  heated  in  a  sand-bath  as  long  as  any 
smell  of  H2S  is  evolved  ;  the  temperature  is  then  raised  to  dull  redness 
until  no  more  fumes  are  disengaged.  The  mosaic  gold  is  found  in 
beautiful  yellow  scales  at  the  bottom  of  the  flask,  and  sulphide  of 
mercury  and  calomel  are  deposited  in  the  neck.  The  mercury  appears 
to  be  used  for  effecting  the  fine  division  of  the  tin,  and  the  sal-ammoniac 
to  keep  down  the  temperature  (by  its  volatilisation)  below  the  point  at 
which  the  SnS2  is  converted  into  SnS. 

Mosaic  gold,  like  gold  itself,  is  not  dissolved  by  hydrochloric  or  nitric  acid,  but 
easily  by  aqua  regia.  Alkalies  also  dissolve  it  when  heated.  On  adding  H2S  to  a 
solution  of  stannic  chloride,  the  stannic  sulphide  is  obtained  as  a  yellow  precipitate, 
which  is  sometimes  formed  only  on  boiling.  It  dissolves  easily  in  alkalies  and 
alkali  sulphides,  forming  thiostannates.  The  sodium  salt,  Na2SnS3.2H20,  has 
been  crystallised  in  yellow  octahedra.  When  fused  with  iodine,  SnS2  forms 
SnS2I4,  a  fusible  yellow  body  which  does  not  lose  iodine  when  heated,  and  dis- 
solves in  carbon  disulphide,  forming  a  brown  solution  which  deposits  red  crystals 
like  potassium  dichromate  ;  these  are  decomposed  by  boiling  with  water,  yielding 
Sn02,  sulphur,  iodine,  and  HI, 

Tin  pyrites  contains  either  SnS  or  SnS2,  or  both,  accompanied  by  sulphides  of 
copper  and  iron. 

Stannic  sulphate,  Sn(S04)2,  is  left  as  a  white  mass  when  tin  is  boiled  to  dryness 
with  sulphuric  acid. 

Stannic  phosphate,  Sn3(P04)4,  is  insoluble  in  nitric  acid,  and  is  sometimes  used 
in  separating  phosphoric  acid  in  quantitative  analysis. 

Stannic  arsenate  is  left  in  the  residue  obtained  by  oxidising  alloys  containing 
tin  and  arsenic  with  nitric  acid. 

Tin  is  very  closely  connected  with  silicon  by  the  composition,  hard- 
ness, and  insolubility  of  Sn02,  and  by  the  characters  of  SnCl4.  Among 
metals  it  is  conspicuous  by  the  feebly  basic  character  of  its  oxides  and 
by  the  powerful  reducing  properties  of  SnCl2. 

TITANIUM,  Ti=  47.7. 

256.  This  metal  stands  in  close  chemical  relationship  to  tin  ;  it  is  found  in  con- 
siderable quantity  in  iron  ores  and  clays,  although  no  very  important  practical 
application  has  hitherto  been  found  for  it.  The  form  in  which  it  is  generally  found 
is  titanic  oxide  (or  anhydride),  Ti02,  which  occurs  uncombined  in  the  minerals 
rutile,  anatase,  and  brookite,  the  first  of  which  is  isomorphous  with  tin-stone,  and 
is  extremely  hard,  like  that  mineral,  while  the  second  crystallises  in  the  quadratic 
system  and  the  third  in  the  rhombic.  The  mineral  perowsltite  is  (CaFe)Ti03.  In 
combination  with  oxide  of  iron,  titanic  oxide  is  found  in  iron-sand,  iserine,  or 
menaccanite  (found  originally  in  Menaccan,  in  Cornwall),  which  resembles  gun- 
powder in  appearance,  and  is  now  imported  in  abundance  from  Nova  Scotia  and 
New  Zealand.  Some  specimens  of  this  mineral  contain  40  per  cent,  of  titanic 
oxide  as  ferrous  titanate.  To  extract  titanic  oxide  from  it,  the  finely  ground 
mineral  is  fused  with  three  parts  of  K2C03,  when  CO2  is  expelled  and  potassium 
titanate  (K2Ti03)  formed  ;  on  washing  the  mass  with  hot  water,  this  salt  is  decom- 
posed, a  part  of  its  alkali  being  removed  by  the  water,  and  an  acid  titanate  left, 
mixed  with  the  oxide  of  iron.  This  is  dissolved  in  HC1,  and  the  solution  evapo- 
rated to  dryness,  when  the  titanic  oxide,  and  any  silica  which  may  be  present,  are 
converted  into  the  insoluble  modifications,  and  are  left  on  digesting  the  residue 
again  with  dilute  hydrochloric  acid ;  the  residue  is  washed  with  water  (by 
decantation,  for  titanic  oxide  easily  passes  through  the  filter),  dried,  and  fused  at 
a  gentle  heat  with  KHS04.  This  forms  a  soluble  compound  with  the  titanic 
oxide,  which  may  be  extracted  by  cold  water,  leaving  the  silica  undissolved.  The 
solution  containing  the  titanic  oxide  is  mixed  with  about  twenty  times  its  volume 
of  water,  and  boiled  for  some  time,  when  the  Ti02  is  separated  as  a  white  pre- 
cipitate, exhibiting  a  great  disposition  to  cling  as  a  film  to  the  surface  of  the  flask 
in  which  the  solution  is  boiled,  and  giving  it  the  appearance  of  being  corroded. 
The  titanic  oxide  becomes  yellow  when  strongly  heated,  and  white  again  on 
cooling  ;  it  does  not  dissolve  in  solution  of  potash,  like  silica,  but  when  fused  with 


COMPOUNDS   OF  TITANIUM.  457 

potash  it  forms  a  titanate,  which  is  decomposed  by  water  ;  the  acid  titanate  of 
potassium  which  is  left  may  be  dissolved  in  HC1,  and  if  the  solution  be  neutralised 
with  ammonium  carbonate,  hydrated  titanic  acid,  Ti(OH)4,  is  precipitated,  very 
much  resembling  alumina  in  appearance.  By  dissolving  the  gelatinous  hydrate  in 
cold  HC1,  and  dialysing,  a  solution  of  titanic  acid  in  water  is  obtained,  which  is 
liable  to  gelatinise  spontaneously  if  it  contains  more  than  i  per  cent,  of  the  acid. 
Titanic  acid  is  employed  in  the  manufacture  of  artificial  teeth,  and  for  imparting 
&  straw-yellow  tint  to  the  glaze  of  porcelain. 

If  a  mixture  of  titanic  acid  and  charcoal  be  heated  to  redness  in  a  porcelain 
tube  through  which  dry  chlorine  is  passed,  titanium  tetrachloride  (TiCl4)  is  obtained 
as  a  colourless  volatile  liquid  (Jb.  p.  136°  C.),  very  similar  to  tetrachloride  of  tin. 
By  passing  the  vapour  of  the  tetrachloride  over  heated  sodium,  the  metallic  titanium 
is  obtained  in  prismatic  crystals  (sp.  gr.  3.6)  resembling  specular  iron  ore  in 
appearance  ;  it  fuses  at  a  very  high  temperature,  but  can  be  prepared  massive  by 
heating  a  mixture  of  TiO2  and  C  in  the  electric  furnace,  when  it  contains  about 
2  per  cent,  of  carbon,  is  hard  enough  to  scratch  rock  crystal  and  has  sp.  gr.  4.87. 
Like  tin,  it  is  said  to  dissolve  in , hydrochloric  acid  with  liberation  of  hydrogen. 
The  most  remarkable  chemical  feature  of  titanium  is  its  direct  attraction  for 
nitrogen,  with  which  it  combines  when  strongly  heated  in  air.  By  passing 
ammonia  gas  over  titanic  oxide  heated  to  redness,  a  yellow  powder  is  formed, 
which  is  nitride  of  titanium  (Ti.2N2).  When  suspended  in  water,  it  is  blue  by 
transmitted  and  yellow  by  reflected  light.  Ti3N4,  corresponding  with  TiCl4,  is  also 
known.  Beautiful  cubes  of  a  copper  colour  and  great  hardness,  formerly  believed 
to  be  metallic  titanium,  are  found  adhering  to  the  slags  of  blast  furnaces  in  which 
titaniferous  iron  ores  are  smelted  ;  these  are  believed  to  consist  of  a  compound  of 
cyanide  with  nitride  of  titanium,  TiCy2.3Ti3N2.  A  similar  compound  is  obtained 
by  passing  nitrogen  over  a  mixture  of  titanic  oxide  and  charcoal  heated  to 
whiteness. 

Violet-coloured  crystals  of  titanium  trichloride  (Ti2Cl6)  are  obtained  by  passing 
hydrogen  charged  with  vapour  of  the  tetrachloride  through  a  red-hot  porcelain 
tube  ;  it  forms  a  violet  solution  in  water,  which  resembles  stannous  chloride  in 
its  reducing  properties. 

Titanium  dichloride.  TiCl2,  is  obtained  by  heating  the  trichloride  to  dull  redness 
in  hydrogen.  It  is  a  black  solid  which  quickly  absorbs  moisture,  and  takes  fire 
if  water  be  dropped  upon  it.  When  dissolved  in  water  or  alcohol,  it  evolves 
hydrogen  from  them.  Bromine  combines  with  it,  causing  much  heat,  and  form- 
ing TiCl2Br.2.  The  dichloride  volatilises  in  hydrogen  without  fusing,  and  if  cooled 
in  hydrogen  it  occludes  the  gas,  and  takes  fire  on  exposure  to  air.  It  glows  when 
heated  on  platinum,  evolving  TiCl4,  and  leaving  a  residue  of  Ti02. 

Titanium  tetrafluoride,  TiF4  is  prepared  like  SiF4,  and  is  a  fuming  colourless 
liquid.  TheJIuotitanates,  e.g.,  K2TiF6,  are  prepared  by  dissolving  Ti02  in  HF  and 
neutralising  with  alkali. 

When  a  solution  of  titanic  oxide  (or  acid  titanate  of  potassium)  in  hydrochloric 
acid  is  acted  on  by  zinc,  a  violet  solution  is  formed,  which  deposits,  after  a  time, 
a  blue  (or  green)  precipitate ;  this  appears  to  be  a  sesquioxlde  of  titanium  (Ti203), 
and  rapidly  absorbs  oxygen  from  the  air,  being  converted  into  titanic  oxide. 
This  oxide  is  also  obtained  in  the  preparation  of  TiCl2  unless  air  be  very  carefully 
excluded.  It  then  forms  small  shining  copper-coloured  crystals  with  a  violet 
reflection,  which  have  the  same  crystalline  form  as  specular  iron  ore  (Fe203). 
Ti.2Q3  is  a  basic  oxide.  The  sulphate  Ti2(S04)3.8Aq  crystallises  from  the  violet 
solution  obtained  by  dissolving  titanium  in  sulphuric  acid.  Nitric  acid  oxidises 
it  to  titanic  sulphate,  Ti(S04)2.3Aq,  which  forms  a  yellowish,  transparent,  deliques- 
cent mass.  Thus.  Ti02  appears  to  possess  feebly  basic  as  well  as  feebly  acid 
properties.  The  patagrio-tttanic  sulphate,  K2Ti(sC)4)3.3Aq.  is  formed  when  TiO2  is 
fused  with  KHS04.  A  titanoug  oxide  (TiO)  is  said  to  be  obtained  as  a  black  powder 
when  titanic  oxide  is  strongly  heated  in  a  crucible  lined  with  charcoal. 

Titanium  tno.nde  Ti03,  is  obtained  as  a  yellow  precipitate,  Ti(OH)6,  when  TiCl4 
is  mixed  with  a  dilute  solution  of  H202  in  alcohol.  It  is  probably  a  peroxide,  and 
is  the  cause  of  the  yellow  colour  developed  by  H202  in  solution  of  titanic  acid 
forming  a  test  for  H202  (p.  64). 

Titanium  digulpkide  is  not  precipitated,  like  tin  disulphide  when  H2S  acts  upon 
the  tetrachloride  ;  but  if  a  mixture  of  the  vapour  of  titanium  tetrachloride  with 
hydrosulphuric  acid  is  passed  through  a  red-hot  tube,  greenish-yellow  scales  of  the 
disulphide,  resembling  mosaic  gold,  are  deposited. 


45* 


THORIUM. 


ZIRCONIUM,  Zr  =  go. 

257.  This  metal  occurs  in  the  rare  minerals  zircon  (sp.  gr.  4.5)  and  hyacinth,  in 
which  the  oxide  zirconia  (Zr02)  is  combined  with  silica  (Zr02.Si02).  The  Zr02  is 
obtained  from  these  minerals  by  heating  with  KHF2,  and  boiling  with  water 
when  K2SiF6  is  left  and  K2ZrF6  dissolved  ;  this  is  heated  with  H2S04  to  expel  HF, 
and  ZrO(OH)2  is  precipitated  by  ammonia  ;  when  this  is  ignited,  it  incandesces, 
loses  water,  and  becomes  Zr02,  which  is  a  feebly  acid  oxide,  liberating  C02  from 
fused  Na^COg,  and  forming  sodium  zirconate.  Na4Zr04. 

Zr  closely  resembles  Si,  and  is  obtained  like  that  element ;  it  exists  in  an 
amorphous  and  a  crystalline  (sp.  gr.  4.25)  form.  It  dissolves  in  HF  and  in  aqua 
regia  and  decomposes  water  slowly  at  100°  C.  Its  melting-point  is  very  high. 
Zinconia  is  more  basic  than  silica,  and  the  metal  displaces  silicon  when  heated 
with  silica.  The  sulphate,  Zr(S04)2.4Aq,  is  decomposed  by  boiling  with  K2S04, 
recalling  the  behaviour  of  titanium.  ZrCl4  is  known  ;  it  is  more  stable  than  SiCl4. 
Evidence  of  the  existence  of  higher  oxides  than  Zr02  has  been  obtained. 

THORIUM,  Thiv  =  23o.8. 

Although  a  rare  element,  thorium  in  the  form  of  thoria,  Th02  (sp.  gr.  10.2),  is 
used  in  considerable  quantity  for  the  manufacture  of  Welsbach  mantles  (p.  155). 
The  mineral  thorite,  Th02.Si02,  is  the  most  fruitful  source  of  thoria  but  it  is  rare, 
and  the  oxide  is  commonly  produced  from  monazite  sand,  which  is  comparatively 
poor  in  thorium,  by  fusion  with  caustic  alkali,  extraction  with  sulphurous  acid  and 
evaporation  of  the  residue  with  strong  H2S04  ;  the  dry  mass  is  added  in  small  doses 
to  water  at  o°  C.  in  which  anhydrous  thorium  sulphate  is  readily  soluble.  Sodium 
sulphate  is  next  added  to  precipitate  cerium  and  thorium  hydroxide,  Th(OH)4,  is 
then  thrown  down  by  some  substance  acting  as  a  feeble  base,  like  sodium  nitrite. 
Thoria  is  more  basic  than  Zr02  but  less  acid,  as  it  does  not  expel  C02  from  fused 
NagCOg.  Its  anhydrous  sulphate,  Th(S04)2,  is  soluble  in  ice-cold  water,  but  when 
the  solution  is  heated  crystals  of  Th(S04)2.4H2O  separate.  Thoria  does  not  dissolve 
in  HC1  or  HN03,  but  when  the  acid  is  expelled  on  the  steam  bath,  the  residue 
dissolves  in  the  water  to  an  emulsion  in  which  acids  cause  a  curdy  precipitate 
soluble  in  pure  water  (compare  metastannic  acid).  NH3  produces  a  bulky  pre- 
cipitate of  hydroxide  which  dissolves  in  cold  nitric  acid  yielding  the  nitrate 
Th(N03)4.6H20.  Thorium  fluoride  is  a  precipitate  insoluble  in  HF  ;  the  double 
fluoride  K2ThF6.4H20  is  a  sparingly  soluble  crystalline  powder. 

Thorium  prepared  by  dissolving  the  hydroxide  in  HC1,  evaporating  with  KC1, 
and  fusing  the  double  chloride  with  sodium,  is  a  grey  crystalline  metal  isomorphous 
with  silicon,  of  sp.  gr.  u.i.  It  is  very  infusible,  burns  in  air  below  a  red  heat, 
dissolves  in  dilute  acids,  and  does  not  decompose  water. 

The  radio-activity  of  thorium  compounds  has  already  been  noticed  (p.  438). 

GERMANIUM,  66=71.5. 

258.  This  occurs  in  argyrodite,  a  silver  ore.  It  is  extracted  by  fusing  the  powdered 
mineral  with  Na2C03  and  S,  extracting  with  water,  neutralising  the  solution  with 
H2S04,  filtering  from  the  precipitated  S,  As2S3,  and  Sb2S3,  and  saturating  with  H2S, 
which  precipitates  white  germanic  sulphide,  GeS2.  This  is  roasted  to  oxide,  from 
which  the  metal  is  reduced  by  heating  with  H  or  C.  It  is  a  white  brittle  metal 
(sp.  gr.  5.47),  melts  about  900°  C.,  and  volatilises  at  higher  temperatures  ;  the 
fused  metal  crystallises  in  octahedra.  It  is  dissolved  by  H2S04,  but  not  by  HC1  ; 
HN03  oxidises  it  to  Ge02. 

Germanium  stands  between  silicon  and  tin  in  the  periodic  table  (p.  302),  but 
it  is  more  nearly  related  to  tin  than  to  silicon ;  its  existence  was  prophesied 
(ekasilicon)  by  Mendeleeff  previously  to  its  discovery  (1885).  It  is  believed  to 
form  two  classes  of  salts,  corresponding  with  oxides  GeO  and  Ge02,  respectively. 
The  only  germanous  salt,  which  is  authentically  known,  however,  is  the  sulphide 
GeS.  Germanic  chloride,  GeCl4,  is  obtained  like  stannic  chloride  and  boils  at 
86°  C.  When  Ge  is  heated  in  HC1  it  yields  germanium  chloroform,  GeHCl3,  which 
boils  at  72°  C.  It  is  doubtful  whether  GeCl2  exists.  Ge02  dissolves  in  HF  and 
the  solution  yields  double  fluorides  like  K2GeF6,  similar  to  the  silico-fluorides. 

Germanic  oxide,  Ge02,  is  white,  and  sparingly  soluble  in  water,  from  which  it 
may  be  crystallised  ;  it  functions  as  an  acid  oxide. 

GeS2  is  a  white  precipitate  obtained  by  adding  H2S  to  a  solution  of  Ge02  in 


LEAD   ORES. 

HC1  or  H2S04.  In  the  absence  of  acid  it  is  somewhat  soluble  in  water.  It  is 
dissolved  by  alkali  sulphides.  When  reduced  by  hot  H  it  yields  GeS  in  dark  grey 
lustrous  crystals,  decomposed  by  potash  into  GeSo,  which  dissolves,  and  Ge  which 
separates. 

CERIUM,  €6  =  139. 

259.  This  element  is  now  classed  with  those  related  to  tin,  but  in  many  respects 
it  resembles  those  of  the  aluminium  group.  It  occurs  chiefly  in  cerite,  which  is 
essentially  a  silicate  of  the  metal  containing  about  60  per  cent,  of  Ce203.  This 
oxide,  ceria,  is  obtained  for  the  manufacture  of  Welsbach  mantles  (p.  155)  from 
monazite  sand,  as  has  been  described  under  thorium. 

The  metal  is  prepared  by  electrolysing  fused  cerous  chloride  Ce2Cl6,  itself  obtained 
by  evaporating  Ce203  with  HC1  and  NH4C1  and  igniting.  Cerium  is  a  grey, 
lustrous,  malleable,  ductile  metal,  unchanged  by  dry  air,  but  becoming  iridescent 
in  moist  air  ;  its  sp.  gr.  is  6.7  and  it  melts  about  700°  C.  It  burns  in  air  more 
easily  than  magnesium  does,  and  with  a  brighter  light  ;  it  is  soluble  in  dilute  acid, 
and  decomposes  water  slowly. 

Three  oxides,  cerous  oxide.  Ce203,  eerie  oxide,  Ce02,  and  a  peroxide,  Ce03,  are 
known.  The  first  is  obtained  by  igniting  the  oxalate"in  hydrogen.  It  is  grey,  and 
rapidly  oxidises  to  the  pale  yellow  Ce02,  which  is  easily  reduced  again  to  Ce203  ; 
thus  when  it  is  boiled  with  HC1  it  liberates  Cl  and  dissolves  as  Ce2Cl6.  The  per- 
oxide is  a  reddish  yellow  precipitate  formed  on  adding  NH3  and  H202to  a  solution 
of  a  cerous  salt. 

Ce203  is  a  stronger  base  than  Ce02  which,  however,  has  no  acid  properties.  The 
cerous  salts  (corresponding  with  Ce2O3)  are  colourless  and  more  stable  than  the  eerie 
salts  (corresponding  with  Ce02),  which  are  yellow  or  red,  and  are  easily  reduced  to 
cerous  salts.  No  eerie  chloride  is  known,  but  the  fluoride,  CeF4.H20,  yielding  the 
double  fluoride  2CeF4.3KF.2H20,  has  been  obtained. 

LEAD. 

Pb"  =  2O5.4  parts  by  weight. 


260.  Lead  owes  its  usefulness  in  the  metallic  state  chiefly  to  its  softness 
and  fusibility.  The  former  quality  allows  it  to  be  easily  rolled  into  thin 
sheets  and  to  be  drawn  into  the  form  of  tubes  or  pipes  ;  it  is  indeed  the 
softest  of  the  metals  in  common  use,  and  at  the  same  time  the  least 
tenacious,  so  that  it  can  only  be  drawn  with  difficulty  into  thin  wire,  and 
is  then  very  easily  broken.  The  ease  with  which  it  makes  a  dark  streak 
upon  paper  shows  how  readily  minute  particles  of  the  metal  may  be 
abraded.  Its  want  of  elasticity  also  recommends  it  for  some  special 
uses,  as  for  deadening  a  shock  or  preventing  a  rebound. 

In  fusibility  it  surpasses  all  the  other  metals  commonly  employed  in 
the  metallic  state,  except  tin,  for  it  melts  at  617°  F.  (325°  C.),  and  this 
circumstance,  taken  in  conjunction  with  its  high  specific  gravity  (11.4), 
particularly  adapts  it  for  the  manufacture  of  shot  and  bullets.  For  one 
of  its  extensive  uses,  however,  as  a  covering  for  roofs,  it  would  be  better 
suited  if  it  were  lighter  and  less  fusible,  for  in  case  of  fire  in  houses  so 
roofed,  the  fall  of  the  molten  lead  frequently  aggravates  the  calamity. 
Its  resistance  to  strong  acids  is  turned  to  account  in  manufacturing 
chemistry. 

With  the  exception,  perhaps,  of  the  ores  of  iron,  none  is  more  abun- 
dant in  this  country  than  the  chief  ore  of  lead,  galena,  a  sulphide  of 
lead  (PbS).  This  ore  might  at  the  first  glance  be  mistaken  for  the  metal 
itself,  from  its  high  specific  gravity  (7.5)  and  metallic  lustre.  It  is  found 
forming  extensive  veins  in  Cumberland,  Derbyshire,  and  Cornwall,  tra- 
versing a  limestone  rock  in  the  first  two  counties,  and  a  clay  slate  in  the 
last.  Spain  also  furnishes  large  supplies  of  this  important  ore.  Galena 


4^0  EXTRACTION   OF   LEAD. 

presents  a  beautiful  crystalline  appearance,  being  often  found  in  large 
isolated  cubes,  which  readily  cleave  or  split  up  in  directions  parallel  to 
their  faces.  Blende  (sulphide  of  zinc)  and  copper  pyrites  (sulphide  of 
copper  and  iron)  are  frequently  found  in  the  same  vein  with  galena,  and 
it  is  usually  associated  with  quartz  (silica),  heavy  spar  (barium  sulphate), 
or  fluor  spar  (calcium  fluoride).  Considerable  quantities  of  sulphide  of 
silver  are  often  present  in  galena,  and  in  many  specimens  the  sulphides 
of  bismuth  and  antimony  are  found. 

Though  the  sulphide  is  the  most  abundant  natural  combination  of  lead, 
it  is  by  no  means  the  only  form  in  which  this  metal  is  found.  The  metal 
itself  is  occasionally  met  with,  though  in  very  small  quantity,  and  the 
carbonate  of  lead  (PbC03),  white  lead  ore  or  cerussite,  forms  an  important 
ore  in  the  United  States  and  in  Spain.  The  sulphate  of  lead,  anglesite 
(PbS04),  is  also  found  in  Australia,  and  is  largely  imported  into  this 
country  to  be  smelted. 

261.  The  extraction  of  lead  from  galena  is  effected  by  one  of  three 
methods,  the  first  of  which  is  the  oldest,  and  is  still  employed  in  the 
Flintshire  works. 

(i)  Advantage  is  taken  of  the  circumstance  that,  in  the  case  of  many 
metals,  when  a  combination  of  the  metal  with  oxygen  is  raised  to  a  high 
temperature  in  contact  with  a  sulphide  of  the  same  metal,  the  oxygen 
and  sulphur  unite,  and  the  metal  is  liberated  (self -reduction),  thus, 
PbS  +  2  PbO  =  Pb3  +  SO2.  Since  galena,  when  heated  with  free  access  of 
air,  becomes  to  a  great  extent  oxidised  to  PbO,  it  will  be  apparent  that 
the  necessary  mixture  of  oxide  and  sulphide  can  be  obtained  by  roasting 
the  galena  for  a  certain  time,  namely,  until  two-thirds  of  the  lead  has 
become  oxide.  This  change  cannot  be  brought  about,  however,  without 
the  simultaneous  oxidation  of  some  of  the  PbS  into  lead  sulphate 
(PbS04) ;  fortunately,  this  is  of  no  consequence,  since  PbS  and  PbS04 
react  with  each  other  at  a  high  temperature,  in  accordance  with  the 
equation,  PbS04  +  PbS  =  Pb2  +  2SO2. 

It  will  now  be  understood  that  the  essential  operations  in  this  metal- 
lurgical process  consist  in  roasting  the  ore  (PbS)  in  presence  of  air  until 
a  sufficient  proportion  of  it  has  been  oxidised,  and  in  then  raising  the 
temperature  in  order  that  the  mixture  of  PbS,  PbO,  and  PbS04,  pro- 
duced by  the  roasting,  may  react  in  the  sense  of  the  above  equations. 

The  ore,  having  been  separated  by  mechanical  treatment,  as  far  as  possible,  from 
the  foreign  matters  associated  with  it,  is  mixed  with  a  small  proportion  of  lime  to 
flux  the  siliceous  matter  of  the  ore,  and  spread  over  the  hearth  of  a  reverberatory 
furnace  (Fig.  228),  the  sides  of  which  are  considerably  inclined  towards  the  centre, 
so  as  to  form  a  hollow  for  the  reception  of  the  molten  lead. 

During  the  first  or  roasting  stage  of  the  smelting  process  the  temperature  is  kept 
below  that  at  which  galena  fuses.  The  ore  is  stirred  from  time  to  time,  to  expose 
fresh  surfaces  to  the  action  of  the  atmospheric  oxygen.  When  the  roasting  is 
sufficiently  advanced,  some  fuel  is  thrown  into  the  grate,  the  damper  is  slightly 
raised,  and  the  doors  of  the  furnace  are  closed,  so  that  the  charge  may  be  heated  to 
the  temperature  at  which  the  oxide  and  sulphate  of  lead  act  upon  the  unaltered 
sulphide,  furnishing  metallic  lead. 

During  this  part  of  the  operation  the  contents  of  the  hearth  are  constantly  raked 
up  towards  the  fire-bridge,  so  as  to  facilitate  the  separation  of  the  lead,  and  to 
cause  it  to  run  down  into  the  hollow  provided  for  its  reception.  It  is  also  found 
that  the  separation  of  the  lead  from  the  slags  is  much  assisted  by  occasionally 
throwing  open  the  doors  to  chill  the  furnace.  After  about  four  hours  the  charge 
is  reduced  to  a  pretty  fluid  condition,  the  lead  having  accumulated  at  the  bottom  of 
the  depressed  portion  of  the  hearth  with  the  slag  above  it  ;  this  slag  consists  chiefly 


SMELTING   LEAD   ORES. 


461 


of  the  silicates  of  lime  and  of  oxide  of  lead,  and  would  have  contained  a  larger  nrn 
portion  of  the  latter  if  the  lime  had  not  been  added  as  a  flux  at  the  commencement 
of  the  operation.  In  order  still  further  to  reduce  the  quantity  of  lead  in  the  SM 
a  few  more  shovelfuls  of  lime  are  now  thrown  into  the  hearth,  together  with 
little  small  coal,  the  latter  serving  to  reduce  to  the  metallic  state  the  oxide  of  lead 
displaced  by  the  lime  from  its  combination  with  the  silica.  But  since  silicate  of 
lime  is  far  less  fusible  than  silicate  of  lead,  the  effect  of  this  addition  of  lime  is  to 
dry  up  the  slags  to  a  semi-solid  mass,  and  it  will  now  be  seen  that  if  the  whole  of 
the  lime  had  been  added  at  the  commencement  of  the  smelting,  the  diminished 
fusibility  of  the  slag  would  have  opposed  an  obstacle  to  the  separation  of  the 
metallic  lead. 

During  the  last  hour  or  so  the  temperature  is  very  considerably  raised,  and  at  the 
expiration  of  about  six  hours,  when  the  greater  portion  of  the  lead  is  thought  to 
have  separated,  the  slag  is  raked  out  through  one  of  the  doors  of  the  furnace 
and  the  melted  metal  allowed  to  run  out  through  a  tap-hole  in  front  of  the 
lowest  portion  of  the  hearth  into  an  iron  basin,  from  which  it  is  ladled  into  pig- 
moulds.  The  rich  slags  are  worked  up  again  with  a  fresh  charge  of  ore. 


Fig-.  228. — Furnace  for  smelting-  lead  ores. 

In  the  smelting  of  galena  a  very  considerable  quantity  of  lead  is!  carried  off  in 
the  form  of  vapour  (lead-fume)  ;  and  in  order  to  condense  this,  the  gases  from  the 
furnace  are  made  to  pass  through  flues,  the  aggregate  length  of  which  is  sometimes 
three  or  four  miles,  before  being  allowed  to  escape  up  the  chimney.  When  these 
flues  are  swept,  many  tons  of  lead  are  recovered  in  the  forms  of  oxide  and 
sulphide. 

It  has  lately  been  asserted  that  the  reactions  stated  above  as  being  representa- 
tive of  the  changes  which  occur  in  the  Flintshire  lead-smelting  process,  have  no 
real  existence.  Instead,  it  is  maintained,  the  greater  part  of  the  S  is  removed 
directly  as  S02,  leaving  a  product  containing  about  3-5  per  cent,  of  S,  which  is 
then  liquated,  when  the  greater  part  of  the  lead  separates,  much  oxygen  being  at 
the  same  time  absorbed,  and  a  slag,  having  the  composition  PbS.PbO,  formed.  This 
must  be  thickened  with  lime  and  removed  from  the  lead  to  prevent  its  sulphur  from 
passing  into  the  metal.  It  is  also  stated  that  a  volatile  compound,  PbS.S02,  is 
formed  in  the  furnace,  and  is  the  cause  of  lead  fume. 

The  treatment  of  galena  in  Bessemer  converters,  whereby  the  same  reactions  that 
occur  in  the  Flintshire  furnace  could  easily  be  effected,  has  been  suggested. 

(2)  Poor  lead  ores,  rich  in  silica,  are  roasted  until  nearly  free  from 
sulphur,  mixed  with  coke  and  flux  (iron  ore  and  lime),  and  smelted  in 
small  blast-furnaces ;  the  lead  is  thus  reduced  from  its  oxide  by  the 
coke,  and  the  gangue  is  fluxed  as  ferrous  and  calcium  silicates. 

A  small  blast-furnace  for  this  process  is  shown  in  Fig.  229.  Air  is  supplied  to  the 
furnace  through  three  blast-pipes  (A),  and  the  ore  and  fuel  being  charged  in  at  B, 
the  lead  runs  into  a  cavity  (C)  at  the  bottom  of  the  furnace,  whilst  the  slag  flows 


462 


THE   IMPROVING  PROCESS. 


over  into  a  reservoir  (D)  outside  the  furnace.  The  charge  is  sprinkled  with  water 
through  the  rose  (E)  fixed  just  above  the  opening  into  the  chimney  (F),  to  prevent 
it  from  being  blown  away  by  the  current  of  air. 

(3)  In  the  third  process  for  smelting  lead  ores,  mostly  adopted  on 
the  Continent,  advantage  is  taken  of  the  fact  that  iron  will  desulphurise 
galena  at  a  high  temperature  ;  PbS  +  Fe  =  Pb  +  FeS.  The  galena  is 
mixed  with  scrap  iron  (or,  what  comes  to  the  same  thing,  iron  ore  and 
coke),  and  charged  into  a  small  blast-furnace. 

262.  Some  varieties  of  lead,  particularly  those  smelted  from  Spanish 
ores,  are  known  as  hard  lead,  their  hardness  being  chiefly  due  to  the 
presence  of  antimony  ;  and  since  this  hardness  interferes  materially 
with  some  of  the  uses  of  the  metal,  such  lead  is  generally  subjected  to 
an  improving  or  calcining  process,  in  which  the  impurities  are  oxidised 
and  removed,  together  with  a  portion  of  the  lead,  in  the  dross.* 


Fig-.  230. 


Fig.  229. 


To  effect  this,  6  or  8  tons  of  the  hard  lead  are  fused  in  an  iron  pot  (P,  Fig.  230). 
and  transferred  to  a  shallow  cast-iron  pan  (C)  measuring  about  10  feet  by  5.  In 
this  pan,  which  is  set  in  the  hearth  of  a  reverberatory  furnace,  and  is  about  8  inches 
deep  nearest  the  grate,  and  9  inches  at  the  other  end,  the  lead  is  kept  in  fusion  by 
the  flame  which  traverses  it  from  the  grate  G  to  the  flue  F,  for  a  period  varying 
with  the  degree  of  impurity,  some  specimens  being  found  sufficiently  soft  after  a 
single  day's  calcination,  whilst  others  must  be  kept  in  a  state  effusion  for  three  or 
four  weeks.  The  workman  judges  of  the  progress  of  the  operation  by  a  peculiar 
flaky  crystalline  appearance  assumed  by  a  small  sample  on  cooling.  When  suffi- 
ciently purified,  the  metal  is  run  off  and  cast  into  pigs. 

At  first  sight  it  is  not  intelligible  how  antimony  should  be  removed 
from  lead  by  calcination,  since  lead  is  the  more  easily  oxidised  metal. 

*  The  following  analyses  illustrate  the  percentage  composition  of  hard  lead  : 

Pb.  Sb.  Cu.  Fe. 


English 
Spanish 


99.27 
95.81 


o-57 
3-66 


O.I2 
0.32 


O.O4 
O.2I 


PATTINSON'S  DESILVERISING  PROCESS. 


463 


The  result  must  be  ascribed  to  the  tendency  of  antimony  to  form  an 
acid  oxide,  Sb2O5,  which  combines  with  the  base  oxide  of  lead.  The 
dross  (antimonate  of  lead)  formed  in  this  process,  when  reduced  to  the 
metallic  state,  yields  an  alloy  of  lead  with  30  or  40  per  cent,  of  antimony, 
which  is  much  used  for  casting  type  furniture  for  printers. 

263.  Extraction  of  silver  from  lead. — The  lead  extracted  from  galena 
often  contains  a  sufficient  quantity  of  silver  to  allow  of  its  being  pro- 
fitably extracted.  Previously  to  the  year  1829  this  was  practicable 
only  when  the  lead  contained  more  than  n  ounces  of  silver  per  ton,  for 
the  only  process  then  known  for  effecting  the  separation  of  the  two 
metals  was  that  of  cupellation,  which  necessitates  the  conversion  of  the 
whole  of  the  lead  into  oxide,  which  has  then  to  be  separated  from  the 


Fig-.  231. — Pattinson's  desilverisiiig;  process. 

silver,  and  again  reduced  to  the  metallic  state,  thus  consuming  so  large 
an  amount  of  labour  that  a  considerable  yield  of  silver  must  be  obtained 
to  pay  for  it.  By  the  simple  and  ingenious  operation  known  as  Pattin- 
son's desilvering  process,  a  very  large  amount  of  the  lead  can  be  at  once 
separated  in  the  metallic  state  with  little  expenditure  of  labour,  thus 
leaving  the  remainder  sufficiently  rich  in  the  more  precious  metal  to 
defray  the  cost  of  the  far  more  expensive  process  of  cupellation,  so  that 
2  or  3  ounces  of  silver  per  ton  can  be  extracted  with  profit.  Pattmson 
founded  his  process  upon  the  observation  that  when  lead  containing  a 
small  proportion  of  silver  is  melted  and  allowed  to  cool,  being  constantly 
stirred,  a  considerable  quantity  of  the  lead  separates  in  the  form  of 
crystals  containing  a  very  minute  proportion  of  silver,  almost  the  whole 
of  this  metal  being  left  behind  in  the  portion  still  remaining  liquid. 


464  CUPELLATION. 

Eight  or  ten  cast-iron  pots,  set  in  brick -work,  each  capable  of  holding  about 
6  tons  of  lead,  are  placed  in  a  row,  with  a  fire-place  underneath  each  of  them 
(Fig.  231).  Suppose  that  there  are  ten  pots  numbered  consecutively,  that  on  the 
extreme  left  of  the  workman  being  No.  I,  and  that  on  his  extreme  right  No.  icx 
About  6  tons  of  the  lead  containing  silver  are  melted  in  pot  No.  5,  the  metal 
skimmed,  and  the  fire  raked  out  from  beneath  so  that  the  pot  may  gradually  cool,, 
its  liquid  contents  being  constantly  agitated  with  a  long  iron  stirrer.  As  the 
crystals  of  lead  form,  they  are  well  drained  in  a  perforated  ladle  (about  10  inches 
wide  and  5  inches  deep)  and  transferred  to  pot  No.  4.  When  about  iths  of  the 
metals  have  thus  been  removed  in  the  crystals,  the  portion  still  remaining  liquid, 
which  retains  the  silver,  is  ladled  into  pot  No.  6,  and  the  pot  No.  5,  which  is  now 
empty,  is  charged  with  fresh  argentiferous  lead  to  be  treated  in  the  same  manner. 

When  pots  Nos.  4  and  6  have  received,  respectively,  a  sufficient  quantity  of  the 
crystals  of  lead  and  of  the  liquid  part  rich  in  silver,  their  contents  are  subjected  to 
a  perfectly  similar  process,  the  crystals  of  lead  being  always  passed  to  the  left,  and 
the  rich  argentiferous  alloy  to  the  right.  As  the  final  result  of  these  operations, 
the  pot  No.  10,  to  the  extreme  right,  becomes  filled  with  a  rich  alloy  of  lead  and 
silver,  sometimes  containing  300  ounces  of  silver  to  the  ton,  whilst  pot  No.  I,  to 
the  extreme  left,  contains  lead  in  which  there  is  not  more  than  half  an  ounce  of 
silver  to  the  ton.  This  lead  is  cast  into  pigs  for  the  market.  The  ladle  used  in 
the  above  operation  is  kept  hot  by  a  small  temper  pot  containing  melted  lead.  A 
fulcrum  is  provided  at  the  edge  of  each  pot,  for  resting  the  ladle  during  the 
shaking  of  the  crystals  to  drain  off  the  liquid  metal.  Any  copper  present  in  the 
lead  is  also  left  with  the  silver  in  the  liquid  portion.* 

In  Parkes'  process  for  desilvering  lead,  advantage  is  taken  of  the 
fact  that  fused  lead  only  dissolves  a  small  proportion  of  zinc,  and  that 
zinc  alloys  more  readily  with  silver  than  does  lead,  so  that  when  zinc 
(about  2  per  cent.)  is  stirred  into  molten  argentiferous  lead,  the  bulk 
of  it  speedily  rises  to  the  surface  again,  bringing  with  it  the  silver  and 
some  lead.  Thus,  a  dross  consisting  of  these  three  metals  and  the 
oxides  of  zinc  and  lead  t  is  obtained.  This  is  distilled  with  carbon  to 
recover  the  zinc,  and  the  alloy  of  lead  and  silver  left  in  the  retort  is 
cupelled.  The  desilverised  lead  is  freed  from  zinc  by  the  improving 
process  (p.  462). 

264.  In  order  to  extract  the  silver  from  the  rich  alloy,  it  is  subjected 
to  a  process  of  refining,  or  cupellation,  which  is  founded  upon  the 
oxidation  suffered  by  lead  when  heated  in  air,  and  upon  the  absence  of 
any  tendency  on  the  part  of  silver  to  combine  directly  with  oxygen,  so 
that  by  melting  the  lead  and  exposing  it  to  a  blast  of  air  it  may  be 
oxidised,  and  the  oxide  carried  away  by  the  blast,  leaving,  eventually, 
pure  silver  on  the  cupel. 

The  refinery  or  cupelling  furnace  (Fig.  232)  in  which  this  operation  is  performed 
is  a  reverberatory  furnace,  the  hearth  of  which  consists  of  a  cupel  (C),  made  by 
ramming  moist  powdered  bone-ash  mixed  with  a  little  wood-ash  into  an  oval  iron 
frame  about  4  inches  deep,  and  provided  with  four  cross-bars  at  the  bottom,  each 
about  4  inches  wide.  When  this  frame  has  been  well  filled  with  bone-ash,  part  of 
the  latter  is  scooped  out,  so  as  to  leave  the  sides  about  2  inches  thick  at  the  top 
and  3  inches  at  the  bottom,  the  bone-ash  being  left  about  i  inch  thick  above  the 
iron  cross-bars. 

The  cupel,  which  is  about  4  feet  long  by  z\  feet  wide,  is  fixed  so  that  the  flame 
from  the  grate  (Gr)  passes  across  it  into  the  chimney  (B),  and  at  one  end,  the 
nozzle  (N)  of  a  blowing  apparatus  directs  a  blast  of  air  over  the  surface  of  the 
contents  of  the  cupel.  The  latter  is  carefully  dried  by  a  gradually  increasing 
heat,  and  is  then  heated  to  redness  ;  the  alloy  of  lead  and  silver,  having  been  pre- 
viously melted  in  an  iron  pot  (P)  fixed  by  the  side  of  the  furnace,  is  ladled  in 

*  The  employment  of  a  jet  of  steam  for  stirring  the  bath  of  lead  has  much  reduced  the 
time  and  labour  required  in  the  above  process.  This  also  removes  the  copper  as  oxide,  and 
the  antimony  is  carried  off  in  the  steam. 

f  The  addition  of  a  little  Al  diminishes  the  amount  of  oxide  in  the  dross. 


CUPELLATION. 


through  a  gutter  until  the  cupel  is  nearly  filled  with  it  ;  a  film  of  oxide  soon 
makes  its  appearance  upon  the  surface  of  the  lead,  and  is  fused  by  the  high  tem- 
perature. When  the  blast  is  directed  upon  the  surface,  it  blows  off  this  film  of 
oxide,  and  supplies  the  oxygen  for  the  formation  of  another  film  upon  the  clean 
metallic  surface  thus  exposed.  A  part  of  the  oxide  of  lead  or  litharge  thus 
formed  is  at  first  absorbed  by  the  porous  material  of  the  cupel,  but  the  chief  part 
of  it  is  forced  by  the  blast  through  a  channel  cut  for  the  purpose  in  the  opposite 
end  to  that  at  which  the  blast  enters,  and  is  received,  as  it  issues  from  A,  in  an 
iron  vessel  placed  beneath  the  surface.  In  proportion  as  the  lead  is  in  this 
manner  removed  from  the  cupel,  fresh  portions  are  supplied  from  the  adjoining 
melting-pot,  and  the  process  is  continued  until  about  5  tons  of  the  alloy  have 
been  added. 

The  cupellation  is  not  continued  until  the  whole  of  the  lead  has  been  removed, 
but  until  only  2  or  3  cwts.  of  that  metal  are  left  in  combination  with  the  whole  of 
the  silver  (say  1000  ounces)  contained 
in  the  5  tons  of  alloy.  The  metal 
is  run  through  a  hole  made  in  the 
bottom  of  the  cupel,  which  is  then 
again  stopped  up,  so  that  a  fresh 
charge  may  be  introduced.  The 
fumes  of  oxide  of  lead  which  are 
freely  evolved  during  this  process  are 
carried  off  by  a  hood  and  chimney 
(H)  situated  opposite  to  the  blast  of 
air. 

When  three  or  four  charges  have 
been  cupelled,  so  as  to  yield  from 
3000  to  5000  ounces  of  silver  alloyed 
with  6  or  8  cwts.  of  lead,  the  removal 
of  the  latter  metal  is  completed  in 
another  cupel,  since  some  of  the 
silver  is  carried  off  with  the  last 
portions  of  litharge.  The  appear- 
ances indicating  the  removal  of  the 
last  portion  of  lead  are  very  striking  ; 
the  surface  of  the  molten  metal, 
which  has  been  hitherto  tarnished, 
becomes  iridescent  as  the  film  of 
oxide  of  lead  thins  off,  and  after- 
wards resplendently  bright,  and  when 
the  cake  of  refined  silver  is  allowed 
to  cool,  it  throws  up  from  its  surface 
a  variety  of  fantastic  arborescent 
excrescences,  caused  by  the  escape  of 
oxygen  which  has  been  mechanically 
absorbed  by  the  fused  silver,  and  is  given  off  during  solidification. 

The  litharge  obtained  from  the  cupelling  furnaces  is  reduced  to  the  metallic 
state  by  mixing  it  with  small  coal,  and  heating  it  in  a  furnace  similar  to  that  em- 
ployed in  smelting  galena. 

265.  On  the  small  scale,  lead  may  easily  be  extracted  from  galena  by  mixing  300 
grains  with  450  grains  of  dried  sodium  carbonate  and  20  grains  of  charcoal,  intro- 
ducing the  mixture  into  a  crucible,  and  placing  in  it  two  tenpenny  nails,  heads 
downwards.  The  crucible  is  covered  and  heated  in  a  moderate  fire  for  about 
half  an  hour.  The  remainder  of  the  nails  is  carefully  removed  from  the  liquid 
mass,  which  is  then  allowed  to  cool,  the  crucible  broken,  and  the  lead  extracted 
and  weighed.  In  this  process  the  sulphur  of  the  galena  is  removed,  partly  by  the 
sodium  of  the  carbonate  and  partly  by  the  iron  of  the  nails,  the  excess  of  sodium 
carbonate  serving  to  flux  any  silica  with  which  the  galena  may  be  mixed. 

Or  300  grains  of  galena  may  be  mixed  with  600  grains  of  sodium  carbonate  and 
200  grains  of  nitre  (which  oxidises  the  sulphur),  and  fused  for  half  an  hour. 

To  ascertain  if  it  contains  silver,  the  button  of  lead  is  placed  on  a  small  bone 
ash  cupel  (Fig.  233),  and  heated  in  a  muffle  (Fig.  235),  until  the  whole  of  the  lea 
is  oxidised  and  absorbed  into  the  bone-ash  of  the  cupel,  leaving  the  minute  glo 
of  silver. 

2  G 


Fig-.  232. — Cupellation  furnace. 


466 


APPLICATIONS   OF   LEAD. 


A  gas  muffle  furnace,  also  capable  of  being  used  as  a  crucible  furnace,  is 
.shown  in  Fig.  234. 

Small  globules  of  lead  may  be  conveniently  cupelled  on  charcoal  before  the 
blowpipe,  by  pressing  some  bone-ash  into  a  cavity  scooped  in  the  charcoal, 
placing  the  lead  upon  its  surface,  and  exposing  it  to  a  good  oxidising  flame 
(p.  156)  as  long  as  it  decreases  in  size.  If  any  copper  be  present,  the  bone-ash 
will  show  a  green  stain  after  cooling.  Pure  lead  gives  a  yellow  stain. 


Fig.  234. — Muffle  and  crucible  furnace. 


Fig.  235. — Muffle  furnace. 


266.  Uses  of  lead. — The  employment  of  this  metal  for  roofing,  &c., 
has  been  already  noticed.  Its  fusibility  adapts  it  for  casting  type  for 
printing,  but  it  would  be  far  too  soft  for  this  purpose ;  accordingly, 
type-metal  consists  of  an  alloy  of  4  parts  of  lead  with  i  of  antimony.  A 
similar  alloy  is  used  for  the  bullets  contained  in  shrapnel  shells,  since 
bullets  of  soft  lead  would  be  liable  to  be  jambed  together,  and  would  not 
scatter  so  well  on  the  explosion  of  the  shell.  On  the  other  hand,  rifle 
bullets  are  made  of  very  pure  soft  lead,  in  order  that  they  may  more 
easily  take  the  grooves  of  the  rifle. 

Small  shot  are  made  of  lead  to  which  about  40  Ibs.  of  arsenic  per  ton 
has  been  added.  The  arsenic  dissolves  in  the  lead,  hardening  it  and 
causing  it  to  form  spherical  drops  when  chilled.  The  fluid  metal  is 
poured  through  a  sort  of  colander  fixed  at  the  top  of  a  lofty  tower  (or 
at  the  mouth  of  a  deserted  coal  shaft),  and  the  minute  drops  into  which 
the  lead  is  thus  divided  are  allowed  to  fall  into  a  vessel  of  water,  after 
having  been  chilled  by  the  air  in  their  descent.  They  are  afterwards 
sorted,  and  polished  in  revolving  barrels  containing  plumbago.  If  too 
little  arsenic  is  employed,  the  shot  are  elongated  or  pyriform  ;  and  if 
the  due  proportion  has  been  exceeded,  their  form  is  flattened  or 
lenticular. 

Composition  tube  ("  compo-pipe  ")  used  by  plumbers  is  made  of  lead 
hardened  by  a  little  antimony.  /Solder  has  been  already  noticed  (p.  452). 

Leaden  vessels  are  much  used  in  manufacturing  chemistry,  on  account 


CORROSION   OF  LEAD.  467 

of  the  resistance  of  this  metal  to  the  action  of  acids.  Neither  concen- 
trated sulphuric,*  hydrochloric,  nitric,  or  hydrofluoric  acid  will  attack 
lead  at  the  ordinary  temperature.  The  best  solvent  for  the  metal  is 
nitric  acid  of  sp.  gr.  1.2,  since  the  nitrate  of  lead,  being  insoluble  in  an 
acid  of  greater  strength,  would  be  deposited  upon  the  metal,  which  it 
would  protect  from  further  action. 

Lead  is  easily  corroded  in  situations  where  it  is  brought  in  contact 
with  air  highly  charged  with  carbonic  acid  gas,  when  it  absorbs  oxygen, 
forming  oxide  of  lead,  which  combines  with  C02  and  water  to  produce 
the  basic  carbonate  of  lead,  PbC03.Pb(OH)2.  The  lead  of  old  coffins  is 
often  found  converted  into  a  white  earthy-looking  brittle  mass  of  basic 
carbonate,  with  a  very  thin  film  of  metallic  lead  inside  it.  The  basic 
carbonate  is  formed  as  a  crystalline  silky-looking  precipitate  when  a 
piece  of  clean  lead  is  left  in  distilled  water  for  a  few  minutes. 

When  lead  is  exposed  to  the  joint  action  of  air  and  of  the  acetic  acid 
contained  in  beer,  wine,  cider,  &c.,  it  becomes  converted  into  acetate  of 
lead  or  sugar  of  lead,  which  is  very  poisonous.  Hence  the  accidents 
arising  from  the  reprehensible  practice  of  sweetening  cider  by  keeping 
it  in  contact  with  lead,  and  from  the  accidental  presence,  in  beer  and 
wine  bottles,  of  shot  which  have  been  employed  in  cleansing  them.  The 
action  of  water  upon  leaden  cisterns  has  been  already  noticed.  Contact 
with  air  and  sea- water  soon  converts  lead  into  oxide  and  chloride. 

267.  Oxides  of  lead. — Five  compounds  of  lead  with  oxygen  are 
known— Pb20,  PbO,  Pb2O3,  Pb304,  Pb02. 

Lead  suboxide,  or  plumbous  oxide,  Pb20,  is  obtained  by  heating  lead 
oxalate;  2PbC204  =  Pb2O  +  CO  +  3C02.  "it  is  a  black  powder  which  is 
decomposed  by  acids,  yielding  plumbic  salts  and  metallic  lead. 

The  bright  surface  of  lead  soon  tarnishes  when  exposed  to  the  air, 
becoming  coated  with  a  dark  film,  which  is  believed  to  consist  of  sub- 
oxide  of  lead.  In  a  very  finely  divided  state,  lead  takes  fire  when  thrown 
into  the  air,  and  is  converted  into  oxide  of  lead. 

The  lead  pyrophorus,  for  exhibiting  the  spontaneous  combustion  of  lead,  is  pre- 
pared by  placing  some  lead  tartrate  in  a  glass  tube 
•closed  at  one  end  (Fig.  236),  drawing  the  tube  out  to  a 
narrow  neck  near  the  open  end,  and  holding  it  nearly 
horizontally,  whilst  the  lead  tartrate  is  heated  with  a  gas 
•or  spirit  flame  as  long  as  any  fumes  are  evolved ;  the 
neck  is  then  fused  with  a  blowpipe  flame  and  drawn  off. 
Lead  tartrate  (PbC4H406),  when  heated,  leaves  a  mix- 
ture of  metallic  lead  with  charcoal,  which  prevents  the 
lead  from  fusing  into  a  compact  mass.  This  mixture 
may  be  preserved  unchanged  in  the  tube  for  any  length 
of  time  ;  but  when  the  neck  is  broken  off  and  the  con- 
tents scattered  into  the  air,  they  inflame  at  once,  pro- 
ducing thick  fumes  of  oxide  of  lead.  Lead  tartrate  is  Fig.  236. 
prepared  by  adding  solution  of  lead  acetate  to  a  solution 

of  tartaric  acid  constantly  stirred,  as  long  as  a  precipitate  is  formed.     The  precipi- 
tated lead  tartrate  is  collected  upon  a  filter,  washed  several  times,  and  dnec 
gentle  heat. 

Lead  monoxide,  or  protoxide  of  lead,  PbO,  is  sometimes  found  in 
nature,  crystallised  in  rhombic  octahedra,  and  is  prepared  on  a  large 
scale  by  heating  lead  in  air.  When  the  metal  is  only  moderately  heated, 
the  oxide  forms  a  yellow  powder  (sp.  gr.  9.2),  which  is  known  in 

*  It  has  been  found  that  pure  lead  is  slowly  acted  on  by  sulphuric  acid,  hydrogen  being: 
-evolved.  The  presence  of  a  little  antimony  almost  entirely  prevents  the  action. 


468  RED   LEAD. 

commerce  as  massicot,  but  at  a  higher  temperature  the  oxide  melts,  and 
on  cooling  forms  a  brownish  scaly  mass,  which  is  called  litharge  (\i6os, 
stone ;  apyvpos,  silver).  The  litharge  of  commerce  often  has  a  red 
colour,  caused  by  the  presence  of  some  red  oxide  of  lead  ;  from  i  to  3, 
per  cent,  of  finely  divided  metallic  lead  may  also  sometimes  be  found 
in  it.  When  heated  to  dull  redness,  litharge  assumes  a  dark  brown 
colour,  and  becomes  yellow  on  cooling.  At  a  bright  red  heat  it  fuses,. 
and  readily  attacks  clay  crucibles,  forming  a  fusible  silicate  of  lead,  and 
soon  perforating  the  sides.  When  boiled  with  distilled  water,  PbO  is 
dissolved  in  small  quantity,  yielding  a  solution  which  is  decidedly 
alkaline,  and  becomes  turbid  when  exposed  to  the  air,  absorbing 
carbonic  acid  gas,  and  depositing  lead  carbonate.  The  presence  of  a  small 
quantity  of  saline  matter  in  the  water  hinders  the  dissolution  of  the 
oxide ;  but  organic  matter,  and  especially  sugar,  favours  it.  Oxide  of 
lead  is  a  powerful  base,  and  has  a  strong  tendency  to  form  basic  salts. 
Hot  solutions  of  potash  and  soda  dissolve  it  readily,  and  deposit  it  in 
pink  crystals  on  cooling;  according  to  some,  such  solutions  contain 
sodium  or  potassium  plumbite,  K2Pb02. 

Litharge,  from  its  easy  combination  with  silica  at  a  high  temperature, 
is  much  used  in  the  manufacture  of  glass,  and  in  glazing  earthenware. 
The  assayer  also  employs  it  as  a  flux.  A  mixture  of  litharge  with  lime 
is  sometimes  applied  to  the  hair,-  which  it  dyes  of  a  purplish-black 
colour,  due  to  the  formation  of  lead  sulphide  from  the  sulphur  existing 
in  hair.  Dhil  mastic,  used  by  builders  in  repairing  stone,  is  a  mixture 
of  i  part  of  massicot  with  10  parts  of  brick-dust,  and  enough  linseed  oil 
to  form  a  paste ;  it  sets  into  a  very  hard  mass,  which  is  probably  due 
partly  to  the  formation  of  lead  silicate,  and  partly  to  the  drying  of  the 
linseed  oil  by  oxidation  favoured  by  the  oxide  of  lead. 

Lead  sesquioxide,  Pb203,  is  obtained  as  a  yellow  precipitate  by  dis- 
solving PbO  in  caustic  soda  and  adding  sodium  hypochlorite.  Cold 
HC1  dissolves  it  to  a  yellow  liquid,  which  slowly  evolves  chlorine. 
Nitric  acid  partly  dissolves  it,  leaving  a  brown  residue  of  Pb02.  Heat 
converts  it  into  PbO. 

Eed  lead,  or  minium,  Pb304,  is  prepared  by  heating  massicot  in  air  to 
about  300°  0,  when  it  absorbs  oxygen,  and  becomes  converted  into  red 
lead.  The  massicot  for  this  purpose  is  prepared  by  heating  lead  in  a 
reverberatory  furnace  to  a  temperature  insufficient  to  fuse  the  oxide 
which  is  formed,  and  rejecting  the  first  portions  which  contain  iron,, 
cobalt  and  other  metals  more  easily  oxidisable  than  lead,  as  well  as  the 
last,  which  contain  copper  and  silver,  less  easily  oxidised  than  lead. 
The  intermediate  product  is  ground  to  a  fine  powder  and  suspended  in 
water ;  the  coarser  particles  are  thus  separated  from  the  finer,  which 
are  dried,  and  heated  on  iron  trays  placed  in  a  reverberatory  furnace, 
till  the  requisite  colour  has  been  obtained.  Minium  is  largely  used  in 
the  manufacture  of  glass,  whence  it  is  necessary  that  it  should  be  free 
from  the  oxides  of  iron,  copper,  cobalt,  &c.,  which  would  colour  the 
glass.  It  is  also  employed  as  a  common  red  mineral  colour,  and  in  the 
manufacture  of  lucifer  matches.  Red  lead  becomes  dark  brown  when 
heated,  and  regains  its  original  colour  when  cooled. 

When  minium  is  treated  with  dilute  nitric  acid,  lead  nitrate,  Pb(N03)2, 
is  obtained  in  solution,  and  peroxide  of  lead  (Pb02)  is  left  as  a  brown 
powder,  showing  that  minium  is  probably  a  compound  of  the  oxide  and 


LEAD  PEROXIDE.  469 

peroxide  of  lead.  The  minium  obtained  by  heating  massicot  in  air  till  no 
further  increase  of  weight  is  obtained,  has  the  composition  2PbO.PbCX 
or  Pb304,  which  would  appear  to  represent  pure  minium ;  commercial 
minium,  however,  has  more  frequently  a  composition  corresponding  with 
3PbO.Pb02,  but  when  this  is  treated  with  potash,  PbO  is  dissolved  out, 
and  2PbO.Pb02  remains.  Minium  evolves  oxygen  at  a  red  heat, 
becoming  PbO;  hence  the  necessity  for  keeping  the  temperature 
about  300°  C.  during  its  preparation.  Hydrochloric  acid,  heated  with 
minium,  evolves  chlorine  by  reaction  with  the  Pb02  contained  in  it,  and 
leaves  the  white  sparingly  soluble  PbCl2  formed  from  the  PbO  contained 
in  the  Pb304.  A  mixture  of  dilute  nitric  acid  and  sugar,  or  some  other 
oxidisable  body,  will  dissolve  minium  entirely  as  Pb(N03)2.  Glacial 
acetic  acid  dissolves  minium,  without  evolution  of  gas,  to  a  colourless 
liquid,  which  deposits  Pb02  when  exposed  to  air,  or  evaporated,  or 
diluted ;  a  hot  saturated  solution  deposits  colourless  crystals  of  lead 
tetr  acetate  Pb(C2H302)4  on  cooling. 

Peroxide,  or  dioxide,  or  puce  oxide  of  lead,  Pb02,  is  found  in  the  mineral 
kingdom  as  heavy  lead  ore,  forming  black,  lustrous,  six-sided  prisms.  It 
may  be  prepared  from  red  lead  by  boiling  it,  in  fine  powder,  with  nitric 
acid,  diluted  with  five  measures  of  water,  washing  and  drying.  The 
dioxide  of  lead  easily  imparts  oxygen  to  other  substances ;  sulphur, 
mixed  with  six  times  its  weight  of  Pb02,  may  be  ignited  by  friction ; 
hence  this  oxide  is  a  common  ingredient  in  lucifer-match  compositions. 
Its  oxidising  property  is  frequently  turned  to  account  in  the  laboratory ; 
for  example,  in  absor bing  sulphur  dioxide  from  gaseous  mixtures  by  con- 
verting it  into  sulphate  of  lead ;  PbO2  +  S02  =  PbS04.  Dioxide  of  lead 
is  not  dissolved  by  dilute  acids,  and  has  no  basic  properties,  although 
certain  salts  of  the  type  PbX4  are  known ;  it  is  even  sometimes  called 
plumbic  anhydride,  for  it  acts  upon  potassium  hydroxide,  yielding 
potassium  plumbate  (K2Pb03.3H20.),  which  has  been  crystallised  from 
an  alkaline  solution,  but  is  decomposed  by  pure  water.*  Lead  dioxide 
evolves  01  from  HC1  when  heated,  and  gives,  at  first,  a  brown  solution 
(containing  Pb014)  which  yields  a  brown  precipitate  with  ammonia,  but 
if  the  solution  be  boiled  till  all  the  01  is  expelled,  it  becomes  colourless 
Pb012,  and  gives  a  white  precipitate  with  ammonia.  PbO  is  converted 
into  Pb02  by  ozone  and  by  hydrogen  peroxide. 

Lead  peroxide  is  almost  the  only  available  material  for  making  the  "  active 
mass"  for  electric  accumulators  or  storage  or  secondary  cells.  When  two  lead 
plates,  one  coated  with  Pb02,  are  immersed  in  dilute  H2S04  an  electrical  pressure 
of  about  2  volts  is  created,  and  if  the  current  be  used,  both  plates  become  coated 
with  PbS04  before  the  energy  ceases  to  flow.  The  ultimate  change  may  be  ex- 
pressed thus  :  — Pb  +  Pb0.2  +  2H2S04  =  2PbS04  +  2H20.  If,  when  this  stage  has  been 
reached,  current  be  passed  into  the  cell  in  the  direction  opposite  to  that  of  the 
current  which  has  been  used,  the  PbS04  on  the  one  plate  will  be  oxidised  to  H2S04 
and  Pb02,  while  that  on  the  other  will  be  reduced  to  Pb  and  H2S04.  Hence  the 
cell  will  again  be  ready  to  deliver  current,  which,  however,  will  be  smaller  m 
amount  than  that  used  to  charge  the  cell  by  the  inevitable  loss  due  to  resistance,  etc. 
It  will  be  seen  that  during  discharge  the  free  H2S04  disappears  from  the  cell, 
while  during  charging  it  is  liberated  again  ;  thus  by  watching  the  indications  of  a 

*  Advantage  is  taken  of  the  tendency  for  PbO  to  absorb  O  when  heated  with  an  alkali  in 
Kassner's  oxygen  process.     A  mixture  of  CaO  and  FbO  is  heated  in  air,  CaPbO3  being  pro- 
duced.    This  is  heated  (below  100°  C.)  in  CO2,  when  it  becomes  CaCO3  and  PbO2 ;  th 
is  then  made  to  part  with  half  its  oxygen  by  a  red  heat,  after  which  the  CaCO3  is  canst 
by  being  heated  in  a  current  of  steam.     The  mixture  of  CaO  and  PbO  thus  regenerated 
put  through  the  same  cycle  of  operations. 


470  WHITE   LEAD. 

hydrometer  immersed  in  the   liquid,   the   progress   of  either  operation  may  be 
judged. 

Lead  hydroxide,  Pb(OH)2,  has  not  been  obtained,  but  Pb(OH)2.PbO  is  formed  as 
a  white  precipitate  when  air  and  water,  free  from  C02,  attack  lead,  hydrogen 
peroxide  being  formed  at  the  same  time  nearly  in  the  proportion  represented  by  the 
equation— Pb  +  2H20  +  02  =  Pb(OH)2  +  H202  (of.  footnote,  p.  63).  The  same 
hydroxide  is  precipitated  by  alkalies  from  solutions  of  lead  salts.  It  becomes  PbO 
when  heated  to  145°  C.  The  compound  Pb(OH)2.2PbO  crystallises  in  octahedra 
from  a  solution  of  basic  lead  acetate  mixed  with  ammonia. 

Lead  nitrate,  Pb(ISr03)2,  crystallises  in  white  octahedra  from  a  solu- 
tion of  lead  or  its  oxide  in  dilute  nitric  acid.  It  dissolves  easily  in  water, 
but  not  in  nitric  acid  or  in  alcohol.  It  is  employed  in  dyeing  and 
calico-printing.  Several  sparingly  soluble  basic  lead  nitrates  are  known. 
When  digested  with  water  and  metallic  lead,  the  nitrate  gives  a 
yellow  solution,  which  deposits  vellow  scaly  crystals  of  the  compound 
Pb.OH.N03.Pb.OH.N02. 

268.  Lead  carbonate,  PbC03,  is  found  in  nature,  as  cerussite,  in 
transparent  rhombic  crystals  isomorphous  with  aragonite.  It  may  be 
precipitated  by  mixing  solutions  of  ammonium  carbonate  and  lead 
acetate,  or  by  passing  C02,  into  a  weak  solution  of  lead  acetate.  Potas- 
sium and  sodium  carbonates  precipitate  basic  lead  carbonates. 

White  lead,  or  ceruse,  is  a  basic  carbonate,  or  combination  of  lead  car- 
bonate, PbC03,  with  variable  proportions  of  lead  hydroxide,  Pb(OH)2. 
This  substance  is  a  constant  product  of  the  corrosive  action  of  air  and 
water  upon  the  metal.  Its  formation  is,  of  course,  very  much  encouraged 
by  the  presence  of  organic  matters  in  a  state  of  decay,  which  evolve  OO2. 

White  lead  is  manufactured  on  the  large  scale  by  several  processes, 
which  depend,  however,  upon  the  same  principle,  namely,  the  formation 
of  a  basic  lead  salt,  which  is  subsequently  decomposed  by  C02.  The 
chemistry  of  the  commonest  process  may  be  stated  as  follows  ;  lead 
oxide,  PbO,  with  acetic  acid,  HC2H302,  yields  lead  acetate  Pb(02H3O2)2, 
conveniently  written  PbA2.  This  combines  with  lead  hydroxide,  form- 
ing basic  lead  acetate,  PbA2.2Pb(OH)2.  This  is  decomposed  by  carbonic 
acid  gas,  yielding  basic  lead  carbonate  and  normal  lead  acetate ; 
3[PbA2.2Pb(OH)2]  +  C02  =  2[2Pb003.Pb(OH)2]  +  sPbA2  +  4H20.  The 
normal  acetate,  in  contact  with  lead,  atmospheric  oxygen,  and  water 
is  converted  into  the  basic  acetate;  PbA2  +  Pb2  +  O2  +  2H20  = 
PbA2.2Pb(OH)2;  this  is  again  acted  on  by  C02,  and  the  process  is  con- 
tinuous. To  effect  these  changes,  lead  is  exposed  to  the  simultaneous 
action  of  air,  water  vapour,  carbon  dioxide,  and  acetic  acid  vapour. 

In  the  oldest  process  (still  used  to  make  the  best  pigment),  commonly  known  as 
the  Dutch  process,  metallic  lead,  in  the  form  of  square  gratings  cast  from  the 
purest  lead,  is  placed  over  earthen  pots  containing  a  small  quantity  of  common 
vinegar  ;  a  number  of  these  pots  being  built  up  into  heaps,  together  with  alternate 
layers  of  dung  or  spent  tan,  the  heaps  are  entirely  covered  up  with  the  same 
material.  The  metal  is  thus  exposed  to  conditions  most  favourable  to  its  oxida- 
tion, viz.,  a  very  warm  and  moist  atmosphere  produced  by  the  fermentation  of  the 
organic  matters  composing  the  heap,  and  the  presence  of  a  large  quantity  of  acid 
vapour  generated  from  the  acetic  acid  of  the  vinegar.  The  lead  is  therefore  soon 
converted  into  oxide,  a  portion  of  which  unites  with  the  acetic  acid  to  form  the 
tribasic  acetate  of  lead,  which  is  then  decomposed  by  the  carbonic  acid  gas, 
evolved  from  the  fermenting  dung  or  tan,  yielding  carbonate  of  lead,  which 
combines  with  another  portion  of  the  oxide  of  lead  and  water  to  form  the  white 
lead.  The  neutral  acetate  of  lead  left  after  the  removal  of  the  oxide  of  lead  from 
the  tribasic  acetate,  is  now  ready  to  take  up  an  additional  quantity  of  the  oxide, 


LEAD   POISONING. 

and  the  process  is  thus  continued  until,  in  the  course  of  a  few  weeks,  the  lead 
has  become  coated  with  a  very  thick  crust  of  white  lead  ;  the  heaps  are  then 
destroyed,  the  crust  detached,  washed  to  remove  adhering  acetate  of  lead,  ground 
to  a  paste  with  water,  and  dried.  Eolled  lead  is  not  so  easily  converted  as  cast 
lead. 

Other  processes  for  making  white  lead  exist,  but  for  a  description  of  them  larger 
works  on  technical  Chemistry  must  be  consulted. 

The  usual  composition  of  white  lead  is  expressed  by  the  formula 
Pb(OH)2.2PbC03,  though  other  basic  carbonates  of  lead  are  often  mixed 
with  it. 

White  lead  being  very  poisonous,  its  use  by  painters  and  others  is 
generally  attended  with  symptoms  of  lead  poisoning,  arising  in  many 
cases,  probably,  from  neglecting  to  wash  the  hands  before  eating,  the 
effect  of  lead  being  cumulative,  so  that  minute  doses  may  show  their 
combined  action  after  many  days.  Diluted  sulphuric  acid  and  solutions 
of  the  sulphates  of  magnesia  and  the  alkalies  are  sometimes  taken 
internally  to  counteract  its  effect ;  they  are  of  doubtful  efficacy. 

All  paints  containing  lead,  and  cards  glazed  with  white  lead,  are 
blackened  even  by  minute  quantities  of  sulphuretted  hydrogen,  from 
the  production  of  black  sulphide  of  lead.  If  the  blackened  surface 
remain  exposed  to  the  light  and  air.  it  is  bleached  again,  the  sulphide 
of  lead  (PbS)  being  oxidised  and  converted  into  white  sulphate  of 
lead  (PbSO4),  but  this  does  not  happen  in  the  dark.  A  little  sulphide 
of  lead  or  powdered  charcoal  is  sometimes  mixed  with  commercial  white 
lead  to  give  it  a  bluish  tint.  It  is  probable  that  white  lead  owes  a 
part  of  its  value  in  oil-painting  to  the  formation  of  a  lead-salt  with  the 
fatty  acid.  Its  "covering"  power  is  due  to  its  amorphous  character, 
which  renders  it  completely  opaque.  Pure  white  lead  is  easily  soluble 
in  acetic  and  dilute  nitric  acids. 

Lead  sulphate,  PbSO4,  is  found  naturally  as  anglesite  or  lead  vitriol, 
in  transparent  rhombic  prisms  (sp.  gr.  6.3)  isomorphous  with  celestine 
and  heavy  spar,  and  is  obtained  as  a  heavy  granular  precipitate  when 
sulphuric  acid  is  added  to  a  salt  of  lead.  Stirring  much  promotes  the 
precipitation.  Lead  sulphate  is  very  slightly  soluble  in  water,  and  even 
less  so  in  dilute  sulphuric  acid  and  in  alcohol.  It  is  soluble  in  strong 
sulphuric  and  hydrochloric  acids,  in  sodium  chloride  and  thiosulphate, 
and  in  ammonium  acetate  and  tartrate.  At  a  red  heat  it  fuses  without 
decomposition. 

An  acid  lead  sulphate,  PbH2(S04)2.Aq,  has  been  crystallised.  The  minerals 
lanarkite  "and  leadhillite  are  compounds  of  sulphate  and  carbonate  of  lead, 
PbS04(PbC03)2.H20.  The  chromates  of  lead  have  been  already  noticed. 

Lead  phosphate,  Pb3(P04)2,  and  arsenate,  associated  with  lead  chloride  and  ( 
bonate,  are  found  in  certain  minerals.  . 

269.  Lead  chloride  (PbCl2  =  2  vols.)  forms  the  mineral  termed  horn  lead.     It 
one  of  the  few  chlorides  which  are  not  readily  soluble  in  water,  and  is  Pfecip 
when  hydrochloric  acid  or  a  soluble  chloride  is  added  to  a  solution  of  lead.     tio\\\vg 
water  dissolves  about  -^thof  its  weight  of  lead  chloride,  and  deposits  it  in  beau 
shining  white  needles  on  cooling.     Cold  water  dissolves  abont  rfoth  of  its  weigni 
It  fuses  easily  (510°  C.)  and  solidifies  again  to  a  horny  mass,  like  fusee 
chloride.     It  is  converted  into  vapour  at  a  high  temperature.     Lead  chloride  ais- 
solves  easily  in  strong  HC1,  and  is  precipitated  by  water.     The  solution  oi  leaa 
chloride  in    water  is   precipitated  by  adding  strong   HC1  ;  hence,  a  di 
solution,  when  cold,  retains  very  little  lead  chloride.     Like  silver  c 
chloride  is  soluble  in  sodium  thiosulphate.  .  ,  .       . 

The  lead  oxychloride  (PbCl2.PbO)  is  formed  when  lead  chloride  is  he  i ti-d m  air, 
and  occurs  in  nature  as  matlocldte.  Pattimon's  oseychlonde,  PbCl.OH,  is 


47 2  LEAD  SULPHIDES. 

employed  as  a  substitute  for  white  lead  in  painting,  being  prepared  for  this  purpose 
by  decomposing  finely  powdered  galena  with  concentrated  hydrochloric  acid 
(PbS  +  2HCl:=PbCl2  +  H2S),  washing  the  resulting  lead  chloride  with  cold  water, 
dissolving  it  in  hot  water,  and  adding  lime-water,  which  precipitates  the  oxy- 
chloride  ;  2PbCl2  +  Ca(OH)2  =  2PbCl(OH)  +  CaCl2. 

Cassel  yellow  ( Paris  yellow,  patent  yellow,  mineral  yellow)  is  another  oxychloride 
of  lead  (PbCl2.7PbO),  prepared  by  heating  a  mixture  of  litharge  and  sal-ammoniac. 
It  has  a  fine  golden-yellow  colour,  is  easily  fused,  and  crystallises  in  octahedra  on 
cooling.  Turner's  yellow,  PbCl2.3PbO.  is  made  by  allowing  a  strong  solution  of 
NaCl  to  react  with  PbO.  The  mineral  mendipite  is  an  oxychloride  of  lead 
(PbCl2.2PbO)  which  occurs  in  colourless  prismatic  crystals. 

Lead  tetracliloride,  PbCl4,  probably  exists  in  the  brown  solution  of  Pb02  in  cold 
HC1,  which  gives  a  brown  precipitate  of  Pb02  when  diluted.  A  solution  made  by 
suspending  PbCl2  in  water  and  passing  chlorine  maybe  supposed  to  contain  chloro- 
plumbic  acid,  H2PbCl6,  for  with  salts  of  rubidium  and  ammonium  it  yields  yellow 
crystalline  precipitates  of  Rb2PbCl6  and  (NH4)2PbCl6  respectively.  When  the 
latter  is  added  to  strong  H2S04  a  heavy  oil  (sp.  gr.  3. 18)  separates  ;  this  is  PbCl4. 

Lead  chlorobromide  (PbBrCl)  has  been  found  in  crystals  resembling  lead 
chloride  among  the  furnace-products  in  smelting  lead  carbonate  ore. 

Lead  iodide  (PbI2)  is  obtained  as  a  bright  yellow  precipitate  on  mixing  solutions 
of  nitrate  or  acetate  of  lead  and  potassium  iodide.  If  it  be  allowed  to  settle,  the 
liquid  poured  off,  and  the  precipitate  dissolved  in  boiling  water  (with  one  or  two 
drops  of  hydrochloric  acid),  it  forms  a  colourless  solution,  depositing  golden 
scales  as  it  cools.  Hydriodic  acid  converts  metallic  lead  into  PbI2.  Like  mercuric 
iodide,  PbI2  dissolves  in  the  alkali  iodides.  When  heated,  it  becomes  red,  then 
black,  fuses,  und  becomes  a  yellow  crystalline  mass  on  cooling.  It  is  decomposed 
by  light  with  liberation  of  iodine. 

270.  Sulphides  of  lead. — Lead  sulphide,  PbS,  is  found  as  galena 
(p.  459).  It  fuses  when  strongly  heated,  and  vaporises  in  a  current  of 
gas,  condensing  in  small  crystals.  When  heated  in  air,  it  is  converted 
into  a  mixture  of  PbO  and  PbS04.  Strong  HC1  dissolves  it  when 
heated,  evolving  H2S.  Nitric  acid  dissolves  it  partly  as  lead  nitrate, 
leaving  some  undissolved  lead  sulphate  mixed  with  sulphur.  Lead 
sulphide  is  obtained  as  a  black  precipitate  when  hydrosulphuric  acid  or 
a  soluble  sulphide  acts  upon  a  solution  containing  lead,  even  in  minute 
proportion. 

A  persulpldde  of  lead,  the  composition  of  which  has  not  been  ascertained,  is 
formed  as  a  red  precipitate  when  a  solution  of  lead  is  mixed  with  a  solution  of  an 
alkaline  sulphide  saturated  with  sulphur  (or  with  solution  of  ammonium  sulphide 
which  has  been  kept  till  it  has  acquired  a  red  colour).  It  is  probably  PbS5. 

Lead  chlorosulphide  (PbS.PbCl2)  is  obtained  as  a  bright  red  precipitate  when 
hydrosulphuric  acid  is  added  in  small  quantity  to  a  solution  of  lead  chloride  in 
hydrochloric  acid,  or  when  freshly  precipitated  PbS  is  heated  with  solution  of 
PbCl2.  It  is  decomposed  by  hot  water, 

Lead  selenide  (PbSe)  occurs  associated  with  the  sulphide  in  some  lead  ores  ;  it 
much  resembles  galena,  and  has  the  same  crystalline  form. 

Tin  group  of  metals. — This  group  comprises  Ti,  Zr,Co,Th,Ge,  Sn  and 
Pb.  These  metals  belong  to  the  group  of  elements  which  includes  C  and 
Si,  the  higher  salt-forming  oxide  being  R02,  which  in  most  cases  behaves 
as  a  feeble  acid  oxide,  resembling  C02  and  Si02.  Their  tetrafluorides 
have  a  tendency  to  combine  with  the  alkali  fluorides  to  form  compounds 
which  recall  the  salts  of  hydrofluosilicic  acid,  and  their  tetrachlorides  form 
similar  double  salts  with  alkali  chlorides  (e.#.,2NH4Cl.Pb014,2KCl.SnCl4), 
which  resemble  the  double  chlorides  formed  by  metals  of  the  platinum 
group. 

THALLIUM,  Tl  =  202.6. 

271.  The  discovery  of  this  metal  in  1861  was  one  of  the  first  results  of  the 
application  of  the  new  method  of  testing  by  observation  of  coloured  lines  in  the 


THALLIUM.  473 

spectrum  of  a  flame,  described  at  p.  328.  Crookes  was  examining  the  spectrum 
obtained  by  holding  in  the  flame  of  a  Bunsen  burner  the  deposit  formed  in  the 
flues  of  a  sulphuric  acid  chamber,  in  which  pyrites  was  employed  as  the  source  of 
sulphur.  A  green  line  appeared  in  the  spectrum,  which  a  less  acute  and  practised 
observer  might  have  mistaken  for  one  of  the  lines  due  to  barium  (see  Fig.  213), 
with  which  it  nearly  coincides  in  position  ;  but  the  line  was  much  brighter  than 
that  of  barium,  and  on  instituting  a  searching  analysis  of  the  deposit,  a  metal  was 
obtained  which  did  not  agree  in  properties  with  any  hitherto  described,  and  was 
named  thallium  from  8a\\6s,  a  young  shoot,  in  allusion  to  the  vernal  green  colour 
of  its  spectrum  line.  It  has  since  been  detected  in  several  mineral  waters  ;  but 
the  pyrites  obtained  from  Spain  and  Belgium  appears  to  be  its  best  source.  From 
the  flue-dust  of  the  sulphuric  acid  chambers  the  metal  is  extracted  by  a  simple 
process,  but  large  quantities  must  be  operated  on  to  obtain  any  considerable 
amount.  The  deposit  is  treated  with  boiling  water,  and  the  solution  mixed  with 
much  strong  hydrochloric  acid,  which  precipitates  the  thallium  as  thallous 
-chloride  (T1C1)  ;  this  is  converted  into  acid  thallous  sulphate  (T1HS04)  by  treat- 
ment with  sulphuric  acid,  and  this  salt  having  been  purified  by  recrystallisation, 
is  decomposed  by  zinc,  which  precipitates  metallic  thallium  in  a  spongy  form, 
fusible  into  a  compact  mass  in  an  atmosphere  of  coal  gas. 

Thallium  is  now  classed  with  the  metals  of  the  aluminium  group  (p.  393), 
although  it  differs  considerably  from  these  in  the  stability  of  its  lower  oxide  T120. 

In  external  characters  thallium  is  very  similar  to  lead;  (sp.  gr.  n.8.;  m.  p. 
590°  C.;  volatile  below  800°  C.)  ;  but  it  tarnishes  much  more  rapidly  when  ex- 
posed to  air,  and  the  streak  which  it  makes  on  paper  soon  becomes  yellowish, 
being  converted  into  thallous  oxide,  T120.  If  a  tarnished  piece  of  the  metal  be 
allowed  to  touch  the  tongue,  a  strongly  alkaline  taste  is  perceived,  for  the  thallous 
oxide  (T120)  is  very  soluble  in  water,  so  that  the  tarnished  metal  becomes  bright 
when  immersed  in  water.  If  granulated  thallium  be  exposed  to  moist  air  in  a 
warm  place,  it  absorbs  oxygen  and  C02.  On  boiling  with  water  and  filtering,  the 
alkaline  solution  deposits  white  needles  of  thallous  carbonate  (T12C03),  and  afterwards 
yellow  needles  of  thallous  hydroxide  (T10H).  The  ready  solubility  of  the  oxide 
seemed  to  require  thallium  to  be  classed  among  the  alkali-metals,  a  view  which 
was  encouraged  by  the  circumstance  that  its  specific  heat  proved  it  to  be  mona- 
tonric,  like  potassium  and  sodium.  But  thallium  appears  to  be  more  nearly  related 
to  another  monatomic  metal,  silver,  by  the  sparing  solubility  of  its  chloride  and 
the  insolubility  of  its  sulphide.  The  circumstance  that  it  may  be  kept  unaltered 
in  water,  and  may  be  precipitated  from  its  salts  by  zinc,  at  once  removes  it  from 
the  group  of  alkali-metals.  The  ready  solubility  of  its  oxide  in  water  is  only  an 
•exaggeration  of  the  behaviour  of  the  oxides  of  lead  and  silver,  both  of  which 
dissolve  slightly  in  water,  yielding  alkaline  solutions.  Moreover,  its  hydroxide  is 
far  less  stable  than  those  of  potassium  and  sodium,  for  it  becomes  T120  when  dried 
in  vacuo  over  oil  of  vitriol.  Dilute  H9S04  acts  on  thallium  as  on  zinc,  evolving 
hydrogen.  It  is  not  much  affected  by  "dilute  HN03  in  the  cold  ;  even  on  heating, 
the  action  is  slow  unless  the  acid  is  very  weak.  On  cooling,  the  solution  becomes 
filled  with  needles  of  thallous  nitrate.  Thallium  burns  in  oxygen  with  a  beautiful 
green  flame,  and  the  thallous  chlorate  has  been  recommended  for  the  manufacture 
of  green  fires  in  place  of  barium  chlorate  (page  186). 

Thallous  sulphate,  T1.,S04,  is  obtained  by  dissolving  thallium  in  sulphuric  acid 
and   evaporating;   the"  acid  sulphate,  T1HS04,  first  produced,  being  decomposed 
by  further  heating.     T12S04  is  isomorphous  with  K2S04,  and  it  foTmsthallout  <ilnni. 
TlAl(S04)2.i2Aq,  crystallising  like  potash-alum,.  Thallous  chloride,  T1C1,  resernbh 
lead  chloride,  being  precipitated  by  adding  HC1  to  a  solution  of  a  thallous  salt, 
and  being  dissolved   by  boiling  water,    from   which   it  crystallises  on    cooling. 
Thallous    iodide,  Til,  is    obtained  as  a   yellow  precipitate  on  adding  potassi 
iodide  to  a  thallous  salt ;  when  dried  and  heated,  it  fuses  to  a  red  liquid,  wnicf 
remains  red  after  solidifying,  and  changes,  after  a  time,  to  yellow.     When  spre 
on  paper,  the  yellow  iodide  becomes  red  when  heated,  and  remains  red  on  cooling, 
but  becomes  yellow  when  rubbed  with  a  hard  body.      Thallous  sulpindc    Il2fc, 
is  deposited  as  a  brownish-black  precipitate  oh  adding  ammonium  sulphide  to 
thallous  salt.     Thallic  oxide,  T1203,  is  obtained  by  adding  sodium  hypocnloi 
thallous  chloride  mixed  with  excess  of  sodium  carbonate.     It  is  a  dark  r< 
stance,  which  evolves  oxygen  and  leaves  thallous  oxide  when  heated.     It  is  also 
a  basic  oxide,  its    sulphate    having  the  composition  Tl2(S04)3.H2O.6Aq.     ^J*r*~ 
chloride,  T1C13,  is  formed  by  heating  thallium  in  excess  of  chlorine  ;  it  i 


474  COPPEK  ORES. 

and  crystallisable.  By  passing  Cl  through  a  solution  of  KOH  in  which  T1203  is 
suspended,  a  liquid  is  obtained  which  gives  a  violet  precipitate  with  barium 
salts  ;  this  precipitate  is  alleged  to  contain  T102. 

Thallous  silicate  can  take  the  place  of  alkali  silicate  in  glass,  and  thallium  glass,. 
made  from  thallous  carbonate,  red  lead  and  sand  is  similar  to  flint-glass,  but  has  a 
higher  sp.  gr.  (5.6)  and  refractive  index.  It  is  also  more  fusible  and  harder  than 
ordinary  flint-glass. 

Salts  of  thallium,  like  those  of  lead,  are  poisonus. 


COPPER. 

Cu"  =  63.i  parts  by  weight. 

272.  Metallic  copper  is  met  with  in  nature  more  abundantly  than 
metallic  iron,  though  the  compounds  of  the  latter  metal  are  of  more 
frequent  occurrence  than  those  of  the  former.*     A  very  important  vein, 
of  metallic  copper,  of  excellent  quality,  occurs  near  Lake  Superior,  in 
North  America,  from  which  6000  tons  were  extracted  in  1858.     Metallic 
copper  is  also  sometimes  found  in  Cornwall,  and  copper  sand,  containing 
metallic  copper  and  quartz,  is  imported  from  Chili. 

The  most  important  English  ore  of  copper  is  copper  pyrites,  which  is 
a  double  sulphide,  containing  copper,  iron,  and  sulphur  in  the  propor- 
tions indicated  by  the  formula  Cu2S.Fe2S3.  It  may  be  known  by  its 
beautiful  brass-yellow  colour  and  metallic  lustre.  Copper  pyrites  is 
found  in  Cornwall  and  Devonshire,  and  is  generally  associated  with 
arsenical  pyrites  (FeS2.FeAs2),  tin-stone  (Sn02),  quartz,  fluor  spar,  and 
clay.  A  very  attractive  variety  of  copper  pyrites  is  called  variegated 
copper  ore,  or  peacock  copper,  in  allusion  to  its  rainbow  colours ;  its 
simplest  formula  is  Cu3FeS3.  This  variety  is  found  in  Cornwall  and 
Killarney. 

Copper  glance  (Cu2S)  is  another  Cornish  ore  of  copper,  of  a  dark  grey 
colour  and  feeble  metallic  lustre. 

Grey  copper  ore,  also  abundant  in  Cornwall,  is  essentially  a  compound 
of  the  sulphides  of  copper  and  iron  with  those  of  antimony  and  arsenic, 
but  it  often  contains  silver,  lead,  zinc,  and  sometimes  mercury. 

Malachite,  a  basic  carbonate  of  copper,  is  imported  from  Australia 
(Burra-Burra),  and  is  also  found  abundantly  in  Siberia.  Green  mala- 
chite, the  most  beautifully  veined  ornamental  variety,  has  the  composi- 
tion CuCO3.Cu(OH)2,  and  blue  malachite  is  2CuC03.Cu(OH)2. 

Red  copper  ore  (Cu20)  is  found  in  West  Cornwall,  and  the  black  oxide 
(CuO)  is  abundant  in  the  north  of  Chili. 

273.  The  seat  of  English  copper  smelting  is  at  Swansea,  which  is 
situated  in  convenient  proximity  to  the  bituminous  coal  employed  in  the 
furnaces.     The  chemical  process  by  which  copper  is  extracted  from  the 
ore  includes  three  distinct  operations — (i)  the  roasting,  to  expel  the 
arsenic  and  part  of  the  sulphur,  and  to  convert  the  sulphide  of  iron  into 
oxide  of  iron,  the  copper  remaining  as  sulphide ;  (2)  the  fusing  with 
silica,  to  remove  the  oxide  of  iron  as  silicate,  and  to  obtain  the  copper  in 
combination  with  sulphur  only  ;  and  (3)  the  roasting  of  this  combination 

*  Copper  is  not  at  all  frequently  found  in  animals  or  vegetables  ;  but  Church  has  made 
the  remarkable  observation  that  the  red  colouring-matter  (turacine)  of  the  feathers  of  the 
plantain-eater  (touraco)  contains  as  much  as  7  per  cent,  of  copper.  It  has  also  been  found 
in  the  blood  of  the  cuttle-fish,  as  luemocyanin,  which  is  blue  in  its  oxidised  condition  in  the 
arterial  blood,  and  colourless  in  the  venous  blood. 


COPPER  SMELT 


475 


of  copper  with  sulphur,  in  order  to  expel  the  latter  and  obtain  metallic 
copper  by  the  process  of  self -reduction,  Cu2S  +  2CuO  =  Cu4  +  S02. 

The  details  of  the  smelting  process  appear  somewhat  complicated, 
because  it  is  divided  into  several  stages  to  allow  of  the  introduction  of 
the  different  varieties  of  ore  to  be  treated.  Thus,  the  first  roasting 
process  is  unnecessary  for  the  oxides  and  carbonates  of  copper,  and 
the  fusion  with  silica  is  not  needed  for  those  ores  which  are  free  from 
iron,  so  that  they  may  be  introduced  at  a  later  stage  in  the  operations. 
Owing  to  the  fact  that  rich  ores  of  copper  and  copper  precipitates  are 
now  much  worked,  the  omission  of  the  earlier  processes  is  frequently 
practised,  the  ore  being  directly  smelted  to  white  metal  (fine  metal)  as 
described  below. 

The  processes  of  the  older  practice  could  be  reduced  in  number  if  the  original  ore 
were  a  pure  copper  pyrites,  but  since  the  ores  as  worked  always  contain  a  larger 
proportion  of  iron  and  sulphur  than  copper  pyrites  does,  the  first  two  operations 
are  designed  to  produce  a  material  (coarse  metal)  which  shall  be,  in  effect,  a  pure 
copper  pyrites. 

(i)  Calcining  or  roasting  the  ore  to  expel  arsenic  and  part  of  the  sulphur. — The 
ores  having  been  sorted,  and  broken  into  small  pieces,  are  mixed  so  as  to  contain 
from  8  to  10  per  cent,  of  copper, 
and  roasted,  in  quantities  of  about 
three  tons,  for  at  least  twelve  hours, 
on  the  spacious  hearth  (H,  Fig. 
237)  of  a  reverberatory  furnace 


(Fig.  109,  p.  132)  at  a  temperature 
insufficient  for  fusion,  being  occa- 
sionally stirred  to  expose  them 
freely  to  the  action  of  the  air, 
which  is  admitted  into  the  furnace 

through    an    opening  (0)    in    the  *°'  23°' 

side    of   the    hearth    upon    which 

the  ore  is  spread.     The  oxygen  of  the  air  converts  a  part  of  the  sulphur  into 
and  the  bulk  of  the  As  into  As406,  which  passes  off  in  the  form  of  vapour.    A  part 
of  the  sulphide  of  iron  is  converted  into  ferrous  sulphate  (FeS04)  by  absorb] 
oxygen  at  an  early  stage  of  the  process,  and  this  sulphate  is  afterwards  decompose 
at  a  higher  temperature,  evolving  SO0  and  S03,  and  leaving  oxide  of  iron.     A  por 
tion  of  the  sulphide  of  copper  is  also"  con  verted  into  oxide  of  copper  during  tne 
roasting,  so  that  the  roasted  ore  consists  essentially  of  a  mixture  of  oxide 
phide  of  copper  with  oxide  and  sulphide  of  iron.     Since  the  sulphide  of  iron  is 
easily  oxidised  than  sulphide  of  copper,  the  greater  part  of  the  J 
unaltered  in  the  roasted  ore.  ,     , 

During  the  roasting  of  copper  ore  dense  white  fumes  escape  from  the '  i»rna£ 
This  copper  smoke,  as  it  is  termed,  contains  As406,  S02,   S03,  and  I 
being  derived  from  the  fluor  spar  associated  with  the  ore  ;  if  allowed 
these  fumes  seriously  contaminate  the  air  in  the  neighbourhood,  so 
usually  condensed  in  flues  and  rain-chambers  by  showers  of  water. 


476  COPPER  SMELTING. 

(2)  Fusion  for  coarse  metal  to  remove  the  oxide  of  iron  by  dissolving  it  with  silica, 
at  a  high  temperature. — The  roasted  ore  is  now   mixed    with   metal    slag   from 
process  4,  and  with  ores  containing  silica  and  oxides  of  copper,  but  no  sulphur  ;  the 
mixture  is  introduced  into  the  orejurnace  (Fig.  238)    (the  hearth  of  which  is  made 
narrower  than  that  of  the  roasting  furnace,  since  a  higher  temperature  is  required) 
and  fused  for  five  hours  at  a  higher  temperature  than  that  employed  in  the  previous 
operation.     In  this  process  fluor  spar  is  sometimes  added  in  order   to  increase 
the  fluidity  of  the  slag. 

The  oxide  of  copper  attacks  the  sulphide  of  iron  still  contained  in  the  roasted 
ore,  with  formation  of  sulphide  of  copper  and  oxide  of  iron,  but  since  there  is  more 
sulphide  of  iron  present  than  the  oxide  of  copper  can  decompose,  the  excess  of  sul- 
phide of  iron  combines  with  the  sulphide  of  copper  to  form  a  fusible  compound, 
which  separates  from  the  slag,  and  collects  in  the  form  of  a  matte  or  regulus  of 
coarse  metal,  in  a  cavity  (C)  on  the  hearth  of  the  furnace  :  it  is  run  out  into  a  tank 
of  water  (T)  in  order  to  granulate  it,  so  that  it  may  be  better  fitted  to  undergo  the 
next  operation. 

The  oxide  of  iron  combines  with  the  silica  contained  in  the  charge,  to  form  a 
fusible  ferrous  silicate  (ore-furnace  slag),  which  is  raked  out  into  moulds  of  sand, 
and  cast  into  blocks  used  for  rough  building  purposes  in  the  neighbourhood. 

The  composition  of  the  coarse  metal  corresponds  pretty  closely  with  the 
formula  CuFeS2.  It  contains  from  33  to  35  per  cent,  of  copper  ;  whilst  the 
original  ore,  before  roasting,  is  usually  sorted  so  that  it  may  contain  about  8.5  per 
cent. 

The  ore-furnace  slag  is  approximately  represented  by  the  formula  FeO.Si02  ; 
but  it  contains  a  minute  proportion  of  copper,  as  is  shown  by  the  green  efflores- 
cence on  the  walls  in  which  it  is  used  around  Swansea.  Fragments  of  quartz  are 
seen  disseminated  through  this  slag. 

(3)  Calcination  of  the  coarse  metal  to  convert  the  greater  part  of  the  sulphide,  of  iron 
into  oxide. — The  granulated  coarse  metal  is  roasted  at  a  moderate  temperature 
for   twenty-four  hours,  as  in  the  first  operation,  so  that  the  oxygen  of  the  air  may 
decompose  the   sulphide  of  iron,   removing  the  sulphur  as   sulphuric  acid,  and 
leaving  the  iron  in  the  form  of  oxide. 

(4)  Fusion  J "or  white  metal  to  remove  the  whole  of  the  iron  as  silicate. — The  roasted 
coarse  metal  is  mixed  with  roaster  and  refinery  slags  from  processes  5  and  6,  and 
with  ores  containing  carbonates  and  oxides  of  copper,  and  fused  for  six  hours,  as 
in  the  second  operation.     Any  sulphide  of  iron  which  was  left  unchanged  in  the 
roasting  is  now  converted  into  oxide  of  iron  by  the  oxide  of  copper,  the  latter 
metal  taking  the  sulphur.     The  whole  of  the  oxide  of   iron  combines  with  the 
silica  to  form  a  fusible  slag,  the  composition  of  which  is  approximately  represented 
by  the  formula  3Fe0.2Si02. 

The  matte  QIC  regulus  of  white  metal,  which  collects  beneath  the  slag,  is  nearly 
pure  cuprous  sulphide  (Cu2S).  The  white  metal  is  run  into  sand-moulds 
and  cast  into  ingots.  The  tin  and  other  foreign  metals  usually  collect  in 
the  lower  part  of  the  ingot,  so  that,  for  making  best  selected  copper,  the 
upper  part  is  broken  off  and  worked  separately,  the  inferior  copper  obtained 
from  the  lower  part  of  the  ingot  being  termed  tile-copper.  The  ingots  of 
white  metal  often  contain  beautiful  tufts  of  metallic  copper  in  the  form  of 
copper  moss. 

The  slag  separated  from  the  white  metal  (jnetal  slag)  is  much  more  fluid  than 
the  ore-furnace  slag,  and  contains  so  much  silicate  of  copper  that  it  is  preserved 
for  use  in  the  melting  for  coarse  metal. 

(5)  Roasting  the  ivhite  metal  to  remove  the  sulphur  and  obtain  blister  copper. — The 
ingots  of  white  metal  (to  the  amount  of  about  3  tons)  are  placed  upon  the  hearth 
of  a  reverberatory  furnace,  and  heated  for  four  hours  to  a  temperature  just  below 
fusion,   so  that  they  may  be  oxidised  at  the  surface,  the  sulphur  passing  off  as 
sulphurous  acid   gas,   and  the  copper  being  converted   into  oxide.     During  this 
roasting  the  greater  part  of  the  arsenic,  generally  present  in  the  fine  metal,  is 
expelled  as  As406.     The  temperature  is  then  raised,  so  that  the  charge  may  be 
completely  fused,   after   which   it   is  lowered   again  till   the  twelfth  hour.     The 
oxide  of  copper  now  acts  upon  the  sulphide  of  copper  to  form  metallic  copper  and 
sulphurous  acid  gas,  which  escapes,  with  violent  ebullition,  from  the  melted  mass  ; 
Cu2S  +  2CuO  =  S02  +  Cu4.     When  this  ebullition  ceases,   the  temperature  is  again 
raised  so  as  to  cause  the  complete  separation  of  the  copper  from  the  slag,  and  the 
metal  is  run  out  into  moulds  of  sand.     Its  name  of  blister  copper  is  derived  from 


REFINING  COPPEE. 


477 


the  appearance  caused  by  the  escape  of  the  last  portions  of  S02  from  the  metal 
when  solidifying  in  the  mould. 

The  slag  (roaster  slag)  is  formed  in  this  operation  by  the  combination  of  a 
part  of  the  oxide  of  copper  with  silica  derived  from  the  sand  adhering  to 
the  ingots  and  from  the  hearth  of  the  furnace.  The  slag  also  contains  the 
silicates  of  iron  and  of  other  metals,  such  as  tin  and  lead,  which  might  have 
been  contained  in  the  white  metal.  This  slag  is  used  again  in  the  melting  for 
white  metal. 

(6)  Refining  to  remove  foreign  metals.— This  process  consists  in  slowly  fusing 
7  or  8  tons  of  the  blister   copper   in   a   reverberatory  furnace,   so  that   the  air 
passing  through  the  furnace  may  remove  any  remaining  sulphur  as  sulphurous 
acid   gas,  and  may  oxidise  the  small  quantities  of  iron,   tin,  lead,  &c.,  present 
in  the  metal.     Of  course,  a  large  proportion  of  the  copper  is  oxidised  at  the 
same  time,   and   the  cuprous  oxide,   together  with  the  oxides    of  the  foreign 
metals,  combine  with  the  silica  (from  the  hearth    or  from   adhering   sand),   to 
form  a  slag  which  collects  upon  the  surface  of  the  melted  copper.*    A  portion  of 
the  cuprous  oxide  is  dissolved  by  the  metallic  copper,  rendering  it  brittle  or  dry 
copper. 

(7)  Toughening  or  poling  to  remove  a  part  of  the  oxygen  and  bring  the  copper  to 
tough-pitch. — After  about  twenty  hours  the  slag  is  skimmed  from  the  metal,  a 
quantity  of  anthracite  is  thrown  over  the  surface  to  prevent  further  oxidation,  and 
the  metal  is  poled — i.e..  stirred  with  a  pole  of  young  wood — until  a  small  sample, 
removed  for  examination,  presents  a  peculiar  silky  fracture,  indicating  it  to  be  at 
tough-pitch,  when  it  is  cast  into  ingots. 

Products  obtained  in  smelting  Ores  of  Copper. 


In  100  parts. 

Ore. 

Roasted 
Ore. 

Coarse 
Metal. 

Roasted 
Coarse 
Metal. 

White 
Metal. 

Blister 
Copper. 

Refined 
Copper. 

Tough- 
pitch 
Copper. 

CO 

(2) 

(3) 

(4) 

ft)' 

(6) 

(7) 

Copper 

8.2 

8.6 

33-7 

33-7 

77-4 

98.0 

99-4 

99.6 

Iron    . 

17.9 

17.6 

33-6 

33-6 

0.7 

°-5 

trace 

trace 

Sulphur 

19.9 

12.5 

29.2 

13.0 

21.0 

0.2 

trace 

trace 

Oxygen 

I.O 

4-5 

II.O 

0.4 

0.03 

Silica  . 

34-3 

34-3 

Slags. 

Ore 
Furnace. 

Metal. 

Roaster. 

Refinery. 

(2) 

(4) 

fc) 

(6) 

Oxide  of  iron  (FeO)     . 

54-o 

50.0 

28.0 

3-1 

Suboxide  of  copper  (Cu20)  . 

0-5 

0.9 

16.9 

39-2 

Silica    

45-° 

33-8 

47-5 

47-4 

The  chemical  change  during  the  poling  appears  to  consist  in  the  removal  of  the 
oxygen  contained  in  the  cuprous  oxide  present  in  the  metal,  by  the  reducing 
action  of  the  combustible  gases  disengaged  from  the  wood.  The  presence  of  a 
small  proportion  of  cuprous  oxide  is  said  to  confer  greater  toughness  upon  the 
metal,  so  that  if  the  poling  be  continued  until  the  whole  of  the  oxygen  i, 
removed,  over-poled  copper  of  lower  tenacity  is  obtained.  On  the  other  hand, 
the  brittleness  of  under-poled  copper  is  due  to  the  presence  of  cuprous  oxide 
in  too  large  proportion.  Tough-cahe  copper  is  that  which  has  been  poled  to  the 
proper  extent. 

The  addition  of  about  0.07  per  cent,  of  phosphorus,  as  copper  phosphide,  be 

*  When  the  removal  of  arsenic,  which  forms  an  acid  oxide,  is  specially  desired,  it  is 
advantageous  to  line  the  hearth  with  a  basic  material,  such  as  that  used  in  tl 
processes. 


478  WET   EXTRACTION   OF   COPPER. 

the  final  poling,  shortens  the  process  and  increases  the  density  of  the  metal.  The 
copper  phosphide  is  made  by  dissolving  about  7  per  cent  of  phosphorus  in  melted 
copper. 

When  the  copper  is  intended  for  rolling,  a  small  quantity  (not  exceeding  ^  per 
cent.)  of  lead  is  generally  added  to  it  before  it  is  ladled  into  the  ingot  moulds. 
Apparently  the  oxide  of  lead  formed  by  the  action  of  the  air  assists  in  removing 
some  of  the  impurities  in  the  form  of  slag  (scorijication) . 

The  chemical  changes  which  take  place  during  the  above  processes  will  be  more 
clearly  understood  after  inspecting  the  table  on  page  477,  which  exhibits  the 
composition  of  the  products  obtained  at  different  stages  of  the  process,  these  being 
distinguished  by  the  same  numerals  as  were  employed  in  the  above  description. 

Blue  metal  is  the  term  applied  to  the  regulus  of  white  metal  (from  process  4) 
when  it  still  contains  a  considerable  proportion  of  sulphide  of  iron,  in  con- 
sequence of  a  deficient  supply  of  oxide  of  copper  in  the  furnace.  Pimple  metal  is 
obtained  in  the  same  operation  when  the  oxide  of  copper  is  in  excess,  so  that  a 
portion  of  the  copper  is  reduced,  as  in  process  5,  with  evolution  of  sulphurous 
acid  gas,  which  produces  the  pimply  appearance  in  escaping.  The  reduced  copper 
gives  a  reddish  colour  to  the  pimple  copper.  Coarse,  or  Uacli  copper,  is  a  similar 
intermediate  stage  between  white  metal  and  blistered  copper.  Tile  copper  is 
that  extracted  from  the  bottoms  of  the  ingots  of  white  metal,  when  the  tops 
have  been  detached  for  making  best  selected  copper.  Rosette  or  rose  copper  is 
obtained  by  running  water  upon  the  toughened  metal,  so  as  to  enable  the  metal 
to  be  removed  in  films.  Anglesea  or  Mona  copper  is  a  very  tough  copper,  reduced 
by  metallic  iron  from  the  Hue  water  of  the  copper  mines,  which  contains  sulphate 
of  copper. 

The  application  of  the  Bessemer  converter  to  the  refining  of  blister  copper  has 
been  attempted,  but  the  impurities  to  be  oxidised  are  incapable  of  giving,  by  their 
combustion,  a  temperature  sufficiently  high  to  keep  the  copper  in  fusion.  The 
converter  is,  however,  employed  on  the  Continent  for  the  conversion  of  fused 
white  metal  into  blister  copper,  there  being  sufficient  sulphur  in  the  white  metal 
to  yield  a  temperature  high  enough  to  maintain  the  fusion  of  the  copper. 

For  the  extraction  of  copper  from  poor  ores  (3  per  cent.  Cu)  a  wet 
method  is  generally  adopted.  This  is  rendered  economically  possible  by 
the  fact  that  when  moist  copper  sulphide  is  exposed  to  the  air*  it 
becomes  oxidised  to  copper  sulphate,  which  may  be  dissolved  in  water. 
The  recovery  of  the  copper  from  the  solution  is  effected  by  the  intro- 
duction of  pig-iron,  when  this  metal  takes  the  place  of  the  copper 
which  is  precipitated,  CuS04  +  Fe  =  FeS04  +  Cu.  The  copper  precipitate 
thus  obtained  is  melted  and  refined.  Electrolytic  deposition  of  the 
copper  from  the  solution  is  also  practised. 

Two  other  methods  of  dissolving  the  copper  sulphide  from  the  ore  are  employed. 
In  the  one.  the  ore  is  treated  with  a  solution  of  a  ferric  salt  containing  common 
salt.  The  former  converts  the  Cu2S  of  the  ore  into  Cu2Cl2,  which  is  dissolved  by 
the  solution  of  salt;  Cu2S  +  Fe2Cl6  =  2FeCl2+Cu2Cl.2+S.  The  dissolved  copper  is 
then  precipitated  by  iron.  In  the  second  method  (applied  to  the  spent  pyrites  of 
the  vitriol  works,  p.  226)  the  ore  is  submitted  to  a  chlorinating  roasting — that  is  to 
say,  it  is  ground,  mixed  with  NaCl  and  roasted  ;  the  copper  sulphide  is  thus 
converted,  first  into  sulphate  by  roasting,  and  then  into  chloride  by  double 
decomposition  with  the  salt.  The  copper  chloride  is  leached  out  and  the  copper 
is  precipitated  by  iron. 

The  crude  blister  copper  or  precipitate  copper  obtained  by  the  above 
processes  is  now  largely  refined  by  electrolysis.  For  this  purpose  the 
metal  is  cast  into  plates  which  are  suspended  in  a  bath  of  copper  sul- 
phate solution,  acid  with  H2SO4,  and  are  made  the  anodes,  the  cathodes 
being  thin  sheets  of  pure  copper.  When  a  current  (0.2  volt  pressure) 
is  passed  through  the  solution  from  a  dynamo,  the  anodes  dissolve  and 
the  copper  is  deposited  on  the  cathodes. 

*  The  ore  is  exposed  in  heaps,  kept  constantly  moist. 


IMPURITIES   IN  COPPER. 

The  copper  refined  in  this  manner  is  almost  chemically  pure,  but 
requires  remelting  before  being  hammered  or  rolled,  on  account  of  the 
crystalline  condition  in  which  it  is  deposited.  In  this  process  the  gold, 
silver,  and  other  metals  (except  iron,  which  passes  into  solution),  which 
may  be  present  in  the  blister  copper,  remain  in  the  tanks  in  the  form 
of  a  fine  mud. 

274.  For  the  purpose  of  illustration,   copper  may  be   extracted  from  copper 
pyrites  on  the  small  scale  in  the  following  manner  : 

200  grains  of  the  powdered  ore  are  mixed  with  an  equal  weight  of  dried  borax, 
and  fused  in  a  covered  earthen  crucible  (of  about  8  oz.  capacity),  at  a  full  red 
heat  for  about  half  an  hour.  The  earthy  matters  associated  with  the  ore  are 
dissolved  by  the  borax,  and  the  pure  copper  pyrites  collects  at  the  bottom  of  the 
crucible.  The  contents  of  the  latter  are  poured  into  an  iron  mould  (scorifying 
mould,  Fig.  239),  and  when  the  mass  has  set,  it  is  dipped  into  water.  The  semi- 
mettalic  button  is  then  easily  detached  from  the  slag  by  a  gentle  blow  ;  it  is 
weighed,  finely  powdered  in  an  iron  mortar,  and  introduced  into  an  earthen 
crucible,  which  is  placed  obliquely 
over  a  dull  fire,  so  that  it  may  not 
become  hot  enough  to  fuse  the  ore, 
which  should  be  stirred  occasionally 
with  an  iron  rod  to  promote  the 
oxidation  of  the  sulphur  by  the  air. 
When  the  odour  of  S02  is  no  longer 
perceptible,  the  crucible  is  placed  in  a 
Fletcher's  injector  furnace  (Fig.  225), 
and  exposed  for  a  few  minutes  to  a  Fig.  239. 

bright  red  heat,  in  order  to  decompose 

the  sulphates  of  iron  and  copper.  When  no  more  white  fumes  of  S03  are  perceived, 
the  crucible  is  lifted  from  the  furnace,  held  over  the  iron  mortar,  and  the  roasted 
ore  quickly  scraped  out  of  it  with  a  steel  spatula.  This  mixture  of  the  oxides  of 
copper  and  iron  is  reduced  to  a  fine  powder,  mixed  with  600  grains  of  dried 
carbonate  of  soda  and  60  grains  of  powdered  charcoal,  returned  to  the  same 
crucible,  covered  with  200  grains  of  dried  borax,  and  again  heated  in  the  furnace 
for  twenty  minutes.  The  crucible  is  then  allowed  to  cool,  and  carefully  broken 
to  extract  the  button  of  metallic  copper,  which  is  weighed  to  ascertain  the 
amount  contained  in  the  original  ore. 

275.  Effect  of  impurities  upon  the  quality  of  copper. — The  information 
possessed  by  chemists  upon  this  subject  is  still  very  limited.     It  has  been 
already  mentioned  that  the  presence  of  a  small  proportion  of  cuprous 
oxide  in  commercial  copper  is  found  to  increase  its  toughness.     It  is 
believed  that  copper,  perfectly  free  from  metallic  impurities,  is  not  im- 
proved in  quality  by  the  presence  of  the  oxide,  but  that  this  substance 
has  the  effect  of  counteracting  the  red-shortness  (see  p.  408)  of  com- 
mercial copper,  caused  by  the  presence  of  foreign  metals. 

Sulphur,  even  in  minute  proportion,  appears  seriously  to  injure  the 
malleability  of  copper.  Arsenic  is  almost  invariably  present  in  copper, 
very  frequently  amounting  to  o.i  per  cent.,  and  does  not  appear  to 
exercise  any  injurious  influence  in  this  proportion;  indeed,  its  presence 
is  stated  to  increase  the  malleability  and  tenacity  of  the  metal.  Phos- 
phorus is  not  usually  found  in  commercial  copper.  When  purposely  added 
in  quantity  varying  from  0.12  to  0.5  per  cent.,  it  increases  the  hardness 
and  tenacity  of  the  copper,  though  rendering  it  somewhat  red-short. 

Tin,  in  minute  proportion,  is  also  said  to  increase  the  toughness  of 
copper,  though  any  considerable  proportion  renders  it  brittle.  Anti- 
mony is  a  very  objectionable  impurity,  and  is  by  no  means  uncommon 
in  samples  of  copper.  Nickel  is  believed  to  harden  copper  in  which  it 
occurs.  Bismuth  and  silver  are  very  generally  found  in  marketable 


480  PROPERTIES   OF  COPPER. 

copper,  but  their  effect  upon  its  quality  has  not  been  clearly  deter- 
mined. All  impurities  appear  to  affect  the  malleability  and  tenacity 
of  copper  more  perceptibly  at  high  than  at  low  temperatures. 

The  conducting  power  of  copper  for  electricity  is  affected  in  an  extra- 
ordinary degree  by  the  presence  of  impurities.  Thus,  if  the  conducting 
power  of  chemically  pure  copper  be  represented  by  100,  that  of  the  very 
pure  native  copper  from  Lake  Superior  has  been  found  to  be  93,  that  of 
the  copper  extracted  from  the  malachite  of  the  Burra  Burra  mines  in 
South  Australia  was  89,  whilst  that  of  Spanish  copper,  remarkable  for 
containing  much  arsenic,  was  only  14. 

Copper  can  be  obtained  in  octahedral  crystals.  When  copper  sul- 
phate is  heated  with  a  very  strong  solution  of  sugar,  crystalline  copper 
is  deposited. 

276.  PROPERTIES  OF  COPPER. — The  most  prominent  character  which 
confers  upon  copper  so  high  a  rank  among  the  useful  metals  is  its  malle- 
ability, which  allows  it  to  be  readily  fashioned  under  the  hammer,  and 
to  be  beaten  or  rolled  into  thin  sheets  ;  among  the  metals  in  ordinary 
use,  only  gold  and  silver  exceed  copper  in  malleability,  and  the  com- 
parative scarcity  of  those  metals  leads  to  the  application  of  copper  for 
most  purposes  where  great  malleability  is  requisite. 

Although,  in  tenacity  or  strength,  copper  ranks  high  among  metalsy 
it  is  still  very  far  inferior  to  iron,  for  a  copper  wire  of  Yfrth  inch  in 
diameter  will  support  only  468  Ibs.,  while  a  similar  iron  wire  will  carry 
705  Ibs.  without  breaking ;  and,  in  consequence  of  its  inferior  tenacity, 
copper  is  less  ductile  than  iron,  and  does  not  admit  of  being  so  readily 
drawn  into  exceedingly  thin  wires. 

The  comparative  ease  with  which  copper  may  be  fused  allows  it  to 
be  cast  much  more  readily  than  iron  ;  for  it  will  be  remembered  that  the 
latter  metal  can  be  liquefied  only  by  the  highest  attainable  furnace  heat, 
whereas  copper  melts  at  1057°  C.,a  temperature  generally  spoken  of  as- 
a  bright  red  heat. 

As  one  of  the  most  sonorous  of  metals,  copper  has  been,  from  time 
immemorial,  employed  in  the  construction  of  bells  and  musical  instru- 
ments. Its  high  conductivity  for  electricity  is  turned  to  account  in 
telegraphic  communication,  its  conducting  power  being  almost  equal 
to  that  of  silver,  which  is  the  best  of  electric  conductors.  In  conduc- 
tivity for  heat,  copper  is  surpassed  only  by  silver  and  gold. 

Copper  is  not  so  hard  as  iron,  and  is  somewhat  heavier,  the  specific 
gravity  of  cast  copper  being  8.92,  and  that  of  hammered  or  drawn 
copper  8.95. 

The  resistance  of  copper  to  the  chemical  action  of  moist  air  gives  it  a> 
great  advantage  over  iron  for  many  uses,  and  the  circumstance  that  it 
does  not  decompose  water  in  presence  of  dilute  sulphuric  acid  enables  it 
to  be  employed  as  the  negative  plate  in  galvanic  couples. 

Nitric  acid  is  the  best  solvent  for  copper,  but  the  presence  of  nitrous 
acid  seems  to  be  necessary  for  the  attack  of  the  metal  (see  p.  146). 
Hydrochloric  acid  attacks  it  in  presence  of  oxidising  agents. 

277.  When  copper  is  placed  in  a  solution  of  salt  in  water,  no  percep- 
tible action  occurs ;  but  in  the  course  of  time,  if  the  air  be    allowed 
access,  it  becomes  covered  with  a  green  coating  of  oxychloride  of  copper 
(CuCl2.3Cu0.4H2O),  the  action  probably  consisting,  first,  in  the  conver- 
sion of  the  copper  into  oxide  by  the  air,  and  afterwards  in  the  decom- 


NEED   FOR  CLEANLINESS   IN   COOKING  UTENSILS.  481 

position  of  the  oxide  by  the  sodium  chloride  ;  4CuO  +  2NaCl  -f  H,0  = 
CuCL,.3CuO  +  2NaOH.  The  surface  of  the  copper  is  thus  corroded, 
and  in  the  case  of  a  copper-bottomed  ship,  the  action  of  sea-water  not 
only  occasions  a  great  waste  of  copper,  but  roughens  the  surface  of  the 
sheathing,  and  affords  points  of  attachment  to  barnacles,  &c.,  which 
injure  the  speed  of  the  vessel.  Many  attempts  have  been  made  to 
obviate  this  inconvenience.  Zinc  has  been  fastened  here  and  there  to 
the  outside  of  the  copper,  placing  the  latter  in  an  electro-negative 
condition  ;  the  copper  has  been  coated  with  various  compositions,  but 
with  very  indifferent  success.  Muntz  metal,  or  yellow  sheathing,  or 
malleable  brass,  an  alloy  of  3  parts  of  copper  and  2  parts  of  zinc,  has 
been  employed  with  some  advantage  in  place  of  copper,  for  it  is  very 
much  cheaper  and  somewhat  less  easily  corroded  ;  but  the  difficulty  is  by 
no  means  overcome.  Copper  containing  about  o.  5  per  cent,  of  phosphorus 
is  said  to  be  corroded  by  sea- water  much  less  easily  than  is  pure  copper. 

278.  The  use  of  copper  for  culinary  vessels  has  occasionally  led  to 
serious  consequences,  from  the  poisonous  nature  of  its  compounds,  and 
from  ignorance  of  the  conditions  under  which  these  compounds  are 
formed.     A  perfectly  clean  surface  of  metallic  copper  is  not  affected  by 
any  of  the  substances  employed  in  the  preparation  of  food,  but  if  the 
metal  has  been  allowed  to  remain  exposed  to  the  action  of  the  air,  it 
becomes  covered  with  a  film  of  oxide  of  copper,  and  this  subsequently 
combines  with   water  and  carbonic  acid  gas  derived  from  the  air  to 
produce  a  basic  carbonate  of  copper,*   which,   becoming  dissolved  or 
mixed   with   the   food   prepared    in   these  vessels,  confers   upon  it   a 
poisonous  character.     This  danger  may  be  avoided  by  the  use  of  vessels 
which  are  perfectly  clean  and   bright,  but   even  from  these  certain 
articles  of  food  may  become  contaminated  with  copper,  for  this  metal 
is  more   likely  to  be  oxidised  by  the  air  when  in  contact  with  acids 
(vinegar,  juices  of  fruits,  &c.),  or  with  fatty  matters,  or  even  with 
common  salt;  and  if  oxide  of  copper  be  once  formed,  it  will  be  readily 
dissolved  by  such  substances.     Hence  it  is  usual  to  coat  the  interior  of 
copper  vessels  with  tin,  which  is  able  to  resist  the  action  of  the  air, 
even  in  the  presence  of  acids  and  saline  matters. 

279.  Alloys  of  copper. — Copper  forms  a  greater  number  of  useful 
alloys   than  any  other  metal.     Those  of  copper  with   tin  (gun-metal 
and    bronze)  have  been  already  noticed  (p.  452).     With    from   one- 
third  to  one-half  its  weight  of  zinc,  copper  forms  brass,  much  harder 
than  copper,  and  capable  of  being  hammered  into  thin  leaves  as  a  sub- 
stitute for   gold.     The  most   important   alloys  of   which  copper  is  a 
predominant  constituent  are  the  following  : — 

Brass — 64  copper,  36  zinc  (sp.  gr.  8.3). 

Muntz  metal— 60  to  64  copper,  40  to  36  zinc  (sp.  gr.  8.2). 

German  silver — 61  copper,  19.5  zinc,  19.5  nickel. 

Aich  or  Gedge's  metal— 60  copper,  38.2  zinc,  1.8  iron. 

Sterro-metal — 55  copper,  42.4  zinc,  2.6  iron. 

Bell  metal — 78  copper,  22  tin. 

Speculum  metal — 66.6  copper,  33.4  tin. 

Bronze — 85  copper,  10  tin,  5  zinc. 

Gun-metal — 90.5  copper,  9.5  tin  (sp.  gr.  8.5). 

Bronze  coinage — 95  copper,  I  zinc,  4  tin. 

Aluminium  bronze— 90  copper,  10  aluminium. 

*  Often  erroneously  called  verdigris,  which  is  really  a  basic  acetate  of  copper. 

2  H 


482  ALLOYS   OF  COPPEK. 

Brass  is  made  by  melting  copper  in  a  crucible,  and  adding  rather  more 
than  half  its  weight  of  zinc.  An  alloy  containing  3  2  per  cent,  of  copper 
and  68  per  cent,  of  zinc  would  correspond  with  the  formula  Zn2Cu  ;  thus 
ordinary  brass  may  be  regarded  as  a  solidified  solution  of  this  compound 
in  copper.  A  small  quantity  of  tin  is  added  to  brass  intended  for 
door-plates,  which  renders  the  engraving  much  easier.  When  it  has  to 
be  turned  or  filed,  about  2  per  cent,  of  lead  is  usually  added  to  it,  in 
order  to  prevent  it  from  adhering  to  the  tools  employed.  Brass  cannot 
be  melted  without  losing  a  portion  of  its  zinc  in  the  form  of  vapour. 
When  exposed  to  frequent  vibration  (as  in  the  suspending  chains  of 
chandeliers),  it  suffers  an  alteration  in  structure  and  becomes  extremely 
brittle.  The  solder  used  by  braziers  consists  of  equal  weights  of  copper 
and  zinc.  In  order  to  prevent  ornamental  brass-work  from  being  tar- 
nished by  the  action  of  air,  it  is  either  lacquered  or  bronzed.  Lacquering 
consists  simply  in  varnishing  the  brass  with  a  solution  of  shellac  in  spirit, 
coloured  with  dragon's  blood.  Bronzing  is  effected  by  applying  a  solution 
of  arsenic  or  mercury,  or  platinum,  to  the  surface  of  the  brass.  By  the 
action  of  arsenious  oxide  dissolved  in  hydrochloric  acid,  upon  brass,  the 
latter  acquires  a  coating  composed  of  arsenic  and  copper,  which  imparts 
a  bronzed  appearance,  the  zinc  being  dissolved  in  place  of  the  arsenic, 
which  combines  with  the  copper  at  the  surface.  A  mixture  of  corrosive 
sublimate  (mercuric  chloride  HgCl2)  and  acetic  acid  is  also  sometimes 
employed,  when  the  mercury  is  displaced  by  the  zinc,  and  precipitated 
upon  the  surface  of  the  brass,  with  which  it  forms  a  bronze-like  amalgam. 
For  bronzing  brass  instruments,  such  as  theodolites,  levels,  &c.,  a  solution 
of  chloride  of  platinum  is  employed,  the  zinc  of  the  brass  precipitating 
a  very  durable  film  of  metallic  platinum  upon  its  surface  (PtCl4  +  Zn2  = 
Pt  +  2ZnCl2). 

Aicli  metal  is  a  kind  of  brass  containing  iron,  and  has  been  employed  for  cannon, 
on  account  of  its  great  strength.  At  a  red  heat  it  is  very  malleable. 

Sterro-ntetal  (crre/3p6s,  strong)  is  another  variety  of  brass  containing  iron  and 
tin,  said  to  have  been  discovered  accidentally  in  making  brass  with  the  alloy  of 
zinc  and  iron  obtained  during  the  process  of  making  galvanised  iron  (page  377) . 
It  possesses  great  strength  and  elasticity,  and  is  used  by  engineers  for  the  pumps 
of  hydraulic  presses. 

Aluminium  bronze  has  been  already  noticed. 

A  very  hard  white  alloy  of  77  parts  of  Zn,  17  of  Sn,  and  6  of  Cu,  has  been 
employed  for  the  bearings  of  the  driving-wheels  of  locomotives. 

Other  bearing  alloys  consist  of  copper,  tin,  lead  alloys  (e.g.,  Cu  76.8,  Sn  8.0,  Pb 
15.0,  P  0.2),  and  of  lead,  tin  antimony,  zinc  and  copper  alloys  (e.g.,  white  metals, 
such  as  Pb  40,  Sn  45.5,  Sb  13,  Cu  1.5). 

Iron  and  steel  are  coated  with  a  closely  adherent  film  of  copper,  by  placing 
them  in  contact  with  metallic  zinc  in  an  alkaline  solution  of  oxide  of  copper, 
prepared  by  mixing  sulphate  of  copper  with  tartrate  of  potash  and  soda,  and 
caustic  soda.  The  copper  is  thus  precipitated  upon  the  iron  by  slow  voltaic 
action,  the  zinc  being  the  attacked  metal.  By  adding  a  solution  of  stannate  of 
soda  to  the  alkaline  copper  solution,  a  deposit  of  bronze  may  be  obtained. 

280.  Oxides  of  copper. — Two  oxides  of  copper  are  well  known  in 
the  separate  state,  viz.,  the  suboxide,  Cu2O,  and  the  oxide,  CuO. 
Another  oxide,  Cu40,  has  been  obtained  in  a  hydrated  state,  and  there 
is  some  evidence  of  the  existence  of  an  acid  oxide,  Cu02. 

The  black  oxide  of  copper  (cupric  oxide),  CuO,  is  employed  by  the 
chemist  in  the  ultimate  analysis  of  organic  substances  by  combustion, 
being  prepared  for  this  purpose  by  acting  upon  copper  with  nitric 
acid  to  convert  it  into  cupric  nitrate  (p.  92),  and  heating  this  to 


CUPROUS  OXIDE.  483 

dull  redness  in  a  rough  vessel  made  of  sheet  copper,  when  it  leaves 
the  black  oxide  (sp.  gr.  6.3)  ;  Cu(N03)2  =  2N02  +  0  +  CuO.  At  a  higher 
temperature  the  oxide  fuses  into  a  very  hard  mass  ;  it  evolves  very  little 
oxygen  when  strongly  heated.  Oxide  of  copper  absorbs  water  easily 
from  the  air,  but  it  is  not  dissolved  by  water  ;  acids,  however,  dissolve  it, 
forming  the  salts  of  copper,  whence  the  use  of  oil  of  vitriol  and  nitric 
acid  for  cleansing  the  tarnished  surface  of  copper  ;  a  blackened  coin, 
for  example,  immersed  in  strong  nitric  acid,  and  thoroughly  washed  \ 
becomes  as  bright  as  when  freshly  coined.  Silica  dissolves  oxide  of 
copper  at  a  high  temperature,  forming  cupric  silicate,  which  is  taken 
advantage  of  in  producing  a  fine  green  colour  in  glass. 

Red  oxide  or  suboxide  of  copper  (cuprous  oxide),  Cu90,  is  found  crys- 
tallised in  regular  octahedra,  and  is  formed  when  copper  is  heated  in 
air,  that  portion  of  the  copper-scale  which  is  in  contact  with  the  air 
becoming  CuO,  while  that  in  contact  with  the  metal  is  Cu20.  It  is 
made  by  heating  a  mixture  of  5  parts  of  the  black  oxide  with  4  parts 
of  copper  filings  in  a  closed  crucible.  It  may  also  be  prepared  by  boil- 
ing a  solution  of  cupric  sulphate  with  a  solution  containing  sodium 
sulphite  and  sodium  carbonate  in  equal  quantities,  when  the  cuprous 
oxide  is  precipitated  as  a  reddish-yellow  powder,  which  should  be 
washed,  by  decantation,  with  boiled  water  — 


2CuS04  +  2Na2C03  +  Na2S03  =  Cu20  +  S^a^  +  2C02. 
Cu20  is  precipitated  in  minute  octahedral'  crystals   when  solution  of 
CuS04  mixed  with  glucose  is  boiled  with  excess  of  potash. 

Cuprous  oxide  is  a  feeble  base,  but  its  salts  are  not  easily  obtained 
by  direct  action  of  acids,  for  these  generally  decompose  it  into  metallic 
copper  and  cupric  oxide,  yielding  cupric  salts.  In  the  moist  state  it  is 
slowly  oxidised  by  the  air.  Ammonia  dissolves  cuprous  oxide,  forming 
a  solution  which  is  perfectly  colourless  until  it  is  allowed  to  come  into 
contact  with  air,  when  it  assumes  a  fine  blue  colour,  becoming  converted 
into  an  ammoniacal  solution  of  cupric  oxide.  If  the  blue  solution  be 
placed  in  a  stoppered  bottle  (quite  filled  with  it)  with  a  strip  of  clean 
copper,  it  will  gradually  become  colourless,  the  cupric  oxide  being  again 
reduced  to  cuprous  oxide,  a  portion  of  the  copper  being  dissolved. 
When  copper  filings  are  shaken  with  ammonia  in  a  bottle  of  air,  the 
same  blue  solution  is  obtained  (compare  p.  86).  If  the  blue  solution  be 
poured  into  a  large  quantity  of  water,  a  light  blue  precipitate  of  cupric 
hydroxide  is  obtained.  The  ammoniacal  solution  of  cupric  oxide  has  the 
unusual  property  of  dissolving  paper,  cotton,  tow,  and  other  varieties  of 
cellulose,  this  substance  being  reprecipitated  from  the  solution  on  adding 
an  acid. 

Cuprous  oxide,  added  to  glass,  imparts  to  it  a  fine  red  colour,  which 
is  turned  to  account  by  the  glass-maker. 

Quadrant  o.ride  of  copper,  Cu40,  has  been  obtained  in  combination  with  water, 
by  the  action  of  stannous  chloride  and  potash  upon  a  cupric  salt. 

"  Cuprom  hydride,  Cu2H2,  is  precipitated  when  cupric  sulphate  is  heated  with 
hypophosphorous  acid  ;  or  a  strong  solution  of  cupric  sulphate  may  be  strongly 
acidified  with  dilute  sulphuric  acid,  solution  of  sodium  hypophosphite  added,  and 
heated  till  a  brown  precipitate  forms  ;  this  is  the  hydride,  which  must  not  be 
further  heated,  as  it  is  decomposed  into  its  elements  at  60°  C.  HC1  dissolves  it 
easily,  with  brisk  effervescence  from  escape  of  H,  and  formation  of  a  colourless 
solution  of  cuprous  chloride,  Cu2H2+2HCl:=Cu2Cl2  +  2H2. 

Cuprous  hydrate,  4di2O.H20,  is  obtained  as  a  yellow  precipitate  when  a  solution 


484  COPPER   SULPHATE. 

of  a  cuprous  salt  is  added  to  excess  of  KOH.  If  air  be  excluded,  it  may  be  dried 
at  100°  C.  without  decomposition.  Air  oxidises  it  to  cupric  hydrate.  With  NH3 
it  behaves  like  cuprous  oxide. 

Cupric  hydroxide,  Cu(OH)2,  is  obtained  as  a  blue  precipitate  when  potash  or 
soda  is  added  to  a  cupric  salt.  When  boiled  in  the  liquid,  it  becomes  black  CuO, 
but  if  it  be  allowed  to  dry  over  sulphuric  acid,  it  may  be  heated  to  100°  C.  with- 
out decomposition.  Its  solubility  in  ammonia  and  the  properties  of  the  solution 
have  been  noticed  above.  In  the  presence  of  tartaric  acid,  sugar,  and  many  other 
organic  substances,  cupric  hydroxide  dissolves  in  caustic  potash  and  soda,  form- 
ing dark  blue  solutions.  The  paint  known  as  blue  rerditer  is  cupric  hydroxide 
obtained  by  decomposing  cupric  nitrate  with  calcium  hydroxide. 

Cupric  acid  is  believed  to  be  formed  when  metallic  copper  is  fused  with  nitre 
and  caustic  potash,  and  when  Cu(OH)a  is  digested  with  H202.  The  mass  from 
the  former  reaction  yields  a  blue  solution  containing  K2CuO4  in  water,  which 
is  very  easily  decomposed  with  evolution  of  oxygen  and  precipitation  of  cupric 
oxide.  By  adding  KOH  and  Br  to  a  solution  containing  copper  a  black  precipitate, 
believed  to  be  Cu02,  is  formed  even  in  very  dilute  solutions.  The  existence  of  an 
unstable  oxide  of  copper,  containing  more  than  one  atom  of  oxygen,  is  also  rendered 
probable  by  the  circumstance  that  oxide  of  copper  acts  like  manganese  dioxide 
in  facilitating  the  disengagement  of  oxygen  from  potassium  chlorate  by  heat 
(page  41). 

Cuprous  nitride,  Cu6N2.  is  formed  by  passing  ammonia  over  precipitated  CuO  at 
250°  C.  It  is  a  dark  green  powder  which  decomposes  at  a  high  temperature, 
evolving  heat. 

Cupric  nit  rate,  Cu(N03)2.3Aq,  crystallises  in  blue  prisms  from  a  solution  of  copper 
in  nitric  acid.  It  is  deliquescent  and  soluble  in  water  and  alcohol.  When  heated 
to  65°  C.,  it  becomes  a  green  baalc  nitrate,  Cu(N03)2.3Cu(OH)2.  Cupric  nitrate  is 
used  as  an  oxidising-agent  in  dyeing  and  calico-printing.  Cupric  ammonio-nitrate, 
Cu(N03)2.4NH3,  is  deposited  in  dark  blue  crystals  from  a  mixture  of  cupric  nitrate 
with  excess  of  ammonia. 

281.  Cupric  sulphate. — The  beautiful  prismatic  crystals  known  as 
blue  vitriol,  blue  stone,  blue  copperas,  or  sulphate  of  copper,  have  been 
already  mentioned  as  formed  from  the  residue  in  the  preparation  of 
S02  (p.  218),  by  dissolving  copper  in  oil  of  vitriol,  a  process  occasionally 
used  for  the  manufacture  of  this  salt. 

The  sulphate  of  copper  is  also  manufactured  by  roasting  copper 
pyrites  (Cu2Fe2S4)  with  free  access  of  air,  when  it  becomes  partly 
converted  into  a  mixture  of  cupric  sulphate  with  ferrous  sulphate ; 
Cu2Fe2S4  +  016=2FeS04  +  2CuS04.  The  ferrous  sulphate,  however,  is 
decomposed  by  the  heat,  leaving  ferric  oxide  (see  p.  234).  When 
the  roasted  mass  is  treated  with  water,  the  ferric  oxide  is  left  undis- 
solved,  but  the  cupric  sulphate,  which  withstands  a  higher  temperature 
than  ferrous  sulphate  does,  enters  into  solution,  and  may  be  obtained  in 
crystals  by  evaporation. 

Since  ferrous  sulphate  and  cupric  sulphate  are  isomorphous,  they 
crystallise  together  (v.i.),  and  can  be  separated  only  by  converting  the 
ferrous  into  ferric  sulphate  by  an  oxidising-agent  such  as  nitric  acid. 

The  crystals,  as  they  are  found  in  commerce,  are  usually  opaque,  but 
if  they  are  dissolved  in  hot  water  and  allowed  to  crystallise  slowly,  they 
become  perfectly  transparent,  and  have  then  the  composition  expressed 
by  the  formula  CuS04.5H20  (sp.  gr.  2.28).  If  the  crystals  be  heated  to 
the  temperature  of  boiling  water,  they  lose  four-fifths  of  their  water,  and 
crumble  down  to  a  greyish-white  powder,  which  has  the  composition 
CuS04.H.,0,  and  if  this  be  moistened  with  water,  it  becomes  very  hot, 
and  resumes  its  original  blue  colour.  The  whitish  opacity  of  the 
ordinary  crystals  of  blue  stone  is  due  to  the  absence  of  a  portion  of  the 
water  of  crystallisation.  The  fifth  molecule  of  water  can  be  expelled 


CUPPJC   CHLORIDE.  485 

only  at  a  temperature  of  nearly  200°  0.,  and  is  therefore  generally 
called  water  of  constitution  (see  p.  53),  the  formula  of  the  crystals 
being  then  written  CuS04.H20.4Aq.  The  crystals  dissolve  in  2.5  parts 
of  cold  and  0.5  part  of  boiling  water.  The  solution  reddens  litmus. 

The  sulphate  of  copper  is  largely  employed  by  the  dyer  and  calico- 
printer,  and  in  the  manufacture  of  pigments.  It  is  also  occasionally 
used  in  medicine,  in  the  electrotype  process,  and  in  galvanic  batteries. 
In  agriculture  it  is  found  useful  as  a  preservative,  wheat  which  is  to  be 
sown  being  steeped  in  a  solution  of  it  to  protect  the  grain  from  the 
attack  of  smut. 

When  ammonia  is  added  to  solution  of  cupric  sulphate,  a  basic  sulphate  is  first 
precipitated,  which  is  dissolved  by  an  excess  of  ammonia  to  a  dark  blue  liquid.  On 
allowing  this  to  evaporate,  dark  blue  crystals  of  aniinonio-cupric  sulphate, 
CuS04.4NH3.H20,  are  deposited.  They  lose  their  ammonia  when  exposed  to  the 
air. 

A  tattle  cupric  sulphate,  CuS04.3Cu(OH).2.Aq,  is  found  as  brocliantite. 
Sulphate  of  copper  cannot  easily  be  separated  by  crystallisation  from  the 
sulphates  of  iron,  zinc,  and  magnesium,  because  it  forms  double  salts  with  them, 
which  contain,  like  those  sulphates,  seven  molecules  of  water,  and  are  isomorphous 
with  magnesium  sulphate  (unless  the  CuS04  is  the  predominant  constituent,  when 
the  salts  contain  five  molecules  of  water  and  are  isomorphous  with  cupric  sulphate). 
An  instance  of  this  is  seen  in  the  Mack  vitriol  obtained  from  the  mother-liquor  of 
the  sulphate  of  copper  at  Mansfield,  and  forming  bluish-black  crystals  isomorphous 
with  green  vitriol,  FeS04,7H20.  The  formula  of  black  vitriol  may  be  written 
[CuMgFeMnCoNi]S04.7H20,  the  six  isomorphous  metals  being  interchangeable 
without  altering  the  general  character  of  the  salt. 

Cupric  arsenlte  (Sclieelds  greeti),  CuHAs03,  has  been  noticed  at  p.  270.  It  is 
a  yellowish-green  powder,  insoluble  in  water,  but  easily  soluble  in  acids  and  alkalies. 
Its  solution  in  potash  has  a  dark  blue  colour,  and  deposits  cuprous  oxide  when 
boiled,  potassium  arsenate  being  produced.  Emerald  green  has  also  been  noticed 
(p.  271). 

The  basic  enpric  phosphates  compose  the  minerals  tagllite  and  libethenite. 
The  basic   cirpric  carbonate*  have  been  noticed  as  forming  the  very  beautiful 
mineral  blue  malacJiite,  a~urite,  or  cliewylite,  and  green  malachite. 

Mineral  green,  CuC03.Cu(OH).2,  has  the  same  composition  as  green  malachite, 
and  is  prepared  by  mixing  hot  solutions  of  sodium  carbonate  and  cupric  sulphate. 
When  boiled  in  the  liquid,  it  is  gradually  converted  into  black  oxide  of  copper. 
The  green  deposit  formed  on  old  copper  by  exposure  to  air  has  the  same  compo- 
sition. 

The  blue  precipitate  produced  in  cupric  solutions  by  alkaline  carbonates  in  the 
cold  is  CuC03.Cu(OH).2.Aq. 

Cupric  silicates  are  found  in  the  minerals  dioptase,  or  emerald  copper,  and  chry- 
socolla,  CuH2Si04.HaO. 

282.  Chlorides  of  copper. — The  chloride  of  copper  (cupric chloride), 
CuCl,,  is  produced  by  the  direct  union  of  its  elements,  when  it  forms  a 
brown  mass,  which  fuses  easily,  and  is  decomposed  into  chlorine  and 
cuprous  chloride,  the  latter  being  afterwards  converted  into  vapour. 
When  dissolved  in  water,  it  gives  a  solution  which  is  green  when  con- 
centrated, and  becomes  blue  on  dilution.  The  hydrated  cupric  chloride 
is  readily  prepared  by  dissolving  the  black  oxide  in  hot  hydrochloric 
acid,  and  allowing  the  solution  to  crystallise ;  it  forms  green  needle-like 
crystals  (CuCl,.2H,0)  which  become  blue  when  dried  in  vacua.  A 
solution  of  chloride  of  copper  in  alcohol  burns  with  a  splendid  green 
flame,  and  the  chloride  imparts  a  similar  colour  to  a  gas  flame. 

Oxychloride  of  copper   (Cud2.3CuO.4H,O)  is  found  at  Atacama  in 
prismatic  crystals,  and  is  called  atacamite.     The  paint  Brunswick  green 
has  the  same  composition,  and   is  made   by  moistening   copper  wit] 
solution  of  hydrochloric  acid  or  sal-ammoniac,  and  exposing  it  to  the 


486  CUPROUS  CHLORIDE. 

air  in  order  that  it  may  absorb  oxygen;  Cu4-j- 2HC1  + 3H.,0  +  O4  = 
CuCl2.3Cu0.4H20.  It  is  also  made  by  boiling  cupric  sulphate  with 
chloride  of  lime.  The  Brunswick  green  of  the  shops  frequently  consists 
of  a  mixture  of  Prussian  blue,  chromate  of  lead,  and  barium  sulphate. 

Subchloride  of  copper  (cuprous  chloride),  Cu,Clv,  is  formed  as  a 
sublimate  when  copper  is  heated  in  HC1  gas.  It  is  also  produced  when 
fine  copper  turnings  are  shaken  with  strong  hydrochloric  acid  in  a 
bottle  of  air;  Cu2  +  2HCl  +  0  =  Cu2Cl2  +  H20.  The  cuprous  chloride 
dissolves  in  the  excess  of  hydrochloric  acid,  forming  a  brown  solution, 
from  which  water  precipitates  it  white,  for  this  is  one  of  the  few  chlorides 
insoluble  in  water.  When  exposed  to  light,  it  assumes  a  purplish -grey 
tint.  A  copper  plate  dipped  into  a  strong  neutral  solution  of  cupric 
chloride  acquires  a  thin  coating  of  cuprous  chloride  upon  which  photo- 
graphs may  be  taken.  Cuprous  chloride  may  be  prepared  as  described 
on  p.  140. 

If  the  solution  in  HC1  be  moderately  diluted  and  set  aside,  it  deposits 
tetrahedral  crystals  of  cuprous  chloride.  Ammonia  (free  from  air)  dissolves 
cuprous  chloride  to  a  colourless  liquid  which  becomes  dark  blue  by  contact  with  air, 
absorbing  oxygen  ;  it  is  used  as  a  test  for  acetylene  (p.  140).  The  solution  may  be 
preserved  in  a  colourless  state  by  keeping  it  in  a  well- stoppered  bottle,  quite  full, 
with  strips  of  clean  copper.  When  copper,  in  a  finely  divided  state,  is  boiled  with 
solution  of  ammonium  chloride,  the  solution  deposits  colourless  crystals  of  the  salt, 
Cu2Cl2(NH3)2.  If  the  solution  of  this  salt  be  exposed  to  the  air,  blue  crystals  are 
deposited,  having  the  formula  Cu2Cl.2.CuCl2.4NH3.H20,  and  on  further  exposure,  a 
compound  of  this  last  salt  with  ammonium  chloride  ia  deposited.  The  solution  of 
cuprous  chloride  in  hydrochloric  acid  is  employed  for  absorbing  carbonic  oxide  in 
the  analysis  of  gaseous  mixtures.  When  this  solution  is  exposed  to  air  it  absorbs 
oxygen,  and  deposits  cupric  oxychloride.  A  strong  solution  of  ammonium  or 
sodium  or  potassium  chloride  readily  dissolves  the  cuprous  chloride,  even  in  the 
cold,  forming  soluble  double  chlorides,  such  as  Cu2Cl24KCl.  The  solution  in 
potassium  chloride  does  not  absorb  oxygen  quite  so  easily  as  that  in  ammonium 
chloride. 

(htprvtu  iodide,  Cu2I2,  is  a  very  insoluble  white  precipitate  formed  when  a 
mixture  of  cupric  and  ferrous  sulphates  is  added  to  the  solution  of  an  iodide  ; 
2CuS04  +  2FeS04  +  2KI  =  Cu2I2  +  Fe2(S04)3  +  K2S04.  It  is  also  precipitated, 
together  with  iodine,  when  cupric  sulphate  is  added  to  an  iodide  ;  2CuS04  +  4KI  = 
Cu2I2  +  I2  +  2K2S04. 

283.  Sulphides  of  copper. — Copper  has  a  very  marked  attraction  for 
sulphur,  even  at  the  ordinary  temperature.  A  bright  surface  of  copper 
soon  becomes  tarnished  by  contact  with  sulphur,  and  hydrosulphuric  acid 
blackens  the  metal.  Finely  divided  copper  and  sulphur  combine  slowly 
at  the  ordinary  temperature,  and,  when  heated  together,  they  combine 
with  combustion.  A  thick  copper  wire  burns  easily  in  vapour  of  sulphur 
(p.  212).  Copper  is  even  partly  converted  into  sulphides  when  boiled 
with  sulphuric  acid,  as  in  the  preparation  of  sulphurous  acid  gas.  This 
great  attraction  of  copper  for  sulphur  is  taken  advantage  of  in  the  pro- 
cess of  kernel  roasting  for  extracting  the  copper  from  pyrites  containing 
as  little  as  i  per  cent,  of  the  metal.  The  pyrites  is  roasted  in  large 
heaps  (p.  209)  for  several  weeks,  when  a  great  part  of  the  iron  is  con- 
verted into  peroxide,  and  the  copper  remains  combined  with  sulphur, 
forming  a  hard  kernel  in  the  centre  of  the  lumps  of  ore.  This  kernel 
contains  about  5  per  cent,  of  copper,  and  can  be  smelted  with  economy. 
Children  are  employed  to  detach  the  kernel  from  the  shell,  which  con- 
sists of  ferric  oxide  mixed  with  a  little  cupric  sulphate,  which  is  washed 
out  with  water. 


CUPRIC   SULPHIDE.  487 

The  subsulphide  of  copper,  or  cuprous  sulphide  (Cu2S),  has  been  men- 
tioned among  the  ores  of  copper  and  among  the  furnace  products  in 
smelting,  when  it  is  sometimes  obtained  in  octahedral  crystals.  It  is 
formed  when  H2S  is  passed  over  red-hot  CuO,  and  when  coal-gas  is 
passed  over  red-hot  CuS.  It  is  not  attacked  by  hydrochloric  acid,  but 
nitric  acid  dissolves  it  readily.  Copper  pyrites  is  believed  to  contain 
the  copper  in  the  form  of  cuprous  sulphide,  its  true  formula  being 
Cu2S.Fe2S3  ;*  for  if  the  copper  be  present  as  cupric  sulphide,  CuS,  the 
iron  must  be  present  as  ferrous  sulphide,  and  the  mineral  would  have 
the  formula  CuS.FeS.  Now,  FeS  is  easily  attacked  by  dilute  sulphuric 
or  hydrochloric  acid,  which  is  not  the  case  with  copper  pyrites.  Nitric 
acid,  however,  attacks  it  violently. 

Sulphide  of  copper,  or  cupric  sulphide  (CuS),  occurs  in  nature  as  indigo 
copper  or  blue  copper,  and  may  be  obtained  as  a  black  precipitate  by  the 
action  of  hydrosulphuric  acid  upon  solution  of  cupric  sulphate.  When 
this  precipitate  is  boiled  with  sulphur  and  ammonium  sulphide,  it  is 
dissolved  in  small  quantity,  and  the  solution  on  cooling  deposits  fine 
scarlet  needles  containing  a  higher  sulphide  of  copper  combined  with 
sulphide  of  ammonium.  When  copper  and  sulphur  are  heated  together 
in  atomic  proportions  to  a  temperature  below  the  boiling-point  of  sulphur 
(448°  C.),  CuS  is  produced;  but  at  a  higher  temperature  this  is  con- 
verted into  Cu0S.  Pentasulphide  of  copper  (CuS5)  is  obtained  by  decom- 
posing cupric  sulphate  with  potassium  pentasulphide  ;  it  forms  a  black 
precipitate  distinguished  from  the  other  sulphides  of  copper  by  its  solu- 
bility in  potassium  carbonate.  The  sulphides  of  copper,  when  exposed 
to  air  in  the  presence  of  water,  are  slowly  oxidised  and  converted  into 
cupric  sulphate,  which  is  dissolved  by  the  water.  It  appears  to  be  in 
this  way  that  the  blue  ivater  of  the  copper  mines  is  formed.  By 
thoroughly  washing  CuS  with  dil.  H2S04  and  then  with  water,  it  can  be 
made  to  pass  into  solution,  but  it  is  immediately  precipitated  by  saline 
matter. 

Phosphide  of  copper,  cupric  phosphide  (Cu3P2),  obtained  as  a  black  powder  by 
boiling  solution  of  cupric  sulphate  with  phosphorus,  or  by  passing  PH3  into  a 
solution  of  CuS04,  has  been  already  mentioned  as  a  convenient  source  of  phosphine. 
Another  phosphide,  obtained  by  passing  vapour  of  phosphorus  over  finely  divided 
copper  at  a  high  temperature,  is  employed  in  Abel's  composition  for  magneto- 
electric  fuses,  in  conjunction  with  Cu2S  and  KC103.  Phosphide  of  copper  em- 
ployed for  toughening  commercial  copper  is  made  by  running  melted  copper  into 
a  conical  iron  crucible  lined  with  loam,  at  the  bottom  of  which  are  placed  sticks 
of  phosphorus  which  have  been  coated  with  copper  by  soaking  them  in  cold  solu- 
tion of  CuS04. 

Silicon  may  be  made  to  unite  with  copper  by  strongly  heating  finely  divided 
copper  with  silica  and  charcoal.  A  bronze-like  mass  is  thus  obtained  containing 
about  5  per  cent.  Si.  It  is  said  to  rival  iron  in  ductility  and  tenacity,  and  fuses 
at  about  the  same  temperature  as  bronze. 

SILVER. 

Ag'  =  107.1  parts  by  weight. 

284.  In  silver  we  meet  with  the  first  metal  hitherto  considered  which 
is  not  capable  of  undergoing  oxidation  in  the  air,  and  this,  in  conjunc- 
tion with  its  beautiful  appearance,  occasions  its  manifold  ornamental 

*  Crystals  of  Cu2S.Fe2Ss  are  obtained  by  shaking  faintly  aininoniacal  Cu2Cl2  solution  with 


488  EXTRACTION   OF  SILVEE. 

uses,  which  are  much  favoured  also  by  the  great  malleability  and 
ductility  of  this  metal  (in  which  it  ranks  only  second  to  gold),  for 
the  former  property  enables  it  to  be  rolled  out  into  thin  plates  or 
leaves,  so  that  a  small  quantity  of  silver  suffices  to  cover  a  large 
surface,  whilst  its  ductility  permits  the  wire-drawer  to  produce  that 
extremely  thin  silver  wire  which  is  employed  in  the  manufacture  of 
silver  lace. 

Silver,  although  pretty  widely  diffused,  is  found  in  comparatively 
small  quantity,  and  hence  it  bears  a  high  value,  which  adapts  it  for  a 
medium  of  currency. 

As  might  be  expected  from  its  want  of  direct  attraction  for  oxygen, 
silver  is  found  frequently  in  the  metallic  or  native  state,  crystallised  in 
cubes  or  octahedra,  which  are  sometimes  aggregated  together,  as  in  the 
silver-mines  of  Potosi,  into  arborescent  or  dendritic  forms  ;  it  generally 
contains  copper  and  gold,  and  sometimes  mercury.  Silver  is  more 
frequently  met  with,  however,  in  combination  with  sulphur,  forming 
the  sulphide  of  silver  (Ag,S),  which  is  generally  associated  with  large 
quantities  of  the  sulphides  of  lead,  antimony,  and  iron.  The  largest 
supplies  of  silver  are  obtained  from  the  United  States,  Mexican,  Peruvian, 
and  Australian  (Broken  Hill)  mines,  but  the  quantity  furnished  by 
Saxony  and  Hungary  is  by  no  means  insignificant.  Silver  chloride 
is  found  in  considerable  quantity  in  the  spongy  deposits  of  silica  round 
the  Great  Salt  Lake  in  Utah. 

The  process  by  which  silver  is  extracted  from  galena  has  been  already 
described  under  the  history  of  lead.  Silver  may  be  separated  from 
copper,  in  the  ores  of  which  (particularly  grey  copper  ore)  it  frequently 
exists  to  a  considerable  extent,  by  taking  advantage  of  the  facility  with 
which  the  former  metal  is  dissolved  by  melted  lead.  The  process  of 
liquation,  as  it  is  termed,  consists  in  fusing  the  argentiferous  copper 
with  about  thrice  its  weight  of  lead,  arid  casting  the  alloy  thus  obtained 
into  cakes  or  discs,  which  are  afterwards  gradually  heated  upon  a 
hearth,  so  contrived  that  the  lead,  which  melts  much  more  easily  than 
the  copper,  may  flow  off  in  the  liquid  state,  carrying  with  it.  in  the 
form  of  an  alloy,  the  silver  which  was  associated  with  the  copper, 
leaving  this  last  metal  in  porous  masses,  having  the  form  of  the  original 
discs,  upon  the  hearth.  The  lead  and  silver  are  separated  by  the  pro- 
cess of  cupellation  (p.  464). 

In  the  extraction  of  silver  from  its  ores  the  method  adopted  depends 
upon  the  conditions  at  the  locality  where  the  ore  is  mined.  Thus, 
where  fuel  is  available  it  is  customary  to  smelt  the  ore  either  with  lead 
ores  or  copper  ores,  the  noble  metal  being  eventually  obtained  either 
in  solution  in  lead  or  in  a  copper  matte.  In  the  latter  case  the  silver 
may  be  extracted  by  taking  advantage  of  the  fact  that  by  carefully 
roasting  a  mixture  of  the  sulphides  of  copper  and  silver  the  copper  may 
be  completely  oxidised  to  oxide  and  the  silver  to  sulphate,  so  that  when 
the  roasted  mass  is  leached  with  water,  silver  sulphate  passes  into  solu- 
tion ;  the  metal  is  precipitated  from  this  by  introducing  metallic 
copper,  and  the  precipitate  is  refined  by  roasting  it  to  oxidise  the 
impurities,  and  fusing  it.  Dissolution  in  lead  followed  by  cupellation 
frequently  forms  a  convenient  method  for  refining  silver,  but  electro- 
lytic refining  of  the  metal  on  the  same  lines  as  those  adopted  for  copper 
(p.  478)  is  becoming  general ;  the  electrolyte  is  a  dilute  solution  of  silver 


THE  AMALGAMATION  PROCESS. 


489 


nitrate,  the  crude  silver  cast  into  plates  forms  the  anode,  while  sheets 
of  pure  silver  constitute  the  cathodes. 

Where  fuel  is  scarce  an  amalgamation  process  is  adopted.  That  in 
vogue  in  Mexico  is  complicated  in  its  chemical  details,  but  primarily 
depends  upon  the  reduction  of  the  silver  from  the  form  of  chloride  by 
means  of  mercury  (iron  being  sometimes  substituted  as  a  reducing- 
agent),  AgCl  +  Hg  =  HgCl  +  Ag,  and  the  dissolution  of  the  reduced 
silver  in  mercury,  which  is  subsequently  distilled,  leaving  the  silver 
to  be  refined  as  described  above. 

The  crushed  ore  is  made  into  a  mud  with  water,  and  mixed  with  common  salt, 
mercury,  and  roasted  copper  pyrites  (magistral?),  the  mixing  being  generally  per- 
formed by  the  feet  of  mules.  A  hot  solution  of  CuS04  and  more  mercury  are  then 
added,  and  after  these  have  been  well  mixed  with  the  charge  the  whole  is  stirred 
up  with  water,  when  the  heavy  silver  amalgam  sinks  to  the  bottom.  It  is  drawn 
off  and  filtered  through  canvas,  in  order  to  separate  the  semi-solid  amalgam  from 
the  excess  of  mercury.  The  amalgam  is  then  distilled,  the  arrangement  shown  in 
Fig.  240  being  often  employed  ;  in  this  the  amalgam  is  spread  on  iron  trays 
.arranged  on  an  upright  beneath  an  iron  bell,  the  lower  part  of  which  stands  in 
water,  whilst  the  upper  portion  is  surrounded  by  burning  fuel,  the  heat  of  which 
distils  the  mercury  into  the  water. 

It  would  appear  that  in  this  process  the  CuS04 
•(which  is  added  both  as  such  and  in  the  form  of 
magistral)  reacts  with  the  common  salt,  yielding 
cupric  chloride.  The  CuCl2  then  reacts  with  the 
silver  sulphide  of  the  ore.  yielding  silver  chloride, 
which  is  dissolved  by  the  solution  of  salt  and  reduced 
by  the  mercury.  The  excess  of  mercury  then 
.amalgamates  with  the  silver. 

In  another  class  of  processes  for  extracting 
silver  from  its  ores,  these  are  roasted  with 
common  salt,  whereby  the  silver  sulphide  is 
first  converted  into  sulphate  by  oxidation, 
and  then  into  chloride  by  double  decomposi- 
tion with  the  NaCJ.  The  silver  chloride  is 
•dissolved  out  of  the  mass  by  means  of  a  strong 
solution  of  common  salt,  from  which  the  silver 
is  afterwards  precipitated  in  the  metallic  state 

by  copper,  or  as  silver  iodide,  the  silver  iodide  being  reduced  by  zinc, 
and  the  zinc  iodide  used  to  precipitate  a  fresh  portion  of  silver. 
Sodium  thiosulphate  is  also  employed  to  dissolve  out  the  silver  chloride, 
•and  the  solution  precipitated  by  sodium  sulphide,  the  silver  sulphide 
thus  obtained  being  roasted  to  remove  the  sulphur  and  leave  metallic 
silver. 

Although  silver  is  capable  of  resisting  the  oxidising  action  of  the 
atmosphere,  it  is  liable  to  considerable  loss  by  wear  and  tear,  in  con- 
sequence of  its  softness,  and  is  therefore  always  hardened,  for  useful 
purposes,  by  the  addition  of  a  small  proportion  of  copper.  The  standard 
silver  employed  for  coinage  and  for  most  articles  of  silver  plate  in  this 
country,  contains,  in  1000  parts,  925  of  silver  and  75  of  copper,  whilst 
that  used  in  France  contains  900  of  silver  and  100  of  copper.  English 
standard  silver  is  said  to  have  a  fineness  of  925,  and  French,  of  900. 

Standard  silver,  for  coining  and  other  purposes,  is  whitened  by  being 
heated  in  air  and  immersed  in  diluted  sulphuric  acid,  which  dissolves 
out  the  oxide  of  copper,  leaving  a  superficial  film  of  nearly  pure  silver. 
Dead  or  frosted  silver  is  produced  in  this  manner.  Oxidised  silver  is 


Fig.  240. 


49°  ELECTRO-PLATING. 

covered  with  a  thin  film  of  sulphide  by  immersion  in  a  solution  obtained 
by  boiling  sulphur  with  potash. 

The  solder  employed  in  working  silver  consists  of  5  parts  of  silver, 
2  of  zinc,  and  6  of  brass. 

Plated  articles  are  manufactured  from  copper  or  one  of  its  alloys, 
which  has  been  united,  by  rolling,  with  a  thin  plate  of  silver,  the 
adhesion  of  the  latter  being  promoted  by  first  washing  the  surface  of 
the  copper  with  a  solution  of  silver  nitrate,  when  a  film  of  this  metal  is 
deposited  upon  its  surface,  the  copper  taking  the  place  of  the  silver  in 
the  solution. 

Electro-plating  consists  in  covering  the  surface  of  baser  metals  with  a 
coating  of  silver,  by  connecting  them  with  the  negative  (or  zinc)  pole  of 
the  galvanic  battery,  and  immersing  them  in  a  solution  made  by  dis- 
solving silver  cyanide  in  potassium  cyanide,*  the  positive  (copper  or 
platinum)  pole  being  connected  with  a  silver  plate,  also  immersed  in  the 
solution  ;  the  current  gradually  decomposes  the  silver  cyanide,  and 
this  metal  is  of  course  (see  p.  324)  deposited  upon  the  object  connected 
with  the  negative  electrode,  whilst  the  cyanogen  liberated  at  the  silver 
plate  attacks  the  silver,  so  that  the  solution  is  always  maintained  at  the 
same  strength,  the  quantity  of  silver  dissolved  at  this  electrode  being 
precisely  equal  to  that  deposited  at  the  opposite  one. 

Brass  and  copper  are  sometimes  silvered  by  rubbing  them  with  a 
mixture  of  10  parts  of  silver  chloride  with  i  of  corrosive  sublimate 
(mercuric  chloride)  and  100  of  bitartrate  of  potash.  The  silver  and 
mercury  are  both  reduced  to  the  metallic  state  by  the  baser  metal,  and 
an  amalgam  of  silver  is  formed,  which  readily  coats  the  surface.  The 
acidity  of  the  bitartrate  of  potash  promotes  the  reduction.  The  surface 
to  be  silvered  should  always  be  cleansed  from  oxide  by  momentary 
immersion  in  nitric  acid,  and  washed  with  water.  For  dry  silvering,  an 
amalgam  of  silver  and  mercury  is  applied  to  the  clean  surface,  and  the 
mercury  is  afterwards  expelled  by  heat. 

Silvering  upon  glass  is  effected  by  means  of  certain  organic  substances 
which  are  capable  of  precipitating  metallic  silver  from  its  solutions. 
Looking-glasses  have  been  made  by  pouring  upon  the  surface  of  plates 
of  glass  a  solution  containing  silver  tartrate  and  ammonium  tartrate. 
On  heating  the  glass  plates  to  a  certain  temperature  the  tartrate  is 
reduced,  and  the  metallic  silver  is  deposited  in  a  closely  adhering  film. 
Glass  globes  and  vases  are  silvered  internally  by  a  process  which  is 
exactly  similar  in  principle.  The  coating  is  rendered  more  adherent  by 
sprinkling  it  with  a  weak  solution  of  potassio-mercuric  cyanide,  which 
amalgamates  the  silver. 

Small  surfaces  of  glass  for  optical  purposes  may  be  silvered  in  the  following 
manner  :  Dissolve  one  gram  of  AgN03  in  20  c.c.  of  distilled  water,  and  add  weak 
NH3  carefully  until  the  precipitate  is  almost  entirely  dissolved.  Filter  the  solution 
and  make  it  up  to  100  c.c.  with  distilled  water.  Then  dissolve  2  grains  of  AgN03. 
in  a  little  distflled  water,  and  add  it  to  a  litre  of  boiling  distilled  water.  Add  1.66 
gram  of  Rochelle  salt  (tartrate  of  potassium  and  sodium),  and  boil  till  the  pre- 
cipitated silver  tartrate  becomes  grey  ;  filter  while  hot.  Clean  the  glass  to  be 
silvered  very  thoroughly  with  HNO3r  distilled  water,  KOH,  distilled  water,  alcohol, 
distilled  water  ;  place  it  in  a  clean  glass  or  porcelain  vessel,  with  the  side  to  be 
silvered  uppermost.  Mix  equal  measures  of  the  two  silver  solutions  (cold),  and 

*  A  solution  of  potassium  cyanide  in  10  parts  of  water,  with  50  grains  of  silver  chloride 
dissolved  in  each  pint  of  the  liquid,  will  answer  the  pujrpose. 


PROPEETIES   OF  SILVER. 


49 1 


pour  the  mixture  in  so  as  to  cover  the  glass,  which  will  be  silvered  in  about  an 
hour.     After  washing,  it  may  be  allowed  to  dry,  and  varnished. 

Very  good  mirrors  may  be  made  by  adding  ammonia  to  weak  silver  nitrate  till 
the  precipitate  just  redissolves,  then  a  little  potash,  then  ammonia  till  the  liquid 
is  clear,  and  then  a  very  little  glycerine.  If  a  watch-glass  be  floated  on  this  liquid, 
and  a  gentle  heat  applied,  a  good  mirror  will  be  formed  in  a  few  minutes. 

Pure  silver  is  easily  obtained  from  standard  silver  by  dissolving  it  in 
nitric  acid,  with  the  aid  of  heat,  diluting  the  solution  with  water,  adding 
solution  of  common  salt  as  long  as  it  produces  any  fresh  precipitate  of 
silver  chloride,  washing  the  precipitate  by  decantation  as  long  as  the 
washings  give  a  blue  tinge  with  ammonia,  and  fusing  the  dried  precipi- 
tate with  half  its  weight  of  dried  sodium  carbonate  in  a  brisk  fire,  when 
a  button  of  silver  will  be  found  on  breaking  the  crucible — 
'  2AgCl  +  Xa2C03  =  Ag2  +  2NaCl  +  0  +  C02. 

The  pure  silver  employed  by  Stas  in  his  researches  on  atomic  weights 
was  prepared  by  distilling  the  metal. 

When  fused  in  air,  silver  occludes  oxygen,  a  portion  of  which  it 
evolves  during  solidification,  causing  sprouting  on  the  surface  of  the 
partly  solidified  metal,  and  sometimes  projection  of  portions  of  the 
mass.  After  cooling,  it  still  retains  oxygen,  which  can  only  be  ex- 
pelled by  heating  to  about  600°  C.  in  a  vacuum.  This  may  amount  to 
0.025  per  cent,  by  weight,  and  has  to  be  taken  into  consideration  in 
determining  atomic  weights  in  terms  of  silver.* 

285.  Properties  of  silver. — The  brilliant  whiteness  of  silver  distin- 
guishes it  from  all  other  metals.  It  is  lighter  than  lead,  its  specific 
gravity  being  10.53  ;  harder  than  gold,  but  not  so  hard  as  copper;  more 
malleable  and  ductile  than  any  other  metal  except  gold,  which  it  sur- 
passes in  tenacity.  It  fuses  at  a  somewhat  lower  temperature  than 
gold  or  copper  (960°  C.),  and  is  the  best  conductor  of  heat  and  elec- 
tricity. It  is  comparatively  easily  distilled.  It  is  not  oxidised  by  dry 
or  moist  air,  either  at  the  ordinary  or  at  high  temperatures,  but  is  oxi- 
dised by  ozone,  and  tarnished  by  air  containing  sulphuretted  hydrogen, 
from  the  production  of  silver  sulphide,  which  is  easily  removed  by  solu- 
tion of  potassium  cyanide.  Pure  H2S  does  not  attack  silver.  It  is 
unaffected  by  dilute  acids,  with  the  exception  of  nitric,  and  in  this  case 
the  presence  of  nitrous  acid  is  essential ;  but  hot  concentrated  sulphuric 
acid  converts  it  into  silver  sulphate,  and  when  boiled  with  strong  hydro- 
chloric acid  it  dissolves  to  a  slight  extent  in  the  form  of  silver  chloride, 
which  is  precipitated  on  adding  water.  Strong  hydriodic  acid  dissolves 
silver,  evolving  hydrogen ;  silver  iodide  is  precipitated  on  addition  of 
water.  The  alkali  hydroxides  do  not  act  on  silver  to  the  same  extent 
as  on  platinum  when  fused  with  it ;  hence  silver  basins  and  crucibles 
are  much  used  in  the  laboratory. 

Colloidal  silver  appears  to  be  formed  by  the  action  of  certain  reducing-agents 
on  a  solution  of  silver  nitrate,  and  has  lately  been  applied  in  medicine.  When  a 
solution  of  ferrous  citrate  is  added  to  one  of  silver  nitrate,  a  red  solution  which 
deposits  a  lilac  precipitate  is  obtained  ;  this  precipitate  is  washed  with  ammonium 
nitrate  solution,  and  is  then  found  to  contain  over  97  per  cent,  of  silver,  and  to  be 
soluble  in  water  to  a  red  solution.  By  similar  methods  an  insoluble  «ll<>trn/nr 
xilw  and  an  insoluble  goM-lllte  allotroph'  *ilrer  have  been  obtained.  The  physic 
properties  of  silver  deposited  as  a  mirror  seem  to  show  that  it  is  colloidal  silver. 

*  At  300°  C.  and  15  atmospheres  pressure  Ag  absorbs  as  much  oxygen  as  corresponds 
with  the  formula  Ag4O. 


492  LUNAR   CAUSTIC. 

286.  Oxides  of  silver. — There  are  three  compounds  of  silver  with 
oxygen — the  suboxide,  Ag40  ;  the  oxide  Ag20  ;  and  the  peroxide,  pro- 
bably Ag20.,,  which  is  not  known  in  the  pure  state.  The  oxide  alone 
has  any  practical  interest,  as  being  the  base  of  the  salts  of  silver. 

Silver  oxide  (Ag20)  is  obtained  as  a  brown  precipitate  when  solution 
of  silver  nitrate  is  decomposed  by  potash,  or,  better,  poured  into  an 
excess  of  lime-water.  "When  alcoholic  solutions  of  KOH  and  AgN03 
are  mixed  at  -  40°  C.  a  white  precipitate  of  silver  hydroxide,  AgOH,  is 
produced  ;  as  the  temperature  rises,  however,  it  becomes  dark  from  loss 
of  water  and  formation  of  Ag20.  The  oxide  is  a  powerful  base,  slightly 
soluble  in  water,  to  which  it  imparts  a  weak  alkaline  reaction.  A  tem- 
perature of  270°  C.  decomposes  it  into  its  elements.  It  acts  as  a 
powerful  oxidising-agent.  When  moist  freshly  precipitated  silver  oxide 
is  covered  with  a  strong  solution  of  ammonia,  and  allowed  to  stand  for 
some  hours,  it  becomes  black,  crystalline,  and  acquires  dangerously  ex- 
plosive properties.  The  composition  of  this  fulminating  silver  is  not 
accurately  known,  but  it  is  supposed  to  be  a  silver  nitride,  NAg3,  cor 
responding  in  composition  with  ammonia. 

Silrer  peroxide  is  a  black  precipitate  obtained  by  mixing  solutions  of  potassium 
persulphate  and  AgN03.  With  ammonium  persulphate  there  is  less  precipitate,  and 
if  NH3  be  present  there  is  a  violent  evolution  of  nitrogen,  the  silver  salt  acting 
catalytically  to  decompose  the  mixture  in  the  sense  of  the  equation  3(NH4).2S208 + 
8NH3  =  6(NH4)2S04  +  N2.  The  peroxide  is  also  deposited  on  the  anode  during  the 
electrolysis  of  silver  salts  as  black  octahedra  which  dissolve  in  HN03  to  a  deep 
brown  solution  of  strongly  oxidising  properties. 

Silver  nitrate  (AgN03),  or  lunar  caustic  (silver  being  distinguished  as 
luna  by  the  alchemists),  is  procured  by  dissolving  silver  in  nitric  acid,* 
with  the  aid  of  a  gentle  heat,  evaporating  the  solution  to  dryness,  and 
heating  the  residue  till  it  fuses,  in  order  to  expel  the  excess  of  acid.  It 
fuses  at  218°  C.  For  use  in  surgery,  the  fused  nitrate  is  poured  into 
cylindrical  moulds,  so  as  to  cast  it  into  thin  sticks  ;  but  for  chemical 
purposes  it  is  dissolved  in  water  and  crystallised,  when  it  forms  colour- 
less square  tables  (sp.  gr.  4.3),  easily  soluble  in  water  and  alcohol.  The 
action  of  nitrate  of  silver  as  a  caustic  depends  upon  the  facility  with 
which  it  parts  with  oxygen,  the  silver  being  reduced  to  the  metallic 
state,  and  the  oxygen  combining  with  the  elements  of  the  organic 
matter.  This  effect  is  very  much  promoted  by  exposure  to  sunlight  or 
diffused  daylight.  Pure  silver  nitrate  is  not  changed  by  exposure  to 
light,  but  if  organic  matter  be  present,  a  black  deposit,  containing 
finely  divided  silver,  is  produced.  Thus,  the  solution  of  silver  nitrate 
stains  the  fingers  black  when  exposed  to  light,  but  the  stain  may  be 
removed  by  potassium  cyanide  or,  more  safely,  by  tincture  of  iodine. 
If  solution  of  silver  nitrate  be  dropped  upon  paper  and  exposed  to 
light,  black  stains  will  be  produced,  and  the  paper  corroded.  Silver 
nitrate  is  a  frequent  constituent  of  marking-inks,  since  the  deposit  of 
metallic  silver  formed  on  exposure  to  light  is  not  removable  by  washing. 
The  linen  is  sometimes  mordanted  by  applying  a  solution  of  sodium  car- 
bonate before  the  marking-ink,  when  the  insoluble  silver  carbonate  is 
precipitated  in  the  fibre,  and  is  more  easily  blackened  than  the  nitrate, 
especially  if  a  hot  iron  is  applied.  Marking-inks  without  preparation, 
are  made  with  silver  nitrate  containing  an  excess  of  ammonia,  which 

*  For  3  ounces  of  silver,  take  if  fluid  ounce  of  strong  nitric  acid,  and  5  fluid  ounces  of 
water. 


SILVER    CHLORIDE.  493 

appropriates  the  nitric  acid,  and  hastens  the  blackening  on  exposure  to 
light  or  heat.  Hair-dyes  often  contain  AgN03.  The  important  use  of 
this  salt  in  photography  has  been  noticed  already  (p.  236). 

In  order  to  prepare  silver  nitrate  from  standard  silver  (containing  copper),  the 
metal  is  dissolved  in  moderately  strong  nitric  acid,  and  the  solution  evaporated  to 
dryness  in  a  porcelain  dish,  when  a  blue  residue  containing  the  nitrates  of  silver 
and  copper  is  obtained.  The  dish  is  now  moderately  heated  until  the  residue  has 
fused,  and  become  uniformly  black,  the  blue  copper  nitrate  being  decomposed 
and  leaving  black  copper  oxide,  at  a  temperature  which  is  insufficient  to  decom- 
pose the  silver  nitrate.  To  ascertain  when  all  the  copper  nitrate  is  decomposed, 
a  small  sample  is  removed  on  the  end  of  a  glass  rod,  dissolved  in  water,  filtered, 
and  tested  with  ammonia,  which  will  produce  a  blue  colour  if  any  copper  nitrate 
be  left.  The  residue  is  treated  with  hot  water,  the  solution  filtered  from  the 
copper  oxide  and  evaporated  to  crystallisation. 

Silver  nitrate  forms  crystalline  double  salts  with  one  molecule  of  potassium  or 
ammonium  nitrate.  It  absorbs  ammonia  with  evolution  of  heat,  and  silrei- 
ammonio-nltrate,  AgN03.2NH3,  may  be  crystallised  from  a  strong  solution  of  silver 
nitrate  saturated  with  ammonia. 

Silrer  nitrite,  AgN0.2,  is  obtained  as  a  white  precipitate  from  KN02  and  AgNO«. 
It  is  soluble  in  hot  water  and  crystallises  in  prisms.  By  long  boiling  with  water 
it  is  decomposed,  2AgN02  =  AgN03  +  Ag  +  NO.  Silrer  Itijponitrlte,  Ag2N20.,  (see 
p.  103). 

Silrer  carbonate,  Ag2C03,  is  obtained  in  transparent  yellow  crystals  when  moist 
silver  oxide  is  acted  on  by  C02.  It  dissolves  in  solution  of  CO^  like  CaC03.  and 
is  deposited  in  crystals  when  the  solution  is  exposed  to  the  air.  It  is  feebly 
alkaline  to  moist  test-paper.  It  bears  heating  to  nearly  the  boiling-point  of  oil, 
and  fuses  just  before  decomposition.  Silver  carbonate  forms  a  yellowish  white 
precipitate  when  silver  nitrate  is  decomposed  by  an  alkaline  carbonate. 

287.  Silver  chloride,  AgCl,  is  an  important  compound,  as  being  the 
form  into  which  silver  is  commonly  converted  in  extracting  it  from  its 
ores,  and  in  separating  it  from  other  metals.  It  separates,  as  a  white 
curdy  precipitate,  when  solution  of  hydrochloric  acid  or  a  chloride  is 
mixed  with  a  solution  containing  silver.  The  precipitate  is  brilliantly 
white  at  first,  but  soon  becomes  violet,  and  eventually  black,  if  exposed 
to  daylight,  or  more  rapidly  in  sunlight,  the  chloride  of  silver  being 
reduced  to  subchloride  (Ag2Cl),  with  separation  of  chlorine  (see  p.  236). 
The  blackening  is  more  rapid  in  the  presence  of  an  excess  of  silver 
nitrate  or  of  organic  matter,  upon  which  the  liberated  chlorine  can  act. 
In  the  presence  of  chlorine  the  blackening  does  not  occur ;  nor  will  per- 
fectly dry  AgCl  darken.  If  the  white  silver  chloride  be  dried  in  the 
dark  and  heated  in  a  crucible,  it  fuses  at  457°  C.  to  a  brownish  liquid, 
which  solidifies,  on  cooling,  to  a  transparent,  nearly  colourless  mass 
(sp.  gr.  5.59),  much  resembling  horn  in  external  characters  (horn  silver) ; 
a  strong  heat  converts  it  into  vapour,  but  does  not  decompose  it.  If 
fused  silver  chloride  be  covered  with  hydrochloric  acid,  and  a  piece  of 
zinc  placed  upon  it,  it  will  be  found  entirely  reduced,  after  a  few  hours, 
to  a  cake  of  metallic  silver;  the  first  portion  of  silver  having  been 
reduced  in  contact  with  the  zinc,  and  the  remainder  by  the  galvanic 
action  set  up  by  the  contact  of  the  two  metals  beneath  the  liquid.  Fusion 
with  Na.,C03  reduces  AgCl,  first  converting  it  into  Ag2C03  which  breaks 
up  into  ~Ag,,  O,  and  CO..  Silver  chloride  is  slightly  soluble  in  strong 
HCJ,  and  in  strong  solutions  of  alkali  chlorides.  Potassium  cyanide 
dissolves  it  readily,  and  the  solution  is  used  in  electro-plating.  Ammonia 
readily  dissolves  silver  chloride,  and  the  solution  deposits  colourless 
crystals  of  the  chloride  when  evaporated.  If  the  ammonia  be  very 
strong  the  solution  deposits  a  crystalline  compound  of  silver  chloride 


494  SILVEE  HALIDES. 

with  ammonia,  2AgC1.3NH3.  The  absorption  of  ammoniacal  gas  by 
silver  chloride  has  been  noticed  at  p.  82,  and  the  photographic  appli- 
cation of  the  chloride  at  p.  236. 

From  photographic  fixing  solutions  containing  sodium  hyposulphite  the  silver 
cannot  be  precipitated  by  salt,  because  the  silver  chloride  is  soluble  in  the  hyposul- 
phite. A  piece  of  sheet  copper  left  in  this  for  a  day  or  two  will  precipitate  the 
silver  at  once  in  the  metallic  state. 

Several  chemists  have  claimed  to  have  isolated  a  dark  silver  sub-chloride,  to 
wrhich  the  formulae  Ag2Cl  and  Ag4Cl3  have  been  ascribed.  The  interest  in  this 
supposed  sub-chloride  arises  from  the  fact  that  metallic  silver  cannot  be  found  in 
the  silver  chloride  which  has  been  darkened  by  light,  although  chlorine  has 
undoubtedly  been  removed.  By  adding  a  reducing-agent  (such  as  SnCl2)  to  an 
ammoniacal  solution  of  AgCl,  a  black  precipitate  is  obtained,  which  becomes 
coloured  pink  or  brown  (according  to  the  nature  of  the  reducing-agent)  when  it  is 
washed  with  nitric  acid.  A  number  of  such  coloured  salts  has  been  obtained 
by  Carey  Lea  from  the  halides  of  silver  ;  these  are  termed  photo-salts  of  silver  and 
are  supposed  to  be  identical  with  the  products  of  the  action  of  light  on  the  silver 
halides  ;  they  appear  to  consist  of  the  normal  silver  halides  with  small  admixtures 
of  sub-halides.  They  are  dissolved  by  ammonia  with  the  exception  of  a  slight 
residue  of  silver. 

Silver  bromide  (AgBr)  is  a  rare  Chilian  mineral,  bromargyrite.  Asso- 
ciated with  AgCl  it  forms  the  mineral  embolite.  It  much  resembles  the 
chloride,  but  is  somewhat  less  easily  dissolved  by  ammonia.  Dry  silver 
bromide  does  not  absorb  NH3.  It  melts  at  427°  C. ;  sp.  gr.  6.35.  When 
heated  to  700°  C.  in  HC1,  silver  bromide  is  converted  into  the  chloride, 
but,  at  the  ordinary  temperature,  HBr  converts  silver  chloride  into 
bromide.  Modern  photographic  plates  are  made  with  silver  bromide. 

Ammonium  bromide  is  dissolved  in  a  warm  aqueous  solution  of  gelatine  and 
a  solution  of  silver  nitrate,  less  than  equivalent  to  the  bromide,  is  poured  in,  the 
room  being  lighted  by  red  light.  The  mixture,  with  the  finely  divided  silver 
bromide  suspended  in  it,  is  warmed  for  some  time  in  order  to  "ripen"  the 
emulsion.  By  this  expression  it  is  implied  that  the  silver  bromide  becomes  more 
sensitive  to  light,  a  fact  which  has  not  been  explained  ;  the  sole  effect  of  the 
ripening  on  the  silver  bromide,  so  far  as  has  been  observed,  is  the  aggregation  of  the 
particles,  so  that  they  become  somewhat  coarser.  The  emulsion  is  now  allowed  to 
set,  and  washed  in  water  to  remove  the  ammonium  nitrate  produced  by  the  inter- 
action of  the  NH4Br  and  AgNO3,  and  the  excess  of  NH4Br  ;  if  the  latter  be 
not  present  during  the  manufacture  of  the  emulsion  a  less  sensitive  plate  is  produced. 
The  gelatine  emulsion  is  again  melted  and  poured  on  to  the  plates. 

What  has  been  said  (p.  493)  with  reference  to  the  action  of  light  on  AgCl  maybe 
applied  to  AgBr.  The  chemistry  of  the  action  and  of  the  development  of  the 
invisible  image  is  even  yet  shrouded  in  mystery. 

Silver  iodide  (Agl)  is  also  found  in  the  mineral  kingdom.  It  is  worthy 
of  remark  that  silver  decomposes  hydriodic  acid  much  more  easily  than 
hydrochloric  acid,  forming  silver  iodide,  and  evolving  hydrogen.  The 
silver  iodide  dissolves  in  hot  hydriodic  acid,  and  the  solution  deposits 
crystals  of  Agl, HI,  which  are  decomposed  in  the  air.  If  the  hot  solu- 
tion be  left  in  contract  with  silver,  prisms  of  Agl  are  deposited.  By 
adding  silver  nitrate  to  potassium  iodide,  the  silver  iodide  is  obtained  as 
a  yellow  precipitate,  which,  unlike  the  chloride,  does  not  dissolve  in 
ammonia,  but  is  bleached,  forming  2AgLNH3,  which  is  also  produced 
when  dry  silver  iodide  absorbs  ammonia. 

Silver  iodide  is  remarkable  for  its  behaviour  when  heated.  It  becomes  more 
yellow  as  the  temperature  rises  and  melts  to  an  orange  liquid  at  527°  C.  The 
melted  mass  contracts  considerably  on  solidifying  and  on  cooling,  until  the  tem- 
perature is  116°  C.,  whereupon  a  sudden  expansion  occurs,  concomitant  with  the 
passage  of  the  red  amorphous  to  the  yellow  crystalline  modification.  When  the 


SALTS   OF  SILVEE. 

molten  iodide  is  poured  into  cold  water  it  becomes  yellow,  but  remains  amorphous. 
The  sp.  gr.  of  the  fused  iodide  is  5.6. 

Silver  iodide  is  the  most  stable  of  the  silver  halides  ;  when  exposed  to  light  it 
requires  a  more  vigorous  sensitislng-agent  (I.e..  halogen-absorbent)  than  do  the 
other  halides  in  order  that  it  may  undergo  photo-reduction.  It  dissolves  in  a 
boiling  saturated  solution  of  silver  nitrate,  and  the  solution,  on  cooling,  deposits 
crystals  having  the  composition  AgI.AgN03  ;  these  are  sensitive  to  light  since 
the  halogen-absorbent  (AgN03)  is  ready  to  hand.  The  crystals  are  decomposed 
by  water  with  separation  of  silver  iodide. 

Silver  fluoride,  AgF,  is  deliquescent  and  very  soluble  in  water,  forming  crystals 
which  may  contain  one  or  two  molecules  of  water.  It  fuses  to  a  horny  mass,  like 
AgCl,  but  is  reduced  to  the  metallic  state  when  heated  in  moist  air.  Ammonia 
also  reduces  it  to  the  metallic  state  when  heated.  Fused  AgF  conducts  the  electric 
current  without  undergoing  decomposition. 

Silrer  sulphide  (Ag2S)  is  found  as  silrer  glance,  which  may  be  regarded  as  the 
chief  ore  of  silver  ;  it  has  a  metallic  lustre,  and  is  sometimes  found  in  cubical  or 
octahedral  crystals.  The  minerals  known  as  roslclers  or  red  silrer  ores  contain 
sulphide  of  silver  combined  with  the  sulphides  of  arsenic  and  antimony.  The  black 
precipitate  obtained  by  the  action  of  hydrosulphuric  acid  upon  a  solution  of  silver 
is  silver  sulphide.  It  may  also  be  formed  by  heating  silver  with  sulphur  in  a 
covered  crucible.  Silver  sulphide  is  remarkable  for  being  soft  and  malleable,  so 
that  medals  may  even  be  struck  from  it.  It  is  not  dissolved  by  diluted  sulphuric 
or  hydrochloric  acid,  but  nitric  acid  readily  dissolves  it.  Metallic  silver  dissolves 
silver  sulphide  when  fused  with  it,  and  becomes  brittle  even  when  containing  only 
i  per  cent,  of  the  sulphide.  Ag2S  fuses  unchanged,  but  when  roasted  in  air  it 
becomes  Ag2S04. 

Silrer  sulphate,  Ag2S04,  forms  a  crystalline  precipitate  when  a  strong  solution  of 
silver  nitrate  is  stirred  with  dilute  sulphuric  acid.  It  requires  200  parts  of  cold 
water  to  dissolve  it.  It  fuses  at  654°  C.  AgHS04  has  been  crystallised. 

Silrer  sulphite,  Ag2S03,  forms  a  white  precipitate  when  sulphurous  acid  is  added 
to  silver  nitrate.     Boiling  with  water  reduces  it  to  metallic  silver  ; 
Ag2S03  +  H20   =  Ag2  +   H2S04. 

Silrer  orthophoxphate,  Ag3P04,  forms  a  yellow  precipitate  when  sodium  phosphate 
is  added  to  silver  nitrate  (p.  259).  It  is  soluble  in  nitric  acid  and  in  ammonia,  and 
is  thus  distinguished  from  silver  iodide. 

Silrer  arsenite,  Ag3As03,  is  obtained  as  a  yellow  precipitate  when  ammonia  is 
cautiously  added  to  a  mixture  of  silver  nitrate  and  arsenious  acid  ;  it  is  soluble  in 
nitric  acid  and  in  ammonia.  Silrer  ar  senate,  Ag3As04,  is  a  red  precipitate,  soluble 
in  nitric  acid  and  in  ammonia,  formed  when  silver  nitrate  is  added  to  arsenic  acid. 

Silrer  sulpharsenlte,  Ag3AsS3,  is  found  as  light  red  silrer  ore. 

Silrer  mlphantimonate,  Ag3SbS3,  is  dark  red  silrer  ore. 

MERCURY. 

Hg"  =  199  parts  by  weight  =  2  vols. 

288.  Mercury  (quicksilver)  is  conspicuous  among  metals  by  its  fluidity, 
and  among  liquids  by  its  not  wetting  or  adhering  to  most  solids,  such 
as  glass,  a  property  of  great  value  in  making  philosophical  instruments. 
It  is  the  only  metal  which  is  liquid  at  the  ordinary  temperature,  and 
since  it  does  not  freeze  until  -39°  F.  (-39°. 5  0.),  this  metal  is  particularly 
adapted  for  the  construction  of  thermometers  and  barometers.  Its  high 
boiling-point  (662°  F.,  357°  C.)  and  low  specific  heat  (0.033)  also  recom- 
mend it  for  the  former  purpose,  as  its  high  specific  gravity  (13.54)  does 
for  the  latter,  a  column  of  about  30  inches  in  height  being  able  to 
counterpoise  a  column  of  the  atmosphere  having  the  same  sectional  area. 
The  symbol  for  mercury  (Hg)  is  derived  from  the  Latin  name  for  this 
element,  hydrargyrum  (vSwp,  water,  referring  to  its  fluidity,  apyvpos, 
silver). 

Mercury  is  not  met  with  in  this  country,  but  is  obtained  from  Idna 


496 


EXTRACTION  OF   MERCURY. 


(Austria),  Almaden  (Spain),  China,  and  New  Almaden  (California).  It 
occurs  in  these  mines  partly  in  the  metallic  state,  diffused  in  minute 
globules  or  collected  in  cavities,  but  chiefly  in  the  state  of  cinnabar, 
which  is  mercuric  sulphide,  HgS  (sp.  gr.  8.2). 

The  metal  is  extracted  from  the  sulphide  at  Idria  by  roasting  the  ore 
in  a  kiln  (Fig.  241),  which  is  connected  with  an  extensive  series  of  con- 


Fig'.  241.  —  Extraction  of  mercury  at  Idria. 

densing-chambers  built  of  brickwork.  The  sulphur  is  converted,  by  the 
air  in  the  kiln,  into  sulphurous  acid  gas,  whilst  the  .mercury  passes  off 
in  vapour  and  condenses  in  the  chambers. 

At  Almaden,  the  extraction  is  conducted  upon  the  same  principle, 
but  the  condensation  of  the  mercury  is  effected  in  earthen  receivers 
(called  aludels)  opening  into  each  other,  and  delivering  the  mercury  into 
a  gutter  which  conveys  it  to  the  receptacles. 

The  cinnabar  is  placed  upon  the  arch  (A,  Fig.  242)  of  brickwork,  in  which  there 
are  several  openings  for  the  passage  of  the  flame  of  the  wood  fire  kindled  at  B  ; 

this  flame  ignites  the  sulphide  of 
mercury,  which  burns  in  the  air 
passing  up  from  below,  forming  sul- 
phurous acid  gas  and  vapour  of 
mercury  (HgS  +  02  =  Hg  +  S02), 
which  escape  through  the  flue  (F) 
into  the  aludels  (C),  where  the  chief 
part  of  the  mercury  condenses  and 
runs  down  into  the  gutter  (G).  The 
sulphurous  acid  gas  escapes  through 
the  flue  (H),  and  any  mercury  which 
may  have  escaped  condensation  is 
Fig-.  242.  collected  in  the  trough  (D),  the  gas 

finally    passing    out    through     the 
chimney  (E),  which  provides  for  the  requisite  draught. 

In  the  Palatinate  the  cinnabar  is  distilled  in  cast-iron  retorts  with 
lime,  when  the  sulphur  is  left  in  the  residue  as  calcium  sulphide  and 
sulphate,  whilst  the  mercury  distils  over  — 

4HgS  +  4CaO  =  sCaS  +  CaS04  +  Hg4. 


The  mercury  found  in  commerce  is  never  perfectly  pure,  as  may  be  shown  by 
scattering  a  little  upon  a  clean  glass  plate,  when  it  tails  or  leaves  a  track  upon  the 
glass,  which  is  not  the  case  with  pure  mercury.  Its  chief  impurity  is  lead,  which 
may  be  removed  by  exposing  it  in  a  thin  layer  to  the  action  of  nitric  acid  diluted 
with  two  measures  of  water,  which  should  cover  its  surface,  and  be  allowed  to 
remain  in  contact  with  it  for  a  day  or  two  with  occasional  stirring.  The  lead  is 
far  more  easily  oxidised  and  dissolved  than  the  mercury,  though  a  little  of  this 
also  passes  into  solution.  The  mercury  is  afterwards  well  washed  with  water  and 


LOOKING-GLASSES.  497 

dried,  first  with  blotting-paper,  and  then  by  a  gentle  heat.  Mercury  is  easily 
freed  from  mechanical  impurities  by  squeezing  it  through  a  duster.  Zinc,  tin  and 
bismuth  are  sometimes  present  in  the  mercury  of  commerce,  and  may  be  partly 
removed,  as  oxides,  by  shaking  the  mercury  in  a  large  bottle  with  a  little  powdered 
loaf-sugar  for  a  few  minutes,  and  straining  through  cloth.  The  sugar  appears  to 
act  mechanically  by  dividing  the  mercury. 

289.  In  its  chemical  properties  mercury  much  resembles  silver,  being 
unaffected  by  ordinary  air  and  tarnished  by  air  containing  H2S.     In 
course  of  time,  however,  it  becomes  oxidised,  as  may  be  seen2  in  old 
instruments  containing  mercury  and  air  ;  and  it  is  slowly  oxidised  when 
heated  in  air,  which  is  not  the  case  with  silver.     It  also  appears  to 
undergo  a  partial  oxidation  when  reduced  to  a  fine  state  of  division,  as 
in  those  medicinal  preparations  of  the  metal  which  are  made  by  tritu- 
rating it  with  various  substances  which  have  no  chemical  action  upon  it, 
until  globules  of  the  metal  are  no  longer  visible.     Blue  pill  and  grey 
powder,  or  hydrargyrum  cum  cretd,  afford  examples  of  this,  and  probably 
owe   much  of  their  medicinal  activity  to  the  presence  of  one  of  the 
oxides  of  mercury. 

Nitric  acid  (containing  nitrous  acid)  dissolves  mercury,  and  converts 
it  into  two  nitrates — mercurous,  HgN03,  corresponding  with  AgN03, 
and  mercuric,  Hg(NO3)2.  Hot  concentrated  sulphuric  acid  also  con  verts 
it  into  mercurous  (Hg2S04)  and  mercuric  (HgSO4)  sulphates.  Mercury 
is  precipitated  from  solutions  of  its  salts  by  reducing-a  gents,  stannous 
chloride,  for  example,  in  what  looks  like  a  dark  grey  powder ;  but  if 
this  be  boiled  in  the  liquid,  the  minute  globules  of  which  it  is  composed 
gradually  unite  into  fluid  mercury.  Conversely,  if  mercury  be  dili- 
gently triturated  with  chalk  or  grease,  it  may  be  divided  into  extremely 
minute  globules  which  behave  like  a  powder. 

290.  Uses  of  Mercury. — One  of  the  chief  uses  to  which  mercury  is 
devoted  is  the  silvering  of  looking-glasses,  which  is  effected  by  means  of 
an  amalgam  of  tin  in  the  following  manner :  A  sheet  of  tinfoil  of  the 
same  size  as  the  glass  to  be  silvered  is  laid  perfectly  level  upon  a  table, 
and  rubbed  over  with  metallic  mercury,  a  thin  layer  of  which  is  after- 
wards poured  upon  it.     The  glass  is  then  carefully  slid  on  to  the  table, 
so  that  its  edge  may  carry  before  it  part  of  the  superfluous  mercury 
with  the  impurities  upon  its  surface ;  heavy  weights  are  laid  upon  the 
glass,  so  as  to  squeeze  out  the  excess  of  mercury,  and  in  a  few  days  the 
combination  of  tin  and  mercury  is  found  to  have  adhered  firmly  to  the 
glass  ;  this  coating  usually  contains  about  i  part  of  mercury  and  4  parts 
of  tin.     In  this  and  all  other  arts  in  which  mercury  is  used  (such  as 
barometer-making)   much  suffering  is  experienced  by  the  operatives, 
from  the  poisonous  action  of  the  mercury. 

The  readiness  with  which  mercury  unites  with  most  other  metals  to 
form  amalgams  is  one  of  its  most  striking  properties,  and  is  turned  to 
account  for  the  extraction  of  silver  and  gold  from  their  ores.  The  attrac- 
tion of  the  latter  metal  for  mercury  is  seen  in  the  readiness  with  which 
it  becomes  coated  with  a  silvery  layer  of  mercury,  whenever  it  is  brought 
in  contact  with  that  metal,  and  if  a  piece  of  gold  leaf  be  suspended  at  a 
little  distance  above  the  surface  of  mercury,  it  will  be  found,  after  a 
time,  silvered  by  the  vapour  of  the  metal,  which  rises  slowly  even  at 
the  ordinary  temperature.  From  the  surface  of  rings  which  have  been 
accidentally  whitened  by  mercury  it  may  be  removed  by  a  moderate 


49^  RED   OXIDE   OF   MERCURY. 

heat,  or  by  warm  dilute  nitric  acid,  but  the  gold  will  afterwards  require 
burnishing. 

Zinc  plates  are  amalgamated,  as  already  explained  (p.  14),  for  use  in 
the  galvanic  battery.  An  amalgam  of  6  parts  of  mercury  with  i  part 
of  zinc  and  i  of  tin  is  used  to  promote  the  action  of  frictional  electrical 
machines. 

The  addition  of  a  little  amalgam  of  sodium  to  metallic  mercury  gives 
it  the  power  of  adhering  much  more  readily  to  other  metals,  even  to 
iron.  Such  an  addition  has  been  recommended  in  all  cases  where 
metallic  surfaces  have  to  be  amalgamated,  and  especially  in  the  extrac- 
tion of  silver  and  gold  from  their  ores  by  means  of  mercury.  Gold 
amalgam  and  cadmium  amalgam  are  used  by  dentists.  Sodium  amalgam, 
in  contact  with  water,  forms  a  convenient  source  of  nascent  /'atomic) 
hydrogen. 

Iron  and  platinum  are  the  only  metals  in  ordinary  use  which  can  be 
employed  in  contact  with  mercury  without  being  corroded  by  it.  Mer- 
cury, however,  adheres  to  platinum. 

The  following  definite  compounds  of  mercury  with  other  metals  have  been 
obtained  by  combining  them  with  excess  of  mercury,  and  squeezing  out  the  fluid 
metal  by  hydraulic  pressure,  amounting  to  60  tons  upon  the  inch  ;  Pb0Hg,  AgHg, 
FeHg,*  Zn2Hg,  CuHg,  PtHg2.  AgHg  has  been  found  in  nature,  in  dodecahedral 
crystals. 

A  very  beautiful  crystallisation  of  the  amalgam  of  silver  (Arbor  Dianee)  may  be 
obtained  in  long  prisms  having  the  composition  Ag2Hg3,  by  dissolving  400  grains 
of  silver  nitrate  in  40  measured  ounces  of  water,  adding  160  minims  of  concen- 
trated nitric  acid,  and  1840  grains  of  mercury ;  in  the  course  of  a  day  or  two 
crystals  of  2  or  3  inches  in  length  will  be  deposited. 

291.  Oxides  of  Mercury. — Two  oxides  of  mercury  are  known — the 
suboxide,  Hg20,  and  the  oxide,  HgO ;  both  combine  with  acids  to  form 
salts.  Suboxide  of  mercury,  black  oxide,  or  mercurous  oxide,  Hg20,  is 
obtained  by  decomposing  calomel  with  solution  of  potash,  and  washing 
with  water;  Hg2Cl2  + 2KOH  =  Hg2O  + 2KC1  +  H20.  It  is  very  easily 
decomposed,  by  exposure  to  light  or  to  a  gentle  heat,  into  mercuric 
oxide  and  metallic  mercury. 

Red  oxide  of  mercury,  or  mercuric  oxide  (HgO),  is  formed  upon  the 
surface  of  mercury,  when  heated  (237°  C)  for  some  time  to  its  boiling- 
point  in  contact  with  air.  The  oxide  is  black  while  hot,  but  becomes 
red  on  cooling.  It  is  used,  under  the  name  of  red  precipitate,  in  oint- 
ments, and  is  prepared  for  this  purpose  by  dissolving  mercury  in  nitric 
acid,  evaporating  the  solution  to  dryness,  triturating  the  mercuric  nitrate 
with  an  equal  weight  of  mercury,  and  heating  as  long  as  acid  fumes  are 
evolved;  Hg(N03)2  +  Hg2  =  3HgO  +  N203.  The  name  nitric  oxide  of 
mercury  refers  to  this  process.  It  is  thus  obtained,  after  cooling,  as  a 
brilliant  red  crystalline  powder  (sp.  gr.  i  i.o),  which  becomes  nearly  black 
when  heated,  and  is  resolved  into  its  elements  at  a  red  heat.  It  dissolves 
slightly  in  water,  and  the  solution  has  a  very  feeble  alkaline  reaction. 
A  bright  yellow  modification  of  the  oxide  is  precipitated  when  a  solution 
of  corrosive  sublimate  is  decomposed  by  potash  (HgCl2  + 2KOH  = 
HgO  +  2KC1  +  H20) ;  the  yellow  variety  is  chemically  more  active  than 
the  red. 

*  Hg3Fe2  has  been  obtained  by  the  action  of  finely  divided  iron  on  sodium  amalgam  in 
presence  of  water. 


SALTS   OF  MERCURY.  499 

When  mercuric  oxide  is  attacked  by  strong  ammonia  it  becomes  converted  into 
a  yellowish -white  powder  which  possesses  the  properties  of  a  strong  base,  absorb- 
ing carbonic  acid  eagerly  from  the  air,  and  combining  readily  with  other  acids 
It  is  easily  decomposed  by  exposure  to  light,  and  if  rubbed  in  a  mortar  when 
dry,  is  decomposed  with  slight  detonations,  a  property  in  which  it  feebly  resembles 
fulminating  silver  (p.  492).  The  composition  of  this  substance  is  represented  by 
the  formula  NHg"2.OH.Aq.  When  exposed  in  racuo  over  oil  of  vitriol,  it  loses 
Aq,  becoming  NHg"2.OH,  or  diinercuramnioniutn  hydroxide,  which  is  a  brown 
explosive  base.*  When  treated  with  aqueous  ammonia  it  yields  Millon's  luxe, 
3(2HgO.NH3).2H20,  which  is  not  decomposed  by  boiling  potash,  but  explodes  if 
evaporated  to  dryness  with  the  potash.  This  base  will  deprive  all  soluble  and 
most  insoluble  salts  of  their  acids  ;  thus  it  will  remove  sulphates  and  chlorides 
from  impure  soda  solution. 

By  passing  ammonia  gas  over  the  yellow  oxide  of  mercury  as  long  as  it  is 
absorbed,  and  heating  the  compound  to  about  127°  C.  in  a  current  of  ammonia  as 
long  as  any  water  is  evolved,  a  brown  explosive  powder  is  obtained  which  is 
believed  to  be  a  nitride  of  mercury,  N2Hg"3,  representing  a  double  molecule  of 
ammonia  in  which  the  hydrogen  has  been  displaced  by  mercury.  It  yields  salts  of 
ammonium  when  decomposed  by  acids. 

292.  The  salts  formed  by  the  oxides  of  mercury  with  the  oxygen-acids  are  not 
of   great   practical   importance.     Protonitrate  of  mercury,  or   mercurous    nitrate, 
Hg(N03)Aq,  is  obtained  when  mercury  is  dissolved  in  cold  HN03  diluted  with  five 
volumes  of  water.     The   prismatic   crystals  which  are  sometimes  sold  as  proto- 
nitrate  of  mercury  consist  of  a  basic  nitrate,  Hg4(N03)3OH,  prepared  by  acting  with 
dilute  nitric  acid  upon  mercury  in  excess.     When  this  salt  is  powdered  in  a  mortar 
with  a  little  common  salt,  it  becomes  black  from  the  separation  of  mercurous 
oxide— 2Hg4(N03)3OH  +  6NaCl  =  6NaN03  +  6HgCl  +  HgaO  +  H20;   but  the  normal 
nitrate  is  not  blackened  (Hg(N03)  +  NaCl  =  HgCl  +  NaN03).     Mercurous  nitrate  is 
soluble  in  a  little  hot  water,  but  much  water  decomposes  it  into  nitric  acid  and  a 
basic  nitrate  ;  2Hg(N03)  +  H20  =  Hg2N03.OH  +  HN03. 

y it-rate  of  mercury  or  mercuric  nitrate,  2Hg(N03)2.Aq,  is  formed  when  mercury 
is  dissolved  in  an  excess  of  strong  nitric  acid,  and"  the  solution  boiled  until  it  is 
no  longer  precipitated  by  NaCl.  Water  decomposes  it,  precipitating  a  yellow  basic 
nitrate,  which  leaves  mercuric  oxide  when  long  washed  with  water.  Mercuric 
nitrate  stains  the  skin  red.  When  nitric  acid  is  heated  with  an  excess  of  mercuric 
oxide,  the  solution,  on  cooling,  deposits  crystals  of  a  basic  mercuric  nitrate; 
Hg.2(N03)3.OH.Aq. 

Mercurous  sulphate  (Hg.2S04)  is  precipitated  as  a  white  crystalline  powder  when 
dilute  sulphuric  acid  is  added  to  a  solution  of  mercurous  nitrate. 

Mercuric  sulphate  (HgS04)  is  obtained  by  heating  2  parts  by  weight  of  mercury 
with  3  parts  of  oil  of  vitriol,  and  evaporating  to  dryness.  Mercurous  sulphate  is 
first  produced,  and  is  oxidised  by  the  excess  of  sulphuric  acid.  It  forms  a  white 
crystalline  powder,  which  becomes  brown-yellow  when  heated,  and  white  again 
on  cooling.  It  is  decomposed  by  water  into  a  soluble  acid  sulphate,  and  an 
insoluble  yellow  basic  sulphate  of  mercury,  HgS04.2HgO,  known  as  turbith  or 
turpetJi  mineral,  said  to  have  been  so  named  from  its  resembling  in  its  medicinal 
effects  the  root  of  the  Convolculua  turpetkum. 

293.  Chlorides  of  Mercury. — The  chlorides  are  the  most  important 
of  the  compounds  of  mercury,  one  chloride  being  calomel  (HgCl)  and  the 
other  corrosive  sublimate  (HgCL,).     Vapour  of  mercury  burns  in  chlorine 
gas,  corrosive  sublimate  being  produced. 

Corrosive  sublimate,  chloride  of  mercury,  bichloride  or  perchloride  of 
mercury,  or  mercuric  chloride,  is  manufactured  by  heating  2  parts  by 
weight  of  mercury  with  3  parts  of  strong  sulphuric  acid,  and  evapo- 
rating to  dryness,  to  obtain  mercuric  sulphate — 

Hg   +  2H,S04  =  HgS04  +  2H20   +   S02, 

*  It  has  been  stated  that  by  heating  it  for  some  time  in  a  current  of  dry  ammonia,  it 
undergoes  further  change,  becoming-  the  oxide  of  mercurammonium,  (XHg".2).2O,  winch 
is  very  explosive,  and  combines  with  water  to  form  a  hydrate  which  produces  salts  with 
the  acids. 


500  CORROSIVE   SUBLIMATE. 

which  is  mixed  with  i  J  part  of  common  salt  and  heated  in  glass  vessels 
(HgS04  +  2NaCl  =  Na2SO4  +  HgCl2),  when  sodium  sulphate  is  left,  and 
the  corrosive  sublimate  is  converted  into  vapour,  condensing  on  the 
cooler  part  of  the  vessel  in  lustrous  colourless  masses,  which  are  very 
heavy  (sp.  gr.  5.4),  and  have  a  crystalline  fracture.  It  fuses  very 
easily  (288°  C.)  to  a  perfectly  colourless  liquid,  which  boils  at  303°  C., 
emitting  an  extremely  acrid  vapour,  which  destroys  the  sense  of  smell 
for  some  time.  This  vapour  condenses  in  fine  needles,  or  sometimes  in 
octahedra.  Corrosive  sublimate  dissolves  in  twice  its  weight  of  boiling 
water,  but  requires  16  parts  of  cold  water,  so  that  the  hot  solution 
readily  deposits  long  four-sided  prismatic  crystals  of  the  salt.  It  is 
remarkable  that  alcohol  and  ether  dissolve  corrosive  sublimate  much 
more  easily  than  water  does,  boiling  alcohol  dissolving  about  an  equal 
weight  of  the  chloride,  and  cold  ether  taking  up  one-third  of  its  weight. 
By  shaking  the  aqueous  solution  with  ether,  the  greater  part  of  the 
corrosive  sublimate  is  removed,  and  remains  dissolved  in  the  ether  which 
rises  to  the  surface.  An  aqueous  solution  of  ammonium  chloride  will 
take  up  corrosive  sublimate  more  easily  than  pure  water  will,  a  soluble 
double  chloride  (sal  alembroth)  being  formed,  which  may  be  obtained  in 
tabular  crystals,  HgCl2.2NH4Cl.H20.  A  solution  of  corrosive  sublimate 
in  water  containing  sal-ammoniac  is  a  very  efficacious  bug-poison. 

Sulphuric  acid  does  not  decompose  mercuric  chloride,  though  it  attacks 
mercurous  chloride.  Hydrochloric  acid  combines  with  it,  forming  crys- 
talline compounds  HCl.HgOl,  and  HC1.2HgCl2,  which  lose  HC1  when 
exposed  to  air.  A  crystalline  compound,  HgCl2.H2S04,  is  formed  by 
the  action  of  hydrochloric  acid  on  mercuric  sulphate. 

The  poisonous  properties  of  corrosive  sublimate  make  it  the  most 
powerful  antiseptic,  and  are  very  marked,  so  little  as  three  grains  having 
been  known  to  cause  death  in  the  case  of  a  child.  The  white  of  egg  is 
commonly  administered  as  an  antidote,  because  it  is  known  to  form  an 
insoluble  compound  with  corrosive  sublimate,  so  as  to  render  the  poison 
inert  in  the  stomach.  The  compound  of  albumin  with  corrosive 
sublimate  is  also  much  less  liable  to  putrefaction  than  albumin  itself, 
and  hence  corrosive  sublimate  is  sometimes  employed  for  preserving 
anatomical  preparations  and  for  preventing  the  decay  of  wood  (by  com- 
bining with  the  vegetable  albumin  of  the  sap).  Mercuric  chloride 
unites  with  many  other  chlorides  to  form  soluble  double  salts,  and  with 
mercuric  oxide,  forming  several  oxychlorides,  which  have  no  useful 
applications. 

Mercuric  chloride  has  been  found  native  in  one  of  the  Molucca  Islands. 

White  precipitate,  employed  for  destroying  vermin,  is  deposited  when 
a  solution  of  corrosive  sublimate  is  poured  into  an  excess  of  solution  of 
ammonia ;  HgC]2  +  2NH3  =  NH4C1  +  NH2Hg"Cl  (white  precipitate). 

The  true  constitution  of  white  precipitate  has  been  the  subject  of  much  discus- 
sion, but  the  changes  which  it  undergoes,  under  various  circumstances,  appear  to 
lead  to  the  conclusion  that  it  represents  ammonium  chloride,  NH4C1,  in  which  half 
of  the  hydrogen  has  been  displaced  by  mercury.  When  boiled  with  potash  it  yields 
ammonia  and  mercuric  oxide;  NH2Hg"Cl  +  KOH  =  NH3  +  HgO  +  KCl.  If  it  be 
boiled  with  water,  it  is  only  partly  decomposed  in  a  similar  manner,  leaving  a  yellow 
powder  having  the  composition  (NH2HgCl).HgO,  produced  according  to  the 
equation  2(NH2HgCl)  +  H20  =  NH4Cl  +  (NH2HgCl).HgO.  A  compound  correspond- 
ing with  this  yellow  powder,  but  containing  mercuric  chloride  in  place  of  oxide,  is 
precipitated  when  ammonia  is  gradually  added  to  solution  of  corrosive  sublimate 


CALOMEL.  CQI 

in  large  excess,  the  result  being  a  compound  of  white  precipitate  with  a  molecule  of 
undecomposed  mercuric  chloride  (NH2HgCl).HgCl2.  A  compound  having  the  same 
formula  as  the  yellow  powder,  and  probably  identical  with  it,  is  obtained  by  the 
action  of  dilute  hydrochloric  acid  on  Millon's  base  (p.  499)  ;  it  loses  water  at 
200  C.  and  is  •mercuranunonlum,  chloride  hydrate,  NHg2Cl.H20. 

If  white  precipitate  be  heated  to  about  315°  C.,  it  evolves  ammonia,  and  yields 
a  sublimate  of  ammoniated  mercuric  chloride,  HgCl2.NH3,  leaving  a  red  crystalline 
powder  which  is  insoluble  in  water  and  in  diluted  acids,  and  is  unchanged  by  boil- 
ing with  potash  ;  it  may  be  represented  as  a  compound  of  mercuric  chloride  with 
ammonia  in  which  the  whole  of  the  hydrogen  has  been  displaced  by  mercury, 
JS2Hg  3.2HgCl2.  When  strongly  heated,  white  precipitate  yields  a  sublimate  of 
calomel ;  3NH2Hg"Cl  =  3HgCl  +  N  +  2NH3.  White  precipitate  inflames  in  contact 
with  chlorine  or  bromine.  If  it  be  mixed  with  about  twice  its  weight  of  iodine  and 
moistened  with  alcohol,  an  explosion  occurs  in  about  half  an  hour,  from  production 
of  nitrogen  iodide. 

When  solution  of  corrosive  sublimate  is  added  to  a  hot  solution  of  sal-ammoniac, 
mixed  with  ammonia,  a  crystalline  deposit  is  obtained  on  cooling  the  liquid  ;  this 
is  also  obtained  when  ammoniacal  mercuric  chloride  is  precipitated  by  an  alkaline 
carbonate  ;  it  is  known  as  fusible  white  precipitate,  and  represents  two  molecules  of 
ammonium  chloride,  in  which  one-fourth  of  the  hydrogen  has  been  displaced  by 
mercury,  its  composition  being  N2H6Hg"Cl2.  The  same  compound  is  formed  when 
white  precipitate  is  boiled  with  solution  of  sal-ammoniac — 
NH2Hg"Cl  +  NH4C1  =  N2H6Hg"Cl2. 

The  above  compounds  possess  a  special  interest  for  the  chemist,  as  they  were 
among  the  first  to  attract  attention  to  the  mobility  of  the  hydrogen  in  ammonia, 
which  has  since  been  so  well  exemplified  in  the  artificial  production  of  organic 
bases  by  the  action  of  ammonia  upon  the  iodides  of  the  alcohol-radicles.  The 
relation  of  these  compounds  to  each  other  is  here  exhibited  : 

White  precipitate NH2Hg"Cl 

Produced  with  corrosive  sublimate  in  excess        .     (NH2HgCl).HgCl2 
„  by  boiling  with  water  ....     (NH2HgCl).HgO 

11  „  sal-ammoniac    .         .     N0H6Hg"Cl2 

by  heating  to  315°  C N2~Hg"3.2HgCl2 

According  to  Kammelsberg  the  infusible  or  true  white  precipitate  loses  half  of 
its  N  as  NH3  when  it  is  boiled  with  an  alkali,  while  the  fusible  white  precipitate 
loses  three-quarters  of  its  N  as  NH3  under  the  same  treatment ;  he  concludes  that 
they  are  both  double  compounds  of  ammonium  chloride  and  mercurammoniuin 
chloride,  the  infusible  being  NHg2Cl.NH4Cl,  and  the  fusible  NHg2C1.3NH4Cl. 

294.  Calomel,  subchloride  or  protochloride  of  mercury,  or  mercuroiw 
chloride  (HgCl),  unlike  corrosive  sublimate,  is  insoluble  in  water,  so 
that  it  is  precipitated  when  hydrochloric  acid  or  a  soluble  chloride  is 
added  to  mercurous  nitrate.  The  simplest  mode  of  manufacturing  it 
consists  in  intimately  mixing  a  molecular  weight  of  corrosive  sublimate 
with  an  atomic  weight  of  metallic  mercury,  a  little  water  being  added 
to  prevent  dust,  drying  the  mixture  thoroughly,  and  subliming  it; 
HgCl2  +  Hg=2HgCl.  But  it  is  more  commonly  made  by  adding 
another  atomic  weight  of  mercury  to  the  materials  employed  in  the  pre- 
paration of  corrosive  sublimate ;  HgS04  +  Hg  +  2NaCl  =  2HgCl  +  Na2S04. 
The  calomel  condenses  as  a  translucent,  fibrous  cake  on  the  cool  part  of 
the  subliming  vessel.  For  medicinal  purposes,  the  calomel  is  obtained 
in  a  very  fine  state  of  division  by  conducting  the  vapour  into  a  large 
chamber  so  as  to  precipitate  it  in  a  fine  powder  by  contact  with  a  large 
volume  of  cold  air.  Steam  is  sometimes  introduced  to  promote  its  fine 
division.  Sublimed  calomel  always  contains  some  corrosive  sublimate, 
so  that  it  must  be  thoroughly  washed  with  water  before  being  employed 
in  medicine.  When  perfectly  pure  calomel  is  sublimed,  a  little  is  always 
decomposed  during  the  process  into  metallic  mercury  and  corrosive 
sublimate. 

Calomel  is  met  with  either  as  a  semi-transparent  fibrous  mass,  or  an 


5O2  IODIDES   OF  MEECUEY. 

amorphous  powder,  with  a  slightly  yellow  tinge.  Light  slowly  decom- 
poses it,  turning  it  grey  from  separation  of  mercury.  It  is  heavier  than 
corrosive  sublimate  (sp.  gr.  7.18),  and  does  not  fuse  before  subliming; 
it  may  be  obtained  in  four-sided  prisms  by  slow  sublimation.  Dilute 
acids  will  not  dissolve  it,  but  boiling  nitric  acid  gradually  converts  it 
into  mercuric  chloride  and  nitrate,  which  pass  into  solution.  Boiling 
hydrochloric  acid  turns  it  grey,  some  mercury  being  separated,  and 
mercuric  chloride  dissolved.  Mercuric  nitrate  dissolves  it,  forming 
mercuric  chloride  and  mercurous  nitrate.  Alkaline  solutions  convert 
it  into  black  mercurous  oxide,  as  is  seen  in  black-wash,  made  by  treating 
calomel  with  lime  water  ;  Hg?Cl2  +  Ca(OH)2  =  Hg20  +  CaCl2  +  H20.  Solu- 
tion of  ammonia  converts  it  into  a  grey  compound  (NH2Hg.,Cl),  which  is 
the  analogue  of  white  precipitate  (NH2Hg"Cl),  containing  Hg'2  in  place 
of  Hg".  Calomel  is  found  as  horn  quicksilver  at  Idria  and  Almaden, 
crystallised  in  rhombic  prisms. 

It  is  asserted  that  calomel  is  dissociated  by  heat  into  Hg  and  HgCl2  so  that  its 
vapour  density  does  not  decide  its  molecular  weight.  When,  however,  the 
vaporisation  is  performed  in  presence  of  HgCl2,  so  that  the  dissociation  is  hindered 
(p.  313),  the  vapour  density  is  found  to  be  about  117.5,  showing  that  HgCl  is  most 
probably  the  molecular  formula  for  calomel.  The  presence  of  metallic  mercury  in 
calomel  vapour  is  shown  by  the  deposition  of  minute  globules  of  mercury  on  a  cold 
tube  coated  with  gold  immersed  in  the  vapour  at  440°  C. 

Mercurom  Iodide,  Hgl,  is  a  green  unstable  substance,  formed  when  iodine  is 
triturated  with  an  excess  of  mercury  and  a  little  alcohol,  or  by  precipitating 
mercurous  nitrate  with  potassium  iodide.  It  owes  its  green  colour  to  the  presence 
of  excess  of  mercunr  ;  when  precipitated  in  a  solution  containing  HN03  it  is  yellow. 
With  care,  it  may  be  sublimed  in  yellow  crystals,  isomorphous  with  mercurous 
chloride,  but  if  sharply  heated  it  is  decomposed  into  Hg  and  Hgl.2.  Potassium 
iodide  decomposes  it  in  a  similar  way,  dissolving  the  mercuric  iodide.  When 
mercuric  chloride  is  boiled  with  HC1  and  copper  the  solution  gives  with  KI  a  dark 
red  precipitate  of  mercui'oso-mer  curie  iodide,  insoluble  in  excess  of  the  KI. 

Mercuric  iodide,  or  iodine  scarlet,  HgI2,  is  the  bright  red  precipitate  produced  by 
potassium  iodide  in  mercuric  chloride.  At  the  moment  of  precipitation  it  is  yellow, 
rapidly  becoming  fawn  coloured  and  red.  When  the  dry  mercuric  iodide  is  heated, 
it  becomes  bright  yellow  at  temperatures  above  126°  C.,  and  remains  so  on  cooling 
until  touched  with  a  hard  body,  when  it  becomes  red  again,  the  colour  spreading 
from  the  point  touched.  Under  the  microscope,  the  red  iodide  is  seen  to  be 
octahedral  and  the  yellow  to  consist  of  rhombic  tables.  When  the  yellow  iodide  is 
heated,  it  fuses  easily  (238°  C.),  becomes  brown,  and  is  converted  into  a  colourless 
vapour  which  condenses  in  yellow  crystals  on  a  cold  surface. 

A  very  beautiful  experiment  is  made  by  gently  heating  mercuric  iodide  in  a  large 
porcelain  crucible  covered  with  a  dial-glass  ;  the  yellow  iodide  is  deposited  in 
crystals  projecting  from  the  under  surface  of  the  glass,  and  if  this  be  placed  o-n  the 
table  with  the  crystals  upwards,  and  some  of  these  be  touched  with  a  needle,  the 
red  spots  appear  like  poppies  among  corn,  and  the  blush  gradually  spreads  over  the 
entire  field,  attended  by  a  rustling  movement  caused  by  the  change  in  crystalline 
form.* 

The  transformation  of  the  yellow  HgI2  into  the  red  HgI2  evolves  3000  gram-units 
of  heat.  Mercuric  iodide  dissolves  in  hot  alcohol,  and  crystallises  in  red  octahedra, 
Ether  also  dissolves  it.  It  is  freely  soluble  in  solutions  of  mercuric  chloride  and 
potassium  iodide.  The  latter  yields  yellow  prisms  of  2(HgI2.KI).3Aq.  The  solution 
of  this  salt  mixed  with  potash  forms  Nettfer'if  solution,  which  gives  a  brown 
precipitate  with  very  minute  quantities  of  ammonia — 

2HgI2  +  3KOH  +  NH3  =  NHg2I.H20  +  3KI  +  2H20. 

The  vapour  density  of  mercuric  iodide  is  of  course  very  high,  being  15.68  times 
that  of  air,  showing  that  the  formula  HgI2  represents  two  volumes. 

295.  Sulphides  of  Mercury. — When  mercury  is  triturated  with  sul- 
phur, the  black  subsulphide  of  mercury,  or  mercurous  sulphide  (Hg2S),  is 

*  The  author  is  indebted  for  this  experiment  to  Mr.  Herbert  Jackson,  of  King's  College. 


VERMILION.  503 

formed  ;  it  was  termed  by  old  writers  Ethiopia  mineral,  and  is  an 
unstable  compound  easily  resolved  into  metallic  mercury  and  mercuric 
sulphide  (HgS).  The  latter  has  been  mentioned  as  the  principal  ore  of 
mercury,  and  is  important  as  composing  vermilion.  The  native  mer- 
curic sulphide,  or  cinnabar,  is  found  sometimes  in  amorphous  masses, 
sometimes  crystallised  in  six-sided  prisms  varying  in  colour  from  dark 
brown  to  bright  red.  It  may  be  distinguished  from  most  other 
minerals  by  its  great  weight  (sp.  gr.  8.2),  and  by  its  red  colour  when 
scraped  with  a  knife.  Neither  hydrochloric  nor  nitric  acid,  separately, 
will  dissolve  it,  but  a  mixture  of  the  two  dissolves  it  as  mercuric 
chloride,  with  separation  of  sulphur.  Some  specimens  of  cinnabar  have 
a  bright  red  colour,  so  that  they  only  require  grinding  and  levigating  to 
be  used  as  vermilion  ;  and  if  the  brown  cinnabar  in  powder  be  heated 
for  some  time  at  120°  F.  (49°  C.)  with  a  solution  of  sulphur  in  potash, 
it  is  converted  into  vermilion. 

Of  the  artificial  mercuric  sulphide  there  are  two  varieties — the  black, 
which  is  precipitated  when  corrosive  sublimate  is  added  to  hydrosulpburic 
acid  or  a  soluble  sulphide,  and  the  red  (vermilion),  into  which  the  black 
variety  is  converted  by  sublimation,  or  by  prolonged  contact  with 
solutions  of  alkali  sulphides  containing  excess  of  sulphur,  though,  so 
far  as  is  known,  the  conversion  is  effected  without  chemical  change,  the 
red  sulphide  having  the  same  composition  as  the  black. 

In  Idria  and  Holland,  6  parts  of  mercury  and  I  of  sulphur  are  well  agitated 
together  in  revolving  casks  for  several  hours,  and  the  black  sulphide  thus  obtained 
is  sublimed  in  tall  earthen  pots  closed  with  iron  plates,  when  the  vermilion 
is  deposited  in  the  upper  part  of  the  pots,  and  is  afterwards  ground  and  levigated. 
One  of  the  wet  processes  for  making  vermilion  consists  in  triturating  300  parts  of 
mercury  with  114  parts  of  sulphur  for  two  or  three  hours  and  digesting  the  black 
product,  at  about  120°  F.  (49°  C.),  with  75  parts  of  caustic  potash  and  400  of  water 
until  it  has  acquired  a  fine  red  colour.  The  vermilion  made  by  the  dry  process 
is  the  more  highly  prized.  The  permanence  of  vermilion  paint,  is,  of  course, 
attributable  to  the  circumstance  that  it  resists  the  action  of  light,  of  oxygen, 
carbonic  acid,  aqueous  vapour,  and  even  of  the  sulphuretted  hydrogen,  and 
sulphurous  or  sulphuric  acid  which  contaminate  the  air  of  towns,  whereas  the  red 
paints  containing  lead  are  blackened  by  sulphuretted  hydrogen,  and  all  vegetable 
and  animal  reds  are  liable  to  be  bleached  by  atmospheric  oxygen  and  by  sulphurous 
acid. 

The  conversion  of  the  black   mercuric  sulphide  into  the  red  form  is  quickly 
effected   by  boiling   it  with  freshly  prepared  ammonium  poly  sulphide   (made  by 
saturating  ammonia  with  H2S  and  dissolving  sulphur  in  the  liquid,  gently  warmed, 
until  it  has  a  dark  sherry  colour).     If  this  solution  be  poured  upon  the  freshly 
precipitated  black  sulphide,   and  boiled  for  a  minute,   the  sulphide  assumes  a 
crystalline   appearance,    and    a   bright  vermilion   colour   (Herbert  Jackson).     - 
appears  that  the  black  form  is  more  soluble  than  the  red,  so  that  when  the  pplysu 
phide  solution  becomes  saturated  with  the  black  form  it  is  supersaturated  with  tm 
red,  which  therefore  separates  ;  another  portion  of  the  black  then  dissolves,  ar 
on,  until  the  conversion  is  complete.  ,      , 

If  the  black  sulphide  be  boiled  with  potassium  sulphide  and  potash,  it  is 
and  the  solution  deposits  white  needles  of  HgS.K2S.5H20,  which  are  decompos 
"wi  it- Gi* 

When  the  black  precipitated  mercuric  sulphide  is  boiled  with  solution  of  corro- 
sive sublimate,  it  is  converted  into  a  white  chloromlphide  of  mercury,  t\\ 
which  is  also  formed  when  a  small  quantity  of  hydroRulphuric  acic   is  aoo 
corrosive  sublimate,  becoming  yellow,  brown,  and  black  on  adding  mor 

Vermilion  may  be  prepared  bv  adding  HgCl2  to  a  slight  excess  of  dilute  aim 
nearly  dissolving  the  precipitate  in  sodium  thiosulphate  (hyposulphite)  and  h 
when  a  bright  yellow    precipitate   is  obtained,   which  becomes 
boiling. 


504  EXTE ACTION  OF  PLATINUM. 

By  suspending  HgS  in  air-free  water  and  passing  H2S,  a  dark-coloured  solution 
of  colloidal  mercuric  sulphide  can  be  obtained. 

At  1560°  C.  the  vapour  density  of  mercuric  sulphide  is  78,  indicating 
that  the  molecule  has  dissociated  into  Hg  +  Hg  -f  S2. 

Mercury  belongs  to  the  Magnesium  family  of  metals  (p.  383). 

PLATINUM. 

Pt=  193.3  Pai'ts  by  weight. 

296.  Platinum  (platina,  Spanish  diminutive  of  silver)  is  remarkable 
for  (i)  its  high  specific  gravity  of  21.5  ;  (2)  its  very  high  fusing-point, 
1775°  G- »  (3)  its  slight  expansion  when  heated,  which  allows  it  to  be 
sealed  into  glass  without  cracking  by  unequal  contraction  on  cooling ; 
(4)  its  being  unchanged  by  air  at  all  temperatures  ;  (5)  its  resistance 
to  the  action  of  strong  acids ;  (6)  its  power  of  inducing  the  combination 
of  oxygen  with  other  bodies  ;  (7)  its  being  found  in  nature  only  in  the 
metallic  state.  It  is  found  distributed  in  flattened  grains  through  alluvial 
deposits  similar  to  those  in  which  gold  is  found  ;  indeed,  these  grains  are 
generally  accompanied  by  grains  of  gold,  and  of  a  group  of  very  rare 
metals  only  found  in  platinum  ores,  viz.,  palladium,  iridium,  osmium, 
rhodium,  and  ruthenium.  Russia  furnishes  the  largest  supply  of 
platinum  from  the  Ural  Mountains,  but  smaller  quantities  are  obtained 
from  Brazil,  Peru,  Borneo,  Australia,  and  California. 

The  process  for  obtaining  the  platinum  in  a  marketable  form  is  rather 
a  chemical  than  a  metallurgical  operation.  The  ore  containing  the  grains 
of  platinum  and  the  associated  metals,  is  heated  with  hydrochloric  acid 
to  dissolve  base  metals,  and  then,  in  retorts,  under  slightly  increased 
pressure  to  hasten  the  dissolution,  with  aqua  regia,  which  dissolves 
palladium,  rhodium,  platinum,  and  a  little  iridium  as  chlorides.  The 
osmium  in  the  ore  partly  distils  as  osmic  acid  and  partly  remains 
undissolved  as  an  alloy  with  the  iridium  (osmiridiuni),  together  with 
ruthenium,  chrome  iron  ore,  and  titanic  iron.  The  solution  containing 
the  platinum  as  PtCl4  is  neutralised  with  Na,C03  and  the  palladium  is 
precipitated  as  cyanide,  Pd(CN)2,  by  the  addition  of  mercuric  cyanide. 
The  platinum  is  now  precipitated  by  the  addition  of  ammonium  chloride, 
with  which  platinic  chloride  combines  to  form  a  yellow,  sparingly  soluble 
salt  (ammonium  platinochloride  (NH4)2PtCJ6  or  2NH4Cl.PtCl4).*  This 
precipitate  is  collected,  washed,  and  heated  to  redness,  when  all  its 
constituents,  except  the  platinum,  are  expelled  in  the  form  of  gas,  that 
metal  being  left  in  the  peculiar  porous  condition  in  which  it  is  known 
as  spongy  platinum.  To  convert  this  into  compact  platinum  it  is  melted 
in  a  lime  furnace  by  means  of  the  oxyhydrogen  blowr-pipe  (Fig.  243), 
whence  it  is  poured  into  an  ingot  mould  made  of  gas-carbon.  The 
melted  platinum  absorbs  oxygen,  as  melted  silver  does,  and  evolves  it 
again  on  cooling. 

This  method  is  now  modified  by  fusing  the  ore  with  6  parts  of  lead,  and  treating 
the  alloy  with  dilute  nitric  acid  (i  :  8),  which  dissolves  most  of  the  lead,  together 

*  When  rhodium  is  present,  the  liquid  from  which  this  precipitate  has  been  deposited  will 
have  a  rose  colour.  The  precipitate  is  then  mixed  with  bisulphate  of  potassium  and  a  little 
bisulphate  of  ammonium,  and  heated  to  redness  in  a  platinum  dish.  The  rhodium  is  then 
converted  into  a  double  sulphate  of  rhodium  and  potassium,  which  may  he  removed  from  the 
spongy  platinum  by  boiling  with  water. 


PKOPERTIES   OF  PLATINUM.  505 

with  copper,  iron,  palladium,  and  rhodium.  The  residue,  containing  platinum  lead 
and  indium,  is  treated  with  dilute  aqua  regia,  which  leaves  the  indium  undfoeolved' 
The  lead  is  precipitated  by  sulphuric  acid,  and  the  solution  of  platinic  chloride 

tT6iltCCi  RS  clDOVG. 

Another  process  based  upon  the  use  of  lead  consists  in  fusing  the  platinum  ore 
m  a  small  reverberatory  furnace,  with  an  equal  weight  of  lead  sulphide  and  the  same 
quantity  of  lead  oxide  when  the  sulphur  and  oxygen 
escape  as  S02,  and  the  reduced  lead  dissolves  the 
platinum,  leaving  undissolved  a  very  heavy  alloy 
of  osmium  and  iridium,  which  sinks  to  the  bottom. 
The  upper  part  of  the  alloy  of  lead  and  platinum  is 
then  ladled  out  and  cupelled  (p.  465),  when  the 
latter  metal  is  left  in  a  spongy  condition,  the  lead 
being  removed  in  the  form  of  oxide. 


Its  resistance  to  the  action  of  high  tem- 
peratures and  of  most  chemical  agents 
renders  platinum  of  the  greatest  service  in 
chemical  operations.  It  will  be  remem- 
bered that  platinum  stills  are  employed, 
even  on  the  large  scale,  for  the  concen- 
tration of  sulphuric  acid.  In  the  form  of 

basins,  small  crucibles,  foil,  and  wire,  this  metal  is  indispensable  to  the 
analytical  chemist.  Unfortunately,  it  is  softer  than  silver,  and  there- 
fore ill-adapted  for  wear,  and  is  so  heavy  that  even  small  vessels  must 
be  made  very  thin  in  order  not  to  be  too  heavy  for  a  delicate  balance. 
Commercial  platinum  generally  contains  a  little  iridium,  which  hardens 
it  and  increases  its  elasticity.  Its  malleability  and  ductility  are  very 
considerable,  so  that  it  is  easily  rolled  into  thin  foil  and  drawn  into  fine 
wires  ;  in  ductility  it  is  surpassed  only  by  gold  and  silver,  and  it  has 
been  drawn,  by  an  ingenious  contrivance  of  Wollaston's,  into  wire  of 
only  3-^.i.^th  of  an  inch  in  diameter,  a  mile  of  which  (notwithstanding 
the  high  specific  gravity  of  the  metal)  would  only  weigh  a  single  grain. 

This  remarkable  extension  of  the  metal  was  effected  by  casting  a  cylinder  of  silver 
around  a  very  thin  platinum  wire  obtained  by  the  ordinary  process  of  wire-drawing  ; 
when  the  cylinder  of  silver,  with  the  platinum  wire  in  its  centre,  was  itself  drawn 
out  into  an  extremely  thin  wire,  of  course,  the  platinum  core  would  have  become 
inconceivably  thin,  and  when  the  silver  casing  was  dissolved  off  by  nitric  acid, 
this  minute  filament  of  platinum  was  left.  Platinum  is  sometimes  employed  for 
the  touch-holes  of  fowling-pieces  on  account  of  its  resistance  to  corrosion.  An 
alloy  of  4  parts  platinum,  3  parts  silver,  and  I  part  copper  is  used  for  pens. 

The  widest  application  of  platinum,  however,  is  in  the  form  of  wire 
for  conveying  the  electric  current  to  the  filament  in  an  electric 
incandescence  lamp.  As  such  lamps  must  be  vacuous  the  leading-in 
wires  must  be  hermetically  sealed  in  the  glass,  which  is  possible  only 
with  platinum,  its  coefficient  of  expansion  being  nearer  to  that  of  glass 
than  is  the  coefficient  of  any  other  metal. 

The  remarkable  power  possessed  by  platinum,  of  inducing  chemical 
combination  between  oxygen  and  other  gases,  has  already  been  noticed. 
Even  the  compact  metal  possesses  this  property,  as  may  be  seen  by 
heating  a  piece  of  platinum  foil  to  redness  in  the  flame  of  a  gas-burner, 
rapidly  extinguishing  the  gas,  and  turning  it  on  again,  when  the 
cold  stream  of  gas  will  still  maintain  the  metal  at  a  red  heat,  in  con- 
sequence of  the  combination  with  atmospheric  oxygen  at  the  surface  of 
the  platinum. 
A  similar  experiment  may  be  made  by  suspending  a  coil  of  platinum  wire  in  the 


506  PLATINUM   BLACK. 

flame  of  a  spirit  lamp  (Fig.  244),  and  suddenly  extinguishing  the  flame,  when  the 
metal  is  intensely  heated,  by  placing  the  mouth  of  a  test-tube  over  it ;  the  wire 
will  continue  to  glow  by  inducing  the  combination  of  the  spirit  vapour  with  oxygen 
on  its  surface.  By  substituting  a  little  ball  of  spongy  platinum  for  the  coil  of 
platinum  wire,  and  mixing  some  fragrant  essential  oil  with  the  spirit,  an  elegant 
perfuming  lamp  has  been  contrived.  Upon  the  same  principle  an  instantaneous 
light  apparatus  has  been  made,  in  which  a  jet  of  hydrogen  gas 
is  kindled  by  impinging  upon  a  fragment  of  cold  spongy  platinum, 
Y/hich  at  once  ignites  it  by  inducing  its  combination  with  the 
oxygen  condensed  within  the  pores  of  the  metal  (Dobfireiner'x 
lattt/j').  Spongy  platinum  is  obtained  in  a  very  active  form  by 
heating  the  ammonio-chloride  of  platinum  very  gently  in  a  stream 
of  coal  gas  or  hydrogen  as  long  as  any  fumes  of  HC1  are  evolved. 
If  platinum  be  precipitated  in  the  metallic  state  from  a  solution, 
it  is  obtained  in  the  form  of  a  powder,  called  platinum  black, 
which  possesses  this  power  of  promoting  combination  with  oxygen 
in  the  highest  perfection.  This  form  of  platinum  may  be  obtained 
Fig.  244.  by  boiling  solution  of  platinic  chloride  with  Rochelle  salt  (potas- 

sium sodium  tartrate),  or  by  dropping  it  into  a  boiling  mixture  of 
3  vols.  glycerine  and  2  vols.  KOH  of  sp.  gr.  1.08,  when  the  platinum  black  is  pre- 
cipitated, and  must  be  filtered  off,  washed,  and  dried  at  a  gentle  heat. 

Platinum  in  this  form  is  capable  of  absorbing  800  times  its  volume  of  oxygen, 
which  does  not  enter  into  combination  with  it,  but  is  simply  condensed  into  its 
pores,  and  is  available  for  combination  with  other  bodies.  A  jet  of  hydrogen 
allowed  to  pass  on  to  a  grain  or  two  of  this  powder  is  kindled  at  once,  and  if  a 
few  particles  of  it  be  thrown  into  a  mixture  of  hydrogen  and  oxygen,  explosion 
immediately  follows.  A  drop  of  alcohol  is  also  inflamed  when  allowed  to  fall 
upon  a  little  of  the  powder.  Platinum  black  loses  its  activity  after  having  been 
heated  to  redness.  It  has  been  stated  that  platinum  black  is  really  an  oxide,  and 
that  the  combustion  of  hydrogen  and  oxygen  in  presence  of  platinum  is  to  be 
explained  by  the  formation,  at  first,  of  an  unstable  hydride  of  platinum,  with  de- 
velopment of  heat,  which  is  oxidised  with  a  still  further  development  of  heat. 
By  a  continued  repetition  of  these  changes,  the  platinum  is  raised  to  the  tempera- 
ture necessary  for  ignition. 

Although  platinum  resists  the  action  of  hydrochloric  and  nitric  acids, 
unless  they  are  mixed,  and  is  unaffected  at  the  ordinary  temperature  by 
other  chemical  agents,  it  is  easily  attacked  at  high  temperatures  by 
phosphorus,  arsenic,  carbon,  boron,  silicon,  and  by  a  large  number  of 
the  metals  ;  the  caustic  alkalies  and  alkaline  earths  also  corrode  it  whei 
heated,  so  that  some  discretion  is  necessary  in  the  use  of  vessels  mad( 
of  this  costly  metal.*  When  platinum  is  alloyed  with  10  parts  of  silver, 
both  metals  may  be  dissolved  by  nitric  acid. 

If  platinum  be  dissolved  in  4  or  5  parts  of  melted  tin,  and  the  alloy  boil* 
with  hydrochloric  acid  mixed  with  an  equal  bulk  of  water,  glistening  scales  ai 
left,  resembling  graphite,  and  soiling  the  fingers.  This  contains  platinum,  tin, 
chlorine,  hydrogen,  and  oxygen.  By  treatment  with  warm  dilute  ammonia,  it 
becomes  brownish,  and  when  dried  in  a  vacuum  over  sulphuric  acid,  has  the 
composition  Ptv,Sn304H2.  When  this  is  heated  in  dry  oxygen,  it  becomes  Pt2Sn304. 
Heated  in  hydrogen  it  leaves  a  greyish  almost  infusible  powder  containing  Pt2Sn3. 

297.  OXIDES  OF  PLATINUM. — Only  one  compound  of  platinum  with  oxygen  is 
known  in  the  separate  state,  the  other  having  been  obtained  in  combination  with 
water.  Platinou*  oxide,  PtO,  is  precipitated  as  a  black  hydrate  by  decomposing- 
platinous  chloride  with  potash,  and  neutralising  the  solution  with  dilute  sulphuric 
acid.  It  is  a  feeble  base,  and  decomposes  when  heated,  leaving  metallic  platinum. 
Platinic  oxide,  Pt02,  is  also  a  weak  base,  but  is  characteristically  an  acid  oxide. 

Platinic  lt,ydroj'ide,  Pt(OH)4,  is  obtained  by  boiling  platinic  chloride  \vith  potash, 
and  treating  the  precipitate  with  acetic  acid  ;  this  leaves  a  nearly  white  powder, 
Pt(OH)4.2H20.  At  100°  C.  this  becomes  brown  Pt(OH)4.  Acids  dissolve  it,  forming- 

*  When  platinum  leaf  is  heated  with  HC1  at  150°  in  a  sealed  tube  it  dissolves,  but  the 
chloride  is  subsequently  reduced  by  the  hydrogen  evolved,  and  the  metal  reappears  as 
crystals  on  the  sides  ol  the  tube.  The  same  lias  been  observed  of  yold  and  silver  leaf. 


PLATINIC   CHLORIDE. 


507 


platinic  salts.     Alkalies  dissolve  it,  forming  platinates.     Heat  reduces  the  oxides 
and  hydroxides  to  metallic  platinum. 

Sodium  platinate,  Na20.3Pt02.6Aq,  may  be  crystallised  from  a  solution  of  the 
hydroxide  in  soda.  Calcium  platinate  is  convenient  for  the  separation  of  platinum 
from  iridium,  which  is  generally  contained  in  the  commercial  metal  ;  for  this 
purpose,  the  platinum  is  dissolved  in  nitre-hydrochloric  acid,  the  solution 
evaporated  till  it  solidifies  on  cooling,  the  mixed  chlorides  of  iridium  and  platinum 
dissolved  in  water,  and  decomposed  with  an  excess  of  lime  without  exposure  to  light ; 
the  platinum  then  passes  into  solution  as  calcium  platinate.  and  the  platinic  acid 
may  be  separated  as  a  calcium  salt  from  the  filtered  solution,  by  exposure  to  light. 
If  platinic  hydroxide  be  dissolved  in  diluted  sulphuric  acid  and  the  solution  mixed 
with  excess  of  ammonia,  a  black  precipitate  of  fulminating  platinum  is  obtained, 
which  detonates  violently  at  about  400°  F.  (204°  C.).  This  compound  is  said  to 
have  a  composition  corresponding  with  the  formula  N2H2Ptiv.4H20,  or  a  com- 
bination of  water  with  a  double  molecule  of  ammonia  (N2H6),  in  which  4  atoms  of 
hydrogen  are  exchanged  for  i  atom  of  tetravalent  platinum. 

298.  Chlorides  of  Platinum. — The  per  chloride  or  platinic  chloride, 
(PtCl4),  is  the  most  useful  salt  of  the  metal,  and  may  be  prepared  by 
dissolving  scraps  of  platinum-foil  in  a  mixture  of  four  measures  of 
hydrochloric  acid  with  one  of  nitric  acid  (6.5  grams  of  platinum  require 
56  c.c.  of  hydrochloric  acid),  evaporating  the  liquid  at  a  gentle  heat  to 
the  consistence  of  a  syrup,  redissolving  in  hydrochloric  acid,  and  again 
evaporating  to  expel  excess  of  nitric  acid.  The  syrupy  liquid  solidifies, 
on  cooling,  to  a  red-brown  mass,  which  is  very  deliquescent,  and  dis- 
solves easily  in  water  or  alcohol  to  a  red-brown  solution.  If  the  con- 
centrated solution  be  allowed  to  cool  before  all  the  free  hydrochloric 
acid  has  been  expelled,  long  brown  prismatic  crystals  of  a  combination 
of  platinic  chloride  with  hydrochloric  acid  are  obtained  (PtCl4.2HC1.6Aq). 
If  these  are  heated  in  dry  HC1,  the  anhydrous  PtCl4  is  obtainecF  in  a 
non-deliquescent  condition ;  it  decomposes  Na2C03,  evolving  C02. 
Platinic  chloride  is  remarkable  for  its  disposition  to  form  sparingly 
soluble  double  chlorides  with  the  chlorides  of  the  alkali  metals  and  the 
hydrochlorides  of  organic  bases,  a  property  of  great  value  to  the  chemist 
in  effecting  the  detection  and  separation  of  these  bodies.  These  double 
chlorides  are  generally  regarded  as  platinochlorides  or  chloroplatinates, 
derived  from  hydrogen  platinochloride,  or  chloroplatinic  acid,  H2PtCl6. 

A  good  example  of  this  has  lately  been  afforded  in  the  separation  of  potassium, 
rubidium,  and  caesium.  The  chlorides  of  these  three  metals  having  been 
separated  from  the  various  other  salts  contained  in  the  mineral  water  in  which 
they  occur,  are  precipitated  with  platinic  chloride,  which  forms  combinations 
with  all  the  three  chlorides.  The  platino-chloride  of  potassium  is  more  easily 
dissolved  by  boiling  water  than  are  those  of  rubidium  and  cesium,  and  is  removed 
by  boiling  the  mixed  precipitate  with  small  portions  of  water  as  long  as  the  latter 
acquires  a  yellow  colour.  The  remaining  platino-chlorides  of  rubidium  and 
caesium  are  then  heated  in  a  current  of  hydrogen,  which  reduces  the  platinum  to 
the  metallic  state,  and  the  chlorides  may  then  be  extracted  by  water,  in  which  they 
are  very  soluble. 

Potassium  platinochloride  (2KCl.PtCl4)  forms  minute  yellow  octa- 
hedral crystals  ;  those  of  rubidium  and  caesium  have  a  similar  r.omposi- 
tion  and  crystalline  form.  Sodium  platinochloride  differs  from  these 
in  being  very  soluble  in  water  and  alcohol ;  it  may  be  crystallised  in 
long  red  prisms,  having  the  composition  2NaCl.PtCl4.6Aq.  Ammonium 
platinochloride  (2NH4Cl.Pt014)  has  been  already  noticed  as  the  form  m 
which  platinum  is  precipitated  in  order  to  separate  it  from  other  metals. 
It  crystallises,  like  the  potassium-salt,  in  yellow  octahedra,  which  are 
very  sparingly  soluble  in  water  and  insoluble  in  alcohol.  It  is  the  torm 


5O8  PLATINOUS   CHLORIDE. 

into  which  nitrogen  is  finally  converted  in  analysis  in  order  to  determine 
its  weight.  When  heated  to-  redness,  this  salt  leaves  a  residue  of  spongy 
platinum.  Silver  nitrate,  added  in  excess  to  platinic  chloride  containing 
HC1,  precipitates  all  the  platinum  as  2AgCl.Pt014,  a  yellow  precipitate 
decomposed  by  water. 

Platinic  chloride  is  sometimes  used  for  browning  gun-barrels,  &c., 
under  the  name  of  muriate  ofplatina. 

Protocldorlde,  or  plat i turns  chloride  (PtCl2). — Platinic  chloride  may  be  heated  to 
450°  F.  (232°  C.)  without  decomposition,  but  above  that  temperature  it  evolves 
chlorine,  and  is  slowly  converted  into  the  platinous  chloride,  which  is  reduced,  at 
a  much  higher  temperature,  to  the  metallic  state.  Platinous  chloride  forms  a  dingy 
green  powder,  which  is  insoluble  in  water  and  in  HN03  and  H2S04,  but  dissolves 
in  hot  HC1,  and  in  solution  of  platinic  chloride,  yielding  in  the  former  a  bright  red, 
in  the  latter  a  very  dark  brown-red  solution.  Platinous  chloride  is  capable  of 
absorbing  ethylene,  C2H4.  At  250°  C.  it  absorbs  CO  and  forms  the  crystalline  com- 
pounds PtCl2.CO,  PtCl2(CO)2,  and  (PtCl2)2(CO)3,  and  the  non-volatile  compound 
PtCl2.2COCl2  ;  the  first  of  these  volatilises  unchanged.  The  solution  of  PtCl2  in 
HC1  is  not  precipitated  by  KC1,  but  a  soluble  double  chloride  (2KCl.PtCl2)  may  be 
crystallised  |from  the  liquid.  If  NH4C1  be  added  to  the  hydrochloric  solution,  a 
double  salt,  2NH4Cl.PtCl2.  ammonium-  cldoroplatimte,  may  be  obtained  in  yellow 
crystals  by  evaporation.  If,  instead  of  NH4C1,  free  NH3  be  added  in  excess  to  the 
boiling  solution  of  platinous  chloride  in  HC1.  brilliant  green  needles  (f/reen  suit  of 
Maynus)  are  deposited  on  cooling,  which  contain  the  elements  of  platinous  chloride 
and  ammonia,  PtCl2(NH3)2 ;  but  from  the  behaviour  of  this  compound  with 
chemical  agents,  its  true  formula  would  appear  to  be  N2H6Pt"Cl2,  in  which  the 
place  of  two  atoms  of  hydrogen  in  2  molecules  of  NH4C1  is  occupied  by  platinum. 
By  heating  this  salt  with  an  excess  of  ammonia,  the  solution,  on  cooling, 
deposits  yellowish- white  prismatic  crystals  of  diplatosamine  hydrochlorlde, 
N4H]0Pt".2HCl.Aq,  the  production  of  which  may  be  represented  by  the  equation 
N2H6Pt"Clo  +  2NH3  =  N4H10Pt".2HCl.  By  decomposing  a  solution  of  this  salt  with 
silver  sulphate,  the  dl platosamine  mlpltate  is  obtained. 

N4H10Pt".2HCl  +  Ag2S04  =  N4H10Pt".H2S04  +  2AgCl. 

When  the  solution  of  diplatosamine  sulphate  is  treated  with  barium  hydroxide, 
barium  sulphate  is  precipitated,  and  a  powerfully  alkaline  solution  is  obtained, 
which  yields  crystals  of  diplatosamine  liydrate,  N4H10Pt".2H20,  a  strong  alkali 
which  may  be  iregarded  as  a  compound  of  water  with  4  molecules  of  ammonia 
(N4H12),  in  which  two  atoms  of  hydrogen  are  exchanged  for  platinum.  The  dipla- 
tosamine hydrate  has  a  strong  resemblance  to  the  alkalies,  eagerly  absorbing  C02 
from  the  air,  and  expelling  NH3  from  its  salts.  When  the  hydrate  of  diplatosamine 
is  heated  to  1 10°  C.  it  gives  off  water  and  ammonia,  and  becomes  converted  into  a 
grey  insoluble  substance,  which  is  platoxamine  hydrate,  N.2H4Pt".H20,  and  may  be 
regarded  as  a  compound  of  water  with  a  double  molecule  of  ammonia  (N2H6),  in 
which  one-third  of  the  hydrogen  is  exchanged  for  platinum.  This  substance  is  also 
a  base,  and  forms  salts,  most  of  which  are  insoluble  ;  the  hydrochloride  (N2H4Pt,2HCl) 
is  isomeric  with  the  green  salt  of  Magnus,  and  may  be  obtained  from  that  com- 
pound by  dissolving  in  a  hot  solution  of  (NH4)2S04*from  which  it  crystallises  on 
cooling.* 

If  the  platosamine  liydrochloride,  suspended  in  boiling  water,  be  treated  with 
chlorine,  it  is  converted  into  platinamine  h-ydrochlorid-e,  N2H2Ptiv.4HCl.  The  con- 
version of  the  platosamine  hydrochloride  into  platinamine  hydrochloride  may 
be  represented  by  the  equation  N2H4Pt.2HCl  +  Cl2  =  N2H2Pt.4HCl.  By  boiling 
the  platinamine  hydrochloride  with  silver  nitrate,  it  is  converted  into  platinamine 
nitrate,  N2H2Pt(HN03)4  ;  and  when  this  is  dissolved  in  boiling  water  and  decom- 
posed by  ammonia,  the  platinam ine  hydrate  (N2H0Pt.4H20)  is  obtained  in  yellow 
prismatic  crystals,  having  the  same  composition  as  that  assigned  to  fulminating 
platinum. 

*  The  salts  of  diplatosamine  are  distinguished  from  those  of  platosamine  by  the  action  of 
nitrous  acid,  which  gives  a  tine  blue  or  green  precipitate  or  coloration  with  the  former.  For 
the  cause  of  this  change,  and  for  many  other  interesting  points  in  the  history  of  these 
platinum  compounds,  the  reader  is  referred  to  the  elaboi-ate  and  accurate  memoir  by  Hado\v, 
Journal  of  the  Chemical  Society,  August  1866. 


PROPERTIES  OF  PALLADIUM.  509 

Some  of  the  salts  of  diplatinamim  (N4H8Ptiv)  have  been  obtained,  this  base  being 
derived  from  4  molecules  of  ammonia  in  which  H4  have  been  exchanged  for  Ptiv 

Potassium  platinonitrite,  K2Pt(N02)4,  crystallises  when  a  hot  mixture  of  potassium 
nitrite  and  potassium  platinous  chloride  solution  is  allowed  to  cool ;  it  readily 
combines  with  2  atomic  proportions  of  a  halogen.  The  acid  H0Pt(N09),  has  been 
prepared. 

Platinw  iodide,  PtI4,  is  a  dark  brown  amorphous  substance  which  is  soluble 
in  HI,  yielding  a  purple-red  solution  containing  2HI.PtI4.9Aq,  which  may  be 
crystallised.  Hence  the  dark  red  colour  when  an  acid  solution  of  PtCl4  is  added 
to  potassium  iodide. 

The  sulphides  of  platinum  correspond  in  composition  with  the  oxides  and 
chlorides,  and  may  be  obtained  by  the  action  of  hydrosulphuric  acid  upon  the 
respective  chlorides,  as  black  precipitates.  PtS2  combines  with  alkaline  sulphides 
to  form  soluble  compounds.  K2S.3PtS.PtS0  is  obtained  by  fusing  spongy  platinum 
with  KOH  and  sulphur. 

Platinum  phosphide,  PtP2,  and  arsenide,  PtAs^  are  lustrous  metallic  bodies  formed 
by  direct  combination  at  a  high  temperature. 

PALLADIUM,  Pd=io5.2. 

299.  This  metal  is  found  in  small  quantity  associated  with  native  gold  and 
platinum.   It  presents  a  great  general  resemblance  to  platinum,  but  is  distinguished 
therefrom  by  being  far  more  easily  oxidised,  and  by  forming  an  insoluble  cyanide. 
This  circumstance  is  taken  advantage  of  in  separating  palladium  from  the  platinum 
ores  (p.  504).     The  cyanide  yields  spongy  palladium  when  heated,  which  may  be 
fused  in  the  same  manner  as  platinum.     When  alloyed  with  native  gold,  palladium 
is  separated  by  fusing  the  alloy  with  silver,  and  boiling  it  with  ni+-  ic  acid,  which 
leaves  the  gold  undissolved.  The  silver  is  precipitated  from  the  solution  as  chloride, 
by  adding  NaCl,  and  metallic  zinc  is  placed  in  the  liquid,  which  precipitates  the 
palladium,  lead,  and  copper  as  a  black  powder.    This  is  dissolved  in  HN03,  and  the 
solution  mixed  with  an  excess  of  NH3,  which  precipitates  the  lead  oxide,  leaving  the 
copper  and  palladium   in  solution.     On   adding  HC1  in   slight   excess,  a  yellow 
precipitate  of  palladamlne  liydrochloride  (N2H4Pd.2HCl)  is  obtained,  which 'leaves 
metallic  palladium  when  heated. 

Palladium  is  much  lighter  (sp.  gr.  n.8)  than  platinum;  it  is  malleable  and 
ductile  like  that  metal  from  which  it  is  distinguished  by  being  stained  black  by 
an  alcoholic  solution  of  iodine.  It  is  capable  of  being  highly  polished  and  is 
useful  for  mirrors.  It  melts  at  1500°  C.  It  is  unchangeable  in  air  unless  heated, 
when  it  becomes  blue  from  superficial  oxidation,  but  regains  its  whiteness  when 
further  heated,  the  oxide  being  decomposed.  Unlike  platinum,  it  may  be  dissolved 
by  nitric  acid,  forming  palladium  nitrate,  Pd(N03)2,  which  is  sometimes  employed 
in  analysis  for  precipitating  iodine  from  the  iodides,  in  the  form  of  black  palladium 
iodide  (PdI2).  Palladium  is  useful,  on  account  of  its  hardness,  lightness,  and 
resistance  to  tarnish,  in  the  construction  of  philosophical  instruments  ;  alloyed  with 
twice  its  weights  of  silver,  it  is  used  for  small  weights.  Its  capacity  for  absorbing 
hydrogen  has  been  already  noticed  (p.  49). 

Palladium  forms  three  oxides  ;  Pd.,0  is  formed  when  the  metal  is  heated  in  air  : 
PdO  is  left  when  Pd(N03)2  is  gently  heated  ;  Pd00  is  precipitated  by  boiling 
PdCl4  with  Na,2CO3.  Palladia  chloride  (PdCl4)  is  "very  unstable,  being  easily 
decomposed,  eve~n  in  solution,  into  palladom  chloride  (PdCl2)  and  free  chlorine. 
The  latter  chloride  is  reduced  by  hydrogen  in  the  cold,  and  may  be  applied  as 
a  test  for  this  gas.  Both  the  chlorides  form  double  salts  with  the  alkali  chlorides  ; 
ammonium  chloropalladite,  PdCl2.2NH4Cl,  has  a  dark  green  colour.  PdCl  is  said  to 
be  formed  when  PdCl2  is  gently  heated.  Pulverulent  palladium  cat-hide  is  formed 
when  the  metal  is  heated  in  the  flame  of  a  spirit-lamp,  or  in  gaseous  hydrocarbons. 

RHODIUM,  Rh=io2.2. 

300.  Rhodium,  another  of  the  metals  associated  with  the  ores  of  platinum,  hot* 
acquired  its  name  from  the  red  colour  of   many  of   its  salts  (p68oi>,  a   rose). 

is  obtained  from  the  solution  of  the  ore  in  aqua  regla  by  precipitating  the  platin 
with   ammonium  chloride,  neutralising   with  sodium  carbonate,  adding  mercuric 
cyanide  to  separate  the  palladium,  and  evaporating  the  filtered  solution  to  dry- 
ness  with  excess  of  hydrochloric  acid.     On  treating  the  residue  with  alcohol,  tl 
double  chloride  of  rhodium  and  sodium  is  left  undissolved  as  a  red  powder,     i5y 


510  OSMIUM. 

heating  this  in  a  tube  through  which  hydrogen  is  passed,  the  rhodium  is  reduced 
to  the  metallic  state,  and  the  sodium  chloride  may  be  washed  out  with  water, 
leaving  a  grey  powder  of  metallic  rhodium.  Avhich  is  fused  by  the  oxyhydrogen 
blow-pipe  at  200°  C.,  and  forms  a  very  hard  malleable  metal  (sp.  gr.  12.1)  not 
dissolved  even  by  aqua  regla,  although  this  acid  dissolves  it  in  ores  of  platinum, 
because  it  is  alloyed  with  other  metals.  If  platinum  be  alloyed  with  30  per  cent,  of 
rhodium,  however,  it  is  not  affected  by  aqua  regia,  which  will  probably  render  the 
alloy  useful  for  chemical  vessels.  Rhodium  may  be  brought  into  solution  by 
fusing  it  with  bisulphate  of  potash,  when  S02  escapes,  and  a  double  sulphate  of 
rhodium  and  potassium  is  formed,  which  gives  a  pink  solution  in  water.  When 
rhodium  is  melted  with  zinc  and  the  alloy  is  boiled  with  an  acid,  the  rhodium 
is  left  as  a  black  powder  which  is  apparently  an  allotropic  form  of  the  metal, 
for  when  it  is  heated  it  explodes,  but  remains  metallic  rhodium.  Finely  divided 
rhodium  is  oxidised,  when  heated  in  air,  to  KhO.  There  appear  to  be  three  other 
oxides,  namely,  Rh203,  which  is  left  when  the  nitrate  is  gently  heated  ;  Rh02, 
formed  when  the  metal  is  fused  with  KOH  and  KN03  ;  Rh63,  formed  by  heating 
the  hydrated  dioxide  (which  is  a  green  precipitate  obtained  when  chlorine  is 
passed  into  potash  containing  Kh203)  with  nitric  acid.  The  sesquioxide  (Rh203)  is 
the  most  stable  of  these  ;  it  is  not  easily  decomposed  by  heat,  and  is  insoluble  in 
acids,  though  it  is  a  basic  oxide,  and  its  salts,  which  have  a  red  colour,  are  obtained 
by  indirect  methods. 

The  salts  of  rhodium  are  only  of  one  type— RX3.  Rhodium,  trichloride,  RhCl3, 
obtained  by  heating  the  metal  in  chlorine,  has  a  brownish-red  colour  and  is 
insoluble  ;  it  may,  however,  be  obtained  in  a  red  solution  by  dissolving  the 
hydrated  Rh203  in  HC1.  Rhodium  recalls  chromium  in  that  its  salts  are 
capable  of  existing  in  two  forms  ;  thus,  when  the  red  solution  of  rhodium  chloride 
is  boiled  with  a  strong  solution  of  alkali,  black  Rh(OH)3  is  thrown  down,  but  when 
the  alkali  is  added  by  degrees,  yellow  Rh(OH)3  is  precipitated  ;  this  dissolves  to  a 
yellow  solution  in  acids,  which  becomes  red  only  on  boiling.  Like  chromium,  too, 
rhodium  salts  form  a  series  of  amines  (p.  434).  RhCl3  forms  two  classes  of  double 
salts  with  the  alkali  chlorides — for  instance,  K3Rh016.3H20  and  K2RhCl5.H20. 
The  double  chloride  of  rhodium  and  sodium  (3NaCl.RhCl3)  is  prepared  by  heating 
a  mixture  of  pulverulent  rhodium  and  NaCl  in  a  current  of  chlorine.  It  crystallises 
in  red  octahedra  with  QAq.  On  boiling  a  solution  of  RhCl3  with  NH3  in  excess, 
a  yellow  ammoniated  salt  (RhCl3.5NH3)  may  be  crystallised,  from  which  the 
metallic  rhodium  may  be  obtained  by  ignition. 

With  sulphur,  rhodium  combines  energetically  at  a  high  temperature  ;  a  mono- 
sulphide  and  a  sesquisulphide  have  been  obtained. 

An  alloy  of  gold  with  between  30  and  40  per  cent,  of  rhodium  has  been  found  in 
Mexico. 

An  alloy  of  platinum  with  10  per  cent,  of  rhodium  is  used  as  one  of  the  metals, 
platinum  being  the  other,  of  the  thermo-electric  couple  used  as  a  pyrometer. 

OSMIUM,  08=189.6. 

301.  This  metal  is  characterised  by  its  yielding  a  very  volatile  acid  oxide  (jwosm'u; 
anhydride,  Os04),  the  vapours  of  which  have  a  very  irritating  odour  ((5<r/u^,  odour'). 
It  occurs  in  the  ores  of  platinum  in  flat  scales,  consisting  of  an  alloy  of  osmium, 
iridium,  ruthenium,  and  rhodium.  This  alloy  is  also  found  associated  with  native 
gold,  and,  being  very  heavy,  it  accumulates  at  the  bottom  of  the  crucible  in 
which  the  gold  is  melted.  The  osmium  alloy  is  extremely  hard,  and  has  been 
used  to  tip  the  points  of  gold  pens.  When  a  grain  of  it  happens  to  be  present 
in  the  gold  which  is  being  coined,  it  often  seriously  injures  the  die.  When  tl 
platinum  ore  is  treated  with  aqua  rer/ia,  this  alloy  is  left  undissolved,  together  wit 
grains  of  chrome-iron  ore  and  titanic  iron.  To  extract  osmium  from  this  residiw 
it  is  heated  in  a  porcelain  tube  through  which  a  current  of  dry  air  is  passed,  when 
the  osmium  is  converted  into  perosmic  anhydride,  the  vapour  of  which  is  carried 
forward  by  the  current  of  air  and  condensed  in  bottles  provided  to  receive  it. 
The  perosmic  anhydride  forms  colourless  prismatic  c^stals  which  fuse  and 
volatilise  below  the  boiling-point  of  water,  yielding  a  most  irritating  vapour, 
resembling  chlorine.  It  is  very  soluble  in  water,  giving  a  solution  which  exhales 
the  same  odour  and  stains  the  skin  black  ;  tincture  of  galls  gives  a  blue  precipitate 
with  the  solution.  Its  acid  properties  are  feeble,  for  it  neither  reddens  litmus 
nor  decomposes  the  carbonates,  and  its  salts  are  decomposed  by  boiling  their 
solutions.  Its  solution  in  HC1  gives  a  black  precipitate  of  OsS4,  with  H2S.  By 


RUTHENIUM.  5  1  1 

passing  a  mixture  of  CO  and  vapour  of  Os04  through  a  red-hot  porcelain  tube 
amorphous  osmium  is  obtained,  and  may  be  converted  into  the  crystalline  form  by 
fusing  it  with  tin  and  dissolving  in  HC1,  when  blue  lustrous  cubical  crystals  of 
osmium  are  obtained,  which  scratch  glass,  and  are  heavier  than  any  other  body 
having  the  specific  gravity  22.48.  It  can  be  fused  in  the  electric  arc. 

By  dissolving  perosmic  anhydride  in  potash,  potassium,  pet-ornate,  KOsO,,  is 
supposed  to  be  formed,  but  this  has  not  been  isolated.  When  alcohol  is  added 
to  this  solution  the  Os04,  is  presumably  reduced  to  OsO.,,  for  rose-coloured 
crystals  of  pofasrivm  osmate,  K2O.Os03.2H20,  are  deposited  ;  by  treating  this  salt 
with  nitric  acid,  osmlc  acid,  H20s04,  is  obtained  as  a  sooty-black  powder,  which 
tends  to  oxidise  in  air,  yielding  an  odour  of  perosmic  anhydride. 

"When  Os04  is  dissolved  in  solution  of  S02,  osmium  sulphite,  OsS03,  is  obtained  ; 
this  is  almost  the  only  osmium  oxy-salt  which  is  known.  By  adding  an  alkali  to 
the  solution,  hydrated  osmium  monoxide,  OsO.»H20,  is  obtained  as  a  blue-back 
powder  soluble  in  HC1  to  a  blue  solution  and  easily  oxidised.  Os003  and  Os02  are 
obtained  by  heating  potassium  osmochlorlde,  3KC1.0sC]3,  and  osnrichlorlde, 
2KC1.0sCl4,  respectively  with  an  alkali  carbonate  in  absence  of  air. 

Osmium,  dlchlorlde,  OsCl2,  and  tetrachloride,  OsCl4,  are  obtained  as  two  distinct 
sublimates  when  the  metal  is  heated  in  chlorine  ;  OsCl2  is  less  votatile,  and  forms 
green  needles,  whilst  OsCl4  is  a  dark-red  powder.  By  mixing  Os  with  KC1,  heating 
the  mixture  in  chlorine,  treating  the  mass  with  water,  and  evaporating,  red 
octahedra  of  2KC1.0sCl4  separate,  whilst  from  the  mother  liquor  3KC1.0sCl3.3H20 
is  crystallised.  When  osmic  acid  is  heated  with  HC1  and  alcohol  and  the  solution 
is  evaporated,  crystals  having  the  formula  Os.2Cl7.7H20  are  formed  ;  these  are  red 
when  dry,  but  dissolve  in  water  and  in  alcohol  to  a  green  solution  ;  by  adding  KC1 
to  the  alcoholic  solution,  K2OsCl6  is  precipitated,  and  when  the  filtrate  is  evaporated, 
OsCl3.3H20  crystallises. 

Several  compounds  of  osmium  salts  with  ammonia  (psmamines)  are  known,  and 
a  "potassium  osmiamate"  KNOs03,  is  obtained  by  the  action  of  NIL  on  a  solution 
of  Os04  in  KOH. 

RUTHENIUM,  Ru  = 


302.  In  the  process  of  extracting  osmium  from  the  residue  left  on  treating  the 
platinum  ore  with  aqua,  ref/ia,  by  heating  in  a  current  of   air,  square  prismatic 
crystals  of  rutJtenium  dioxide  (Ru02)  are  deposited  nearer  to  the  heated  portion  of 
the  tube  than  the  perosmic  anhydride,  for  the  dioxide  is  not  itself  volatile,  being 
only  carried  forward  mechanically  ;  or  it  may  be  that  the  volatile  Eu04  is  formed 
in  the  hot  part  of  the  tube,  and  dissociated  into  Ru02  and  02  in  a  cooler  part. 
When  Ku02  is  heated  in  H  the  metal  is  obtained  ;  it  can  be  melted  (1800°  C.)  in 
the  electric  arc,  and  is  then  a  grey  metal,  very  hard,  brittle  when  cold  but  malle- 
able when  hot  ;  its  sp.  gr.  is  12.26.     It  is  insoluble  in  acids.     When  fused  with 
zinc  it  yields  an  allotropic  form  similar  to  that  described  above  for  rhodium. 

When  ruthenium  is  heated  at  1000°  C.  in  oxygen  the  volatile  oxide  Ru04  is 
formed,  and  may  be  isolated  if  rapidly  cooled,  but  when  allowed  to  cool  slowly 
it  decomposes.  The  same  oxide  may  be  obtained  by  heating  ruthenium  with 
KN03  and  KOH,  and  saturating  the  solution  of  the  fused  mass  with  chlorine, 
when  Ru04  sublimes.  It  is  soluble  in  water,  melts  at  25.5°,  and  sublimes  easily  ; 
at  107°  it  decomposes  explosively.  It  is  decomposed  by  light,  yielding,  apparently, 
RuO3. 

The  oxides  RuO  and  Ru203  are  probably  also  known.  Ruthenates  analogous  to 
the  osmates  have  been  prepared.  RuCl2  and  RuCl3  are  formed  when  the  metal  is 
heated  in  chlorine.  The  latter  is  insoluble  in  cold  water,  but  dissolves  in  absolute 
alcohol  to  a  purple-violet  solution  which  becomes  indigo-blue  from  absorption  of 
water  and  formation  of  RuCl2.OH  ;  the  solution  gradually  deposits  Ru(OH)3. 
Double  chlorides  analogous  to  those  of  osmium  exist. 

Sulphates  corresponding  with  RuO  and  Ru203  have  been  obtained. 

IRIDIUM,  Ir=  191.5. 

303.  Named  from  Iris,  the  rainbow,  in  allusion  to  the  varied  colours  of  its  com- 
pounds, this  metal  occurs  in  the  insoluble  alloy  from  the  platinum  ores.     It  is  also 
sometimes  found  separately,  and  occasionally  alloyed  with  platinum,  the  alloy 

*  A  mineral  found  in  Borneo,  and  named  laurfte,  contains  sulphides  of  ruthenium  and 
osmium.  It  forms  small  lustrous  granules. 


512 


THE  PLATINUM  GROUP  OF  METALS. 


crystallising  in  octahedra,  which  are  even  heavier  than  platinum  (sp.  gr.  22.3).  If 
the  insoluble  osmiridium  alloy  left  by  aqua  regla  be  mixed  with  common  salt  and 
heated  in  a  current  of  chlorine  a  mixture  of  the  sodio-chlorides  of  the  metals  is 
obtained  and  may  be  extracted  by  boiling  water.  If  the  solution  be  evaporated 
and  distilled  with  nitric  acid,  the  osmium  is  distilled  off  as  perosmic  anhydride, 
and  by  adding  ammonium  chloride  to  the  residual  solution,  the  iridium  is  pre- 
cipitated as  a  dark  red-brown  ammonio-chloride,  2NH4Cl.IrCl4,  which  leaves 
metallic  iridium  when  heated.  Like  platinum,  it  then  forms  a  grey  spongy  mass, 
but  is  oxidised  when  heated  in  air,  and  may  be  fused  (2200°  C.)  with  the  oxy- 
hydrogen  blowpipe  to  a  hard  brittle  mass  (sp.  gr.  22.4),  which  doe-  not  oxidise  in 
air.  Like  rhodium,  it  is  not  attacked  by  aqua  regla,  unless  alloyed  with  platinum. 
By  fusion  with  zinc  it  yields  an  allotropic  form  similar  to  that  described  for 
rhodium.  The  product  of  the  oxidation  of  finely  divided  iridium  in  air  is  the 
sesquloxide  (Ir203),  which  is  a  black  powder  used  for  imparting  an  intense  black  to 
porcelain  ;  it  is  insoluble  in  acids.  The  monoxide  (IrO)  is  also  more  easily  acted 
upon  by  alkalies  than  by  acids  ;  its  solution  in  potash  becomes  blue  when  exposed 
to  air,  from  the  formation  of  the  dioxide  (Ir02).  The  trioxlde  (Ir03)  is  green.  The 
dichloride  (IrCI2)  and  tetrachloride  (IrCl4)  of  iridium  resemble  the  corresponding 
chlorides  of  platinum  in  forming  double  salts  with  the  alkali  chlorides.  There 
is  also  a  trichloride  (IrCl3),  the  solution  of  which  has  a  green  colour,  and  gives  a 
yellow  precipitate  with  mercurous  nitrate,  and  a  blue  precipitate,  soon  becoming 
white,  with  silver  nitrate.  Double  compounds  of  the  chloride  with  ammonia 
(irldamlnes)  are  known.  Iridium  resembles  palladium  in  its  disposition  to  combine 
with  carbon  when  heated  in  the  flame  of  a  spirit-lamp. 

Salts  of  iridium  correspond  with  the  oxides  IrO  and  Ir203. 

An  iridio- platinum  allot/  containing  from  15  to  20  per  cent,  of  iridium  has  been 
found  very  useful  for  making  standard  rules  and  weights,  on  account  of  its  inde- 
structibility, extreme  rigidity,  hardness,  and  high  density. 

The  following  table  exhibits  a  general  view  of  the  analytical  process  by  which 
the  remarkable  metals  associated  in  the  ores  of  platinum  may  be  separated  from 
each  other,  omitting  the  minor  details  which  are  requisite  to  ensure  the  purity  of 
each  metal : 

Analysis  of  the  Ore  of  Platinum. 
Boil  with  aqua  regla. 


Dissolved  ; 
PLATINUM,  PALLADIUM,  RHODIUM. 

Add  ammonium  chloride. 

Undissolved  ; 
IRIDIUM,  OSMIUM,  RUTHENIUM. 
Chrome  iron,  Titanic  iron,  &c. 

Heat  in  a  current  of  dry  air. 

Precipitated  ; 
PLATINUM 

2NH4Cl!ptCl4. 

Solution  ; 
Neutralise  with  sodium  carbonate; 
add  mercuric  cyanide. 

Volatilised  ; 
OSMIUM 
as  Os04. 

Carried 
forward  by 
the  current  ; 
RUTHENIUM 
as  Ru02. 

Residue  ; 
Mix  with  sodium 
chloride,  and  heat  in  a 
current  of  chlorine. 
Treat  with  boiling  ivater. 

Precipitated  ; 
PALLADIUM 
as  PdCy2. 

Solution  ; 
Evaporate  with 
hydrochloric  acid. 
Treat  with  alcohol. 
Insoluble  ; 
RHODIUM 
as  3NaCl.RhCl3. 

Dissolved  ; 
IRIDIUM 
as 
2NaCl.IrCl4. 

Residue  ; 
Titanic  iron, 
Chrome  iron, 
&c. 

304.  The  platinoid  metals  fall  into  two  classes  according  to  the  proximity  which 
exists  between  their  specific  gravities  and  between  their  atomic  weights— viz., 
Os,  Ir,  Pt,  and  Ru,  Rh  and  Pd.  Gold  is  associated  with  the  former  class  by  its 
sp.  gr.,  atomic  weight,  and  insolubility,  whilst  silver  is  related  to  the  latter  class 
also  by  its  atomic  weight  and  sp.  gr.,  and  by  its  solubility  in  nitric  acid,  resembling 
that  of  Pd.  The  first  member  of  each  class  (Os  and  Ru)  gives  a  volatile  tetroxide, 
whilst  the  highest  state  of  oxidation  of  the  remaining  metals  is  R03.  In  the 
periodic  classification  (p.  302),  they  fall  in  the  same  group  as  Fe,  Co  andiKi,  with 
which  they  have  several  features  in  common,  such  as  the  marked  colour  of  their 
salts,  their  infusibility  and  their  tendency  to  form  salts  in  two  stages  of  oxidation. 


EXTRACTION  OF  GOLD.  513 

GOLD. 
Au=:  195.7  parts  by  weight. 

305.  The  individuality  of  gold  among  metals  is  strongly  marked,  on 
account  of  its  colour,  its  high  specific  gravity.  19.3,  its  extreme  malle- 
ability and  ductility,  its  perfect  resistance  to  air,  its  high  conducting 
power  for  heat  and  electricity,  its  high  fusirig-point,  1064°  C.,  its 
resistance  to  acids,  and  its  rarity  and  consequent  intrinsic  value. 
Gold  is  one  of  those  few  metals  which  are  always  found  in  the  metallic 
state,  and  is  remarkable  for  the  extent  to  which  it  is  distributed,  though 
in  small  quantities,  over  the  surface  of  the  earth.  The  principal  sup- 
plies of  this  metal  are  derived  from  Australia,  the  Transvaal  Colony,. 
California,  Mexico,  Brazil,  Peru,  and  the  Ural  Mountains.  Small 
quantities  have  been  occasionally  met  with  in  our  own  islands,, 
particularly  at  Wicklow,  at  Cader  Idris  in  Wales,  Leadhills  in  Scot- 
land, and  in  Cornwall. 

The  mode  of  the  occurrence  of  gold  in  the  mineral  kingdom  resembles 
that  of  the  ore  of  tin,  for  it  is  either  found  disseminated  in  the  primi- 
tive rocks,  or  in  alluvial  deposits  of  sand,  which  appear  to  have  been 
formed  by  the  disintegration  of  those  rocks  under  the  continued  action 
of  torrents.  In  the  former  case,  the  gold  is  often  found  crystallised  in 
cubes  and  octahedra,  or  in  forms  derived  from  these,  and  sometimes 
aggregated  together  in  dendritic  or  branch-like  forms.  In  the  alluvial 
deposits,  the  gold  is  usually  found  in  small  scales  (gold  dust),  but  some- 
times in  masses  of  considerable  size  (nuggets),  the  rounded  appearance  of 
which  indicates  that  they  have  been  subjected  to  attrition.  Australian 
gold  is  the  purest,  especially  that  from  Victoria. 

The  extraction  of  the  particles  of  gold  from  the  alluvial  sands  is 
effected  by  taking  advantage  of  the  high  specific  gravity  of  the  metal 
(19.3),  which  causes  it  to  remain  behind,  whilst  the  sand,  which  is  very 
much  lighter  (sp.  gr.  2.6),  is  carried  away  by  water.  The  washing  is 
commonly  performed  by  hand,  in  wooden  or  metal  bowls,  in  which  the 
sand  is  shaken  up  with  water,  and  the  lighter  portions  dexterously 
poured  off,  so  as  to  leave  the  grains  of  gold  at  the  bottom  of  the  vessel. 
On  a  somewhat  larger  scale,  the  auriferous  sand  is  washed  in  a  cradle 
or  inclined  wooden  trough,  furnished  with  rockers,  and  with  an  opening 
at  the  lower  end  for  the  escape  of  the  water.  The  sand  is  thrown  011  to 
a  grating  at  the  head  of  the  cradle,  which  retains  the  large  pebbles, 
whilst  the  sand  and  gold  pass  through,  the  former  being  washed  away 
by  a  stream  of  water  which  is  kept  flowing  through  the  trough. 

When  the  gold  is  disseminated  through  masses  of  quartz  or  other 
rock,  much  labour  is  expended  in  crushing  the  latter  before  the  gol 
can  be  separated.  This  is  effected  either  by  passing  the  coarse  fragments 
between  heavy  rollers  of  hard  cast-iron,  or  by  stamping  them,  with 
_wooden  beams  shod  with  iron,  in  troughs  through  which  water  is  con- 
tinually flowing.  . 

In  some  cases  it  is  found  advantageous  to  smelt  the  ore  by  fusing  r 
with  some  substance  capable  of  uniting  with  the  gold,  and  ot 
afterwards  readily  separated  from  it.     Lead  is  peculiarly  adapted  ioi 
this  purpose ;  the  crushed  ore  is  mixed  with  a  suitable  proportion,  ei 
of  metallic  lead,  or  of  litharge  (oxide  of  lead)  and  charcoal,  o 


5 14  REFINING  GOLD. 

of  galena  (sulphide  of  lead),  together  with  some  lime  and  oxide  of  iron 
•or  clay,  to  flux  the  silica,  and  is  fused  on  the  hearth  of  a  reverberatory 
furnace,  when  the  fused  lead  dissolves  the  particles  of  gold,  and  collects 
'beneath  the  lighter  slag.  The  lead  is  afterwards  separated  from  the 
.gold  by  cupellation  (see  p.  464). 

In  smelting  the  ores  of  gold  in  Hungary,  the  metal  is  concentrated  by  means 
^of  sulphide  of  iron.  The  ore  consists  of  quartz  and  iron  pyrites  (FeS2),  containing 
=a  little  gold.  On  fusing  the  crushed  ore  with  lime,  to  flux  the  quartz,  the  pyrites 
ioses  half  its  sulphur,  and  becomes  ferrous  sulphide  (FeS),  which  fuses  and  sinks 
<!>elow  the  slag,  carrying  with  it  the  whole  of  the  gold.  If  this  product  be  roasted 
so  as  to  convert  the  iron  into  oxide,  and  be  then  again  fused  with  a  fresh  portion 
of  the  ore,  the  oxide  of  iron  will  flux  the  quartz,  whilst  the  fresh  portion  of  FeS 
will  carry  down  the  whole  of  the  gold  contained  in  both  quantities  of  ore.  This 
operation  having  been  repeated  until  the  FeS  is  rich  in  gold,  it  is  fused  with  a 
certain  quantity  of  lead,  which  extracts  the  gold  and  falls  to  the  bottom.  The 
lead  is  then  cupelled  in  order  to  obtain  the  gold. 

When  the  ores  of  lead,  silver,  or  copper  contain  gold,  it  is  always  found  to  have 
accompanied  the  silver  extracted  from  them,  and  is  separated  from  it  by  a  process 
to  be  presently  noticed. 

Gold  is  sometimes  separated  from  the  impurities  remaining  with  it 
after  extraction  by  washing,  by  the  process  of  amalgamation,  which  con- 
sists in  shaking  the  mixture  with  mercury  in  order  to  dissolve  the  gold- 
dust,  and  straining  the  liquid  amalgam  through  chamois  leather,  which 
allows  the  excess  of  mercury  to  pass  through,  but  retains  the  solid 
portion  containing  the  gold,  from  which  the  mercury  is  then  separated 
by  distillation.* 

Chlorine  (or  bromine)  water  is  sometimes  employed  to  extract  the  gold 
by  converting  it  into  AuCl3,  the  gold  being  afterwards  precipitated  from 
the  solution  by  adding  ferrous  sulphate,  or  by  nitration  through  charcoal 
which  retains  the  gold,  which  is  subsequently  separated  by  burning  the 
charcoal. 

The  cyanide  process,  particularly  applicable  to  the  extraction  of 
gold  from  the  tailings  or  material  which  contains  the  metal  so  finely 
divided  that  it>  has  escaped  separation  by  the  washing  process,  depends 
on  the  solubility  of  gold  in  a  i  per  cent,  solution  of  potassium  cyanide 
in  presence  of  air  ;  Au2  +  4KCN  +  H.2O  +  0  =  2(AuCN.KCN)  +  2KOH.t 
The  soluble  double  cyanide  of  Au  and  K  is  decomposed  either  by  running 
the  solution  through  boxes  containing  zinc  which  precipitates  the  gold, 
or  by  electrolysing  the  solution  when  the  gold  is  deposited  on  the 
oathode. 

Gold,  as  found  in  nature,  is  generally  alloyed  with  variable  propor- 
tions of  silver  and  copper,  the  separation  of  which  is  the  object  of  the 
gold  refiner.  It  may  be  effected  by  means  of  nitric  acid,  which  will 
dissolve  the  silver  and  copper,  provided  that  they  do  not  bear  too  small 
a  proportion  to  the  gold.  Sulphuric  acid,  however,  being  very  much 
cheaper,  is  generally  employed.  The  alloy  is  fused  and  poured  into 
water,  so  as  to  granulate  it  and  expose  a  larger  surface  to  the  action  of 
the  acid ;  it  is  then  boiled  with  concentrated  sulphuric  acid  (oil  of 
vitriol),  which  converts  the  silver  and  the  copper  into  sulphates,  with 

*  A  small  quantity  of  sodium  dissolved  in  the  mercury  has  been  found  very  materially  to 
facilitate  the  amalgamation  of  gold  and  silver  ores,  apparently  because  the  amalgam  of 
.sodium  is  more  highly  electro-positive  than  mercury,  in  relation  to  the  gold. 

f  It  is  said  that  H2O2  is  produced,  the  equation  being — 

Au2  +  8KCX  +  O4  +  4H2O  =  aKAu(CN)4  +  6KOH  +  H2O0. 


STANDAED   GOLD.  -r- 

evolution  of  sulphurous  acid  gas,  whilst  the  gold  is  left  untouched.  In 
order  to  recover  the  silver  from  the  solution  of  the  sulphates  in  water, 
scraps  of  copper  are  introduced  into  it,  when  that  metal  decomposes  the 
sulphate  of  silver,  producing  sulphate  of  copper,  and  causing  the  deposi- 
tion of  the  silver  in  the  metallic  state.  Finally,  the  sulphate  of  copper 
may  be  obtained  from  the  solution  by  evaporation  and  crystallisation. 
This  process  is  so  effectual  when  the  proportion  of  gold  in  an  alloy  is 
very  small,  that  even  -^  part  of  this  metal  may  be  profitably  extracted 
from  100  parts  of  an  alloy,  and  much  gold  has  been  obtained  in  this 
way  from  old  silver  plate,  coins,  &c.,  which  were  manufactured  before 
so  perfect  a  process  for  the  separation  of  these  metals  was  known.  On 
boiling  old  silver  coins  or  ornaments  with  nitric  acid,  they  are  generally 
found  to  yield  a  minute  proportion  of  gold  in  the  form  of  a  purple 
powder.  But  this  plan  of  separation  is  not  so  successful  when  the  alloy 
contains  a  very  large  quantity  of  gold,  for  the  latter  metal  protects  the 
copper  and  silver  from  the  solvent  action  of  the  acid.  Thus,  if  the  alloy 
contains  more  than  ith  of  its  weight  of  gold,  it  is  customary  to  fuse  it 
with  a  quatity  of  silver,  so  as  to  reduce  the  proportion  of  gold  below 
that  point  before  boiling  it  with  the  acid.  Again,  if  the  alloy  contains 
a  large  quantity  of  copper,  it  is  found  expedient  to  remove  a  great  deal 
of  this  metal  in  the  form  of  oxide  by  heating  the  alloy  in  a  current  of 
air. 

Gold  which  is  brittle  and  unfit  for  coining,  in  consequence  of  the  pre- 
sence of  small  quantities  of  foreign  metals,  is  sometimes  refined  by 
melting  it  with  oxide  of  copper  or  with  a  mixture  of  nitre  and  borax, 
when  the  foreign  metals,  with  the  exception  of  silver,  are  oxidised  and 
dissolved  in  the  slag.  Another  process  consists  in  throwing  some  cor- 
rosive sublimate  (mercuric  chloride)  into  the  melting-pot,  and  stirring 
it  up  with  the  metal,  when  its  vapour  converts  the  metallic  impurities 
into  chlorides,  which  are  volatilised.  An  excellent  method  consists  in 
fusing  the  gold  with  a  little  borax,  and  passing  chlorine  gas  into  it 
through  a  clay  tube.  Antimony,  arsenic,  &c.,  are  carried  off  as  chlorides, 
whilst  the  silver,  also  converted  into  chloride,  rises  to  the  surface  of  the 
gold  in  a  fused  state,  afterwards  solidifying  into  a  cake,  which  is  reduced 
to  the  metallic  state  by  placing  it  between  plates  of  wrought-iron  and 
immersing  it  in  diluted  sulphuric  acid. 

When  the  crude  gold  is  made  the  anode  in  an  electrolytic  cell  con- 
taining nitric  acid,  the  foreign  metals  dissolve  in  the  acid  while  the  gold 
is  deposited  as  a  sludge,  conveniently  caught  by  surrounding  the  anode 
with  a  bag  of  cloth.  This  forms  another  method  of  refining  gold.  _ 

Pure  gold,  like  pure  silver,  is  too  soft  to  resist  the  wear  to  which  it  is 
subjected  in  its  ordinary  uses,  and  it  is  therefore  alloyed  for  coinage  in 
this  country  with  ^th  of  its  weight  of  copper,  so  that  gold  coin  con- 
tains i  part  of  copper  and  n  parts  of  gold.  The  gold  used  for  articles 
of  jewellery  is  alloyed  with  variable  proportions  of  copper  and  silver. 
The  alloy  of  copper  and  gold  is  much  redder  than  pure  gold. 

The  English  sovereign  contains  91.67  per  cent,  of  gold  and  8.33  per 
cent,  of  copper.  Its  sp.  gr.  is  17.157,  and  its  weight  is  123.274  grains. 

The  Australian  sovereign  contains  silver  in  place  of  copper,  and  i 
lighter  in  colour  than  pure  gold. 

The  degree  of  purity  of  gold  is  generally  expressed  by  quoting  it  « 
of  so  many  carats  fine.     Thus,  pure  gold  is  said  to  be  24  carats  fine : 


516  ASSAYING  GOLD. 

English  standard  gold  22  carats  fine,  that  is,  contains  22  carats  of  gold 
out  of  the  24.  Gold  of  18  carats  fine  would  contain  18  parts  of  gold 
out  of  the  24,  or  |thsof  its  weight  of  gold.  The  other  legal  standards 
are  15,  12,  and  9  carat  gold.  The  fineness  sometimes  refers  to  the 
quantity  of  gold  in  1000  parts  of  the  alloy  ;  thus,  English  coin  has  a 
fineness  of  916.7,  German  and  American  coin,  of  900. 

In  order  to  impart  to  gold  ornaments  the  appearance  of  pure  gold, 
they  are  heated  till  the  copper  in  the  outer  layer  is  oxidised,  and  then 
dipped  into  nitric  or  sulphuric  acid,  which  dissolves  the  copper  oxide  and 
leaves  a  film  of  pure  gold. 

Pure  gold  is  easily  prepared  from  standard  or  jeweller's  gold  by  dissolving  it 
in  hydrochloric  acid  mixed  with  one-fourth  of  its  volume  of  nitric  acid,  evaporating 
the  solution  to  a  small  bulk  to  expel  excess  of  acid,  diluting  with  a  considerable 
quantity  of  water,  filtering  from  the  separated  silver  chloride,  and  adding  a  solution 
of  green  sulphate  of  iron,  when  the  gold  is  precipitated  as  a  dark-purple  powder, 
which  may  be  collected  on  a  filter,  well  washed,  dried,  and  fused  in  a  small  clay 
crucible  with  a  little  borax,  the  crucible  having  been  previously  dipped  in  a  hot 
saturated  solution  of  borax,  and  dried,  to  prevent  adhesion  of  the  globules  of  gold. 
The  action  of  ferrous  sulphate  upon  the  trichloride  of  gold  is  explained  by  the 
equation— 2AuCl3  +  6FeS04  =  Au2  +  F2Cl6  +  2Fe2(S04)3.  The  gold  precipitated  by 
ferrous  sulphate  appears,  under  the  microscope,  in  cubical  crystals. 

By  employing  oxalic  acid  instead  of  ferrous  sulphate,  and  heating  the  solution, 
the  gold  is  precipitated  in  a  spongy  state,  and  becomes  a  coherent  lustrous  mass 
under  pressure.  The  rnetal  is  employed  in  this  form  by  dentists. 

When  standard  gold  is  being  dissolved  in  aqua  regla,  it  sometimes  becomes 
coated  with  a  film  of  silver  chloride  which  stops  the  action  of  the  acid  ;  the 
liquid  must  then  be  poured  off,  the  metal  washed,  and  treated  with  ammonia, 
which  dissolves  the  silver  chloride  ;  the  ammonia  must  then  be  washed  away 
before  the  metal  is  replaced  in  the  acid.  In  the  case  of  jeweller's  gold,  it  is  advisable 
to  extract  as  much  silver  and  copper  as  possible  by  boiling  it  with  nitric  acid, 
before  attempting  to  dissolve  the  gold.  Gold  lace  should  be  incinerated  to  get  rid 
of  the  cotton  before  being  treated  with  acid. 

The  genuineness  of  gold  trinkets.  <fcc.,  is  generally  tested  by  touching  them  with 
nitric  acid,  which  attacks  them  if  they  contain  a  very  considerable  proportion  of 
copper,  producing  a  green  stain,  but  this  test  is  evidently  useless  if  the  surface  be 
gilt.  The  weight  is,  of  course,  a  good  criterion  in  practised  hands,  but  even  these 
have  been  deceived  by  bars  of  platinum  covered  with  gold.  The  specific  gravity 
maybe  taken  in  doubtful  cases  ;  that  of  sovereign  gold  is  17.157. 

In  assaying  gold,  the  metal  is  wrapped  in  a  thin  piece  of  paper  together  with 
about  three  times  its  weight  of  pure  silver,  and  added  to  twelve  times  its  weight  of 
pure  lead  fused  in  a  bone-ash  cupel  (see  p.  465)  placed  in  a  muffle  (or  exposed  to 
a  strong  oxidising  blow-pipe  flame),  when  the  lead  and  copper  are  oxidised,  and  the 
fused  oxide  of  lead  dissolves  that  of  copper,  both  being  absorbed  by  the  cupel. 
When  the  metallic  button  no  longer  diminishes  in  size,  it  is  allowed  to  cool, 
hammered  into  a  flat  disc  which  is  annealed  by  being  heated  to  redness,  and  rolled 
out  to  a  thin  plate,  so  that  it  may  be  rolled  up  by  the  thumb  and  finger  into 
a  cornette,  which  is  boiled  with  nitric  acid  (sp.  gr.  1.18)  to  extract  the  silver  ;  the 
remaining  gold  is  washed  with  distilled  water,  and  boiled  with  nitric  acid  of 
sp.  gr.  1.28,  to  extract  the  last  traces  of  silver,  after  which  it  is  again  washed. 
heated  to  redness  in  a  small  crucible,  and  weighed. 

The  stronger  nitric  acid  could  not  be  used  at  first,  since  it  would  be  likely  to  break 
the  cornette  into  fragments  which  could  not  be  so  readily  washed  without  loss. 
The  addition  of  the  three  parts  of  silver  (quartatioii)  is  made  in  order  to  divide  the 
alloy,  and  permit  the  easy  extraction  of  the  silver  by  nitric  acid,  which  cannot  be 
effected  when  the  gold  predominates. 

306.  The  physical  characters  of  gold  render  it  very  conspicuous 
among  the  metals  ;  it  is  the  heaviest  of  the  metals  in  common  use,  with 
the  exception  of  platinum,  its  specific  gravity  being  19.3.  In  malleability 
and  ductility  it  surpasses  all  other  metals  ;  the  former  property  is  turned 
to  advantage  for  the  manufacture  of  gold  leaf,  for  which  purpose  a  bar 


PEOPERTIES   OF  GOLD. 

of  gold,  containing  96.25  per  cent,  of  gold,  2.5  per  cent,  of  silver,  and 
1.25  per  cent,  of  copper,  is  passed  between  rollers  which  extend  it' into 
the  form  of  a  riband  ;  this  is  cut  up  into  squares,  which  are  packed 
between  layers  of  fine  vellum,  and  beaten  with  a  heavy  hammer ;  these 
thinner  squares  are  then  again  cut  up  and  beaten  between  layers  of  gold- 
beater's skin  until  they  are  sufficiently  thin.  An  ounce  of  gold  may 
thus  be  spread  over  100  square  feet ;  282,000  of  such  leaves  placed  upon 
each  other  form  a  pile  of  only  i  inch  high.  These  leaves  will  allow 
light  to  pass  through  them,  and  always  appear  green  or  blue  when  held 
up  to  the  light,  though  they  exhibit  the  ordinary  colour  of  gold  bv 
reflected  light. 

If  a  gold  leaf  adhering  to  a  glass  plate  be  heated  to  nearly  the  boiling-point  of 
oil  for  some  time,  it  becomes  nearly  transparent  and  invisible  by  transmitted  light, 
though  still  showing  the  colour  of  gold  by  reflected  light ;  if  it  be  pressed  with  a 
moderately  hard  body,  it  again  transmits  a  green  light.  When  gold  wire  or  leaf  is 
deflagrated  by  electricity  on  a  glass  plate,  the  finely  divided  metal  transmits  ruby, 
-  violet,  or  green  light,  according  to  its  thickness,  though  it  has  the  golden  colour 
by  reflected  light.  On  heating  these  deposits  to  dull  redness  on  the  glass,  they  all 
change  to  the  ruby  colour  while  still  golden  by  reflection.  Pressure  with  a  hard 
body  changes  the  colour  of  the  transmitted  light  from  red  to  green.  A  solution  of 
gold  trichloride,  containing  0.6  grain  of  gold  in  a  quart,  if  shaken  with  a  little 
solution  of  phosphorus  in  ether,  in  a  chemically  clean  bottle,  gives  a  ruby-red 
liquid  in  which  the  reflected  colour  of  gold  may  be  seen  by  bringing  the  solar  rays 
to  a  focus  in  the  liquid  by  a  convex  lens.  This  liquid  will  continue  to  deposit  fine 
particles  of  gold  for  many  months.  The  first  deposits  are  blue  by  transmitted  light, 
and  the  last  are  ruby.  The  supernatant  liquid  is  eventually  colourless.  If  a  little 
sodium  chloride  be  added  to  the  ruby  liquid,  it  transmits  a  blue  light,  and  the  gold 
which  has  remained  suspended  for  six  months  may  be  deposited  in  a  few  hours. 
By  using  a  filter  arranged  so  that  the  liquid  is  passed  through  the  paper  in  a  radial 
instead  of  an  a.nal  direction  as  is  usual,  the  particles  of  gold,  which  pass  through 
in  ordinary  axial  filtration,  may  be  collected  on  the  paper,  having  the  various 
colours,  and  leaving  the  liquid  colourless.  These  colours  of  finely  divided  gold  are 
taken  advantage  of  in  painting  upon  porcelain,  and  the  well-known  magnificent 
ruby-red  glass  owes  its  colour  to  the  same  cause.  T^-h  of  a  grain  of  gold  is  capable 
of  imparting  a  deep  rose  colour  to  a  cubic  inch  of  fluid. 

The  extreme  ductility  of  gold  is  exemplified  in  the  manufacture  of 
gold  thread  for  embroidery,  in  which  a  cylinder  of  silver  having  been 
covered  with  gold  leaf  it  is  drawn  through  a  wire-drawing  plate  and 
reduced  to  the  thinness  of  a  hair ;  in  this  way  6  ounces  of  gold  are 
drawn  into  a  cylinder  two  hundred  miles  in  length.  Although  fusing 
at  about  the  melting-point  of  copper,  gold  is  seldom  cast,  on  account  of 
its  great  contraction  during  solidification. 

Gold  is  not  even  affected  to  the  same  extent  as  silver  by  exposure  to 
the  atmosphere,  for  sulphuretted  hydrogen  has  no  action  upon  it,  arid 
hence  no  metal  is  so  well  adapted  for  coating  surfaces  which  are  required 
to  preserve  their  lustre. 

The  gold  is  sometimes  applied  to  the  surfaces  of  metals  in  the  form 
of  an  amalgam,  the  mercury  being  afterwards  driven  off  by  heat. 
Metals  may  also  be  gilt  by  means  of  a  boiling  solution  prepared  by 
dissolving  gold  in  aqua  regia,  and  adding  an  excess  of  bicarbonate 
of  potash  or  of  soda.  But  the  most  elegant  process  of  gilding  is  that  of 
electro-gilding,  in  which  the  object  to  be  gilt  is  connected  by  a  wire 
with  the  zinc  end  of  the  galvanic  battery,  and  immersed  in  a  solution 
of  cyanide  of  gold  in  cyanide  of  potassium,  in  which  is  also  placed  a 
gold  plate  connected  with  the  copper  end  of  the  battery,  and  intended, 


518  SALTS   OF   GOLD. 

by  gradually  dissolving,  to  take  the  place  of  the  gold  abstracted  from 
the  solution  at  the  negative  pole. 

A  gold  crucible  is  very  useful  in  the  laboratory  for  effecting  the  fusion 
of  substances  with  caustic  alkalies,  which  would  corrode  a  platinum 
crucible.  The  only  single  acid  which  attacks  gold  is  selenic,  H2SeO4, 
which  the  gold  reduces  to  selenious  acid,  H0Se03.  A  mixture  of  hydro- 
chloric with  one-third  of  its  volume  of  nitric  acid  is  usually  employed 
for  dissolving  gold.  It  is  also  dissolved  by  a  mixture  of  sulphuric  acid 
with  a  little  nitric,  the  latter  becoming  reduced  to  nitrous  acid,  which 
precipitates  the  gold  again  in  the  metallic  state  on  pouring  the  solution 
into  a  large  volume  of  water.  On  account  of  its  high  resistance  to 
sulphuric  acid,  platinum  vitriol  retorts  are  now  frequently  lined  with 
gold.  Fused  caustic  alkalies  are  not  without  action  on  gold,  but  they 
attack  platinum  more  strongly. 

307.  OXIDES  OP  GOLD. — Three  compounds  of  gold  with  oxygen  have  been 
obtained,  Au20,  AuO,  and  Au.203,  but  none  of  them  is  of  any  great  practical  im- 
portance. 

Aurous  oxide,  Au.20,  obtained  by  decomposing  aurous  chloride  with  potash,  is  a 
violet-coloured  powder  which  is  decomposed  by  hydrochloric  acid — 
3Au20  +  6HCI  =  2AuCl3  +  3H20  +  Au4. 

Auric  oxide,  Au203,  is  obtained  by  gently  heating  auric  hydroxide,  Au(OH).,. 
This  is  prepared  by  heating  a  weak  solution  of  auric  chloride  with  excess  of  potash, 
and  adding  sodium  sulphate,  when  auric  hydroxide  is  precipitated,  of  a  brown 
colour  like  ferric  hydroxide.  It  is  very  unstable,  evolving  oxygen  when  exposed  to 
light.  Nitric  acid  dissolves  it,  and  it  is  reprecipitated  by  water.  It  dissolves  in 
potash,  and  the  solution  yields  crystals  of  potassium  aurate,  KAu02.3Aq.  By  heat- 
ing Au(OH)3  at  1 60°  C.  AuO  is  formed. 

When  precipitated  gold  is  attacked  by  chlorine  gas,  it  yields  auroxoauric  chloride, 
AuCl.AuCI3,  a  dark  red  hard  substance  decomposed  by  water  into  AuCl  and  AuCl3, 
or  auric  chloride,  which  may  also  be  obtained  by  dissolving  gold  in  hydrochloric 
acid  with  one-fourth  of  its  volume  of  nitric  acid,  and  evaporating  on  a  water  bath 
to  a  small  bulk  ;  on  cooling,  yellow  prismatic  crystals  of  a  compound  of  the  tri- 
chloride with  hydrochloric  acid  (AuCl3.HC1.4Aq)  are  deposited,  from  which  the 
hydrochloric  acid  may  be  expelled  by  a  gentle  heat  (not  exceeding  120°  C.),  when 
the  trichloride  forms  red-brown  deliquescent  crystals  of  AuCl3.2Aq,  dissolving  very 
readily  in  water,  giving  a  bright  yellow  (solution  which  stains  the  skin  and  other 
organic  matter  purple  when  exposed  to  light,  depositing  finely  divided  gold  ;  the 
solution  appears  to  contain  an  acid,  ELjAuClgO,  of  which  the  silver  salt  is  known. 
Almost  every  substance  capable  of  combining  with  oxygen  reduces  the  gold  to  the 
metallic  state.  The  inside  of  a  perfectly  clean  flask  or  tube  may  be  covered  with  a 
film  of  metallic  gold  by  a  dilute  solution  of  the  trichloride  mixed  with  citric  acid 
and  NH3,  and  gently  heated.  The  facility  with  which  it  deposits  metallic  gold, 
and  the  resistance  of  the  deposited  metal  to  atmospheric  action,  has  rendered 
AuCl3  very  useful  in  photography.  Alcohol  and  ether  readily  dissolve  the  trichlo- 
ride, the  latter  being  able  to  extract  it  from  its  aqueous  solution.  Ked  crystals  of 
AuCl3  are  sublimed  when  thin  gold  foil  is  gently  heated  in  a  current  of  chlorine. 
Trichloride  of  gold  (like  platinic  chloride)  forms  crystallisable  compounds  with 
the  alkali  chlorides  and  with  the  hydrochlorides  of  organic  bases,  and  affords  great 
help  to  the  chemist  in  defining  these  last.  Aurochloride  of  sodium  forms  reddish- 
yellow  prismatic  crystals  (NaCl.AuCl3.2Aq),  which  are  sold  for  photographic  pur- 
poses. 

Protochloride  of  gold,  or  aurous  chloride  (AuCl),  is  obtained  by  gently  heating 
the  trichloride,  when  it  fuses  and  is  decomposed  at  177°  C.,  leaving  the  protochlo- 
ride,  which  is  reduced  to  metallic  gold  at  about  205°  C.  Aurous  chloride  is 
sparingly  soluble  in  water,  and  of  a  pale  yellow  colour.  Boiling  water  decomposes 
it  into  metallic  gold  and  the  trichloride. 

Fulminating  gold  is  obtained  as  a  buff  precipitate  when  ammonia  is  added  to 
solution  of  auric  chloride  ;  its  composition  is  not  well  established,  but  appears  to 
be  Au2034NH3  or  2(NH3.NAu'").3H20.  It  explodes  violently  when  gently  heated. 

The  Sel  d'or  of  the  photographer  is  a  hyposulphite  (thiosulphate)  of  gold  and 


PUEPLE   OF   CASSIUS. 


519 


sodium,  Au2S2O3.3Na2SoO3.4Aq,  which  is  obtained  in  fine  white  needles  by  pourin" 
a  solution  of  I  part  of  auric  chloride  into  a  solution  of  3  parts  of  sodium  hypo*- 
sulphite,  and  adding  alcohol,  in  which  the  double  salt  is  insoluble.  Its  formation 
may  be  explained  by  the  equation — 

8Xa.2S203  +  2AuCl3  =  Au.2S20;?.3Xa.2S203  +  6XaCl  +  2Xa.2S406. 
It  is  doubtful  whether  the  above  formula  represents  the  true  constitution  of  this 
salt,  for  it  is  not  decomposed  by  adds  in  the  same  manner  as  ordinary  thiosulphates 
are.*     HX03  separates  all  the  gold  in  the  metallic  state. 

Purple  of  Caszhis,  which  is  employed  for  imparting  a  rich  red  colour  to  glass  and 
porcelain,  is  a  compound  of  gold,  tin,  and  oxygen,  which  are  believed  to  be  grouped 
according  to  the  formula  Au.2Sn03.Sn.Sn034Aq.f  It  maybe  prepared  by  adding 
stannous  chloride  to  a  mixture  of  stannic  chloride  and  auric  chloride  ;  7  parts  of 
gold  are  dissolved  in  aqua  reyia  and  mixed  with  2  parts  of  tin  also  dissolved  in 
aqua  rctjla  ;  this  solution  is  largely  diluted  with  water,  and  a  weak  solution  of 
i  part  of  tin  in  hydrochloric  acid  is  added,  drop  by  drop,  till  a  fine  purple  colour  is 
produced.  The  purple  of  Cassius  remains  suspended  in  water  in  a  very  fine  state 
of  division,  but  subsides  gradually,  especially  if  some  saline  solution  be  added,  as  a 
purple  powder.  The  fresh  precipitate  dissolves  in  ammonia,  but  the  purple  solu- 
tion is  decomposed  by  exposure  to  light,  becoming  blue,  and  finally  colourless, 
metallic  gold  being  precipitated,  and  stannic  oxide  left  in  solution. 

The  snljthldex  of  y  old  are  not  thoroughly  known.  Gold  does  not  combine  directly 
with  sulphur,  but  if  it  be  heated  with  sulphur  and  alkali  sulphides,  it  forms  soluble 
compounds.  In  this  way,  sodium  awrowlphide,  XaAuS.4Aq,  may  be  obtained  in 
colourless  prisms  soluble  in  alcohol.  When  H.2S  is  passed  into  solution  of  AuCl3,  a 
black  precipitate  of  Au.2S.Au2S3  or  Au.2S.2  is  obtained  — 

2AuCl3"  +  3H2S^=  Au.2S2  +  S  +  6HC1. 

The  precipitate  is  soluble  in  alkali  sulphides.  The  precipitated  sulphide  of  gold  is 
not  dissolved  by  the  acids,  with  the  exception  of  aqua  reyla.  Nitric  acid  oxidises 
the  sulphur,  leaving  metallic  gold.  When  hydrosulphuric  acid  is  added  to  a  boil- 
ing solution  of  auric  chloride,  the  metal  itself  is  precipitated — 

8AuCl3  +  3H2S  +  i2H.20  =  Au8  +  24HC1  +  3H2S04. 

A  yellowish-grey  brittle  arsenide  of  (/old  (AuAs.,)  has  been  found  in  quartz  in 
Australia. 

*  It  appears  to  be  sodium,  (inrothiosulphate,  Na3AuS4O6.2Aq,  which  is  supported  by  the 
preparation  of  a  corresponding  barium  salt  and  by  decomposing  this  with  sulphuric  acid 
when  aurothiomlphuric  acid,  H:jA.uS4O6,  is  obtained. 

f  Debray  asserts  that  it  is  merely  a  mixture  of  precipitated  gold  and  stannic  hydrate. 


ORGANIC    CHEMISTRY. 


308.  The  division  of  chemistry  into  inorganic  and  organic  was  ori- 
ginally intended  to  distinguish  mineral  substances  from  those  derived 
from  animal  and  vegetable  life ;  but  since  many  of  the  latter  may  now 
be  produced  in  the  laboratory  from  the  elements  obtainable  from  mineral 
sources,  it  has  become  usual  to  define  organic  chemistry  as  the  chemistry 
of  the  compounds  of  carbon,  since  this  element  is  always  present  in  the 
substances  formerly  spoken  of  as  organic. 

Organic  chemistry  differs  from  inorganic  in  being  chiefly  concerned 
with  the  compounds  produced  by  the  arrangement,  in  different  pro- 
portions or  in  different  positions,  of  the  elements  carbon,  hydrogen, 
oxygen,  and  nitrogen,  though  the  other  elements  occasionally  enter  into 
the  composition  of  organic  compounds. 

Perhaps  the  most  striking  difference  between  compounds  of  carbon 
and  those  of  other  elements  is  the  large  number  of  atoms  contained  in 
one  molecule  of  the  majority  of  carbon  compounds.  So  far  as  evidence 
is  available  it  is  rare  in  inorganic  chemistry  to  find  a  compound  whose 
molecule  contains  so  many  as  six  atoms  of  any  one  element ;  yet  the 
majority  of  carbon  compounds  contain  more  than  six  atoms  of  carbon 
in  the  molecule,  so  that  it  would  appear  to  be  a  characteristic  property 
of  carbon  to  combine  with  itself. 

A  useful  practical  distinction  between  organic  and  inorganic  substances 
is  afforded  by  their  behaviour  when  heated.  An  organic  substance  is 
either  converted  into  vapour  when  moderately  heated,  or  decomposed 
into  volatile  products,  generally  leaving  a  residue  of  charcoal,  which 
burns  away  when  heated  in  air. 

Upon  this  is  based  the  ultimate  analysis  of  organic  compounds  for  the 
purpose  of  ascertaining  the  relative  proportions  of  their  elements.* 

The  nuiltinf/  a  cotnbvxtion,  as  it  is  technically  called,  consists  in  burning  the 
organic  compound  so  as  to  convert  its  carbon  into  C02  and  its  hydrogen  into 
H20,  from  the  weight  of  which  the  proportions  of  those  elements  are  obtained 
by  calculation.  The  substance  to  be  analysed,  having  been  carefully  dried  and 
weighed  (about  0.5  gram),  is  placed  in  a  small  boat-shaped  tray  of  porcelain  or 
platinum,  which  is  introduced  into  one  end  of  a  glass  tube  about  30  inches  long, 
of  which  about  24.  inches  are  filled  with  small  fragments  of  carefully  dried  cupric 
oxide.  The  end  of  the  tube  where  the  boat  is  placed  is  connected  with  an  appa- 
ratus for  transmitting  air  or  oxygen,  which  has  been  purified  from  C0.2  by  passing 
through  potash,  and  from  H.2O  by  calcium  chloride.  To  the  other  end  of  the  tube 
is  attached,  by  a  perforated  cork,  a  weighed  tube  (B)  filled  with  small  fragments 
of  calcium  chloride  to  absorb  H20,  and  to  this  is  joined,  by  a  caoutchouc  tube,  a 
Inilb-apparatus  (C)  containing  strong  potash  to  absorb  C02,  and  a  small  guard-tufa 

*  For  exact  details  of  the  methods  of  organic  analysis  the  reader  must  consult  works  on 
analytical  chemistry. 


ULTIMATE   ORGANIC  ANALYSIS. 


521 


with  calcium  chloride  to  prevent  loss  of  water  from  the  potash.  The 
;md  guard  tube  are  accurately  weighed.  The  cotnbmt  ion-tube  is  supported  in  ;i 
gas-furnace,  and  that  portion  which  contains  the  CuO  is  heated  to  redness.  Tin- 
end  containing  the  boat  is  then  gradually  heated,  so  that  the  organic  substance  is 
slowly  vaporised  or  decomposed.  The  vapour  or  the  products  of  decomposition, 
an  passing  over  the  red-hot  cupric  oxide,  will  acquire  the  oxygen  necessary  to 


Fig-.  245. — Apparatus  for  organic  analysis. 

convert  the  C  into  CO2  and  the  H  into  H.2O,  which  are  absorbed  in  the  potash 
bulbs  and  calcium-chloride  tube.  At  the  end  of  the  process,  which  commonly 
occupies  about  an  hour,  a  slow  stream  of  pure  air  or  oxygen  is  passed  through. 
Avhilst  the  entire  tube  is  red-hot,  in  order  to  burn  any  charcoal  which  may  remain 
in  the  boat,  and  to  carry  forward  all  the  CO.2  and  H.2O  into  the  absorption 
apparatus.  The  weight  of  the  C0.2  is  given  by  the  increase  in  weight  of  the  calcium 
•chloride. 

When  nitrogen  is  present  in  the  substance,  it  may  be  partly  converted  into  X0.2. 
which  would  increase  the  weight  of  the  absorption-apparatus.  To  avoid  this, 
three  or  four  inches  of  the  front  end  of  the  combustion-tube  are  filled  with  metallic 
•copper,  which,  being  heated  to  redness,  absorbs  the  0  from  the  N0.2.  leaving  X. 
which  passes  through  the  absorption-apparatus  and  escapes.  When  it  is  desired  to 
make  a  determination  of  the  nitrogen, 
the  combustion-tube  is  arranged  in  the 
same  way.  but  the  absorption-apparatus 
is  exchanged  for  a  bent  tube  to  permit 
the  collection  of  the  gas  in  a  measured 
tube  tilled  with  strong  potash.  Before 
commencing  the  combustion,  the  air  is 
swept  out  of  the  tube  by  a  stream  of 
pure  CO.,.  which  is  continued  during  the 
combustion,  and  is  absorbed  by  the 
potash,  the  nitrogen  being  collected  and 
measured. 

Another  method  of  estimating  nitro- 
gen in  organic  substances  consists  in 
heating  them  with  xoda-Hme.  when  the 
X  is  evolved  as  XH,.  which  is  absorbed 
by  hydrochloric  acid  in  the  absorption 
bulb  shown  in  Fig.  246.  and  precipi- 
tated by  platinic  chloride,  the  weight 
of  X  being  calculated  from  that  of  the 

Pt<  '14.2XH4C1  obtained  :  or  the  NHS  is  absorbed  in  a  known  quantity  of  acid  w  hi. 
is  afterwards  titrated  with  a  standard  solution  of  alkali,  and  the  quantity  \\ 
has  been  neutralised  by  the  evolved  ammonia  thus  determined. 

Kirtfldlir*  method  of  estimating  nitrogen  consists  in  oxidising  the  substance  DA 
heating  it  with  H.,S04  and  acid  potassium  sulphate  (KHS04).  whereby  the  . 
converted  into  XH,.  which  forms  ammonium  sulphate.     The  XH,  is  sn  >seMnentlv 
liberated  by  boiling  with  alkali,  absorbed  by  hydrochloric  acid  and   dete 
either  with  platinic  chloride  or  standard  alkali,  as  described  above. 

'   \ur  and  phoxphoru*  are   estimated   in  organic   compounds   by  coi 


246.— Estimation  of  nitrogen. 


522        DETERMINATION  OF  MOLECULAR  FORMULAE. 

them  into  sulphuric  and  phosphoric  acids,  respectively,  by  the  action  of  powerful 
oxidising-agents  (nitric  acid,  chloric  acid,  bromine,  &c.),  and  determining  these- 
acids  by  the  usual  methods.  The  halogen*  are  determined  by  oxidising  the 
substance  by  heating  it  with  strong  HNO3  under  pressure,  whereby  the  halogen 
is  converted  into  its  hydrogen  compound  and  may  be  precipitated  by  AgNO;;  and 
weighed  as  silver  halide. 

The  proportion  of  oxygen  in  an  organic  substance  is  generally  ascertained  In- 
difference, that  is,  by  deducting  the  sum  of  the  weights  of  all  the  other  elements 
from  the  total  weight  of  the  substance. 

As  an  example  of  the  ultimate  analysis  of  an  organic  compound,  that  of  alcohol 
may  be  given  (volatile  liquids  are  weighed  in  a  small  glass  bulb  with  a  thin  stemr 
the  end  of  which  is  sealed  for  weighing,  and  broken  off  when  the  bulb  is  intro- 
duced into  the  combustion-tube)  :  — 

.5  gram  alcohol,  burnt  with  ctipric  oxide,  as  above,  gave  .9565  gram  C00  and 
.5869  gram  H20. 

Since  44  grams  C02  contain  12  grams  C.,  \\  of  .9565,  or  .2608,  is  the  weight  of 
C  found. 

Since  18  grams  H20  contain  2  grams  H,  T%  of  .5869,  or  .0652,  is  the  weight  of 
H  found. 

The  sum  of  C  and  H  is  .2608 +  .0652,  or  .3260.  Deducting  this  from  .5  gram 
alcohol,  we  have  .174  gram  for  the  weight  of  O  contained  in  it. 

So  that  .5  gram  alcohol  contains — 

.2608  gram  carbon      or  52. 16  per  cent. 
.0652     „       hydrogen,,   13.04         „ 
.1740    ,,       oxygen      ,,  34.80         ,, 

It  is  usual  to  express  the  results  of  such  an  analysis  in  an  empirical  formula,  which 
gives,  in  the  simplest  form,  the  relative  number  of  atoms  of  the  elements  present. 

309.  To  deduce  the  empirical  formula  from  the  percentage  composition,  the  per- 
centage of  each  element  is  divided   by  its  atomic  weight,  and  the  ratio  of  the 
resulting  quotients  expressed  in  its  lowest  terms  ;  thus — 

52.16  divided  by  12  gives    4.34  atomic  weights  of  carbon 
13.04  „  i      „      13.04         „  .,          hydrogen 

34.80  „          1 6      .,        2.17         „  „          oxygen 

If  the  ratio  4.34  :  13.04  :  2.17  be  expressed  in  its  lowest  terms,  it  becomes 
2  :  6  :  i,  giving  for  the  empirical  formula  of  alcohol,  C.>H60. 

The  question  now  arises  whether  this  formula  is  a  true  representation  of  the 
molecule  or  indivisible  particle  of  alcohol,  or  whether  the  molecule  should  be 
written  C4H1202,  or  C6H1803,  or  in  any  other  form  which  would  preserve  the  ratio 
established  beyond  dispute  by  the  above  analysis. 

310.  To  deduce  the  molecular  formula  of  a  compound  from  vY-s-  enipirical  formula 
the  molecular  weight  of  the  compound  must  be  determined,  for  it  is  evident  that 
the  formula  C2H60  represents  2  atoms  of  C,  weighing  12x2,  6  atoms  of  H,  Aveigh- 
ing  1x6,  and  i  atom  of  0,  weighing  16  ;  the  sum  of  these  numbers,  or  46,  would 
be    the  weight  of   alcohol  represented  by  C2H60,  whereas  the  formula    C4H12O2 
would  express  46  x  2  parts  by  weight,  and  C6H180:5  would  express  46  x  3  parts  by 
weight  of  alcohol. 

The  methods  for  determining  the  molecular  weight  of  a  volatile  compound  have 
been  described  at  p.  292. 

In  the  case  of  a  substance  which  cannot  be  converted  into  vapour  without 
decomposition,  the  molecular  weight  is  determined  by  the  cryoscopic  method 
(p.  319),  or  is  inferred  from  a  consideration  of  the  chemical  relations  of  the  sub- 
stance, and  its  determination  is  sometimes  a  difficult  matter.  The  general 
character  of  the  latter  method  will  be  seen  from  the  following  examples  : 

Determination  of  the  molecular  formula  of  anacid. — The  substance  yielded,  on 
combustion  with  cupric  oxide,  in  100  parts — carbon,  40.  hydrogen,  6.66,  oxygen 
53-33  5  which  lead  to  CH20  as  the  simplest  or  empirical  formula  of  the  acid. 

The  acid  was  found  to  give  only  one  class  of  salts  with  K  and  Na,  showing  that 
it  only  contains  one  atom  of  H  exchangeable  for  a  metal,  or  is  monobasic  (p.  104). 

By  neutralising  the  acid  with  ammonia,  and  stirring  with  solution  of  silver 
nitrate,  a  crystalline  silver  salt  was  obtained,  which  was  purified  by  recrystal- 
lisation  from  hot  water,  dried,  weighed  in  a  porcelain  crucible  of  known  weight, 
and  gradually  heated  to  redness.  On  again  weighing  the  crucible,  after  cooling, 
it  was  found  to  contain  a  quantity  of  metallic  silver  amounting  to  64.66  per  cent, 
of  the  weight  of  the  salt.  Now,  as  a  general  rule,  a  silver  salt  is  formed  from  an 


DETERMINATION  OF  MOLECULAR  FORMULAE.       52$ 

acid  by  the  displacement  of  an  atom  of  hydrogen  by  an  atom  of  silver  •  so  that 
what  remains  of  a  silver  salt,  after  deducting  the  silver,  represents  the  acid 
itself  minn*  a  quantity  of  hydrogen  equivalent  to  the  silver. 

From  the  silver  salt       ....     100.00 
Deduct  the  silver        .        .         .      64.66 


Acid  residue        .         .        .         -35-34 

Then  64  66  4«-  •  108  -' Aff  ln  om  '"wlf"}  -  .  ,c  -,„  .  enfftcifj  ''''*'<?«*  in 
1611  b4'66  Ag  '  I08  lf«fe  of  the  salt  j  '  •  ^-M  -  59{   ime  >>>t>iec(d^ 
To  the  acid  residue   ......     50 

Add  the  hydrogen  equivalent  to  an  atom  of  Ag       i 

Molecular  weight  of  the  acid       .         .     60 

The  formula  CH.20  represents   12  +  2+16  =  30.     Hence  the  molecular  formula  is 
C.Jf4Oo  =  6o  ;  and  the  silver  salt  is  C2H3Ag02. 

Determination  of  the  molecular  formula  of  an  organic  base. — The  substance  yielded 
on  combustion  with  cupric  oxide,  in  100  parts,  carbon  77.42,  hydrogen  7.53.  A 
determination  of  nitrogen  gave  15.05  per  cent,,  so  that  there  was  no  oxygen. 
These  numbers  lead  to  C6H7N  as  the  simplest  or  empirical  formula  of  the  base. 
By  dissolving  the  base  in  hydrochloric  acid  and  adding  platinic  chloride,  a  yellow 
crystalline  precipitate  was  obtained,  resembling  the  ammonio-platinic  chloride 
formed  when  ammonia  is  treated  in  the  same  way.  This  precipitate  was  washed 
with  alcohol,  dried,  weighed  in  a  porcelain  crucible,  and  heated  to  redness,  when 
t  left  a  residue  of  metallic  platinum,  which  amounted  to  32.72  per  cent,  of  the 
weight  of  the  salt.  As  a  general  rule,  a  platinum-chloride  salt  is  formed  by  the 
combination  of  PtCl4  with  two  molecules  of  the  hydrochloride  of  the  base  ;  in  the 
case  of  the  ammonio-platinic  chloride,  the  formula  is  Pt014.2(NH3.HCl)  ;  so  that 
what  remains  of  a  platinum  salt  after  deducting  the  platinum  represents  two 
molecules  of  the  base  +  two  molecules  of  HC1  +  4  atoms  of  chlorine. 

From  the  platinum  salt          .         .         .     100.00 
Deduct  the  platinum        .         .       32.72 

Remainder       ....       67.28 

Then  33.7a  Pt :  ^SftfcSjT)  :  :  **' «»* 

Hence  two  inols.  base +  2  mols.  HC1  +  4  atoms  01  =  400.9 
Deduct  2HC1  +  C14  =215.0 

Weight  of  two  molecules  of  the  base    .  185.9 

The  molecular  weight  of  the  base,  therefore,  is  92.9.     The  formula  C6H7N  repre- 
sents 72  +  7  +  14-93.     This  is  therefore  the  molecular  formula. 

The  law  of  ere n  numbers  is  sometimes  a  useful  guide  in  fixing  molecular  formula. 
It  may  be  thus  expressed  :  The  total  number  of  atoms  of  monad  or  triad  clement* 
united  witlt  carbon  in  an  organic  compound  must  be  an  even  number.  The  law  is  a 
result  of  the  tetrad  nature  of  carbon,  as  will  be  seen  in  the  next  few  pages. 

For  example,  the  empirical  formula  for  glycol,  deduced  from  ultimate  analysis,  i^ 
CH30  ;  but  this  is  an  impossible  formula,  by  the  law  of  even  numbers,  and  the 
molecular  formula  for  glycol  must  be  at  least  double  this,  C.,H602. 

311.  The  ultimate  analysis  of  an  organic  compound  serves  to  decide  its 
empirical  formula — i.e.,  the  formula  expressing  the  ratio  between  the 
number  of  atoms  of  each  element  in  the  compound ;  a  determination  of 
the  molecular  weight  decides  whether  the  molecular  formula  (i.e.,  the 
formula  expressing  the  actual  number  of  atoms  of  each  element  in  one 
molecule  of  the  compound)  is  identical  with,  or  a  multiple  of,  the  em- 
pirical formula.  Thus,  the  empirical  formula  for  benzene  is  CH,  but 
its  molecular  formula  is  undoubtedly  six  times  this — viz.,  C6H6. 

From  what  was  said  in  the  chapter  on  nitrogen,  and  again  on  p.  191, 
it  will  be  apparent  that  much  light  may  be  thrown  upon  the  behaviour 
of  compounds  by  a  study  of  the  way  in  which  the  component  atoms  are 


.524  STRUCTURAL  FORMULAE. 

combined  together.  In  this  manner  the  existence  of  radicles  in  com- 
pounds can  be  traced,  and  it  becomes  possible  to  assign  a  constitutional 
or  rational  formula — i.e.,  a  formula  which  indicates  the  radicles  that 
•compose  it — to  a  compound.  Furthermore,  it  becomes  necessary,  in  the 
case  of  carbon  compounds,  to  provide  some  working  hypothesis  which 
shall  account  for  the  fact  that  many  substances  exist  which  have 
•different  properties,  but  nevertheless  have  the  same  ultimate  composition 
and  the  same  molecular  formula  :  such  cases  are  included  under  the 
term  isomerism,  which  will  shortly  receive  closer  attention.  The 
necessary  hypothesis  is  supplied  by  supposing  the  atoms  in  the  compound 
to  be  linked  together  by  bonds  in  such  a  way  that  this  linkage  can  be 
represented  by  a  graphic  or  structural  formula  on  one  plane,  as  explained 
on  p.  101. 

It  is  only  by  such  a  study  of  the  structure  of  carbon  compounds  that  any 
success  has  been  achieved  in  the  main  object  of  chemistry,  namely,  the 
synthesis  of  compounds.  The  study  involves  a  careful  consideration  of 
the  reactions  of  the  compound,  and  many  examples  will  be  met  with 
hereafter;  the  following  may,  however,  be  now  quoted  as  a  typical 
simple  case. 

312.  Example. — Determination  of  the  rational  or  structural  formula  of  alcohol. 
When  sodium  is  placed  in  alcohol,  it  is  dissolved  with  the  evolution  of  much 
hydrogen,  and  the  alcohol  is  converted  into  a  crystalline  substance  called  sodium 
ethoxide,  which  has  the  composition  C2H5ONa.  Comparing  this  with  the  formula 
of  alcohol,  it  is  seen  that  Na  has  been  substituted  for  one  atom  of  H.  Since  the 
-compound  still  contains  H5,  it  might  be  supposed  that  by  the  use  of  an  excess 
of  Na  more  might  be  substituted  for  H,  producing  ultimately  a  compound  C2Na60. 
But  this  is  not  the  case  ;  Na  can  be  substituted  in  this  way  for  only  one  of  the  6 
atoms  of  H  in  alcohol  ;  hence  it  is  seen  that  one  atom  of  the  six  is  on  a  different 
footing  from  the  other  five.  This  would  be  expressed  by  writing  the  formula 
C2H5OH. 

Again,  when  alcohol  is  acted  on  by  hydrogen  chloride,  and  distilled  at  a  low 
temperature,  it  yields  water  and  a  very  volatile  liquid  known  as  ethyl  chloride, 
having  the  composition  C9H5C1.  This  decomposition  would  be  expressed  by  the 
equation,  C.2H5OH  +  HC1  =  C2H5C1  +  HOH,  from  which  it  is  evident  that  the  Cl  of 
the  HC1  has  been  exchanged  for  OH  in  the  alcohol,  leading  to  the  conclusion  that 
alcohol  is  made  up  of  at  least  two  separate  groups,  and  that  one  way  of  writing 
its  rational  formula  is  C2H5'OH. 

313.  By  investigating  the  nature  of  the  radicles  contained  in  an 
organic  substance,  this  may  generally  be  assigned  to  one  of  the  following- 
divisions  : 

(1)  HYDROCARBONS,  composed  of  carbon  and  hydrogen  only,  in  various 
modes  of  grouping  ;  as  ethyl  hydride  or  ethane,  C,H.'H. 

Hydrocarbons  from  which  hydrogen  has  been  removed  give  rise  to 
hydrocarbon  radicles,  thus,  C2H5  is  the  hydrocarbon  radicle,  ethyl,  from 
ethane ;  like  all  other  radicles  they  are  incapable  of  a  separate  existence 
(p.  94).  Since  in  chemical  reactions  the  hydrocarbon  radicles  behave 
towards  other  radicles  analogously  to  the  manner  in  which  the  metals 
behave  towards  the  non-metals,  they  are  frequently  termed  positive 
radicles,  other  radicles  such  as  (OH),(COOH),  etc.,  being  termed  negative. 

(2)  ALCOHOLS,  composed  of  carbon,  hydrogen,  and  oxygen,  and  con- 
taining one  or  more  hydroxyl  (OH)  radicles ;  as  ethyl- alcohol,  C2H5'OH. 

(3)  ALDEHYDES,  or  dehydrogenated  alcohols  ;  products  of  the  partial 
oxidation  of  the  alcohols,  containing  the  group  (COH) ;  as  ethyl-aldehyde, 
CH3-COH. 

(4)  ACIDS,   the  products  of   the  further  oxidation   of  the  alcohols, 


CLASSIFICATION  OF  CARBON  COMPOUNDS.  525 

containing  one  or  more  carboxyl  radicles,  C02H;  as  acetic  acid,  CH  -COOH 
' 


(5)  KETONES,  formed  from  the  acids  by  the  substitution  of  a  hydro- 
carbon radicle  for  the  OH  in  the  carboxyl  ;  so  that  the  ketones  contain 
the  group  CO  ;  as  acetic  ketone  or  acetone,  CH3'CO'CH3. 

(6)  ETHERS,  formed  from  the  alcohols  by  the  substitution  of  a  hydro- 
carbon radicle  for  the  H  in  the  hydroxyl,  as  ethyl-ether,  C.,H5'0'C,H.. 

(7)  HALOID  COMPOUNDS,  formed  from  the  foregoing  groups  by  the 
substitution  of  a  halogen  radicle  for  hydrogen  or  hydroxyl  ;  as  chloro- 
form, CHC13  ;  ethyl  chloride,  C2H5C1  ;  acetyl  chloride,  CH3'CO'C1. 

(8)  ETHEREAL  SALTS  (or  esters),  formed  from  the  acids  by  the  sub- 
stitution of  a  hydrocarbon  radicle  for  the  hydrogen  in  the  carboxyl  radicle  • 
as  ethyl  acetate,  CH3-CO'OC2H5. 

(9)  ORGAXO-MIXERAL   COMPOUNDS,    formed    upon    the    type   of    the- 
chlorides  of  metals  or  non-metals  by  the  substitution  of  hydrocarbon 
radicles  for  the  chlorine  ;  as  zinc  ethide,  Zn(C2H5)2. 

(10)  AMMONIA-DERIVATIVES,  formed  upon  the  model  of  ammonia,  NH.,,. 
by  the  substitution  of  a  radicle  for  hydrogen  ;  as  ethylamine  NH  -C  H 
acetamide,  NH2'C2H3O. 

(n)  CYANOGEN  COMPOUNDS,  containing  the  group  CIS";  as  hydro- 
cyanic acid,  H'C]S\ 

(12)  PHENOLS,  resembling  the  alcohols  in  composition,  by  containing 
the  hydroxyl  group,   but  resembling  the  acids  in  some  of  their  pro- 
perties, and  not  yielding  aldehydes  when  partially  oxidised  ;  as  phenok 
CGH5-OH. 

(13)  QUINONES,  formed  from  hydrocarbons  by  the   substitution  of  a 
group   of   two   oxygen   atoms  for  two  hydrogen  atoms  ;    as  quinane, 
C6H4(02),  from  benzene,  C6HG. 

Compounds  for  which  sufficient  evidence  of  a  rational  formula  bas- 
net been  obtained  are  classified  according  to  similarity  in  properties,. 
ultimate  composition,  or  products  of  decomposition.  The  following  are 
the  most  important  of  such  classes  : 

(14)  CARBOHYDRATES,  or  compounds  containing  six,  or  some  multiple 
of  six,  atoms  of  carbon,  together  with  some  multiple  of  the  group  H20  ; 
as  starch,  C6H100,,  glucose,  C6H]206,  sugar,  C12H22On. 

(15)  GLUCOSIDES,  or  compounds  which  yield  glucose  as  one  of  their 
products  of  decomposition  ;  as  salicin,  C]3H1807. 

(16)  ALBUMINOIDS  and  GELATINOIDS,  or  compounds  containing  C,  H, 
N,   and  O,    often    with   small  quantities  of  S,  and  sometimes  of   P, 
distinguished  by  their  tendency  to  putrefy  when  moist  ;  albumin,  fibrin. 
and  casein  are  examples  of  such  compounds,  but  they  cannot  at  present 
be  represented  by  satisfactory  formulae. 

(17)  HKTEROCYCLIC  COMPOUNDS.  —  The  nature  of  these  will  be  explained 
later. 

With  few  exceptions,  one  or  other  of  the  typical  formulae  cited  in  the 
foregoing  classification  contains  a  hydrocarbon  radicle  ;  it  is,  indeed, 
possible  to  build  up  the  members  of  each  group  by  starting  with  one  or 
other  of  the  hydrocarbons.  Hence,  nearly  all  organic  compounds  are 
either  hydrocarbons  or  hydocarbon  derivatives. 

In  1813  Chevreul  showed  that  a  fat  is  composed  of  glycerine  and  a  fulfil  </<•!</. 
and  in  1848  Kolbe  obtained  hydrocarbons  by  electrolysing  salts  of  fatty  acids. 
Later  the  aromatic  substances,  like  the  essential  oils  and  balsams,  were  studied  and 


526  PARAFFIN  HYDROCARBONS. 

found  to  yield  hydrocarbons  richer  in  carbon  than  those  obtainable  from  the  fatty 
compounds.  A  classification  of  hydrocarbons  into  a  fatty*  and  an  aromatic  series 
was  a  natural  consequence.  But  in  the  advance  of  a  science  definitions  become 
blurred  by  more  accurate  knowledge,  and,  for  a  reason  which  will  be  apparent 
later,  the  terms  open-chain  and  closed-chain  (or  acyclic  and  cyclic)  have  been 
adopted  as  more  accurately  expressing  the  differences  implied  by  the  words  fatty 
and  aromatic  respectively.  Even  this  division  is  losing  its  aptness,  for  bodies  of 
fatty  nature  have  been  detected  among  closed-chain  compounds.  For  this  reason 
no  actual  division  is  made  in  the  following  pages. 


HYDROCARBONS. 

314.  As  will  be  explained,  these  are  either  saturated  or  unsaturated, 
accordingly  as  they  behave  towards  chemical  agents. 

SATURATED  HYDROCARBONS. 

Paraffin  Series  of  Hydrocarbons. — The  only  hydrocarbon  which 
contains  one  atom  of  carbon  is  methane  or  marsh  gas,  CH4,  the  more 
important  properties  of  which  have  been  already  considered. 

It  has  been  seen  that  when  CH4  undergoes  metalepsis  with  chlorine,  one  of  its 
H  atoms  is  exchanged  for  Cl,  the  compound  CH3C1  being  produced  (p.  174).  Now 
there  are  several  other  methods  of  producing  a  compound  of  this  formula,  and, 
whichever  be  adopted,  the  product  always  has  the  same  properties,  showing  that 
only  one  compound  of  the  formula  CH3C1  exists.  It  is  contrary  to  experience, 
acquired  in  other  cases,  to  suppose  that  all  the  methods  of  producing  CH3C1 
would  result  in  the  substitution  of  Cl  for  the  same  H  atom,  and  it  may  be  fairly 
inferred  that  whilst  one  method  would  produce  CHHHC1,  another  would  produce 
CHHC1H,  a  third  CHC1HH,  and  a  fourth  CC1HHH.  In  each  case  the  substance 
produced  is  the  same.  It  is  therefore  supposed  that  all  the  four  H  atoms  in 
methane  have  an  equal  position  with  regard  to  the  carbon  atom,  so  that  which- 
ever is  substituted  the  centre  of  gravity  of  the  molecule  will  remain  the  same. 

It  is  in  order  to  express,  or  to  attempt  to  explain,  this  equality  of  position  of 

the  hydrogen  atoms  in  relation  to  the  carbon,  that  they  are  often  represented  on 

•   paper  as  symmetrically  arranged  round  the  centre  carbon 

H  atom  (Fig.  247),  so  that  whichever  H  is  exchanged  for  Cl, 

I  the  figure  has  only  to  be  turned  round  in  order  to  appear  the 

H  —  C  —  H  same.     On  paper  the  atoms  are,  of  necessity,  written  on  the 

same  plane,  but  it  is  not  to  be  supposed  that  this  represents 

H  their  arrangement  in  the  molecule.     At  present  we  have  no 

satisfactory  knowledge  of  the  shapes  of  molecules,  but  we 

Fi»-  247- — Methane.     are  obliged  to  think  of  them  as  having  three  dimensions. 

The   most  fruitful  hypothesis    as  to   the   structure   of   the 

methane  molecule  is  that  the  carbon  atom  occupies  the  centre  of  a  regular  tetra- 
hedron, the  hydrogen  atoms  being  attached  to  the  four  angles  thereof. 

Inasmuch  as  methane  has  the  formula  CH4,  generally  written  as  in 
Fig.  247,  it  must  be  regarded  as  a  saturated  compound  devoid  of  any 
residual  affinity  such  as  that  possessed  by  CO  (p.  136). 

In  the  case  of  all  other  hydrocarbons  it  is  assumed  that  the  carbon 
atoms  are  directly  united  together,  since  it  does  not  appear  to  be  possible 
for  H  to  behave  other  than  as  a  monovalent  element,  so  that  it  cannot 
be  supposed  to  act  as  an  intermediary,  that  is,  in  a  manner  represented 
by  the  expression  0-H-C.  Of  those  hydrocarbons  which  have  two  carbon 
atoms,  or  a  two-carbon  nucleus,  there  are  at  least  three,  of  which  two, 
ethylene,  C2H4,  and  acetylene,  C2H2,  have  received  notice  (pp.  142  and 
137)  and  will  be  referred  to  again.  The  third  is  called  ethane,  and  has 

*  Attempts  have  been  made  to  substitute  aliphatic  for  fatty. 


HOMOLOGOUS  SERIES.  527 

the  formula  C.H6,  which  is  generally  represented  as  shown  in  Fig   248 
but  is  equally  well  written  H3C  CH3. 

The  evidence  for  this  formula  is  of  a  similar  character  to  that  for  the  methane 
formula,  only  one  compound  C2H5C1  being  obtainable.     If  two  regular  tetrahedra 
be  placed  with  one  solid  angle  of  each  in  contact,   a  two- 
carbon  nucleus  will  be  represented  in  which  each  carbon  is               H     H 
at  the  centre  of  a  tetrahedron,  the  six  H  atoms  being  at  the                |       | 
remaining  three  angles  of  each  tetrahedron  (see  Fig.  257).  H  —  C C H 

Ethane  is  also  a  saturated  hydrocarbon,  for  all  the 
bonds  of  the  two  carbon  atoms  are  satisfied.     Pass- 
ing to  those  hydrocarbons  which  contain  three  car-     Fi£-  248.— Ethane. 
bon  atoms,  or  a  three-carbon  nucleus,  that  which  is 
saturated,  and  therefore  contains  the  highest  number  of  hydrogen  atoms, 
is  C3H8,  called  propane,  and  is  represented  as  in  Fig.  240,  or  more  simply 
as  CH3-OH2-CH3. 

The  evidence  for  this  formula  is  derived  from  the  methods  H     H     H 

by  which  propane  is  prepared,  and  will  be  appreciated  when 

these  are  described.     The  reasoning  applied  to  methane  will  H  —  C  —  C  —  C H 

not  serve  in  this  case,  for  two  compounds  of  the  formula  |       |       | 

C3H7C1  are  known,  as  will  be  explained  later.  H     H     H 

A  comparison  of  these  three   hydrocarbons  will    Yig.  249.— Propane, 
show  that  ethane  may  be  regarded  as  derived  from 
methane,  and  propane  from  ethane,  by  substituting  CH3  for  H.     By 
continuing  this  process  a  whole  series  of  hydrocarbons  is  obtained,   each 
of  which  is  saturated  and  differs  from  the  one  preceding  it  by  CH2. 
Thus  butane,   the    next  member  of  the  series,   is   CH^CH^CH^CHg, 
pentane  is  CH3-CH2-CH2-CH2'CH3,  and  so  on.      Any  series 'of  carbon 
compounds,  each  member  of  which  differs  from  the  one  preceding  it  by 
OH2,  is  called  an  homologous  series,  and  the  compounds  are  homologues 
of  each  other. 

It  will  be  seen  that  in  the  homologous  series  under  consideration,  the 
number  of  hydrogen  atoms  must  always  exceed  twice  the  number  of 
carbon  atoms  by  2,  and  that  a  general  formula  for  the  series  may  there- 
fore be  written  CwH2n+2.  Since  each  terminal  carbon  atom  has  three 
hydrogen  atoms  attached  to  it,  the  general  formula  may  be  extended  to 
H3C-CHH2K-OHo.  As  already  stated,  hydrocarbons  which  conform  with 
this  general  formula  are  termed  saturated  because  they  cannot  have  any 
free  affinities  by  which  other  elements  can  attach  themselves  to  the 
molecule.  It  must  be  understood  that  this  title  does  not  represent  a 
mere  theoretical  speculation,  but  is  the  expression  of  actual  experience, 
since  it  is  found  to  be  impossible  to  produce  a  new  compound  from  any 
of  these  hydrocarbons  save  by  substitution  ;  for  example,  no  compound 
containing  chlorine  can  be  obtained  from  methane  except  by  exchanging 
one  or  more  atoms  of  01  for  one  or  more  atoms  of  H.  On  account  of  this 
inactivity  the  series  has  been  called  the  paraffin  series  of  hydrocarbons, 
the  name  paraffin  (parum,  little,  affinis,  affinity)  having  been  originally 
bestowed  upon  the  wax-like  substance  obtained  in  the  distillation  of  coal 
and  peat,  because  of  its  resistance  to  chemical  agents ;  this  solid  was 
subsequently  shown  to  consist  mainly  of  saturated  hydrocarbons. 

The  paraffin  hydrocarbons  may  be  regarded  as  the  hydrides  of  posi- 
tive radicles  of  the  general  formula  0MH2jl+1,  the  formula  for  the 
hydrocarbons  being  C,ZH.7H+1H.  These  radicles  have  been  termed  alkyl 


528  PETROLEUM  OIL. 

radicles ;  they  are  obviously  monovalent.  They  are  designated  similarly 
to  the  hydrocarbons  which  constitute  their  hydrides,  the  suffix  ~yl  being 
substituted  for  -ane. 

The  natural  source  of  the  paraffin  hydrocarbons  is  the  oil  known  as 
petroleum,  mineral  naphtha,  or  rock-oil.  This  is  found  in  nearly  all 
countries,  but  especially  at  Baku,  on  the  Caspian  Sea,  and  in  Canada 
and  Pennsylvania,  and  occurs  in  almost  all  geological  formations.  It  is 
to  be  noted,  however,  that  the  Russian  petroleum  consists  largely  of 
hydrocarbons  (naphthenes)  allied  to  the  aromatic  series  (q.v.),  whilst 
that  of  Pennsylvania  consists  almost  entirely  of  a  mixture  of  paraffin 
hydrocarbons. 

The  Pennsylvanian  oil-wells  discharge  large  volumes  of  gas  containing 
H,  CH4,  and  C2H6,  which  are  used  for  heating  and  lighting  in  the 
neighbouring  district.  The  liquid  pumped  out  of  the  wells  still  retains- 
a  quantity  of  ethane  in  solution.  It  consists  chiefly  of  members  of  the 
paraffin  series,  of  which  a  list  is  here  given — 


Methane  CH4  Gas 

Ethane  C2H6          „ 

Propane  C3H8          „ 

Butane  C4H10  „ 

Boils  at 

Pentane  C5H12  36°  C. 

Hexane  C6H14  69° 


Boils  at 


Heptane          (V^io          9^°  ^- 

Octane  (V^is  125° 

Nonane  ^'<)H20  149° 

Decane  ( '10H2.,  173° 

Dodecane        ^12^26  214° 

Hexadecane  C^H^  287° 


The  liquid  constituents  of  the  petroleum  are  separated  by  the  process 
of  fractional  distillation,  which  depends  upon  the  difference  in  their 
boilin  g-poin  ts. 

When  the  petroleum  is  heated,  the  hydrocarbons,  ethane,  propane,  and  butane, 
are  evolved  in  the  gaseous  state  ;  these  are  collected  and  subjected  to  the  action 
of  a  condensing  pump,  which  liquefies  a  portion  of  them,  yielding  the  liquid  sold 
as  cymogene.  (sp.  gr.  0.59),  which  is  used  in  freezing-machines,  on  account  of  the 
cold  produced  by  its  rapid  evaporation.  It  consists  chiefly  of  butane,  C4H10. 

The  portion  which  first  distils  over  requires  special  condensation,  for  it  boils  at 
18°  C. ;  it  contains  a  considerable  proportion  of  pentane,  and  is  sold  as  rli'xjnhnc 
(sp.  gr.  0.62),  being  used  as  an  anaesthetic,  and  for  a  standard  of  light.  The 
portion  which  distils  over  about  60°  C.  consists  mainly  of  hexane,  and  is  sold  as 
petroleum  spirit,  petroleum  ether,  or  gasolene  (sp.  gr.  0.66)  ;  it  is  used  for  dissolving 
india-rubber.  The  next  fraction  is  chiefly  heptane,  and  is  collected  until  the 
temperature  rises  to  110°  C.;  its  sp.  gr.  is  0.7,  and  it  is  used,  in  some  kinds  of 
lamps,  as  a  burning  oil,  and  as  a  solvent,  under  the  names  naphtha,  ligroin,  and 
benzoline.  The  next  fraction  is  collected  below  150°  C.,  and  is  known  as  ben-zinc 
(sp.  gr.  0.74),  a  solvent  which  must  not  be  confounded  with  benzene,  the  coal-tar 
product.  A  similar  fraction  is  the  petrol  burnt  in  the  engines  of  motor-cars.  The 
Iterosene  oil,  so  much  in  use  for  paraffin  lamps,  is  the  portion  which  distils  between 
150°  and  300°  C.,  and  is  generally  refined  by  agitation  with  about  2  per  cent,  of 
sulphuric  acid  (which  removes  the  olefines  contained  in  the  oil)  before  being  sent 
into  the  market.  It  is  unsafe  to  use  oils  of  low  boiling-point  as  illuminants  in 
ordinary  lamps,  because  they  so  easily  evolve  vapour,  which  forms  an  explosive 
mixture  with  air,  and  bursts  the  lamp. 

The  temperature  at  which  the  hydrocarbon  evolves  enough  vapour  to  form  an 
inflammable  mixture  with  the  air  above  it  is  termed  its  flashing-point.  Xo  paraffin 
oil  is  considered  safe  for  burning,  in  England,  which  kindles  from  a  flame 
brought  near  to  its  surface  when  it  is  heated  to  38°  C.  (100°  F.)  in  an  open  vessel ;  a 
teacup  placed  in  a  basin  of  hot  wrater  in  which  a  thermometer  is  plunged, 
answers  for  a  rough  test.  In  a  closed  vessel,  where  the  vapour  more  rapidly 
accumulates  in  sufficient  quantity,  the  flashing-point  is  much  lower,  and  no  oil  is 
considered  safe  which  kindles  at  or  below  23°  C.  (73°  F.)  in  a  covered  vessel  when 
a  flame  is  brought  near  its  surface  :  a  small  beaker  covered  with  a  piece  of  tin 


FRACTIONAL  DISTILLATION. 


529 


plate  having  a  small  hole  for  introducing  a  match,  may  be  placed  in  warm  water 
for  the  close  text. 

The  distillation  of  the  petroleum  is  finally  pushed  until  a  tarry  residue  is  left 
in  the  retort.  The  distillate  above  300°  C.  consists  of  heavy  (sp.  gr.  0.9)  lulncut- 
iiuj  HI?*  containing  parqffin-ivax,  which  melts  at  about  55°  C.,  and  may,  therefore, 
be  separated  from  the  oils  by  freezing  ;  this  wax  contains  the  highest  known  homo- 
logues  of  the  paraffin  series.  The  softer  varieties  of  paraffin  are  known  as  vaseline. 

Ozokerite,  a  crude  form  of  which  is  known  as  ceresln,  is  imported  from  Galicia, 
Hungary,  and  Kussia,  for  the  manufacture  of  candles.  It  consists  of  solid  hydro- 
carbons which  appear  to  contain  a  smaller  proportion  of  hydrogen  than  do  the 
paraffin  hydrocarbons  ;  its  melting-point  varies  from  60°  C.  to  100°  C. 

Paraffin  oils,  both  illuminating  and  lubricating,  and  paraffin-wax  are  also 
obtained  by  distilling  certain  minerals  allied  to  coal,  such  as  the  Torbane  Hill 
mineral,  or  Boghead  cannel,  found  at  Bathgate,  in  Scotland.  Such  shale  oils  con- 
tain more  olefines  than  do  the  American  oils. 

All  the  oils  above  mentioned  are  colourless  when  quite  pure,  although  the  com- 
mercial products  are  frequently  yellow  or  brown. 

315.  On  the  small  scale,  the  process  of  fractional  distillation  for  the  separation  of 
liquids  of  different  boiling-points  is  conducted  in  a  flask  (A,  Fig.  250)  provided 


Fig.  250.— Fractional  distillation. 

with  a  long  neck  through  which  a  thermometer  (T)  passes  to  indicate  the  tempera- 
ture at  which  the  liquid  boils.  The  first  portion  which  distils  over  will,  of  course, 
consist  chiefly  of  that  liquid  which  has  the  lowest  boiling-point,  particularly  if  the 
neck  of  the  flask  consist  of  a  series  of  bulbs  and  thus  expose  a  large  surface  to  be 
cooled  by  the  air  ;  if  the  receiver  (R)  be  changed  at  stated  intervals  corresponding 
with  a  certain  rise  in  the  temperature,  a  series  of  liquids  will  be  obtained,  con- 
taining substances  the  boiling-point  of  which  lie  within  the  limits  of  temperature 
between  which  the  liquids  were  collected. 

When  these  liquids  are  again  distilled  separately  in  the  same  way,  a  great  part 
of  each  is  generally  found  to  distil  over  within  a  few  degrees  on  either  side  of 
some  particular  temperature,  which  is  the  boiling-point  of  the  substance  of  which 
that  liquid   chiefly  consists  ;   and   if   the  receivers    be  again  changed  at  stated 
intervals,  a  second   series  of   distillates  will   be   obtained,  the   boiling-points  o 
which  are  comprised  within  a  narrower  range  of  temperature.     It  will  be  evider 
that,  by  repeated  distillations,  the  original  mixture  will  eventually  be  resolved 

2  L 


530 


METHANE. 


into  a  number  of   liquids,  each   distilling   over  entirely  at  about  one  particular 
temperature,  which  is  the  boiling-point  of  its  chief  constituent. 

316.  Methane,  or  methyl  hydride,  CH4.  The  following  must  be  added 
to  the  description  of  methane  which  has  already  been  given  (p.  144). 

To  prepare  the  pure  gas,  methyl  iodide  is  dropped  slowly  into  a  flask 
A  (Fig.  251)  containing  a  copper-zinc  couple  (p.  21)  covered  with  dilute 

alcohol  ;  the  flask  is  very  gently 
heated,  whereupon  methane  is 
evolved  in  accordance  with  the 
equation  —  CH3I  +  C2H5OH  + 
Zn=  CH3H  +  Zni.OC2H5,  and 
passes  up  the  tube  B  contain- 
ing granulated  zinc  which 
decomposes  any  unchanged 
CH3T,  allowing  the  methane 
to  be  collected  in  the  usual 
manner  from  the  delivery 
tube.  Methane  is  also  formed 
when  zinc  methide  is  decom- 
posed by  water,  Zn(CH3)2  + 
2HOH  =  Zn(OH)2  +  2CH4,  and 
by  the  action  of  sodium  amal- 
gam and  water  (to  supply  H) 
on  carbon  tetrachloride,  CC14  + 
H8  =  CH4  +  4HC1,  and  bypass- 
ing a  mixture  of  CS2  vapour 
and  H3S  (or  steam)  over  red-hot 
copper,  CS2  +  2H2S  +  Cu8  = 
4Cu2S  +  CH4.  The  last  two  methods  are  of  great  importance,  since 
they,  amount  to  the  preparation  of  the  gas  from  its  elements,  and, 
therefore,  to  the  synthesis  of  the  paraffin  hydrocarbons  generally,  for 
the  majority  of  these  can  be  built  up  from  marsh-gas  by  the  aid  of  a 
few  elements  which  act  as  intermediaries. 

Methane  is  nearly  inodorous  ;  its  sp.  gr.  is  0.56  (air=i);  it  burns 
with  a  feebly  luminous  flame  ;  water  dissolves  about  5  per  cent.,  and 
alcohol  50  per  cent,  of  the  gas.  It  boils  at  -  160°  C.,  but  is  liquid  at 
-  11°  0.,  under  180  atmospheres  pressure  ;  the  sp.  gr.  of  the  liquid  is 
0.415  at  —  164°  C. 

When  methane  is  mixed  with  chlorine  and  exposed  to  sunlight,  a 
violent  reaction  occurs,  and  often  an  explosion,  HC1  being  formed,  and 
C  separated  ;  but  when  the  Cl  is  diluted  with  C02  and  allowed  to  act 
gradually,  chlorine  substitution-products  are  obtained. 

CH4  +    C12  =    HC1  +  CH3C1  monochloromethane. 
CH4  +  2C12  =  2HC1  +  CH2C12  dichloromethane. 
CH4  +  3C10  =  3HC1  +  OH018  chloroform. 
CH4  +  4013  =  4HC1  +  CC14      tetrachloromethane. 

The  chlorine  in  these  compounds  is  not  precipitated  by  silver  nitrate, 
like  the  Cl  in  HC1  and  the  chlorides  of  the  raetals. 

Ethane,  or  ethyl  hydride,  C2H6,  is  prepared  from  ethyl  iodide,  C2H6I, 
just  as  methane  is  prepared  from  methyl  iodide.  It  is  also  formed 
when  methyl  iodide  is  heated  with  zinc  in  a  sealed  tube,  2CH3 


Fig-.  251. — Preparation  of  methane. 


ZnI 


;  hence,  ethane  has  been  termed  dimethyl. 


NUCLEAL  SYNTHESIS. 


531 


Ethane  is  evolved  from  the  anode  when  a  solution  of  potassium  acetate, 
CH3COOK,  is  electrolysed  ;  this  salt  dissociates  into  the  ions  CH3COO  and  K,' 
the  former  of  which  breaks  up  into  C2H6  and  C02,  whilst  the  latter  reacts  with 
the  water  to  form  KOH  and  H,  which  is  evolved  at  the  cathode  ;  the  KOH 
absorbs  the  C02,  so  that  the  ultimate  result  may  be  approximately  represented 
by  the  equation  2CH3COOK  +  2H20  =  C2H6  +  2KHC03  +  H2. 

Ethane  resembles  methane  in  properties,  but  is  more  easily  liquefied 
(46  atm.)  ;  it  is  about  twice  as  soluble  in  alcohol  as  methane  is. 

Propane,  or  pi'opyl  hydride,  C3H8,  is  prepared  by  the  action  of  nascent 
hydrogen  on  propyl  iodide,  C3H7I  +  H2  =  C3H8  +  HI.  It  is  also  formed 
when  a  mixture  of  ethyl  iodide  and  methyl  iodide  is  heated  with  zinc, 
CH3-CH2-I  +  CH3I  +  Zn  =  CH3-CH2-CH3  +  ZnI2,  the  reaction  being  of 
importance  as  confirming  the  constitution  of  propane  (Fig.  249),  for  it 
shows  that  the  hydrocarbon  is  formed  by  the  combination  of  methyl 
with  ethyl.  Propane  is  a  colourless  gas  which  boils  at  -  45°  C. 

It  will  have  been  noticed  that  precisely  similar  methods  serve  for 
the  preparation  of  methane,  ethane,  and  propane.  This  is  illustrative 
of  the  fact  that  the  members  of  an  homologous  series  of  carbon  com- 
pounds can  generally  be  prepared  from  the  members  of  another  homo- 
logous series  by  the  same  reaction ;  thus  the  series  of  alkyl  iodides 
(CH3I,  C2HJ,  C8H7I,  <fec.)  yield  the  corresponding  series  of  alkyl 
hydrides  (hydrocarbons)  by  metalepsis  with  (nascent)  hydrogen.  For 
each  series  of  carbon  compounds,  therefore,  there  is  a  number  of  general 
methods  of  formation. 

It  will  be  noted  that  the  hydrocarbons  which  are  of  industrial  im- 
portance are  either  natural  products,  like  the  parafiins,  or  are  obtained, 
like  benzene,  as  products  of  destructive  distillation,  a  process  the 
mechanism  of  which  has  not  yet  been  explained.  Acetylene  alone  is 
manufactured  by  a  process  which  may  be  said  to  be  well  understood. 
For  the  purposes  of  chemical  investigation,  however,  several  methods 
are  available  for  preparing  hydrocarbons,  and  are  more  or  less  generally 
applicable,  whatever  the  family  to  which  the  desired  hydrocarbon  may 
belong. 

Nucleal  synthesis  or  nucleal  condensation  is  the  most  general  of  these 
methods.      The  term  implies  the  creation  of  a  new  carbon  nucleus, 
either  by  adding  another  carbon  atom  to  an  existing  nucleus  or  by 
converting  a  single  bond  between  two  carbon  atoms  in  the  molecule 
into  a  double  or  treble  bond  (intra-molecular  condensation).     In  the 
case  of  the  paraflftns,  in  which  the  carbon  atoms  are  always  singly  linked, 
the  process  must  consist  in  adding  new  carbon  atoms  to  the  nucleus, 
and  for  this  purpose  two  substituted  hydrocarbons  are  treated  with  an  - 
agent  capable  of  removing  the  substituent  from  each,  leaving  the  carbon  . 
atoms  of  the  two  nuclei  to  combine  at  the  points  thus  exposed.     The 
equation  given  above  for  the  formation  of  propane  from  ethyl  or  methyl 
iodides  illustrates  the  process;    in  general  terms — RI  +  IR'  +  Na2  = 
2NaI  +  R-R',  in  which  R  and   R'  may  be  the  same  or  different  alkyl 
nuclei.     The  halogen  substitution-products  and  sodium  or  zinc  as  the 
halogen  remover  are  best  suited  for  the  method  (Wurtz's  reaction). 

A  less  general  method  is  the  removal  of  carbon  as  C0?  from  an 
organic  acid  by  heating  it  with  alkali,  as  in  the  preparation  of  methane 
by  heating  sodium  acetate  with  caustic  soda  (p.  144)-  This  method  is 
of  much  importance  in  the  paraflin  series,  and  is  expressed  by  the 
general  equation  R'COONa  +  NaOH  =  RH  +  NaOCOONa.  In  a  sense 


532  ISOMEEIC  BUTANES. 

it  is  the  converse  of  the  first  method,  since  it  forms  a  new  carbon 
nucleus  by  removing  carbon  from  an  existing  one. 

A  similar  removal  of  carbon  dioxide  from  salts  of  organic  acids  may 
be  effected  by  electrolysis  (see  ethane,  p.  531),  and  this  method  is 
applicable  to  several  classes  of  hydrocarbons.  It  generally  involves  a 
nucleal  condensation. 

Other  methods  for  preparing  paraffins  are  (i)  treatment  of  alkyl 
halides  with  nascent  hydrogen,  RCl  +  H2  =  RH  +  HC1  (see  methane),  and 
(2)  interaction  of  alkyl  iodides  with  zinc  alkyl  compounds,  2R1  +  ZnR,  = 
2(R.R)  +  ZnI2  (see  ethane). 

Butane,  04H10,  is  made  by  treating  ethyl  iodide  with  zinc  (not  in 
excess)  in  a  sealed  tube  at  150°  C.  ;  2C2H5I  +  Zn  ==  ZnI2  +  C  4H10.  It  is 
much  more  easily  condensed  to  a  liquid  than  is  either  of  the  preceding 
hydrocarbons,  and  is  much  more  soluble  in  alcohol.  Liquid  butane 
(sp.  gr.  0.6)  boils  at  i°  C.  Since  butane  is  prepared  from  ethyl  iodide, 
it  may  be  regarded  as  diethyl  in  the  same  sense  that  ethane  is  dimethyl, 
and  it  is  justifiable  to  write  its  formula,  CH3'CH2'CH2'CH3,  or  as  in 
Fig.  252. 

H    H    H 

H      H     H     H  H-C-C-C-H 

I        I         I        I  III 

H-C-C-C-C-H  H      C      H 


H     H     H     H 

Fig.  252. — Normal  butane. 


1 1' 


SH 


Fig-.  253. — Secondary 
butane. 


For  ethyl  iodide  is  the  iodine  substitution  product  of  ethane, 
CH3'CH3,  and  its  formula  is  CH3'CH2L  "When  the  diad  zinc  acts 
upon  this,  it  must  take  the  I2,  which  it  requires  to  form  zinc  iodide,, 
from  two  molecules  of  ethyl  iodide,  leaving  the  residues  to  combine 
and  produce  butane,  thus : 

CH3-CH2I  +  Zn  +  ICH2-CH3  =  ZnI2  +  CH3-CH2-CH2-CH3. 

There  is  a  second  hydrocarbon  of  the  formula  C4H]0 ;  it  is  prepared 
by  the  action  of  nascent  hydrogen  on  a  compound  called  tertiary  butyl 
iodide  (q.v.),  C4H9I.  It  might  be  mistaken  for  butane  but  for  the  fact 
that  it  will  not  liquefy  until  cooled  to  -  17°  C.  This  second  butane 
has  been  called  secondary  butane  or  isobutane  ('ia-os,  equal),  the  first 
butane  being  termed  normal  butane,  from  norma,  a  rule,  because  it  is 
the  product  of  the  usual  general  methods  of  formation  ot  the  paraffins, 
and  possesses  the  physical  properties  which  the  hydrocarbon,  C4H10,. 
should  possess  from  its  position  in  the  homologous  series  of  paraffins 
(e.g.,  a  boiling-point  about  30°  lower  than  the  next  higher  member  in 
the  series).  In  order  to  explain  the  existence  of  this  secondary  butane 
it  is  supposed  that  the  four  carbon  atoms  are  arranged  in  space  differ- 
ently from  the  manner  in  which  they  are  arranged  in  the  case  of  normal 
butane.  A  little  consideration  will  show  that  the  only  possible  second 
method  of  arrangement  of  the  carbon  atoms  on  one  plane  is  that  shown 
in  Fig.  253,  in  which  the  fourth  C  atom  is  attached  to  the  central  C  atom 
of  the  propane  formula.  The  same  arrangement  may  be  expressed  by 
the  formula  CH3-C(CH3)H'CH3  or  (OH8)f :  OH;CH3,  and  may  be  cle- 


ISOMEPJDES.  533 

scribed  as  consisting  of  methane  in  which  three  atoms  of  H  have  been 
exchanged  for  methyl,  that  is  as  trimethylmethane.  Tertiary  butyl  iodide 
has  the  formula  CH3-C(CH3)I-CH3,  and  the  action  of  nascent  hydro- 
gen in  converting  it  into  trimethylmethane,  or  secondary  butane,  is 
apparent. 

Pentane,  C5H12.  Three  hydrocarbons  of  this  formula  exist ;  that  which 
is  made  by  the  general  methods,  and,  therefore,  has  a  right  to  the  title 
normal  pentane,  is  a  colourless  liquid,  boiling  at  36°  C.  Secondary  pen- 
tane, or  isopentane,  boils  at  28°  C.,  and  tertiary  pentane  or  tetramethyl- 
methane,  at  9°  C.  To  account  for  the  existence  of  these  three  hydro- 
carbons, it  is  necessary  to  suppose  that  the  five  carbon  atoms  are 
arranged  in  three  different  ways;  this  will  be  found  to  be  pos- 
sible, the  results  being  indicated  in  Figs.  254-256,  or  by  the  formulae 
CH3-CH2-CH2-CH2-CH3,  CH3-CH2-C(CH3)H-CH3,  andC(CH3)4. 

H2    H 
Ho   H2   H2  H3C  — C  — C  — CH3  H3C\       /CH3 

H3c-c-c-c-CH3  I  ir/cVH 

CH3  H3C  "H3 

Fig.  254.— Normal  Fig.  256.— Tertiary 

pentane.  Fig.  255. — Iso-pentaue.  pentane.* 

If  it  were  possible  to  arrange  the  5  carbon  atoms  in  a  way  essentially 
different  from  any  of  these  three,  a  fourth  pentane  might  be  expected  to 
exist.  It  will  be  evident  that  the  greater  the  number  of  carbon  atoms 
in  the  hydrocarbon,  the  greater  the  variety  of  arrangement  and  therefore 
the  greater  the  number  of  possible  isomerides.  Thus,  there  may  be  dis- 
covered 802  compounds  of  the  formula  C13H28. 

Isomerides  are  those  compounds  which  have  the  same  percentage 
composition  and  the  same  molecular  weight,  but  different  properties. 
Cases  of  isomerism  are  very  numerous  among  the  carbon  compounds ; 
attempts  have  been  made  to  explain  them  by  reference  to  the  arrange- 
ment of  the  atoms  of  the  compounds  in  space,  although  in  some  cases 
special  difficulty  is  experienced  ;  these  will  be  referred  to  in  due  course. 

Polymerides  have  the  same  percentage  composition,  but  different 
molecular  weights  ;  e.g.,  C2H2  and  C6H6 ;  CH2O  and  C6H1206. 

Since  the  valency  of  carbon  is  always  four,  there  can  only  be  three 
modes  in  which  the  carbon  atoms  can  be  linked  to  each  other,  giving 
rise  to  three  main  classes  of  isomerides,  which  are  illustrated  by  the 
three  classes  of  paraffin  hydrocarbons.  Normal  paraffins  are  those  in 
which  all  the  carbon  atoms  are  united  in  a  single  chain  without  branches. 
so  that  the  formula  begins  and  ends  with  CH3,  every  other  link  being 
CH2  (Fig.  254).  Secondary  paraffins  or  iso-paraffins,  have  at  least  one 
branch,  that  is,  at  least  one  carbon  atom  is  united  with  three  other 
carbon  atoms,  as  in  Fig.  255.  Tertiary  paraffins  or  neo-paraffins,  have  at 
least  one  carbon  atom  united  to  four  others,  as  in  Fig.  256. 

The  remaining  hydrocarbons  of  the  paraffin  series  do  not  need 
detailed  consideration  here.  Those  from  hexane  to  pentadecane  (C15H32) 
are  colourless  liquids  the  boiling-points  of  which  increase,  in  the  normal 
series,  by  about  30°  C.  for  each  increment  of  CH,.  Those  in  the  normal 
series,  from  hexadecane  (C16H34)  to  pentatriacontane  (C33H72),  the  highest 

*  That  this  is  really  the  constitution  of  neo-pentane  is  shown  by  the  steps  for  obtain  inn 
it  synthetically ;  acetone,  H3C(CO)CH3,  treated  with  FC15,  yields  H3C(CCI2)CH3,  ai 
acted  on  by  zinc  methyl,  gives  H3C[C(CH3)2]CH3,  or  neo-pentam-. 


534  CONSTITUTION  OF   UNSATURATED  HYDROCARBONS. 

known  member,  are  colourless  solids  of  which  the  melting-point  increases 
by  3-4°  C.  for  each  increment  of  CH2,  that  of  hexadecane  being  19°  C. 

UNSATURATED  HYDROCARBONS. 

317.  All  hydrocarbons  which  do  not  correspond  with  the  general 
formula  CHH2)Z+2  are  found  to  be  capable  of  combining  directly  with  the 
halogens  without  exchanging  hydrogen  for  them.  Such  are,  there- 
fore, termed  unsaturated  hydrocarbons.  No  hydrocarbon  has  yet  been 
discovered  which  contains  an  uneven  number  of  hydrogen  atoms,  nor 
has  any  unsaturated  hydrocarbon  containing  only  one  atom  of  carbon 
ever  been  isolated.  To  account  for  these  facts  it  is  supposed  that 
all  unsaturated  hydrocarbons  contain  two  or  more  carbon  atoms 
which  are  united  to  each  other  by  two  or  three  atom-fixing  powers, 

thus  :—  H>C  =  C/H,  and  H  -  C=  C  -  H. 


It  may  be  said  that,  in  a  hydrocarbon,  an  unsaturated  carbon  atom  cannot  exist  ; 
if  there  be  not  a  sufficiency  of  other  elements  to  saturate  the  carbon  atom,  it  will 
combine  by  all  its  available  atom-fixing  powers  with  another  carbon  atom.  The 
fact  that  no  such  hydrocarbon  as  H3C  -  CH2  is  known,  is  in  support  of  this 

statement.  Of  these  two  carbon  atoms  the  unsaturated  one  will  take  up  an  atom- 
fixing  power  of  the  saturated  carbon  atom,  at  the  expense  of  one  of  the  hydrogen 
atoms  united  to  this  latter,  forming  H2C  =  CH2,  in  which  neither  carbon  atom  can  be 
said  to  be  unsaturated,  although  the  compound  as  a  whole  is  unsaturated.  Treatment 
of  this  compound  with  chlorine  will  open  up  the  double  linking,  yielding  H2C  -  CH2. 

Cl   Cl 
If  the  compound  were  represented  by  the  formula  H2C  -  CH2,  there  would  be  no 

apparent  reason  wrhy,  when  the  compound  is  mixed  with  the  proper  proportion 
of  chlorine,  one  carbon  atom  alone  should  not  combine  with  Cl  yielding  H2C  -  CH2, 

'      Cl 
a  result  which,  however,  has  never  been  obtained.     The  same  objection  applies  to 

a  third  possible  method  of  representing  this  hydrocarbon,  viz.  :  H3C  -  CH  ;  more- 

over, if  this  formula  were  correct  the  addition  of  chlorine  to  the  hydrocarbon 

Cl 
might  be  expected  to  produce  H.,C  -  CH,  whereas  there  is  evidence  that  the  two 

Cl 

chlorine  atoms  in  the  compound  formed  by  addition  of  chlorine  to  C2H4  are 
attached  to  different  carbon  atoms. 

A  similar  line  of  reasoning  serves  for  supporting  the  formula  HC—  CH  for  the 
hydrocarbon  C2H2. 

If  two  regular  tetrahedra  be  placed  with  one  edge  of  each  coincident,  there  will 
be  two  solid  angles  of  each  tetrahedron  left  unattached.  Such  an  arrangement 
may  be  supposed  to  represent  the  structure  of  the  hydrocarbon  C2H4  in  space  ; 
each  carbon  atom  would  occupy  the  centre  of  a  tetrahedron,  and  each  hydrogen 
atom  would  be  attached  to  a  free  solid  angle.  By  placing  the  two  tetrahedra 
with  one  face  of  each  coincident,  the  structure  of  the  hydrocarbon  C2H2  may  be 
represented. 

The  following  figures  (Fig.  257)  may  represent  hydrocarbons  containing  singly- 
linked,  doubly-linked,  and  trebly-linked  carbon  atoms  respectively. 

Olefine  Series  of  Hydrocarbons.  —  The  Olefine  hydrocarbons  are 
unsaturated  hydrocarbons  containing  a  pair  of  doubly-linked  carbon 
atoms  ;  they  correspond  in  composition  with  the  general  formula  CMH2W. 
The  first  three  members  of  the  homologous  series  are  ethylene,  H2C  :  CH2  ; 
propylene,  H2C  :  CH'CH3  ;  and  butylene,  H2C  :  CH-CH2'CH3.  It  will  be 
seen  that  the  nomenclature  adopted  differs  from  that  for  the  paraffins  by 
the  substitution  of  the  suffix  -ylene  for  -ane,  an  alternative  name  for  the 
olefines  being  alkylenes. 


ETHYLENE.  535 

The  defines  are  found  in  petroleum -oil  and  in  the  products  of  the 
destructive  distillation  of  coal,  wood,  &c.  The  first  three  members  of 
the  series  are  gaseous  under  ordinary  conditions  ;  the  majority  of  the 
remainder  are  colourless  liquids,  but  the  highest  members  are  solid.  A 
gradation  of  boiling-points  and  melting-points  is  observed,  similar  to' that 
existing  in  the  paraffin  series.  The  properties  of  ethylene  may  be  con- 
sidered as  typical  of  those  of  the  other  members  of  this  group  of  hydro- 
carbons. 


Fig.  257. 

Oleflant  gas,  ethylene,  or  ethene,  C2H4,  is  obtained  by  the  action  of 
powerful  dehydrating  agents  on  alcohol ;  C2H5'OH  =  C2H4  +  HOH.  It 
may  be  prepared,  as  described  at  p.  142,  by  heating  alcohol  with  twice 
its  volume  of  strong  sulphuric  acid  ;  secondary  changes  cause  a  carboni- 
sation of  the  mixture,  and  the  ethene  is  accompanied  by  some  ether 
vapour,  and  by  CO2  and  SO2 ;  the  ether  may  be  removed  by  passing 
the  gas  through  strong  sulphuric  acid,  and  the  dioxides  by  potash  or 
soda. 

It  is  also  obtained  by  heating  an  ethyl  halide  with  a  caustic  alkali  in 
alcohol,  e.g.,  C2H5Br  +  KOH  =  CaH4  +  KBr  +  HOH. 

Properties  of  ethylene. — It  has  a  faint  ethereal  odour,  sp.  gr.  0.97,  and 
boils  at  -  103°  C.  Slightly  soluble  in  water;  more  soluble  in  alcohol. 
Burns  with  a  bright  luminous  flame,  which  renders  it  very  useful  as  an 
illuminating  constituent  of  coal-gas.  When  mixed  with  chlorine,  ethy- 
lene combines  with  it  to  form  a  fragrant  liquid  known  as  ethylene  chloride 
or  Dutch  liquid,  C1H,OCH2C1.  Bromine  forms  a  similar  compound 
with  it.  Sulphuric  acid  slowly  absorbs  ethylene,  forming  C2H5HS04, 
sulphethylic  or  sulphovinic  acid  or  ethyl  hydrogen  sulphate,  from  which 
alcohol  may  be  obtained  by  distillation  with  much  water,  and  ethene 
by  heating  it  alone,  0,H,HSO4  +  HOH  =  C2H5OH  +  H2S04,  C,H5HS04  = 
C2H4  +  H2S04.  Sulphuric  anhydride  absorbs  ethene  much  more 
easily,  and  a  strong  solution  'of  S03  in  H,SO4  (fuming  sulphuric 
acid)  is  employed  for  absorbing  it  in  the  analysis  of  coal-gas.  The 
compound  formed  by  SO3  with  ethylene  is  crystalline,  and  is  termed 
carbyl  sulphate  or  ethionic  anhydride,  C2H4  (S03),.  In  contact  with 
water,  this  forms  ethionic  acid,  CH2(OS03H)-CHS(S03H),  and  when 
this  is  boiled  with  water  it  yields  isethionic  acid,  H2C2H4S207  +  HS0  = 
H,S04  +  CH2(OH)-CH2(SO3H).  It  will  be  noticed  that  isethionic  acid 
has  the  same  composition  as  ethyl  hydrogen  sulphate,  but  it  is  a  more 
stable  compound. 

In  presence  of  platinum-black,  ethylene  combines  v  ith  hydrogen  to 


536  PREPARATION   OF   OLEFINES. 

i 

form*  ethane,  C2H6.  With  HBr  and  HI  it  combines  to  form  ethy- 
bromide,  C3ILBr,  and  iodide,  C.,H5I,  respectively. 

Oxidising-agents,  such  as  nitric  and  chromic  acids,  convert  ethene 
into  oxidised  bodies  containing  two  carbon  atoms,  such  as  oxalic  acid, 
C2H2O4,  aldehyde,  C2H4O,  and  acetic  acid,  C9H402. 

From  the  above  description  of  the  properties  of  ethene,  it  will  be  seen 
that  it  differs  greatly  from  methane  and  the  other  paraffins,  in  the  readi- 
ness with  which  it  combines  with  other  bodies,  especially  with  chlorine, 
bromine,  and  sulphuric  anhydride,  forming  addition-products  instead  of 
substitution-prod  u  cts. 

Experiments  which  may  be  performed  with  the  gas  will  be  found  at 

P-  143- 

Propylene,  C3H6  or  CH3-CH:CH2,  occurs  in  small  quantity  in  coal-gas.  It  may 
be  obtained  by  heating  glycerine  with  zinc-dust  ; 

C3H5(OH)3  +  Zn,  =  C3H6  +  H    +  3ZnO. 

In  properties  it  resembles  ethylene,  but  it  is,  of  course,  half  as  heavy  again.  It  is 
more  easily  absorbed  by  strong  sulphuric  acid.  Only  one  propylene  is  known,  but 
another  hydrocarbon,  trimethylene,  has  the  same  formula  (p.  539). 

Bytylene,  C4H8  or  CH3'CH2*CH:CH2,  occurs  largely  in  the  illuminating  gas  made 
by  distilling  the  vegetable  and  animal  oils.  It  is  also  found  in  the  odorous  hydro- 
carbons which  are  evolved  when  cast  iron  is  dissolved  in  hydrochloric  or  dilute 
sulphuric  acid.  It  boils  at  -  5°  C. 

Consideration  of  the  formula  for  butylene  will  show  that  three  isomerides  of  this 
hydrocarbon  can  exist,  viz.,  a-  or  normal  butylene,  CHS'CH0'CH:CH0  ;  /3-  GV  pseiido- 
butylene,  CH3'CH:CH-CH3  ;  and  7-  or  iso-'butylftne  (CH3)2C:CH2/  The  butylene 
described  above  is  the  normal  hydrocarbon.  Pseudo-butylene  exists  in  two  modi- 
fications called  geometrical  isomerides  (see  p.  542). 

Amylene  or  pentylene,  CgH10  or  CH./CH./CH2'CH:CH2,  can  exist  in  five  isomeric 
forms.  They  occur  in  petroleum  and  paraffin  oil.  The  normal  amylene,  which 
has  the  formula  given  above,  boils  at  40°  C. 

The  moderate  oxidation  of  the  olefines,  in  presence  of  water,  produces  com- 
pounds in  which  the  opened  up  bonds  are  attached  to  hydroxyl  groups  ;  thus, 
CH3-CH:CH2  yields  CH3.CHOITCH.2OH. 

General  methods  for  preparing  olefine  hydrocarbons. — (i)  It  is  obvious 
that  if  one  of  the  single  bonds  in  a  paraffin  be  converted  into  a  double 
bond  the  corresponding  olefine  will  be  produced,  e.g.,  propane,  CH3*CH2' 
CH3,  will  become  propylene,  CH'3CH  :  CH2.  Thh  is  a  nucleal  condensa- 
tion, and  may  be  effected  similarly  to  that  by  which  new  paraffins  may 
be  formed  (p.  531).  Thus,  a  dihalogen  substituted  paraffin  may  be 
heated  with  zinc,  CH2Br'CH2Br  +  Zn  =  CH, :  CH2  =  ZnBr2.  For  this 
kind  of  condensation,  however,  heating  a  monohalogen  derivative  with 
an  alcoholic  solution  of  an  alkali  is  generally  best ;  in  this  case  the 
halogen  atom  and  a  hydrogen  atom  are  removed,  presumably  as  hydrogen 
halide,  by  the  alkali ;  CH3'CH2Br  =  CH2 :  CH2  +  HBr. 

(2)  By  the  dehydration  of  the  alcohols  of  the  paraffin  series 
(q.v.)  by  strong  sulphuric  acid,  zinc  chloride,  or  phosphoric  acid,  e.g., 
CH3-CH2-CH2OH  =  CH3-CH  :  CH2  +  HOH. 

The  second  method  frequently  produces  a  mixture  of  the  olefine  and  its  polymerides 
(p.  533),  for  the  olefines  tend  to  polymerise  under  the  influence  of  acids  and 
dehydrating  agents  ;  thus,  when  amylene  is  prepared  in  this  way,  C10H20  and 
C15H30  are  also  produced. 

(3)  The   salts  of   some  of   the   dicarboxylic  acids    (#.r.)    yield    olefines  when 
electrolysed  (cf.  p.  531)  ;  thus  potassium  succinate  yields  ethylene  : 

C02K-CH2-CH2-C02K  +  2HOH  =  CH2:CH2  +  2KHC03  +  H2. 

(4)  The  process  of  nucleal  condensation   may  be  reversed  ;    that  is  to  say,  a 
treble  or  double  linking  may  be  converted   into  a  single  linking  by  treating  the 


ACETYLENE. 


537 


•compound  with  nascent  hydrogen.  Thus  some  of  the  acetylene  compounds  yield 
the  corresponding-  olefine  when  so  treated:  CH  •  CH  +  H2=CH2:  CH2  (similarly, 
ethylene  may  be  transformed  into  ethane — see  above). 

(5)  Wurtz's  reaction  (p.  531)  may  be  applied  to  produce  new  olefines  by  treat ing 
&  mixture  of  a  monohalogen-substituted  olefine  and  an  alkyl  halide  with  sodium. 

318.  Acetylene  Series  of  Hydrocarbons. — The  acetylene  hydro- 
carbons are  unsaturated  hydrocarbons  containing  a  pair  of  trebly-linked 
carbon  atoms  :  they  correspond  in  composition  with  the  general  formula 
CHHo,,_2.  The  first  two  members  of  the  series,  acetylene,  HC  :  CH,  and 
allylene,  H3C'C  :  CH,  are  gaseous  under  ordinary  conditions,  whilst 
most  of  the  others  are  colourless  liquids. 

It  will  be  seen  that  the  hydrocarbon,  C3H4,  is  capable  of  being  represented  by 
the  two  formula;  CHyC  :  CH,  and  CH2  :  C  :  CH2,  so  that  two  modifications  of 
this  compound  may  be  expected  ;  these  have  been  prepared,  the  former  being 
called  <tUi/lcitc  and  the  latter  allene  or  propadiene.*  For  every  true  acetylene  (a 
hydrocarbon  containing  a  pair  of  trebly-linked  carbon  atoms)  there  may  also  be  a 
hydrocarbon  containing  two  pairs  of  doubly-linked  carbon  atoms.  These d'wlejinex 
differ  considerably  in  properties  from  the  acetylenes  ;  they  are  unimportant,  and 
cannot  be  further  considered  here. 

Acetylene,  or  ethine,  C2H2,  is  the  only  hydrocarbon  which  can  be 
formed  in  more  than  mere  traces  by  the  direct  union  of  its  elements. 
Its  preparation  and  most  of  its  properties  have  been  described  at  p.  137. 

Pure  acetylene  may  be  prepared  from  ethylene  by  combining  this 
with  bromine  to  form  ethylene  bromide  which  is  then  heated  with 
caustic  potash  in  alcohol : 

BrH2OCH2Br  +  2KOH  =  HC    :  CH  +  2KBr  +  2HOH  ; 

.and  from  methane  by  converting  this  into  chloroform  which  is  then 
heated  with  sodium  : 

HC    =  CL  +  C13   :  CH  +  Xa(;  =  HC   I  CH  +  6NaCl ; 

These  two  reactions  are  typical  of  the  general  methods  for  preparing 
•acetylene. 

In  the  presence  of  platinum-black  acetylene  combines  with  hydrogen 
to  form  ethene,  CSH4.  Strong  sulphuric  acid  absorbs  acetylene  slowly 
as  it  does  ethene  ;  but  when  the  solution  is  mixed  with  water  and 
distilled,  it  yields,  not  alcohol  as  with  ethene,  but  croton-aldeltyd. 
C3H/CHO  ;  2C,H0  +  H,0  =  C4H60.  Chromic  acid  oxidises  acetylene  to 
acetic  acid;  C2H2  +  H8O  +  0  =  C,H40,.  Alkaline  potassium  perman- 
ganate converts  it  into  oxalic  acid,  C.>H2  +  04  =  C2II204. 

The  most  remarkable  feature  of  acetylene  is  the  facility  with  which 
its  hydrogen  is  displaced  by  metals.  By  heating  sodium  in  acetylene, 
CJEENa,  mono-sodium  acetylide  and  C2Na2,  disodium  acetylide  may  be 
•obtained.  Cuprous  acetylide,  C.,Cu.,  has  been  noticed  at  p.  140. 

Silver  acetylide,  C2Ag2,  is  produced  as  a  white  precipitate  when 
acetylene  is  passed  into"  ammoniacal  silver  nitrate ;  in  absence  of 
ammonia  the  precipitate  is  a  compound  of  the  acetylide  with  silver 
nitrate. 

When  acetylene  is  passed  into  antimonic  chloride,  kept  cool,  crystals 

*  According  to  one  system  of  nomenclature  the  terminations  -dime,  -triene,  -Mn  //< ,  AT.. 
are  used  to  indicate  hydrocarbons  containing:  2.  3,  4,  &c.,  double  linking^  respeci 
position  of  the  double  bonds  are  indicated  by  the  numbers  of  the  C  atoms  inimedu 
•ceding-  them  in  the  chain.    Thus  i  :  4  -hexadiene  is  CH2  :  CH  •  CH2  •  CH  :  CH 
hydrocarbons  containing-  2,  3,  4,  &c.,  treble  bonds  terminate  in  -diinc,  -trnne,  -t< 
respectively. 


538  OPEN-   AND   CLOSED-CHAIN  HYDROCARBONS. 

of  C2H2012*SbCl3  are  formed,  which,  on  heating,  yield  the  acetylene 
dichloride,  C2H2C12,  as  a  liquid  smelling  like  chloroform,  and  boiling  at 
55°  C.  CJEE2C14,  acetylene  tetrachloride  and  C2HC1,  monochlor  acetylene  r 
have  also  been  obtained. 

When  heated  in  a  sealed  tube,  acetylene  is  partially  converted  into  a 
mixture  of  two  liquids,  benzene,  C6H6  and  styrolene,  C8H8.  By  passing 
electric  sparks  through  a  mixture  of  acetylene  with  nitrogen,  hydro- 
cyanic acid  is  produced;  C2H2  +  N2=  2HCN.  Hence  this  acid,  from 
which  a  large  number  of  organic  bodies  may  be  derived,  has  been 
synthetised  from  its  elementary  constituents.  Cuprous  acetylide,  in  con- 
tact with  zinc  and  solution  of  ammonia,  yields  ethylene,  which  is  con- 
vertible into  alcohol,  and  from  this  a  very  large  number  of  organic 
compounds  may  be  made. 

Acetylene  is  regarded  as  one  of  the  most  important  intermediate 
bodies  in  the  synthesis  of  organic  compounds  from  their  elements. 

Allylene,  or  propim,  CH3'C  :  CH,  resembles  acetylene,  but  its  cuprous  compound 
is  yellow  instead  of  red. 

The  hydrocarbon  C4H6  (buti-ne)  can  exist  in  two  forms,  each  of  which  will 
have  a  pair  of  trebly-linked  carbon  atoms,  namely,  CH3'CH2'C  :  CH  (ethylacetylene} 
and  CH3*C  :  C  'CH3  (crotonylene  or  dimethylacetylene} ;  besides  these  true  acetylenes, 
there  is  dtrinyl,  CH2  :  CH'CH  :  CH2,  a  diolefine  found  in  compressed  illuminating 
gas. 

Crotonylene  is  a  liquid  (b.-p.  27°  C.)  ;  its  vapour  is  one  of  the  illuminating- 
hydrocarbons  in  coal-gas.  It  does  not  form  any  metallic  derivatives,  and  it 
appears  that  this  is  generally  the  case  with  those  acetylenes  which  have  not  the 
group  *C  :  CH  in  their  composition. 

The  other  members  of  the  series  have  no  practical  importance  at  present. 
They  are  prepared  by  treating  the  bromo-substitution  products  of  the  paraffins- 
and  defines  with  alcoholic  potash. 

319.  The  paraffins,  olefines,  and  acetylenes  are  supposed  to  have  their 
carbon  atoms  linked  together  in  what  may  be  termed  an  open  chain,  in 
which  there  are  terminal  carbon  atoms,  each  attached  to  only  one  other 
carbon  atom.  The  hydrocarbons  next  to  be  considered,  notably  benzene 
and  its  homologues,  exhibit  properties  which  show  that  while  they  are 
strictly  unsaturated  in  the  sense  that  they  do  not  correspond  with  the 
general  formula  CwH2tt+2  (p.  527),  they  behave  more  like  the  paraffins 
than  the  olefines  towards  chemical  agents.  The  most  fruitful  hypothesis 
in  explanation  of  this  difference  is  that  in  these  hydrocarbons  no  carbon 
atom  is  attached  to  only  one  other  carbon  atom.  This  can  only  be  the 
case  if  the  terminal  carbon  atoms  are  attached  to  each  other,  thus  :- 

C  -  C  -  C  -  0.  Such  hydrocarbons  are  termed  closed-chain  hydro- 
carbons, or  ring  or  cyclic  hydrocarbons — since  the  arrangement  of  the 
carbon  atoms  in  the  form  of  a  ring  is  somewhat  more  convenient,  e.y., 
:  C  -  C  : 

I 
:  C  -  C  : 

The  only  other  series  of  open-chain  hydrocarbons  which  are  known  besides  the 
three  already  considered  are  those  corresponding  with  the  general  formula? 
CwH2H_4and  CWH2W_6.  The  hydrocarbons  of  the  former  series  must  have  either 
one  pair  of  trebly-  and  one  pair  of  doubly-linked  carbon  atoms,  as  in  the  formula 
CH3-CH  :  CH-C  :  CH  (plefine-acetylenes},  or  three  pairs  of  doubly-linked  carbon 
atoms,  as  in  CH3'CH  :  C  :  C  :  CH2  (triolejineg).  The  CMH2w-6  open-chain  hydro- 
carbons must  contain  either  two  trebly-linked  or  four  doubly-linked  carbon  atoms  ; 


CYCLIC   HYDROCAKBONS, 


539 


the  treble  linking  is  the  more  common,  e.g.,  dl-acetylene,  CH  :  C'C  :  CH,  and 
dlpropargyl  (liexadiine),  CH  •  C'CH2'CH2'C  :  CH,  which  is  isomeric  with  benzene. 
Both  these  hydrocarbons  form  copper  and  silver  compounds  like  those  of  acetylene. 

Closed-chain  Hydrocarbons. — It  is  obvious  that  a  closed-chain 
hydrocarbon  must  contain  at  least  three  carbon  atoms,  and  that  such  a 
one  would  be  obtained  if  a  hydrogen  atom  could  be  removed  from  each 
end  of  the  propane  chain,  leaving  the  carbon  bonds  thus  liberated 
to  unite  :  H3C  •  CH2  •  CH3  -  H2  =  H2C  •  CH2  •  CH2.  This  has  not  been 

accomplished  directly,  but  if  a  bromine  atom  is  substituted  for  a 
hydrogen  atom  in  each  CH3  group,  producing  trimethylene  bromide, 
BrHjC  •  CH2 '  CH2Br,  these  bromine  atoms  can  be  removed  by  sodium, 
whereupon  the  gas  trimethylene  *  or  cyclopropane  is  formed  by  nucleal 
condensation  (cf.  p.  531).  Several  polymethylenes  or  cycloparaffins  of  this 
type  have  been  prepared  in  an  analogous  manner.  Pentamethylene  or 

/CH9  '  CH., 
cyclopentane,   CH2\        "     J^TT"'   *s   important   as    a   near    relative    of 

XL/H2  •  OH., 

camphor,  while  hexamethylene  or  cyclchexane  is  transitional  between  the 
paraffins  and  benzene.  All  these  hydrocarbons  are  isomeric  with  the 
olefines,  from  wrhich  they  differ  in  not  being  attacked  by  permanganate ; 
this  is  presumed  to  be  conclusive  that  they  do  not  contain  double  linking, 
and  allies  them  to  the  saturated  hydrocarbons. 

Tetramethylene  has  not  been  prepared,  but  methyltet-ra  methylene  is  known. 
Penta-  and  hexamethylene  (naphthene)  are  found  in  Caucasian  petroleum  ;  the 
former  boils  at  50°  C.  Ileptametlt ylene  boils  at  117°  C.  and  is  related  to  the  acid 
found  in  cork  (suberic  acid). 

When  the  iodo-substitution  products  of  these  hydrocarbons  are  treated  with 
potash,  the  iodine  is  removed  as  HI,  and  a  double  linking  is  introduced;  for 

f"1  TT  T    •    C*  TT  C*  TT  •  O  TT 

instance,  CH2\  :     2  yields  CH\          i     2,   cyclopentene,    which     may    be 

"    CH,  —  CH9  CH2'CH2 

XCH:CH 
termed  a  cydo-olejine.     By  repeating  the  operation,  eyelopentadlene,  CH<'         i     r 

is  obtained  ;  this  is  a  cyclodiolejine  found  in  crude  benzene  and  boils  at  41°  C.  It 
is  easily  attacked  and  yields  addition-products,  indicative  that  it  contains  double 
linking.  If  the  closed  chain  contains  three  double  bonds  it  is  called  a  cyclo- 
triolejine  ;  thus  benzene  is  cycloliexatriene. 

There  are  several  methods  of  producing  nucleal  condensation,  besides  that  here 
given,  for  obtaining  polymethylene  derivatives  ;  some  of  these  will  receive  notice 
in  the  proper  place. 

Benzene  Series  of  Hydrocarbons.— The  general  formula  for  this 
series  is  CWH2M_6  where  n  is  any  whole  number  not  smaller  than  6.  The 
series  was  originally  called  the  aromatic  series  because  the  first  hydro- 
carbons discovered  were  obtained  from  aromatic  balsams  and  resins. 
Benzene  itself  is  CGH6,  and  its  homologues  are  formed  from  it  by  ex- 
changing hydrogen  for  CH3;  thus,  toluene,  C6H5CH3 ;  xylene  C6H4(CH3)3; 
&c.  Before  the  structure  of  these  hydrocarbons  is  considered  some  of 
their  properties  must  be  described. 

320.  Benzene,  C6H6,  occurs  abundantly  in  the  light  oil  obtained 
in  the  distillation  of  coal-tar.  It  is  also  found  in  petroleum.  From 
the  light  oil  it  is  obtained  by  fractional  distillation ;  the  portion  which 
distils  between  79°  and  82°  C.  consists  chiefly  of  benzene,  and  is  purified 
by  cooling  it  below  o°  C.  when  the  benzene  crystallises,  while  the  otl 

*  The  group  CH2  is  termed  methylene. 


540  REACTIONS  OF  BENZENE. 

hydrocarbons  remain  liquid  and  are  removed  by  pressure.  A  charac- 
teristic impurity  of  commercial  benzene  is  thiophen,  C4H4S  (q.v.). 

Benzene  is  an  ethereal  liquid,  having  the  odour  of  coal-gas,  of  which  its 
vapour  is  one  of  the  illuminating  constituents.  Sp.  gr.  0.88  ;  m.-p. 
5.5°  C.  ;  b.-p.  80°  C.  It  is  very  inflammable,  and  burns  with  a  red  smoky 
flame  ;  but  its  vapour,  when  mixed  with  air  or  hydrogen  (as  in  coal-gas), 
burns  with  a  bright  white  flame.  Benzene  is  nearly  insoluble  in  water, 
but  dissolves  in  alcohol  and  ether.  It  is  chiefly  used  for  conversion 
into  aniline  (q.v.),  but  also  for  dissolving  fats,  caoutchouc,  &c.  If 
benzene  be  dropped  into  the  strongest  nitric  acid,  or  into  a  mixture 
of  ordinary  concentrated  nitric  acid  with  an  equal  volume  of  strong 
sulphuric  acid,  a  violent  action  occurs,  red  fumes  are  evolved,  and  the 
liquid  becomes  red.  On  pouring  it  into  several  times  its  volume  of 
water,  a  heavy,  oily  liquid  falls  which  is  nitrobenzene,  C6HrNO.,  ; 
O6H6  +  N02-OH  =  C6H3NO2  +  HOH. 

The  red  fumes  are  the  result  of  a  secondary  reaction  not  expressed  in 
the  equation.  The  sulphuric  acid  is  used  to  combine  with  the  water, 
since  weak  nitric  acid  does  not  act  on  benzene.  Nitrobenzene  has  a 
powerful  odour  of  almonds,  and  is  sold,  dissolved  in  alcohol,  as  Mirbane 
essence,  for  use  in  confectionery  and  perfumery.  It  is,  however,  a 
poisonous  substance  in  large  doses.  It  is  also  largely  employed  for  the 
preparation  of  aniline.  Nitrobenzene  boils  at  209°  C.  ;  its  sp.  gr.  at 
o°  C.  is  1.2  ;  m.-p.  3°  C. 

If  the  mixture  of  nitric  arid  sulphuric  acids  be  boiled  with  the  ben- 
zene, the  liquid  deposits  on  cooling,  a  yellowish  crystalline  solid  which 
is  dinitrobenzene,  C6H4(NO,).,,  a  compound  used  in  some  explosives  ; 

C6H6  +  2(N02'OH)  =  C6H4(N02)2  +  2HOH 


Strong  sulphuric  acid  also  oxidises  part  of  the  hydrogen  in  benzene, 
when  heated  with  it,  leaving  in  its  place  the  sulphonic  group,  or  sulphonic 
acid  residue,  SO./OH,  which  bears  the  same  relation  to  sulphuric  acid, 
SO,(OH)9,  as  nitroxyl,  NO9,  bears  to  nitric  acid,  NO./OH  ;  thus, 
C6H6  +  S6,(OH)2  =  HOH  +  C6H5-S02-OH  (benzene-sulphonic  acid}.  If 
fuming  sulphuric  acid  be  used,  a  second  atom  of  hydrogen  may  be 
exchanged,  forming  benzene-  disulphonic  acid,  C6H4(S02'OH)r 

When  chlorine  is  passed  into  benzene  (containing  a  little  iodine,  which 
assists  the  reaction),  monochlorobenzene,  C6H5C1,  is  formed  ;  it  is  an 
almond-smelling  liquid,  which  boils  at  132°  C.,  is  not  decomposed  by 
caustic  alkalies,  and  is  reconverted  into  benzene  by  water  and  sodium- 
amalgam  (to  yield  nascent  hydrogen).  The  further  action  of  chlorine 
on  benzene  yields 


Dichlorobenzene,  C6H4C1 
Trichlorobenzene,  C6H3C1 


Tetrachlorobenzene,  C6H2C14 
Pentachlorobenzene,  C6HC15 


Hexachlorobenzene,  C6C16 

These  are  all  crystalline  solid  bodies. 

Besides  these  substitution-products,  benzene  is  capable  of  forming  addi- 
tion-products with  chlorine  ;  benzene  dichloride,  C6H6C12 ;  tetrachloride, 
C6H6C14 ;  hexachloride,  C6H6C16.  These  are  less  stable  than  the  substi- 
tution-products ;  thus,  the  hexachloride,  when  heated  with  potash  dis- 
solved in  alcohol,  yields  trichlorobenzene  ; 

C6H6C16  +  3KOH  =  C6H3C13  -f  3KC1   +  3H20. 


CONSTITUTION   OF  BENZENE.  54  r 

When  benzene  is  treated  with  hydrogen  dioxide,  it  is  slowly  converted 
into  hydroxybenzene  or  phenol ;  C6H6  +  H202  =  C6H5'OH  +  H20. 

Benzene  was  so  called  because  it  was  first  prepared  by  distillino- 
benzoic  acid  with  slaked  lime  (3  parts);  C6H5'CO9H  +  G'a(OH)  = 
C6H6  +  CaC03  +  H20.  This  method  is  still  adopted"  for  preparing 
perfectly  pure  benzene. 

Benzene  is  detected  by  first  converting  it  into  nitro-benzene  and 
reducing  this  to  aniline  (q.v.),  which  is  recognised  by  its  reaction  with 
bleaching-powder. 

321.  Constitution  of  benzene. — A  saturated  hydrocarbon  is  one  which 
corresponds  with  the  general  formula  CMH2H+2,  so  that  it  is  evident 
that  benzene  is  an  unsaturated  hydrocarbon.  It  has  been  seen  that 
the  unsaturated  hydrocarbons  already  considered  (ethylene,  acetylene, 
&c.)  are  so  termed  because  of  their  capability  of  uniting  directly  with 
chlorine  or  bromine,  and  it  has  been  noticed  that  the  molecule  of  a 
hydrocarbon  will  combine  with  2,  4,  &c.,  atoms  of  01  or  Br  according  to 
its  degree  of  unsaturation,  so  that  the  final  product  of  such  combination 
is  always  a  compound  of  the  general  type,  C^H^^X^,  where  X  is  Cl 
or  Br.  This  compound  is  a  stable  one  and  does  not  combine  with  any 
more  halogen.  Moreover,  this  reaction  between  the  unsaturated 
hydrocarbon  and  the  halogen  is  the  primary  reaction  between  the  two 
substances. 

The  reaction  between  benzene  and  a  halogen  is  of  a  different  nature 
from  this.  As  has  been  stated  above,  it  is  more  easy  to  obtain  halogen- 
substitution-products — i.e.,  those  in  which  halogen  is  substituted  for 
hydrogen — from  benzene,  than  it  is  to  obtain  mere  addition-products, 
containing  halogen  added  to  the  hydrocarbon.  This  recalls  the  behaviour 
of  paraffin  hydrocarbons. 

It  seems,  then,  that  benzene  resembles  both  the  saturated  and  un- 
saturated hydrocarbons  in  its  behaviour  towards  halogens.  It  differs, 
however,  from  the  former  class  in  that  it  can  form  addition-products 
with  the  halogens,  and  from  the  latter  (e.g.,  its  isomeride  dipropargyl) 
in  that  the  most  saturated  derivative  obtainable  from  it  corresponds 
with  the  general  formula  C)tX.'2n  and  not  with  CMX  2w+2.  When  ben- 
zene is  heated  with  excess  of  hydriodic  acid  it  is  converted  into  the 
hydrocarbon  C6H12,  thus  :  C6H6  +  6HI  =  C6H12  +  I6.  This  benzene 
hexahydride  (cyclohexane)  is  isomeric  with  the  olefine  hexylene,  which, 
however,  might  be  expected  to  become  hexane,  C6H14,  when  heated  with 
excess  of  hydriodic  acid. 

These  facts  with  regard  to  benzene  may  easily  be  explained  on  the 
hypothesis  that  the  six  carbon  atoms  form  a  closed  chain  (p.  538). 
It  will  be  seen  at  once  that  all  closed-chain  compounds  must  contain  a 
carbon  nucleus  which  is  possessed  of  two  fewer  atom-fixing  powers  than 
the  corresponding  carbon  nucleus  in  an  open-chain  compound  has ;  for 
instance,  the  nucleus  •C'C'O'O'O'C'  has  14  atom-fixing  powers,  whilst 
the  nucleus  'O'O'C'C'O'O'  has  only  12  atom-fixing  powers. 

The  closed-chain  formula  for  benzene  must  contain  three  pairs  of 
doubly-linked  carbon  atoms,  if  all  the  affinities  of  each  atom  are  to  be 
represented  as  satisfied  in  the  same  way  as  they  are  represented  in  open- 
chain  compounds.  Since,  as  will  be  shown,  there  is  reason  to  believe 
that  the  structure  of  the  benzene  molecule  in  space  is  symmetrical,  it  is 


542  POSIT10N-ISOMERISM. 

customary  to  represent  these  three  double  bonds  symmetrically  in  the 
formula,  which  is  therefore  written  in  the  form  shown  in  Fig.  258,  and 
known  as  Kekules  benzene  ring. 

Some  support  is  lent  to  this  formula  by  the  fact  that  acetylene  polymerises  into 
benzene  when  it  is  heated,  HC  •  CH  +  HC  •  CH  +  HC  :  CH  becoming 
HC:CH-HC:CH-HC:CH  ;  and  that  allylene  CH  :  OCH3  is  polymerised  by  strong 

H2S04    to    1:3:5   -trimethylbenzene  or  mesitylene  (^.f.).     There   are,   however, 
some  grave  objections  to  Kekule's  formula  which  will  be  noticed 
H  in  the  sequel. 

/     ^  322.    Position-isomerism.  —  Isomerides  have    already 

HC  CH     been  defined  as  compounds  which  have  the  same  percent- 

||  I       age  composition  and    the    same    molecular  weight,  but 

HC  CH    different  properties.      The  isomerism  may  be  due  to  one 

\c^        of   three  causes,     (i)  The  isoineric  compounds  may  be 
H  composed  of   different    radicles,    thus,    the    compounds 

Fig.  258.  C2H5-(X)-C2H5  and  CH3'COC3H7  are  isomeric ;  such 
isomerides  are  sometimes  termed  metamerides.  (2)  The 
isomeric  compounds  may  consist  of  the  same  radicles,  but  these  may  be 
attached  to  different  carbon  atoms  ;  an  example  was  met  with  in  the 
case  of  pentane  (p.  533) ;  such  isomerides  may  be  termed  position- 
isomerides.  (3)  The  isomeric  compounds  may  have  the  same  radicles, 
attached  to  the  same  carbon  atoms  but  differently  situated  in  space 
with  regard  to  each  other;  such  cases  will  be  met  with  hereafter 
(lactic  acids) ;  these  isomerides  are  termed  stereo-isomerides,  and  in 
one  class  of  this  kind  of  isomerides  the  main  difference  between  the 
members  is  in  their  action  on  polarised  light,  each  existing  in  two 
optically  active  forms — namely,  one  which  rotates  the  plane  of  polari- 
sation of  light  to  the  right  (dextro-rotatory)  and  another  which  rotates 
the  plane  equally  to  the  left  (laevo- rotatory) — and  in  two  optically 
inactive  forms. 

An  account  of  the  polarisation  of  light  must  be  sought  in  a  work  on  Physics. 
It  may  be  said  here  that  when  a  ray  of  light  is  passed  through  a  certain  kind  of 
crystal  (a  polariser)  in  a  certain  direction,  it  is  broken  into  two  rays  pursuing 
different  paths.  Each  of  these  rays  is  of  such  a  nature  (polarised)  that  while  it 
will  pass  through  a  similar  crystal  (the  analyser)  placed  with  its  axis  parallel  to 
that  of  the  first,  it  is  extinguished  if  the  second  crystal  be  rotated  through  an 
angle  of  90°.  If,  while  the  axes  of  the  crystals  are  in  this  relative  position,  a 
solution  of  a  dextro-rotatory  compound  be  placed  between  them,  the  ray  will  pass 
again  through  the  analyser  (a  result  expressed  by  saying  that  the  plane  of  polarisa- 
tion has  been  rotated)  and  this  must  be  turned  to  the  right  through  a  certain  angle 
before  the  light  is  again  extinguished  ;  the  measure  of  this  angle  is  a  measure  of 
the  optical  activity  or  rotatory  power  of  the  compound  dissolved.  A  laevo-rotatory 
compound  produces  the  same  effect,  but  in  the  opposite  direction. 

The  instrument  whereby  the  rotatory  power  is  ascertained  is  called  the  polari- 
meter,  and  is  shown  in  Fig.  260.  The  essential  parts  of  it  are  the  prisms  and 
lenses,  the  arrangement  of  which  is  represented  in  Fig.  259.  The  light  from  the 
lamp,  shown  in  Fig.  260  (which  burns  with  a  non-luminous  flame,  made  luminous 
by  the  introduction  of  a  sodium  compound,  so  that  it  yields  light  of  one  colour 
only),  passes  first  through  a  plate  G  cut  from  a  crystal  of  potassium  bichromate  to 
ensure  monochromatism,  then  successively  through  a  lens  F  to  make  the  beam 
parallel,  the  Nicol  polarising  prism  E,  a  quartz  plate  D  covering  one  half  of  the 
field  of  vision,  the  tube  67,  with  glass  ends  and  containing  the  solution  to  be 
examined,  the  Nicol  prism  analyser  B,  and  the  opera-glass  combination  of  lenses  A 
focusing  on  to  the  plate  D.  According  to  the  relative  angular  positions  of  E  and 
J?,  the  field  viewed  through  A  will  be  either  of  uniform  shade  or  will  have  one-half 
darker  than  the  other,  this  effect  being  due  to  the  quartz  plate  D.  In  using  the 


THE   POLARIMETER. 


543 


instrument  the  tube  C  is  inserted  after  the  analyser  has  been  rotated  to  produce 
the  uniform  shade  ;  if  the  solution  has  rotatory  power  the  field  will  no  longer  be  of 
uniform  shade,  the  one  half  or  the  other  being  the  darker  accordingly  as  the 
rotation  is  dextro-  or  laevo-.  The  analyser  is  then  again  rotated  to  produce  the 
uniform  tint,  and  the  angle  of  rotation  is  read  off  on  the  circular  scale  through  one 
of  the  eye  pieces. 


Fig-.  259.  —  Parts  of  the  polarimeter. 
B  a  D 


F     G 


Fig\  260. — Polarimeter. 

Position-isomerides  which  are  mono-substitution  derivatives*  of  a 
hydrocarbon  have  only  been  found  to  exist  in  those  cases  where  the 
carbon  atoms  in  the  nucleus  are  not  all  similarly  united  to  each  other. 
Thus,  two  monobromethanes,  C2H5Br,  have  never  been  prepared,  and 
it  is  concluded  that  more  than  one  cannot  exist  because,  since  there 
are  only  two  carbon  atoms  in  the  nucleus,  these  must  be  similarly 
united  to  each  other.  There  can,  however,  be  two  monobromopropanes 
C3H7Br,  because  the  carbon  nucleus  contains  three  carbon  atoms,  one 
of  which  is  united  with  two  other  carbon  atoms  and  two  hydrogen 
atoms,  whilst  the  other  two  are,  each  of  them,  only  united  to  one  other 
carbon  atom  and  to  three  hydrogen  atoms ;  thus,  the  two  compounds 
H3OCH9-CH2Br  (normal  pi*opyl  bromide)  and  H3OCHBrCH3  (isopropyl 
bromide)  may  be  expected  to  be  different  from  each  other,  probably 
because  the  centre  of  gravity  of  the  molecule  of  each  is  not  the  same, 
owing  to  the  difference  in  the  point  of  attachment  of  the  bromine 
atom.  That  these  two  compounds  exist  there  is  no  doubt,  and  that 
they  have  the  formula?  above  ascribed  to  them  is  rendered  highly 
probable  from  the  methods  of  their  formation,  which  will  be  discussed 
anon. 

*  Substitution-derivatives  are  mono-,  di-,  tri-,  &c.,  accordingly  as  the  element  or  radicle  is 
substituted  for  one,  two,  three,  &c.,  hydrogen  atoms. 


544  POSITION-ISOMEEISM. 

From  what  has  been  said,  it  will  be  understood  that  the  fact  that 
only  one  mono-substitution  product  of  benzene  can  be  found  to  exist,  no^ 
matter  what  the  substituting  element  or  radicle  be,  is  strong  support  in 
favour  of  the  similarity  of  linking  between  all  the  carbon  atoms,  and 
of  the  symmetrical  structure  of  the  molecule.  Thus  monobromobenzene, 
C6H5Br,  can  be  produced  in  several  ways,  yet  it  always  has  precisely 
the  same  properties. 

It  can,  of  course,  be  objected  that  it  may  happen  that  by  the  various  methods  of 
preparing  this  compound  the  same  H  atom  is  always  exchanged  for  Br,  so  that 
this  element  is  always  attached  to  the  same  carbon  atom,  and  could  it  be  attached 
to  some  other  of  the  six  atoms  a  different  monobromobenzene  would  be  produced. 
The  following  line  of  argument,  involving  reactions  which  will  be  understood 
later,  refutes  this  objection.  Monobromobenzene  is  prepared  by  the  direct  action 
of  bromine  on  benzene,  and  may  have  been  formed  by  the  substitution  of  Br  for 
any  one  of  the  six  H  atoms  in  the  benzene  ring  (Fig.  258).  Assume  that  H  (i)  has 

been  substitued,  so  that  the  product  may  be  represented  as  C6BrHHHHH.  By 
treating  this  with  HN03,  the  compound  C6H4Br(N02)  is  produced,  and  it  is  reason- 
able to  admit  that  the  second  H  atom,  which  has  been  exchanged  for  JST0.2,  is  not 
the  same  H  atom  as  that  previously  exchanged  for  Br.  Assume  that  H  (2)  has 

been  exchanged  for  N02,  then  the  nitro-compound  will  be  C6Br(N02)HHHH.  En- 
treating this  with  nascent  hydrogen  (neglecting  another  reaction)  the  Br  may  be 
removed,  and  the  H  whose  place  it  occupied  reinstated,  so  that  nitrobenzene  of  the 

1  3456 

formula  C6H(N0.2)HHHH  is  produced.     By  treatment  with  reducing-agents  this 

is  converted  into  an  amido-substitution-derivative  C6H(NH2)HHHH.  When  this 
is  treated,  under  certain  conditions,  with  nitrous  acids  it  yields  the  compound 

called  diazobenzene,  C6H(N2)HHHH,  and  by  decomposing  this  with  hydrobromic 

acid,  monobromobenzene,  C6HBrHHHH  is  obtained,  and  this  is  found  to  be 
identical  with  the  bromobenzene  produced  directly  from  bromine  and  benzene, 
showing  that  whether  H  (i)  or  H  (2)  is  exchanged  for  Br,  the  same  substance  is 
produced. 

The  cases  of  position-isomerism  among  poly-substitution  derivatives 
of  hydrocarbons  are  very  numerous.  Two  dibromo-derivatives  of 
ethane  are  known  to  exist,  viz.  :  CH2Br-CH,Br  and  CH3'CHBr2.  It 
has  been  found  that  there  &re  four  dibromopropanes,  C3H6Br2,  and 
from  the  methods  of  their  formation  there  is  reason  to  believe  that 
they  are  represented  by  the  formulae,  (i)  CH2Br-CH0-CH9Br, 
(2)  CH3  CHBr-CH2Br,  (3)  CH3'CH2-CHBr,,  and  (4)  CH3'CBiyCH3. 
Only  two  other  methods  of  writing  this  formula  are  possible,  viz., 

(5)  CH2Br-CHBr-CH3  and   (6)  CHBr2'CH2-CH3 ;    but  in  (5)  the  Br 
atoms  are  attached  to  carbon  atoms,  which  are  the  same,  so  far  as  their 
linking  to  other  atoms  is  concerned,  as  the  carbon  atoms  to  which  the 
Br  atoms  are  attached  in  (2),  and  there  is  the  same  similarity  between 

(6)  and  (3).     It  is  evident  that  if  the  number  of  carbon  atoms  in  the 
open-chain  hydrocarbon-nucleus,  or  the  number  of  substituting  bro- 
mine atoms,  be  increased,  the  number  of  forms  in  which  the  formula 
can  be  written  so  that  this  is  essentially  different  each  time,  will  be 
increased.     It  has  been  supposed  that  as  many  isomerides  may  exist  as 
there  are  essential  differences  in  the  formulae  which  can  be  written 
for  the  compound  ;  whilst  many  isomerides,  thus  prophesied,  have  been 
prepared,  the  number  remaining  to  be  discovered  is  so  large  that  some 
hesitancy  may  reasonably  be  shown  in  accepting  the  supposition. 


ORIENTATION  OF  BENZENE.  545 

In  the  case  of  benzene  the  poly-substitution-products  have  been  very 
thoroughly  examined.  Most  of  the  di-substitution-products  are  known 
in  three  isomeric  forms,  but  no  di- substitution-product  of 'benzene  has  been 
'prepared  in  more  than  three  isomeric  forms. 

Thus,  although  benzene  yields  only  one  mono-substitution-product, 
it  forms  three  di-substitution-products,  in  each  of  which  two  atoms  of 
hydrogen  have  been  exchanged  for  radicles  or  for  other  elements. 

There  are,  then,  three  di-bromobenzenes,  all  having  the  formula, 
C6H4Br2,  and  therefore  strictly  isomeric,  and  yet  having  different- 
properties  ;  so  there  are  three  di-nitro-benzenes,  C6H4(NO,)9,  and  three 
benzene  di-sulphonic  acids,  C6H4(S03H),,  and  such  compounds  form 
perfectly  distinct  series,  so  that  if  they  be  distinguished  as  a,  b,  and  c 
compounds,  a-di-bromobenzene  will  yield  a-di-nitrobenzene,  and 
ct-bunzene-di-sulphonic  acid,  while  b-  and  c-di-brornobenzenes  will  also- 
yield  their  proper  series  of  derivatives. 

To  explain  the  existence  of  these  three  isomeric  di  substitution- 
products,  it  is  necessary  to  assume  that  different  pairs  of  hydrogen 
atoms  in  benzene  have  different  chemical  values,  and  that  the  properties 
of  the  di-substitution-products  depend  upon  the  particular  pair  of 
hydrogen  atoms  exchanged.  In  order  to  investigate  this  it  became 
necessary  to  orient  (as  it  is  termed  in  surveying)  the  plan  of  the  ben- 
zene formula,  that  is,  to  mark  the  situation  or  bearing  of  its  different 
parts. 

To  effect  this  orientation  of  the  benzene  ring,  it  is  neces-  £ 

sary  to  distinguish  the  carbon  atoms,  for  which  purpose         /    ^ 
they   are  numbered    consecutively   as    on    a    watch-face    6C  c2 

(Fig.  261). 

The  pairs  of  hydrogen  atoms  occupying  places  i  and  2,     5C  Ci5 

2  and  3,  3  and  4,  4  and  5,  5  and  6,  6  and  i,  bear  the  same  c 

relation  to  the  figure,  and  are  therefore  of  equal  value,  * 

so  that  whichever  pair  is  exchanged  for  other  radicles,         Fig-.  261. 
the  same  di-substitution-product  will  be  obtained. 

Again,  i  and  3,  2  and  4,  3  and  5,  4  and  6,  5  and  i,  6  and  2,  being 
alternate  atoms,  bear  the  same  relation  to  the  figure,  and  their  substitu- 
tion would  give  rise  to  the  same  di-substitution-product. 

But  consecutive  atoms,  such  as  i  and  2,  or  2  and  3,  have  a  different 
relation  to  the  figure  from  that  belonging  to  alternate  atoms,  such  as 
i  and  3,  or  2  and  4,  so  that  the  substitution  of  two  consecutive  atoms 
of  hydrogen  would  give  one  kind  of  derivative  (say  the  a-substitution- 
product),  and  that  of  two  alternate  atoms  would  produce  another  kind 
(say  the  6-substitution-product). 

Lastly,  the  pairs  i  and  4,  2  and  5,  3  and  6,  have  the  t^ame  relation 
to  the  figure,  and,  when  exchanged  for  other  radicles,  would  give 
identical  products,  but  these  would  be  different  from  the  a  and  b  pro- 
ducts, and  may  be  called  the  c-substitution-products. 

As  the  above  lists  exhaust  all  the  possible  pairs  of  hydrogen  atoms, 
there  can  be  only  three  di-substitution  derivatives  of  benzene.  Instead 
of  using  a,  6,  and  c  to  distinguish  the  three  isomerides,  it  is  customary 
to  use  the  prefixes  ortho-,  meta-,  and  para-,  respectively.  When  adjacent 
^hydrogen  atoms  in  the  benzene  ring  are  exchanged  for  other  radicles, 
tie  product  is  an  or^o-compound ;  when  alternate  hydrogen  atoms  are 
substituted,  the  product  is  a  meta-comvound  ;  when  opposite  hydrogen 

2   M 


546  FORMULAE  FOR  BENZENE, 

atoms  are  substituted,  the  product  is  a  para-compound.  This  is  some- 
times denoted  by  figures  prefixed  to  the  formula :  thus  i  :  2-dibromo- 
benzene  is  ortho-dibromobenzene  ;  i  :  3  is  meta- dibromobenzene ;  and  i  :  4 
is  para -dibromobenzene,  all  having  the  formula  C6H4Br2. 

This  fact,  that  there  are  only  three  di-substitution-products  of  benzene,  consti- 
tutes the  main  objection  to  Kekule's  formula.  It  is  not  in  accord  with  experience 
obtained  from  the  open-chain  compounds,  that  a  substitution-derivative  containing 
the  substituent  groups  attached  to  carbon  atoms  doubly  linked  together,  should 
be  identical  with  one  which  contains  the  groups  attached  to  singly-linked  carbon 
atoms  :  thus  i  :  2-dinitrobenzene  should  differ  in  properties  from  i  :  6-dinitro- 
benzene,  though  as  a  fact  these  two  compounds  are  identical,  and  four  di-substitution- 
products  are  not  known.  Kekule  gets  over  this  objection  by  supposing  that  the 
ring  is  in  constant  vibration,  the  double  links  and  single  links  changing  places 
every  swing.  Several  other  formula?  have  been  proposed,  notably  the  so-called 
"  diagonal  formula  "  of  Glaus,  the  conception  underlying  which  will 
be  appreciated  from  Fig.  262. 

An  argument  in  support  of  this  formula  is  the  high  resistance 
shown  by  benzene  and  some  of  its  substitution-products  to  direct 
oxidation  (by  alkaline  permanganate,  for  example),  thus  indicating 
*na*  "ethylenic  linking  " — i.e.,  carbon  doubly  linked,  as  in  ethylene 
— does  not  occur.     On  the  other  hand  many  addition  products  of 
benzene,  in  which  all  the  carbon  atom-fixing  powers  are  not  satisfied 
Fig.  262.         are  so  easily  oxidised  that  ethylenic  linking  may  be  supposed  to 
exist  in  them.     Baeyer  believes  in  the  existence  of  ethylenic  linking 
in  some  benzene  compounds  and  of  central  or  "para-"  Uniting  (much  as  in  Fig. 
262)  in  others. 

Pending  a  better  knowledge  as  to  the  disposition  of  the  fourth  atom-linking- 
power  of  each  carbon  atom,  the  maiority  of  chemists  prefer  to  represent  benzene 
compounds  as  derived  from  a  plain  hexagon. 

Tri-substitution  derivatives  of  benzene,  in  which  the  same  radicle 
is  substituted  for  all  three  atoms  of  hydrogen,  are  found  to  exist  in 
three  isomeric  forms ;  thus,  there  are  three  tribromobenzenes,  C6H3Br3, 
distinguished  as  adjacent  (1:2:3),  symmetrical  (i  13:5),  and  asym- 
metrical (1:2:4).  If  the  substituted  radicles  are  of  two  different 
kinds,  say  chlorine  and  bromine,  six  isomerides  may  be  formed, 
and  if  three  different  radicles  are  introduced,  say  chlorine,  bromine, 
and  NO2,  ten  isomerides  are  possible. 

Tetra-substitution  derivatives  of  benzene  may  also  be  adjacent  (i :  2  : 3  : 4), 
symmetrical  (1:2:4:5),  and  asymmetrical  (1:3:4:5).  With  a 
single  substituted  radicle,  only  these  three  isomerides  are  possible,  but 
two  radicles  may  give  20,  three  radicles  may  give  16,  and  four  radicles 
may  give  30  tetra-substitution-products.  Evidently  only  one  penta- 
substitution-product  is  possible  with  one  radicle. 

The  experimental  investigation  of  the  orientation  of  a  benzene  derivative 
consists  in  attempting  to  introduce  fresh  substituents  into  the  nucleus, 
or  in  exchanging  some  substituent  for  hydrogen ;  how  this  settles  the 
orientation  will  be  understood  from  the  following : 

By  treating  a  dibromobenzene  with  bromine  it  is  possible  to  convert 
it  into  tribromobenzenes  (though  this  means  of  converting  a  dibromo- 
into  a  tribromo-benzene  is  not  the  most  convenient).  It  is  found  that 
the  dibromobenzene  which  boils  at  224°  C.  yields  two  tribromobenzenes, 
whilst  that  which  boils  at  219.5°  ^.  yields  three  tribromobenzenes,  and 
that  which  boils  at  219°  C.  and  melts  at  89°  C.  (the  others  melt  at  about 
i°  C.)  yields  only  one  tribromobenzene.  Now,  an  inspection  of  the 
formulae  for  the  three  dibromobenzenes  as  written  on  the  plane  of  the 
paper,  will  show  that  the  i  :  2 -dibromobenzene  can  only  yield  two 


THE   SETTLEMENT  OF   ORIENTATION. 


547 


tribromobenzenes,  viz.,  1:2:3  and  1:2:4,  since  1:2:5  =  1:2-4 
and  i  :  2  :  6  =  i  :  2  :  3.  Again,  it  will  be  seen  that  the  i  :  3-dibromo- 
benzene  can  yield  three  tribromobenzenes,  viz.,  i  :  2  :  3,  i  :  3  :  4  and 
J.:  3  :  5  (i  :  3  :  6  =  *  :  3  :  4),  whilst  the  i  :  4-dibromobenzene  can  only 
yield  one  tribromobenzene,  viz.,  i  :  2  :  4  (or  i  :  3  :  4,  or  i  :  4  :  5,  or 
1:4:6,  all  these  being  identical  with  1:2:4).  The  diagram  will 
make  this  more  clear  : — 


Br 


Br 


Br 


yields 


Br 


Br 


yields 


Br 


Br 


Br 


yields 


Br 
Br 

Br 
Br 

Bl- 


and 


Br 

/\ 


Br 

Br 


Bi 


Br 


and 
Br  Br  \      /'  Br 


Br 


Br 


Br 


It  is  evident  that,  of  the  three  known  dibromobenzenes,  that  must  be 
the  i  :  2 -derivative  which  yields  two  tribromo-derivatives  ;  that  the  i  :  3- 
derivative  which  yields  three  tribromo-derivatives ;  and  that  the  i  :  4- 
derivative  which  yields  only  one  tribromo- derivative. 

The  orientation  of  tri-substitution  derivatives  may  be  similarly 
settled  by  exchanging  one  of  the  substituents  for  hydrogen,  and  thus 
obtaining  one  or  more  di-derivatives.  If  the  derivative  be  the  1:2:3- 
•derivative  it  will  yield  two  di-derivatives,  viz.,  i  :  2  and  i  :  3  ;  if  it  be 
the  1:3:  5 -derivative  it  can  only  yield  one  di-derivative. 

The  orientation  of  certain  derivatives,  which  may  be  called  standard  derivatives, 
having  been  settled  by  investigations  involving  the  principle  stated  above,  the 
-orientation  of  any  new  compound  may  be  settled  by  converting  it  into  one  of 
these.  Chief  among  these  standards  are  the  bromo-derivatives  and  the  carboxylic 
acids  (phthalic  acid,  &c.).  Thus,  the  orientation  of  a  newly  discovered  nitro- 
derivative  could  be  settled  by  submitting  it  to  a  treatment  (such  as  that  indi- 
cated on  p.  544)  which  would  exchange  the  N02  groups  for  Br  atoms  ;  a  study  of 
the  properties  of  the  bromo-derivative  thus  produced  would  decide  its  orientation 
and  therefore  that  of  the  original  nitro-derivative. 

It  is  to  be  noticed  that  a  polyvalent  element  can  never  be  substituted  for  several 
hydrogen  atoms  in  the  benzene-nucleus  ;  thus,  C6H40  is  not  known. 

The  desire  to  prophesy  what  compound  will  be  produced  when  a  benzene  deri- 
vative is  treated  with  a  substituting  agent,  has  led  to  the  formulation  of  several  rules. 
Thus,  it  has  been  laid  down  that,  when  in  a  compound  C6H5X,  X  is  •N02,-S02OI 
or  -COOH,  any  new  radicle  entering  into  C6H5X  will  take  up  the  meta-posit 
to  X.     If  X  be  any  other  group,  the  newly  entering  substituent  will  generally 
produce  the  para-derivative,  but  accompanied  by  a  little  of  the  ortho-  and  some- 
times of  the  meta-derivative. 

If  X  be  an  element  or  radicle  which  forms  a  compound  HX,  capable  of  c 
oxidation  to  HOX,  the  newly  entering  substituent  will  take  the  meta-position  ; 


ALKYL  BENZENES. 

if,  on  the  other  hand,  it  be  not  so  capable  of  oxidation,  the  newly  entering  sub- 
stituent  will  take  up  the  ortho-  and  para-positions  (Crum  Brown  and  Gibson).  Thus, 
the  introduction  of  a  substituent  into  C6H5C1  will  give  ortho-  and  para-derivatives 
because  HC1  is  incapable  of  direct  oxidation  to  HOC1,  whilst  its  introduction  into 
C6H5*COOH  will  give  a  meta-derivative  because  HCOOH  is  capable  of  direct 
oxidation  to  HOCOOH. 

323.  Homologues  of  Benzene.  —  These  are  derivatives  of  benzene 
containing  alkyl  radicles  in  place  of  hydrogen,  such  substituting  radicles 
being  termed  side-chains.  Methylbenzene  (toluene),  C6H5'CH3,  dimethyl- 
benzenes  (xylenes),  C6H4(CH3)2,  trimethylbenzenes,  C6H3(CH3)3  (see  Fig. 
263),  and  tetramethylbenzenes,  C6H2(CH3)4,  occur  in  coal-tar;  numerous 
others,  such  as  ethylbenzene,  C6H5'CH2'CH3,  methylethylbenzene, 
C6H4(CH3)(CH2-CH3),  &c.,  have  been  prepared  synthetically. 


CCH, 


Methylbeazene  i :  2-Dimethylbenzene        i :  3 : 5-Triinethylben- 

or  toluene.  or  orthoxylene.  zene  or  mesitylene. 

Fig.  263. 

The  residues  of  the  benzene  hybrocarbons,  or  aromatic  radicles,  are 
named  similarly  to  the  alkyl  radicles;  thus,  corresponding  with  methyl,, 
ethyl, and  propyl,  there  are  phenyl,  G^^methylphenyl  or  to/?//,*C6H4'CH3, 
dimethylphenyl  or  xylyl,  C6H3(CH3)2. 

Isomerism  among  these  alkylbenzenes  is  similar  to  that  among  other 
substituted  benzenes,  except  that  there  may  be  cases  of  isomerism  in 
the  side-chains.  Thus  there  is  only  one  methylbenzene  and  one  ethyl- 
benzene,  but  there  are  two  propylbenzenes,  one  containing  the  normal 
propyl  group,  the  other  the  iso-group  (p.  567).  These  have  the  empirical 
formula  C9H12,  which  also  belongs  to  trimethylbenzene,  of  which  there 
are  three  isomerides,  as  of  other  tri-substitution  derivatives,  and  to 
methylethylbenzene,  a  di-substitution-product  also  existing  in  three- 
forms. 

Toluene  and  the  xylenes  are  alone  of  any  great  practical  importance 
among  these  homologues.  They  are  extracted  from  the  coal-tar  obtained 
by  the  distillation  of  coal  for  the  manufacture  of  coal-gas.  A  large 
quantity  of  the  tar  is  distilled  in  an  iron  retort,  when  water  passes  over,, 
holding  salts  of  ammonia  in  solution,  and  accompanied  by  a  brown,  oily, 
offensive  liquid  which  collects  upon  the  surface  of  the  water.  This  is 
the  light  oil  containing  the  benzene  hydrocarbons.  To  purify  it,  it  is 
shaken  with  sulphuric  acid,  which  removes  aniline  and  other  basic 
compounds,  and  afterwards  with  caustic  soda,  to  dissolve  carbolic  acid 
(phenols).  It  is  then  subjected  to  a  process  of  fractional  distillation, 
similar  in  principle  to  the  process  described  at  p.  529. 

*  Much  confusion  is  caused  by  modern  nomenclature  of  hydrocarbon  radicles.  It  was- 
proposed  to  call  radicles,  such  as  tolyl  and  xylyl,  alphyl  radicles.  Lately,  however,  this 
term  has  been  applied  to  alkyl  and  substituted  alkyl  (benzyl)  radicles,  while  tolyl,  &c.,  have 
been  termed  arryl  radicles,  and  benzyl,  C6H5-  CH2,  xylylene,  C6H4(CH2)2,  &c.,  have  been, 
called  alpharryl  or  aralkyl  radicles. 


AROMATIC   HYDROCARBONS. 

Toluene,  C6H5'CH3,  is  always  present  in  commercial  benzene.  It  was 
originally  distilled  from  balsam  of  Tolu,and  may  be  prepared  by  distilling 
toluic  acid,  C6H4(CH3)CO2H,  with  lime.  It  resembles  benzene  in  odour 
but  it  does  not  solidify  even  at  -  20°  C.  It  boils  at  no0  C.  and 
its  sp.gr.  is  0.871.  Benzene  may  be  converted  into  toluene  by  nrst 
obtaining  bromobenzene,  C6H5Br,  and  treating  this  with  methyl  iodide 
and  sodium,  in  the  presence  of  ether,  C6H.Br  +  CH3I  +  Na,  = 
C6H5-CH3  +  NaBr  +  Nal.  Under  the  action  of  oxidising-agents,  toluene 
yields  benzoic  acid. 

Toluene  is  used  chiefly  for  making  aniline  dyes,  and  artificial  oil  of 
bitter  almonds  ;  it  is  also  used  as  a  solvent. 

Xylene,  C6H4(CH3)2,  being  a  di-substitution-product,  exists  in  three 
forms ;  but  besides  these  there  is  a  fourth  hydrocarbon  of  the  formula 
Qfto»  namely,  ethylbenzene,  which,  however,  is  a  metameride  of  xylene. 
The  portion  of  the  light  oil  which  distils  at  136-141°  contains  about 
70  per  cent,  of  metaxylene  (isoxylene),  20  per  cent,  of  paraxylene,  and  10 
per  cent,  of  orthoxylene.  The  mixture  is  used  as  a  solvent. 

By  shaking  the  mixture  with  H2S04  of  80  per  cent,  strength,  the  metaxylene  is  dis- 
solved ;  by  treating  the  residue  with  ordinary  strong  H2S04,  the  orthoxylene  is  ex- 
tracted leaving  the  paraxylene.  The  action  of  the  H2S04  is  to  convert  the  xylene 
into  a  sulphonic  acid,  C6H3(CH3)2'S02OH,  from  which  the  hydrocarbon  can  be 
obtained  by  dilution  with  water  and  distillation.  Orthoxylene  boils  at  142°  C.  ; 
metaxylene  at  139°  C.  ;  &ndpara&ylene&t  138°  C.  (m.  p.  15°  C.).  By  oxidation  the 
methyl  groups  may  be  successively  converted  into  COOH  groups,  yielding  toluic  acids, 
C6H4  (CH3)  (COOH),  and  phthalic  acids,  C6H4(COOH)2,  of  each  of  which  there 
are  three,  yielded  respectively  by  ortho-,  rneta-,  and  paraxylene.  Oxidising-agents 
do  not  act  equally  on  the  three  isomerides,  however.  Chromic  acid  oxidises 
orthoxylene  completely  to  C02  and  H20,  but  converts  para-  and  metaxalene  into 
para-  and  metaphthalic  acid  respectively.  Dilute  HN03  oxidises  the  ortho-  and 
paraxylene  to  ortho-  and  paratoluic  acid  respectively,  while  metaxylene  is  not 
attacked. 

Metltylene  is  i  :  3  :  5-trimethylbenzene,  C6H3(CH3)3,  obtained  by  the  action  of 
sulphuric  acid  on  acetone,  3(CH3-CO-CH3)r=C6H3(CH3)3  +  3H20,  and  by  heating 
allylene  with  strong  H2S04,  3CH  i  C-CH3  =  C6H3(CH3)3  ;  it  boils  at  165°  C.  and  is 
metameric  with  cumene,  or  isopropylbenzene,  C6H5'CH(CH3)2.  Durene  is  i  :  2  : 4  :  5- 
tetramethylbenzene  (in.  p.  79°  C.)  and  has  an  odour  of  camphor  ;  it  is  metameric 
with  cymene  or  i  :  ^-methyluopropylbenzene,  C6H4(CH3)'CH(CH3).2,  which  is  found 
in  oil  of  cummin  and  is  a  product  of  the  dehydration  of  camphor. 

324.  The  chief  distinction  between  benzene  hydrocarbons  and  open-chain 
hydrocarbons  resides  in  the  ease  with  which  the  former  may  be  con- 
verted into  nitro-substitution-products  by  the  action  of  strong  nitric  acid, 
and  into  sulphonic  acids  by  the  action  of  strong  sulphuric  acid.  Moreover, 
the  homologues  of  benzene  easily  undergo  oxidation  resulting  in  the 
conversion  of  the  side-chains  into  the  group  carboxyl,  COOH,  character- 
istic of  acids. 

General  methods  for  preparing  benzene  hydrocarbons  are  :  (i)  The  distillation  of 
the  corresponding  carboxylic  acid  with  lime,  which  removes  C02  from  the  carboxyl 
group  :  C6H4(CH3XCOOH)  =  C6H5-CH3  +  C02.  (2)  The  interaction  of  the  bromo- 
substitution  derivative  and  an  alkyl  iodide  with  sodium  in  ether  :  C6H5'Br  +  C.2H5*I 
+  Nsuj  =  C6H6-C2H5  +  Nal  +  NaBr  (Fittig's  reaction,  cf.  the  general  methods  for 
preparing  paraffins,  p.  531).  (3)  The  interaction  of  a  benzene  hydrocarbon  with  an 
alkyl  iodide  in  the  presence  of  ALCL,  the  precise  function  of  which  is  not  under- 
stood ;  C6H5-CH3  +  2CH3C1  =  C6H3(CH3)3  +  2HC1.  (Jf-riedel  and  ( 'ruff*  reaction.) 

325.    The  above  benzene   hydrocarbons  contain,  as  side-chains,  the  residues  ot 
saturated   open-chain  hydrocarbons.      There  also  exist   hydrocarbons  containing 
residues  of  define  and  acetylene  hydrocarbons.     The  olejine-benzencs  correspond 
with  the  general  formula  CMH2n_10,  and  the  acetylene-benzenes  correspond  witt 
general  formula  C«H2>1_12. 


550  HYDKOAROMATIC  HYDROCARBONS. 

Cinnamene,  styrolene,  or  styrene,  C6H5'CH  :  CH2,  is  phenyl-ethylene.  It  is 
obtained  by  distilling  cinnarnic  acid  with  lime  ;  CgHg-CH  :  CH'COOH  +  Ca(OH).2  = 
C8H8  +  CaC03  +  H20.  It  can  also  be  prepared  by  distilling  balsam  of  storax,  or  "by 
distilling  the  resin  known  as  dragon's  blood  with  zinc  dust.  Cinnamene  is  a 
fragrant  liquid  of  sp.  gr.  0.924,  and  boiling-point  145°  C.  It  resembles  the  olefine 
hydrocarbons  in  uniting  directly  with  chlorine,  bromine,  and  iodine.  When  heated 
in  a  sealed  tube  to  200°  C.,  it  becomes  a  transparent  solid  known  as  metacinna- 
mene,  or  metastyrolene,  which  is  polymeric  with  cinnamene,  into  which  it  is  recon- 
verted by  distillation.  When  heated  with  hydrochloric  acid  to  170°  C.,  cinnamene 
is  converted  into  di-cinnamene,  C16H16. 

Phenylacetylene,  C6H5'C  :  CH,  a  liquid  boiling  at  139°  C.,  yields  the  explosive 
silver  and  copper  derivatives  characteristic  of  the  true  acetylenes  (p.  538]. 

Hydroaromatic  hydrocarbons.  —  When  heated  with  hydriodic  acid  the 
aromatic  hydrocarbons  are  converted  into  the  corresponding  hexamethylenes 
(p.  539)  ;  thus  benzene  yields  hexamethylene  \(liexahijdrobenzene,  benzenehexa- 

hydride   or   naphthene],  H2C/CH2'  CH2)>CH2,    while  toluene  yields  methylhexa- 
MDH2°  CHo 

methylene  (Jieaeahydrotoluene  or  heptanaphthene),  H2C<^      2       2^>CH'CH3.     These 

° 


are  colourless  liquids,  boiling  at  81°  C.  and  103°   C.   respectively,  and   occur  in 
Caucasian  petroleum. 
When  monobromohexahydrobenzene  is  heated  with  quinolene  it  undergoes  nucleal 

condensation,  yielding  tetrahydi-o'bemene  (cylcohexene),  H2C<^       2     T  /CH,  and 

MJJHjj'CH^f 

when  the  dibromo-derivative  of  this  is  similarl)'  treated,  dihydrobenzene  (cyclohexa- 

/  CTT'CTT  \ 
diene),  HC^  2^:CH,  is  obtained.     The  relation  of  these  two  compounds  to 


benzene  (cycloJiexatriene)  is  apparent,  and  it  will  be  seen  that,  if  the  formula? 
are  correct,  cases  of  isomerism  among  the  substitution  derivatives  should  exceed 
those  found  among  the  corresponding  benzene  derivatives.  For  in  both  cases 
the  character  of  the  derivative  may  be  expected  to  be  influenced  by  the  position 
of  the  double  bond  or  bonds  relatively  to  the  substituent  or  substituents. 

Thus     H2C<^CH2'C   [V-Br    should    differ    from    H2C/  CH2'CH'2  ^CHBr,    and 
MJH2  •  CHjj/  ^  CH  :  CH' 

HC/CH-CH2  \CBr  from  H0C/  CH2'CH  V<Br.    Many  such  isomerides  are  known, 
M3H'CBr^  \CH  :  CBr/ 


and.  the  nomenclature  used  to  distinguish  them  consists  in  numbering  the  C  atoms. 
as  in  benzene  (No.  I  being  always  one  to  which  a  substituent  is  attached),  and  insert- 
ing the  symbol  A  before  the  number  of  that  C  atom  which  is  doubly  linked  to  the  one 
following  it  ;  thus  the  above  bromo-derivatives  are  A  i-bromocyclohexene, 
A  5-bromocyclohexene,  A  4,  6-orthodibromocyclohexene,  and  A  i,  5-orthodibromo 
cyclohexene,  respectively. 

326.  Hydrocarbons  containing  more  than  one  benzene- 
nucleus.  —  These  hydrocarbons  can  be  classified  into  several  groups  :  (i) 
Those  which  contain  benzene-nuclei  directly  united,  such  as  dipkenylt 
C6H5'C6H5.  (2)  Those  in  which  two  or  three  nuclei  are  united  by  one 
carbon  atom,  as  in  diphenyl-methane,  C6H5'CH2'C6H.,  and  triphenyl- 
methane,  CH(C6H5)3.  (3)  Those  which  contain  two  benzene-nuclei 
united  by  two  carbon  atoms,  like  dibenzyl,  C6H5-CH./CH«/C6H5. 
(4)  Those  which  contain  condensed  nuclei,  as  explained  under  naphtha- 
lene and  anthracene. 

Many  of  the  derivatives  of  these  hydrocarbons  are  of  importance  in 
the  arts,  but,  with  the  exception  of  those  from  naphthalene  and  an- 
thracene, the  hydrocarbons  do  not  form  the  raw  materials  for  making 
them. 

Diphenyl  or  plienyl-phenyl,  C6H5*C6H5,  is  prepared  by  the  action  of  sodium  on 
bromobenzene  dissolved  in  ether;  2C6H5Br  +  2Na2=:(C6Hg)2-i-2XaBr,  a  mode  of 


DIPHENYL. 


551 


formation  which  settles  its  constitution.  It  may  also  he  obtained  by  passing 
benzene  vapour  over  red-hot  pumice-stone  ;  2C6H5H  =  (C6H5)2  +  H2  ;  or  by  distillin^ 
potassium  phenol  with  potassium  benzoate,  C6H5'OK  +  C6H5'CO.,K  =  (C6H,)2  +  K2CO,  • 
potassium  oxalate  may  be  substituted  for  benzoate,  2C6H5OK  +  (COOK)2= 
(C6H5)2  +  2CO(OK)2.  It  is  also  found  among  the  last  products  of  the  distillation 
of  coal-tar  (at  about  260°  C.)  Diphenyl  crystallises  from  alcohol  or  ether  in 
leafy  crystals  which  have  a  pleasant  odour  and  are  insoluble  in  water.  It  fuses 
at  71°  C.,  and  boils  at  254°  C.  When  it  is  dissolved  in  glacial  acetic  acid,  and 
treated  with  chromic  acid,  one  of  the  C6H,  groups  is  destroyed,  while  the  other 
forms  benzoic  acid,  C6H5-C02H.  It  forms  numerous  substitution  derivatives,  like 
benzene  ;  since  it  may  be  regarded  as  already  being  a  mono-substituted  benzene, 
containing  phenyl  in  the  place  of  H,  its  mono-substitution  derivatives  will  be 
di-substituted  benzenes  and  occur  in  three  isomeric  modifications.  Its  di-deriva- 
tives  occur  in  many  forms,  for  substitution  may  occur  in  each  ring.  The  orienta- 

3'     2'          2      3 

tion  is  expressed  as  follows  :  4'^  \4.  Phenyl-tolyls,  C6H5'C6H4-CH3, 

5'    6'          65 

and  ditolyls,  Ct5H4(CH3)-C6H4(CH3),  are  examples  of  mono-  and  di-substituted 
diphenyl  ;  the  4-  and  4  :  4'-derivatives  are  the  most  common.  By  treating  a  mix- 
ture of  i  :  4-C6H4Br2  and  C6H5Br  with  sodium,  i  :  ^-diphenylbenzene.  C6H4(C6H5).,, 
is  obtained  ;  it  melts  at  205°  C. 

DipJienylmethane  (benzylbenzene),  C6H5'CH2'CgH5.  It  is  obvious  that  toluene  may 
be  regarded  as  phenylmethane,  CH3(C6H5),  and  just  as  toluene  may  be  prepared  by 
the  interaction  of  methyl  chloride  and  benzene  in  presence  of  A12C16,  so  diphenyl- 
methane,  CH2(C6H5  )2,  can  be  prepared  from  phenylmethyl  chloride,  commonly 
called  benzyl  chloride  (</.v.),  C6H5'CH2C1,  and  benzene  in  presence  of  A12C16  ; 
C6H5H  +  C6H5-CHaCl  =  C6H5-CH2-C?H5  +  HCl.  It  crystallises  in  needles  which 
smell  like  the  orange  and  dissolve  in  alcohol  and  ether  ;  it  melts  at  26°  C.  and  boils 
at  261°  C.  Chromic  acid  oxidises  it  to  diphenyl-ketone  (q.r.).  When  passed 
through  a  red-hot  tube  it  undergoes  the  same  kind  of  condensation  as  benzene  does 
when  it  yields  diphenyl  (p.  550)  under  the  same  conditions  ;  the  product,  dipheny- 

r*  FT 

lene-methane*  QY  Ji-uorene,  '  6    4)>CH2,  is  found  in  the  last  runnings  (300°-  305°  C.) 

C6H4 

from  coal-tar  and  crystallises  from  alcohol  with  a  blue  fluorescence.  Oxidation 
converts  it  into  diphenylene  ketone.  It  melts  at  113°  C.  and  boils  at  295°  C. 
Triphenylmethane,  CH(C6H5)3,  is  obtained  by  the  interaction  of  chloroform  and 
benzene  in  presence  of  A12C16  ;  3C6H5H  -H  CHC13  =  CH(C6H5)3  +  3HC1.  It  crystallises 
in  colourless  prisms,  which  when  formed  from  a  benzene  solution  contain  ^one 
molecule  of  benzene  of  crystallisation.  It  dissolves  in  hot  alcohol,  melts  at  93°  C., 
and  boils  at  359°  C.  The  aniline  dyes  are  derivatives  of  this  hydrocarbon. 

Dibenzyl,  C6H~-CH2-CHvC6H5.  Toluene  can  give  rise  to  two  hydrocarbon  residues 
or  radicles,  viz.,'tolyl,  C6H4'CH3.  and  benzyl,  C^-CH^  When  the  chloride  of  the 
latter  radicle  is  treated  with  sodium,  dibenzyl  is  produced,  2(C6H5-CH2Cl)  +  Na2- 
C6H5-CH2-CH2-C6H5  +  2XaCl.  It  may  also  be  regarded  as  dipkenylethaM  ;  it  melts 
at  52°  C.  and  boils  at  284°  C.  ;  when  oxidised  it  yields  benzoic  acid.  Dip/ie/n/l- 
•'tltylene,  or  xtilbene,  or  toluylene,  C6H5'CH  :  CH'C6H5,  is  formed  by  treating 
benzal  chloride  (</.r.)  with  sodium;  2C6H3-CHCl2  +  Na,2  =  C6H5-C]  ['L^+. 

2NaCl.     Also  by  partially  oxidising  toluene  or  dibenzyl,  by  passing  it  over  hot 
PbO.     It  crystallises  in  prisms,  melts  at  125°  C.,  boils  at  306°  C.  and  dissolves 
hot  alcohol.     It  contains  true  ethylenic  linking,  for  the  first  action  of  broi 
it  is  the  formation  of  the  dibromide  C6H5-C!TBrCHBrC6H?.    Vijtiw/lwtyleM  or 
tolane,  C6H5'C  :  C'C6H5,  is  formed  by  boiling  stilbene  dibromide  with  alc< 
potash.     It  melts  at  60°  C.,  and  behaves  as  an  acetylene,  save  that,  not  conta.n.n; 


a   -C  i   CH     group     it     yields     no     metallic     derivative. 

which 


C6H5'C  •   C-C  :  C-C^isof  importance  as  the  hydrocarbon  ^f 
is  descended  ;  it  melts  at  88°  C. 

327.  Naphthalene,  C10H8,  is  a  crystalline  hydrocarbon  with  an  odoui 
of  coal-gas?  and  is  occasionally  deposited  in  gas-pipes  in  cold  weather, 
causing  an  obstruction.  It  is  a  very  common  product  oJ 

*  (C6H4)"  is  called  phenylene,  bj  analogy  with  <C2H4)",  ethylcne. 


552  NAPHTHALENE. 

high  temperature  upon  substances  rich  in  carbon  ;  coal  and  wood  yield 
it  on  distillation  ;  marsh-gas,  alcohol  vapour,  and  ether  vapour,  when 
passed  through  a  red-hot  tube,  deposit  crystals  of  naphthalene  in  the 
cooler  part.  Burmese  petroleum  and  Rangoon  tar  contain  naphthalene. 

When  coal-tar  is  distilled,  the  benzene  hydrocarbons  which  distil  over 
in  the  light-oil,  are  succeeded,  as  the  temperature  rises,  by  a  yellow  oil 
which  is  heavier  than  water.  This,  known  as  dead-oil,  is  much  more 
abundant  than  the  light-oil,  amounting  to  about  one-fourth  of  the 
weight  of  the  tar,  and  containing  those  constituents  of  the  tar  which 
have  a  high  specific  gravity  and  boiling-point.  When  the  temperature 
has  risen  to  about  200°  C.,  the  distilled  liquid  partly  solidifies  on  cooling, 
from  the  crystallisation  of  naphthalene.  This  portion  is  pressed  to 
expel  the  liquid  part,  washed  successively  with  caustic  soda  and  sulphuric 
acid,  and  distilled  ;  or  the  washed  naphthalene  may  be  sublimed. 

Properties.  —  Transparent  crystals,  smelling  of  gas,  melting  at  80°  C., 
and  inflammable,  burning  with  a  smoky  flame.  It  sublimes  much 
below  its  boiling-point  (218°  C.).  Insoluble  in  water,  soluble  in  alcohol, 
ether,  and  benzene. 

In  its  chemical  relations,  naphthalene  is  closely  connected  with 
benzene,  but  it  shows  a  greater  disposition  to  form  addition-products 
with  chlorine  and  bromine,  with  which  it  also  yields  numerous  substi- 
tution-products. Naphthalene  absorbs  chlorine,  forming  a  yellow  liquid, 
naphthalene  dichloride,  C10H8C12,  and  a  crystalline  solid,  naphthalene 
tetrachloride,  C10H8C14.  The  non-existence  of  C10H8C13  is  in  accordance 
with  the  law  of  even  numbers  (p,  523). 

Naphthalene  is  used  for  making  phthalic  acid,  into  which  it  is  con- 
verted by  oxidation  ;  for  increasing  the  illuminating  value  of  coal-gas 
(albo-carbon  light)  ;  and  as  an  insecticide.  Many  of  its  derivatives  are 
used  for  making  synthetic  dyes. 

Constitution  of  naphthalene.  —  The  similarity  of  the  behaviour  of  naphthalene 
with  that  of  benzene  indicates  an  analogous  structure  for  these  two  compounds, 
and  since  when  it  is  oxidised  naphthalene  yields  a  benzene  dicarboxylic  acid, 
C6H4(COOH)2,  it  must  be  assumed  to  contain  a  benzene  ring.  Thus,  six  of  the 
ten  carbon  atoms  are  accounted  for  ;  two  of  the  remaining  four  must  be  attached 
directly  to  two  of  the  carbon  atoms  of  the  benzene  ring,  otherwise  a  dicarboxylic 
acid  could  not  have  been  obtained  by  oxidation  ;  moreover,  since  the  dicarboxylic 
acid  proves  to  be  phthalic  acid,  which  is  believed  to  have  the  carboxyl  groups 
attached  to  adjacent  carbon  atoms  of  the  ring,  the  two  carbon  atoms  must  be 
attached  to  the  benzene  ring  in  the  ortho-position  to  each  other.  The  two 

remaining  carbon  atoms  are  believed  to  form  a 
closed  chain  with  the  two  just  considered.  Post- 
Pining,  for  the  moment,  the  evidence  for  this  belief, 
*^e  f°rnmla  to  which  it  gives  rise  may  be  regarded 
as  consisting  of  two  benzene  rings,  so  condensed 
together  that  they  have  two  carbon  atoms  in  com- 
mon. Fig.  264  furnishes  a  representation  of  the 
C/32  structure  of  naphthalene  (the  H  atoms,  attached 
one  to  each  numbered  C  atom,  having  been  omitted) 
5^  and  at  the  same  time  indicates  the  numbering  of 

the  carbon  atoms  for  purposes  of  orientation.     To 
Fig-.  264.  avoid  the  representation  of  ethylenic  linking  ((•/. 

p.  546)  many  chemists  omit  the  five  double  bonds 
in  the  formula.     The  Greek  letters  are  sometimes  used  instead  of  the  numbers. 

That  naphthalene  consists  of  two  benzene-nuclei  condensed  as  represented  by  the 
formula  is  supported  by  the  following  facts  :  —  When  nitronaphthalene  is  oxidised 
nitrophthalic  acid,  C6H3(NOo)(COOH)2.  is  produced  ;  from  this  reaction  it  is 
evident  that  the  nitro-group  in  nitronaphthalene  is  in  a  benzene  ring,  whether 


i 
6  C. 

^^  *k/    ^\ 


ANTHRACENE. 


553 


there  be  a  second  benzene  ring  or  not,  and  we  may  suppose  that  it  occupies  the 
position  8  in  the  formula  (Fig.  264).  By  reducing  the  nitronaphthalene  it  becomes 
amidonaphthalene,  that  is,  the  nitre-group  has  become  an  amido-group,  and  it  is 
reasonable  to  suppose  that  the  new  group  occupies  the  same  position  as  the  nitro- 
grpup  did.  Now  if  this  amidonaphthalene  be  oxidised  it  is  not  an  amidophthalic 
acid  which  is  obtained,  but  simply  phthalic  acid  itself  ;  since  an  oxidising  action 
cannot  substitute  H  for  NH2,  it  must  be  concluded  that  it  is  the  ring  in  which  the 
NH2  group  was  situated  that  has  been  removed  by  the  oxidation,  and  yet  a  benzene 
ring  compound  (phthalic  acid)  has  been  left,  showing  that  the  naphthalene  must 
•contain  two  such  rings. 

It  is  found  that  two  isomerides  of  every  mono-substitution  product  of  naphtha- 
lene exist  ;  this  is  in  accord  with  the  formula,  for  it  will  be  seen  that  whilst  the 
carbon  atoms  i,  8,  4  and  5,  are  similarly  situated  towards  the  whole  molecule, 
they  are  differently  situated  from  2,  3,  6  and  7,  which,  however,  are  similarly 
.situated  towards  the  molecule.  When  a  substituent  takes  up  any  of  the  first-named 
positions,  it  is  termed  an  a-derivative,  whilst  the  other  positions  yield  /3-derivatives. 
It  will  be  found  that  10  di-  and  14  tri-derivatives  are  possible  ;  all  the  mono-,  di-, 
.and  tri-chloronaphthalenes  are  known  and  orientated,  so  that  the  orientation  of  a 
new  derivative  may  be  settled  by  its  conversion  into  one  of  these.  The  I  :  8-deriva- 
tives  are  sometimes  called  peri-derivatives. 

The  general  expression  for  the  naphthalene  hydrocarbons  would  be  CMH2H-12. 
Examples  of  members  of  the  homologous  series  are  methyl- naphthalenes,  C10H7'CH3, 
•and  ethyl-naphthalenex,  C10H/C2H5.  These  are  liquid  even  at  low  temperatures,  and 
are  constituents  of  coal-tar. 

OPT 

Ethene-naphthalene,  or   acemphthene,   C10H6<^-     2,   which  is    found    in    small 

quantity  in  coal-tar  is  obtained  by  passing  vapour  of  a -ethyl-naphthalene 
through  a  red-hot  tube,  when  hydrogen  is  separated.  It  forms  colourless  prisms 
(m.-p.  95°  C.;b.-p.  277°). 

/-ITT 

Acetylene- naphthalene,  C10H6/..     ,  is  obtained  as  a  fusible  solid  (92°  C.)  by 

XCH 
passing  vapour  of  acenaphthene  over  red-hot  lead  oxide,  which  removes  H2. 

Dinaphthyl,  C10H7'C10H7,  is  produced  when  vapour  of  naphthalene  is  passed 
through  a  red-hot  tube,  by  the  oxidising  action  of  Mn02  with  H2S04  on  naphtha- 
lene, and  by  treating  C10H7Br  with  Na.  It  forms  scaly  crystals,  m.-p.  154°  C. 

The  naphthalenes  behave  in  a  rather  characteristic  way  with  picric  acid.  If 
they  be  dissolved  in  hot  alcohol  and  mixed  with  a  hot  solution  of  picric  acid  in 
alcohol,  stellate  tufts  of  yellow  or  red  needles  are  deposited  on  cooling.  These 
consist  of  a  compound  of  single  molecules  of  the  naphthalene  and  picric  acid. 

Hydronaphthalenes. — Like  the  aromatic  hydrocarbons,  naphthalene  readily 
forms  hydrogen  addition-products  when  treated  with  nascent  hydrogen  or  hydriodic 
acid.  These  products  range  from  dihydronaphthalene,  C10H10  to  dodekahijdro- 
naphthalene,  C10H18,  in  which  all  the  double  bonds  have  been  converted  into  single 
bonds,  leaving  the  molecule  capable  of  attaching  10  atoms  of  H.  When  the  hydro- 
genisation  is  in  one  ring  only — which  is  the  case  with  the  di-  and  the  tetra-hydro- 
naphthalenes  most  easily  obtained — the  hydrogenised  ring  has  properties  resembling 
those  of  an  open-chain  hydrocarbon,  so  that  the  molecule  is  more  like  a  phenyl 
derivative,  having  an  open  side-chain,  than  a  naphthalene.  The  substitution 
derivatives  of  such  hydronaphthalenes  are  therefore  distinguished  as  tinnmitlc  (ar-) 
or  alicydic  (ac-)  accordingly  as  the  substituent  is  in  the  phenyl  ring  or  the  liy<ln>- 
genised  ring.  Thus  C6H4  :  C4H7(NH2)  is  ac-amidotetrahydronaphtlmlrnr. 
C6H3(NH2)  :  C4H8  is  ar-amidotetrahydronaphthalene,  whilelC6H3(NH2)  :  C4H7(NH,) 
is  an  ar-ac-derivative. 

328.  Anthracene,  C14H10,  is  found  among  the  last  products  of  the 
distillation  of  coal-tar  (especially  from  Newcastle  coal),  and  may  be 
distinguished  from  naphthalene  by  its  being  almost  insoluble  in  alcohol 
and  fusing  only  at  213°  C.  It  crystallises  in  colourless  tables  having 
a  blue  fluorescence,  and  boils  at  351°  C.  That  fraction  of  the  coal-tar 
distillate  which  comes  over  at  about  360°  C.  solidifies  on  cooling  to  a 
mass  of  crude  anthracene.  It  is  freed  from  liquid  hydrocarbons  by 


554  PHENANTHEENE. 

pressure,  washed  with  light  petroleum,  and  purified  by  crystallisation 
from  hot  benzene,  or  by  sublimation  as  for  naphthalene.  Commercial 
anthracene  is  employed  for  the  manufacture  of  alizarin. 

Anthracene  is  formed  when  vapour  of  toluene  is  passed  through  a  red-hot 
tube  containing  pumice-stone  to  expose  a  large  heated  surface  ;  2C7H8  = 
C14H10  +  3H2.  Lead  oxide,  by  oxidising  the  H,  effects  the  change  at  a  lower 
temperature.  It  absorbs  chlorine,  forming  crystals  of  anthracene  dlchloride, 
C14H10C12,  and  chloranthracene,  C14H9C1.  With  nitric  acid,  anthracene  behaves  in  a 
different  way  from  benzene  and  naphthalene,  showing  less  disposition  to  the 
formation  of  nitro-compounds.  When  heated  with  nitric  acid  it  undergoes- 
oxidation  and  is  converted  into  a  yellow  crystalline  body  called  antliraqu'mone, 
C14H802  or  (C6H4)2(CO)2. 

Constitution  of  anthracene.  —  From  the  fact  that  anthracene  can  be  obtained 
synthetically  from  benzene  and  tetrabromethane  in  the  presence  of  A12C16,  it  is 
concluded  that  this  hydrocarbon  has  a  constitution  represented  by  the  formula 

C6H4<^>C6H4;   thus,  C6H6 


CH 


CH       CH       CH  CH       CO       CH 

Anthracene.  Anthraquinone. 

Fi<>.  265. 

The  C6H4  groups  constitute  two  benzene  rings  (Fig.  265).  whilst  the  central  carbon 
atoms  may  be  regarded  as  the  residue  of  a  third  ring  which  has  two  carbon  atoms 
in  common  with  each  of  the  other  rings.  By  treatment  with  hydrogenising  agents 
(hydriodic  acid,  for  example)  the  para-union  between  the  central  carbon  atoms  may 

be  opened  up  and  dihydroanthracene  or  anthracene  dlhydrlde.  C6H4<^      2Nc(3H4. 

CH2 

formed.  Support  is  lent  to  this  formula  for  anthracene  by  the  synthesis  of  ant  lira- 
quinone  (</.t\). 

The  orientation  of  anthracene-substitution-products  is  expressed  similarly  to 
that  of  naphthalene  derivatives.  Three  mono-substitution-produets  are  possible — • 
viz.,  the  a-  and  j8-,  like  the  a-  and  /3-naphthalene  derivatives,  and  the  7-  or  meso-deri- 
vatives,  containing  a  substituent  in  place  of  the  H  of  one  of  the  middle  carbon 
atoms,  which  may  be  numbered  9  and  10. 

Paranthracene  (C14H10)2.  crystallises  in  plates  from  a  cold  saturated  solution  of 
anthracene  in  benzene  exposed  to  sunshine.  It  does  not  fuse  until  heated  to 
244°  C.,  when  it  is  converted  into  anthracene.  Bromine  and  nitric  acid  attack  it 
with  difficulty. 

Phenanthrene,  C14H10,  is  isomeric  with  anthracene,  which  it  accompanies  in  coal- 
tar.  It  is  more  soluble  in  petroleum  spirit  and  in  alcohol  than  is  anthracene  ; 
the  former  solvent  serves  to  separate  it  from  the  bulk  of  the  crude  anthracene, 
the  separation  being  finished  by  fractional  distillation.  It  is  used  for  making 
blacks.  It  melts  at  99°  C.,  and  boils  at  340°  C. 

Phenanthrene  is  formed  when  stilbene  or  orthoditolyl  is  passed  through  a  red- 
hot  tube  ;  since  stilbene  is  known  to  contain  ethylenic  linked  carbon  (p.  546), 
and  ditolyl  to  be  a  diphenyl  derivative,  it  is  concluded  that  phenanthrene  has 

C  IT  -CH 

the    constitution    . 6    4  ••    ",  which   is    confirmed    by  the    fact   that  its  oxidation 
C6H4'CH 

C6H4-COOH 
yields  aiphenic  acid,   • 


Retene,  C18H18,  is  a  methylisopropytyhenanthrem  found  in  wood-tar. 

ie,    y^4  ~9H,  and pleenc,  9loH(5~9.H,  which  contain  the  naphthylene 
CH  -  CH  Ci^e  -  CH 


TURPENTINE. 


555 


group  C10H6,  are  similar  to  anthracene  in  properties.  The  former  melts  at  250°  C. 
and  boils  at  448°  C.  ;  it  is  a  final  product  in  coal-tar  distillation,  and  owes  its 
name  to  its  yelloAv  colour  in  the  crude  state  ;  when  purified  it  is  white  with  a 
violet  fluorescence.  Picene  melts  at  364°  C.,  a  higher  melting-point  than  that  of 
any  other  hydrocarbon  ;  it  is  found  in  the  tar  from  lignite,  and  is  highly  insoluble. 
Fluomnthrene  (idryl~),  C15H10,  andpyrene,  C16H10,  occur  in  -'stubb"  or  "»tupp,"  the 
unctuous  matter  Avhich  distils  during  the  Avinning  of  mercury  from  Idrian  ores. 

329.  Terpene  Hydrocarbons. — Oil  of  turpentine,  C,0H16,  is  obtained 
by  distilling  the  viscous  exudation  procured  by  cutting  into  the  bark 
of  various  species  of  pine.  Several  varieties  of  turpentine  are  met 
with  in  commerce,  of  which  the  two  best  known  are  the  common 
turpentine  which  is  obtained  from  the  Scotch  fir,  and  Venice  turpentine 
from  the  larch.  These  are  both  solutions  of  colophony,  or  common 
rosin,  in  oil  of  turpentine,  and,  when  distilled,  yield  from  75  to  90  per 
cent,  of  rosin,  which  remains  in  the  still,  and  from  25  to  10  percent,  of 
the  oil,  commonly  sold  as  spirits  of  turpentine. 

The  oil  of  turpentine  boils  at  158° — 160°  C.,and  hasthesp.gr.  0.864. 
It  is  very  sparingly  soluble  in  water,  but  dissolves  in  alcohol  and  ether. 
It  burns  with  a  smoky  luminous  flame.  Its  property  of  dissolving  resins 
and  fats  renders  it  useful  in  preparing  paints  and  varnishes.  It  is  also 
a  good  solvent  for  caoutchouc. 

Oil  of  turpentine  is  the  representative  of  a  large  class  of  hydro- 
carbons called  the  terpenes,  derived  like  itself  from  the  vegetable  king- 
dom. All  the  members  of  this  group  contain  the  same  proportions  of 
carbon  and  hydrogen,  and  the  greater  number  have  the  same  molecular 
formula  as  turpentine,  C10H16.  The  terpenes  resemble  each  other  in 
their  liability  to  suffer  conversion  into  isomerides,  in  their  optical 
activity  (p.  542),  in  their  solidification  by  absorption  of  oxygen  when 
exposed  to  air,  in  their  combination  with  water  to  form  crystalline 
hydrates,  and,  above  all,  in  their  tendency  to  combine  with  hydrochloric 
acid  to  form  crystalline  compounds. 

The  essential  oils  of  bergamotte,  birch,  chamomile,  caraway,  hops,  juniper, 
lemons,  myrtle,  nutmeg,  orange,  parsley,  pepper,  savin,  thyme,  tolu,  and 
valerian  are  all  terpenes  (for  the  most  part  mixtures  of  terpenes)  of  the 
formula  C10H16,  accompanied  by  its  oxygenated  derivatives  (alcohols, 
aldehydes,  and  ketones). 

Essential  oil  of  poplar  is  a  di-terpene,  C20H32.  The  oils  of  calamus, 
cascarilla,  cloves,  cubebs,  patchouli,  cedar,  and  rosewood  are  sesrjui-terpenes, 
(J15H2J. 

The  essential  oils  are  generally  extracted  from   the  flowers,   fruit, 
leaves,  or  seeds,  by  distillation  with   water,  the  portion  of  the  plant 
selected    being  suspended  in  the  still  by  means  of  a  bag  or  cage,  to 
prevent  it  from  being  scorched  by  contact  with  the  hot  sides  of  the 
still,  and  so  contaminating  the  distillate  with  empyreumatic  matters. 
The  water  which  distils  over  always  holds  a  little  of  the  essential  oil  in 
solution,  and  it  is  in  this  way  that  the  fragrant  distilled  waters  of  the 
druggist  are  obtained.     When  the  essential  oil  is  present  in  large  pn 
portion,  it  collects  as  a  separate  layer  on  the  surface  of  the  water,  tror 
which  it  is  easily  decanted.    The  oil  which  is  dissolved  in  the  water  may 
be  separated  from  it  by  saturating  the  liquid  with  common  salt,  whe 
the  oil  rises  to  the  surface  ;  or  by  shaking  it  with  ether,  which  dis 
the  oil  and  separates  from  the  water,  the  ethereal  solution  floating  o 
the  surface,  and  leaving  the  oil  when  the  ether  is  distilled  off. 


TEEPENES. 

In  cases  like  that  of  jasmine,  where  the  delicate  perfume  of  the  flower 
would  be  injured  by  a  high  temperature,  the  flowers  are  pressed  between 
woollen  cloths  saturated  with  oil  of  poppy-seeds,  which  thus  acquires  a 
powerful  odour  of  the  flower.  Carbon  bisulphide  is  also  sometimes 
employed  as  a  solvent  for  extracting  the  essential  oils. 

330.  The  terpenes  are  all  polymerides  of  the  formula  C5H8.  A  hydrocarbon 
having  this  molecular  formula  and  belonging  to  the  diolefines  (p.  537)  is  called 
isoprene  (b.-p.  37°  C.),  and  appears  to  have  the  constitution  CH2  :  C(CH3)'CH  :  CH2 
(methyldirinyl')  ;  many  terpenes  yield  isoprene  (liemiterpene)  Avhen  heated,  and 
isoprene  polymerises  to  dipentene. 

A  few  terpenes  of  minor  importance,  except  that  they  are  the  hydrocarbons 
corresponding  with  some  valuable  essential  oils,  appear  to  be  open-chain  compounds 
of  the  olefine,  diolefine  and  triolefine  series.  Rhodinol,  C10H20O,  and  geran'ml, 
C10H180,  are  alcohols  belonging  to  these  terpenes,  and  are  constituents  of  the  oils 
of  geranium,  roses,  and  pelargonium  ;  Unalool,  C10H]80,  is  a  similar  alcohol  from  the 
oils  of  lavender,  bergamotte,  limes,  and  marjoram.  Citral,  C^H^O,  is  an  aldehyde 
found  in  lemon  oil,  lemon-grass  oil,  and  verbena  oil.  By  snaking  a  mixture  of 
citral  and  acetone  with  baryta  water  and  distilling,  an  oil,  pseudo'wnone,  C13H200, 
is  obtained  ;  this  open-chain  ketone  is  converted  by  treatment  with  sulphuric  acid 
into  a  hydroaromatic  ketone  of  the  same  molecular  formula,  iontme,  the  odour  of 
which  resembles  that  of  the  oil  from  the  root  of  the  violet.  lonone  is  made  in  the 
above  manner  and  sold  as  "artificial  oil  of  violets." 

The  majority  of  the  terpenes,  however,  appear  to  be  cyclic  compounds  and  fall 
into  two  classes  accordingly  as  they  absorb  two  or  four  atoms  of  bromine,  indicat- 
ing one  or  two  ethylenic  linkings  respectively  in  the  molecule.  Those  which 
absorb  four  atoms  of  bromine  comprise  limonene,  dipentene,  sylre^trine^nAtej^ino- 
lene  as  chief  members.  They  yield  I  :  4-benzenedicarboxy'lic  acid  (terephthalic 
acid)  when  oxidised,  thus  indicating  that  they  contain  a  benzene  nucleus  which 
probably  has  two  alkyl  groups  in  the  I  :  4-positions.  Moreover,  when  dehydro- 
genised they  yield  cymene,  which  is  I  :  4-methylisopropylbenzene  (p.  549),  and 
contains  two  H  atoms  fewer  than  the  terpenes  contain.  These  terpenes  appear, 
therefore,  to  be  isomeric  modifications  of  dihydrocymene, 


The  terpenes  which  absorb  only  two  atoms  of  bromine,  and  have  therefore  only 
one  ethylenic  linking,  are  closely  related  to  camphor  (</.r.),  the  constitution  of 
which  has  been  much  discussed  ;  the  chief  axe  pinene,  camphene,  and  fenc/iene. 

Two  terpenes  terplnene  and  phellondrene,  do  not  appear  to  contain  ethylenic 
linking,  as  they  do  not  combine  with  bromine.  They  combine  with  N203. 

The  terpenes  boil  at  about  the  same  temperature  (155°—  1  80°  C.),  so  that  their 
separation  by  fractional  distillation  is  not  possible,  and  fractional  crystallisation  of 
some  of  their  compounds  is  the  only  available  method  of  purifying  them.  Most  of 
them  combine  with  NOC1  to  form  crystalline  compounds,  C10H16'NOC1,  nitroso- 
chlorides. 

Limonene  exists  in  two  forms  :  Desctrolimonene  (citrene,  hesperidene,  carvene) 
occurs  in  oil  of  orange-peel  and,  with  pinene,  in  oil  of  citron  ;  it  boils  at  175°  C., 
and  has  sp.  gr.  0.846.  Lcerolimonene  has  the  same  properties,  except  that,  as  its 
name  implies,  it  rotates  the  plane  of  polarised  light  in  the  opposite  direction  ;  it 
occurs  with  he  vopinene  in  "oil  of  fir-wool."  Each  limonene  yields  two  nitroso- 
chlorides,  which  are  isomerides,  differing  only  in  their  physical  properties.  When 
equal  volumes  of  the  two  limonenes  are  mixed,  dipentene  (cinene)  is  produced  ; 
this  has  no  action  on  polarised  light  ;  it  is  found  with  sylvestrene  in  Kussian  and 
Swedish  turpentine,  and  is  a  product  of  'the  destructive  distillation  of  caoutchouc 
and  of  the  polymerisation  of  isoprene  ;  acids  convert  it  into  terpinene. 

Sylvestrene  (b.-p.  176°  C.)  is  a  very  stable  terpene,  known  only  in  a  dextro-form  ; 
it  is  characterised  by  giving  a  blue  colour  with  acetic  anhydride  and  strong 
H2S04. 

Terpinolene  (b.-p.  183°  C.),  obtained  by  heating  terpineol  (</.''.)  with  oxalic  or 
formic  acid,  has  not  been  found  in  nature. 

Terpinene  (b.-p.  180°  C.),  found  in  oil  of  cardamoms,  is  one  of  the  most  stable 
compounds  of  this  group,  and,  with  phellandrene  (b.-p.  170°  C.),  which  occurs  in 
dextro-  and  Isevo-form,  is  characterised  by  its  compound  with  N203  (nitrosite). 


INDIA-RUBBER. 

Plwne  (terjtene)  is  the  chief  constituent  of  turpentine  oil,  the  d^-tnnn  /„-/„• 
tewtralene)  being  characteristic  of  American  and  English  turpentine  and 
fovopinene  (tereberthew)  of  French  turpentine  ;  an  inactive  pinene.  has  also  been 
obtained.  All  three  forms  boil  at  155°  C.  When  HC1  is  passed  into  oil' of  tur 
pentine,  well-cooled,  demtrafinene  hydrochloride,  C10H17C1,  is  obtained.  This  is 
called  artificial  camphor,  since  it  resembles  the  natural  product  in  its  crystals  and 
its  odour  ;  it  melts  at  125°  C.  and  boils  at  208°  C.,  and  is  optically  inactive,  though 
the  hydrochloritle  from  Irevopinene  is  laevo-rotatory. 

('amphene  is  solid,  melting  at  48°  C.  and  boiling  at  160°  C.  It  occurs  in  three 
optical  modifications,  and  is  prepared  by  heating  pinene  hydrochloride  with  a 
feeble  alkali  (aniline)  ;  it  has  been  detected  in  oil  of  ginger  and  citronella  oil 
On  oxidation  it  yields  camphor. 

Fenchem,  from  oil  of  fennel,  exists  in  the  usual  three  optical  modifications  which 
boil  at  about  150°  C. 

Hydroterpenes  are  also  known.  Chief  among  them  is  menthene,  C]0H18,  obtained 
from  oil  of  peppermint.  B.-p.  169°  C. 

331.  Caoutchouc,  or  india-rubber,  may  be  classed  among  the  terpene 
hydrocarbons,  its  chief  constituent  (a  so-called  polyprene)  having  the 
empirical  formula  C5HS,  but  a  molecular  formula  (C5H8)B.  It  is 
procured  from  a  milky  exudation  furnished  by  several  tropical  plants, 
particularly  by  the  Hcevcea  guianensis  and  Jatropha  or  Siphonia  elastica. 
Incisions  are  made  in  these  trees,  and  the  milky  liquid  thus  obtained 
is  spread  upon  a  clay  bottle-shaped  mould,  which  is  then  suspended 
over  a  fire  ;  a  layer  of  caoutchouc  is  thus  deposited,  and  its  thickness 
is  afterwards  increased  by  repeated  applications  of  the  milky  liquid, 
the  mould  being  eventually  broken  out  of  the  caoutchouc  bottle  thus 
formed.  The  dark  colour  of  commercial  india-rubber  is  believed  to 
be  due  to  the  smoke  from  the  fire  over  which  it  is  dried,  for  pure 
caoutchouc  is  white,  and  may  be  obtained  by  dissolving  india-rubber 
in  chloroform,  and  precipitating  with  alcohol ;  the  precipitate  forms 
a  gummy  mass  when  dried.  Commercial  india-rubber  contains  a  small 
quantity  of  albumin,  derived  from  the  original  milky  liquid,  this 
being  really  a  solution  of  albumin  holding  in  suspension  about  30  per 
cent,  of  caoutchouc,  which  rises  to  the  surface  like  cream  when  the 
juice  is  mixed  with  water  and  allowed  to  stand,  becoming  coherent  and 
elastic  when  exposed  to  air.  It  will  be  remembered  that  many  of  the 
chief  uses  of  caoutchouc  depend  upon  its  physical  rather  than  upon  its 
chemical  properties,  its  lightness  (sp.  gr.  0.93)  and  impermeability  to 
water  adapting  it  for  waterproof  clothing,  life-buoys,  <fec.,  while  its  re- 
markable elasticity  gives  rise  to  a  still  greater  variety  of  applications. 

For  the  manufacture  of  waterproof  cloth  caoutchouc  is  dissolved  in  rectified 
turpentine,  and  the  solution  is  spread,  in  a  viscid  state,  over  the  surfaces  of  two 
pieces  of  cloth  of  the  same  size,  which  are  then  laid  face  to  face  and  passed 
between  rollers,  the  pressure  of  which  causes  perfect  adhesion  between  the  sur- 
faces. Waterproof  felt  is  made  by  matting  together  fibres  of  cotton  impregnated 
with  a  solution  of  caoutchouc  in  naphtha,  and  passing  the  felt  between  rollers. 
When  kept  for  a  long  time,  its  strength  and  waterproof  qualities  are  deteriorated, 
in  consequence  of  the  oxidation  of  the  caoutchouc,  which  is  thus  converted  into  a 
resinous  substance  resembling  shell-lac  and  easily  dissolved  by  alcohol. 

Caoutchouc  is  slowly  dissolved  by  carbon  disulphide,  benzene,  chloroform,  coal- 
naphtha,  petroleum,  turpentine,  and  the  fixed  oils. 

Marine  glue  is  a  solution  of  caoutchouc  with  a  little  shell-lac  in  coal-naphtha. 

The  alkalies  and  diluted  acids  are  without  action  on  caoutchouc.  When  gently 
warmed,  it  becomes  far  more  soft,  pliable,  and  extensible;  it  fuses  at  about 
250°  F.  (121°  C.)  to  an  oily  liquid,  which  becomes  viscid  on  cooling,  but  will  not 
solidify,  and  is  useful  for  lubricating  stop-cocks.  When  further  heated  m  air,  it 
burns  with  a  bright  smoky  flame.  Heated  in  a  retort,  caoutchouc  is  decomposed 


GUTTA-PERCHA. 

into  several  hydrocarbons,  among  which  are  isoprene,  dipentene  (caoutchene),  and 
heveene,  a  sesquiterpene,  C15H24  (b.-p.  260°  C.). 

Vulcanised  rubber,  the  chemical  constitution  of  which  is  not  understood,  is  pro- 
duced by  incorporating  india-rubber  with  2  or  3  per  cent,  of  sulphur,  which  not 
only  greatly  increases  its  elasticity,  but  prevents  it  from  cohering  under  pressure, 
and  from  adhering  to  other  surfaces  unless  strongly  heated.  It  also  becomes  in- 
soluble in  turpentine  and  naphtha.  Ordinary  vulcanised  rubber  generally  contains 
more  sulphur  than  is  stated  above,  which  causes  it  to  become  brittle  after  a  time  ; 
for  some  purposes,  such  as  the  manufacture  of  overshoes,  other  substances  are 
added  besides  sulphur,  such  as  lead  carbonate  and  zinc  oxide. 

When  a  sheet  of  caoutchouc  is  allowed  to  remain  for  some  time  in  fused  sulphur 
at  120°  C.,  it  absorbs  12  or  15  per  cent,  without  any  material  alteration,  but  if  it 
be  heated  for  a  short  time  to  150°  C.  it  becomes  vulcanised  ;  and  when  still  further 
heated,  is  converted  into  the  black  horny  substance  called  vulcanite  or  ebonite,  and 
used  for  the  manufacture  of  combs,  &c.,  and  as  an  electrical  insulator. 

Vulcanised  caoutchouc  is  sometimes  made  by  mechanically  incorporating  the 
sulphur  with  india-rubber  softened  by  heat  ;  or  by  immersing  the  rubber  in  a 
mixture  of  sulphur  with  chloride  of  lime,  or  in  carbon  disulphide  mixed  with 
2.5  per  cent,  of  S2C12.  It  can  also  be  made  by  dissolving  the  sulphur  in  turpen- 
tine, which  is  afterwards  used  to  dissolve  the  caoutchouc  ;  when  the  turpentine 
has  evaporated,  a  mixture  of  caoutchouc  and  sulphur  is  left,  which  may  be  easily 
moulded  into  any  required  shape,  and  afterwards  vulcanised  by  exposure  to  highr 
pressure  steam  having  a  temperature  of  about  140°  C. 

By  treating  vulcanised  caoutchouc  with  sodium  sulphite,  the  excess  of  sulphur 
above  2  or  3  per  cent,  may  be  dissolved  out.  The  whole  of  the  sulphur  may  be 
removed,  and  the  caoutchouc  devulcanised,  by  boiling  with  a  10  per  cent,  solution 
of  caustic  soda. 

Caoutchouc  is  by  no  means  rare  in  the  vegetable  world,  being  found  in  the 
milky  juices  of  the  poppy  (and  thence  in  the  opium),  of  the  lettuce,  and  of  the 
eupJwrbium  and  asclepia  families. 

Gutta-percha  (empirical  formula  C5H8),  like  caoutchouc,  is  originally 
a  milky  exudation  from  incisions  made  into  the  wood  of  the  Isonandra 
ptrcha,  a  native  of  the  Eastern  Archipelago.  This  juice  soon  solidifies, 
when  exposed  to  air,  to  a  brown  mass  heavier  than  caoutchouc  (sp.  gr. 
0.98)  and  differing  widely  from  it  by  being  tough  and  inelastic  when 
cold,  and  becoming  quite  soft  and  plastic  when  heated  nearly  to  the 
boiling-point  of  water.  Being  impervious  to  water,  it  is  used  as  a 
waterproof  material  and  for  water-pipes,  and  its  want  of  conducting 
power  for  electricity  is  turned  to  account  for  insulating  telegraph 
cables. 

Gutta-percha  is  dissolved  by  those  substances  which  dissolve  caout- 
chouc. It  is  not  affected  by  diluted  acids  and  alkalies,  and  is  used  for 
keeping  hydrofluoric  acid.  It  melts  easily,  and  is  afterwards  decom- 
posed, yielding  products  similar  to  those  from  caoutchouc. 

Commercial  gutta-percha  contains  only  about  80  per  cent,  of  the  hydrocarbon, 
which  may  be  dissolved  out  by  boiling  with  ether  ;  the  solution,  when  evaporated, 
leaves  the  hydrocarbon  as  a  white  powder  fusing  at  100°  C.  The  portion  insoluble 
in  ether  contains  two  resinous  bodies  soluble  in  boiling  alcohol,  which  deposits, 
on  cooling,  a  white  crystalline  resin,  of  the  empirical  formula  C10H160,  and  retains 
in  solution  an  amorphous  resin,  C20H32O.  The  existence  of  these  bodies  renders 
it  probable  that  gutta-percha  is  C20H32,  the  crystalline  resin  being  C20H>So02.  Ex- 
posure to  air  and  light  gradually  converts  pure  gutta-percha  into  these  resinous 
bodies. 

332.  Camphors. — Closely  allied  to  the  essential  oils  are  the  different 
varieties  of  camphors,  which  are  formed  by  oxidation  of  the  hydrocarbons 
contained  in  the  essential  oils.  Recently  they  have  been  shown  to  be 
alcohols  or  ketones,  and  in  a  strict  classification  should  receive  notice 


CAMPHOR. 


under  these  headings.     Their  natural  connection  with  the  parent  hydro 
carbons,  however,  warrants  their  consideration  here. 

Menthol  or  mentkocamphor    C10H200,  is  a  secondary  alcohol,  forming  the  chief 
constituent  of  oil  ot  peppermint  ;  its  relationship  to  cymene  (p.  549),  fs  indicated 

by  the  formula,  CH3'CH<^^^H>CH-CH(CH3)2.     It  melts  at  42°  C.  and  boils 

at  212°  C.  ;  it  is  used  for  external  application  as  an  anti-neuralgic.     Heated  with 
dilute  H2S04  it  yields  menthene,  and  by  oxidation  it  becomes  menthone  a  keton^ 
differing  from  menthol  in  that  CO  is  substituted  for  CHOH  in  the  above  formi 
and  also  occurring  in  oil  of  peppermint.     It  boils  at  206°  C.  and  occurs  in  dextro' 
and  laevo-form. 

Terpin,  C10H18(OH).2,  is  a  dihydric  alcohol  existing  in  a  cis-  and  trans-form  (see 
fumarlc  acid)  :  the  former  melts  at  104°  C.,  boils  at  258°  C.,  and  combines  readily  with 
one  mol.H20  to  form  terpin  hydrate  (m.-p.  117°  C.),  which  is  a  product  of  the  action 
of  dilute  acids  on  turpentine,  limonene,  and  dipentene.  Trans-terpin  melts  at  157°  C 
boils  at  264°  C.,  and  forms  no  hydrate.  When  terpin  hydrate  is  heated  with  dilute 
acid  it  yields,  besides  cineol,  C10H18O  (the  chief  constituent  of  eucalyptus  oil) 
dipentene,  &c.,  terpineol,  a  monohydric  alcohol  melting  at  35°  C.  and  probably 

PTT  .  pTT 


An  isomeric  terPineol  melts  at  69°  C. 

Can-one  or  carvoL  C10H140,  boils  at  225°  C.,  and  occurs  in  dextro-.  hevo-,  and 
inactive  form,  like  limonene,  to  which  it  is  closely  related.     It  is  probably  a  ketone 

CH'CH  PIT 

of  the  form  CH3C'^.2>CH'C^3,  differing  from  limonene  by  having  0 


in  place  of  H2.     d-Carvone  occurs  in  liunnnel  oil  and  oil  of  dill,  and  when  heated 
with  KOH,  becomes  1:4:  2-inethylisopropylphenol,  or  carvacrol  (q.i\). 

Japan  or  common  camphor  (C10H160)  is  found  deposited  in  minute 
crystals  in  the  wood  of  the  Laurus  camphora,  or  camphor  laurel,  from 
which  it  is  obtained  by  chopping  up  the  branches  and  distilling  them 
with  water  in  a  still,  the  head  of  which  is  filled  with  straw,  whereon 
the  camphor  condenses.  It  is  purified  by  subliming  it  in  large  glass 
vessels  containing  a  little  lime. 

Camphor  passes  into  vapour  easily  at  the  ordinary  temperature  of 
the  air,  and  is  deposited  in  brilliant  octahedral  crystals  upon  the  sides 
of  the  bottles  in  which  it  is  preserved.  It  fuses  at  347°  F.  (175°  C.), 
and  boils  at  399°  F.  (204°  C.),  and  is  very  inflammable,  burning  with  a 
bright  smoky  flame.  It  is  sometimes  dissolved  in  the  oil  used  for  the 
lamps  of  magic-lanterns,  to  increase  its  illuminating  power.  Camphor 
is  lighter  than  water  (sp.  gr.  0.985),  and  whirls  about  upon  its  surface 
in  a  remarkable  way,  dissolving  meanwhile  very  sparingly  (i  part  in 
1000),  alcohol  and  ether  being  its  appropriate  solvents. 

An  alcoholic  solution  of  ordinary  camphor  is  dextro-rotatory,  but  the  camphor 
from  some  species  of  Matrwaria  is  leevo-rotatory.  When  the  two  are  mixed  an 
inactive  camphor  is  produced. 

When  distilled  with  P205  ordinary  camphor  yields  cymene.  C10H14,  and  when 
heated  with  iodine  it  yields  carvacrol,  C10H140.  The  former  is  I  :  4-methyliso-pro- 
pylbenzene  of  which  carvacrol  is  the  hydroxy-derivative,  the  OH  group  being  in  the 
2-position.  It  would  seem  from  this  that  camphor  must  be  derived  from  a  benzene 
ring  having  a  methyl,  an  isopropyl,  and  an  oxygen  atom  in  the  1:4:  2-positions 
respectively.  The  oxygen  does  not  appear  to  be  present  as  an  OH  group,  but  rather 
as  a  ketonic  group  (CO),  and  ethylenic  linking  seems  to  be  absent  in  the  molecule 
as  addition-products  are  not  easily  formed.  These  facts  led  to  the  formula 

CH  'CO 

(CH3)2CH-C^~  -^C-CH3  as  the  most  probable  representation  of  camphor. 

' 


560  RESIN. 

The  oxidation  of  camphor  with  nitric  acid,  however,  produces  successively  cam- 
phoric acid,  C10H1604,  campJianic  acid,  C10H1605,  and  camplim-onic  acid,  C9H140(i. 
Xow  the  last  of  these  is  an  open-chain  compound — trimethyltricarballylic  acid,. 
COOH-C(CH3)2-C(CH3)(COOH)-CH2-COOH.  There  is  no  isopropyl  group  in  this 
compound,  but,  instead,  two  CH3  groups  attached  to  a  C  atom  itself  attached  to- 
two  other  C  atoms.  It  is  therefore  probable  that  camphor  is  more  correctly 

CH2-CO 

expressed  by  the  formula  CH^-C(CH3)9^C-CH3  than  by  that  given  above. 
XCH2-CH/ 

As  stated  on  p.  557  camphene,  which  contains  an  ethylenic  linking,  is  readily 

CH  :  CH 
oxidised  to  camphor,  indicating,  the  formula  CH/  C(CHL)2— >C'CHo  for  camphene. 

\CHaCHa  / 
Pinene  and  fenchene  have  similar  constitutions. 

The   reactions  of  camphor    generally  produce  either  benzene   derivatives  (e.t/. 
cymene)  or  compounds  which  may  be  regarded  as  derivatives  of  the  pentamethylene 
ring  (p.  539).     Camphoric  acid  (v.s.)  is  of  the    latter  type,  being  a  dibasic  acid. 
COOH  COOH 

probably  of  the  form  CH— C(CH3)2 — -^ C'CHo,   the   lower   part   of   which   con- 

x     CH2-CH2     / 

stitutes  the  5-carbon  ring,  there  being  no  bond  between  the  COOH  groups.  It 
occurs  in  six  isomeric  forms,  two  dextro-rotatory,  two  laevo-rotatory,  and  two- 
inactive  ;  the  common  dextro-form  melts  at  187°  C. 

Borneo  camphor,  C]0H18O,  is  obtained  from  the  exudation  of  the  Dryobalan-ops 
cam-pit  ora.  It  is  neither  so  fusible  nor  so  volatile  as  common  camphor  (m.-p.  203°  C. ; 
b. -p.  212°  C.)  and  has  a  different  odour  ;  it  also  crystallises  in  prisms  instead  of 
octahedra.  When  camphor  is  reduced  in  alcoholic  solution  by  sodium  it  yields 
Borneo  camphor,  and,  conversely,  when  this  is  oxidised  with  HX03  it  yields 
common  camphor.  Hence  Borneo  camphor  is  believed  to  be  an  alcohol,  borneol.  of 
similar  formula  to  that  of  camphor  save  that  CH(OH)  takes  the  place  of  CO. 
Borneol  occurs  in  dextro-form  (borneo  camphor),  laevo-form,  and  inactive  form,  the- 
two  latter  occurring  in  baldrian  oil  (baldrian  camp/tor'). 

Fenchone,  C10H160  (m.-p.  5°  C.  ;  b.-p.  I93°C.)  is  a  ketonic  camphor,  distinguished 
from  Japan  camphor  by  the  fact  that  it  yields  meta-cymene  instead  of  para-cymene- 
when  dehydrated.  By  reduction  it  yields  fenchyl  alcohol. 

333.  Resins  and  Balsams. — Resins  are  probably  oxidation-products 
of  essential  oils,  and  the  natural  products  occur  dissolved  in  the  oils  as 
they  exude  from  the  tree,  the  mixture  being  known  as  an  oleoresin. 
The  balsams  are  oleoresiris  characterised  by  the  presence  of  considerable 
proportions  of  aromatic  acids. 

Colophony  or  common  rosin  is  best  known  among  the  resins,  which 
are  generally  distinguished  by  their  resinous  appearance,  fusibility,  in- 
flammability, burning  with  a  smoky  flame,  insolubility  in  water,  and 
solubility  in  alcohol.  They  are  all  rich  in  carbon  and  hydrogen,  and 
contain  a  small  proportion  of  oxygen  ;  they  generally  have  an  acid 
character  (resin  acid),  being  soluble  in  alkalies. 

Kosin  melts  between  100°  C.  and  135°  C.  and  consists  largely  of  aUetic  ac'xl.. 
C19H2802  ;  it  is'  used  in  making  varnishes  and  soaps,  and  is  destructively  distilled 
to  procure  rosin  spirit  and  rosin  oil.  Other  resins  used  for  varnish-making  are 
copal,  sandarach,  shellac,  animi,  and  elemi.  To  make  a  spirit  varnish  the  resin 
is  dissolved  in  alcohol  or  wood  spirit  (acetone),  but  the  commoner  varnish  is  an 
oil  varnish  made  by  dissolving  the  resin  in  a  drying  oil,  like  linseed  oil  and 
turpentine. 

Guaicum  resin  is  distinguished  by  its  tendency  to  become  blue  under  the 
influence  of  the  more  refrangible  and  chemically  active  (violet  rays)  of  the 
solar  spectrum,  as  well  as  under  that  of  certain  oxidising-agents,  like  chlorine 
and  ozone. 

Amber,  a  fossil  resinous  substance,  more  nearly  resembles  this  class  of  bodies 
than  any  other,  and  contains  several  resinous  bodies.  It  is  distinguished  by  its 
insolubility,  for  alcohol  dissolves  only  about  one-eighth  and  ether  about  one-tenth, 


CLASSIFICATION  OF  ALCOHOLS.  561 

of  it.     After  fusion,  however,  it  becomes  soluble  in  alcohol,  and  may  be  used  for 
varnishes. 

Balsam  of  Peru,  balsam  of  Tolu,  and  Storax  are  characterised  by  the  presence  of 
cinnamic  acid,  while  gum  benzoin  is  the  parent  substance  of  benzoic  acid. 

DERIVATIVES   OF  HYDROCARBONS. 

334.  As  has  been  already  indicated,  all  carbon  compounds  may  be 
considered  as  derivatives  of  the  hydrocarbons,  containing  one  or  more 
elementary  atoms  or  compound  radicles  in  place  of  hydrogen,  and  in 
every  compound  there  is  a  characteristic  hydrocarbon  radicle,  which  is 
monovalent,  divalent,  or  trivalent  accordingly  as  one,  two,  or  three 
hydrogen  atoms  have  been  removed  from  a  saturated  hydrocarbon  in 
order  to  form  it.  Typical  hydrocarbon  radicles  are  (CH3)',  (CSH4)",  and 


I.  ALCOHOLS. 

335.  These  compounds  are  comparable  with  the  metallic  hydroxides, 
for  they  contain  one  or  more  (OH)'  groups,  and  react  with  acids  forming 
water  and  salts  containing  hydroc-arbon  radicles.  Thus,  the  reaction 
C,H5-OH  +  H9S04  =  C9H5HSO4  +  HOH  is  comparable  with  the  reaction 
XaOH  +  H2SO4  =  NaH  SO4  +  HOH.  Just  as  a  divalent  or  a  trivalent 
metal  forms  a  hydroxide  containing  two  or  three  hydroxyl  groups,  so  a 
divalent  or  trivalent  radicle  forms  an  alcohol  containing  two  or  three 
such  groups,  e.g.,  C2H4(OH)2,  C3Hs(OH)3.  Hence  alcohols  are  classified 
into  monohydric,  dihydric,  trihydric,  &c.,  accordingly  as  they  have  one, 
two,  three,  &c.,  OH  groups. 

Several  general  methods  for  preparing  the  alcohols  exist.  Thus  they 
may  be  formed  from  the  halogen  substitution  derivatives  of  the  corre- 
sponding hydrocarbons  by  treating  them  with  moist  silver  oxide  — 
C.,HJ  +  AgOH  =  CJLOH  +  AgI;  from  the  ethereal  salts  (q.v.)  by 
saponification—  CH3-COOC2H5  (ethyl  acetate)  +  HOH  =  CH3COOH  + 
C.,H3OH  ;  from  hydrocarbon  derivatives  containing  the  NH2  group  by 
treatment  with  nitrous  acid  —  C2H5-NH2  (ethylamine)  +  NO'OH  = 
C,H,OH  +  N2  +  HOH.  This  last  reaction  is  typical  of  a  widely  applic- 
able method  for  introducing  an  OH  group  into  a  compound,  and  is 
strictly  comparable  with  the  reaction  between  ammonia  and  nitrous 
acid  at  ordinary  temperature  (p.  106). 

Alcohols  have  a  slightly  basic  tendency.  They  easily  undergo  oxida- 
tion, whereby  hydrogen  is  removed  with  or  without  the  introduction  of 
an  equivalent  quantity  of  oxygen.  The  products  are  the  aldehydes  (or 
ketones)  and  acids. 

Monohydric  alcohols  of  the  paraffin  series  —These  contain  OH 
in  place  of  one  H  atom  in  a  paraffin  hydrocarbon  ;  consequently  there 
is  an  homologous  series  of  these  alcohols  corresponding  with  the  homo- 
logous series  of  hydrocarbons,  CH4  yielding  CH3-OH,  C2H6  yielding 
C,H5-OH,  C3H8  yielding  C3H/OH,  and  so  on.  Thus,  there  is  a  general 
formula,  CHH2w+1OH,  for  this  series  of  alcohols.  The  substance  origin- 
ally called  alcohol  will  be  considered  first. 

Alcohol,  C9H5-OH,  is  systematically  termed  ethyl  alcohol.  It  has 
been  already  stated  that  it  can  be  obtained  synthetically  by  combining 
C  and  H  to  form  acetylene,  C.,H9,  which  may  be  converted  into  ethene, 


562  FERMENTATION. 

C3H4,  by  nascent  hydrogen  ;  ethene  can  be  combined  with  sulphuric 
acid  to  form  ethyl  hydrogen  sulphate,  C2EL:HS04,  from  which  alcohol 
may  be  made  by  distillation  with  water.  Or  C2H4  may  be  combined 
with  HI  to  obtain  ethyl  iodide,  C2H5I,  which,  when  distilled  with 
caustic  potash,  yields  alcohol,  C2H5I  -KKOH  =  C2H5'OH  4-  KI.  The  fact 
that  ethyl  iodide  (moniodoethane),  CH8*CH9I,  will  give  alcohol  in  this 
reaction  justifies  the  formula  CH3'CH2OH  for  this  compound. 

In  nature,  alcohol  is  found  in  some  unripe  fruits.     It  occurs  in  coal- 
-tar, in  bone-oil,  and  in  the  products  of  distillation  of  wood. 


.  —  Alcohol  is  usually  made  by  the  fermention  of  glucose  or  grape- 
'sugar  brought  about  by  yeast.  For  a  laboratory  experiment,  two  ounces  (or 
60  grammes)  of  brown  sugar  may  be  dissolved  in  a  pint  (or  500  c.c.)  of  water  in  a 
flask,  and  about  a  table-spoonful  of  brewers'  yeast  (or  of  German  yeast  rubbed  up 
with  water)  added  ;  in  a  warm  room,  fermentation  soon  begins,  as  indicated  by  the 
froth  on  the  surface  caused,  by  bubbles  of  C02.  By  closing  the  flask  with  a  cork 
furnished  with  a  tube  dipping  under  water,  the  rate  of  fermentation  may  be 
inferred  from  the  escaping  gas.  When  very  little  more  gas  is  disengaged  (usually 
after  about  24  hours)  the  flask  is  fitted  with  a  tube  connected  with  a  condenser,  and 
the  liquid  distilled  as  long  as  the  distillate  smells  strongly  of  alcohol.  The  distillate 
is  then  rectified,  or  submitted  to  a  second  distillation  in  a  smaller  flask  or  retort, 
when  the  first  portion  which  distils  over  will  be  much  richer  in  alcohol.  This  is 
placed  in  a  narrow  bottle,  and  dried  potassium  carbonate,  in  powder,  is  added  by 
degrees,  with  frequent  shaking,  as  long  as  the  liquid  dissolves  it.  On  standing,  two 
layers  are  formed,  the  lower  containing  the  potassium  carbonate  dissolved  in  water, 
and  the  upper  containing  the  alcohol  with  about  10  per  cent,  of  water.  This  upper 
layer  is  transferred  to  a  small  flask  or  retort,  and  allowed  to  remain  for  some  hours 
in  contact  with  powdered  quick-lime  to  remove  the  water  ;  the  alcohol  is  then 
distilled  off  in  a  water-bath. 

The  mode  of  action  of  the  yeast  in  causing  the  production  of  alcohol 
from  sugar  is  not   yet  known.     Yeast  is  a  vegetable  substance  (torula 
or  saccharomyces  cerevisice)  which  develops  from  minute  spores  or  germs 
carried  by  the  air  ;  when  these  come  in  contact  with  a  liquid  containing 
the  nutriment  necessary  for  the  yeast  plant, 
they  multiply  into  a  number  of  round  or  oval 
cells   arranged  in  branching   chains,    visible 
under  the  microscope  (Fig.  266).     It  is  during 
this  growth  of  the  yeast  that  the  conversion 
of  the  sugar  into  alcohol  occurs.     The  pure 
yeast  spores  will  not   produce   alcohol   from 
pure  sugar,  because  it  does  not  contain  the 
substances  required  to  nourish  the  yeast  ;  but 
when  the  spores  are  introduced  into  grape- 
juice,  or  infusion  of  malt  (wort),  which  contain 
the  necessary  albuminous  matters  and  phos- 
phates, &c.,  they  grow  and  cause  the  forma- 
Fig.  265,  tion  of  alcohol.     The  crop  of  yeast  thus  raised 

may  be  used  to  ferment  fresh  portions  of 
sugar,  and  is  the  more  efficacious  because,  when  it  is  removed  from  the 
surface  of  the  liquid  in  which  it  has  grown,  it  is  accompanied  by  some 
of  the  nutrient  materials.  When  yeast  is  added  to  a  solution  of  cane- 
sugar  (C12H220H)  it  causes  it  to  become  glucose,  by  combining  with  the 
elements  6f  a  molecule  of  water  ;  CJ2H22On  +  H20  =  2C6H1206.  The  bulk 
of  the  glucose  is  then  decomposed  into  alcohol  and  carbonic  acid  gas; 
C6H10O6  -  2C2HfiO  +  2C02.  About  95  per  cent,  of  the  glucose  undergoes 
this  change,  and  the  remainder  is  converted  into  other  substances,  of 


PROPERTIES  OF  ALCOHOL.  563 

which  the  most  important  are  glycereiie,  C3H5(OH)3,  (about  3  per  cent.), 
succinic  acid,  C,H4(C02H)2  (about  0.5  per  cent.),  and  some  of  the  higher- 
members  of  the  paraffin  alcohols  (fusel  oil),  which  are  always  present  in 
fermented  alcoholic  liquids.  The  liquid  rises  in  temperature  during  fer- 
mentation, on  account  of  the  development  of  heat  in  the  formation  of 
carbon  dioxide.  The  specific  gravity  of  the  solution  decreases  as  the 
fermentation  proceeds,  because  solution  of  alcohol  is  lighter  than 
solution  of  sugar.  A  solution  containing  more  than  one-third  of  its 
weight  of  sugar  is  not  fermented  by  yeast,  and  when  the  alcohol 
produced  in  the  fermentation  amounts  to  about  one-sixth  of  the  weight 
of  the  liquid,  the  growth  of  the  yeast,  and  therefore  the  fermentation, 
is  arrested.  No  fermented  liquor,  therefore,  can  contain  so  much  as 
20  per  cent,  of  alcohol ;  port  wine,  the  strongest  fermented  drink, 
contains  at  most  1 7  per  cent.  The  yeast  does  not  grow,  and  ferment- 
ation does  not  occur,  at  temperatures  below  o°  C.  (32°  F.)  or  above 
35°  C.  (95°  F.),  25-30°  C.  being  most  favourable.  The  fermentation  is 
also  arrested  by  strong  acids,  and  by  antiseptics  such  as  common  salt, 
kreasote,  corrosive  sublimate,  sulphurous  acid,  and  turpentine.  Air 
is  not  essential  to  the  fermentation,  but  favours  it,  In  sweet  wort 
(infusion  of  malt)  the  yeast  increases  to  six  or  eight  times  its  original 
weight. 

Recently  it  has  been  shown  that  the  liquid  obtained  by  triturating  yeast  with 
sand  and  filtering  is  capable  of  fermenting  sugar.  All  traces  of  yeast  cells  having 
been  removed  by  the  filtration  it  must  be  concluded  that  yeast  contains  an 
unorganised  alcoholic  ferment. 

On  the  large  scale,  alcohol  is  usually  made  from  the  starch  contained  in  potatoes, 
rice,  and  other  grains.  The  starch,  C6H1005,  is  converted  either  into  glucose, 
by  heating  it  with  very  diluted  sulphuric  acid  (afterwards  neutralised  with  chalk) — 
when  it  combines  with  a  molecule  of  water  and  becomes  glucose,  C6H1206 — or 
into  maltose,  G12S220U,  by  mixing  it  with  infusion  of  malt ;  the  glucose,  or 
maltose,  is  fermented  by  yeast.  The  wash,  as  it  is  termed,  is  then  distilled,  the 
stills  being  constructed  with  much  ingenuity,  to  effect  the  concentration  of  the 
alcohol  at  the  least  expense. 

Even  woody  fibre,  paper,  linen,  &c.,  which  have  the  same  empirical 
formula  as  starch,  may  be  converted  into  glucose  by  the  action  of  sul- 
phuric acid,  and  may  thus  be  made  to  yield  alcohol.  New  bread,  made 
with  yeast,  contains  about  0.3  per  cent,  of  alcohol,  and  stale  bread  about 
0.12. 

336.  Properties  of  alcohol. — Characteristic  odour  and  burn- 
ing taste;   sp.  gr.  of  pure  or  absolute  alcohol  0.794  at  15°  C. 
Freezes  at  -  112°  C. ;    boiling-point  78°. 3  C. ;  takes  fire  when 
a  flame  is  brought  near  its  surface,  and  burns  with  a  pale, 
smokeless   flame.     Evaporates  easily  when  exposed  to  the  air, 
without  combining  with  oxygen.     Kept  in  a  badly  stoppered 
bottle,  it  absorbs  water  from  the  air.     Alcohol  may  be  mixed 
with  water  in  all  proportions,  evolving  a  little  heat,  and  giving 
a  mixture  rather  smaller  in  bulk  than  the  sum  of  its  consti- 
tuents.    This  may  be  shown  by  filling  the  vessel  (Fig.  267) 
with  water  up  to  the  neck  joining  the  two  globes,  carefully  Fiy.  267. 
filling  the  upper  globe  to  the  brim  with  (methylated)  alcohol, 
inserting  the  stopper,  and  inverting  the  vessel,  when  the  contraction 
of  the  mixture  will  leave  a  vacuum  in  the  tube.     The  greatest  contrac- 
tion occurs  when  the  volumes  of  alcohol  and  water  are  nearly  equal 
(at  o°  C.,  53.9  measures  of  alcohol  to  49.8  of  water).     The  attraction 


564  PEOOF  SPIRIT. 

of  alcohol  for  water  affords  one  reason  for  its  power  of  preserving 
animal  and  vegetable  substances  from  putrefaction  by  removing  the 
water  necessary  for  that  change. 

By  oxidation  alcohol  is  converted  first  into  aldehyde,  CH3'CHO,  and 
then  into  acetic  acid,  CH3'COOH. 

Next  to  water,  alcohol  is  the  most  valuable  simple  solvent.  It  is  especially  useful 
for  dissolving  resins  and  alkaloids  which  are  insoluble  in  water.  Many  salts  are 
capable  of  combining  with  alcohol,  just  as  they  do  with  water  of  crystallisation  ; 
examples  of  such  alcoholates,  as  they  are  termed,  are — 

LiC1.4C2H60  ;  CaCl2.4C2H60  ;  MgCl2.6C2H60  ;  Mg(N03)2.6C2H60. 

Ethoxides  or  ethylates  are  compounds  formed  by  the  exchange  of  hydrogen  in 
alcohol  for  metals  ;  they  correspond  with  the  hydroxides,  having  C2H5  in  place 
of  H  ;  e.g.,  sodium  ethoxide,  C2H5.ONa,  aluminium  ethoxide,  (C2H50)6A12.  Sodium 
ethoxide  is  used  in  surgery  as  a  caustic.  Water  decomposes  the  ethoxides,  yielding 
alcohol  and  hydroxides  ;  C2H5ONa  +  HOH  =C2H5OH  +  NaOH. 

Barium  ethoxide.  (C2H50)2Ba,  is  obtained  by  the  action  of  anhydrous  baryta  on 
absolute  alcohol.  A  trace  of  water  precipitates  barium  hydroxide  from  the  solution. 
On  heating  the  alcoholic  solution,  the  barium  ethoxide  precipitates,  being  less 
soluble  in  hot  alcohol. 

Aluminium,  ethoxide,  (C2H50)6A12,  is  produced  by  heating  aluminium  in  alcohol 
with  a  little  iodine  or  stannic  chloride.  It  melts  at  135°  C.  and  distils  unchanged  at 
240°  C.  under  23mm.  pressure. 

Thallium  ethoxide,  C2H5OT1,  is  a  liquid  remarkable  for  its  high  specific  gravity 
(3.68)  and  great  refractive  and  dispersive  action  upon  light. 

The  simplest  chemical  test  fur  alcohol  is  to  add  to  the  suspected  liquid  hydro- 
chloric acid  and  enough  potassium  dichromate  to  colour  it  orange-yellow,  to 
divide  it  between  two  test-tubes  for  comparison,  and  to  heat  one  of  them  till  the 
liquid  boils  ;  if  alcohol  be  present,  the  liquid  will  become  green,  and  evolve  the 
peculiar  fragrant  smell  of  aldehyde — 

2Cr03  +  6HC1  +  3C2H60  =  Cr2Cl6  (green)  +  6H20  +  3C2H40. 

Alcohol  may  also  be  recognised  by  the  production  of  acetic  acid  when  its  vapour 
is  mixed  with  air  and  exposed  to  the  action  of  platinum-black,  which  acts  by 
favouring  oxidation  ;  C2H60  +  02  =  C.2H402  (acetic  acid)  +  H20.  If  a  small  beaker 
be  wetted  with  alcohol  and  inverted  over  a  watch-glass  containing  a  few  grains 
of  platinum  black,  the  liquid  will  soon  become  acid  to  litmus. 

In  contact  with  air  and  heated  platinum  alcohol  yields  much  aldehyde,  as  well  a& 
ascetic  acid  (see  Lamp  without  jiame,  p.  506). 

337.  The  usual  method  of  determining  the  strength  of  alcohol  is  to 
take  its  specific  gravity  by  measuring  a  few  cubic  centimetres  of  it  into 
a  light  stoppered  bottle,  the  weight  of  which  has  been  ascertained.  The 
weight  of  i  c.c.  of  the  alcohol  in  grammes  will  be  its  specific  gravity,, 
very  nearly.  Rectified  spirit  has  the  sp.  gr.  0.838,  and  contains  84  per 
cent,  by  weight  of  alcohol ;  proof  spirit  (spiritus  tenuior)  has  sp.  gr.  0.92, 
and  contains  only  49  per  cent,  by  weight  of  alcohol  ;  this  is  the  weakest 
spirit  which  will  answer  to  the  old  rough  proof  of  firing  gunpowder  which 
has  been  moistened  with  it  and  kindled.  Any  spirit  weaker  than  this 
leaves  the  powder  too  wet  to  explode,  and  is  said  to  be  below  proof,  whilst 
a  stronger  spirit  is  termed  over  proof. 

A  spirit  of  30  per  cent,  (or  degrees),  for  example,  over  proof,  is  one 
which  requires  100  measures  of  it  to  be  diluted  with  water  to  130- 
measures,  in  order  to  reduce  it  to  the  strength  of  proof  spirit.  A  spirit 
of  30  per  cent,  below  proof  contains,  in  every  100  measures,  70  measures 
of  proof  spirit.  Some  confusion  occasionally  arises,  in  commerce,  from 
the  practice  of  calling  the  percentage  of  proof  spirit,  in  a  weak  spirit, 
the  percentage  of  alcohol,  which  amounts  to  only  about  half  the  per- 
centage of  proof  spirit.  Ordinary  alcoholic  liquids  must  be  distilled 


MONOHYDRIC  ALCOHOLS.  565 

before  their  alcoholic  strength  can  be  ascertained  by  specific  gravity,  on 
account  of  the  presence  of  sugar,  colouring-matter,  &c. 

A  measured  quantity  of  the  liquid  is  rendered  slightly  alkaline  with  sodium 
carbonate,  to  retain  volatile  acids,  and  distilled  in  a  flask  or  retort  connected  with 
a  good  condenser,  as  long  as  the  distillate  contains  alcohol  ;  usually  one-third  of 
the  bulk  may  be  distilled  over  for  wines,  and  more  for  spirits.  The  volume  of  the 
distillate  is  then  made  equal  to  that  of  the  liquid  before  distillation,  by  adding 
water,  and  the  specific  gravity  is  determined  and  compared  with  a  Table  of 
alcoholic  strengths,  which  has  been  prepared  by  ascertaining  the  sp.  gr.  of  alcohol 
of  various  strengths.  Since  the  volume  of  the  weak  spirit  obtained  is  the  same  as 
that  of  the  original  liquid,  the  percentage  of  alcohol  indicated  by  the  Table  will  be 
that  present  in  the  liquid  under  examination. 

The  weakest  fermented  alcoholic  liquor  is  porter,  which  contains  about  4  per 
cent,  by  weight  of  alcohol  ;  the  strongest  is  port,  which  contains  about  17  per  cent. 
Distilled  spirits  vary  greatly  in  strength,  50  per  cent,  of  alcohol  being  about  the 
average,  though  some  samples  contain  70  per  cent. 

Methylated  spirit  is  a  mixture  of  90  parts  by  weight  of  rectified  spirit  with 
10  parts  of  purified  wood-spirit  added  to  it  by  the  Excise  in  order  to  prevent  its  use 
for  drinking.  It  may  be  distinguished  by  its  odour,  and  by  becoming  red-brown 
with  strong  sulphuric  acid.  Since  wood  spirit  has  proved  an  insufficient  deterrent, 
f  per  cent,  by  vol.  of  mineral  naphtha  (sp.  gr.  o'8)  is  now  also  added  ;  its  presence 
may  be  recognised  by  the  spirit  becoming  turbid  when  mixed  with  water. 

When  vapour  of  alcohol  is  passed  through  a  red-hot  tube,  it  is  decomposed  into  a 
large  number  of  products,  among  which  are  naphthalene,  benzene,  phenol,  aldehyde, 
acetic  acid,  acetylene,  ethene,  marsh  gas,  carbonic  oxide,  and  hydrogen.  A  mixture 
of  one  molecular  weight  of  alcohol  (46)  and  four  molecular  weights  of  water  (72) 
crystallises  at  -34°  C.  When  a  weak  spirit  is  cooled,  ice  separates  until  the  com- 
pound C2H60.4H20  is  left  as  the  unfrozen  liquid,  and  when  the  temperature 
reaches  -34°  it  remains  constant  till  the  whole  has  solidified. 

338.  The  principal  members  of  the  class  of  monohydric  alcohols  derived 
from  the  hydrocarbons  of  the  paraffin  series,  at  present  known,  are  shown 
in  the  following  table  : 

Monohydric  alcohols,  CMH.2rt+j'OH. 


Chemical  Xame. 

Source.* 

Formula. 

Boiling-point.t 

I.  Methyl  alcohol 

Distillation  of  wood   .        -v 

CH3'OH 

66°  C. 

2.  Ethyl          , 

Fermentation  of  sugar 

C2H5'OH 

78°  „ 

3-  Propyl 

„                grapes      . 

C3H/OH 

97°  » 

4.  Butyl           , 

beet  . 

C4H9-OH 

117°  » 

5.  Amyl           , 

„               potatoes  . 

C5Hn-OH 

137°  „ 

6.  Caproyl       , 

grapes       . 

C6H13-OH 

157°  „ 

7.  (Enanthyl  , 

/Distillation  of  castor  oil\ 
(     with  potash    .         .         / 

C7H15'OH 

175°  „ 

8.  Capryl 

Essential  oil  of  hog-weed  . 

C8H17-OH 

191°     » 

9.  Nonvl          , 

Nonane  from  petroleum 

C9H19'OH 

213°     » 

10.  Rutyl 

Oil  of  rue    .... 

C10H21-OH 

1  6.  Cetyl 

Spermaceti. 

CjgHgg'OH 

27.  Ceryl           , 

Chinese  wax 

CasHo-OH 

30.  Melissyl      , 

Bees'  -wax   .... 

CjoH^OH 

The  usual  gradation  in  properties  attending  gradation  in  composition  among  the 
members  of  homol  no-mis  s«rifis.  is  strikinerlv  exemplified  in  the  alcohols.     Ine  first 

seven   members   of   the   series   are   liquid   at   the   ordinary   temperature, 
peculiar  and  powerful  odours,  and   may  be  easily  distilled  unchanged^ 
and   ethyl   alcohols  mix  in  all   proportions  with  water,  but  the  t 

f  Of  the  normal  alcohol  (p.  567). 


Of  the  commonest  isomeride. 


566  WOOD-SPIKIT. 

propyl  achohol,  though  feebly  soluble  in  water,  is  not  so  to  an  unlimited  extent, 
while  butyl  alcohol  is  less  soluble,  and  amyl  alcohol  is  very  sparingly  soluble,  in 
water.  Caproyl  alcohol,  the  next  member,  is  insoluble  in  water,  while  capryl 
alcohol  is  not  only  insoluble,  but  possesses  an  oily  character,  leaving  a  greasy  stain 
upon  paper.  The  three  last  members  in  the  Table  are  solids  of  a  wax-like  character. 
Those  members  of  the  series  of  alcohols  which  may  be  distilled  without  decom- 
posing show  a  nearly  regular  increase  in  the  boiling-point  for  each  addition  of 
CH2  in  the  formula  ;  it  will  be  seen  from  the  Table  that,  excluding  the  difference 
between  methyl  and  ethyl  alcohols,  the  average  difference  in  boiling-point  is 
19.5°  C.  for  each  CH2  added. 

339.  Methyl  alcohol,  CH3'OH,  is  met  with,  in  a  very  impure  state, 
as  wood-spirit,  or  pyroxylic  spirit,  or  pyroligneous  ether,  or  wood-naphtha. 
When  wood  is  distilled,  the  condensed  products  separate  into  two  layers, 
the  lower  of  which  is  wood-tar,  and  the  upper  is  a  mixture  of  water 
with  methyl  alcohol,  pyroligneous  or  acetic  acid,  CH3'CO2H,  acetone, 
CH3-COCH3,  methyl  acetate,  CH3COOCH3,  &c.  On  distilling  this 
upper  layer,  the  portion  collected  below  iooc  C.  contains  these  bodies; 
on  adding  chalk  and  re-distilling,  the  acetic  acid  is  retained  in  the  still 
as  calcium  acetate,  and  the  distillate  is  sold  as  wood-naphtha.  Its  yellow 
colour  is  probably  due  to  pyroxanthin,  and  the  milkiness  produced  by 
adding  water  is  due  to  certain  oily  substances  which  cause  its  peculiar 
odour.  In  order  to  obtain  methyl  alcohol,  the  wood-naphtha  is  distilled 
with  quick-lime  to  remove  water,  and  heated  with  fragments  of  fused 
calcium  chloride,  which  dissolves  in  the  methyl  alcohol  to  form  a 
crystalline  compound,  CaCl2(CH40)4.  This  mixture  is  then  poured  into 
a  retort  placed  in  a  water-bath,  and  heated  to  100°  C.  as  long  as  acetone 
and  methyl-acetate  distil  over.  An  equal  weight  of  water  is  then  added, 
which  decomposes  the  compound  with  Ca012,  and  on  continuing  the 
distillation,  methyl  alcohol  passes  over  accompanied  by  some  water, 
which  may  be  removed  by  contact  with  quick -lirne  and  distillation. 

Methyl  alcohol  is  more  easily  obtained  pure  by  boiling  the  wood- 
naphtha  with  anhydrous  oxalic  acid  in  a  flask  with  a  long  condensing- 
tube,  or  a  reversed  condenser,  until  the  methyl  alcohol  is  converted  into 
methyl  oxalate,  (CO 'OCH^,  which  separates  in  crystals  on  cooling.  The 
crystals  are  collected  on  a  filter,  washed  with  water,  and  distilled  with 
solution  of  potash  ;  (COOCH3)2  +  2KOH  =  (COOK),  +  2(CH3'OH).  The 
methyl  alcohol  distils  over  with  some  water,  which  may  be  removed  by 
quicklime. 

Much  methyl  alcohol  is  now  obtained  by  distilling  the  refuse  of  the  beet-root 
sugar  manufactory,  and  has  become  important  as  the  source  of  many  methyl- 
compounds  employed  in  making  dyes. 

Methyl  alcohol  in  an  impure  state  is  used  as  a  solvent  for  resins  in  making 
varnishes. 

Clean  magnesium  dissolves  in  absolute  methyl  alcohol  even  at  ordinary  tem- 
perature, evolving  hydrogen  and  forming  crystals  of  magnesium  rnethoxide  com- 
bined with  methyl  alcohol  (CH30)2Mg  +  3CH3OH. 

Properties  of  methyl  alcohol. — Much  resembling  ethyl  alcohol,  with  a 
somewhat  different  odour;  sp.  gr.  0*7997  at  16°  C.,  b.-p.  66°  C. ; 
rn.-p.  -  95°  C.,  very  inflammable,  burning  with  a  pale  flame.  In 
presence  of  air  and  platinum-black,  yields  formic  aldehyde  (HCHO)  and 
formic  acid  (HC02H) ;  CH3OH  +  02  =  HC02H  +  H2O.  The  formic  acid 
may  be  distinguished  from  acetic  by  its  property  of  reducing  silver 
ammonio-nitrate  to  the  metallic  state  when  warmed  with  it.  Hence, 
methyl  and  ethyl  alcohols  may  be  distinguished  by  distilling  them  with 


ISOMERIC   ALCOHOLS. 


567 


dilute  sulphuric  acid  and  potassium  dichromate,  when  the  former  yields 
formic  and  the  latter  acetic  acid. 

A  suitable  apparatus  for  distilling  small  quantities  of  liquids  in  making  such 
tests  is  shown  in  Fig  268.  The  condenser  consists  of  a  vessel  containing  cold 
water  and  surrounded  by  a  jacket,  the 
lower  part  of  which  terminates  in  a 
tube.  The  vapour  entering  by  the 
side  tube  condenses  within  the  jacket. 

340.  Isomerism  among  the 
monohydric  alcohols,  —  Since 
methyl  and  ethyl  alcohols  are 
mono  -  substitution  derivatives 
from  methane  and  ethane  re- 
spectively, it  is  riot  surprising 
that  no  position  isomerides  of 
these  compounds  are  known 
(see  p.  542).  It  has  already 
been  noticed  that  two  mono- 
substitution  derivatives  of  pro- 
pane are  possible,  namely,  those 
which  have  the  substituent 
attached  to  the  end  of  the  three  - 
carbon-chain,  and  those  in  which 
the  substituent  is  attached  to 
the  centre  carbon  atom  ;  the 
former  kind  is  known  as  the  normal  propyl  derivative,  the  latter  as  the 
isopropyl  derivative.  Thus,  the  general  formula  for  a  normal  propyl 
derivative  is  CH3'CH2-CH.,X',  whilst  that  for  an  isopropyl  derivative 
is  CH3-CHX'-CH3  or  X'CH:(CH3)2.  Hence  there  is  a  normal  propyl 
alcohol  and  an  isopropyl  alcohol, 

Since  butane  may  be  regarded  as  methylpropane  (a  mono-substitution 
product  of  propane)  it  may  be  expected  to  exist  in  two  modifications 
(P-  532)-  The  first  of  these,  normal  butane,  can  yield  two  mono-substi- 
tution derivatives,  viz.,  CH3-CH2'CH2'CH2X'  and  CH3'CH2'CHX'-CH3; 
whilst  the  second,  secondary  butane,  can  also  yield  two  mono-substitution 
derivatives,  viz.,  (CH3)2  :  CH«CH2X'  and  (CH3)2  :  CX'-CH3.  Hence 
there  should  be  four  butyl  alcohols. 

Pentane  is  methylbutane,  but  it  only  exists  in  three  —  instead  of  four 
—  modifications  (p.  519)  because  the  methylbutanes  corresponding  with 
the  second  and  third  formulas  given  above  would  have  the  same  struc- 
ture. By  writing  the  formulas  for  a  mono-substitution-product  of  pen- 
tane,  it  will  be  found  that  eight  different  compounds  are  possible,  and 
in  many  cases  eight  are  known  ;  eight  pentyl  (amyl)  alcohols,  for  instance. 

All  these  isomeric  alcohols  are  divided  into  three  classes  as  follows  : 
(i)  Those  in  which  the  OH  group  is  attached  to  a  carbon  atom,  which  is 
itself  attached  to  only  one  other  carbon  atom  ;  these  are  called  primary 


Fig.  268. 


alcohols  and  contain  the  group  - 


OH 


(2)  Those  in  which  the  OH 


group  is  attached  to  a  carbon  atom,  which  is  itself  attached  to  two  other 
carbon  atoms  ;  these  are  called  secondary  alcohols,  and  contain  the  group 

:C/H    .     (3)  Those  in  which  the  OH  group  is  attached  to  a  carbon 
OH 


568  PRIMARY,    SECONDARY,    AND   TERTIARY  ALCOHOLS. 

atom,   itself   attached  to  three  other  carbon  atoms  ;  these  are  called 
tertiary  alcohols,  and  contain  the  group  i  OOH. 

The  following  list  of  alcohols  will  furnish  examples  of  the  three 
classes  : 

Methyl  alcohol  ....     H'CH2OH  Primary. 

Ethyl  alcohol      ....     CH3'CH2OH  Primary. 

Normal  propyl  alcohol        .         .     CH3'CH2-CH2OH  Primary. 

Isopropyl  alcohol        .         .         .     (CH3)2  :  CHOH  Secondary. 

Normal  butyl  alcohol          .         .     CH3-CH2'CH2-CH2OH  Primary. 

Primary  isobutyl  alcohol    .         .     (CH3)2  :  CH'CH2OH  Primary. 

P  FT  •  C1-  FT 

Secondary  butyl  alcohol                    '    3  ^TT2\CHOH  Secondary. 


Tertiary  butyl  alcohol         .         .     (CH3)3  \  COH  Tertiary. 

Of  the  eight  pentyl  alcohols,  4  are  primary,  3  secondary,  and  I  tertiary. 

Greater  facility  in  naming  these  numerous  compounds  is  attained  by  taking 
methyl  al'cohol  or  carbinol  as  the  starting-point,  and  supposing  the  alcohols  to 
be  derived  from  it  by  substitution  of  alcohol  radicles  for  the  hydrogen  in  the 
methyl  group.  Then,  the  primary  alcohols  will  be  mono-substitution  derivatives 
of  carbinol,  as  shown  in  the  following  formula;  : 

Carbinol,  CH3'OH.  Primary  propyl  alcohol,  or  ethyl  carbinol,  CH2(C2H5)-OH. 
Primary  butyl  alcohol,  or  propyl  carbinol,  CH2(C3H7)'OH.  Primary  iso-butyl  alco- 
hol, or  iso-propyl  carbinol,  CH2(C3HT)'OH  (the  difference  here  consisting  in  propyl, 
CH2(CH2CH3),  formed  by  the  methylation  of  ethyl,  CH2(CH3),  and  iso-propyl, 
CH(CH3)2,  formed  by  the  di-methylatlon  of  methyl. 

The  secondary  alcohols  may  be  regarded  as  di-substitution-products  of  carbinol  ; 
secondary  propyl  alcohol  or  dimethyl  carbinol,  CH(CH3)2'OH,  is  evidently  iden- 
tical with  iso-propyl  alcohol.  Secondary  butyl  alcohol  is  ethyl  methyl  carbinol, 
CH(C2H5)(CH)3'OH.  Secondary  amyl  alcohol  is  methyl  propyl  carbinol  — 

CH(CH3)(C3H7)-OH. 

Another  secondary  amyl  alcohol  is  di-ethyl  carblnol,  CH(C2H5)2'OH.  The  tertiary 
alcohols  would  be  tri-substitution-products  of  carbinol.  Tertiary  butyl  alcohol  is 
trimethyl  carblnol,  CfCHoVOH.  Tertiary  pentyl  alcohol  is  ethyl  dimeth  ill  carbinol. 
C(C2H5)(CH3)2-OH.* 

The  three  classes  of  alcohols  are  distinguished  by  their  behaviour 
under  the  action  of  oxidising-agents,  which  also  serves  to  settle 
their  constitution.  When  oxidised,  a  primary  alcohol  yields  an 
aldehyde,  and  ultimately  an  acid,  containing  the  same  number  of 

carbon  atoms  as  the  alcohol  ;  thus,  ethyl  alcohol,  CH3'C^    2  ,  yields 

OH 

ethyl  aldehyde,  CILO^     ,  and  acetic  acid  OIL'Cx  A  secondary 

XH  XOH 

alcohol  ytelds  a  ketone  containing  the  same  number  of  carbon  atoms  ; 

thus,  secondary  propyl  alcohol,  (CH3)2  :  C/       ,  yields  di-methyl  ketone, 

H 

(CH3)2  :  C  :  0  ;  a  tertiary  alcohol  is  either  broken  up  into  two  or  more 
acids  containing  less  carbon,  or  it  may  yield  a  ketone  containing  one 
atom  less  carbon  than  itself,  the  atom  of  carbon  being  oxidised  to 
carbonic  or  formic  acid  ;  thus,  tertiary  butyl  alcohol,  C(CH3)3'OH  yields 
acetone,  (CH8)3  :  CO,  and  formic  acid,  H'COOH. 

Another  method  for  distinguishing  between  a  primary,  secondary,  and  tertiary 
alcohol  is  as  follows  :  The  alcohol  is  converted  into  the  corresponding  iodide  by 

*  According-  to  another  system,  the  alcohols  are  named  by  adding  -ol  to  the  name  of  the 
parent  hydrocarbon  ;  thus  CH3'OH  is  methanol,  C.HyOH  is  propanol.  Tolyhydric  alcohols 
are  distinguished  as  diols,  tr/ol8,>&c.  ;  CHaOH'CH8OH  is  ethanedtol,  CH2OH'CHOH-CH2OH 
is  propanetriol,  CH2OH'CH2-CH2OH  is  n^ropanediol. 


GENERAL  METHOD  FOR  PREPARING  ALCOHOLS.      569 

distilling  with  iodine  and  phosphorus  (see  ethyl  iodide)  ;  the  iodide  is  distilled  with 
.a  mixture  of  silver  nitrite  with  dry  sand  (to  dilute  it),  when  the  corresponding 
nitro-paraffin  is  obtained  ;  thus  ethyl  iodide  yields  nitro-ethane  (C2H5N02)— 

CH3-CH2-I  +  AgN02  =  CH3-CH2-N02  +  Agl. 

The  distillate  is  mixed  with  potassium  nitrite  and  weak  potash,  and  dilute 
sulphuric  acid  is  gradually  added  ;  if  the  alcohol  be  primary,  a  red  solution  of 
the  corresponding  potassium  nitrolate  will  be  obtained,  the  nitro-paraffin  having 
been  converted  into  the  corresponding  nitrolic  acid  by  the  nitrous  acid  ;  thus, 
nitro-ethane  yields  nitrolic  acid  — 

CH3-CH2-N0.2  +  HN02=  CH3-C(N02)  :  NOH  +  H20. 

Nitrolic  acids  are  colourless,  but  their  alkali  salts  have  a  dark  red  colour  ;  they 
•are  very  unstable,  being  decomposed  into  nitrous  oxide  and  a  fatty  acid  ;  thus 
nitrolic  acid  yields  nitrous  oxide  and  acetic  acid.  If  the  alcohol  be  secondary,  a 
blue  solution  of  a  pseudonitrol  will  be  obtained  ;  thus  secondary  amyl  alcohol, 
CH(CH3)(C3H7)-OH,  would  yield  the  secondary  nitro-paraffin,  CH(CH3)(C3H7)-N02. 
which  would  be  converted  by  HN02  into  the  pseudonitrol,  C(NO)(CH3)(C3H7)'N02, 
.giving  a  blue  solution.  If  the  alcohol  be  tertiary,  no  colour  is  produced,  the 
tertiary  nitre-paraffins  being  unattacked  by  nitrous  acid. 

The  simplest  general  method  for  preparing  tlie  alcohols  consists  in 
treating  the  corresponding  halogen  substitution  derivatives  of  the 
hydrocarbons  with  moist  silver  oxide,  which  behaves  as  if  it  were  AgOH  ; 
thus,  if  normal  butyl  bromide  be  so  treated,  it  yields  normal  butyl 
alcohol,  CH3-CH2-CHvCHaBr  +  AgOH  =  CH3-CH,-CH/CH,OH  +  AgBr. 
The  secondary  bromide,  "CH3-CH8-CH2BrCH3,  yields  the  secondary 
alcohol.  The  tertiary  bromide  yields  the  tertiary  alcohol. 

As  the  alcohols  form  the  basis  for  the  production  of  a  large  number 
of  compounds  on  the  small  scale,  their  general  reactions  will  be  best 
understood  when  these  other  compounds  are  considered.  Here  it  need 
only  be  mentioned  that  they  dissolve  alkali  metals  with  evolution  of 
hydrogen,  forming  the  corresponding  metallic  alkyloxide  or  alcoholate, 
like  aE 


341.  JVorwal  propyl    alcohol,  or  ethyl  carbinol,  C3H7'OH,  or  C2H5-CH2'OH,   is 
'found  in  the  latter  portions  of  the  distillate  obtained  in  rectifying  crude  spirit  of 
wine.     It   smells  like  ialcohol,  has  the    sp.  gr.  0.804,  and  boils  at  97°  c-    When 
mixed  with  water  it  may  be  separated  by  saturating  with  calcium  chloride,  when 
the  propyl  alcohol  rises  to  the  surface,  which  would  not  be  the  case  with  ethyl 
alcohol.     When  oxidised,  it  yields  propionic  aldehyde,  C2Hg'CHO,  and  propionic 
•acid,  C2Hg-C02H.     Iso-propyl  alcohol  boils  at  83°  C.,  and  is  obtained  by  reducing 
acetone  with  nascent  hydrogen. 

The  butyl  alcohol.  C4H9'OH,  originally  so  called,  and  mentioned  in  the  table  at 
p.  565  as  obtained  by  the'  fermentation  of  beet-root,  and  also  by  the  distillation  of 
crude  spirits,  is  now  called  fermentation  butyl  alcohol,  or  primary  isobutyl  alcohol. 
to  distinguish  it  from  the  normal  butt/I  alcohol,  which  is  the  real  member  of  this 
homologous  series  of  alcohols.  Fermentation  butyl  alcohol  boils  at  108  C.,  and 
smells  of  fusel  oil,  which  often  contains  it.  It  has  sp.  gr.  0.802,  and  is  much  lett 
soluble  in  water  than  propyl  alcohol  is,  requiring  ten  times  its  weight  to  dissolve 
Most  salts  soluble  in  water  cause  it  to  separate  on  the  surface  of  the  I"!"1.*}- 
Normal  butyl  alcohol,  or  prop  t/  1  carbinol,  C3H7'CH2-OH,  has  sp.  gr.  0.810,  and  boih 
at  117°  C.  It  is  obtained  by  acting  upon  butyl  aldehyde  with  water  and  s 
amalgam,  to  furnish  nascent  hydrogen,  C3H/CHO  +  H2  =  C3H/CH2'OH. 

342.  The  history  of  amyl  alcohol  resembles   that  of  butyl  alcohol,  the  i 
having  been  originally  given  to   the  well-known  offensive   and  poisonous  Liqul< 
called  fusel  oil,  obtained  in  the  distillation  of  spirits  from  fermented  gram  or 
potatoes.     This  contains,   however,  at  least  two  isomenc  alcohols,  vix.,  <*">'•  "//' 
tarbinol,  (CH3)a  :  CH'CH2-CH2'OH  (b.-p.  131°  C),  WOOL  secondary  butyl  (o 

carbinol,  °H3)>CH-CH2OH  (b.-p.  127°  C.)  ;  this   latter  is  optically  art  ire,  for  it 

contains  an  asymmetric  carbon  atom  (see  xteren-i*onieri*m').     Fusel   oil   has  the 
sp.  gr.  0.83,  and  is  so  sparingly,  soluble  in  water  that  it  separates  from  it 


570          OLEFINE  AND  ACETYLENE  ALCOHOLS. 

in  distilled  spirits  on  dilution  with  water,  rendering  the  liquid  turbid.  Its  odour 
is  very  characteristic,  and  the  vapour  occasions  coughing  and  a  sensation  of 
swelling  of  the  head. 

On  writing  the  formula;  for  the  possible  amyl  alcohols,  it  will  be  found  that  4 
are  primary,  3  secondary,  and  I  tertiary,  and  that  3  of  them  have  an  asymmetric 
carbon  atom,  so  that  each  exists  in  a  Ia3vo-.  dextro,  and  inactive  form  making. 
14  amyl  alcohols  in  all. 

Tertiary  amyl  alcohol,  dimethylethyl  carlinol,  (CH3)2C2H5COH,  is  a  liquid 
(b.-p.  102°  C)  smelling  of  camphor,  and  used  as  a  substitute  for  chloral  as  a 
narcotic  ;  it  is  prepared  from  the  amyl  alcohol  of  fusel  oil. 

343.  Normal  hexyl  alcohol,  CgH^CIL/OH,  boiling  at  157°  C.,  is  not  that  pro- 
duced by  fermentation,  but  is  obtained  from  the  essential  oil  of  an  umbelliferous 
plant,  Heracleumgiganteum,  which  contains  hexyl  butyrate,  and  yields  the  alcohol 
when  distilled  with  potash,  C3H/COOC6H13+KOH  =  C6H13-OH  +  C3H7-COOK. 

The  fermentation  hexyl  alcohol,  or  caproyl  alcohol  (b.-p.  150°  C.),  is  that  obtained 
by  distilling  fermented  grape-husks  ;  it  has  a  more  unpleasant  smell  than  the 
normal  alcohol. 

Normal  capryl  or  octyl  alcohol,  C8H17'OH,  is  obtained  from  the  essential  oil  of 
the  cow-parsnip  or  hog-weed  (Heracleum,  spondyliuni),  an  umbelliferous  plant,  by 
distilling  it  with  potash,  which  decomposes  the  octyl  acetate,  of  which  the  oil 
chiefly  consists,  CH3-COOC8H17  +  KOH  =  C8H17'OH  +  CH3'COOK  (potassium  acetate). 
It  has  the  sp.  gr.  0.83,  and  boils  at  199°  C. 

Cetyl  alcohol,  C16H33'OH,  or  ethal,  is  obtained  from  spermaceti,  found  in  the 
brain  of  the  sperm-whale.  This  substance  is  cetin  or  cetyl  palmitate,  and  when 
boiled  for  some  time  with  potash  dissolved  in  alcohol,  it  yields  cetyl  alcohol  and 
potassium  palmitate;  C15H31-COOC16H33  +  KOH  =  C16H33-OH  +  C15H31'COOK.  On 
mixing  the  alcoholic  solution  with  water,  the  cetyl  alcohol  is  precipitated  in  the 
solid  state,  being  insoluble  in  water.  Cetyl  alcohol  is  a  crystalline  body,  fusing  at 
4O°.5  C.,  and  boiling  at  344°  C. 

Ceryl  alcohol,  C27H55'OH,  is  prepared  from  Chinese  ivax,  the  produce  of  an 
insect  of  the  cochineal  tribe.  It  consists  chiefly  of  cerotln  or  ceryl  cerotate^ 
CaeHgg'COOC^Hgg,  and  when  fused  with  potash  gives  ceryl  alcohol  and  potassium 
cerotate.  By  treating  the  fused  mass  with  water,  the  cerotate  is  dissolved,  and  the 
ceryl  alcohol  is  left,  and  may  be  obtained  in  crystals  by  dissolving  it  in  ether.  Its 
f  using-point  is  79°  C.  It  occurs  in  flax.  Kecent  analyses  seem  to  show  that  ceryl 
alcohol  is  C^H^OH. 

Melissyl  alcohol,  or  myricyl  alcohol,  C30H61'OH,  is  derived  from  bees' -wax .  When 
this  is  boiled  with  alcohol,  about  one-third  of  its  weight  is  left  undissolved  ;  this 
is  myricin  or  mellissyl  palmitate,  C15H31'COOC30H61.  When  fused  with  potash  it 
yields  potassium  palmitate  and  melissyl  alcohol,  which  is  a  crystalline  substance, 
fusing  at  85°  C. 

344.  Monohydric   Alcohols    of    the    Oleflne   and    Acetylene 
Series. — These  may  be  regarded  as  formed  from  the  olefine  and  acetylene 
hydrocarbons  in  the  same  manner  that  the  ordinary  alcohols  are  derived 
from  the  paraffin  hydrocarbons.     They  therefore  correspond  with  the 
general    formulae    C^Haj^OH    and    CnH2B_3OH.      Those    which    are 
known  are  primary  alcohols  ;  thus,  allyl  alcohol  is  CH2 :  CH'CH,OH, 
derived  from  propylene.     The  alcohol  from  ethylene,  CH., :  CH'OH,  is  a 
secondary  alcohol  (vinyl  alcohol)  and  probably  exists  in   crude  ether, 
but  it  cannot  be  isolated  because  it  is  immediately  transposed  into 
aldehyde,  CH3'CHO  ;  this  is  in  accord  with  other  experience  of  the 
grouping  :  0  :  OHOH,  which  is  always  found  to  be  unstable. 

The  alcohols  of  these  two  classes  are,  of  course,  unsaturated  compounds, 
and  readily  combine  with  H  to  form  the  alcohols  of  the  preceding 
class. 

Allyl  alcohol,  C3H5'OH,  or  CH2  :  CH'CH2OH,  is  obtained  by  heating  four  parts  of 
glycerol  with  one  part  of  crystallised  oxalic  acid  in  a  retort  at  195°  C.,  so  long 
as  water  passes  over,  and  afterwards  raising  the  temperature,  when  the  allyl  alcohol 
distils  (addition  of  a  little  NH4C1  facilitates  the  change).  The  glycerol  is  first 
converted  into  monoformin — 


AROMATIC  ALCOHOLS. 


571 


CH2OH-CHOH-CH,OH  +  (COOH)2  -  CH2OH'CHOH'CH2(OCHO)  +  C02  +  H20. 
The  monoformin  is  then  decomposed  into  allyl  alcohol,  C09  and  H00  • 
CH2OH-CHOH-CH2(OCHO)  =  CH2  :  CH-CH2OH  +  H20  +  c62. 

It  has  a  pungent  smell,  sp.  gr.  0*87,  b.-p.  96°. 6  C.  By  very  careful  oxidation  it 
yields  glycerol,  but  when  oxidised  by  Ag20  it  yields  acrylic  aldehyde  or  acrolein, 
CH2  :  CH-CHO,  and  acrylic  acid,  CH2  :  CH'COOH.  This  shows  it  to  be  a  primary 
alcohol.  Crude  wood  spirit  contains  a  little  allyl  alcohol. 

Propargyl  ov  propinyl  alcohol,  C3H3-OH,  or  CH  •  C'CH2OH,  is  the  alcohol  corre- 
sponding with  allylene.  It  is  obtained  by  boiling  bromallyl  alcohol  (itself  obtained 
by  a  somewhat  intricate  process),  CH2 :  CBrCH2OH,  with  KOH ;  CH2 :  CBrCH2OH 
+  KOH  =  CH  :  C  -CH2OH  +  KBr  +  HOH.  It  is  a  fragrant  liquid  of  sp.  gr.  0.97  and 
b.-p.  115°  C. ;  it  burns  with  a  luminous  flame.  Since  it  contains  the  CH  :  C. 
group,  it  is  capable  of  yielding  metallic  derivatives  ;  cuproso-propargyl  alcohol, 
CCu  :  C  :CH2OH  is  a  green  precipitate. 

345.  Monohydric  Alcohols  of  the  Benzene  Hydrocarbons. — 

It  would  seem  at  first  sight  as  though  the  hydroxyl  compound  produced 
by  introducing  OH  in  the  place  of  one  of  the  H  atoms  of  benzene  should 
be  an  alcohol.  If  the  structure  of  benzene  be  correctly  represented  by 
the  benzene  ring,  however,  this  alcohol  would  partake  of  the  nature  of  a 
tertiary  alcohol,  since  the  OH  would  be  combined  to  a  carbon  atom 
itself  attached  by  three  atom-fixing  powers  to  two  other  carbon  atoms. 
As  a  fact,  however,  the  hydroxy-substitution-products  of  the  benzene 
hydrocarbons  cannot  be  classed  with  the  alcohols  when  the  substitution 
occurs  in  the  benzene  nucleus.  Such  compounds  as  C6H5(OH),C6H4(OH)2, 
06H4(OH)(CH3),  differ  to  such  an  extent  from  the  alcohols  that  they  are 
classed  apart  as  phenols. 

Only  such  hydroxy-derivatives  of  benzene  hydrocarbons  are  alcohols 
(aromatic  alcohols)  as  have  OH  substituted  for  H  in  the  side-chain  ;  thus, 
whilst  C6H4(OH)CH3  is  a  phenol,  its  isomeride,  C6H,-CH2OH,  is  a 
primary  alcohol,  and  may  be  termed  benzyl  alcohol  or  phenyl  carbinol 
(p.  568).  Secondary  alcohols,  e.g.,  C6H5'CHOH-CH3  (from  ethyl  ben- 

/CH3 

zene),    and  tertiary    alcohols,  e.g.,    C6H5'C(OH)^  ^        (from  isopropyl 

CH3 

benzene),  also  exist,  as  in  the  paraffin  series.  For  every  alcohol  there  is 
an  isomeric  phenol,  and  it  is  possible  to  have  a  phenol-alcohol,  e.g., 
C6H4(OH)-CH2OH  (from  hydroxy toluene),  or  any  other  substituted 
aromatic  alcohol  (Fig.  269). 


a 


OH 


Ben/yl  alcohol         Orthohydroxytolueue  Orthohydroxybenzyl 

C6H5  CH2OH.  (a  phenol).  alcohol  (a  phenol-alcohol). 

Fig.  269. 

Like  the  paraffin  alcohols,  the  aromatic  alcohols  may  be  prepared  from 
the  halogen  substituted  hydrocarbons  by  the  action  of  moist  silver  oxi 
or  an  alkali,  but  the  substituted  halogen  must,  of  course,  be  in  the  sid 
chain,  e.g.,  C6H3'CH2C1  (benzyl  chloride). 


Benzyl  alcohol,  or  phenylcarbinol,  C6H5'CH2OH,  may  be  obtained  from  t^i:yl 
aldehyde    (bitter-almond    oil)   by   the   action   of   reducing-agents  ;    since    Denz 
aldehyde  is  itself  capable  of  undergoing  oxidation,  it  is  possible  to  o 


572  MERC  APT  AN. 

reduction  product,  benzyl  alcohol,  and  its  oxidation-product,  benzoic  acid,  by  heat- 
ing it  with  alcoholic  potash  ;  2C,.H5-CHO  +  KOH  =  C6H5-CH2OH  ^-C6H5'COOK. 

It  can  also  be  made  from  benzoic  acid  by  the  action  of  nascent  H,  generated  by 
•adding  Na-amalgam  to  a  boiling  solution  of  the  acid  ;  C6H5'COOH  +  H4  = 
C6H5'CH2OH  +  H2O.  The  balsams  of  Tolu  and  of  Peru  and  storax  yield  benzyl 
alcohol  when  distilled  with  alkalies  which  decompose  the  benzyl  benzoate. 
C6H5'COO(C6H5CH2),  and  cinnamate  contained  in  them. 

Benzyl  alcohol  is  an  oily  liquid  heavier  than  water  (sp.  gr.  1.06),  boiling  at 
206°  C.  Oxidising-agents  convert  it  into  benzaldehyde  and  benzoic  acid,  proving 
it  to  be  a  primary  alcohol. 

Salicyl  alcohol,  or  hydroxybenzyl  alcohol,  C6H4(Ofl)-CH2OH,  shows  the  properties 
of  a  phenol  (#.r.)  as  well  as  those  of  a  primary  alcohol,  and  is  a  type  of  the  phenol 
alcohols.  It  is  a  di-substituted  benzene,  and  therefore  exists  in  three  isomeric 
forms.  The  i  :  2-derivative  was  first  called  saligenin,  made  from  salicin,  a  crystal- 
line substance  extracted  from  willow-bark.  This  substance  is  a  glucoside,  and 
when  hydrolysed  (p.  265)  yields  glucose  (C6H1006)  and  salicyl  alcohol ; 

C6H4(OC6Hn05)-CH2OH  +  HOH  -  C^O^GH)  +  C6H4(OH)-CH2OH. 
I   :  2-salicyl    alcohol  forms   tabular  crystals,  soluble  in    hot  water,  alcohol,  and 
ether,  fusing  at  82°  C.  and  subliming  at  100°  C.     When  oxidised  it  yields  salicyl 
•aldehyde,  C6H4(OH)  -CHO,  and  salicylic  acid,  C6H4(OH)'COOH.    It  gives  an  intense 
blue  colour  with  ferric  chloride  (cf.  Phenol*). 

Cinnatnyl  alcohol  is  the  primary  alcohol  corresponding  with  the  unsaturated 
hydrocarbon  cinnamene  (p.  550)  ;  its  formula  is  C6H5'CH  :  CH'CH2OH,  phenyl 
ally  I  alcohol.  It  also  is  obtained  from  storax-,  a  fragrant  balsam  exuded  by  the 
Styrax  officinale,  a  tree  found  in  Syria  and  Arabia,  sometimes  used  as  a  pectoral 
remedy.  When  this  is  digested  for  some  hours  with  a  weak  solution  of 
soda,  and  the  residue  extracted  with  a  mixture  of  ether  and  alcohol,  needle- 
like  crystals  of  styracin  are  obtained.  This  substance  is  cinnamyl  cinnamate, 
C6H5'CH  :CH-COO(C6H5-CH  :  CH'CH2),  and  yields  cinnamyl  alcohol  and  potassium 
cinnamate  when  distilled  with  KOH  ;  C9H9-C9H702  +  KOH  =  C9H9'OH  +  KC9H70.2. 

The  alcohol  smells  of  hyacinths,  melts  at  33°  C.  and  boils  at  250°.  It  dissolves 
sparingly  in  water,  but  easily  in  alcohol  or  ether.  When  oxidised  it  yields 
cinnainic  aldehyde  and  cinnamic  acid. 

Alcohols  of  the  hydrocarbons  containing  more  than  one  benzene  nucleus  are  of 
minor  importance.  Diplienylcarbinol  (Jbenzhydrol),  (C6H5)2CH.OH,  is  a  secondary 
alcohol  obtained  by  reducing  benzophenone  (</.'•.)  ;  it  melts  at  68°  C. 

Triphewylearbvnol,  (C6H5)3C.OH,  is  a  tertiary  alcohol,  important  from  its 
relation  to  the  "  aniline  dyes."  It  is  formed  by  oxidising  triphenylmethane 
•(P-  ^550  with  chromic  acid  in  glacial  acetic  acid,  melts  at  159°  and  boils  at  360°  C. 

Naphthalene  and  anthracene  alcohols  also  exist. 

346.  Thio-alcohols  or  mercaptans  are  analogous  to  the  alcohols,  but  contain  S  in 
place  of  O,  and  as  the  latter  are  hydroxides  of  the  alcohol  radicles,  so  the 
thio-alcohols  (R'SH)  are  the  hydrosulphides.  The  thw-etherx,  R2S,  or  sulphides  of 
the  alcohol  radicles,  may  also  be  considered  here  ;  they  are  the  analogues  of  the 
ethers,  R20. 

Mercaptan,  C2H5'SH,  was  named  from  its  remarkable  action  on  mercury  com- 
pounds (mercurio  upturn).  It  is  made  (for  making  sulphonal)  by  distilling  KSH 
with  C2H5C1  in  alcoholic  solution,  or.  on  a  smaller  scale,  with  calcium  sulphethy- 
late  (q.v.) :— Ca(C2H5S04)2  +  2KSH  =  CaS04  +  K2S04  +  2(C2H5'SH). 

A  solution  of  KSH  is  made  by  saturating  potash  of  sp.  gr.  1.3  with  H2S,  and  this  is 
distilled,  in  a  salt-and-water  bath,  with  an  equal  volume  of  solution  of  calcium 
.sulphethylate  of  sp.  gr.  1,3.  The  mercaptan  forms  the  upper  layer  of  the  distillate, 
and  is  characterised  by  its  powerful  smell  of  garlic.  It  is  a  volatile  liquid,  of 
sp.  gr.  0.835,  and  boils  at  36°  C.  A  drop  exposed  to  the  air  is  frozen  to  a  crystal- 
line mass  by  its  own  evaporation.  It  burns  with  a  blue  flame.  Mercaptan  i.s 
sparingly  soluble  in  water,  but  dissolves  in  alcohol  and  ether.  It  is  unaffected  by 
•caustic  alkalies,  but  alkali  metals  act  on  it  as  in  the  case  of  alcohol,  displacing 
hydrogen  and  forming  mercaptides,  e.g.,  C2H5'SK,  which  are  crystalline  bodies 
soluble  in  water. 

Mercuric  oxide  evolves  much  heat  with  mercaptan,  forming  a  white  crystalline 
inodorous  compound  ;  HgO  +  2(C2H5-SH)  =  H2O  +  (C2H5S)2Hg  (mercuric*  mercap? 
tide).  This  is  insoluble  in  water,  but  may  be  crystallised  from  alcohol,  or  from 
strong  HC1.  Potash  doos  not  decompose  it.  H2S  converts  the  mercury  into 
sulphide  and  reproduces  mercaptan.  Mercaptides  (thio-etlwxides)  of  other 


GLYCOLS. 

metals    may  be   precipitated   by    metallic    salts   from   an   alcoholic    solution   of 
mercaptan. 

By  distilling  mercuric  thio-ethylate,  di-ethyl  sulphide  or  thw-ether,  C,H  -S'C  H 
maybe  obtained;  (C2H6S)2Hg  =  (C2H5)2S  +  HgS.  This  may  also  be  prepared2  by 
distilling  potassium  sulphethy late  with  potassium  sulphide;  2KC0H5SO;  +  K.,S  = 
2K2S04  +  (CoH5)2S.  It  resembles  mercaptan,  but  boils  at  91°  C."  Its  alcoholic 
solution  gives,  with  mercuric  chloride,  a  white  crystalline  precipitate  of 
(C2H5)2S-HgClo. 

Allyl  sulphide,  (C3H5)2S,  is  the  main  constituent  of  essential  oil  of  garlic,  and 
occurs  in  several  cruciferous  plants.  It  boils  at  140°  C.,  dissolves  sparingly  in 
water,  and  behaves  like  ethyl  sulphide. 

Ethyl  duulphide,  (C2H5)2S2,  is  obtained  when  potassium  disulphide  and  sul- 
phethylate  are  distilled.  It  may  also  be  formed  by  heating  mercaptan  to  150°  C. 
with  sulphur;  2(C2H5SH)  +  S2=(C2H5)2S2  +  H2S  ;  or  by  decomposing  sodium  mer- 
captide  with  iodine  ;  2(C2H5SNa)  + 12  =  2NaI  +  (C2H5)2S2.  It  is  an  alliaceous  liquid, 
boiling  at  151°  C.  Ethyl  sulphoxide,  (C2H5).2OS,  is  a  syrupy  liquid  resulting  from 
the  action  of  dilute  nitric  acid  on  ethyl  sulphide. 

Ethyl  sulphone,  (C2H5)2SO2,  is  a  very  stable  crystalline  body  formed  when  ethyl 
sulphide  is  oxidised  by  strong  nitric  acid  ;  it  fuses  at  70°  C.  and  boils  at  248°  C.r 
but  sublimes  at  100°  C.  It  is  soluble  in  water  and  alcohol. 

When  ethyl  sulphide  and  ethyl  iodide  are  heated  together  with  a  little  water 
for  some  hours  in  a  flask  with  an  inverted  condenser,  the  mixture,  on  cooling,, 
deposits  colourless  prisms  of  tri-ethyl-sulphine  iodide,  (C2H5)3S'I,  which  are  soluble 
in  water  and  alcohol,  but  insoluble  in  ether.  This  compound  is  remarkable  for 
producing  a  series  of  compounds  in  which  the  iodine  may  be  exchanged  for  other 
chlorous  radicles,  giving  rise  to  tri-etht/l-sulphine  salts,  in  which  the  S  is  quad- 
rivalent ;  thus,  in  the  iodide,  it  is  attached  to  four  monad  radicles,  viz.,  (C2H5)o 
and  I.  By  decomposing  the  iodide  with  silver  hydroxide,  the  tri-ethyl-fidpkine 
]tydro,vide,  (C2H5)3S'OH,  is  obtained  ;  it  is  a  deliquescent  crystalline  body  pos- 
sessing the  properties  of  a  powerful  caustic  alkali. 

Compounds  similar  to  the  foregoing  have  been  obtained  from  the  alcohols  formed 
by  the  other  radicles  of  this  series. 

347.  Dihydric  Alcohols,  or  Glycols. — The  dihydric  alcohols  may 
be  regarded  as  derived  from  the  saturated  hydrocarbons  by  the  substitu- 
tion of  hydroxyl  groups  for  two  H  atoms  ;  equally  well,  they  may  be 
said  to  be  olefine  hydrocarbons  which  have  combined  with  two  hydroxyl 
groups,  and  this  is  the  view  expressed  by  their  nomenclature  ;  ethylene 
glycol,  C.,H4(OH).,,  and  propylene  glycol,  C3H6(OH)2,  are  examples.  Like 
the  monohydric  alcohols,  a  general  method  for  their  preparation  consists 
in  the  treatment  of  the  corresponding  bromo- derivatives  with  alkalies, 
or,  what  is  equivalent,  an  alkali  carbonate,  or  lead  hydroxide,  and 
water. 

The  simplest  glycol  would  be  CH9(OH)2  from  methane  ;  but  this  has 
never  been  isolated,  and  it  appears  "to  be  a  fact  that  no  compound  can 
exist  which  has  two  hydroxyl  groups  attached  to  one  carbon  atom  (cf.  the 
non-existence  of  carbonic  acid,  OC(OH)2 ;  p.  127).  There  is  evidence  to 
show  that  in  all  the  glycols  the  OH  groups  are  attached  to  different 
carbon  atoms.  For  example,  ethylene  glycol  is  CH2OH*CH2OH,  not 
CH3-CH(OH)2,  and  cannot  exist  in  isomeric  forms  ;  propylene  glycol  may 
be  either  CH2OH'CH2-CH2-OH,  or  CH3-CHOITCH2OH,  the  former 
of  which  contains  two  primary  alcohol  groups,  and  may  be  termed  a 
diprimary  glycol,  whilst  the  latter  is  a  secondary -primary  glycol.*  Since 
disecondary,  ditertiary,  secondary-tertiary  and j  primary-tertiary  glycols 

*  The  glycols  are  either  a-,  £-,  or  y-,  &c.,  glycols  accordingly  as  the^OH  groups  are 
attached  to  the  1:2,  1:3,  1:4,  &c.,  C  atoms  of  the  chain,  respectively  ;  thus — 

CH2OH  •  CH2  •  CH2OH 
is  /3-propyleue  glycol,  the  a.jsorneride  being  CH3-  CHOH '  CH2OH. 


5/4  PEEPAKATION  OF  GLYCOL. 

are  also  possible,  the  cases  of  isomerism  among  the  glycols  are  very 
numerous. 

The  OH  groups  in  the  glycols  are  capable  of  the  same  transformations 
as  is  the  OH  in  a  monohydric  alcohol ;  the  H  in  them  can  be  exchanged  for 
alkali  metals  ;  the  hydroxyl  groups  can  be  exchanged  for  acid  radicles,  &c. 
Two  series  of  such  substituted  glycols  exist,  those  in  which  both  OH 
groups  have  undergone  the  change,  and  those  in  which  only  one  has  been 
altered;  thus,  CH9ONa'CH9OH  and  CH2ONa'CH,ONa ;  CH9C1'CH9OH 
and  CH2C1-CH2C1/ 

The  oxidation  of  the  glycols  yields  the  same  kind  of  products  as 
those  from  the  oxidation  of  the  alcohols  ;  but  since  there  are  two 
alcoholic  groups  to  be  oxidised,  a  very  large  number  of  products  is  ob- 
tainable; for  example,  the  two  primary  alcohol  groups  in  CH,OH'CH2OH 
can  both  be  oxidised  to  aldehyde  groups,  CHO'CHO,  or  to  acid  groups, 
COOH'COOH;  or  only  one  of  them  may  be  so  oxidised,  yielding  alcohol- 
aldehydes,  CHO'CH2OH,  or  alcohol  acids,  COOH'CH2OH ;  aldehyde- 
acids,  CHO'COOH,  will  also  be  possible.  If  the  glycol  contain  a 
secondary  alcohol  group  (:  CHOH),  ketone-alcohols,  ketone-aldehydes, 
ketone-acids,  and  diketones  may  also  be  prepared.  Hence  the  glycols  give 
rise  to  a  very  large  number  of  derivatives,  many  of  which  are  very 
important,  although  the  same  cannot  be  said  of  the  glycols  them- 
selves. 

The  dialcohols,  alcohol-aldehydes,  alcohol-acids,  and  alcohol-ketones, 
containing  the  group  CH2OH,  are  frequently  termed  hydroxy-  or  oxy- 
derivatives  of  the  corresponding  paraffin  compounds.  Thus  CH2OIT 
CH2OH  may  be  regarded  as  hydroxyethyl  alcohol  (oxyethyl  alcohol},  i.e., 
ethyl  alcohol,  in  which  H  has  been  exchanged  for  OH  ;  CH2OH'CHO  as 
hydroxyacetic  aldehyde,  and  CH,OH'COOH  as  hydroxyacetic  acid. 

The  glycols  are  somewhat  viscid,  neutral  liquids.  The  increase  in  the 
number  of  OH  groups  in  an  alcohol  seems  to  tend  to  increase  the  boil- 
ing point,  the  viscidity  and  the  solubility  in  water ;  solubility  in  alcohol 
and  ether  decreases.  The  glycols  have  a  sweetish  taste,  a  property  much 
enhanced  in  glycerol  and  the  sugars. 

Glycol,  CH2OH'CH2OH,  or  ethylene  glycol,  is  a  much  more  artificial  product  than 
alcohol,  having  been  discovered  as  lately  as  1856.  It  is  prepared  by  decomposing 
ethylene  bromide  with  potassium  carbonate.  Ethylene  (p.  535)  is  first  converted 
into  ethylene  bromide  by  passing  it  slowly  into  50  grams  of  bromine  under 
water,  well  cooled,  until  the  bromine  is  bleached,  or  nearly  so.  The  heavy  layer 
of  ethylene  bromide  is  shaken  with  a  little  weak  potash,  the  upper  watery  layer 
drawn  off,  and  50  grams  of  the  bromide  heated  with  40  of  potassium  car- 
bonate, and  100  of  water,  for  eighteen  hours,  in  a  flask  provided  with  a  reversed 
condenser  (Fig.  270)  ;  when  the  bromide  no  longer  condenses  and  runs  back, 
the  condenser  is  placed  in  its  proper  position  and  the  contents  of  the  flask  distilled. 
After  all  the  water  has  passed  over,  the  flask  is  strongly  heated  by  a  large  Bunsen 
burner,  when  the  glycol  distils.  The  reaction  is  expressed  by  the  equation 
C2H4Br2  +  K2C03  +  H20  =  C2H4(OH)2  +  2KBr  +  C02,  which  exemplifies  the  tendency 
of  alkaline  reagents,  in  the  presence  of  water,  to  effect  the  substitution  of  hydroxyl 
for  halogens. 

Glycol  is  a  colourless  liquid,  less  mobile  than  alcohol,  and  almost  inodorous. 
It  has  a  sweet  taste,  sp.  gr.  1.125  at  o°,  and  the  high  boiling-point  197°  C.  Its 
vapour  is  inflammable,  but  will  not  take  fire  at  common  temperatures  like 
alcohol.  Glycol  mixes  with  water  and  alcohol  in  all  proportions,  but  ether  does 
not  dissolve  it. 

Sodium  dissolves  in  glycol,  as  in  alcohol,  evolving  hydrogen,  and  yielding 
monosodium  glycol,  CH2OH'CH2ONa,  corresponding  with  sodium  ethoxide, 
C2H5'ONa.  On  heating  this  with  more  sodium,  a  second  atom  of  H  is  displaced, 


OXIDATION  OF   GLYCOL. 


yielding  disodium  glycol,   C2H4(ONa)2.      Water  converts    both   compounds  into 
glycol  and  sodium  hydroxide. 

Glycol  chlmhydrin  is  glycol  in  which  Cl  has  been  substituted  for  one  hvdroxol 
group  ;  CH2OH-CH2C1  ;  and  is  prepared  by  saturating  glycol  with  HC1,  and  heatmg 
in  a  sealed  tube  to  100°  C.  ;  C2H4(OH)2  +  HC1  =  C2H4-OH-C1  +  HOH.  It  has  alsS 
been  obtained  by  the  combination  of  ethylene,  C2H4,  with  hypochlorous  acid 
C10H.  It  permits  the  conversion  of  a  dihydric  into  a  monohydric  alcohol  for  it 
yields  ethyl  alcohol  when  acted  on  by  (the  nascent  hydrogen  from)  water  and 
sodium-amalgam;  C2H4-OH-C1  +  2H  =  C2H5-OH  +  HC1.  When  oxidised  it  yields 
monochloracetic  acid,  CH2C1'COOH,  in  which  it  is  obvious  that  the  Cl  cannot  be 
attached  to  the  same  carbon  atom  as  that  to  which  the  0  and  OH  are  attached 
(or  the  substance  would  not  be  an  acid)  ;  this  proves  that  glycol  chlorhydrin 
must  contain  Cl  and  OH  attached  to  different  carbon  atoms,  and  settles  the 
constitution  of  glycol. 


Fig-.  270. — Reversed  condenser. 

The  first  stage  in  the  oxidation  of  glycol  is  the  formation  of  glycol  dialdehyde, 
or  glyoxal ;  the  relation  of  this  body  to  glycol  is  shown  thus  :  glycol, 
CH2OH-CH2OH  ;  glyoxal,  CHO'CHO. 

The  further  oxidation  of  glycol  yields  two  acids,  glycollic  acid,  COOH'CH2OH, 
and  oxalic  acid,  COOH'COOH.' 

The  glycols  from  the  hydrocarbons  containing  one  or  more  benzene  nuclei, 
have  the  hydroxyl  groups  in  the  side-chains  ;  they  have  been  little  studied. 

Hydrobenzoin,  (C6H5)CHOH  :  CHOH(C6H5),  toluylene-glycol,  is  derived  from 
stilbene  (p.  551);  it  crystallises  in  plates,  and  melts  at  134°  C.  An  isonieride, 
isohydrohen-oin,  melts  at  119°  C.  and  occurs  in  two  optically  active  and  one 
inactive  forms  ;  both  isomerides  are  produced  when  benzaldehyde  (<?.<•.)  is  reduced 
with  nascent  hydrogen. 

The  pinacones  are  di-tertiary  glycols,  obtained,  together  with  secondary  alcohols, 
by  the  action  of  nascent  hydrogen  on  the  ketones.  Thus,  acetone  undergoes  a  con- 
densation according  to  the  equation,  2(CH3)2CO  +  H2  =  (CH3)2(HO)C-C(OHXCH3)2, 
dimethyl  p'macone, 

348.  Trihydric  Alcohols,  or  Glycerols.— These  may  be  regarded 
as  derived  from  saturated  hydrocarbons,  by  substituting  three  OH  groups 
for  three  H  atoms.  Since  two  OH  groups  cannot  remain  combined 
with  one  carbon  atom  (p.  573),  there  can  be  no  glycerol  which  contains 


576  PREPARATION   OF   GLYCERINE. 

fewer  than  three  carbon  atoms;  thus,  C3H5(OH)3  must  be  the  first 
member  of  the  series.  The  radicles  of  the  glycerols  may  obviously  be 
regarded  as-trivalent  radicles — e.g.  (C3H5)"',  glyceryl  or  propenyl.  Com- 
paratively few  of  the  glycerols  are  known  ;  what  was  said  with  regard 
to  isomerism,  substitution  derivatives,  and  oxidation  products  of  the 
glycols,  applies  with  even  more  cogency  to  glycerols,  where  there  are- 
three  hydroxyl  groups  to  be  substituted  and  three  alcoholic  groups  to  be 
oxidised.  It  will  be  noted,  however,  that  a  glycerol  formed  from  an  open- 
chain  saturated  normal  hydrocarbon  must  always  contain  at  least  one 
secondary  alcoholic  group. 

Glycerine,  or  Glycerol,  C3H,(OH)3,  or  CH2OH'CHOH-CH2OH,  was 
formerly  termed  the  sweet  principle  of  fats,  on  account  of  the  facility  with 
which  it  may  be  prepared  from  most  of  the  natural  fats,  which  are 
thence  called  glycerides.  Glycerine  is  also  formed  during  the  alcoholic 
fermentation  of  sugar,  and  is  present  in  small  quantity  in  beer  and 
wine. 

Preparation  of  glycerine. — Glycerine  is  contained  in  the  refuse  liquor 
(spent  lyes)  of  the  soap-maker,  being  always  produced  when  oils  and  fats 
are  saponified  by  alkalies,  and  remaining  in  solution  when  the  soap  is 
separated  by  adding  salt.  The  chemistry  of  the  saponification  of  oils- 
and  fats  will  be  considered  under  the  head  of  ethereal  salts,  to  which  class 
these  bodies  belong.  The  soap  lyes  are  concentrated  until  most  of  the 
salt  has  crystallised  and  most  of  the  water  evaporated.  The  crude 
glycerine  thus  obtained  is  distilled  under  diminished  pressure  in  a 
current  of  superheated  steam,  when  water  passes  over  first  and  is  fol- 
lowed by  glycerine,  the  temperature  of  the  receiver  being  high  enough 
to  prevent  much  of  the  superheated  steam  from  condensing.  The  more 
or  less  dilute  glycerine  thus  obtained  is  concentrated  in  a  vacuum  pan. 

Only  within  recent  years  have  methods  of  evaporation  been  so  far  improved  that 
it  has  paid  the  soap-maker  to  recover  glycerine  from  his  lyes.  The  candle-maker 
used  to  be  the  sole  producer.  In  this  industry  palm-oil  is  decomposed  by  super- 
heated steam  to  obtain  palmitic  acid  for  making  candles.  The  operation  is  con- 
ducted in  a  still,  and  the  distillate  consists  of  a  layer  of  palmitic  acid  floating  on 
an  aqueous  solution  of  glycerine.  The  latter  is  drawn  off  and  concentrated  as 
described  above,  the  process  being  simplified  by  the  absence  of  salt.  The  palmitic 
acid  solidifies  to  a  white  crystalline  substance. 

Previously  to  1850,  glycerine  was  made  only  on  a  laboratory  scale  by  the  process 
discovered  by  Scheele  in  1779,  which  consisted  in  boiling  olive  oil  with  lead 
oxide  (litharge,  PbO)  and  water,  when  lead  oleate,  or  lead  plaster,  remained,  while 
the  glycerine  dissolved  in  the  water  from  which  it  was  obtained  by  evaporation, 
after  precipitating  the  dissolved  lead  by  H2S. 

Glycerine  has  been  made  artificially  from  propylene  by  com- 
bining it  with  chlorine  to  form  propylene  chloride,  CH,C1'CHC1'CH3, 
which  is  heated  with  iodine  chloride  to  convert  it  into  propenyl 
tri-iodide,  CH2I'CHI-OH2I ;  by  heating  this  in  a  sealed  tube,  with  much 
water,  at  160°  0.,  it  is  converted  into  glycerine;  C3H5I3  +  3HOH  == 
C3H5(OH)3  +  3HI.  This  synthesis,  together  with  the  fact  that  glycerine 
can  be  made  by  oxidising  ally!  alcohol,  CH2  :  CITCH2OH,  establishes 
the  constitution  of  glycerol,  if  it  be  admitted  that  one  carbon  atom 
cannot  hold  two  OH  groups. 

Properties  of  glycerine. — Resembles  syrup  in  taste  and  consistence  ; 
sp.  gr.  1.269  at  12°  C. ;  boils  at  290°  C.,  but  then  undergoes  partial 
decomposition.  At  12  mm.  pressure  it  boils  at  170°  C.  It  is  slightly 


PEOPEETIES  OF  GLYCERINE.  577 

volatile  at  100°  C.,  but  not  at  the  ordinary  temperature.  If  kept  at 
o°  C.  for  some  time,  a  strong  aqueous  solution  of  glycerine  deposits 
crystals,  especially  if  a  ready-made  crystal  be  introduced  ;  pure  glycerine 
solidifies  at  -  40°  0.  to  a  gummy  mass,  which  melts  at  17°  C.  It  does 
not  inflame  until  heated  to  150°  C.,  when  it  burns  with  a  flame  resem- 
bling that  of  alcohol.  It  absorbs  water  easily  from  the  air,  and  dissolves 
without  limit  in  water  and  alcohol,  but  is  insoluble  in  ether. 

On  account  of  its  never  drying,  glycerine  is  useful  in  many  cases  when 
it  is  desired  to  keep  any  substance  moist  and  supple.  Water  mixed 
with  an  equal  weight  of  glycerine  is  sometimes  used  in  gas-meters,  being 
much  less  easily  frozen  than  water,  and  less  liable  to  dry  up.  Glycerine 
is  used  in  pharmacy,  but  its  chief  application  is  in  making  nitro- 
glycerine (q.v.). 

Glycerine  possesses  extensive  solvent  powers,  like  alcohol,  dissolving 
most  substances  which  are  soluble  in  water,  and  some  others,  such  as- 
metallic  oxides,  which  are  insoluble  in  water. 

A  characteristic  property  of  glycerine  is  that  of  yielding  an  exceedingly 
pungent  and  irritating  substance,  known  as  acrolein,  or  acrylic  aldehyde? 
C.,H3'CHO,  when  sharply  heated,  or  subjected  to  the  action  of  dehy- 
drating agents,  03H3(OH)3  =  C3H3'CHO  +  2H2O.  The  best  test  for 
identifying  glycerine  is  to  mix  it  with  powdered  KHS04  and  heat  it 
strongly,  when  the  intolerable  odour  of  acrolein  is  perceived.  It  is  this 
substance  which  causes  the  offensive  smell  of  smouldering  candles  made 
of  tallow  and  other  glycericles. 

By  treatment  with  a  mixture  of  nitric  and  sulphuric  acids  glycerine 
is  converted  into  nitroglycerine  or  glyceryl  trinitrate,  C3H5(N03)3,  a 
powerfully  explosive  compound  which  will  be  described  in  the  section 
on  ethereal  salts. 

As  glycerol  contains  two  primary  alcohol  groups,  CH2OH,  which  are  known  to 
be  oxidisable  first  to  aldehyde  groups,  CHO,  and  then  to"  acid  groups,  COOH,  and 
also  a  secondary  alcohol  group,  which  is  oxidisable  to  a  ketone  group,  CO,  no  fewer 
than  ii  oxidation-products  of  glycerol  are  theoretically  possible.  Only  six,  how- 
ever, are  at  present  known,  namely  :  glyceric  aldehyde,  CHO*CHOH'CH2OH  : 
dihydroxyacetene,  CH2OH-CO'CH2OH  ;  glyceric  acid,  COOH-CHOH'CH2OH  : 
tartronic  acid,  COOH'CHOITCOOH  ;  mesoxalic  acid,  COOH'C(OH)2-COOH  ;  and 
hydroxypyroracemic  acid,  CH0OH'CO'COOH.  Except  the  last  named,  all  these 
are  obtainable  by  the  direct  oxidation  of  glycerol.  When  H202  (in  presence  of  a 
small  quantity  of  a  ferrous  salt)  is  the  oxidant,  a  mixture  of  glyceric  aldehyde  and 
dihydroxyacetone  is  formed  which  was  originally  supposed  to  be  a  single  com- 
pound and  was  called  "  glycerose."  Dilute  nitric  acid  produces  glyceric  and 
tartronic  acids,  while  oxidation  with  bismuth  nitrate  and  nitre  forms  mesoxa 
acid.  More  energetic  oxidising-agents  yield  glycollic  acid,  CH2OH'COOH  ;  oxalic 
acid,  COOH-COOH  ;  and  glyoxylic  acid,  CHO'COOH. 

When  reduced  with  hydriodic  acid  glycerol  yields  allyl  iodide,  CH2  :  CH  -,H21  ; 
isopropyl  iodide,  CH3'CHrCH3  ;  and  propylene,  CH3'CH  :  CH2. 

Two  compounds   corresponding  with   the  ethoxides  may  be  05*~n~_!j^JP 
action  of  sodium  ethoxide  on  glycerol  in  alcohol,  sodium  propenoxide,  C3H6(OH>2UiNa, 
and  disodium  .  propenoxlde,  C.,H5OH(ONa)2.  7/7 

By  treating  a-chlorhydrin  (V/.r.),  with  BaO,  HC1  is  abstracted  and  glyctde 

is  obtained  :  ^'  °H*      ,„-  HC1  =  0<?*2_W  ;  this  is  a  colourless  liquid,  boiling 

HOC'OH2Orl  NL±I2U±1 

with  decomposition  at  "162°  C.     It  combines  with  water  to  form  glycerol. 

349.  Tetrahydric  and  Higher  Polyhydric  Alcohols-.—Alcohols 
ntaining  4,  5,  6,  7,  8,  and  9  hydroxyl  groups  are  known. 

eatin    t 


contanng  4,  5,    ,  7,    ,  an     9    yroxy   group  . 

of  hydroxyl  groups  present  in  an  alcohol  is  ascertained  by  heating  t 


578  POLYHYDEIC  ALCOHOLS. 

^alcohol  with  acetic  anhydride,  (CH3CO)20,  and  sodium  acetate,  when  as 
many  acetic  acid  radicles  (acetyl,  CH3CO)  enter  into  the  composition  of 
the  alcohol,  as  there  are  hydroxyl  groups  in  the  alcohol ;  for  example, 
the  compound  called  erythrite  is  known  to  be  a  tetrahydric  alcohol, 
because  it  forms  an  acetate  containing  four  acetyl  groups ; 

C4H6(OH)4  +  4(CH3CO)20  =  C4H6(OCH3CO)4  +  4CH3COOH. 
The  lowest  member  of  each  series  of  polyhydric  alcohols  must  have  at 
least  as  many  carbon  atoms  as  it  has  OH  groups,  otherwise  one  carbon 
atom  would  have  to  hold  two  hydroxyl  groups,  and  the  compound  would 
break  up  (p.  573).  The  derivatives  and  oxidation-products  of  these 
alcohols  are  similar  in  constitution  to  those  of  glycol. 

Most  of  the  higher  alcohols  that  are  known  are  obtained  from  natural 
sources ;  they  are  many  of  them  sweet,  and  some  were  for  long  classed 
with  the  sugars,  with  which,  indeed,  they  are  closely  connected. 

Erythrite,  erythritol,  or  phycite,  C4H6(OH)4,  or  CH2OH-[CHOH]o-CH2OH,  is 
obtained  from  certain  lichens,  such  as  the  Itoccella  tinctoria,  or  Orchella  weed,  by 
boiling  with  milk  of  lime,  filtering,  precipitating  the  excess  of  lime  by  C02, 
•evaporating  the  filtrate  to  a  small  bulk,  and  treating  with  alcohol,  when  erythrite 
crystallises  in  prisms,  which  fuse  at  126°  C.  and  sublime  at  300°,  though  not  quite 
undecornposed.  It  is  easily  soluble  in  water,  and  has  a  sweet  taste  ;  sparingly 
soluble  in  cold  alcohol,  and  insoluble  in  ether. 

In  several  of  its  reactions  erythrite  resembles  glycerine.  When  it  is  dissolved 
in  nitric  acid,  and  sulphuric  acid  added,  it  yields  a  crystalline  precipitate  of  nitro- 
erythrite,  C4H6(N03)4,  which  is  explosive  like  nitroglycerine. 

If,  in  the  treatment  of  the  lichen,  cold  milk  of  lime  be  used,  the  filtrate,  when 
saturated  with  C02,  gives  a  mixed  precipitate  of  calcium  carbonate  and  erytlu-ni, 
which  may  be  extracted  by  alcohol,  and  crystallised.  Erythrin  is  erythrite  di- 
orsellinate,  C4H6(OH)2(OC8H703)2,  and  belongs  to  the  class  of  ethereal  salts.  It 
appears  to  exist  as  such  in  the  lichen,  and  is  decomposed  into  erythrite  and  calcium 
orsellinate  when  boiled  with  calcium  hydroxide.  Erythrite  exists  ready  formed  in 
certain  algcc,  notably  in  Protococcus  vulgaris.  This  natural  erythrite  is  optically 
inactive.  Both  it  a,nd  another  inactive  form  (believed  to  be  internally  compensated 
—see  p.  621)  may  be  synthetised  from  divinyl  CH2  :  CH'CH  :  CH2  by  adding  Br 
to  form  two  dibromides,  which  are  stereoisomerides  and  can  be  oxidised  by  per- 
manganate to  corresponding  bromhydrins  CHoBr[CHOH]2CH2Br  ;  these  yield  the 
natural  erythrite  and  its  isomeride  (m.  p.  72°  C.)  when  treated  with  KOH  and 
water.  A  dextro-  and  a  lasvo-erythritol  have  also  been  obtained. 

Arabite,  or  araUtol,  CH2OH-|~CHOH]3-CH2OH,  is  obtained  by  reducing  arabiwnt 
(q.v.)  with  nascent  hydrogen.  It  melts  at  102°  C. 

Mannite,ormawm'^,CH2OH'[CHOH]4-CH2OH,ahexahydric  alcohol, 
is  a  sweet  substance  contained  in  manna,  from  which  it  may  be  ex- 
tracted by  boiling  with  alcohol,  when  it  crystallises,  on  cooling,  in  fine 
needles,  fusing  at  166°  C.  It  is  rather  sparingly  soluble  in  cold  water 
and  alcohol,  but  easily  on  heating,  and  is  insoluble  in  ether.  When 
oxidised  in  presence  of  platinum  black,  it  yields  the  sugar  mannose, 
C6H1906  (q.v.),  and  when  this  is  further  oxidised  it  becomes  mannonic 
acid,  CH2OH-[CHOH]4-C02H.  The  natural  mannite  is  dextro-rotatory  ; 
a  IJEVO-  and  an  inactive  form  are  also  known,  as  will  be  explained  later, 

By  treatment  with  nitric  acid,  mannite  is  converted  into  an  explosive  crystalline 
body,  which  is  nitromannite,  or  mannyl  hexanitrate,  C6H8(N03)6,  re-converted  into 
mannitol  by  (NH4)2S.  When  treated  with  HI,  mannite  becomes  secondary  hexyl 
iodide, 

CH2OH-CHOH-CHOH-CHOH-OHOH-CH2OH  +  n  HI  = 

CH3-CH2-CH2-CH2-CHrCH.5  +  6HOH  +  I10. 

Mannite  is  found  among  the  products  of  the  viscous  fermentation  of  saccharine 
liquors,  when  they  are  said  to  become  ropy  ;  beet-root  juice  is  especially  liable  to 
this  change. 


CONSTITUTION   OF  ALDEHYDES. 

Mamiite  is  an  important  substance  in  vegetable  chemistry,  since  it  occurs  not 
only  in  manna,  the  dried  exudation  of  the  Ornus,  or  manna  ash,  growing  in  the 
South  of  Europe,  but  also  in  the  sap  of  the  common  ash  (Fraaeinu*  excelsior*)  of  the 
larch,  apple,  cherry,  and  lime  ;  in  the  leaves  of  the  syringa  and  privet  •  in  the  bulbs 
of  Cyclamen  europawm  (sow-bread),  in  the  bark  of  the  wild  cinnamon  in  some 
lichens,  seaweeds,  sugar-cane,  mushrooms,  celery,  asparagus,  olives,  and  onions 
The  seaweed  Laminaria  saccliarina,  or  sugar-wrack,  contains  12  per  cent  of 
mannite,  which  is  sometimes  found  as  an  efflorescence  on  the  surface  of  the  weed. 
It  has  also  been  found  in  the  root  of  the  monkshood  (Aeonitum  napellus).  The 
Agaricus  Integer,  a  common  fungus,  contains  when  dry  about  20  per  cent,  of 
mannite. 

Mannitane,  C6H8(OH)40,  is  prepared  by  heating  mannite  to  200°  C. ;  CriH8(OH)6  = 
C6H8(OH)40  +  H20.  It  is  a  viscous  substance  very  similar  to  glycerol.  and  form- 
ing compounds  when  heated  with  the  fatty  acids  which  closely  resemble  the 
glycerides,  and  are  saponified  by  alkalies  in  the  same  way. 

Dulcite,  or  chdcitol,  is  isomeric  with  mannite,  and  much  resembles  it.  It  is 
extracted  from  Madagascar  manna  by  boiling  water.  It  is  nearly  twice  as  soluble 
in  water  as  mannite  is,  but  much  less  soluble  in  alcohol.  It  melts  at  188°  C. 

Sorbitol,  C6H8(OH)6,  another  isomeride  of  mannite,  is  found  in  the  berries  of  the 
mountain  ash  (tiorbus  aucuparia).  It  is  more  fusible  (110°  C.)  than  the  others. 

II.  ALDEHYDES. 

350.  These  compounds  are  the    first  products  of  the  oxidation   of 

^H2 

all  alcohols   containing  the  primary  alcoholic  group  -C\         ,    which 

XOH 

//VL 
becomes  'C  ?       +  HOH.     They  differ  from  the  parent  alcohols  by  two 

atoms  of  hydrogen ;  thus,  ethyl  alcohol,  CH3'CH,OH,  yields  acetic 
aldehyde,  CH3'CHO,  and  so  on,  there  being  one  or  more  aldehydes 
corresponding  with  each  of  the  alcohols  already  described.  They 
readily  pass  by  oxidation  into  the  corresponding  acids,  the  group 

^°  //> 

•C  \       becoming    'C  \        ,  and  are  named  after  the  acids  into  which 

H  OH 

they  are  converted.  Since  the  oxidation  of  primary  alcohols  to 
aldehydes  consists  merely  in  the  removal  of  H2  (whence  the  name — 
al[cohol]  dehyd\rogenatum\),  and  since  the  aldehyde  in  all  its  reactions 
appears  still  to  contain  the  hydrocarbon  radicle  which  was  con- 
tained in  the  alcohol,  the  above  view  of  the  constitution  of  these  com- 
pounds may  be  presumed  to  be  correct.  It  is  supported  by  the  fact 
that  when  an  aldehyde  reacts  with  PC15  the  oxygen  atom  is  exchanged 
for  two  chlorine  atoms,  CH3'CHO  +  P015  =  CH3'CHCla  +  POC13,  showing 
that  the  aldehyde  cannot  contain  the  0  °in  the  form  of  OH.  For  when 
a  compound  containing  OH  reacts  with  PClb,  the  OH  is  exchanged  for  Cl 
and  II Cl  is  a  product  of  the  reaction,  e.g.,  CH3'CH2OH +  PC15  = 
CH,'CH2C1  +  POC13  +  HC1.  Position  isomerism  can  only  occur  in  the 
radicle  of  the  aldehyde ;  thus,  in  the  general  formula,  R'CHO,  R  may 
occur  in  isomeric  forms,  but  there  are  no  secondary  and  tertiary 
aldehydes  in  the  sense  that  there  are  secondary  and  tertiary  alcohols. 

As  already  stated  (p.  573),  glycols  of  the  type  R'CH(OH)2  do  not 
exist,  although  many  compounds  are  known  which  might  be  expected 
to  yield  them  under  appropriate  treatment ;  for  instance,  by  analogy 
with  the  reaction  between  ethyl  chloride  and  moist  silver  oxide,  that 


580  PARAFFIN  ALDEHYDES. 

between  this  oxide  and  ethylidene  chloride,  CH3'CHC12,  might  be  expected 
to  yield  ethylidene  glycol  CH3'CH(OH)2,  but  as  a  fact  yields  aldehyde 
and  water,  CH3'CH(OH)2,  becoming  CH3'CHO  +  HOH.  Thus  the 
aldehydes  may  be  regarded  as  the  anhydrides  of  these  unknown 
glycols,  and  it  may  be  supposed  that  the  latter  are  the  true  products  of 
oxidation  of  the  primary  alcohols,  being  formed  by  the  substitution  of 
OH  for  a  second  H  atom  in  the  parent  hydrocarbon  ;  the  glycol  thus 
formed,  however,  at  once  passes  into  its  anhydride,  the  aldehyde.  This 
view  of  the  process  of  oxidation  is  supported  by  the  oxidation  of  the 
aldehyde  to  the  acid,  consisting  of  the  substitution  of  OH  for  H.  The 
following  formulae  make  these  remarks  clear,  but  it  must  be  remem- 
bered that  the  alcohol  is  not  formed  by  oxidation  of  the  hydrocarbon  : 

/H  /OH  /OH;  0  0 

R-C(-H  R-C^-H  R-CeOH  R  C\ 

\H  \H  NH  H  XOH 

Hydrocarbon.         Primary  Unknown  Aldehyde.  Acid. 

alcohol. 

R\      /H  Rv      /OH 

R><H  K><H 

Hydrocarbon.  Secondary  Unknown  Ketone. 

alcohol.  glycol. 

The  aldehydes  are  unsaturated  in  the  sense  that  the  oxygen  atom  is 
doubly  linked  to  carbon,  and  they  show  a  tendency  to  combine  as  a 
whole  with  other  compounds,  the  aldehyde  group  'CH  =  0  becoming 

*CH/        .     This  tendency  leads  to  the  formation  of   derivatives  of 


the  aforesaid  unknown  glycols  and  to  a  number  of  nucleal  condensa- 
tions (p.  531),  which  render  the  aldehydes  useful  in  building  up  new 
carbon  nuclei.  The  chief  reactions  of  this  kind  will  be  noticed  in  the 
description  of  acetic  aldehyde,  the  behaviour  of  which  is  identical  with 
that  of  the  majority  of  aldehydes. 

The  readiness  with  which  the  aldehydes  undergo  oxidation  to  the 
corresponding  acids  makes  them  powerful  reducing-agents. 

351.  Aldehydes  from  the  Paraffin  Alcohols. — The  oxidation  of 
the  primary  alcohols  is  not  the  only  general  reaction  for  preparing  the 
aldehydes  of  this  series.  They  may  be  obtained  by  distilling  a  dry 
mixture  of  calcium  formate  and  the  calcium  salt  of  the  acid  corre- 
sponding with  the  adlehyde  required. 

HCOOV  C2H5COOV  C2H5COH 

>Ca    +  _)>Ca    =  +     2CaCO3 

HCOO  C2H5COO  C2H5COH 

Calcium  Calcium  Propionic 

formate.  propionate.  aldehyde. 

Formic  aldehyde,  formaldehyde,  or  methyl  aldehyde,  H'CHO,  is  a  gas 
and  boils  at  —  2 1  °  C.  It  is  formed  when  a  mixture  of  methyl  alcohol 
vapour  and  air  is  passed  over  a  red-hot  platinum  wire,  CH3tOH  +  0  = 
H'CHO  +  HOH.  It  is  now  made  on  a  large  scale  by  a  secret  process 
and  sold  in  aqueous  solution  containing  40  per  cent,  under  the  name  of 
formaline  f or  use  as  an  antiseptic  and  in  the  manufacture  of  dye-stuffs  ; 


ALDEHYDE.  581 

the  solution  has  a   suffocating  odour   and  reduces  ammoniacal  silver 

nitrate. 

Formaldehyde  is  formed  when  a  mixture  of  CO  and  H2  is  treated  in  an  ozoniser 
(p.  65)  and  in  small  quantity  when  calcium  formate  is  destructively  distilled.  By 
cautiously  oxidising  methyl  alcohol  with  Mn02  and  H2S04  some  of  the  CH3OH 
is  oxidised  to  H'CHO  and  combines  with  more  CH3OH  to  form  methylal  or 
formal  (inethylene  dimethyl  ether"),  CH2(OCH3)2,  a  liquid  (b.-p.  42°  C.)  used  as  a 
soporific  and  as  a  solvent ;  when  this  is  distilled  with  a  dilute  acid  it  yields 
formaldehyde  and  methyl  alcohol. 

Paraformaldehyde  is  a  solid  polymeride  (CH20)X  formed  when  an  aqueous 
solution  of  formaldehyde  is  allowed  to  evaporate  ;  when  heated  it  is  converted  into 
another  polymeride,  tr'wxymethylene  or  meta  formaldehyde  (CH20)3  which  melts  at 
171°  C.  and  then  becomes  the  gas  CH20.  By  prolonged  contact  with  lime-water 
formaldehyde  is  polymerised  to  a  mixture  of  sugars  (formose),  a  change  which  may 
occur,  through  some  agency,  in  the  synthesis  of  sugar  by  plants,  since  formaldehyde 
has  been  found  in  green  plants. 

Formaldehyde  is  used  in  synthetic  chemistry  for  introducing  the  methylene 
group  (CH2)  into  compounds,  its  oxygen  atom  readily  combining  with  H2  and 
removing  them  as  water,  leaving  the  :  CH,,  group  to  take  their  place,  thus  : 
K-NH2  +  0  :  CH2  =  R'N  :  CH2  +  H20. 

Acetic  aldehyde,  CH3-CHO,  is  obtained  by  distilling  alcohol  with 
potassium  bichromate  and  sulphuric  acid.  This  process  requires  much 
care,  on  account  of  the  violence  of  the  action  and  the  volatility  of  the 
aldehyde. 

Three  parts  of  potassium  bichromate,  in  crystals  free  from  powder,  are  placed  in 
a  flask  or  retort  surrounded  by  ice  (or  by  a  mixture  of  sodium  sulphate  crystals 
with  half  their  weight  of  HC1),  and  a  mixture  of  2  parts  of  ordinary  alcohol, 
4  parts  sulphuric  acid,  and  12  parts  of  water,  also  previously  cooled  in  ice,  is  added. 
The  flask  or  retort  is  then  connected  with  a  condenser  containing  iced  water,  and 
the  refrigerating  mixture  removed,  when  the  aldehyde  will  generally  be  distilled 
over  by  the  heat  attending  the  reaction.  The  impure  aldehyde  thus  obtained  is 
re-distilled  on  the  water-bath  in  the  apparatus  shown  in  Fig.  271.  The  aldehyde, 


Fig.  271.— Preparation  of  aldehyde. 

freed  from  alcohol  and  aqueous  vapour  which  condense  in 
passes  over  and  is  dissolved  in  dry  ether  contained  in  the 
The  ethereal  solution  of  aldehyde  is  saturated  with  dry  ammonia,  wheieupor 


582  PROPERTIES   OF  ALDEHYDE. 

whole  of  the  aldehyde  is  separated  in  the  form  of  colourless  crystals  of  aldeliy de- 
ammonia,  which  is  sparingly  soluble  in  ether  ;  this  is  drained  upon  a  filter,  and 
distilled  with  diluted  sulphuric  acid  in-  a  flask  or  retort,  heated  by  a  water-bath,  and 
connected  with  a  condenser  filled  with  ice  water.  The  aldehyde  may  be  freed  from 
water  by  standing  over  fused  calcium  chloride,  and  distillation. 

The  preparation  of  aldehyde  illustrates  the  use  of  K2Cr2O7  and 
H3S04  as  an  oxidising-agent  upon  organic  bodies.  Neglecting  certain 
secondary  reactions,  the  production  of  aldehyde  may  be  represented  by 
the  equation — 

3(CH3-CH2OH)  +  K20'2Cr03  +  4(H20'S03)  = 
3(CH3-CHO)  +  7H20  +  K2OS03  +  Cr203'3S03. 

On  a  large  scale,  aldehyde  is  obtained  as  a  by-product  in  the  manu- 
facture of  alcohol,  when  it  comes  over  with  the  first  portion  of  the 
distillate.  Commercial  alcohol  generally  contains  a  little  aldehyde. 

Aldehyde  may  also  be  obtained  by  distilling  a  mixture  of  an  acetate 
and  a  formate  (see  above). 

Properties  of  aldehyde. — Sp.  gr.  0.80  at  o°  0. ;  boiling-point  20°. 8  C. 
Aldehyde  has  a  peculiar  acrid  odour,  which  affects  the  eyes.  It  mixes 
in  all  proportions  with  water,  alcohol,  and  ether.  It  has  a  great  dis- 
position to  combine  with  oxygen  to  form  acetic  acid  :  CH3-CHO  +  0  = 
CH3-COOH.  Hence  aldehyde  acts  as  a  reducing-agent,  and  one  of  the 
tests  for  it  is  the  reduction  of  silver  from  its  salts.  If  a  few  crystals  of 
aldehyde-ammonia  be  dissolved  in  water,  a  little  silver  nitrate  added, 
and  a  gentle  heat  applied,  the  silver  will  be  deposited  on  the  sides  of 
the  vessel,  giving  them  the  reflecting  power  of  a  mirror.  A  general 
test  for  aldehydes  is  their  power  of  restoring  the  red  colour  to  a 
solution  of  a  salt  of  rosaniline  which  has  been  bleached  by  sulphurous 
acid. 

Another  characteristic  property  of  aldehydes  is  that  of  forming 
crystalline  compounds  with  sodium  bisulphite.  If  aldehyde  be 
mixed  with  a  saturated  solution  of  NaHS03,  it  forms  a  crystalline 
compound,  which  is  the  sodium  salt  of  ethylidene  glycol  sulphonic  acid, 
CH3-CH(OH)(S02ONa),  combined  with  H20  ;  from  this  the  aldehyde 
may  be  obtained  by  distillation  with  either  acid  or  alkali. 

When  mixed  with  potash,  and  gradually  heated  to  boiling,  most  of 
the  paraffin  aldehydes  yield  brown-yellow  substances  of  peculiar  odour, 
known  as  aldehyde  resins  ;  their  chemical  constitution  is  uncertain. 

Nascent  hydrogen  (water  and  sodium  amalgam)  converts  aldehyde 
into  alcohol ;"  OH^CHO  +  H2  =  CH3-CH2OH  (alcohol). 

Aldehyde  combines  with  ammonia  forming  a  compound,  aldehyde- 
ammonia,  which  is  probably  an  amine  of  the  hypothetical  ethylidene 
glycol,  CH3-CH(OH)(NHS) ;  with  HCN"  to  form  ethylidene  cyanohydrin 
or  lactonitrile,  CH3'CH(OH)(CN);  with  alcohol  to  iovrndiethyl  ethylidene 
ether  or  acetal,  CH3'CH(OC2H5)2,  a  liquid  which  boils  at  104°  C.  and  is 
formed  in  old  wine  and  in  the  last  runnings  of  spirit  stills. 

When  there  is  no  other  compound  with  which  aldehyde  can  combine, 
it  tends  to  combine  with  itself  or  polymerise. 

For  example,  perfectly  pure  acetic  aldehyde  can  be  kept  unchanged,  but  in  the 
presence  of  a  very  little  dilute  acid  or  of  zinc  chloride  it  is  converted  into  aldol, 
which  is  a  (secondary)  alcohol-aldehyde,  CH3-CHOH'CH2-CHO  (hydroxy-fadyric 
aldehyde) ;  this  resembles  aldehyde  in  appearance  and  general  reactions,  but  its 
sp.  gr.  is  1. 1 20  and  it  does  not  distil  unchanged  ;  it  becomes  viscous  on  standing. 


OLEFINE  ALDEHYDES. 


583 


A  condensation  of  two  or  more  molecules  in  this  way  occurs  in  many  other  com- 
pounds, and  is  always  termed,  by  analogy,  an  aldol  condensation. 

By  adding  a  drop  of  strong  H2S04  to  aldehyde,  much  heat  is  evolved  and  the 
liquid  becomes  specifically  heavier  (sp.  gr.  o.99at  20°  C.)  :  this  liquid  is  paraldehude 
<^H1203,  or  /0-CH(CHA 

CH3-CH<  3 

N 


It  boils  at  124°  C.  and  melts  at  10°  C.  ;  it  is  less  soluble  in  hot  water  than  in  cold, 
and  when  distilled  with  dilute  H2S04  it  becomes  aldehyde  again.  Metaldelujde  is  a 
stereoisomeride  of  paraldehyde,  produced  in  the  same  way,  but  at  o°  C.  It  forms 
white  crystals,  insoluble  in  water,  but  soluble  in  ether  and  in  alcohol  ;  it  sublimes 
when  heated  to  112°  C.,  without  melting,  and  when  heated  in  a  sealed  tube  at  116° 
C.,  it  becomes  aldehyde  again  ;  the  crystals  are  said  to  become  brittle  and  opaque 
after  a  time,  owing  to  a  further  polymerisation  to  C8H]604,  tetraldehyde. 

Other    characteristic     reactions     of     the    aldehydes     are     the    formation     of 

aldoximes   by  reaction  with    hydroxylamine    (p.    103):    CH3'CH|0  +  H^:N-OH  = 


phenylhy 

<!<>](  ide  h 


(acetaldoxime)  ;    and   the  formation  of   hydrazones  with 
ydrazine;  CH3-CHO  +  H2:N-NHC6H5  =  HOH  +  CH3-CH:N-NHC6H5  (acetal- 
di'Jti/de  ltydra:one. 

Aldehyde,  in  the  form  of  paraldehyde,  and  some  of  its  derivatives,  such  as  acetai 
(>•-?.),  are  used  as  soporifics  (cf.  chloral).  Aldehyde  also  finds  application  in  the 
manufacture  of  dyes. 

352.  The  chief  known  homologues  of  acetic  aldehyde  are  shown  in  the  following 
table  :* 

Chemical  Xame.  Source.  Formula. 

Propionic  aldehyde      Oxidation  of  propyl  alcohol          .  C2H5    •  CHO     (49°) 

Butyric  „        .  „  butyl          „  .  C3H7    •  CHO     (74°) 

Valeric  „        .  „  amyl  „  .  C4H9    •  CHO  (102°) 

Caproic  .   /  Distillation  of  calcium  formatej  CH      .  CHO  (128°) 

^     with  calcium  caproate       .       J 

(Enanthic       .,        .       Distillation  of  castor  oil        .         .  C6H]3   •  CHO  (155°) 

Caprylic         .,  „  .,  .        .  C7H15  •  CHO  (160°) 

Kutic  „       .      Oil  of  rue C9H19  •  CHO    - 

Laurie  „       .  „  .....  CnH23  •  CHO     [44-5°] 

Myristic         „ C^H^ '  CHO      52.5°] 

Palmitic        „ .        .  C15H31  •  CHO      58.5°] 

Stearic  „  .         .         .        .        .      -.        .  C^H^  •  CHO      63.5^ 

Acetic,  propionic,  and  butyric  aldehydes  occur  among  the  products  of  the  oxidis- 
ing action  of  a  mixture  of  manganese  dioxide  with  sulphuric  acid  upon  albumin, 
fibrin,  and  casein. 

Thioaldehydes,  in  which  sulphur  takes  the  place  of  oxygen,  are  known  only  in 
polymeric  form,  corresponding  with  the  polymerised  aldehydes.  TrtohioformM* 
dehtjde  (CH2S)3  melts  at  216°  C.,  trithioacetadehyde  (CH3CHS)3,  occurs  in  an  a  and 
|8  form  melting  at  101°  and  125°  C.  respectively.  Mercaptal  is  the  thio-denvative, 
corresponding  with  acetai  (p.  582).  By  oxidation  the  thio-aldehydfs  yirl 
sulphones. 


.  . 

353.  Aldehydes    from    the    Olefine    Alcohols.  — Acrolein,   or  acrylic   aMehya* 
CH0:CH-CHO,  the  aldehyde  of  allyl  alcohol,  is  prepared  by  distilling  glvcerftw  ' 
twice  its  weight  of  KHS04,  which  abstracts  the  elements  of  two  molecules  on 
C,H5(OH)3=C.-H3-CHO  +  2H2O.     The  crude  acrolein    is    shaken    with     I 
remove  S02,  and  rectified  over  CaCL,  to  remove  the  water. 

Acrolein  is  a  liquid  distinguished"  by  a  very  powerful  irritating  odour, 
sp.  gr.  0-84,  and  boils  at  52°  C.     It  dissolves  sparingly  in  water,  but  easil 
and  ether.     Unlike  most  aldehydes,  it  does  not  combine  with  NaHM>,  . 
forms  a  resinous  body  with  alkali,  and  reduces  ammoniacal  AgJs03,  whi< 
it  into  acrylic  acid,  C0H.,-C02H.     Sodium  amalgam  and  water  (nascent  li 
convert  it  into  allyl  alcohol,  C2H3'CH2OH.     When  kept,  acrolein  b 

*  The  boiling-points  are  in  round  brackets  (...),  the  melting-points  in  square  b™ 
Centigrade  scale.     According  to  the  new  system  the  aldehydes  are  named  ] 
the  termination  -at  being  substituted  for  -ol  (see  foot-note  p.  568). 


584  AROMATIC  ALDEHYDES. 

solid,  disacryl,  probably  a  polymeride.  HC1  gas  passed  into  acrolein  converts  it 
into  a  crystalline  body,  ft-chloropropylaldehyde,  CH201'CH2'CHO,  which,  when 
distilled  with  potash,  yields  metacrolein,  C9H12O3  (m.-p.  45°  C.),  corresponding  with 
paraldehyde. 

Crotonic  aldehyde,  CH3'CH:CITCHO,  is  prepared  by  heating  acetic  aldehyde  to 
100°  C.  for  two  days  in  contact  with  ZnCl2  and  a  little  water.  The  ZnCl2  acts  as 
a  dehydrating  agent;  2(CH3-CHO)  =  H20  +  C3H5'CHO  (aldehyde  condensation'). 
The  unchanged  aldehyde  is  distilled  off,  some  water  added,  and  the  distillation 
continued,  when  water  and  crotonic  aldehyde  distil  over.  It  has  an  irritating- 
odour  like  acrolein,  boils  at  104°  C..  and  is  sparingly  soluble  in  water.  When 
oxidised  by  air  or  silver  oxide,  it  yields  crotonic  acid,  C3H5'C02H.  It  occurs  in 
some  kinds  of  fusel  oil. 

353«.  Aldehydes  from  Dihydric  and  Polyhydric  Alcohols.— 

These  may  be  di-  or  poly-aldehydes  and  aldehyde-alcohols  ;  the  latter  are 
of  much  importance,  as  they  include  several  sugars,  like  glucose  and 
mannose.  These  compounds  are  not  considered  under  this  heading, 
however,  for  their  near  relationship  to  compounds  in  other  classes  will 
be  best  set  forth  by  treating  them  in  a  separate  section.  The  student 
is  therefore  referred  to  the  chapter  on  carbohydrates  for  a  description 
of  the  sugars. 

Glyoxal,  or  oxalic  aldehyde,  CHO'CHO,  is  prepared  by  slowly  oxidising  acetic 
aldehyde  with  dilute  nitric  acid.  It  occurs  among  the  products  of  the  regulated 
action  of  nitric  acid  on  alcohol  and  glycol.  (See  p.  575.) 

It  is  a  deliquescent  solid,  soluble,  in  water,  alcohol,  and  ether,  forming  a  crys- 
talline compound  with  two  mols.  NaHS03,  and  reducing  silver  nitrate,  becoming 
oxidised  to  oxalic  acid,  C02H/C02H,  and  glyoxylic  acid,  CHO'C02H.  Alkalies 
oxidise  one  CHO  group  and  reduce  the  other,  forming  glycollic  acid,  CH2OITCOOH. 
With  ammonia,  it  yields  gly  cosine  ;  3C2H202  +  4NH3:=6H20  +  N4(C2H2J3.  Glyoxal 
combines  with  2HCN  to  form  the  nitrile  of  tartaric  acid,  CH(OH)(CN)'CH(OH)(CN). 

Gly  eerie  aldehyde  or  glycerose,  CH2OH'CHOH'CHO,  is  an  aldehyde-alcohol 
obtained  by  the  careful  oxidation  of  glycerol  (p.  577).  By  condensation  it  is  con- 
verted into  acrose,  one  of  the  sugars. 

354.  Aldehydes  from  the  Aromatic  Alcohols. — Benzaldehyde, 

benzole  aldehyde,  or  bitter-almond  oil,  C6H5-CHO,  was  originally  made  by 
distilling  the  moistened  bitter-almond  cake  from  which  the  fixed  oil  had 
been  extracted  by  pressure.  The  cake  was  placed  in  a  perforated  vessel 
and  subjected  to  the  action  of  steam,  which  carried  over  the  oil  and 
deposited  it  as  a  heavy  layer  on  standing. 

The  bitter-almond  oil  does  not  exist  ready  formed  in  the  almond, 
but  is  a  product  of  the  decomposition  of  the  bitter  substance,  amygdalin, 
C20H27NOn,  of  which  the  bitter  almond  contains  about  5  per  cent. 
This  substance  is  a  glucoside,  and  is  decomposed,  in  the  presence  of 
water  and  of  a  peculiar  albuminoid  ferment  present  in  the  almond 
and  known  as  emulsin*  into  glucose,  bitter  almond-oil,  and  hydrocyanic 
acid,  C20H?7N011  +  2H2O=2C6H1206  +  C7H6O  +  HCN.  The  presence  of 
hydrocyanic  acid  renders  the  crude  oil  of  bitter  almonds  poisonous.  It 
may  be  purified  either  by  re-distilling  with  lime  and  ferrous  chloride, 
when  the  HCN  is  converted  into  a  ferrocyanide  ;  or  by  shaking  it  with 
an  equal  volume  of  a  strong  solution  of  NaHS03,  which  combines  with 
the  benzoic  aldehyde  to  form  a  crystalline  compound,  from  which  the 
pure  oil  may  be  obtained  by  distillation  with  sodium  carbonate. 

Benzaldehyde  is  now  made  artifically  from  toluene.  When  chlorine 
is  passed  into  boiling  toluene,  preferably  in  sunlight,  benzol  chloride, 

*  The  terms  zymase,  enzyme,  and  liydrolyst  have  be?n  applied  to  such  unorganised 
ferments. 


BENZALDEHYDE.  585 

C6H.-CHC12,  is  produced.     By  heating  this  with  lime  under  pressure,  it 
is  converted  into  bitter-almond  oil — 

C6H5-CHCL>  +  Ca(OH)2  =  CaCl.2  +  H20  +  C6H5'CHO. 
Or  the  chlori nation  of  the  toluene  is  stopped  when  benzyl  chloride, 
CgH.5-CH8Cl,  has   been   formed,  and  this  is    then    heated    with    lead 
nitrate — 

2C6H5-CH2C1  +  Pb(N03)3  -  2C6H5-CHO  +  PbCl2  +  2HN02. 

Benzoic  aldehyde  is  a  colourless  or  pale  yellow  liquid,  of  characteristic 
odour,  boiling  at  179°  C.,  and  of  sp.  gr.  1.05.  It  is  very  sparingly 
soluble  in  water,  but  dissolves  in  alcohol,  and  is  precipitated  on  addition 
of  water.  It  is  often  sold  in  alcoholic  solution.  The  oxidising  action 
of  air  gradually  converts  benzoic  aldehyde  into  crystals  of  benzoic  acid  ; 
C6H5-CHO  +  0  =  C6H,-C02H.  The  presence  of  hydrocyanic  acid  retards 
this  conversion. 

The  aromatic  aldehydes  show  reactions  very  similar  to  those  of  the 
fatty  aldehydes.  They  are,  however,  less  powerful  reducing-agents, 
and  instead  of  resinifying  with  alkalies,  they  are  converted  into  the 
corresponding  alcohol  and  acid,  one  part  being  reduced  and  the  other 
oxidised  :  2C6H5-CHO  +  KOH  =  C6H5'CH2OH  +  C6H5'COOK. 

Moreover,  with  NH3  they  do  not  combine  directly,  but  are  converted 
into  compounds  like  hydrobenzamide,  a  crystalline  substance,  m.-p. 
noc  C. ;  3(C6H5-CHO)  +  2NH3  =  (C6H5-CH)3-N2  +  3H20. 

They  show  a  remarkable  tendency  to  condense  with  other  compounds 
under  influence  of  dehydrating  agents,  the  aldehydic  oxygen  combining 
with  two  H  atoms  from  the  other  compound.  Thus  by  action  of  HC1 
gas  on  a  mixture  of  benzaldehyde  and  acetic  aldehyde,  cinnamic  alde- 
hyde is  formed ;  C6H5CHO  +  CH3'CHO  =  C6H5'CH  :  OH'CHO  +  H20. 

Beuzaldehyde  dissolves  in  a  strong  solution  of  Na.2S03,  and  if  dilute  H2S04  be 
added,  drop  by  drop,  to  the  solution,  voluminous  crystals  of  C6H5'CHONaHS03 
are  deposited  ;  these  dissolve  on  heating  but  are  deposited  again  on  cooling.  By 
reduction  with  Na-amalgam,  benzaldehyde  yields  benzyl  alcohol  and  hydro- 
benzoin  (p.  575). 

Benzaldoxime,  C6H5'CH  :  N'OH  exists  in  an  a-form  (m.-p.  35°  C.),  and  a 
0-form  (m.-p.  125°  C.),  which  passes  into  the  a-form  when  heated.  These  are 
stereoisomerides  (see  acetoximes). 

Cmii'tnic',  or  cumic  aldehyde,  or  cuminol, is  I  :  ^-itopropylfanz&ldekydt,  C6H4'C3H/ 
CHO,  and  occurs  in  the  aromatic  oils  of  cummin,  caraway,  and  water-hemlock,  all 
umbelliferous  plants  ;  it  is  extracted  from  the  oil  by  shaking  with  solution  of 
NaHSOo,  which  forms  a  crystalline  compound  with  it.  It  is  liquid,  fragrant,  and 
boils  at  235°  C. 

Cinnamic  aldehyde,  C6H5'CH  :  CH'CHO,  occurs  in  the  essential  oils  of  cinnamo 
and  cassia,  and  is  very  similar  in  its  chemical  properties  to  benzaldehyde.    When 
oxidised,  it  yields  cinnamic  acid,  C8H/C02H.  It  may  be  obtained  from  benzoic  and 
acetic  aldehydes,  as  above  mentioned. 

355.  The  hydroxy-aromatic  aldehydes,  like  salicylic  aldehyde, 
C6H4(OH)-CHO  (hydroxybenzaldehyde),  have  an  OH  attached  directly 
to  the  benzene  ring,  and  are  therefore  phenol  aldehydes,  corresponding 
with  the  phenol  alcohols  (p.  5  7 1 ).     Besides  their  formation  by  oxidation 
of  these  alcohols,  the  hydroxy-aromatic  aldehydes  are  produced  by  I 
nucleal  condensation  between  the  phenols  and  chloroform,  producec 
heating  the  mixture  with  aqueous  alkali  (Reimer's  reaction). 
(\.H5-OH  +  CHC13  +  4KOH  =  C6H4(OK)'CHO  +  3KC1 
Phenol.       Chloroform.  Potassium  salicylaldeliyde. 


5"86  FUEFUEAL. 

The  potassium  compound  is  distilled  with  dilute  acid  to  obtain  the 
aldehyde. 

In  this  reaction  the  alkali  is  required  to  absorb  the  HC1  which  is  formed  when 
water  alone  is  used,  and  which  must  be  removed  to  prevent  back  action,  the 
change  being  reversible. 

Salieyl  aldehyde  is  0rMe»-hydroxybenzaldehyde,  there  being,  of  course,  three 
isomerides  of  this  disubstitution  product.  It  exists  in  oil  of  spir&a  (meadow- 
sweet), and  is  made  by  oxidising  saligenin  (p.  572),  or  from  phenol  as  described 
above.  Its  sp.  gr.  is  1.17,  and  it  boils  at  196°  C.  It  dissolves  in  alcohol,  but 
sparingly  in  water.  It  resembles  benzaldehyde  in  most  reactions  but  exhibits  some 
characteristic  of  its  phenol  character,  such  as  the  ferric  chloride  coloration 
and  the  exchange  of  H  for  K  by  treatment  with  KOH  forming  C6H4(OK)'CHO. 
Like  other  orthohydroxyaldehydes  it  stains  the  skin  yellow. 

Anisic  aldehyde,  C6H4(OCH3)-CHO,  is  paramethojnjlenzaUehtjde.  the  methyl 
derivative  of  parasalicylic  aldehyde  ;  it  is  prepared  by  heating  the  essential  oils  of 
anise  and  fennel  (both  umbelliferous  plants)  with  dilute  HXO^,  being  forme  d  by 
the  oxidation  of  anethol  (#.r.)  which  these  oils  contain.  It  is  a  fragrant  li'iuid, 
boiling  at  248°  C. 

Dihydroxybenzaldehydes  are  also  known.     The  I  :  3  ^-derivative. 


aldehyde,  C6HS(OH;.2-CHO[CHO  :  (OH)2=i  :  3  14]  is  obtained  from  pyroeatechol, 
C6H4(OH>»,  and  chloroform  by  Reimer's  reaction  (r.*.)  ;  it  melts  at  153°  C.  When 
methylpyrocateehol,  C6H4(OH)(OCH3),  is  similarly  treated  it  yields  the  methyl 
derivative  of  protocatechuic  aldehyde,  CgHgCOHXOCH^-CHO  ;  this  is  m/< 
an  aromatic  substance,  much  used  for  flavouring,  extracted  from  the  po»i- 
Vanilla  planifolia,  a  Mexican  orchidaceous  plant,  by  boiling  them  with  alcohol. 
It  forms  needles,  melts  at  80°  C.,  and  sublimes.  It  is  sparingly  soluble  in  water, 
Vanillin  is  now  made  artificially  by  oxidising  eoniferine,  C^H.^Og,  by  chromic  acid. 
Coniferine  is  a  crystalline  glucoside.  extracted  from  pinewood  ;  when  oxidised  it 
yields  glycora  nillin,  the  glucoside  of  vanillin,  C^^CCH^O  C6HUO5)-CHO.  which 
yields  glucose  and  vanillin  on  hydrolysis. 

Piperonal  or  heliatropine  is  m'ethyleneprotocatecJnite  aldehyde  C6H3(O.2CH 
made  by  oxidising  piperic  acid  (j.r.)    It  melts  at  263°  C.  and  is  valued  tV       ka 
odour  of  heliotrope. 

356.  Pyromucic  aldehyde,  furfural,  or  furfurol,  C4H3OCHO.  is  the  aldehy. 


furfurane  (#.*'.).  O<  "  •     .     It  is  prepared  by  distilling  the  bran  of  wheat. 

^CH  =CH 

freed  from  starch  and  gluten  by  steeping  in  a  cold  weak  solution  of  potash,  with 
half  its  weight  of  sulphuric  acid,  previously  diluted  with  an  equal  bulk  of  water,  a 
current  of  steam  being  forced  through  the  mixture  :  the  furfural  distils  over  with 
the  water,  from  which  it  may  be  separated  by  adding  common  salt.  A  hundred 
parts  of  bran  yield  about  three  of  furfural.  It  is  a  product  of  the  hydrolysis  of 
certain  carbohydrates,  particularly  such  as  are  pentiws.  It  is  also  present  in 
fusel  oil  from  crude  spirits.  Furfural  is  a  colourless  liquid  smelling  of  bitter 
almonds,  of  sp.  gr.  1.17  and  boiling-point  162°  C.  It  dissolves  in  twelve  time-  its 
weight  of  water,  and  is  freely  soluble  in  alcohol.  Strong  sulphuric  acid  dis> 
it  to  a  purple  liquid,  from  which  water  precipitates  it  unchanged.  It  becomes 
brown  when  exposed  to  the  air.  Furfural  combines  with  XaHSO3,  reduce-  silver, 
and  yields  an  intense  red  colour  with  aniline  acetate.  With  ammonia  it  behaves 
as  an  aromatic  aldehyde,  forming  furfwraniide  (C4H3OCH)3X.>.  in  which  three 
molecules  of  furfural  have  exchanged  O"3  for  N'"0. 

By  oxidation,  furfural  is  converted  into  pyromucic  acid,  C4H3OCO.2H.    Air.  >ln  -lie 
solution  of  potash  converts  it  into  potassium   pvromucate  and   furfur' 
C4H30-CH?OH. 

Funtsol  is  isomeric  with  furfural,  and  is  prepared,  in  a  similar  way,  from  certain 
varieties  of  furus  (seaweed). 

III.  ACIDS. 

357.  The  acids  are  the  second  oxidation-products  of  the  primary  alcohols. 

The  group  -C\      '    in  the  alcohol  is  converted  into  •(.'  .  carl 

XOH  XOH 

in  the  acid,  so  that  a  general  formula  for  an  acid  is  R'COOH,  where  R  is  a 


FATTY  ACIDS.  587 

hydrocarbon  residue  or  radicle.  This  view  of  the  constitution  of  acids 
is  supported  mainly  by  the  three  following  facts  :  (j)  Two  acids  can 
be  synthetised  from  sodium  -substituted  hydrocarbons  and  CO,,  showing 
that  the  acid  produced  (or  its  sodium  salt)  probably  contains  the  hydro- 
carbon radicle  and  both  the  oxygen  atoms  attached  to  the  same  carbon 
atom;  e.g.,  CH3Na  +  CO2  =  CH3  COONa.  (2)  The  monochlorohydro- 
carbons,  e.g.,  CH3*CH2C1,  can  be  converted  by  double  decomposition  with 
KCN  into  cyanides,  e.g.,  CH3-CH2'C  i  N,  and  when  these  are  boiled  with 
water  the  N  is  removed  as  NH3,  and  an  acid  remains  ;  CH  ,-CHvC  :  N  + 
2HOH  =  CH3-CH2-COOH  +  NH3.  (3)  The  acids  contain  a'hydroxyl 
group,  for,  by  interaction  with  PC15,  they  exchange  0  and  H  for  Cl, 
hydrogen  chloride  being  evolved  (p.  579)  : 

CH3-COOH  +  PC15  =  CH3-COC1  +  POC13  +  HC1. 

It  will  be  found  that  the  formula  H'COOH  is  the  only  formula  which 
can  be  written  for  formic  acid,  which  resembles  all  the  other  acids  in  its 
behaviour. 

Two  methods  generally  applicable  for  producing  the  acids  are  —  (i)  oxi- 
dation of  the  corresponding  alcohol,  R'CH,OH  +  02  =  R-COOH  +  HOH, 
and  (2)  hydrolysis  (p.  265)  of  the  cyanogen  derivatives  of  the  corre- 
sponding hydrocarbons,  R-CN  +  2HOH  =  R'COOH  +  ]S[H3. 

Isomerism  among  the  acids  is  confined  to  the  hydrocarbon  radicles  in 
them  ;  thus  there  will  be  two  acids  of  the  formula  C3H7'COOH,  since 
there  are  two  propyl  radicles. 

The  basicity  of  an  acid  (p.  104)  is  found  to  be  limited  by  the  number 
of  COOH  groups  which  it  contains,  thus  showing  that  it  is  the  H  in 
this  group  which  is  exchanged  for  metals  to  form  salts.  When  an  acid 
contains  two  CO.,H  groups,  it  is  a  dibasic  acid,  or  if  there  are  three 
C4O,H  groups,  it  is  a  tribasic  acid,  and  so  on. 

358.  Acids  from  Monohydric  Paraffin  Alcohols  (Acetic  or  Fatty 
Series).  —  The  acids  originally  obtained  by  decomposing  soap  with  a 
mineral  acid  were  termed  fatty  acids  because  the  soap  had  been  made 
by  saponifying  fat.  Later,  the  more  important  of  them  were  shown  to 
belong  to  the  same  series  of  acids  as  acetic  acid,  hence  the  term  fatty 
acids  was  applied  to  the  series. 

The  fatty  acids  correspond  with  the  general  formula  CMH2/<+1'C001 
and  are  produced,  by  two  general  methods  given  above,  from  the  alcohols 
and  cyanides  of  the  paraffin  series. 

An    important    method    of    obtaining    fatty  acids  consists   in  treating  alkyl 
derivatives    of     ethyl     acetoacetate    (0.r.)    with     an     alkali.     This    compon 
CH.;CO-CH.,-COOC.,H5,  contains  a  CH2  group,  attached  to  two  CO  groups:  wlw 
tliis  is  the  casr  Na  ran  siibstitut.-d  for  the  H  in  the  CH2and  by  treating  the  sodi 
derivative  with  an  alkyl  iodide,  compounds  of  the  type  CH3CO'CHR-C      H  ,H,  ai 
(  '  1  LCOCKo  •COOCoH/are  obtained.     By  treatment  with  potash  these  yiel 
shun 


.jV/\_/  * 

CH  CO'  ^*    —  —          ____ 

In  the  Iatter7ase~the  add  contains  a  secondary  radicle.     The  reaction  is  soim-th 
complicated  bv  the  formation  of  a  ketone. 

The  ethvl  salt  of  the  dibasic  acid  malonic  acid,  CH./COOH).,,  also  conta 
CH.,  group  attached  to  two  CO  groups,  so  that  when  it  is  appropr.aU-Iv 
first  Na  or  Xa,  and  then  one  or  two  alkyl  groups  may  be  substituted  f;;''1  li- 
the CH,  group.     In    this   way   compounds   of    the    type    I 
CR/COOC-HA,   and    from   these   the   corresponding    acids    < 
CiMCOOH),  are  obtained.     When  heated,  these  acids  lose  CO*  yielding  a 


588  ACETIC   SERIES   OF  ACIDS. 

the  acetic  series.  The  preparation  of  ethyl  malonate,  CH2(COOC2H5)2,  is  described 
later  ;  the  reactions  by  which  it  may  be  converted  into  butyric  acid,  for  ex- 
ample, are  as  follows  : 

CH2(COOC2H5)2  +  C2H5ONa  =  CHNa(COOC2H5)2  +  C2H5OH 
CHNa(COOC2H5)2  +  C0H5I  =  CHC2H5(COOC2H5)2  +  Nal 
CHC0H5(COOC2H5)2  +  2KOH  =  CHC2H5(COOK)2  +  2C2H5OH 
CHC2H5(COOK)2  +  2HC1  =  CHC2H5(COOH2)  +  ~2KC1 
CHC2H5(COOH)2  (heated)  =  CH2C2H5(COOH)  +  C02 

As  malonic  acid  can  be  made  from  acetic  acid  (p.  614)  this  series  of  reactions 
serves  for  the  preparation  of  the  homologues  of  acetic  acid  from  the  acid  itself. 

The  principal  members  of  the  series  are  : — 

Monobasic  acids  of  the  acetic  series,  CwH2n+1C08H. 


Acid. 

Source. 

Formula. 

M.-P. 

B.-P. 

Formic  . 

Red  ants,  nettles 

H 

C02H 

9° 

C. 

100.6°  C. 

Acetic   . 
Propionic 

Vinegar       .... 
Oxidation  of  oils 

CH3     • 
C2H5   - 

C02H 
CO2H 

-£ 

C. 

c. 

118° 
140° 

C. 

c. 

Butyric 

Rancid  butter 

C3H7 

C02H 

-   8° 

c. 

163° 

c. 

Valeric  . 

Valerian  root 

C4H9   • 

C02H 

-59° 

c. 

1  86° 

c. 

Caproic 

Rancid  butter 

C^HU 

C02H 

8° 

c. 

205° 

c. 

(Enanthic 

Oxidation  of  castor  oil 

CeH13  ' 

C02H 

-11° 

c. 

223° 

c. 

Caprylic 

Rancid  butter      .         . 

^1^15  ' 

C02H 

t7° 

c. 

237° 

c. 

Pelargonic     . 

Geranium  leaves 

C8H17  * 

CO2H 

13° 

c. 

254° 

c. 

Rutic  or  Capric 

Rancid  butter 

C9H19  • 

C02H 

3i° 

c. 

268° 

c. 

Undecylic 

Oil  of  rue     .... 

C10H21a 

C00H 

29° 

c. 

— 

Laurie  . 

Bay  berries  .... 

CnH?3- 

C02H 

44° 

c. 

— 

Tridecylic 

Cocoa-nut  oil 

C02H 

41° 

c. 

— 

Myristic 

Nutmeg-butter    . 

CjgH^' 

C02H 

54° 

c. 

— 

Pentadecylic 

Agaricus  integer  (a  fungus) 

GUHW' 

C02H 

51° 

c. 

— 

Palmitic 

Palm  oil 

QU^SL' 

C02H 

62° 

c. 

— 

C02H 

60° 

c. 

Stearic  . 

Tallow         .... 

P16™33. 
^iT-ttss 

C02H 

69° 

c. 

— 

Arachidic  or  Butic 

Butter  ;  earth-nut 

COoH 

77° 

c. 

— 

Behenic 

Oil  of  ben    . 

CmH^* 

C02H 

84° 

c. 

— 

Cerotic  . 

Bees'-wax    .... 

^25^51* 

C02H 

78° 

c. 

— 

Melissic 

„           .... 

P       TT        . 

^29^59 

C02H 

9i° 

c. 

— 

As  in  other  homologous  series,  the  volatility  of  the  acids  decreases  as 
the  number  of  carbon  atoms  increases,  so  that  palmitic  acid  and  those 
richer  in  carbon  can  be  distilled  only  under  diminished  pressure  or  in  a 
current  of  superheated  steam.  The  solubility  in  water  diminishes  in 
the  same  order ;  acetic  acid  mixes  with  water  in  all  proportions  while 
palmitic  acid  is  quite  insoluble.  With  the  exception  of  formic  and 
acetic  acids  they  are  decidedly  oily  in  character. 

The  acid  strength  also  diminishes  with  the  increase  in  the  carbon  atoms,  and 
this  is  turned  to  account  in  separating  the  volatile  fatty  acids  from  each  other  by 
the  method  of  partial  saturation.  Suppose  it  to  be  required  to  separate  butyric  and 
valeric  acids.  The  mixture  is  divided  into  equal  parts,  one  of  which  is  exactly 
neutralised  by  soda,  yielding  butyrate  and  valerate  of  sodium.  The  other  half  of 
the  acid  mixture  is  then  added,  and  the  whole  distilled.  Since  butyric  acid  is  the 
stronger  acid,  it  will  expel  the  valeric  acid  from  the  sodium  valerate.  If  the 
mixture  contained  equal  molecules  of  the  two  acids,  the  distillate  would  contain 
valeric  acid  only,  and  the  residue  would  contain  the  sodium  butyrate.  If  the 
valeric  acid  preponderated,  the  residue  would  contain  both  valerate  and  butyrate, 
and,  when  distilled  with  sulphuric  acid,  would  yield  a  fresh  mixture  of  the  acids, 
which  could  be  again  treated  in  the  same  way.  But  if  butyric  acid  preponderated, 
the  residue  would  be  only  sodium  butyrate,  while  the  distillate  would  contain  both 
butyric  and  valeric  acids,  to  be  again  treated  by  partial  saturation. 

The  non-volatile  fatty  acids  may  be  separated  from  each  other  by  fractional  pre- 
cipitation, which  depends  on  the  principle  that  the  insolubility  of  their  barium, 


FORMIC  ACID.  589 

magnesium,  and  lead  salts  increases  with  the  number  of  carbon  atoms.  The 
mixture  of  fatty  acids  is  dissolved  in  alcohol,  and  is  partially  precipitated' by  an 
alcoholic  solution  of  the  acetate  of  Ba,  Mg,  or  Pb.  This  precipitate  will  contain 
the  acid  or  acids  richest  in  carbon.  It  is  filtered  off,  and  another  precipitate  is 
obtained  from  the  solution  in  the  same  way.  This  will  contain  acids  poorer  in 
carbon,  and  so  on.  Each  precipitate  is  decomposed  by  HC1,  and  the  new  mixture 
of  acids  so  obtained  is  subjected  to  the  same  treatment,  until  the  separated  acid  is 
found  to  have  a  constant  melting-point. 

The  constitution  of  the  fatty  acids  is  disclosed  when  they  are  sub- 
jected to  electrolysis,  for  they  then  evolve  one  atom  of  carbon  as  CO., ; 
thus,  acetic  acid  yields  dimethyl  (ethane),  C02  and  H — 

2(CH3-C02H)  =  (CH3)2  +  2C02  +  Ho. 
Again,  valeric  acid  yields  dibutyl,  C02  and  H — 

2(C4H9-C02H)  =  (C4H9)2  +  2C02  +  H2. 

To  prepare  an  acid  higher  in  the  series  from  one  lower  in  the  series, 
advantage  may  be  taken  of  such  reactions  as  the  following : 

(1)  CH3-CH9-COOH  +  H4  =  CH3-CH2-CH9OH. 

(2)  3CH3-CH2-CH2OH  +  PI,  =  3CH3-CH2-CHoI  +  P(OH)3. 

(3)  CH3-CH9-CH9I  +  KCN  =  CH3'CH2'CH9-CN  +  KI. 

(4)  CH3-CH2-CH2CN  +  2HOH  =  CH3-CH2rCH2'COOH  +  NH3. 

359.  Formic  acid,  H'C02H,  was  originally  obtained  from  ants.  It 
occurs  in  nettles  and  other  plants,  in  some  animal  fluids,  and  occasion- 
ally in  mineral  waters.  It  is  prepared  by  distilling  oxalic  acid  with 
glycerine.  30  grams  of  crystallised  oxalic  acid  and  200  c.c.  of  glycerine 
are  heated,  in  a  half-litre  flask  provided  with  a  thermometer  and 
condenser,  to  about  80°  C.,  when  formic  acid  distils  over  together  with 
the  water  of  crystallisation  of  the  oxalic  acid,  and  carbonic  acid  gas  is 
evolved;  C02H'C02H  =  H'C02H  +  C02.  When  the  evolution  of  CO, 
ceases,  a  fresh  quantity  of  oxalic  acid  may  be  introduced  and  the  opera- 
tion continued,  the  same  glycerine  serving  for  the  conversion  of  a  large 
quantity  of  oxalic  acid.  The  formic  acid  first  produced  converts  the 
glycerine  into  monoformin — 

C3H5(OH)3  +  H-C02H  =  C3H5(OH)2(O.CHO)  +  HOH. 

The  monoformin  is  then  decomposed  by  the  water  of  crystallisation  of 
the  oxalic  acid,  the  equation  being  reversed,  and  glycerine  being  repro- 
duced. By  continuing  the  process,  formic  acid  of  56  per  cent,  may  be 
obtained.  To  prepare  the  pure  acid,  this  is  neutralised  with  lead  oxide, 
the  lead  formate  crystallised,  dried,  and  heated  to  100°  C.  in  a  current  of 
dry  HjjS;  (H'CO2)2Pb  +  H2S  =  2H'C02H  +  PbS.  The  formic  acid  is 
carefully  condensed  and  redistilled  with  a  little  lead  formate  to  re- 
move H2S. 

Formic  acid  is  obtained  synthetically  by  heating  caustic  alkalies  to 
100°  C.  in  carbonic  oxide;  CO  +  KOH  =  H'C02K  (potassium  formate) ; 
again,  potassium,  acting  on  carbon  dioxide  in  presence  of  water,  yield 
acid  potassium  carbonate  and  potassium  formate — 

2C02  +  H20  +  K2  =  KHC03  +  H'C02K. 

It  is  also  produced  in  other  reactions  in  which  carbonic  acid  is  acted 
on  by  reducing-agents.     Carbonic   acid  may  be  regarded  as  %*racy- 
formic  acid,  HO'CO.H,  that  is,  formic  acid,  H'C02H,  in  which  U 
substituted  for  H.     When  starch  and  other  organic  bodies  are  violent  y 
oxidised,  they  yield  carbonic  acid,  but  if  they  are  gradually  and  quietly 


590  ACETIC  ACID. 

oxidised,  they  yield  formic  acid.  The  quiet  oxidation  of  organic  bodies 
is  often  effected  by  heating  them  with  Mn02  and  dilute  H,S04. 

Formic  acid  is  also  formed  by  oxidising  methyl  alcohol,  and  when 
hydrocyanic  acid  is  hydrolysed  by  boiling  it  with  dilute  acids,  H'CN  + 
2HOH  =  H-C02H  +  NH3. 

Properties  of  formic  acid.  —  Colourless  liquid,  fuming  slightly  in  air 
and  of  pungent  smell  ;  it  blisters  the  skin.  Formic  acid  boils  at  ioo°.6  C. 
and  melts  at  9°.  Its  sp.  gr.  is  1.22  at  20°.  The  diluted  acid  boils  at 
a  higher  temperature  ;  an  acid  of  77  per  cent,  boils  at  107°. 

The  formates  are  all  soluble  in  water  ;  their  solutions  yield  a  red 
colour  with  ferric  chloride,  and  reduce  silver  from  the  nitrate,  when 
boiled  with  it,  on  account  of  the  tendency  of  formic  acid  to  become 
carbonic  (hydroxyformic)  acid.  Solid  formates  evolve  carbonic  oxide 
(burning  with  a  blue  flame)  when  heated  with  strong  H2S04,  which 
removes  the  elements  of  water;  H'C02H  =  HOH  +  CO.  A  formate 
heated  with  excess  of  baryta  yields  the  oxalate;  (HC02)2Ba== 


> 
Formic  acid  is  used  in  making  some  of  the  coal-tar  dyes. 

Formic  acid  differs  in  some  respects  from  the  other  members  of  the  series.  Thus 
its  powerful  reducing  action  relates  it  to  the  aldehyde  acids  (p.  607)  ;  indeed,  if 
its  formula  be  written  HO'CHO  it  might  be  regarded  as  liydroxy  formaldehyde. 
No  acid  chloride  or  anhydride,  such  as  are  characteristic  derivatives  of  the  higher 
acids  of  the  series,  can  be  obtained  from  formic  acid.  By  loss  of  water  it  yields 
CO  not  (H-CO)20.  which  would  be  the  true  anhydride.  When  heated  at  160°  C. 
it  breaks  up  into  H  &  CO^  the  same  change  occurring  at  the  ordinary  temperature 
in  contact  with  platinum  black. 

360.  Acetic  acid,  or  methyl  -formic  acid,  CH3'C02H,  is  found  either 
free  or  combined  in  many  plants  and  in  some  animal  fluids.  It  is 
obtained  by  the  destructive  distillation  of  wood  or  of  sawdust,  or  spent 
dye-woods.  The  aqueous  layer  in  the  condenser  (p.  566)  is  neutralised 
by  sodium  carbonate,  and  the  methyl  alcohol  and  acetone  are  distilled  off. 
The  evaporated  liquor  deposits  impure  crystals  of  sodium  acetate  which 
are  heated  to  expel  some  tarry  matters,  and  distilled  with  H2S04,  when 
acetic  acid  passes  over;  CH3-C02Na  +  H2S04  =  CH3-C02H  +  NaHS04. 
The  crude  acid  from  wood  is  termed  pyroligneous  acid. 

Acetic  acid  is  also  made  by  the  oxidation  of  alcohol  for  the  produc- 
tion of  vinegar;  CH3'CH2OH  (ethyl  alcohol)  +  02  =  OH3'C02H  +  H20. 
But  this  equation  cannot  be  realised  unless  some  third  substance  be 
present.  It  was  seen  at  p.  564  that  platinum  black  would  answer  the 
purpose,  and  in  some  chemical  works  this  process  has  been  employed 
for  making  acetic  acid.  Weak  fermented  liquors,  such  as  beer  and  the 
lighter  wines,  are  very  liable  to  become  sour,  which  is  never  the  case 
with  distilled  spirits,  however  much  diluted.  This  is  due  to  the  pre- 
sence in  the  fermented  liquid  of  albuminous  (nitrogenised)  matters  and 
salts,  which  afford  nourishment  to  a  microscopic  organism,  termed 
Mycoderma  aceti,  which  appears  to  convey  the  oxygen  of  the  air  to  the 
alcohol. 

Quick  vinegar  process.  —  A  weak  spirit  mixed  with  a  little  yeast  or  beet-root 
juice,  heated  to  about  27°  C.,  is  caused  to  trickle  slowly  from  pieces  of  cord  fixed 
in  a  perforated  shelf  over  a  quantity  of  wood  shavings  previously  soaked  in 
vinegar  to  impregnate  them  with  the  acetic  ferment  or  mother  of  vinegar.  The 
shavings  are  packed  in  a  tall  cask  (Fig.  272)  in  which  holes  have  been  drilled  in 
order  to  allow  the  passage  of  air.  The  oxidation  of  the  alcohol  soon  raises  the 
temperature  to  about  38°  C.,  which  occasions  a  free  circulation  of  air  among  the 


VINEGAR.  59 ! 

shavings.  The  mixture  is  passed  three  or  four  times  through  the  cask,  and  in 
about  thirty-six  hours  the  conversion  into  vinegar  is  completed.  If  the  supply  of 
air  be  insufficient,  alcohol  is  lost  in  the  form  of  aldehyde  vapour,  the  irritatinir 
odour  of  which  pervades  the  air  of  the  factory. 

White- wine  vinegar  is  prepared  from  light  wines  by  a  similar  process.  Malt 
vinegar  is  made  from  infusion  of  malt  fermented  by  yeast  with  free  contact  of  air . 
Vinegar  contains,  on  an  average,  about  5  per 
cent,  of  acetic  acid.  Its  aroma  is  due  to 
the  presence  of  a  little  acetic  ether.  The 
vinegar  of  commerce  is  allowed  to  be  mixed 
with  TT,Vtf  of  its  weight  of  sulphuric  acid  in 
order  to  prevent  it  from  becoming  mouldy. 
By  distilling  vinegar  a  weak  acetic  acid  is 
obtained,  which  may  be  concentrated  by  re- 
distilling and  receiving  separately  the  por- 
tion distilling  between  110°  and  120°  C. 


Pure  acetic  acid  is  prepared  by 
distilling  5  parts  by  weight  of  fused 
sodium  acetate  with  6  parts  of  con- 
centrated sulphuric  acid  (see  above). 
The  distillate  may  be  redistilled  with 
a  little  Mn02  to  remove  S02. 

The    acid    is   also   produced  when  Fio-  272 

CH3Na  is  treated  with  C02  (p.  587), 

and  when    methyl    cyanide   is   hydrolysed   by   boiling    dilute    acids ; 
CH3-C1ST  +  2HOH  =  CH3-COOH  +  NH3. 

Properties  of  acetic  acid. — Colourless,  pleasant  smell,  blistering  the 
skin,  boiling  at  1 18°  C.,  and  giving  a  vapour  which  burns  with  a  flame 
like  that  of  alcohol.  Its  true  melting-point  is  17°  C.,  but  it  maybe 
cooled  far  below  this  without  solidifying,  unless  a  crystal  of  the  acid  be 
introduced,  when  the  whole  crystallises  in  beautiful  plates ;  hence  the 
term  glacial  acetic  acid.  The  sp.  gr.  of  the  pure  acid  is  1.063  at  18°, 
but  the  strength  of  the  acid  cannot,  as  in  other  cases,  be  inferred  from 
the  sp.  gr.,  because  the  latter  is  increased  by  addition  of  water,  till  it 
reaches  1.079  (7°  Per  cent,  of  acid),  when  it  is  diminished  by  more 
water,  so  that  a  43  per  cent,  acid  has  the  same  sp.  gr.  as  the  pure  acid. 

Acetic  acid  is  one  of  the  most  stable  of  the  organic  acids.  It  is 
unattacked  by  most  oxidising-agents.  When  its  vapour  is  passed 
through  a  red-hot  tube  it  yields  several  products,  among  which  marsh 
gas  and  acetone  are  conspicuous.  Most  of  its  salts  are  soluble  in  water, 
so  that  it  is  not  easily  precipitated  ;  but  if  it  be  exactly  neutralised  by 
ammonia,  and  stirred  with  silver  nitrate,  a  crystalline  precipitate  of 
silver  acetate,  CH3'CO9Ag,  is  obtained  ;  mercurous  acetate,  CH3'C02Hg, 
may  be  obtained  in  a  similar  way.  Ferric  chloride  added  to  the  neutral 
solution  gives  a  fine  red  colour. 

361.  Many  of  the  acetates  are  employed  in  the  arts.  Those  formed  by  the 
weaker  bases,  such  as  Fe20^  and  A1203,  are  easily  decomposed  by  boiling  with 
water,  basic  acetates  being" precipitate*d  ;  hence  the  aluminium  m-rtatr  and  femo 
iicrttitc  (red  liquor)  are  much  used  by  dyers  and  calico-printers  as  mordants,  the 
basic  acetates  being  deposited  in  the  fabric,  and  forming  insoluble  compounds 
with  colouring-matters. 

Lead  acetate,  or  avgar  of  lead,  (CH3C02)2Pb.3Aq,  is  the  commonest  commerc 
acetate,  and  is  prepared  by  dissolving  litharge  (PbO)  in  an  excess  of  acetic  acid, 
when  the  solution  deposits  prismatic  crystals  of  the  salt.     On  the  large   scale, 
acetic  acid  vapour  is  passed   through  copper  vessels  with  perforated  shelves  on 
which  litharge  is  placed.     Lead  acetate  is  intensely  sweet  and  very  soluble  in 


592  ACETATES. 

water  (i^  part).  Commonly,  the  solution  is  turbid  from  the  precipitation  of  lead 
carbonate  by  the  carbonic  acid  in  the  water  ;  a  drop  of  acetic  acid  clears  it. 
The  acetate  is  soluble  in  alcohol.  When  heated,  it  fuses  at  75°  C.  and  becomes 
anhydrous  at  100°.  The  anhydrous  salt  melts  when  further  heated,  evolves  the 
pleasant  smell  of  acetone,  and  becomes  again  solid  as  a  basic  lead  acetate,  which 
is  decomposed  at  a  higher  temperature,  evolving  C02  and  acetone,  and  leaving  a 
yellow  residue  of  PbO  mixed  with  globules  of  lead. 

There  are  several  basic  lead  acetates,  but  the  only  one  of  practical  importance 
is  the  tribasic  lead  acetate,  Goulard's  extract  (CH3-C02)2Pb.2PbO.H20,  which  is 
prepared  by  boiling  lead  acetate  with  litharge.  It  forms  needle-like  crystals, 
which  are  very  soluble  in  water,  but  insoluble  in  alcohol.  A  strong  solution  of 
the  salt  is  not  affected  by  the  air,  but  a  weak  solution  is  rendered  turbid  by  the 
smallest  quantity  of  C02  in  air  or  water.  Tribasic  lead  acetate  is  very  useful  in 
the  laboratory  for  precipitating  tannin,  gum,  &c.,  from  vegetable  infusions  in 
order  to  extract  the  alkaloids. 

Verdigris  is  a  mixture  of  several  basic  cupric  acetates  prepared  by  acting  on 
sheet  copper  with  the  refuse  grapes  of  the  wine-press,  which  yield  acetic  acid  by 
oxidation  of  the  alcohol  ;  the  acid  combines  with  the  cupric  oxide  formed  by  the 
action  of  air  upon  the  copper.  Commercial  verdigris  consists  chiefly  of  the 
compound  (CH3'C02)2Cu.Cu0.6H20.  When  this  is  treated  with  water  it  is  only 
partly  dissolved,  the  residue  having  the  composition  (CH3'C02)2Cu.2Cu0.2H20. 
By  dissolving  verdigris  in  acetic  acid,  the  normal  cupric  acetate  may  be  obtained 
in  crystals  of  the  formula  (CH3'C02)2Cu.H20.  It  forms  blue  prisms  soluble  in  water. 
Verdigris  is  used  in  the  manufacture  of  colours,  and  in  dyeing  and  calico-printing. 

Emerald-green  or  cupric  aceto-arsenite,  (CH3'C02)2Cu.Cu3(As03)2.As406,  is  made 
by  boiling  verdigris  with  wrhite  arsenic  and  water.  It  is  used  for  colouring  wall- 
paper and  other  fabrics,  and  is  dangerous  to  the  makers  and  purchasers. 

Sodium  acetate,  CH3.C02Na.3Aq,  prepared  by  neutralising  acetic  acid  with 
sodium  carbonate,  crystallises  in  prisms  which  are  very  soluble  in  water,  and  yields 
one  of  the  best  examples  of  a  supersaturated  solution  (see  p.  51),  which  is  used  in 
foot- warmers  for  railway  carriages,  on  account  of  the  continuous  evolution  of  heat 
during  its  crystallisation.  It  is  four  times  as  effective  as  an  equal  volume  of  water. 

The  acetates  of  sodium  and  potassium  are  remarkable  for  their  fusibility  and 
their  stability  at  high  temperatures  ;  they  do  not  carbonise  so  readily  as  do  most 
salts  of  organic  acids.  Potassium,  sodium,  and  ammonium  acetates  combine  with 
one  and  with  two  molecules  of  acetic  acid  to  form  crystalline  compounds. 

Calcium  acetate,  when  dissolved  in  water  together  with  CaCl2,  yields  the  com- 
pound (CH3-COO)2Ca.CaCl2.ioAq,  which  crystallises  easily,  and  is  sometimes 
produced  for  effecting  the  purification  of  crude  acetic  acid  (Condy's  patent). 

Zinc  acetate,  (CHg-CO^Zn^Aq,  is  remarkable  for  being  capable  of  sublimation 
at  a  moderate  heat,  when  dried. 

Acetic  acid  is  very  useful  in  organic  chemistry  as  a  simple  solvent, 
especially  for  resins  and  hydrocarbons,  such  as  naphthalene  and 
anthracene. 

362.  Acetic  acid  may  be  produced  by  the  reaction  of  zinc  methyl, 
Zn(CH3)2,  with  COC12  (p.  190)  which  yields  acetyl  chloride  (q.v.),  a 
compound  which  furnishes  acetic  acid  when  decomposed  by  water — 
Zn(CH3)2  +  2COC12  =  2CH3-COC1  +  ZnCl2.     CH3'COC1  +  HOH  =  CH3-COOH  +  HC1. 
The  group    CH3'CO,   which   remains  unchanged  during   the    latter 
reaction  is  termed  acetyl,  02H3O,  and  may  be  regarded  as  ethyl,  CH3'CH2, 
in  which  0"  has  been  substituted  for  H2. 

There  is  a  similar  acid  radicle  corresponding  with  each  alcohol  radicle  ; 
a  few  examples  are  here  given — 


Alcohol  radicles. 

Methyl  CH3 

Ethyl  CH3-CH0 

Propyl  C2H5'CH 

Butyl  C3H7-CH 

Amyl  C4H9'CH 


Acid  radicles* 

Formyl  CHO 

Acetyl  CH,-CO 

Propionyl  C2H5'CO 

Butyryl  C3H7'CO 

Valeryl  C4H9'CO 


Termed  acidyl  or  acyl  radicles. 


ACIDS   OF   THE  ACETIC  SERIES. 

It    will    be   seen    later   that  the   alcohol   radicles   combine  in  pairs 

with  oxygen  to  produce  ethers  of  the  type     \0,  the  two  radicles  being 

the  same  or  different.     The  acid  radicles  combine  with  oxygen  in  a 

OH  r*o 

similar  manner  to  produce  acid  anhydrides,  such  as  \Q,  acetic 

CH,CO 

CH3CO  v 
anhydride,  ^      ;0,  aceto-propionic  anhydride. 

C.,H5CO 

Acetic  anhydride,  or  di-acetyl  oxide,  or  anhydrous  acetic  acid  (CHo'CO)  0  is 
prepared  by  distilling  acetyl  chloride  with  an  equal  weight  of  perfectly  anhydrous 
sodium  acetate  ;  CH3COCl  +  CH3-COONa  =  (CH3-CO)00  +  NaCl.  It  distils  over  as 
a  colourless  liquid,  smelling  of  acetic  acid,  but  irritating  the  eyes;  its  sp.  gr.  is 
1.073,  and  boiling-point,  137°  C.  It  dissolves  slowly  in  water,  with  evolution  of 
heat  and  formation  of  acetic  acid  (CH3'CO)20  +  H20  =  2(CH3-COOH). 

Acetic  anhydride  may  also  be  formed  by  heating  lead  acetate  with  carbon 
disulphide  ;  2Pb(CH3'C02)2  +  CS2  =  2(CH3'CO)20  +  2PbS  +  CO^  Also  by  heating 
acetyl  chloride  with  anhydrous  oxalic  acid;  C2H3OC1  +  (COOH).2=:(C2H30)20  + 
HC1  +  CO  +  COg. 

By  carefully  acting  on  acetic  anhydride  with  sodium-amalgam  and  water  (or 
snow),  it  has  been  converted  into  aldehyde  and  alcohol — 

(CH3-CO)20  +  2H2  =  2(CH3-CHO)  +  H20,  and  CH3'CHO  +  H2  =  CH3'CH2'OH. 
With  HC1  it  yields  acetyl  chloride  and  acetic  acid,  (CH3CO)20  +  HC1  =  CH,COC1  + 
CH3COOH. 

Acetyl  dioxide,  or  acetic  peroxide,  (CH3'CO)202,  is  obtained  by  adding  barium 
dioxide  to  an  ethereal  solution  of  acetic  anhydride — 

2(CH3-CO)20  +  Ba02  =  (CH3'CO)202  4-  Ba(CH3'C02)2.. 

It  melts  at  30°  C.  and  is  insoluble  in  water.  It  explodes  violently  when  heated, 
and  has  the  powerful  oxidising  properties  which  would  be  expected  from  its 
chemical  resemblance  to  hydrogen  peroxide. 

363.  Corresponding  with  the  thioalcohols,  the  alkyl  sulphides  and  disulphides 
(p.  572)5  there  are  thioacids,  thioanhydrides,  and  thioperoxides,  the  oxygen  outside 
the  acid  radicle,  having  been  exchanged  for  sulphur  in  each  case. 

Thioacetic  acid,  CH3'COSH,  is  obtained  by  the  action  of  P2S5  on  acetic  acid  : 

5CH3-COOH  +  P2S5  =  5C2H30-SH  +  P205. 

It  is  a  colourless,  evil-smelling  liquid,  boiling  at  93°  C.,  and  sparingly  soluble  in 
water.  Acetyl  sulphide  (thioacetic  anhydride),  (CH3'CO)28,  is  obtained  by  the 
action  of  P2S5  on  acetic  anhydride,  and  acetyl  disulphide  (thioacetic  peroxide), 
(CH3CO)2S2.  by  the  action  of  K2S2  on  acetyl  chloride. 

364.  Propionic  acid,  C2H5'C02H,  is  not  produced  upon  a  large  scale  like  acetic 
acid.     It   is  formed   in  the   putrefaction  of   various  organic  bodies,  and   in  the 
destructive  distillation  of  wood  and  of  rosin.     It   may  be   separated  from  formic 
and  acetic  acids  by  saturating  the  mixture  with  PbO,  evaporating  to  dryness  and 
extracting   with   cold   water.     On   boiling   the   solution,    it    deposits   bane    lead 
propionate,  leaving  the  basic  lead  formate  and  acetate  in  solution.    From  the  lead- 
salt  the  acid  may  be  obtained  by  the  action  of  H2S  or  H2S04. 

Sodium  propionate  is  obtained  by  the  action  of  CO  upon  sodium  ethoxide,  just 
as  sodium  formate  is  obtained  from  sodium  hydroxide  (see  p.  589) — 
CO  +  C2H5-ONa  =  C2H5-C02Na. 

Propionic  acid,  as  would  be  expected,  resembles  acetic  acid.  Its  sp.  gr.  is  0.99, 
and  it  boils  at  140°  C.  It  has  no  practical  importance.  The  propionates  are 
mostly  soluble  in  water,  but  silver  propionate  is  sparingly  soluble.  Lead  propionate 
is  much  more  difficult  to  crystallise  than  lead  acetate. 

Butyric  acid,  C3H7'C02H.  The  normal  acid  (ethylacetic  acid)  is  made  from 
cane  sugar  by  dissolving  it  in  water  (5  parts),  adding  a  little  tartaric  acid  (7^th 
part),  boiling  to  convert  the  sucrose  into  glucose,  and  adding  to  the  cooled 
liquid  some  putrid  cheese  (^th  part)  rubbed  up  in  about  thirty  times  its  weight 
of  milk.  Some  chalk  (£  part)  is  stirred  into  the  mixture,  which  is  then  allowed 
to  ferment  for  a  week  at  a  temperature  of  3O°-35°  C.  The  glucose,  C6H1206,  ui 
goes  the  lactic  fermentation,  and  is  converted  into  lactic  acid,  C3H603,  which  is 

2   P 


594  VALEEIC  ACID. 

converted,  by  the  chalk,  into  calcium  lactate,  forming  a  pasty  mass  of  crystals. 
After  a  time  the  mass  becomes  liquid  again,  evolving  bubbles  of  hydrogen  and 
carbon  dioxide,  and  forming  a  strong  solution  of  calcium  butyrate,  produced  by  the 
butyric  fermentation.  When  this  is  mixed  with  strong  hydrochloric  acid,  the 
butyric  acid  rises  to  the  surface  and  forms  an  oily  layer,  which  may  be  puritied  by 
distillation.  The  passage  of  lactic  acid  into  butyric  acid  is  expressed  by  the 
equation  2C3H603  =  C3H7'C0.2H  +  2C02  +  2H2. 

Butyric  acid  is  a  strongly  acid  liquid,  smelling  of  rancid  butter,  having  the 
sp.  gr.  0.96,  and  boiling  at  163°  C.  It  mixes  readily  with  water,  but  separates 
again  when  the  water  is  saturated  with  a  salt.  The  butyrates  are  rather  less 
soluble  than  the  acetates.  Calcium  butyrate  is  less  soluble  in  hot  water  than  in 
cold.  Silver  butyrate  is  very  sparingly  soluble. 

Butyric  acid  is  found  in  the  products  of  distillation  of  wood  and  of  some  other 
organic  bodies.  It  exists  in  the  perspiration  of  the  skin,  and,  as  a  glyceride,  in 
butter,  in  cod-liver  oil,  and  in  some  vegetable  oils. 

Isobutyrlc  acid  (dimethylacetic  acid)  (CH3)2CH'COOH  boils  at  155°  C.  and  is 
made  from  isopropyl  chloride  through  the  cyanide  reaction  (p.  587). 

Valeric  or  valerianic  acid.  Four  of  these  are  possible  ;  that  commonly  called 
valeric  acid  is  isopropylacetic  acid,  (CH3)2CH'CH2'COOH.  It  is  prepared  by 
oxidising  amyl  alcohol  (fusel  oil)  with  potassium  bichromate  and  sulphuric  acid. 

It  is  an  oily  liquid  smelling  like  old  cheese  ;  its  sp.  gr.  is  0.95,  and  it  boils  at 
174°  C.  It  is  much  less  soluble  in  water  than  are  the  preceding  acids,  requiring 
thirty  times  its  weight.  The  valerates  are,  as  a  rule,  easily  soluble  in  water,  but 
the  silver  salt  is  sparingly  soluble.  Zinc  valerate  is  used  medicinally. 

Valeric  acid  occurs  in  valerian  root,  in  the  elder,  in  the  berries  of  the  guelder 
rose,  and  in  many  other  plants  ;  also  in  some  fish  oils  and  in  the  perspiration. 

Normal  caproic  or  hexylic  acid,  C5Hn*C02H  (sp.  gr.  0.94,  b.-p.  205°  C.),  is  found 
in  butter  from  cows  and  goats,  and  in  Limburg  cheese,  being  one  cause  of  its 
odour  ;  it  is  also  found  in  some  plants,  and  in  the  perspiration.  Caproic  acid  is 
formed,  together  with  butyric  and  acetic  acids,  in  the  butyric  fermentation 
described  above.  It  dissolves  very  sparingly  in  water,  and  has  a  repulsive 
odour.  The  caproates  of  barium  and  calcium  are  rather  sparingly  soluble  in  water, 
and  silver  caproate  is  nearly  insoluble. 

365.  (Enanthic  or  normal  heptylic  acid,  C6H13'C02H,  is  obtained  by  oxidising 
oenanthic  aldehyde  (oenanthol).     It  has  a  faint  odour  and  sp.  gr.  0.93  ;  it  boils  at 
223°  C.     Many  of  the  cenanthates  are  nearly  insoluble    in  water.     The    strong 
solutions  of  the  alkali  oenanthates  become  gelatinous  on  cooling,  like  solution  of 
soap. 

Normal  caprylic  or  octylic  acid,  C7H15-C02H,  is  found  in  the  fusel  oil  from  wines, 
in  old  cheese,  and,  as  a  glyceride,  in  butter,  human  fat,  and  cocoa-nut  oil.  It  is 
the  first  acid  of  this  series  which  is  solid  at  common  temperatures,  forming  needle- 
like  crystals  or  scales  fusible  at  16°  C.  and  boiling  at  237°.  It  has  an  offensive 
smell,  and  is  very  sparingly  soluble  in  water.  The  caprylates,  except  those  of  the 
alkalies,  are  sparingly  soluble  in  water,  but  they  dissolve  in  alcohol. 

Pelargonic  or  normal  nonylic  acid,  C8H17'C02H,  was  originally  obtained  from 
the  essential  oil  of  Pelargonium  roseum,  and  is  found  among  the  products  of 
oxidation  of  oleic  acid  by  nitric  acid.  It  is  also  formed  when  essential  oil  of  rue 
(nonylmethylltetone)  is  oxidised  by  nitric  acid.  It  is  an  oily  liquid,  of  faint  odour, 
crystallising  at  12°  C.  and  boiling  at  253°.  It  has  sp.  gr.  0.91,  and  is  insoluble  in 
water.  The  pelargonates  are  sparingly  soluble  in  water,  except  those  of  the 
alkalies. 

Laurie  or  normal  dodecylic  acid,  CjjH^'CC^H,  is  obtained  from  a  fatty  substance 
found  in  the  fruit  of  the  sweet  bay  (Laurus  nobilis)  and  in  sassafras-nuts  or 
pichurim  beans,  which  are  used  for  flavouring  chocolate,  and  are  the  seeds  of 
another  of  the  Lauraceas  (Nectandra  Puchury).  A  similar  substance  is  found  in 
the  mango  and  in  a  variety  of  cochineal  insect.  The  fat  is  saponified  by  boiling 
with  potash,  the  solution  decomposed  by  hydrochloric  acid,  and  the  separated 
fatty  acid  distilled,  when  lauric  acid  is  found  in  the  first  fractions. 

The  crystals  of  lauric  acid  fuse  at  44°  C.  It  cannot  be  distilled  at  ordinary 
pressures  without  decomposition. 

366.  Palmitic  acid,  C15H31-C02H,  crystallises  in  needles  (m. -p.  62°  C.), 
and  is  the  first  of  the  fatty  acids,  properly  so  called,  which  occur  as 
glycerides  in  the  vegetable  and  animal  fats,  and  form  true  soaps  with 


STEARIC  ACID. 

the  alkalies,  such  soaps  being  the  salts  formed  by  the  fatty  acid  with 
the  alkali-metal,  characterised  by  easily  lathering  when  dissolved  in  soft 
water,  by  being  precipitated  from  their  aqueous  solutions  by  common 
salt,  and  by  giving  an  oily  layer  of  the  melted  fatty  acid  when  boiled 
with  any  of  the  common  acids. 

On  the  large  scale,  palmitic  acid  is  made  from  palm-oil,  as  described 
at  p.  576.  It  is  also  manufactured  by  heating  oleic  acid  with  caustic 
soda: 

CwHjB-COOH  +  2NaOH  =  C15H31'COONa  +  CH3-COONa  +  H2. 

On  the  small  scale,  palm-oil  is  boiled  with  potash,  which  converts  it  into 
potassium  palmitate  and  oleate  ;  on  adding  dil.  H2S04  to  the  solution,  a  mixture  of 


Fig.  273.     Distillation  under  diminished  pressure. 

palmitic  and  oleic  acids  is  precipitated  ;  this  is  washed,  dried,  and  dissolved  in  hot 
alcohol,  from  which  the  palmitic  acid  crystallises  on  cooling,  leaving  the  oleic  acid 
in  solution.  It  may  be  purified  by  distillation  under  diminished  pressure.  An 
arrangement  suitable  for  this  operation  is  shown  in  Fig.  273.  Palm-oil  contains 
the  glycerides  palmitin  and  olein,  which  are  saponified  by  the  potash,  with  liberation 
of  glycerine,  as  will  be  further  explained  under  the  head  of  Ethereal  salts,  to  which 
the  glycerides  belong. 

The  substance  known  as  adipocere,  a  wax-like  mass  left  when  animal  bodies 
decompose  in  the  earth,  is  a  mixture  of  palmitates  of  calcium  and  potasium. 

The  formation  of  palmitic  acid  from  spermaceti  has  been  explained  at  p. 
570. 

Stearic  acid,  C17H35'CO2H,  may  be  prepared  from  suet  by  boiling  it 
with  potash,  decomposing  with  hydrochloric  acid  the  soap  thus  obtained, 
drying  the  separated  fatty  acids,  and  dissolving  in  the  least  possible 
quantity  of  hot  alcohol.  This  retains  the  oleic  acid  in  solution  and 
deposits  a  mixture  of  stearic  and  palmitic  acids  on  cooling ;  the  mixture 
is  well  pressed  in  blotting-paper,  and  repeatedly  crystallised  from 
alcohol  till  it  fuses  at  69°  C.  The  stearic  acid  exists  in  the  suet  and  in 
most  other  solid  fats,  in  the  form  of  the  glyceride  stearin,  mixed  with 
palmitin  and  a  little  olein.  When  saponified  by  the  potash,  these  yield 
the  stearate,  palmitate,  and  oleate  of  potassium,  respectively. 

Stearic  acid  is  a  white  crystalline  solid,  of  the  same  sp.  gr.  as  water, 
fusing  at  69°  C.,  and  not  distilling  without  partial  decomposition,  except 
at  low  pressures  or  in  a  current  of  superheated  steam.  It  is  insoluble  in 


5Q6  ACIDS   OF  THE  ACEYLIC   SEKIES, 

water,  but  dissolves  in  alcohol  and  in  ether.  It  burns  with  a  luminous 
flame.  The  alkalies  dissolve  stearic  acid  on  heating,  forming  stearates, 
which  are  components  of  ordinary  soaps. 

White  curd  soap  made  from  tallow  and  soda  consists  chiefly  of  sodium,  stearate, 
C]7H35'C02Na,  which  may  be  crystallised  from  alcohol.  It  dissolves  in  a  little  water 
to  a  clear  solution,  but  when  this  is  largely  diluted  it  deposits  scaly  crystals  of  the 
acid  sodium  stearate,  (C17H35'C02)2HNa.  Potassium  stearate  behaves  in  a  similar 
way.  The  other  stearates  are  insoluble.  Those  of  calcium  and  magnesium  are 
precipitated  when  hard  water  is  brought  in  contact  with  soap.  Magnesium  stearate 
may  be  crystallised  from  alcohol. 

Stearic  acid  mixed  with  palmitic  acid  is  the  material  of  the  so-called  stearin 
candles. 

Margaric  acid,  C16H33'C02H,  is  obtained  by  boiling  cetyl  cyanide  with  an  alkali. 
It  crystallises  like  palmitic,  and  fuses  at  60°  C. 

367.  Acids  from  Monohydric  Oleflne  Alcohols  (Acrylic  or  Oleic 
Series). — These  correspond  with  the  general  formula  C^EL^jCOOH 
and  contain  the  ethylenic  linking  characteristic  of  the  defines,  e.g., 
CH3'CH  :  CH'COOH,  crotonic  acid.  They  may  be  prepared  from  the 
corresponding  alcohols  and  cyanogen  derivatives  by  the  general  methods 
(p.  587),  and  also  by  two  methods  which  recall  the  preparation  of  the 
olefines.  These  are  (i)  by  nucleal  condensation  from  the  monohalogen 
substituted  fatty  acids,  thus  : 

CH3-CH2-CHC1'COOH  +  KOH  =  CH3'CH  :  CH'COOH  +  KC1  +  HOH, 
and  (2)  by  dehydration  of  the  alcohol  acids  (p.  574)  by  destructive 
•distillation  ;  CH2(OH)-CH2'CH2-COOH  =  CH2 :  OH-CH2'COOH  +  HOH. 
Attention  must  here  be  called  to  the  nomenclature  of  isomerides 
among  derivatives  of  open-chain  hydrocarbons.  The  letters,  a,  /3,  y, 
<fec.,  are  prefixed  to  the  name  of  the  derivative  to  indicate  the  carbon 
atom  to  which  the  substituent  is  attached,  a  signifying  the  atom  next 
the  end  characteristic  group,  j3  the  next  but  one,  y  the  next  but  two, 
and  so  on,  thus  : 

a-Chlorobutyric  acid  =  CH3-CH2'CHC1-COOH 
/3-Chlorobutyric  acid  =  CH3-CHC1-CH2'COOH 
7-Chlorobutyric  acid  =  CH2C1'CH2-CH2-COOH 
It  is  by  no  means  a  matter  of  indifference  whether  an  a,  /3  ,or  y  derivative  is  us 

in  the  two  last  named  reactions  ;  in  both  cases  the  /3-derivative  is  most  easily  coi 

verted  into  the  acid  of  the  olefine  series. 

Having  an  ethylenic  linking,  the  acids  of  the  acrylic  series  show  th* 
property,  characteristic  of  the  olefines,  of  combining  directly  with  two 
atoms  of  bromine  and  with  two  atoms  of  (nascent)  hydrogen.  In  the 
former  case  a  dibro mo-derivative  of  the  corresponding  fatty  acid,  and  in 
the  latter  the  fatty  acid  itself,  is  formed,  the  double  linking  being 
opened  up  in  each  case. 

A  characteristic  reaction  of  the  acids  of  this  series  is  that  when  fused 
with  an  alkali  they  yield  alkali  salts  of  two  acids  of  the  acetic  series, 
the  rupture  of  the  molecule  generally  occurring  at  the  double  linking ; 
thus  acrylic  acid,  CH2 :  CH'COOH  yields  acetate  and  formate,  and 
crotonic  acid  yields  two  molecules  of  acetate. 

This  reaction  is  not  a  criterion  of  the  position  of  the  double  linking  in  the  chain 
because  of  the  influence  which  alkalies  have  in  causing  the  double  bond  to  shift,  mere 
heating  with  aqueous  alkali  sufficing  in  many  cases  to  convert  a  J3y-acid  (one  in 
which  the  double  bond  is  between  the  /3  and  y  carbon  atom)  into  an  a/3-acid. 

Isomerism  among  acids  of  the  acrylic  series  may  bedue  to  variation  in  position  of  the 
doublebonds,  as, for  instance,  CH3-CH  :  CH-CH2-COOHandCH3'CH2-CH:  CH'COOH 


ACRYLIC  ACID.  -Q 


*'  CH*'Cfl  :  W-COOH, 
°f  the  Same  ki^  as  that  between 
Since  the  polymethylenes  (p.  539)  are  isomeric  with  the  defines,  the  monocar- 

waw4^2g  are  isomeric  with  the  acryiic  acids'  i£3n; 

The  following  are  the  best-known  acids  of  the  aeries,  but  although 
they  form  an  homologous  series,  many  of  them  differ  in  structure  so 
much  from  the  type,  acrylic  acid,  and  from  each  other  that  their 
physical  properties  cannot  advantageously  be  compared. 

Acid.  Source.  Formula. 

Acrylic       .         .         .     Oxidation  of  acrolein      .         .     C9H,-C00H 


Angelic  .  .  Angelica  root  ....  cS'Coi 

ryroterebic  .  .  Oxidation  of  turpentine  .        .  C.HQ-C00H 

OlT^610  '  '  Earth-nut  oil  .         .         .         .  C  X'CO. 

°/eic.-         •  •  •  Most  oils          ....  Ci-- 

Erucic        •  •  •  Rape  oil  ...  .  C 


Acrylic  acid,  CH2  :  CH'C02H,  is  obtained  by  heating  acrolein,  the  corresponding 
aldehyde,  (p.  583)  with  water  and  silver  oxide  in  the  dark  :  C2H3'CHO  +  Ag20  = 
C2H3-C02H  +  Ag2.  It  is  also  obtained,  by  the  general  methods  given  above,  from 
bromopropionic  and  hydroxypropionic  acids.  It  is  a  pungent  liquid,  miscible  with 
naiei™nd  boilin£  at  I^°°  c-  Nascent  hydrogen  converts  it  into  propionic  acid, 
O2H5-CO2H.  Fused  with  potassium  hydroxide,  it  yields  potassium  acetate  and 
formate—  CH2  :  CH'C02K  +  KOH  +  H20  =  CH3'C02K  +  H-CO^  +  H0.  -~*  N 
While  it  is  possible  to  write  the  formula  C3H5'COOH,  the  next  homologue 
to  acrylic  acid,  in  four  isomeric  forms,  two  alone  are  known  with  certainty 
viz.,  crotonic  add,  CH3'CH  :  CH'COOH,  which  occurs  in  a  solid  and  a  liquid 
modification,  and  methylacrylic  acid,  CH2:C(CH3)'COOH.  Vinylacetic  acid 
CH2  :  CH-CH2-COOH,  is  also  alleged  to  have  been  obtained. 

Solid  crotonic  acid  occurs  in  crude  pyroligneous  acid,  and  is  obtained  by 
oxidation  of  croton  adelhyde  (p.  584)  with  Ag20.  Its  formation  by  heating  ap- 
dibromobutyric  acid  with  KI  solution  indicates  the  position  of  the  double 
linking  : 

CH3-CHBr-CHBr-COOH  +  2KI  =  CH3'CH  :  CH'COOH  +  2KBr  +  I2. 
It  crystallises  in  needles,  melts  at  72°  C.,  and  boils  at  180°  C.,its  vapour  condensing 
in  plates.  It  is  moderately  soluble  in  water,  and  has  an  odour  like  that  of  butyric 
acid,  into  which  it  is  converted  by  nascent  hydrogen.  Fused,  KOH  converts  it  into 
potassium  acetate—  C3Hg-C02H  +  2KOH  =  2(CH3C02K)  +  H2.  "Liquid" 
crotonic  or  isocrotonic  acid  occurs  in  croton  oil.  When  PC15  acts  on  ethylaceto- 
acetate  (#.».)  it  produces  £-chloroisocrotonic  acid,  CH3'CC1  :  CH'C02H,  which,  by 
treatment  with  nascent  H,  yields  isocrotonic  acid  ;  this  crystallises  in  needles  or 
prisms,  melts  at  15°  C.,  boils  at  169°  C.,  and  is  converted  into  the  solid  acid  at 
1  80°  C.  It  appears  to  be  a  stereoisomeride  of  the  solid  acid,  the  relation  between  the 
two  being  similar  to  that  between  fumaric  and  malaeic  acids  G/.f.).  Methylacryl'u} 
acid  occurs  in  chamomile  oil,  and  has  an  odour  of  mushrooms.  It  is  prepared  by 
a  complicated  process.  It  melts  at  16°  C.  and  boils  at  160°  C.  ;  nascent  H  converts 
it  into  isobutyric  acid,  whilst  with  fused  KOH  it  yields  propionate  and  formate. 

Angelic  acid,  CH3'CH  :  C(CH3)'COOH,  is  obtained  by  boiling  angelica  root  (an 
umbelliferous  plant)  with  lime  and  water,  filtering,  acidifying  with  sulphuric  acid, 
and  distilling.  The  acid  appears  to  be  contained  in  the  root  as  an  ethereal  salt, 
which  is  decomposed  by  the  lime.  Chamomile  flowers  and  some  other  aromatic 
plants  also  yield  this  acid.  It  crystallises  in  prisms,  fusing  at  45°  C.,  and  boiling  at 
185°.  It  has  an  aromatic  odour,  is  soluble  in  hot  water  and  in  alcohol  and 
ether.  When  boiled  for  some  time,  it  is  converted  into  its  stereoisomeride,  tifU* 
acid  (m.-p.  64°  C,,  b.-p.  198°  C.),  which  is  also  obtained  from  croton  oil  (CfrfltM 
tigliwri),  and,  together  with  angelic  acid,  from  cummin  oil  (Cuimnum  cijmuiuni). 
Fused  with  KOH,  angelic  acid  yields  acetate  and  propionate.  There  are  several 
isomerides. 


598  OLEIC  ACID. 

368.  Oleic  acid,  C17H33-C02H,  or  C8H17'CH :  CH[CH2]7-COOH,  the 

most  important  member  of  the  acrylic  series  of  acids,  is  prepared  by 
boiling  olive-oil  with  potash,  and  decomposing  the  solution  with  hydro- 
chloric acid,  which  separates  the  oleic  acid  as  an  oily  layer,  containing 
some  stearic  and  palmitic  acids.  To  purify  it,  it  is  heated  with  litharge 
at  1 00°  C.  for  some  hours,  when  a  mixture  of  oleate,  palmitate,  and 
stearate  of  lead  is  obtained.  The  oleate  is  extracted  from  this  mixture 
by  ether,  and  the  solution  shaken  with  HC1,  which  precipitates  the  lead 
as  Pbd2,  while  the  oleic  acid  remains  dissolved  in  the  ether,  which  rises 
to  the  surface.  The  ether  is  distilled  off  and  the  oleic  acid  is  purified 
by  fractional  distillation  under  diminished  pressure. 

The  olive-oil  contains  the  glyceride  olein,  which  is  decomposed  by 
boiling  with  potash  into  glycerine  and  potassium  oleate.  Olein  is  ii 
general  constituent  of  the  fixed  oils ;  the  soft  soap  made  by  saponifying 
whale  and  seal  oils  with  potash  consists  chiefly  of  potassium  oleate. 
Oleic  acid  is  a  by-product  in  the  manufacture  of  candles,  in  which  its 
presence  would  be  injurious  by  lowering  the  fusing-point.  It  is  used  in 
greasing  wool  for  spinning,  being  much  more  easily  removed  by  alkalies 
than  is  olive-oil,  which  was  formerly  employed.  Ammonium  oleate  is 
sometimes  employed  as  a  mordant  for  the  aniline  dyes  on  cotton. 

Oleic  acid  is  an  oily  liquid  which  crystallises  at  o°  C.  and  melts  at  14°.  When 
distilled,  it  yields  a  number  of  products  of  decomposition,  among  which  sebaclc  ac'n1, 
C'8H16(C02H)2,  is  conspicuous.  In  a  current  of  superheated  steam,  at  250°  C.,  it  may 
be  distilled  without  decomposition.  In  its  commonly  impure  state,  it  absorbs 
oxygen  readily  when  exposed  to  air. 

Fusion  with  KOH  converts  oleic  acid  into  acetate  and  palmitate  (see  p.  596). 

The  constitution  of  oleic  acid  follows  from  the  fact  that  when  treated  with  Br  it 
yields  a  dibromostearic  acid,  which  is  converted  by  alcoholic  potash  into  stearolic 
acid  containing  a  treble  linking.  By  oxidation  stearolic  acid  yields  two  acids,  each 
containing  C9  ;  as  acids  from  acetylene  alcohols  break  up  on  oxidation  at  the  treble 
linking,  stearolic  acid,  must  contain  that  linking  between  the  ninth  and  tenth 
C  atoms,  and  this  must  also  be  the  position  of  the  double  bond  in  oleic  acid. 

By  the  action  of  N203,  oleic  acid  is  converted  into  the  isomeric  elaidic  acid,  which 
is  crystalline,  and  fuses  at  51°  C.  When  oxidised  by  nitric  acid,  oleic  acid  yields 
several  acids  of  the  acetic  and  oxalic  series.  When  heated  with  amorphous 
phosphorus  and  strong  hydriodic  acid  at  about  200°  C.,  it  yields  stearic  acid, 


The  alkali  oleates  are  decomposed  by  much  water  into  free  alkalies  and  insoluble 
acid  oleates.  Sodium  oleate  is  present  in  ordinary  soap,  and  may  be  crystallised 
from  absolute  alcohol. 

Barium  oleate  is  a  crystalline  powder,  insoluble  in  water,  and  sparingly  soluble  in 
boiling  alcohol.  Lead  oleate,  which  forms  the  chief  part  of  lead  plaster,  fuses  at 
80°  C.,  and  solidifies  on  cooling  to  a  translucent  brittle  mass,  soluble  in  ether. 

Erucic  acid,  C8H17'  CH  :CH[CH2]n'  COOH  occurs  as  a  glyceride  in  rape  oil  and  in 
the  fatty  oils  of  mustard  and  grape  seed.  It  fuses  at  34°  C.  When  heated  with 
phosphorus  and  hydriodic  acid,  it  gives  behenic  acid,  C^H^'CO^H.  Heating  with 
HN03  dil.  converts  it  into  the  isomeride  brassidic  acid  (m.-p.  66°  C.). 

369.  Acids  from  Monohydric  Acetylene  Alcohols. — Acids  of  the 
general  form,  CMH2w_3COOH,  may  be  acetylene  derivatives,  containing 
trebly  linked  carbon  atoms,  or  diolefine  derivatives,  containing  two 
doubly  linked  carbon  atoms. 

The  acetylene  acids  are  obtained  from  the  acids  of  the  oleic  series  by 
combining  them  with  two  atoms  of  Br  to  form  dibromacetic  acids  and 
treating  the  products  with  alcoholic  potash  ;  thus,  a/3-dibromopropionic 
acid  yields  propiolic  acid — 

CH2BrCHBrCOOH  +  2KOH  =  CH  •  C'COOH  +  2KBr  +  2HOH. 


ACIDS   OF  THE  AEOMATIC  SEEIES.  599 

They  are  also  obtained  by  heating  monohalogen  substituted  oleic  acids 
with  alkali — 

CH2  :  CBrCOOH  +  KOH  =  CH  •  OCOOH  +  KBr  +  HOH. 
These  methods  should  be  compared  with  those  for  obtaining  acetylenes. 
Another  method  consists  in  heating  the  alkali  acetylides  with  C02— 

CH3  •  CNa  +  C02  =  CH3C  \  OCOONa. 

Like  the  acetylenes,  these  acids  combine  with  two  or  four  atoms  of 
Br  or  other  monovalent  element,  arid  those  which  contain  the  group 
*  C  :  CH  yield  explosive  metallic  derivatives  (p.  538). 

370.  Propiolic    acid,  CH  :  C'C02H,  corresponding  with  propargyl  alcohol,  is 
prepared,  as  its  potassium  salt,  by  heating  potassium  hydrogen  acetylene-dicar- 
boxylate  in  aqueous  solution  ; 

C02H-C  :  C-C02K  =  C02  +  HC  i  C'C02K. 

It  melts  at  6°  C.,  boils  at  144°  C.,  and  yields  explosive  metallic  derivatives.  Just 
as  acetylene  polymerises  to  benzene  (p.  538),  so  propiolic  acid  polymerises  (in 
sunlight)  to  trimesic  acid,  C6H3(COOH)3 

Tetrollc  acid,  C3H3'C02H,  has  no  practical  importance.  It  is  produced  when 
/3-chlorocrotonic  acid  is  heated  at  100°  C.  with  alcoholic  potash.  It  is  also  formed 
by  heating  sodium  allylide  in  carbon  dioxide  ;  m.-p.  76°,  b.-p.  203°  C. 

Sorbic  acid,  CH3'CH  :  CH'CH  :  CH'COOH,  is  a  diolefinic  acid,  produced  by 
boiling  with  acid  or  alkali  the  yellow  fragrant  oil  obtained  by  distilling  the  juice 
of  unripe  mountain-ash  berries  (Sorbus).  By  oxidation  with  K2Mn208  it  yields 
aldehyde  and  tartaric  acid. 

Sorbic  acid  fuses  at  i34°-5  C.,  and  is  decomposed  when  distilled,  unless  in 
presence  of  steam.  It  is  sparingly  soluble  in  water,  but  dissolves  in  alcohol. 

Linoleic  acid,  Cl7H31'COOH,  occurs  as  a  glyceride  in  linseed  oil  and  some  other 
drying  oils.  The  oil  is  saponified  with  KOH,  the  aqueous  solution  is  precipitated 
by  CaCl2  and  the  calcium  linoleate  extracted  by  ether.  It  is  a  yellowish  oil,  not 
altered  by  N203.  Palmitollc  acid  is  an  isomeride.  Homolinoleic  acid  and 
ttearolic  acid,  C8H17'C  i  C[CH2]7-COOH,  are  also  isomerides. 

Linolenic  and  isolinolenic  acids  are  isomerides  of  the  formula  C-^^fiv  belonging 
to  the  CMH2w_g-C02H  series  of  acids.  They  occur  as  glycerides  in  linseed  oil  and 
other  drying  oils. 

371.  Acids  from  Monohydric  Aromatic  Alcohols  (Aromatic  or 
Benzole  Series). — These  may  be  of  two  kinds  : 

(1)  Acids  containing   the   COOH  group   attached   to   the   benzene 
nucleus,  such  as  benzole  acid,  C6H5'COOH,~and  toluic  acid,  C6H4(CH3)' 
COOH.     These  are  obtainable  (a)  by  oxidising  the  hydrocarbons  con- 
taining side-chains  (p.  548),  (b)  by  oxidising  the  corresponding  alcohols 
or   aldehydes,   (c)  by   the  action    of   sodium  and    carbon   dioxide  on 
the     monohalogen    substituted      hydrocarbons — C6H5Br  +  CO,  +  Na,  = 
C6H5COONa  +  NaBr,  (d)  by  fusing  the  alkali   salts  of  the  sulphonic 
acids    (p.    648)    with    alkali   formate  —  C6H5S03Na   +  HCOONa  = 
C6H5COONa  +  NaHS03,  (e)  by  hydrolysis  of  the  cyanogen  substitution 
products  of  the  hydrocarbons— C6H5CN  +  2HOH  =  C6H5COOH  +  NH,. 

(2)  Acids  containing   the  COOH  group  as  part  of  the  side-chain  ; 
these  may  be  regarded  as  open-chain  acids  in  which  aromatic  radicles 
(CJL;  CfiH4(CHA  &c.)  have  been  substituted  for  H,  as  in  phenylacetic 
acid,    C6H3-OH2-COOH,    and    tolylacetic    acid,  C6H4(CH3)'CH,'COOH. 
They  may  be  prepared  by  hydrolysis  of  the  corresponding  cyanogen 
derivatives— C6H5-CH2-CN  +  2HOH  =  C6H5-CH2'COOH  +  NH3. 

The  aromatic  acids  are  crystalline,  volatile,  sparingly  soluble  in 
water,  but  soluble  in  alcohol  and  ether.  They  show  most  of  the  reactions 
of  the  fatty  acids,  and  like  them  are  converted  into  hydrocarbons  when 
heated  with  lime,  which  abstracts  CO2. 


600  BENZOIC  ACID. 

372.  Benzole  acid,  C6H5'C02H  (phenyl  formic  acid).  This  acid  was 
originally  extracted  from  gum  benzoin,  a  resinous  exudation  from  Styrax 
benzoin,  a  tree  of  the  Malay  Islands. 

When  the  gum  is  gently  heated  in  an  iron  or  earthen  vessel,  covered  with 
perforated  paper  and  surmounted  by  a  drum  of  paper,  the  benzoic  acid,  which 
exists  uncombined  in  the  resin,  rises  as  vapour  and  condenses  in  the  drum.  A 
better  yield  is  obtained  by  boiling  the  benzoin  with  lime  and  water,  and  decom- 
posing the  filtered  solution  of  calcium  benzoate  with  hydrochloric  acid. 

It  is  also  made  from  the  urine  of  cows-  and  horses,  which  contains 
hippuric  acid,  easily  convertible  into  benzoic  acid  (see  Hippuric  acid). 

But  the  chief  source  of  modern  benzoic  acid  is  toluene,  C6H5'CH3. 
This  is  directly  convertible  into  benzoic  acid  by  oxidation  with  nitric 
acid,  C6H5-CH3  +  2HNO3  =  C6H.-C02H  +  2HOH  +  2NO. 

It  is  cheaper,  however,  to  convert  the  toluene  into  benzo-trichloride 
by  passing  chlorine  into  it  at  180°  C.,  and  to  heat  the  product  with 
lime ;  C6H5-CH3  +  C16  =  C6H5'CC13  +  3HC1 ;  2C6H5C13  +  4Ca(OH)2  = 
3CaCl2  +  (C6H5-C02)2Ca  +  4HOH.  The  calcium  benzoate  is  decomposed 
by  hydrochloric  acid,  when  benzoic  acid  separates. 

Much  benzoic  acid  is  obtained  as  a  by-product  in  making  benzalde- 
hyde  from  toluene  (p.  584),  for  much  of  the  benzaldehyde  is  converted 
into  benzyl  alcohol  and  calcium  benzoate  by  the  excess  of  lime  used 

(P-  585). 

Benzene,  C6H6,  may  be  partly  converted  into  benzoic  acid  by  oxidising 

it  with  MnO2  and  H2S04.     Addition  of  formic  acid  increases  the  yield 
of  benzoic  acid  ;  C6H6  +  H'C02H  +  0  =  C6H5'C02H  +  H20. 

Properties  of  benzoic  acid. — It  crystallises  in  shining  needles  or  in 
feathery  scales,  usually  having  a  faint  aromatic  odour.  It  fuses  at 
120°  C.  and  boils  at  250°  C.,  subliming  without  decomposition;  it 
volatilises  when  boiled  with  water.  It  is  sparingly  soluble  in  cold 
water  (200  parts),  more  easily  in  hot  water  (24  parts) ;  alcohol  and 
ether  dissolve  it  'readily.  Potash  and  ammonia  also  dissolve  it  imme- 
diately, and  it  is  precipitated  on  adding  an  acid,  Most  of  the  benzoates 
are  soluble,  but  ferric  benzoate  is  obtained  as  a  buff-coloured  precipitate 
when  ferric  chloride  is  added  to  a  neutral  benzoate. 

By  distillation  with  excess  of  lime,  benzoic  acid  yields  benzene — 
C6H5-C02H  +  CaO  =  CaC03  +  C6H6. 

When  vapour  of  benzoic  acid  is  passed  over  heated  zinc-dust,  it  is 
converted  into  bitter-almond  oil  (benzoic  aldehyde) — 
C6H5-C02H  +  Zn  =  C6H5-CHO  +  ZnO. 

By  boiling  with  strong  HNO3,  benzoic  acid  is  converted  into  nitro- 
benzoic  acids,  C6H4(NOj)'CO2H,  of  which  three  exist. 

By  distilling  benzoic  acid  with  PC15,  benzoyl  chloride  is  obtained; 
C6H5-COOH  +  PC15  =  C6H5-COC1  +  POCI3  +  HC1.  This  chloride  bears 
the  same  relation  to  benzoic  acid  as  acetyl  chloride  bears  to  acetic  acid, 
the  radicles  benzoyl  and  acetyl  being  related  in  a  similar  way  to  benzyl 
and  ethyl : 

Ethyl,  CH3-CH2  ;  Acetyl,  CH3'CO  Benzyl,  C6H5'CH2  ;  Benzoyl,  C6H5'CO 

Ethyl  hydride  (ethane),  GH.'CH8  Benzyl  hydride  (toluene),  C6H5'CHS 

Ethyl  hydroxide  (alcohol),  CH3-.CH./OH  Benzyl  hydroxide,  C6H5'CH2OH 

Acetyl  hydride  (aldehyde),  CH3'COH  Benzoyl  hydride,  C6H5'COH 

Acetyl  hydroxide  (acetic  acid),  CH3'COOH  Benzoyl  hydroxide,  C6H5'COOH 


CINNAMIC   ACID.  6oi 

ibenzoyl  oxide,  (C6H5'CO)20,  is  produ 
um  benzoate— 
C6H5-COC1  +  C6H5-COONa  =  (C6H5'CO)20  +  NaCl. 


373.  Benzole  anhydride,  or  dibenzoyl  oxide,  (C6H5'CO)20,  is  produced  by  heatinir 
benzoyl  chloride  with  dry  sodium  benzoate— 


mass  is  washed  with  water  and  the  anhydride  crystallised  from  alcohol.    It 
at  42°  C.  and  boils  at  360°  C.     Boiling  with  water  converts  it  slowly  into 


The  mass 
fuses 
benzoic  acid. 

By  heating  benzoyl  chloride  with  dry  sodium  acetate,  lenzoacetlc  anhydride  is 
obtained  ;  C6H5-COCl  +  CH3-COONa  =  (C6H5-CO)(CH3-CO)0  +  NaCl. 

Benzoic  peroxide  (C6H5'CO)202,  is  obtained  by  acting  on  benzoyl  chloride  with 
barium  dioxide  ;  2C6H5'COC1  +  Ba02  =  (CgHg-CO)^  +  BaCl2.  It  may  be  crystallised 
from  ether.  Like  hydrogen  peroxide,  it  is  decomposed  "explosively  when  mode- 
rately heated.  Alkalies  resolve  it  into  benzoic  acid  and  oxygen. 

374.  Toluic  acids,  or  methyl-lenzoic  adds,  C6H4(CH3)'C02H,  are  obtained  by  oxidis- 
ing the  three  xylenes,  C6H4(CH3)2,  with  dilute  nitric  acid.     The  i  :  2-acid  crystal- 
lises in  needles,  fusing  at  102°  C.,  and  is  sparingly  soluble  in  water. 

Mesttylenic  acid,  1:3:  5-C6H3(CH3)2'C02H,  is  prepared  by  oxidising  mesitylene, 
(P-  549)5  with  dilute  nitric  acid.  It  is  a  crystalline  volatile  acid,  fusing  at  166°  C. 
and  soluble  in  boiling  water  and  in  alcohol. 

Cuminic  or  isopropyl-benzoic  acid,  i  :  4-C6H4(C3H7)'C02H,  is  prepared  from  the 
aldehyde  existing  in  Roman  cummin  oil,  by  boiling  it  with  alcoholic  solution  of 
potash,  which  converts  it  into  cuminic  alcohol  and  potassium  cuuiinate.  On 
adding  an  acid  to  the  aqueous  solution  of  potassium  cuminate,  the  cuminic  acid 
is  precipitated,  and  may  be  crystallised  from  alcohol  ;  it  fuses  at  116°  C.,  and  may 
be  sublimed. 

375.  Phenylolefinecarboxylic  acids  are  those  in  which  the  COOH  group  occurs 
in  an  un  saturated  side-chain  (p.  549). 

Cinnamic  or  B-phenyl-aorylic  acid,  C6H5'CH  :  CH'C02H,  is  prepared  by  boiling 
storax  with  soda,  and  decomposing  the  solution  of  sodium  cinnamate  with  HC1, 
which  precipitates  the  cinnamic  acid  in  feathery  crystals  like  benzoic  acid,  fusing 
at  133°  C.,  boiling  at  300°,  and  subliming  undecomposed.  It  is  soluble  in  boiling 
water  and  in  alcohol. 

Its  connection  with  acrylic  acid  is  shown  by  fusing  it  with  potash,  which  yields 
acetate  and  benzoate  of  potassium,  whilst  acrylic  acid  yields  acetate  and  formate  ; 


Oxidising  agents  convert  cinnamic  acid  into  benzoic  aldehyde  (bitter-almond 
oil);  C6Hg-CH  :  CH-C02H  +  04  =  C6H5'CHO  +  2C02  +  H20.  When  distilled  with 
excess  of  lime,  it  yields  cinnamene  or  phenyl-ethylene  (p.  550). 

Nascent  hydrogen  converts  it  into  fi-phenyl-propionic  acid  or  hydrocinnamic  acid; 
C6H5-CH  :  CH-C02H  +  H2  =  C6H5'CH2-CH2C02H. 

Cinnamic  acid  may  be  obtained  synthetically  by  the  action  of  sodium  acetate 
on  bitter-almond  oil,  in  presence  of  acetic  anhydride,  which  probably  acts  as  a 
dehydrating  agent;  CH3-C02Na  +  C6H5'CHO  =  C6H5-CH  :  CH'C02Na  +  H20  ;  and 
by  heating  benzal  chloride  with  sodium  acetate  — 

C6H5-CHC12  +  CH3-COONa  =  C6H5'CH  :  CH'COONa  +  2HC1. 

Atropic  acid,  a-phenyl-acrylic  acid,  C6H5'C^  ,  is  produced  when  atropine, 

CH2 
theQalkaloid  of  deadly  nightshade,  is  boiled  with  baryta  or  with  HC1.    It  fuses  at 

The'napthoic  acids  (a  and  j8),  C10H7'C02H,  are  monocarboxylic  naphthalenes, 
obtained  by  the  hydrolysis  of  the  corresponding  cyanogen  derivatives. 

376.  Monobasic  Acids  from  Polyhydric  Alcohols.—  As  already 
noticed   (p.    574),  these  acids  may  be  alcohol-  acids,  or  aldehyde-acn 
if  the  polyatomic  alcohol  be  a  glycol,  and  keto-acids,  or  even  toeft 
alcohol-  or  keto-aldehyde-acids,  if  the  alcohol  be  polyhydric,  in  v 
case  it  must  contain  both  primary  and  secondary  alcohol  groups.  -J 

Alcohol-acids  are  termed  hydroxy-acids,  a  title  which  is  warrants 
the  fact  that  they  can  be  prepared  from  the  chloro-substituted  open- 
chain  acids  of  the  foregoing  series  by  treatment  with  silver  oxicl. 
water,    showing   that    OH  has    been  substituted  for  the   01,   as,   t 


•602  GLYCOLLIC  ACID. 

instance,  when  monochloracetic  acid  is  converted  into  glycollic  acid  ; 
CH2C1-COOH  +  AgOH  =  CHOH-COOH  +  AgCl. 

It  will  be  found  that  the  hydrogen  of  the  hydroxyl  group  in  a 
hydroxy-acid  can  be  exchanged  for  a  metal,  just  as  it  is  in  the  hydroxyl 
group  of  an  alcohol,  so  that  the  acid  possesses  the  functions  of  both 
an  alcohol  and  an  acid.  Thus,  the  monobasic  hydroxy-acids  may  con- 
tain two  or  more  H  atoms,  which  can  be  exchanged  for  a  metal,  although 
they  are  strictly  monobasic,  since  they  contain  only  one  C02H  group  ; 
hence  they  are  sometimes  termed  diatomic  (triatomic,  &c.)  monobasic 
-acids. 

Besides  the  treatment  of  the  monohalogen  substituted  fatty  acids 
with  silver  oxide  or  alkali,  referred  to  above,  there  is  a  number  of  other 
methods  available  for  preparing  hydroxy-acids.  One  of  these  is,  of 
course,  the  oxidation  of  the  polyhydric  alcohols  ;  another  is  the 
oxidation  of  fatty  acids  containing  the  group  R2CH,  such  as  iso- 
butyric  acid,  (CH3)2CH  COOH,  which  yields  hydroxyisobutyric  acid, 
•(CH3)2C(OH)'COOH,  when  oxidised  with  alkaline  permanganate.  Or 
the  olefine  acids  may  be  converted  by  hydrolysis  into  hydroxy-acids, 
CH  :  CH-COOH  +  H20  =  CH2'CH(OH)  COOH.  Again,  the  amido- 
.acids  may  be  treated  with  nitrous  acid,  CH2(NH2)'COOH  (amido-acetic 
acid)  +  NO'OH  =  CH2(OH)'COOH  +  N2  +  H20  (cf.  p.  105).  The  general 
method  of  hydrolysing  cyanogen  derivatives  is  also  available  ;  thus  the 
-aldehydes,  when  treated  with  HCN,  yield  cyanohydrins,  such  as 
CH3-CH(OH)'CN,  and  these  may  be  hydrolysed  to  acids  (p.  587). 

The  simplest  hydroxy-acid,  hydroxy  '-formic  acid,  HO'COOH,  would 
be  the  first  anhydride  of  orthocarbonic  acid  (p.  261),  carbon  monoxide 
Tjeing  the  second  anhydride.  It  does  not  exist,  probably  for  the  reason 
already  given  (p.  573),  but  if  it  did,it  might  be  identical  with  carbonic 
acid. 

When  copper  sulphate  solution  is  added  to  a  strong  solution  of  potassium  car- 
bonate, a  deep  blue  solution  is  obtained  which  is  similar  to,  although  less  stable  than, 
the  solutions  obtained  by  adding  copper  sulphate  to  other  hydroxy-acids.  This 
.supports  the  supposition  that  carbonic  acid  is  hydroxy-formic  acid. 


Glycollic  or  hydroxy  acetic  acid,  CH^OH'COaH,  is  a  product  of 
the  oxidation  of  glycol,  CH2OH'CH2OH,  by  dil.  HN03,  but  is  best  pre 
pared  by  the  careful  oxidation  of  alcohol  by  nitric  acid. 

Into  a  narrow  glass  cylinder  (2  inches  in  diameter)  pour  118  cubic  centimetres 
of  80  per  cent,  alcohol  ;  insert  a  funnel  tube  drawn  out  to  a  fine  opening,  to  the 
bottom  of  the  vessel,  and  pour  in  50  c.c.  of  water,  so  as  to  form  a  layer  below  the 
alcohol  ;  then  pour  in  carefully  through  the  funnel  126  c.c.  of  nitric  acid  of 
sp.  gr.  1.35,  to  form  a  layer  below  the  water.  Place  the  vessel  aside,  without 
shaking,  for  about  five  days  at  about  20°  C.,  when  the  three  layers  will  have 
mixed.  Evaporate  the  liquid  upon  the  water-bath,  in  separate  portions  of  about 
20  c.c.  to  a  syrup,  dilute  it  with  10  volumes  of  water,  boil,  and  neutralise  with 
powdered  chalk.  To  the  crystalline  paste  which  forms  on  cooling,  add  an  equal 
bulk  of  alcohol,  and  filter.  The  precipitate  is  boiled  with  water,  and  filtered, 
while  boiling,  from  undissolved  calcium  oxalate.  On  cooling,  it  deposits  calcium 
.glyoxylate,  whilst  calcium  glycollate  remains  in  solution  ;  this  is  boiled  with  a 
little  lime  to  decompose  any  glyoxylate,  and  the  filtered  solution  evaporated  and 
treated  with  enough  oxalic  acid  to  precipitate  the  calcium  as  oxalate,  leaving 
glycollic  acid  in  solution. 

The  action  of  nitric  acid  upon  alcohol  is  of  a  representative  character. 
The  groups  OH3  and  CH2'OH,  contained  in  ethyl  alcohol,  are  converted 
under  the  influence  of  oxidising-agents  into  CHO,  characteristic  of  the 


LACTIC  ACID. 


aldehydes,  and  COOH,  characteristic  of  the  acids  respectively  Accord- 
ingly, we  find,  among  the  products  of  the  oxidation  by  nitric  acid 
acetic  aldehyde,  CH3'CHO  ;  acetic  acid,  CH3'COOH  ;  glyoxal,  CHOCHO- 
glyoxylic  acid,  CHOCOOH;  glycollic  acid,  CHyOH'COOH;  and  oxalic 
acid,  COOH-COOH. 

Glycollic  acid  has  been  obtained  by  allowing  the  vinegar  ferment 
bacterium  aceti,  to  grow  in  a  dilute  solution  of  glycol  (ethene-alcohol) 

Properties  of  glycollic  acid.—  Crystallises  with  some  difficulty  ;  fuses 
at  80°  C.,  and  volatilises  slowly  at  100°.  Very  soluble  in  water,  alcohol 
and  ether. 

As  might  be  expected,  oxidising-agents  convert  it  into  oxalic  acid,  from  which  it 
may  be  obtained  by  reduction.  When  heated  with  sulphuric  acid  it  yields  formic 
aldehyde  and  formic  acid  ;  CH2OH-C02H  =  H-CHO  +  H'C02H.  The  formic  alde- 
hyde is  converted  into  formic  paraldehyde,  (HCOH)3,  and  most  of  the  formic  acid 
is  decomposed  in  H20  and  CO. 

When  glycollic  acid  is  heated  with   HC1  it  yields  chloracetic  acid-  CH0OH- 
2H+HClCH2Cl-C02H  +  H20.     With    PC15    it    yields    chloracetyl    chloride, 


Hydriodic  acid  reduces  glycollic  to  acetic  acid— 

CH2OH-C02H  +  2HI  =  CH3-C02H  +  H20  +I2. 

The  gly  collates  of  calcium,  copper,  and  silver  are  sparingly  soluble  in  cold  water 
but  dissolve  in  boiling  water. 

Glycollic  acid  occurs  in  unripe  grapes,  and  in  the  leaves  of  the  Virginia  creeper. 
It  can  be  made  from  glucose  by  oxidising  it  with  silver  oxide,  in  the  presence 
of  calcium  carbonate  to  keep  the  solution  neutral,  or  else  the  glycollic  acid  becomes 
oxalic  acid. 

377.  Lactic  acids  or  hydroxypropionic  acids,  C2H4(OH)-C02H.  — 
Since  propionic  acid  is  CH3-CH2-COOH,  there  can  be  two  hydroxy- 
propionic acids,  viz.,  the  a-acid,  CH3-CHOITCOOH,  and  the  /3-acid, 
GH2OH-CH2'COOH  ;  the  former  is  called  ethylidetie  lactic  acid,  and  the 
latter  ethylene  lactic  acid. 

Ethylidene  lactic  acid,  CH?-CHOH'COOH,  is  also  known  as  fermenta- 
tion lactic  acid,  being  the  acid  of  sour  milk  produced  by  the  fermenta- 
tion of  the  milk  sugar  by  the  lactic  bacillus.  As  pointed  out  at  p.  593, 
glucose  also  undergoes  this  fermentation,  the  source  of  the  bacillus  in 
that  case  being  putrid  cheese  ;  the  chemical  change  is  expressed  by  the 
equation  C6H1206=--2C3H603. 

On  a  large  scale  a  mash  of  starchy  material,  such  as  maize,  is  treated  with  malt  to 
convert  the  starch  into  maltose,  and  is  then  mixed  with  a  cultivation  of  the  bacillus. 
chalk  being  stirred  in  for  the  purpose  of  neutralising  the  lactic  acid  as  it  is  formed, 
lest  it  kill  the  bacillus.  The  most  favourable  temperature  is  about  50°  C.  When  all 
the  maltose  has  been  converted,  the  solution  of  calcium  lactate  is  treated  with 
sulphuric  acid,  the  precipitated  CaS04  is  filtered  off,  and  the  dilute  lactic  acid 
is  concentrated  in  a  vacuum  pan  to  a  strength  of  about  50  per  cent.,  in  which  form 
it  is  sold  for  use  as  a  mordant  and  as  an  addition  to  the  tanning  liquors  in  leather 
factories. 

Pure  lactic  acid,  obtained  by  decomposing  zinc  lactate  with  H2S,  is  a 
colourless,  strongly  acid  liquid  which  crystallises  when  cooled  and  then 
melts  at  18°  C.  It  can  be  distilled  at  120°  C.  under  12  mm.  pressure, 
but  at  higher  temperatures  it  loses  water,  yielding  a  much  more  stable 

/CH(CH3)C(\ 
compound,  lactide,  O<  xr.Tr/°»  which    melts   at  I25     °-  and 

boils^at  255°  C. 


604  STEREOISOMERISM. 

It  is  characteristic  of  the  a-alcohol  acids  that  they  yield  anhydrides  from  two- 
molecules  by  the  loss  of  water  derived  from  the  alcoholic  groups  or  from  the 
carboxylic  groups,  or  from  both.  Thus  from  two  molecules  of  glycollic  acid  may  be 
obtained,  by  loss  of  one  molecule  of  water,  COOH'CH2-  0  -  CH2COOH  (diglycollic 
acid),  CH2OH-CO-0-CO-CH2OH  (not  known),  or  CH2OH'CO  -0-CH2.COOH 
(glycolglycolUc  acid,  an  ethereal  salt  formed  from  the  add  glycollic  acid  and  the 
alcohol  glycollic  acid).  If  the  first  and  second  of  these  lose  another  mol.  H20  the  same 


compound  will  be  formed,  namely  0<^  No  (diglycollic  anhydride)  ;  from 

CHo'CO 

/-ITT  .rir\ 

the  third,  the  subtraction  of  another  mol.  H20  yields  glycolide,  0<^  ^  ^>0,  of 

CO  *CH2 
which  lactide  is  a  homologue. 

Ethylidene  lactic  acid  is  found  in  the  gastric  juice,  and  in  opium. 

When  lactic  acid  is  heated  at  130°  C.  with  dilute  sulphuric  acid,  in  a  sealed 
tube,  it  yields  aldehyde  and  formic  acid;  C2H5(>C02H  =  CH3'CHO  +  H'C02H. 
Oxidation  with  K2Mn208  converts  this  lactic  acid  into  the  ketonic  acid,  pyruvic 
acid,  CH3'CO'COOH.  This  is  only  to  be  expected,  since  ethylidene  lactic  acid 
contains  a  secondary  alcohol  group  CHOH  (see  p.  568).  Nitric  acid  oxidises  lactic 
acid  to  oxalic  acid.  Chromic  acid  converts  it  into  acetic  acid,  C02  and  H20.  Since 
lactic  acid  is  hydroxypropionic,  it  may  be  reduced  to  propionic  acid  by  strong 
hydriodic  acid  ;  C2H4(OH)-C02H  +  2HI  =  C2Hg-C02H  +  H20  +  I2.  Conversely, 
propionic  acid  may  be  converted  into  lactic  by  the  following  steps  : 
(i)  CH3-CH2-C02H  +  Br.,  =  CH3«CHBrC02H  +  HBr.  ;  (2)  CH3'CHBr-C02H  + 
KOH  =  CH3-CHOH-C02H  +  KBr. 

Lactic  acid  is  producible  from  aldehyde  through  its  HCN  derivative  (see  above). 

The  lactates  are  mostly  soluble  ;  the  most  important  of  them  is  the  zinc  lactate 
(C2H50'C02)2Zn.3H20,  which  is  sparingly  soluble  in  water,  and  is  precipitated 
in  prismatic  crystals  when  zinc  sulphate  is  added  to  lactic  acid  neutralised  by 
ammonia.  Salts  of  the  type  CH3'CHOM'C02M  are  known  :  thus  sodium  sodio- 
lactate,  CHg'CHONa'COoNa,  is  prepared  by  the  action  of  sodium  on  sodium 
lactate. 

378.  Stereoisomerism  as  Illustrated  by  Ethylidene  Lactic 
Acid.  —  Ethylidene  lactic  acid  is  also  found  in  juice  of  flesh  (Liebig's 
extract  of  meat),  in  bile,  and  in  the  urine  of  persons  poisoned  by 
phosphorus.  This  lactic  acid  has  been  termed  sarcolactic  acid  or 
paralactic  acid,  because  it  is  not  identical  in  all  its  properties  with  the 
fermentation  lactic  acid  described  above.  Chemically  speaking,  the 
difference  is  exceedingly  slight,  amounting  mainly  to  a  greater  solubility 
of  zinc  sarcolactate  (which  crystallises  with  2H20)  than  of  zinc  ferment- 
ation lactate,  and  a  smaller  solubility  of  the  calcium  salt  (4H20).  The 
physical  difference  between  the  two  is  considerable,  for  whilst  the  fer- 
mentation acid  is  inactive  towards  polarised  light,  sarcolactic  acid  rotates 
the  plane  of  polarisation  to  the  right.  This  property  leads  to  the 
distinctive  titles,  dextro-ethylidene  lactic  acid  for  sarcolactic  acid,  and 
inactive  ethylidene  lactic  acid  for  the  fermentation  acid.  If  kept  in  a 
desiccator  for  some  time,  the  dextro-acid  becomes  converted  into  an 
anhydride  the  solution  of  which  is  Isevo-rotatory,  but  the  lactide 
obtained  by  heating  the  acid  yields  inactive  lactic  acid  when  dissolved. 
The  salts  of  the  dextro-acid  are  Isevo-rotatory. 

When  cane  sugar  is  fermented  by  means  of  a  certain  bacillus,  a  Icevo- 
ethylidene  lactic  acid  is  produced,  the  salts  of  which  are  dextro-rotatory. 

It  seems  that  there  are  three  ethylidene  lactic  acids,  which  may  be 
distinguished  as  i-,  d-,  and  I-  ethylidene  lactic  acid  respectively.  But 
when  equal  weights  of  the  d-  and  I-  acids  are  mixed  together  the  pro- 
duct is  found  to  be  optically  inactive  ;  hence  it  may  be  concluded  that 
the  inactive  acid  is  made  up  of  an  equal  number  of  molecules  of  the 


STEREOISOMEEISM.  605 

d-  and  I-  acids,  which  neutralise  each  other,  so  that  in  considering  a 
theory  to  account  for  the  existence  of  these  three  acids,  it  is  only 
necessary  to  attempt  to  explain  the  isomerism  of  the  dextro-  and  Isevo- 
modifications.  The  theory  of  position  isomerism,  already  mentioned, 
will  not  suffice  to  furnish  an  explanation,  because  the  only  possible 
position  isomeride  of  ethylidene  lactic  acid,  according  to  the  theory, 
is  ethylene  lactic  acid,  from  which  both  the  d-  and  the  I-  acids  differ 
chemically. 

The  examination  of  a  large  number  of  compounds  which  are  optically 
active  has  shown  that  each  contains  one  or  more  carbon  atoms  to  which 
are  attached  four  different  elements  or  radicles  ;  thus,  in  ethylidene  lactic 
acid,  CH3'CHOH'COOH,  the  middle  carbon  atom  has  each  of  its  atom- 
fixing  powers  satisfied  by  a  different  radicle ;  viz.,  CH3,  H,  OH,  and 
COOH.  Such  a  carbon  atom  is  said  to  be  asymmetric,  and  it  is  believed 
that  an  optically  active  compound  is  one  which  possesses  one  or  more 
asymmetric  carbon  atoms.* 

Several  cases  of  isomerides  differing  from  each  other  in  optical 
activity  have  been  noticed  in  the  preceding  pages  ;  in  each  case  it  will 
be  found  that  the  accepted  formula  for  the  compound  contains  one  or 
more  asymmetric  carbon  atoms.  Thus  three  of  the  14  isomeric  amyl- 
alcohols  (p.  569)  occur  in  the  d-,  1-,  and  i-form  ;  and  in  each  the 
original  methane  carbon  atom  has  four  different  radicles  attached  to 
it,  namely  in  one— OH3,  CH3'CH2,  H  and  CH2OH ;  in  another— 
CH3,  CH3-CH2-CH9,  H  and  OH  ;  and  in  the  third— CH3,  (CH3)2CH,  H 
and  OH. 

Where  a  compound  contains  more  than  one  asymmetric  carbon  atom 
the  cases  of  isomerism  are  more  numerous  and  such  will  receive  notice 
under  Tartaric  Acid  and  the  Sugars. 

No  hypothesis  has  been  suggested  upon  which  it  is  possible  to 
prophesy  whether  a  given  compound,  containing  an  asymmetric  carbon 
atom  will  be  dextro-  or  Isevo-rotatory. 

The  most  fruitful  hypothesis  for  explaining  the  existence  of  d-  and  l- 
isomerides  having  an  asymmetric  carbon  atom  is  that  the  four  groups 
attached  to  this  carbon  atom  are  differently  arranged  in  space,  in  the 
two  isomerides,  which  are  therefore  called  stereoisomerides  (o-rfpeos, 
solid).  If  the  carbon  atom  be  considered  to  occupy  the  centre  of  a 
tetrahedron  in  space,  as  suggested  at  p.  534,  it  will  be  found  that  no 
essentially  different  structures  can  be  made,  unless  each  corner  of  the 
tetrahedron  has  a  different  radicle  attached  to  it. 

For  if  two  tetrahedra  be  constructed,  the  corners  of  which  are  represented  by 
A,  A,  A,  B,  or  A,  A,  B,  B,  or  A.  A,  B,  C,  or  any  combination  of  four  letters,  two  or 
more  of  which  are  the  same,  it  will  be  found  to  be  always  possible  to  put  the  one 
tetrahedron  inside  the  other  in  such  a  manner  that  the  four  letters  on  the  corners 
of  the  one  shall  coincide  with  the  four  letters  on  the  corners  of  the  other.   If,  how- 
ever, the  four  corners  of  each  be  represented  by  the  four  different  letters  A,  B,  0,  D, 
it  will  be  found  possible  so  to  arrange  these  letters  that  the  one  tetrahedron  cannot 
be  introduced  into  the  other  in  such  a  manner  that  the  four  corners  correspond. 
The  arrangement  necessary  will  be  understood  from  the  statement  that  i 
observer  be  opposite  those  faces  of  the  tetrahedra  which  are  similarly  1< 
order  of  the  letters  on  the  one  face,willibe  the  reverse  of  the  order  of  the  letters  on  th 
other  face  ;  if  the  letters  A,  B,  C,  for  instance,  be  in  the  order  of  the  motion  of 
hands  of  a  clock  on  the  face  of  one  tetrahedron  they  will  be  in  the  reverse  orae- 
C,  B,  A,  on  the  face  of  the  other.  Such  an  arrangement  is  depicted  m  Fig.  274,  tr< 

*  Cf.  Amyl  alcohol  (p.  569). 


6o6  STEREOISOMERISM. 

which  it  will  be  seen  that  the  two  arrangements  bear  the  same  relationship  to  each 
other  as  an  object  bears  to  its  image. 


It  is  in  the  above  manner  that  Le  Bel  and  Van't  Hoff  have  sought  to  explain  why 
no  isomerides  of  methane  substitution-products,  except  of  those  of  the  type 
CRjRaRgR^  exist.  If  the  compound  which  is  arranged  in  the  clock-wise  manner 
in  Fig.  274  be  dextro-rotatory,  then  that  which  is  anticlock-wise  will  be  lasvo- 
rotatory. 

The  theory  has  been  tested  by  investigating  compounds  which,  by  the  process  of 
their  formation,  ought  to  contain  an  asymmetric  carbon  atom,  although  they  were 
known  only  in  an  inactive  form.  By  appropriate  treatment  many  such  compounds 
have  been  resolved  into  a  dextro-  and  lasvo-form  ;  the  principal  methods  of  treat- 
ment are — (i)  Crystallisation  from  water,  advantage  being  taken  of  the  greater 
solubility  of  one  of  the  active  forms  ;  in  this  manner  the  zinc-ammonium  salt  of 
i-lactic  acid  has  been  resolved  into  the  zinc-ammonium  salts  of  the  d-  and  Z-acids. 
(2)  Treatment  of  the  inactive  compound  with  another  active  compound,  and 
crystallising  the  product ;  thus,  if  the  inactive  compound  is  acid  it  is  crystallised 
with  an  active  base,  such  as  strychnine  ;  if  it  is  basic  it  is  crystallised  with  an 
active  acid,  such  as  tartaric  acid.  In  either  case,  the  salt  formed  is  separated  by 
crystallisation  into  a  d-  and  I-  modification,  the  one  or  the  other  being  the  more 
soluble.  Fermentation  lactic  acid  is  split  up  by  crystallising  it  with  strychnine, 
the  Z-strychnine  lactate  separating  first.  (3)  Fermentation  of  the  inactive  com- 
pound with  some  bacillus  which  feeds  on  one  of  the  active  forms  rather  than  upon 
the  other  ;  some  fungi  show  a  similar  preference. 

The  second  method  has  proved  the  most  fruitful,  and  by  its  means  optically 
active  sulphur,  tin  and  nitrogen  compounds,  containing  an  asymmetric  S,  Sn,  and 
N  atom  respectively,  have  been  prepared. 

As  Sn  falls  in  the  same  periodic  group  as  C  (p.  302)  and  is  a  true  tetravalent 
element,  the  fact  that  it  forms  optically  active  compounds  is  of  particular  interest. 
By  a  series  of  reactions,  which  will  be  understood  better  after  the  student  has 
perused  the  section  on  organo-mineral  compounds,  an  inactive  methylethylpropyl 

CHg  v  xCgHf 

tin  iodide,  >Sn<          ,  has  been  obtained.     This  obviously  contains  an  asym- 

C2H/     XI 

metric  tin  atom,  and  by  treating  it  with  the  silver  salt  of  an  optically  active 
acid,  d-camphorsulphonic  acid,  so  as  to  exchange  the  iodine  for  the  radicle  of 
the  active  acid,  and  then  evaporating  the  solution,  crystals  are  obtained  which 
are  more  dextro-rotatory  than  is  the  d-camphorsulphonic  acid.  From  these 
crystals  a  dextro-rotatory  methylethylpropyl  tin  iodide  is  obtained  by  treatment 
with  KI. 

Sulphur  is  in  the  sixth  group  of  the  periodic  classification  ;  nevertheless,  there 
are  some  organic  derivatives  of  this  element  in  which  it  appears  to  be  tetravalent, 
e.g.,  the  thetines.  One  of  these  is  prepared  by  the  action  of  bromacetic  acid, 
CH2BrCOOH,  on  methylethylsulphide,  CH3-S'C2H5  ;  it  is  inactive,  and  is  known  as 

Br  .CH3 

methylethylthetine  bromide,          >  S  <  .If  this  view  of  the  structure  of 

C2H/    XCH2-COOH 

the  thetine  is  correct,  the  S  atom  is  asymmetric  and  the  inactive  compound  should 
be  capable  of  yielding  optically  active  components.  By  applying  ^-camphor- 
sulphonic  acid  in  the  manner  described  above,  the  d-form  has  been  isolated. 

The  discovery  of  optically  active  nitrogen  compounds  has  extended  the  theory 
of  the  connection  between  asymmetry  and  optical  activity  to  pentavalent  elements. 


ETHYLENE  LACTIC  ACID. 

If  in  ammonium  iodide,  NHJ,  there  is  substituted  for  each  H  atom  a  different 
hydrocarbon  radicle,  an  asymmetric  nitrogen  compound  will  be  produced  Snr  h 
quaternary  ammonium  compounds  are  well  known,  and  lately  one,  ben-vlvhenvl 
rilylmetkylammommi  iodide,  N(C6H5-CH.2)(C6H5)(C3H5)(CH3)I,  has  been ^  esoTved 
into  optically  active  components  by  the  aid  of  d-camphorsulphonic  acid. 

Ethylene  lactic  acid,  or  fi-hydroxypropionic  acid,CH  (OHVCH 
•C02H,is  also  found  in  juice  of  flesh,  and  is  made  by  treating/3-ioflopro' 
pionic  acid,  CH2I-CH9-C02H,  with  moist  silver  oxide.  Its  formula  is 
confirmed  by  its  formation  from  glycol  chlorhydrin,  CH  Cl'CH  OH 
(and  therefore  from  ethylene,  p.  575),  by  conversion  into  "the  cyano- 
hydrin,  CH2CN.CH2OH,  and  hydrolysis  of  the  latter.  It  is  a  syrupy 
mass,  and  is  distinguished  from  ethylidene  lactic  acid  by  yielding  no- 
anhydrides,  but  acrylic  acid,  CH2 :  CH'C02H,  and  water,  when  heated  ; 
hence  it  is  sometimes  called  hydracrylic  acid.  This  is  characteristic  of 
/3-alcohol  acids,  which  generally  yield  a/3-olefine  acids  when  heated. 

When  oxidised  it  yields  carbonic  and  oxalic  acids  instead  of  acetic.  Its  zinc 
salt  (4H20)  is  very  soluble  in  water. 

379.  Hydroxybutyricacidssirefourmnumber:  thea-acid,CH3'CHo-CH(OHyCO  H 
the  £-acid,  CH3-CH(OH)-CH2'C02H,  the  7-acid,  CH2OH'CH2-CH2-C02H,  and  the V 
iso-acid  (CH3)2:  C(OH)'C02H.    A  fifth,  viz.,  the  /3-iso-acid  (CH3)(CH2OH):  CH'C02H 
is  obviously  possible,  but  is  not  known. 

The  7-hydroxy-acids  are  very  unstable,  and  when  an  attempt  is  made  to- 
liberate  them  from  their  salts  by  addition  of  a  more  powerful  acid  they  immediately 
lose  water,  becoming  "  intramolecular  anhydrides,"  or  lactoms.  These  are  interest- 
ing compounds,  for  they  may  be  regarded  as  internally  formed  ethereal  salts 
(cyclic  esters),  just  as  ethyl  acetate  is  an  externally  formed  ethereal  salt  (c/.glycol- 

glycollic  acid,  p.  604).     Thus,  7-hydroxybutyric  acid,  •     2       2      ,  yields  butyro- 

CH2*COOH 

r^TT  •OTT 

lactone,  •  2\0.     The  acids  containing  five  carbon  atoms  can  yield  5-hydroxy 

CHo'CO 

acids  and  these  lose  water  forming  8-lactones.  Both  7-  and  5-lactones  are  fairly 
stable,  being  only  partially  converted  into  the  corresponding  acids  by  boiling 
water,  but  into  salts  of  these  acids  by  alkalies. 

o.-Hydro.%'ycaproic  acid,  or  leucic  acid ;  see  Leucine. 

RiciTioleic  and  iso-ricinoleic  acids  are  hydroxyoleic  acids,  C17H32(OH)'C02H, 
which  occur  as  glycerides  in  castor  oil. 

379«.  Polyhydroxy-monobasic  acids. — Gly eerie  acid,  CH2OH-CHOH-C02H,  is  a 
primary-secondary-alcohol-acid  ;  it  has  been  already  mentioned  as  an  oxidation 
product  of  glycerine.  When  produced  in  this  way  it  is  optically  inactive,  but  both 
an  I-  and  a  d-  variety  have  been  obtained. 

A  number  of  polyhydric  monobasic  acids  is  produced  by  the  oxidation  of  the 
sugars  ;  these  are  known  as  hexonic  acids,  CH2OH>[CHOH]4'C02H.  They  are 
stereoisomerides  of  each  other,  being  either  d-  acids,  I-  acids,  or  i-  acids.  They 
will  receive  further  notice  under  the  sugars. 

379*.  Aldehyde-acids.—  Glyoxylic,  or  glyoxalic  acid,  CHO'C02H,  is  a  product  of 
the  oxidation  of  glycol  and  of  alcohol.  It  crystallises  in  prisms  and  distils  with 
steam.  Being  aldehydic  in  nature,  it  forms  a  crystalline  compound  with  NaHS08. 
and  reduces  silver  salts,  being  thereby  oxidised  to  oxalic  acid. 

Glycuronic  acid,  CHO-[CHOH]4'C02H,  is  obtained  by  reducing  saccharic  acid 
(q.r.)  with  sodium  amalgam  ;  it  is  a  syrup  which  is  readily  converted  into  a  lactone 
(see  above), 

380.  Monobasic    Acids    from    Hydroxy-Benzenes.— The    OH 
groups  in  these  acids  may  be  attached  either  to  the  benzene  nucleus,  in 
which  case  the  acids  are  phenol  acids,  not  alcohol-acids,  or  they  may 
occur  in  the  side-chain,  in  which  case  the  acid  is  an  alcohol-acid  ;  thus, 
salicylic  acid  is  a  phenol-acid,  C6H4(OH)-COOH,  whilst  pJienyl-glycolhc 
acid  is  an  alcohol-acid,  C6H5-CHOH'COOH. 


608  SALICYLIC  ACID. 

The  most  important  general  reactions  for  obtaining  the  phenolic  acids 
are  as  follows :  (i)  The  sodium  phenols  are  heated  with  CO2  (see 
salicylic  acid).  (2)  The  phenols  are  boiled  with  CC14  and  KOH  ; 
C6H6OH  +  CC14  +  5KOH  =  C6H4(OH)-COOK  +  4KC1  +  3HOH.  (Cf.  the 
method  for  making  hydroxy -aldehydes ;  p.  585.)  (3)  The  homologues 
of  phenol  are  oxidised  by  fusion  with  KOH;  CfiH4(OHVCIL  +  2KOH  = 
C6H4(OK)-COOK  +  3H2. 

The  alcohol-acids  are  made  by  reactions  similar  to  those  used  in 
making  the  paraffin  alcohol-acids. 

Like  the  alcohol-acids,  the  phenol-acids  yield  two  classes  of  salts,  e.g., 
C6H4(OH)-OO1Na,  and  C6H4(ONa)'C02Na,  the  former  being  produced 
when  the  acid  is  dissolved  in  Na2C03,  the  latter  when  NaOH  is  used. 

Hydroxybenzoic  acids,  C~H4(OH)-CO2H.— Being  di-substituted 
benzenes,  these  are  three  in  number.  The  most  important  is  the  1:2- 
acid  or  salicylic  acid.  This  is  prepared  artificially  by  combining  phenol 
with  soda,  and  heating  the  product  in  carbonic  acid  gas. 

The  phenol,  with  half  its  weight  of  NaOH,  is  dissolved  in  a  little  water  and 
evaporated  to  dryness.  This  sodium-phenol  is  powdered,  placed  in  a  flask  or  retort, 
and  heated  at  100°  C.  in  a  slow  stream  of  dry  C02  for  some  hours.  The  tem- 
perature is  then  raised  to  180°  C.,  when  phenol  distils  over,  and  continues  to  do  so 
till  the  temperature  has  risen  to  250°  C.  The  residue  is  dissolved  in  a  small 
quantity  of  water,  and  strong  HC1  added  to  precipitate  the  salicylic  acid,  which 
may  be  purified  by  crystallisation  from  water. 

By  dissolving  phenol  in  soda,  sodium-phenol  is  produced — 

C6H5-OH  +  NaOH  =  C6H5'ONa  +  HOH. 

When  this  is  heated  in  C02,  it  yields  phenol  and  sodio-salicylate  of 
sodium;  2C6H5ONa  +  C02  =  C6H5OH  +  C6H4(ONa)'C02Na;  this  last, 
decomposed  by  HC1,  yields  salicylic  acid — 

C6H4(ONa)-C02Na  +  2HC1  =  C6H4(OH)'C02H  +  2NaCl. 

Salicylic  acid  was  formerly  made  from  oil  of  winter-green  (Gaultheria, 
a  North  American  plant  of  the  heath  order),  which  is  the  methyl 
salicylate,  C6H4(OH)'C02CH3.  Its  original  source  was  salicin,  a  glu- 
coside  extracted  from  willow-bark,  which  yields  the  salicylate  when 
fused  with  potash.  Salicylic  acid  has  been  found  in  the  leaves,  stems, 
and  rhizomes  of  some  of  the  Violacece,  and  in  the  garden-pansy. 

Properties  of  salicylic  acid. — It  forms  four-sided  prisms  which  fuse  at 
155°  C.,  and  sublime,  if  carefully  heated  ;  but  a  temperature  of  220° 
decomposes  it  into  phenol  and  CO2 ;  C6H4(OH)'C02H  =  C02  +  C6H5'OH. 
This  change  occurs  more  readily  in  presence  of  an  alkali,  to  absorb  the 
C02.  It  dissolves  sparingly  in  cold  water,  more  easily  on  heating,  and  is 
soluble  in  alcohol  and  ether.  Its  solution  gives  an  intense  violet  colour 
with  ferric  chloride,  a  reaction  not  exhibited  by  the  p-  and  w-hydroxy- 
benzoic  acids.  It  possesses  antiseptic  properties,  and  is  used  for  the 
preservation  of  articles  of  food,  being  free  from  taste  and  smell.  It  is 
also  used  in  making  dyes,  and  sodium  salicylate  is  a  well-known  anti- 
rheumatic. 

The  salicylates  of  K  and  Na  are  crystalline  :  barium  salicylate  (C6H4OH 
C02)2Ba.Aq,  also  crystallises,  and,  when  boiled  with  baryta- water,  yields  a  sparingly 
soluble  salt,  C6H4BaOC02.2Aq,  in  which  the  diad  Ba  is  exchanged  for  the  H  of  the 
hydroxyl  as  well  as  that  of  the  carboxyl. 

Anisic  acid,  or  para-met  hoxy  benzole  acid,  C6H4(OCH3)'C02H,  is  isomeric  with  oil 
of  winter-green,  and  is  formed  by  the  oxidation  of  its  aldehyde,  which  occurs  in  oil 


GALLIC   ACID.  609 

of  anise  (p.  586).  It  may  be  formed  artificially  from  salicylic  acid  by  heating  its 
potassium  salt  to  220°  C.,  when  it  yields  di-potassium  parahydroxy-benzoate,  which 
is  converted  into  potassium  anisate  when  treated  successively  with  methyl  iodide 
and  caustic  potash — 

2(C6H4(OH)-C02K)  =  C6H5-OH  +  CO.,  -f  C6H4(OK)'C02K. 

C6H4(OK>C02K  +  2CH3[  =  C6H4(OCH3)-C00CH3  (methyl  aniwte)  +  2KI ; 

C6H4tOCH3)-C0.2CH3  +  KOH  =  C^4(f)CR3)'C02KQjo(a^iumani.sflt^  +  CH3'OH. 

Hydrochloric  acid  precipitates  the  anisic  acid,  which  may  be  dissolved  in  alcohol 

and  crystallised.      It  forms  prisms  fusing  at  185°  C.  and  subliming  undecomposed. 

ffydroatytoluic  acids  or  cresatinic  acids  C6H3(CH3)(OH)-COOH  are  ten  in 
number  as  they  are  trisubstitution  products  with  3  different  radicles.  All  the 
possible  isomerides  are  known. 

Protocatechuic  or  dihydroxybenzoic  acid,  C6H3(OH)2-C02H  [C02H:(OH2)  = 
i  :  3  :  4],  is  prepared  by  the  action  of  fused  caustic  soda  on  the  large  class  of 
bodies  known  as  gum-resins,  and  acquired  its  name  from  its  production  in  this 
way  from  catechu  (Cutch  or  Terra  japonica),  a  substance  much  used  in  dyeing 
black,  extracted  by  boiling  water  from  the  inner  bark  wood  of  the  Mimosa  catechu 
of  the  East  Indies  ;  khw,  a  gum-resin  exuding  from  certain  Indian  and  African 
leguminous  plants,  and  employed  in  medicine  as  an  astringent,  also  yields  the 
acid.  It  crystallises  in  plates  or  needles  containing  H20,  which  fuse  at  199°  C., 
and  are  soluble  in  water,  alcohol,  and  ether.  Ferric  chloride  gives  a  green  colour 
with  the  acid,  which  is  changed  to  blue  and  red  by  alkalies.  When  heated,  it  is 
decomposed,  yielding  pyrocatechol ;  C6H3(OH).2-  C02H  =  C02  +  C6H4(OH)2. 

It  will  be  found  that  the  formation  of  this  acid  during  the  potash-fusion  of  an 
organic  substance  often  throws  light  upon  its  constitution. 

Vanillic  or  ^-methyl-protocatech uic  acid,  C6H3(OH)(OCH3)'C02H.is  produced  when 
vanillic  aldehyde  (vanillin)  is  exposed  to  moist  air.  It  may  also  be  made  by 
oxidising  the  glucoside  coniferin  with  potassium  permanganate.  It  crystallises 
in  plates,  fusing  at  211°  C.  and  subliming  unchanged.  When  heated  in  a  sealed 
tube  with  dilute  HC1  at  160°  C.,  it  yields  protocatechuic  acid  and  methyl  chloride  ; 
C6H3<OH)(OCH3)  -C02H  +  HC1  =  C6H3(OH).2-C02H  +  CH3C1. 

381.  Aromatic   Paraffin  Alcohol-acids. — Mandelic  acid  or  jj/ieni/lali/cottic  add, 
C6H5-CH(OH)'C02H,  is   prepared  from  amygdaline   (</.r.)   or   by  the   hydrolysis 
of  the  hydrocyanic  compound    of   benzaldehyde,  C6H5  CH(OH)CN.     It  melts  at 
133°  C.  and  is  soluble  in  water.     It  exists  in  stereoisomeric  forms,  which  is  to  be 
expected  from  the  presence  of  an  asymmetric  carbon  atom. 

382.  Trihydroxybenzoic  acids.— Of  the  six  possible  isomerides  gallic 
acid  is  the  most  important. 

Gallic  acid,  3:4:5-  C6H2(OH)3-CO,H  *  is  produced  by  the  hydro- 
lysis of  the  tannin  in  gall-nuts  (gallotannic  acid),  C13H907'CO,  +  H,0  = 
2C6H,(OH)3-CO,H.  It  is  therefore  prepared  either  by  boiling  the 
tannin  with  dilute  sulphuric  acid,  or  by  keeping  the  moistened  powdered 
nut-galls  some  weeks  in  a  warm  place,  so  that  they  may  undergo 
fermentation,  and  extracting  the  gallic  acid  with  boiling  water,  from 
which  it  crystallises  in  fine  needles  containing  H20.  It  dissolves  in 
3  parts  of  boiling  water  and  100  of  cold  water.  It  becomes  anhydrous 
at  100°  C.,  and  melts  at  about  220°  C.,  yielding  a  crystalline  sublimate 
of  pyrogallol;  C6H2(OH)3-CO2H  =  C6H3(OH)3  +  C02. 

Solution  of  gallic  acid  is  not  precipitated  by  H2S04  or  HC1,  or  by  gelatine. 
Lead  acetate  precipitates  it,  but  the  precipitate  is  soluble  in  acetic  acid.    A 
and  potash  give  a  precipitate  easily  soluble  in  potash.    Copper  sulphate  does  not 
precipitate  it  immediately.     Ferric  salts  give  a  bluish-black  precipitate,  and  the 
alkalies  give  a  brown-red  colour,  especially  on  exposure  to  air.    Alcoholic  alkali 
converts  gallic  acid  into  a  yellow  dye-stuff,  gaUoflarin.  C13H609.     Gallic  a 
found  in  several  vegetable  products,  some  of  which  are  used  in  dyeing  and  t 
as  in  diri-diri,  the  fruit  of  a  leguminous  plant  (Ceegalj/i/iia  roritina).  in 

»  In  expressing  orientation  it  is  customary  to  assume  that  the  characteristic  <rroup  of  a 
compound  occupies  position  i,  and  to  name  the  positions  of  the  other  groups  n 
this.     Thus   3:4:  5-trihydroxy  beuzoic  acid  means  that  if  the  CO2H  group  has  posi 
OH  groups  will  be  3:4:5. 


6lO  TANNIC  ACID. 

mangoes,  and  the  leaves  of  the  wild  vine,  a  tropical  plant  of  the  Moon-seed  order 
(Clssampelos  pare.ira),  useful  in  medicine. 

Gallic  acid  may  be  obtained  artificially  by  heating  di-iodosalicylic  acid  with 
solution  of  potassium  carbonate  to  140°  C.  in  a  sealed  tube — 

C6H2I2(OH)-C02H  +  K2C03  +  H20  =  C6H2(OH)3'C02H  +  2KI  +  C02. 

When  gallic  acid  is  heated  with  4  parts  of  strong  H2S04  to  75°  C.,  it  gives  a 
dark-red  solution  ;  and  if  this  be  cooled  and  poured  into  water,  a  red  precipitate 
is  obtained  which  has  the  composition  C14H808.2Aq,  or  twice  gallic  acid,  minus 
'2H20.  This  was  formerly  termed  rujigallic  acid,  but  is  really  hexa-hydroxy- 
anthraqulnone,  C14H2(OH)602,  for  zinc-dust  reduces  it  to  anthracene,  C14H10. 

Ellagic  acid,  C13H506'C02H,  is  obtained  by  oxidising  gallic  acid  with  arsenic 
anhydride  ;  it  is  a  yellowish  crystalline  powder  sparingly  soluble  in  water  and 
alcohol.  It  is  found  in  bezoar-stones,  the  calculi  sometimes  formed  in  the  intes- 
tines of  wild  goats  in  Persia. 

Basic  bismuth  gallate,  C6H2(OH)3-COOBi(OH)2  is  an  antiseptic  sold  as  dermatol. 

383.  Tannic  acid  or  tannin. — This  name  has  been  applied  to  a  number 
of  plant-constituents,  all  of  which  are  capable  of  precipitating  gelatine, 
and  therefore  of  more  or  less  completely  tanning  hide  into  leather. 
They  are  also  characterised  by  the  dark  blue  or  green  colour  which  they 
give  with  ferrous  salts ;  hence  their  use  in  the  manufacture  of  inks. 
The  tannins  apparently  occur  in  the  plants  as  unstable  glucosides,  and 
when  hydrolysed  they  are  converted  into  glucoses  and  monobasic  acids 
which  seem  to  be  related  to  the  polyhydroxybenzoic  acids.  The  only 
tannic  acid  which  can  be  said  to  be  thoroughly  known  is  that  obtained  from 
gall-nuts,  and  commonly  called  gallotannic  acid,  C13H907'CO,H  +  2H20. 

240  grammes  of  powdered  gall-nuts  are  digested  for  some  hours,  with  frequent 
shaking,  with  1800  cubic  centimetres  of  ether  and  150  of  water.  The  mixture  is 
poured  into  a  funnel  loosely  plugged  with  cotton,  and  the  filtered  liquid  allowed 
to  stand,  when  it  separates  into  two  layers,  the  upper  one  being  the  ethereal 
solution  of  colouring-matter,  &c.,  and  the  lower  an  aqueous  solution  of  tannic 
acid,  which  is  evaporated  to  dryness  at  a  low  temperature. 

Gallotannic  acid  does  not  crystallise,  but  is  left,  on  evaporation,  in 
brownish-white  shining  scales,  which  are  very  easily  soluble  in  water, 
but  sparingly  in  alcohol  and  in  anhydrous  ether.  Its  solution  is 
astringent,  feebly  acid,  and  gives  a  bluish-black  precipitate  with  ferric 
chloride.  H2S04  and  HOI  combine  with  it  to  form  white  precipitates, 
and  a  solution  of  gelatine  precipitates  a  very  insoluble  compound  with 
tannic  acid.  By  hydrolysis  gallotannic  acid  yields  gallic  acid  (p.  609). 

The  view  that  gallotannic  acid  is  identical  with  di-gallic  acid — 

C6H2(OHVCO'O-C6H2(OH)2-COOH, 

which  represents  two  molecules  of  gallic  acid  minus  one  molecule  of  water,  and  is 
produced  by  action  of  dehydrating  agents  (e.g.,  POC13  at  130°  C.)  on  gallic  acid,  has 
been  proved  incorrect. 

Albumin,  starch,  and  most  of  the  alkaloids  are  also  precipitated  by  tannic  acid. 
Common  salt  causes  the  separation  of  tannic  acid  from  its  solution.  Lead 
acetate  precipitates  it  as  basic  tannate,  which  is  insoluble  in  acetic  acid.  Copper 
sulphate  also  precipitates  it  immediately.  Alum  and  potash  added  to  tannic 
acid  give  a  precipitate  insoluble  in  cold  potash.  Potash  or  ammonia  added  to  a 
solution  of  tannic  acid  renders  it  brown,  especially  if  shaken  with  air,  absorption 
of  oxygen  occurring.  Tannic  acid  acts  as  a  reducing-agent  upon  alkaline  cupric 
solutions,  producing  cuprous  oxide.  It  is  decomposed  by  distillation,  one  of  the 
products  being  pyrogallol,  C6H3(OH)3. 

Alcoholic  solutions  of  tannic  acid  and  potash  yield  a  precipitate  of  potassium 
tannate,  C13H9OyC02K,  and  if  this  is  dissolved  in  water,  and  BaCl2  added,  barium 
tannate,  (C13H9CyC02)2Ba,  is  precipitated. 

The  tannic  acids  or  tannins  used  in  commerce,  in  the  form  of  extracts  of 
various  parts  of  plants,  are  slightly  different  in  properties,  and  pending  exact 
knowledge  as  to  their  constitution,  they  are  distinguished  by  names  implying  the 


TANNINS.  6ll 

sources  from  which  they  are  derived.  Thus,  qverci-tannic  acid  is  from  oak-bark, 
quino-tannic  acid  from  cinchona  bark,  caffeo-tannic  acid  from  coffee,  moritannic 
acid  from  fustic  (a  yellow  dyewood  from  a  tree  of  the  Mulberry  order,  Mont* 
tinctoria). 

Sumach,  the  leaves  of  the  Rhm  coriaria,  a  tropical  plant  of  the  Cashew  order, 
and  Myrobalans,  the  fruit  of  several  species  of  Termlnalia,  Indian  trees,  contain 
gallotannic  acid.  Myrobalans  also  contains  ellagitannic  acid,  very  similar  to 
gallotannic  acid,  and  likewise  contained  in  diri-diri. 

The  tannins  may  be  classified  into  pyrogallol-tannin?  and  purocatechol  tannin*, 
accordingly  as  they  yield  pyrogallol  or  pyrocatechol  when  heated.  Those  belonging 
to  the  first  class  yield  gallic  and  ellagic  acids  when  heated  with  alkalies,  .vhilst  - 
those  of  the  latter  class  yield  protocatechuic  acid,  and  either  phlorogiucol  or 
acetic  acid,  by  the  same  treatment.  The  deposit  of  ellagic  acid  which  is  formed 
by  the  oxidation  of  pyrogallol  tannins  is  probably  the  "bloom"  noticed  by 
tanners  on  the  surface  of  leather  prepared  by  means  of  materials  such  as 
myrobalans,  sumach,  and  divi-divi.  The  pyrocatechol  tannins  are  liable  to  deposit 
complex  anhydrides  termed  phlobaphenes,*  which  have  a  red  colour  ;  such  are  the 
tannins  of  oak  bark,  mimosa  and  ralonia. 

Quinic  or  kinic  acid,  or  h-en'ahydrotetrahydroxyben-zoie  acid,  C6Hi7(OH)4'C02H, 
is  a  hydroxy-acid  from  hexahydrobenzene  (p.  550)  found  in  cinchona  bark,  in  coffee 
and  some  other  plants.  It  is  crystalline,  soluble,  and  melts  at  162°  C.  It  gives 
pyrocatechol  when  distilled,  and  protocatechuic  acid  when  fused  with  KOH. 
When  heated  with  Mn02  and  H2S04,  it  is  oxidised  to  quinone,  which  sublimes  in 
yellow  needles. 

383(1.  Hydroxyphenyl-Fatty  and  Olefine  Acids. — These  may  be  regarded  as 
phenols  in  which  a  nucleal  H  atom  has  been  exchanged  for  an  open-chain  acid 
radicle.  There  are  three  position  isomerides  of  each  of  the  monohydroxyacids. 

I  :  2-Hyd)-o.i-yphenylacetic  acid,  C6H4(OH)'CH2-COOH,  melts  at  137°  C.  and  is 
important  as  a  relative  of  indigo. 

i  :  2-Hyd)'o<vy-fi-2)henylacryUc  acid  or  I  :  z-hydroxycinnanric  acid — 

C6H4(OH)'CH :  CH'COOH 
commonly  called  coumaric  acid  is  obtained  from  I  :  2-amidocinnamic  acid — 

C6H4(NH2)-CH  :  CH'COOH 

through  the  diazo-reaction  ;  it  melts  at  208°  C.     Its  salts  are  also  obtained  from 
coumarin  by  heating  it  with  alkalies.     Coumarin  is  the  lactone  of  coumaric  acid, 

C6H4/  |     ,  and  is  the  substance  which  causes  the  smell  of  hay  and  of  the 

XCH  :  CH 

Tonka  bean  (Coumaroma  odorata')  from  which  it  may  be  extracted  by  boiling  with 
alcohol,  when  crystals  of  coumarin  are  deposited  on  cooling.    It  is  made  artificially 
by  heating  salicyl  aldehyde  with  sodium  acetate  and  acetic  anhydride  (cf.  cmnamic 
acid,  p.  601).     The  salts  from  coumarin  are  however  isomeric  with  those  prepare 
from  coumaric  acid,  the  origin  of  the  isornerism  being  still  unknown. 

Caffeic  acid,  or  dihydi-oxy-cinnamic  acid,  [(OH)2  :  (CH  :  CH'G02H)  =  3  :  4 


(m.-p.  213    C.)  on  cooling,  ana  is  soiuoie  in  aicc  KM.     ±L  jic     >  F'vv""»T|: 
heated,  and  is  converted  into  acetate  and  protocatechuate  when  fused  with 
Plperic  Acid  is  derived  from  a  3  :  4-dihydroxyphenyldiolefine  acid,  d- 
'innamenylao-yUc  acid,  by  substituting  methylene,  CH2,  for  the  two 


ctnnameni 

the  two  OH  groups  ;  hence  its  formula  is  3  : 4-CH2<°>C6H3-CH  :  CH'CH  :  CH'COOH. 

It  melts  at  217°  C.  and  is  found  as  a  derivative  of  piperidine  (V/.r.)  in  pepper. 

384.  Dibasic  Acids  from  Paraffin  Hydrocarbons   (Oxalic  or 
Succinic  Series),  CMH2tt(COOH)2. -These  acids  may  be  - 
derived  from  the  hydrocarbons  by  substitution  ot  two 
for  two  H  atoms.     They  are  oxidation  products  of  diprimary 
might  be  expected  (p.  574),  and  are  also  obtainable  by  nucleal  coi 

99,  b:irk  ;  |3»<M,  colour. 


6l2  OXALIC   ACID. 

tion  from  the  fatty  acids,  as  for  instance  when  bromacetic  acid  is 
treated  with  metallic  silver,  producing  succinic  acid  : — 

HOOC'CH2Br  +  BrCH2'COOH  +  Ag2  =  HOOC-CH2-CH2-COOH  +  2AgBr. 

These  methods  are  not  much  used,  however;  more  impoitant  is  the 
introduction  of  the  CN  group  into  a  fatty  acid  and  hydrolysis  of  the 
product.  Thus,  hydrolysis  of  cyanoacetic  acid,  obtained  from  chlor- 
acetic  acid  by  action  of  KCN,  yields  malonic  acid  : — 

CH2C1'COOH     ->     CH2CN-COOH     ->     CH2(COOH)2  (<•/.  p.  587). 

An  analogous  method  is  the  hydrolysis  of  the  dicyanides  of  the  olefine 
radicles,  CH9CN'CH2CN  yielding  succinic  acid,  for  example. 

Isomerism  among  these  acids  is  like  that  among  other  disubstituted 
paraffins  (p.  567). 

/COOH 

The  typical  members  of  the  series  are  malonic  acid,  CH./ 

XCOOH 
CH  COOH 

and  succinic  acid,   •     '  .     Acids  like  the  former,  in  which  the  two 

CH2COOH 

carboxyls  are  attached  to  the  same  carbon  atom  break  up  when  heated 
with  formation  of  C02  and  an  acid  of  the  acetic  series.  Acids  of  the 
succinic  type,  in  which  the  carboxyls  are  attached  to  different  carbon 

CH-CO\ 
atoms,  lose  water  and  yield  internal  anhydrides,  like   •  ">0,  when 

CH2-COX 

heated ;  this  behaviour,  however,  is  not  shown  by  acids  in  which  the 
COOH  groups  are  separated  by  more  than  three  CH2  groups.  Both 
types  lose  C02  when  fused  with  KOH,  yielding  an  acid  of  the  acetic 
series. 

385.  Oxalic  acid,  (C02H)2,  is  the  final  product  of  the  oxidation  of 
glycol,  and  one  of  the  products  of  the  hydrolysis  of  cyanogen, 
CN-CN  +  4HOH  -  COOH-COOH  +  2NH3.  It  is  prepared  on  the  small 
scale  by  oxidising  sugar  with  nitric  acid,  and  on  the  large  scale  by 
oxidising  sawdust  with  potash. 

Preparation  of  oxalic  acid  from  sugar. — 50  grins,  of  sugar  are  gently  heated  in  a 
flask  with  250  c.c.  of  ordinary  concentrated  nitric  acid,  sp.  gr.  1.4.  After  the 
action  commences,  remove  the  heat,  when  the  oxidation  will  continue  violently. 
On  cooling,  part  of  the  oxalic  acid  crystallises,  and  more  is  obtained  by  concen- 
trating the  mother-liquor.  Drain  the  crystals  on  a  funnel,  and  dissolve  them  in  as 
little  boiling  water  as  possible,  so  as  to  purify  the  acid  by  re-crystallisation.  It 
may  be  allowed  to  dry  by  exposure  to  air. 

Preparation  of  oxalic  acid  from  sawdust. — Common  pine  sawdust  is  made  into  a 
thick  paste  with  a  solution  containing  KOH  +  2NaOH  of  sp.  gr.  1.35.  This  is 
spread  on  iron  plates,  dried  up,  and  heated  just  short  of  carbonisation.  The 
cellulose,  C6H1005,  is  thus  oxidised,  with  evolution  of  hydrogen,  and  converted 
into  oxalic  acid,  which  remains  in  the  mass  as  oxalates  of  potassium  and  sodium. 
These  are  dissolved  in  water,  and  boiled  with  lime,  which  produces  the  insoluble 
calcium  oxalate.  together  with  solution  of  the  caustic  alkalies,  which  may  be 
used  again.  The  calcium  oxalate  is  decomposed  by  dilute  sulphuric  acid,  the 
solution  of  oxalic  acid  filtered  from  the  calcium  sulphate  and  crystallised. 

Strictly  speaking,  in  carrying  out  this  process,  the  fused  mass  is  treated  with  a 
small  quantity  of  hot  water,  which  leaves  the  bulk  of  the  sodium  oxalate  undis- 
solved  ;  this  is  decomposed  by  lime,  as  stated  above.  The  liquor,  which  contains 
but  little  oxalate,  is  boiled  to  dryness,  the  residue  heated,  and  the  alkaline 
carbonate  causticised  by  lime.  It  is  worth  noting  that  caustic  soda  alone  would 
produce  very  little  oxalate.  When  potash  is  cheap,  it  may  be  used  alone. 


OXALATES.  613 

Oxalic  acid  occurs  in  sorrel,  rhubarb,  and  many  other  plants.  Potas- 
sium oxalate  is  formed  when  potassium  formate  is  gently  heated  ; 
2(H-CO'OK)  =  H2  +  (CO2K),.  Sodium  oxalate  is  produced  when  sodium,' 
mixed  with  sand  to  moderate  the  action,  is  heated  at  360°  C  in  dry 
C02 ;  Na2  +  2CO2  =  (C02Na)2. 

Properties  of  oxalic  acid. — It  forms  monoclinic  prisms  containing  2Aq, 
which  are  soluble  in  nine  parts  of  cold  water  and  in  alcohol.  It  is  a 
very  strong  acid,  able  to  decompose  the  nitrates  and  chlorides.  In 
large  doses  it  is  poisonous.  "When  gently  heated,  the  crystals  effloresce, 
from  loss  of  water,  and  begin  to  vaporise  slowly  at  100°  C.  When 
sharply  heated  the  crystallised  acid  melts  at  101°  C.  and  the  anhydrous 
at  189°  C.  At  165°  it  sublimes  freely,  part  being  decomposed  into 
formic  acid  and  C03;  (C02H)2  =  ITC02H  +  C02.  A  weak  solution  of 
oxalic  acid  is  decomposed  by  boiling.  When  heated  with  strong 
sulphuric  acid,  (002H)2  =  C02  +  CO  +  H2O,  the  CO  burning  on  applying 
a  flame.  From  twelve  parts  of  warm  oil  of  vitriol  the  acid  crystallises 
in  large  rhombic  octahedra,  which  are  anhydrous.  Oxalic  acid  is  largely 
used  in  dyeing,  calico-printing,  and  bleaching,  in  cleaning  brass,  and  in 
removing  iron-mould  from  linen. 

Normal  potassium  oxalate,  (C02K)2.Aq,  is  moderately  soluble  in  water.  Hydro- 
potassium  oxalate,  ov  potassium  binoxalate,  or  salt  of  sorrel,  is  (C02)2KH.  It  is  also 
Called  essential  salt  of  lemons,  though  lemons  contain  no  oxalic  acid.  It  dissolves 
in  40  parts  of  cold  water,  and  has  occasionally  caused  accidents  by  being  mistaken 
for  cream  of  tartar,  potassium  hydrogen  tartrate,  from  which  it  is  readily  distin- 
guished by  the  action  of  heat,  which  chars  the  tartrate,  but  not  the  oxalate. 

Trikydropotassium  oxalate,  or  potassium  quadroxalate,  (C02)2H3K.2Aq,  is  more 
commonly  sold  as  salt  of  sorrel,  and  sometimes  as  salt  of  lemon.  It  is  even  less 
.soluble  than  the  preceding. 

Sodium  oxalate,  (C02Na)2,  is  found  in  various  plants  which  grow  in  salt  marshes. 
It  is  less  soluble  than  potassium  oxalate.  The  alkali  oxalates,  when  heated,  evolve 
CO  and  leave  carbonates,  (C02K)2=CO  +  CO(OK)2. 

Ammonium  oxalate,  (CO2NH4)2.Aq,  occurs  in  Peruvian  guano.  It  is  used  in 
analysis  for  the  precipitation  of  calcium,  and  crystallises,  in  needles,  from  solution 
of  oxalic  acid  neutralised  with  ammonia. 

Calcium  oxalate,  (C02)2Ca.Aq,  is  often  found  crystallised  in  plant-cells.  Some 
lichens  growing  on  limestones  contain  half  their  w'eight  of  calcium  oxalate.  It  is 
occasionally  found  in  urine  and  in  calculi.  Calcium  chloride  is  the  best  test  for 
oxalic  acid,  giving  a  white  precipitate  insoluble  in  acetic  acid.  When  heated, 
(C02)2Ca  =  CO  +  CaC03. 

Ferrous  oxalate,  (C02)2Fe,  occurs  as  oxalite  in  brown  coal.  Ferric  oxalate, 
(CO2)6Fe0,  when  exposed  to  sunlight  in  presence  of  water,  evolves  COa,  and  deposits 
a  yellow  "crystalline  precipitate  of  (C02)2Fe.2Aq.  Ferric  oxalate  is  used  in  photo- 
graphy. Potassium  ferrous  oxalate,  (C02)4K2Fe,  prepared  by  adding  potassium 
oxalate  in  excess  to  ferrous  sulphate,  is  a  very  powerful  reducing-agent,  used  as 
a  photographic  developer. 

Potassium  chromic  oxalate,  (CO^KgCr.sAq,  is  obtained  in  crystals  so  intensely 
blue  as  to  look  black,  by  dissolving  in  hot  water  I  part  of  potassium  dichromate, 
2  parts  of  hydropotassium  oxalate,  and  2  parts  of  oxalic  acid.  Neither  the  oxalic- 
acid  nor  the  Cr208  can  be  precipitated  from  this  salt  by  the  usual  tests. 

Potassium  calcium  chromic  oxalate,  (C0.2)6KCaCr.3Aq,  is  soluble  in  water,  and 
gives  a  precipitate  of  calcium  oxalate  on  adding  calcium  chloride. 

Barium  chromic  oxalate,  (CO2)1,,Ba8Oa.8Aq,  is  also  a  soluble  salt,  and,  when  d< 
composed  by  sulphuric  acid,  yields  a  red  solution  which  probably  contains  the  acic 
(COjUELCra  or  H3(C02)6Cr-Cr(C02)6H3.  .  , 

Potassium  antimony  5S«^,  (Cot)8K8Sb.6Aqf  obtained  by  dissolving  precipitated 
Sb406  in  hydropotassium  oxalate,  is  used  in  fixing  certain  colours. 

Silver  oxalate,  (C02Ag)2,  is  obtained  as  a  white  precipitate  when  silver  i 
added  to  an  oxalate.     It  explodes  slightly  when  heated,  leaving  metallic  silver. 

Manganese  oxalate,  (C02).2Mn,  is  used  lor  mixing  with  drying-oils. 


614  SUCCINIC  ACID. 

Oxidising-agents  easily  convert  oxalic  acid  into  water  and  C02 ;  if  a 
hot  solution  of  the  acid  be  poured  on  manganese  dioxide,  brisk  effer- 
vescence is  caused  by  the  C02  produced.  A  similar  result  ensues  if 
manganese  dioxide  be  added  to  the  mixture  of  an  oxalate  with  dilute 
sulphuric  acid.  Nascent  hydrogen  reduces  oxalic  acid  to  gly collie  acid  ; 
(C02H)2  +  H4  =  CH2(OH)-C02H  +  H2O. 

386.  Malonic  acid,  CH2(C02H)2,  is  prepared  from  chloracetic  acid,  CH2C1-C02H, 
by  converting  it  into  the  potassium  salt,  and  boiling  this  with  potassium  cyanide, 
when  potassium  cyanacetate,  CH2(CN)'C02K,  is  formed.     This  is  boiled  with  pot- 
ash, which  converts  it  into  potassium  malonate  ;  CH2(CN)'C02K  +  H20  +  KOH  = 
CH2(C02K)2+NH3.     The    excess  of  potash  is  neutralised  by  HC1,  and  calcium 
chloride  added,  which  precipitates  calcium  malonate  ;  by  boiling  this  with  the 
molecular  proportion  of  oxalic  acid,  the  calcium  is  left  as  oxalate,  and  the  solution 
deposits  tabular  crystals  of  malonic  acid.     It  fuses  at  132°  C.  and  afterwards 
decomposes  into  C02  and  acetic  acid  ;  CH2(C02H)2  =  C02  +  CH3-C02H.     It  will  be 
remembered  that  oxalic  acid  is  decomposed  into"C02,  and  formic  acid,  H'C02H. 

Calcium  malonate,  like  the  oxalate,  is  very  slightly  soluble  in  water,  and  is 
found  in  the  sugar  beet ;  the  silver  and  lead  salts  are  insoluble.  Malonic  acid  is 
found  among  the  products  of  oxidation  of  allylene,  amylene,  and  propylene  with 
potassium  permanganate. 

The  other  acids  of  the  malonic  acid  type  are  alkyl  substitution  derivatives 
of  malonic  acid,  and  may  be  built  up  therefrom  by  the  treatment  of  its  ethereal 
salts  first  with  a  sodium  alkyloxide  and  then  with  an  alkjd  iodide.  The  series  of 
reactions  and  their  import  has  been  given  at  p.  587. 

Methylmalonic  acid,  CH3'CH(COOH)2,  is  ethylidene  succinic  acid,  isomeric  with 
succinic  acid,  which  is  an  ethylene  derivative  ;  hence  it  is  called  isosuccinic  acid. 
It  is  prepared  by  hydrolysis  of  a-cyanopropionic  acid,  and  from  ethyl  sodiomalonate 
and  methyl  iodide  (see  above).  It  should  also  be  obtainable  by  treating  ethylidene 
bromide,  CHg-CHBr^  with  KCN  and  hydrolysing  the  cyanide,  but  this  leads  to 
ordinary  succinic  acid.  It  melts  at  130°  C.,  and  decomposes  into  C02  and  pro- 
pionic  acid. 

387.  Succinic  acid,  C2H4(C02H)2,  \&ethylene  succinic  acid,  and  occurs  ready  formed 
in  amber,  from  which  it  was  originally  obtained  by  distillation.     It  is  prepared  by 
the  fermentation  of  tartaric  acid,  which  may  be  regarded  as  dihydroxysuccinic 
acid,  C2H2(OH)2(C02H)2,  and  becomes  reduced  to  succinic  acid. 

The  tartaric  acid  is  neutralised  with  ammonia,  largely  diluted,  and  mixed  with 
a  little  potassium  phosphate,  magnesium  sulphate,  and  calcium  chloride,  to  afford 
mineral  food  for  the  bacteria,  which  soon  grow  if  the  liquid  be  kept  warm  (25°- 
30°  C.).  The  flask  should  be  loosely  closed  to  exclude  air.  After  about  two  months, 
the  ammonium  tartrate  has  become  ammonium  succinate  and  carbonate  ;  it  is 
boiled  to  expel  the  latter,  milk  of  lime  added,  and  again  boiled  as.  long  as  NH3 
is  expelled  ;  the  calcium  succinate  is  decomposed  by  a  slight  deficiency  of  dilute 
H2S04,  the  liquid  filtered  from  the  CaS04  and  evaporated. 

Succinic  acid  crystallises  in  prisms,  which  require  about  20  parts  of  cold  and 
3  parts  of  hot  water  to  dissolve  them.  It  dissolves  in  alcohol  but  sparingly  in 
ether.  When  heated,  it  emits  vapour  at  120°  C.,  fuses  at  185°,  and  at  235°  distils 
as  water  and  succinic  anhydride,  C2H4(CO)20  ;  the  vapours  provoke  coughing  in  a 
remarkable  way,  thus  affording  a  test  for  the  acid.  It  is  very  stable,  and  little 
affected  by  oxidising-agents.  Fusion  with  KOH  converts  it  into  carbonate  and 
propionate  ;  C2H4(C02H)2  +  3KOH  =  CO(OK)2  +  C2H5'C02K  +  2H20. 

Calcium  succinate,  C2H4(CO-2)2Ca.3Aq.  is  somewhat  sparingly  soluble  in  water  ;  it 
occurs  in  the  bark  of  the  mulberry-tree.  Basic  ferric  succinate,  Fe'"2(C4H404)"2(OH)'2, 
is  precipitated  when  ferric  chloride  is  added  to  a  succinate  ;  it  has  a  rich  brown 
colour,  and  its  production  forms  a  good  test  for  succinic  acid,  and  is  useful  in 
quantitative  analysis  for  separating  Fe  from  Mn  and  some  other  metals. 

Malic  acid  is  hydroxysuccinic  acid,  and  is  also  reduced  by  fermentation  to  succinic 
acid.  Both  malic  and  tartaric  acid  are  reduced  to  succinic  acid  by  the  action  of 
hydriodic  acid.  Succinic  acid  has  been  obtained  synthetically  by  boiling  ethene 
dibromide  with  potassium  cyanide  dissolved  in  alcohol,  and  boiling  the  ethene 
cyanide  thus  obtained  with  KOH  dissolved  in  alcohol. 

C2H4Br2  +  2KCN  =  C2H4(CN)2  +  2KBr  ;  and 
C2H4(CN)2  +  2KOH  +  2H20  =  C2H4(C02K)2  +  2N 


FUMAEIC  AND   MALEIC  ACIDS. 


615 


Succinic  acid  is  always  produced  in  small  quantity  in  the  fermentation  of  sugar 
and  is  therefore  always  present  in  beer,  wine  and  vinegar.  It  is  also  produced 
when  nitric  acid  oxidises  fatty  acids  containing  four  or  more  carbon  atoms.  It 
occurs  in  unripe  grapes,  whilst  ripe  grapes  contain  tartaric  (dihydroxysuccinic) 
acid.  It  is  found  in  several  plants,  such  as  lettuce,  poppies,  and  wormwood,  and  in 
certain  lignites.  It  has  also  been  found  in  the  urine  of  the  horse,  goat,  and  rabbit. 

When  electrolysed,  succinic  acid  yields  C2H4,  C02,  and  H,  as  might  be  expected' 
from  its  formula,  C2H4(C02H)2. 

Methylsvccinic  acid,  COOH-CHCCH^-CHa'COOH,  is  also  called  pyrotartaric  acid 
because  it  is  formed  by  distilling  tartaric  acid  (mixed  with  powdered  pumice  to 
diffuse  the  heat).  The  distillate  is  mixed  with  water,  filtered,  evaporated  on  the 
water  bath  and  crystallised  from  alcohol.  It  is  formed  from  propene  as  succinic 
acid  is  from  ethene,  and  crystallises  in  prisms  which  melt  at  112°  C.  and  decompose 
into  water  and  the  anhydride.  Having  an  asymmetric  carbon  atom  it  occurs  in 
stereoisomeric  forms. 

Glutaric  acid,  COOH-CH2-CH2-CH2'COOH,  isomeric  with  pyrotartaric  acid  (and 
with  ethylmalonic  acid  and  dimethylmalonic  acid)  melts  at  97° C.,  and  is  obtained 
from  trimethylene  bromide  (p.  539)  through  the  KCN  reaction.  It  yields  an  anhy- 
dride when  heated. 

The  higher  acids  of  this  series  do  not  yield  anhydrides  ;  the  chief  are  : 

Adipic,  C4H8(COOH)0,  from  oxidation  of  oleic  acid ;   m.-p.  153°  C. 
Pimelic,  C5H10(COOH)2,  „  „          „       „          „  105°  C. 


Suberic,  C^B^COOH)^  „  „          „     cork 

A.zelaic,  C7H14(COOH)2    „  „          „    castor  oil 

distillation  of  oleic  acid 


Sehwic,  C8H16(COOH)2    „ 
Brassi/Uc,  C11H22(COOH)2  f 


Tom  oxidation  of  erucic  acid 
Rocellic,  C15H30(COOH)2,  "     „      Rocella  tinctoria 


140°  C. 
1 06°  C. 

133°  t'. 
n4°C. 
132°  C. 


388.  Dibasic  Acids  from  Oleflne  Hydrocarbons,  CMH2H_404.— 

The  acids  of  this  series  are  rnsaturated,  like  those  of  the  acrylic  series, 
and  can  therefore  combine  with  two  atoms  of  bromine  to  become 
dibromo-derivatives  of  the  acids  of  the  preceding  class,  or  with  two 
atoms  of  hydrogen  to  become  the  acids  of  that  cla^s.  Conversely,  acids 
of  this  series  are  obtained  by  treating  with  KOH  the  dibromo-acids 
of  the  succinic  series. 

The  first  member  of  the  series  has  the  formula  C2H2(C02H)9,  and  might 
obviously  exist  in  two  forms,  C02H'CH  :  CH-C03H  and  CH2":  C(C02H)2. 
There  is  insufficient  evidence  to  show,  however,  that  the  two  &cid$fumanc 
and  maleic,  both  of  which  have  the  molecular  formula  C2H2(C02H)S, 
are  position  isomerides  ;  they  appear  rather  to  be  stereoisomeridt  s. 

The  acid  CH2  :  C(COOH)2,  methylenemalonic  acid,  is  known  only  in  the  form  of 
its  ethereal  salts. 

Futnaric  acid,  C2H2(C02H)2,  is  obtained  by  heating  malic  acid  at  150°  C.  as 
long  as  water  distils  over  ;  C2H3(OH)(C02H)2=C2H2(C02H)2  +  H20.  The  residue  is 
treated  with  cold  water  to  extract  unaltered  malic  acid  and  the  fumaric  acid  is 
crystallised  from  hot  water  or  alcohol.  At  200°  C.  it  partly  sublimes  undecomposed, 
and  the  rest  decomposes  into  water  and  maleic  anhydride.  Heated  with  much 
water  at  150°  C.,  it  is  reconverted  into  malic  acid.  NaOH  at  100°  C.  slowly  converts 
it  into  sodium  malate.  Nascent  hydrogen,  from  water  and  sodium-amalgam,  con- 
verts it  into  succinic  acid,  C2H4(C02H)2.  Hydriodic  acid  effects  the  same  change, 
iodine  being  liberated.  The  fumarates  of  barium,  calcium,  and  lend  :uv  sparingly 
soluble.  Silver  fumarate  is  very  insoluble,  and  explodes  when  heated.  The  alkali 
•fumarates,  when  electrolysed,  yield  C2H2,  C02,  which  forms  a  carbonate,  and  H, 
thus  justifying  the  formula  given  for  the  acid.  Fumaric  acid  is  found  in  several 
plants,  especially  in  fumitory,  Iceland  moss,  truffles,  and  other  fungi.  *  urns 
acid  is  not  oxidised  by  boiling  with  nitric  acid. 

Maleic  acid,  isomeric  with  fumaric  acid,  is  produced  when  malic  acid  i>  -im. 
distilled.     It  is  crystalline,  melts  at  130°  C.  and  is  easily  decomposed  by  heat  in 
water  and  maleic  anhydride.     It  differs  from  fumaric  acid  by  its  ready  M 
in    cold  water,   by  the    solubility  of  its  barium    and   calcium   salts,  and    by  i 


6l6  MALEINOID  AND   FUMAROID   STRUCTURE. 

unpleasant  taste.     It  is  converted  into  fumaric  acid  if  heated  in  a  sealed  tube  at 
200°  C.,  or  if  boiled  with  dilute  acids. 

In  order  to  represent  the  isomerism  between  fumaric  and  maleic  acid, 
it  is  supposed  that  the  C02H  groups  are  differently  situated  with  regard 
to  a  plane  drawn  through  the  two  nucleal  carbon  atoms  of  the  molecule. 
On  the  plane  of  the  paper,  the  supposed  difference  may  be  represented 

H-C-C09H  H-OCO.H. 

by  the  formula?       ••  and  ••  The  first  of  these  two 

H-OC02H          C02H-OH 

formulae  is  called  ihe  plane-symmetrical,  or  cz's-c?'s-formula,  whilst  the  second 
is  called  the  axial-symmetrical,  centri- symmetrical ^  or  c 


H-OCOx. 
Since  maleic  acid  very  easily  foi  ms  an  anhydride,       ••        \O  it  may 

H-c-ccr 

be  supposed  to  have  the  first  formula,  because  the  formation  of  an 
anhydride  would  occur  the  more  easily  the  greater  the  proximity  cf  the 
C02H  groups.*  Many  cises  of  stereoisomerism  among  eth)lenic  «  eri- 
vatives  (cf.  pseudo-but}  lene  and  crotonic  acid)  are  believed  to  be 
explicable  by  formula?  resembling  those  given  above,  so  that  the  expres- 
sions malewtoid  andfumaroid  structure  are  u*ed.t 

The  main  argument  in  favour  of  this  view  of  the  structure  of  the  fumaric  and 
maleic  molecules  is  that  the  former  yields  racemic  acid  and  the  latter  mesotartaric 
acid,  by  oxidation  with  K2Mn208.  Comparison  of  the  above  formula?  with  those 
for  racemic  and  mesotartaric  acids  on  p.  622  shows  that  the  acid  having  the  cis-cis- 
formula  would  be  the  more  likely  to  yield  mesotartaric  acid  than  the  other  acid 
would,  because  in  mesotartaric  acid  both  H  atoms  are  on  one  side  of  the  central 
plane. 

By  grouping  the  H  and  COOH  groups  at  the  four  solid  angles  of  the  two  tetra- 
hedra  represented  in  the  middle  diagram  of  Fig.  257,  so  as  to  produce  the  plane  and 
axial  symmetry  of  the  above  formula?,  some  idea  of  the  possible  stereo-formula^  of 
maleic  and  fumaric  acids  may  be  obtained.  Ingenious  arguments  have  been 
advanced  to  explain  the  conversion  of  the  one  acid  into  the  other  by  supposing 
that,  by  addition  of  elements,  the  double  linking  is  opened  up,  so  as  to  produce  the 
left  hand  diagram  of  Fig.  257,  the  tetrahedra  of  which  then  rotate  on  their  common 
axis,  and,  losing  the  added  elements,  again  assume  the  form  of  the  middle  diagram  ; 
but  this  time  the  COOH  and  H  groups  would  have  assumed  the  opposite  sym- 
metrical relationship  to  that  which  they  had  before.  Such  arguments  are  open  to 
well-found  contradiction  and  cannot  be  detailed  here 

Citraconic  (m.-p.  91°  C.)  and  mesaconic  (m.-p.  202°  C.)  acids,  C3H4(COOH)2.  are 
homologues  of  fumaric  and  maleic  acid,  the  former  being  metliyltualeic  acid,  while 
the  latter  is  niethylfumaric  acid.  Thus  they  have  the  same  relationship  to  each 
other  as  fumaric  and  maleic  have.  Citraconic  acid,  being  the  m-form,  yields  an 
anhydride  which  is  found  in  the  products  of  destructive  distillation  of  citric  acid 
together  with  the  anhydride  of  itaconic  acid  (m.-p.  161°  C.),  another  isomeride  which 
is  methylene  succinic  acid,  COOH*CH2-C(:  CH2)'COOH  ;  hence  these  acids  were 
formerly  termed  pyrocitric  acids.  If  citraconic  acid  be  heated  for  some  time  with 
dilute  HN03  or  strong  HC1,  it  is  converted  into  mesaconic  acid.  Mesaconic  dis- 
solves in  about  40  parts  of  cold  water,  itaconic  in  about  20  parts,  and  citraconic  in 
i  part.  All  three  are  reduced  by  nascent  H  to  pyrotartaric  acid.  They  combine  with 
the  haloid  acids  to  form  isomeric  substitution-products  of  pyrotartaric  acid. 

389.  Of  the  dibasic  acids  from  the  acetylene  hydrocarbons,  acetylene  dicarbonyUc 
acid,  C02H'C  :  C/C02H,  need  alone  be  noticed.  It  is  produced  by  heating 
dibromosuccinic  acid,  C2H2Br2(C02H)2,  with  alcoholic  potash,  whereby  2HBr  are 
removed.  It  crystallises  with  2H20,  and  decomposes  when  fused. 

*  Compare  the  ease  with  which  1:2-  phthalic  acid  yields  an  anhydride  (p.  617). 
f  The  special  term  alloisomerism  or  geometrical  isomerism  has  been  applied  to  these  cases ; 
it  is  not  necessary. 


PHTHALIC   ACIDS.  6l/ 

390.  Dibasic  Acids  from  Aromatic  Hydrocarbons.—  These  are 

obtained  by  oxidising  benzene  hydrocarbons  containing  side-chains. 
Thus,  the  most  important  of  them,  the  three  phthalic  adds,  C6H4(COOH)  ,* 
can  be  prepared  by  oxidising  the  three  xylenes,  C6H4(CH3)2,  and  indeed 
most  other  disubstituted  benzenes  in  which  carbon  is  attached  directly 
to  the  nucleus. 

i  :  2-phthalic  acid  is  the  most  important  isomeride  and  is  charac- 
terised by  yielding  an  anhydride  when  heated,  owing,  no  doubt,  to  the 
fact  that  the  COOH  groups  are  in  the  adjacent  position.  It  is  made 
in  large  quantity,  for  the  manufacture  of  dye-stuffs,  by  oxidising 
naphthalene  with  strong  H2S04  in  presence  of  mercury. 

On  a  small  scale  naphthalene  tetrachloride  is  oxidised  with  HN03.  i  part  of 
C10H8  is  carefully  mixed,  on  paper,  with  2  parts,  by  weight,  of  KC103,  and  added, 
in  small  portions,  to  10  parts  of  strong  HC1.  The  naphthalene  tetrachloride,  C10H8C14, 
thus  formed,  is  washed  with  water  till  free  from  acid,  and  allowed  to  dry.  It  is 
introduced  into  a  flask  and  treated  with  strong  HN03  (sp.  gr.  1.45),  which  must  be 
very  gradually  added,  amounting  to  ten  times  the  weight  of  naphthalene  taken. 
The  mixture  is  heated  till  all  is  dissolved,  the  nitric  acid  boiled  off,  and  the  residue 
distilled,  when  plithallc  anhydride  distils  over  and  is  converted  into  phthalic  acid 

co  POOH 

by  dissolving  in  hot  water  and  crystallising  ;  C6H4/      \0  +  H20  =  C6H4/ 

XCOX  XCOOH 

Phthalic  acid  crystallises  in  rhombic  prisms,  which  are  easily  fusible,  and 
readily  decomposed  into  water  and  the  anhydride.  It  is  sparingly  soluble  in  cold 
water,  but  dissolves  readily  in  hot  water,  in  alcohol,  and  in  ether  ;  with  NH3  and 
BaCl2  it  yields  a  precipitate  of  barium  phthalate.  When  heated  with  lime  to  340°  C., 
it  yields  benzoate  and  carbonate  of  calcium.  Chromic  acid  oxidises  phthalic  acid 
completely  into  C02  and  H20. 

i  :  $-  Phthalic  acid  or  uuphthalic  acid  crystallises  in  needles  ;  it  is  soluble  in 
hot  water,  is  not  precipitated  by  BaCl2  in  presence  of  NH3,  and  yields  no  anhy- 
dride when  heated,  but  sublimes  unchanged. 

i  :  ^-Phthalic  acid,  or  terephtlialic  acid,  is  difficult  to  crystallise,  and  is  in- 
soluble in  water,  so  that  it  is  precipitated  from  its  solutions  in  alkali  by  adding 
acid.  The  barium  salt  is  sparingly  soluble.  The  acid  sublimes  unchanged. 

These  differences  in  the  properties  of  the  three  phthalic  acids  are  of  importance, 
since  the  production  of  one  or  other  of  the  acids  frequently  serves  to  decide  the 
constitution  of  a  benzene  derivative. 

Phthalic  anhydride  crystallises  in  long  prisms,  in.-p.  128°  C.;  b.-p.  284°  C.  It  is 
used  in  making  eosin  dyes. 

By  treating  the  phthalic  acids  with  nascent  hydrogen  a  large  number  of  hydro- 
gen-addition products,  hydrophthalic  acids,  e.g.,  C6H4-H4-(COOH)2,  has  been 
obtained.  These  are  remarkable  for  the  numerous  cases  of  isonierisin  which 
they  exhibit  ;  the  cause  of  this  has  been  traced,  first,  to  the  existence  of  cix- 
and  f?'aft.s'-forms,  as  in  the  case  of  maleic  and  fumaric  acids,  and  secondly,  to 
the  different  positions  of  the  double  linking  between  the  carbon  atoms  of  the 
benzene  nucleus,  e.g.,  the  two  dihydroterephthalic  acids  (cf.  p.  550), 

C0.HCH2'CHC-C0H  and 


Naphtliallc  acids  are  diabasic  acids  from  naphthalene,  C10H6(C02H>2  ;  six  out  of 
ten  possible  isomerides  are  known. 

39  1  .  Dibasic  Hydroxy-  acids.—  These  may  be  regarded  as  oxidation 
products  of  diprimary  polyhydric  alcohols,  or,  in  the  case  of  those 
containing  a  benzene  nucleus,  as  dicarboxylic  acids  from  phenols. 

Tartronic  or  hydroxymalonic  acid,  CH(OH)(C02H)2,  is  formed  by  the  action  of 
nascent  hydrogen  on  mesoxalic  acid  (see  below),  which  is  a  product  of  the  oxidation 
of  uric  acid.  Its  crystals  melt  at  158°  C.  and  are  then  decomposed  mtc  .water,  CO* 
and  an  amorphous  polymer  of  glycolide  (p.  604).  Tartronic  acid  was 


6l8  MALIC   ACID. 

obtained  by  heating  solution  of  dinitrotartaricacid ;  C2H2(ON00)2(CO,>H)o  = 
CH(OH)(C02H)2  +  N2p3  +  C02.  It  is  also  formed  when  glucose  is  oxidised  by  an 
alkaline  cupric  solution,  and  when  glycerine  is  oxidised  by  K2Mn208.  Barium 
tartronate,  from  which  the  acid  is  readily  obtained,  may  be  prepared  by  heating 
glyoxalic  acid  with  potassium  cyanide  and  baryta- water — 

CHOC02H  +  KCN  +  Ba(OH)2  +  HOH  =  CH(OH)(C02)2Ba  +  KOH  +  NH3 
Jfesoxalic  acid  is  regarded  by  some  as  diliydroxymalomc  acid,  C(OH)o(C02H)2, 
but  since  this  compound  contains  two  OH  groups  attached  to  one  carbon  atom, 
it  is  more  probable  that  the  acid  is  a  ketonic  acid  of  the  form  CO(CO2H)2  +  H20, 
a  view  supported  by  the  fact  that  it  forms  a  compound  with  NaHS03,  and  com- 
bines with  hydroxylamine  (see  Ketones}.  It  is  best  obtained  by  boiling  alloxan 
(q.K.)with  baryta  water.  It  crystallises  in  deliquescent  prisms  with  iH20,  and 
melts  without  loss  of  water  at  115°  C. 

Malic,  or  Hydroxysuccinic  acid,  COOH'CH2-CHOH'COOH,  is  one 
of  the  chief  natural  vegetable  acids,  occurring  in  apples,  gooseberries, 
currants,  &c.  Tt  will  be  noted  that  its  alcoholic  C  atom  is  asymmetric, 
hence  it  is  known  in  the  usual  three  optically  isomeric  forms.  Strong 
solutions  of  the  natural  acid  are  dextro-rotatory,  though  when  diluted 
they  are  Isevo-rotatory.  It  is  extracted  from  the  juice  of  the  unripe 
berries  of  the  mountain  ash. 

The  juice  is  boiled,  filtered,  nearly  neutralised  with  milk  of  lime,  and  boiled, 
when  calcium  malate.  C2H3(OH)(C02)2Ca.Aq,  is  precipitated  in  minute  crystals.  This 
is  dissolved  to  saturation  in  hot  nitric  acid  diluted  with  ten  times  its  weight  of  water. 
On  cooling,  crystals  of  hydrocalcium  malate,  [C2H3(OH)(C02H)-C02]2Ca.8Aq,  are 
deposited.  These  are  dissolved  in  hot  water,  and  decomposed  by  lead  acetate,  when 
lead  malate  is  precipitated  ;  this  is  suspended  in  water,  and  H2S  passed,  when 
PbS  remains  precipitated,  and  malic  acid  is  found  in  solution,  from  which  it 
crystallises,  though  not  very  readily,  in  tufts  of  deliquescent  needles. 

The  acid  melts  at  100°  C.  and  at  a  higher  temperature  yields  a  feathery 
sublimate  of  maleic  and  fumaric  acids  and  of  maleic  anhydride.     Oxida- 
tion with  chromic  acid  converts  it  into  malonic  acid,  fusion  with  potash 
into  oxalate  and  acetate.     Hydriodic  acid  reduces  it  to  succinic  acid : 
C2H3(OH)(COOH)2  +  2HI  =  C2H4(COOH)2  +  H20  +  I2. 

By  boiling  bromosuccinic  acid,  C2H3Bi  (COOH).,,  with  AgOH  (silver 
oxide  and  water)  the  Br  is  exchanged  for  OH  and  inactive  malic  acid  is 
produced.  The  d-  and  Z-acids  are  obtained  by  reducing  the  tartaric 
acids  (q.v.\  of  corresponding  activity,  with  HI. 

The  active  forms  are  also  separated  by  crystallising  the  cinchonine  salt  of  the 
inactive  acid  (ef.  p.  606). 

Some  of  the  salts  of  malic  acids  also  occur  in  nature.  Cherries  and  rhubarb 
contain  acid  potassium  malate,  C2H3(OH)(C02H)(C02K),  while  tobacco  contains 
acid  calcium  malate.  Normal  calcium  malate  is  less  soluble  in  hot  water,  and  is 
therefore  precipitated  on  neutralising  the  acid  with  lime-water  and  boiling.  Lead 
malate  forms  a  white  precipitate  containing  3Aq.,  distinguished  by  fusing  under 
water  to  a  gummy  mass,  becoming  crystalline  on  cooling. 

392.  Tartaric  or  dihydroxysuccinic  acid,  CO2H'CHOH  CHOH 
•CO2H,  is  one  of  the  most  important  vegetable  acids,  being  often  found 
in  fruits  associated  with  malic  acid.  It  is  prepared  from  arc/ol  or  tartar, 
a  crude  form  of  acid  potassium  tartrate,  C2H2(OH)2(COOH)(COOK), 
deposited  in  crystalline  crusts  during  the  fermentation  of  grape-juice. 

This  (45  ounces)  is  boiled  with  (2  gallons)  water,  and  neutralised  by  adding 
( 1 2.\  ounces)  powdered  chalk,  which  converts  the  hydropotassium  tartrate  of  the 
argol  into  calcium  tartrate  and  potassium  tartrate — 

2C4H406KH  +  CaC03  =  C4H406K3  +  C4H406Ca  +  H20 


TARTARIC  ACID. 

The  potassium  tartrate  dissolves  and  the  calcium  tartrate  precipitates.  Solution  of 
calcium  chloride  (13^  oz.  dissolved  in  2  pints  of  water)  is  then  added,  to  precipitate 
the  potassium  tartrate  as  calcium  tartrate;  C4H406K2  +  CaCl2=C4H406Ca  +  2KCl. 
The  calcium  tartrate  is  strained  off,  washed,  and  heated  for  half  an  hour  with  dilute 
sulphuric  acid  (13  fluid  ounces  of  acid  in  3  pints  of  water),  when  calcium  sulphate 
remains  undissolved,  and  tartaric  acid  may  be  crystallised  by  evaporating  the 
filtered  solution;  C4H406Ca  +  H2S04  =  C4H406H2+CaS04.  The  crude  acid  is  dis- 
solved in  water,  decolorised  by  animal  charcoal,  and  again  crystallised.  A  little 
sulphuric  acid  is  generally  added  to  promote  the  formation  of  large  crystals. 
These  often  contain  lead  derived  from  the  evaporating  pans. 

Properties  of  tartaric  acid. — The  crystals  are  monoclinic  prisms,  very 
soluble  in  water,  and  fairly  so  in  alcohol,  but  nearly  insoluble  in  ether. 
When  heated  rapidly  to  170°  C.  it  fuses,  and  becomes  an  amorphous 
deliquescent  mass  of  metatartaric  acid,  isomeric  with  it.  At  145°  C.  it 
becomes  tartralic  acid,  C8H10On,  two  molecules  of  the  acid  having  lost  a 
molecule  of  water;  at  180°  C.  it  yields  tartaric  anhydride,  C8H8010.  All 
these  may  be  re-converted  into  tartaric  acid  by  digestion  with  water.  On 
further  heating,  it  undergoes  destructive  distillation,  yielding  chiefly 
pyruvic  and  pyrotartaric  acids,  together  with  dipyrotartracetone,  C8H1208, 
which  has  a  peculiar  odour,  like  that  of  burnt  sugar,  by  which  tartaric 
acid  may  be  recognised. 

Fused  KOH  converts  tartaric  acid  into  acetate  and  oxalate.  Boiled 
with  nitric  acid,  much  of  it  is  oxidised  to  oxalic  acid.  Distilled  with 
sulphuric  acid  and  MnO2,  or  K2Cr207,  it  yields  formic  acid  and  C02. 

Natural  tartaric  acid  is  dextro-rotatory  and  when  heated  with  HI,  in 
strong  aqueous  solution,  at  120°  C.,  in  a  sealed  tube,  it  is  reduced  to 
dextro-malic  acid,  which  is  again  reduced  to  succinic  acid — 

C2H2(OH)2(C02H)2  +  2HI  =  C2H3(OH)(C02H)2  (malic  acid)  +  H20  +  Lj. 

And  C2H3(OH)(C02H)2  +  2HI  =  C2H4(C02H)2  (succinic  acid)  +  H20  +  I2. 
Conversely,  tartaric  acid  can  be  obtained  by  the  treatment  of  dibromo- 
succinic  acid  with  moist  silver  oxide. 

393.  SALTS  OF  TARTARIC  ACID. — A  distinguishing  character  of  tartaric  acid  is 
the  sparing  solubility  of  the  acid  potassium  tartrate,  HK4H406,  which  is  precipi- 
tated in  minute  crystals  when  almost  any  potassium  salt  is  added  to  tartaric  acid, 
and  the  solution  is  stirred  with  a  glass  rod,  when  the  precipitate  attaches  itself  to 
the  lines  of  friction.     Commercially  this  salt  is  known  as  cream  of  tartar,  and  is 
prepared  by  re-crystallising  argol  from   hot  water,  which  dissolves  ^th  of  i 
weight,  and  only  retains  ^th  on  cooling.     It  is  nearly  insoluble  in  alcohol,  whicl 
precipitates  it  from  the  aqueous  solution,  and  this  explains  its  separation  from  Ul 
grape-juice,  as  the  proportion  of  alcohol  increases  during  the  fermentation.    . 
dissolves  easily  in  acids  and  in  alkalies,  which  convert  it  into  normal  tartrate, 
K2C4H406.    When  heated,  it  evolves  the  burnt-sugar  odour,  and  leaves  a  b 
mass  of  charcoal  and  potassium  carbonate  (salt  of  tartar).  ^ 

Sodio-potassiuni,    tartrate,    NaKC4H4064Aq,    Roclielle    or    Seigmttes   xalt,     : 
prepared  by  neutralising  a  boiling  solution  of  sodium  carbonate  with  ci 
tartar,  when  it  crystallises  on  cooling,  in  fine  rhombic  prisms.    1 
medicine.  T,  . 

Calcium  tartrate,  CaC4H406.4Aq,  occurs  in  grapes  and  in  senna  leaves. 
sparingly  soluble  in  water,  and  is  precipitated  when  CaCl2  is  added  to  an  a 
niacal  solution  of  a  tartrate.     It  is  soluble  in  potash  and  in  ammonium  chl 

Cupric  tartrate,  CuC4H4C>3Aq,  is  sparingly  soluble  in  water,  but  disi 
alkalies  to  a  deep  blue   solution,  in  which  two  atoms  of  the  alkali  metal  h.iv 
displaced  H2.     Such  a  solution  is  often  used  in  analysis,  as  alkaline  cupn 
or  Fehliwfs  test.     Tartaric  acid  behaves  in   a  similar  way  with  seven 
metals,  retaining  them  in  alkaline  solutions  when  they  would  otherwise 
cipitated  as  hydroxides  ;  in  the  cases  of  Al  and  Fe,  this  is  turned  to  a 
analysis. 


620  STEEEOISOMERISM. 

Silcer  tartrate,  Ag2C4H406,  is  precipitated  by  silver  nitrate  from  a  normal 
tartrate  ;  it  dissolves  in  ammonia,  and  the  solution  deposits  metallic  silver  when 
heated,  the  tartaric  acid  being  oxidised  to  carbonic  and  oxalic  acids.  This  is 
taken  advantage  of  in  some  processes  for  silvering  mirrors. 

Potassium-antimonyl-tartrate,  K(SbO)C4H406,  or  tartar  emetic,  is  prepared 
by  boiling  cream  of  tartar  (6  oz.)  with  water  (2  pints)  and  (5  oz.)  antimonious 
oxide  ;  Sb203  +  2KHC4H406  =  2KSbOC4H406  +  H2O.  From  the  filtered 
solution,  on  cooling,  the  salt  crystallises  in  rhombic  prisms  of  the  formula 
2KSbOC4H406.Aq.  It  is  soluble  in  three  parts  of  hot  water  and  in  fifteen 
parts  of  cold  water.  The  crystals  lose  their  water  of  crystallisation  at  100°  C., 
and  when  heated  over  200°  the  emetic  loses  the  elements  of  another  molecule 
of  water,  and  becomes  KSbC4H2O6,  which  is  reconverted  into  emetic  by  boiling 
with  water. 

When  barium  chloride  is  added  to  tartar-emetic,  a  precipitate  is  formed, 
according  to  the  equation  2KSbOC4H406  +  BaCl2  =  Ba(SbOC4H406)2  +  2KC1.  By 
decomposing  this  barium  salt  with  sulphuric  acid,  an  acid  solution  is  obtained,  which 
soon  deposits  antimonious  hydroxide,  but  if  it  be  neutralised  with  potash  before 
decomposition  occurs,  it  yields  tartar-emetic.  Hence  it  would  seem  that  the 
emetic  is  the  potassium  salt  of  the  acid  H(SbOC4H40?)  or  C2H2(OH)2(C02)2SbOH, 
which  is  derived  from  tartaric  acid  by  exchanging  one  atom  of  H  in  the 
(C02H)2  for  the  monad  radicle  antimomjl,  Sb'"0".  The  emetic  acid  has  been 
named  tartryl  antimonious  acid,  so  that  tartar-emetic  would  be  potassium  tartryl 
antimonite.  Other  tartryl-antinionites  have  been  obtained.  By  dissolving  Sb2O3 
in  tartaric  acid,  and  adding  alcohol,  a  crystalline  precipitate  of  antimonyl  tartrate, 
(SbO)2C4H406,  is  obtained,  and  this  becomes  tartar-emetic  when  boiled  with 
normal  potassium  tartrate  (SbO).2C4H406+K2C4H406  =  2KSbOC4H406.  For  the 
antimony  in  tartar-emetic  arsenic  or  boron  may  be  substituted. 

When  excess  of  Sb203  is  boiled  with  solution  of  tartaric  acid,  and  the  liquid 
evaporated  to  a  syrup,  it  deposits  crystals  of  H(SbO)C4H406,  which  is  decomposed 
by  water,  and  appears  to  be  identical  with  the  tartryl-antimonious  acid. 

394.  Stereoisomerism  as  illustrated  by  tartaric  acid, — When  natural 
(dextro)  tartaric  acid,  is  heated  with  about  one-tenth  of  its  weight  of 
water,  in  a  sealed  tube  at  175°  C.  for  some  30  hours,  in  the  apparatus 

shown  in  Fig.  275,  it  is 
converted  into  an  inactive 
isomeride,  racemic  acid, 
which  crystallises  with  iH.,0 
in  triclinic  prisms,  meltss  at 
202°  C.  and  is  much  less 
soluble  in  water  than  dextro- 
tartaric  acid  is.  By  pre- 
cipitating as  acid  potassium 
tartrate,  the  unaltered 
tartaric  acid  remaining  in 
the  mother-liquor  obtained 
Fig.  275.— Heating  in  sealed  tubes.  in  crystallising  racemic  acid, 

there  is  left  in  solution  the 

acid  potassium  salt  of  another  inactive  acid,  mesotartaric  acid,  which 
crystallises  in  rectangular  tables  (with  iH20).* 

The  differences  between  racemic  and  mesotartaric  acid  are  sufficiently  marked. 
The  acid  potassium  racemate  is  more  soluble  than  the  tartrate,  while  the  corre- 
sponding mesotartrate  has  not  been  crystallised.  Calcium  racemate,  CaC4H406'4Aq. 
is  less  sparingly  soluble  than  calcium  tartrate  and  than  calcium  mesotartrate, 
CaC4H406.3Aq.  so  that  calcium  sulphate  precipitates  free  racemic  acid  but  neither 
of  the  other  free  acids.  Calcium  racemate  is  insoluble  in  ammonium  chloride  and 

*  For  obtaining  mesotartaric  acid  the  sealed  tube  containing-  the  tartaric  acid  and  water 
should  be  healed  at  165°  C.  for  2  hours. 


STEREOISOMERISM.  62I 

in  dilute  acetic  acid,  which  also  fails  to  dissolve  the  inesotartrate  •  the  tartrate 
however,  is  soluble  in  both. 

Racemic  acid  is  found  mixed  with  the  tartaric  acid  from  certain  samples  of  argol 
and  its  crystals  may  be  distinguished  from  those  of  tartaric  acid  by  the  cloudy 
appearance  which  they  assume  at  100°  C.  due  to  the  loss  of  their  water  of  crystal- 
lisation. 

It  has  been  found  that  racemic  acid,  like  the  inactive  forms  of  other 
compounds  containing  an  asymmetric  carbon  atom,  can  be  split  up  by 
the  methods  referred  to  on  p.  606  into  the  dextro-tartaric  acid  and 
kevo-tartaric  acid,  which  is  practically  identical  with  the  dextro-acid, 
save  that  it  rotates  the  plane  of  polarisation  to  an  equal  extent  to  the 
left. 

The  classical  researches  of  Pasteur  on  sodium-ammonium  racemate  are  the 
foundation  of  stereochemistry. 

The  sodium-ammonium  racemate,  NaNH4C4H406,  has  the  same  crystalline  form 
as  the  tartrate,  but  when  formed  at  a  temperature  below  28°  C.  the  crystals  of  the 
racemate  differ  from  each  other  in  the  position  of  a  certain  unsymmetrical  (hemi- 
hedral)  face  ;  this  is  on  the  right  hand  in  the  one  kind  and  on  the  left  hand  in  the 
other  (enantiomorphous).  When  these  are  picked  out,  and  the  acid  extracted  from 
them,  the  right-handed  crystals  yield  ordinary  dextro-rotatory  tartaric  acid,  whilst 
the  left-handed  crystals  yield  lasvo-tartaric  acid.  From  a  solution  of  cinchonine 
racemate,  cinchonine  lasvo-tartrate  separates  first.  The  mould  penicMlium  glaucum 
consumes  dextro-tartaric  acid  in  preference  to  the  laevo-form  when  growing  in 
racemic  acid. 

By  mixing  equal  weights  of  dextro-  and  laevo-tartaric  acid,  heat 
i>  evolved  and  racemic  acid  is  formed.  So  also  calcium  racemate 
is  precipitated  when  solutions  of  the  I-  and  d-calcium  salts  are 
mixed. 

Three  of  the  isomeric  tartaric  acids  are  thus  accounted  for,  but  the 
fourth,*  mesotartaric  acid,  finds  no  analogue  among  the  isomerides  of 
compounds  containing  an  asymmetric  carbon  atom  so  far  considered. 
Ic  is  not  capable  of  being  split  up  into  active  components,  nor  is  it 
produced  by  mixing  the  active  forms.  It  is  obtained  practically  pure 
by  oxidising  maleic  acid  with  permanganate. 

It  is  supposed  that  this  fourth  tartaric  acid  owes  its  existence  to  the 
fact  that  the  molecule  contains  two  asymmetric  carbon  atoms,  so  that 
it  is  possible  for  the  one  to  have  its  groups  arranged  to  give  dextro- 
rotation  while  the  groups  of  the  other  are  arranged  to  give  laevo- 
rotation.  In  this  cass  the  molecule  would  be  internally  compensated 
and  would  be  optically  inactive,  just  as  the  racemic  acid  molecule  is 
externally  compensated,  consisting  of  two  oppositely  active  molecules. 

Tartaric  acid  belongs  to  the  type  of  two  tetrahedra  having  one  solid  angle  in 
common  (p.  535),  and  to  the  other  solid  angles  of  each  tetrahedron  there  must  be 
three  different  radicles,  H,  OH,  C02H,  attached.     It  is  evident  that  these  three 
radicles  may  be  similarly  or  differently  arranged  around  each  tetrahedron, 
are  similarly  arranged,  then  it  will  be  possible  on  severing  the  tetrahedra  to  place 
one  inside  the   other,   so   that   each   solid  angle  shall  correspond  :  if  they  are 
differently  arranged,    this   will   not   be   possible.     It   is   supposed  that  when  the 
radicles  are  similarly  arranged,  the  tartaric  acid  is  either  dextro-  or  heyo-rotatory, 
according  as  the  arrangement   is  clockwise  or  anti-clockwise  ;  but 
differently  arranged,  the  dextro-rotatory  power  of  one  tetrahedron  wi II  annul 
laevo-rotatory  power  of  the  other,  and  an  inactive  compound  will  result, 
lowing  figures  will  illustrate  what  has  been  said  : 

*  A  fifth  acid,  CO2H-C(OH)2-CH2-CO2H,  which  contains  two  OH  groups  attached  to  the 
same  carbon  atom,  has  not  been  obtained. 


622  MECONIC  ACID. 

C02H  C02H                        C02H  C02H  C00H 

HO-C-H  H-C-OH  HO-C-H  HO-C-H  +          H-C-OH 

H-C-OH  HO-C-H  HO-C-H  H-C-OH  HO'C'H 

C02H  C02H                        C02H  C02H  C02H 

Laevo-tartaric  Dextro-tartaric      Internally  compensated     Externally  compensated  tar- 

acid,  acid.  or  meso-tirtaric  taric  acid. 

acid.  Racemic  acid. 

It  is  worthy  of  note  that  in  whatever  manner  tartaric  acid  is  synthesised  the 
inactive  forms  are  produced,  and  it  is  generally  the  case  that  artificial  compounds 
are  inactive  whether  they  contain  an  asymmetric  carbon  atom  or  not.  This  is  to 
some  extent  confirmatory  of  the  foregoing  theory  ;  for  it  would  seem  to  be  an  even 
chance  which  way  the  groups  arrange  themselves  round  the  asymmetric  carbon 
atom,  so  that  both  forms  are  produced  in  equal  amounts. 

It  is  customary  to  speak  of  externally  compensated  compounds  as  racemlsed  coin- 
pounds  and  the  passage  of  the  active  form  into  the  externally  compensated  inactive, 
as  race  mi  sat  ion.  In  many  cases  such  racemisation  occurs  spontaneously  under 
influences  which  are  somewhat  obscure,  and  the  passage  of  an  unstable  active  form 
into  the  more  stable  active  form  is  known  to  occur. 

395.  Saccharic  acid,  C02H-[CHOH]-4C02H,  is  obtained  by  oxidising  sugar  or 
starch  with  nitric  acid,  stopping  short  of  the  formation  of  oxalic  acid.  Sugar  is 
heated  with  3  parts  of  nitric  acid  of  sp.  gr.  1.3,  till  violent  action  begins.  When 
no  more  red  fumes  are  evolved,  it  is  kept  at  50°  C.  for  some  hours,  diluted  with 
two  or  three  volumes  of  water,  neutralised  with  K2C03.  and  acidified  strongly 
with  acetic  acid.  On  standing,  acid  potassium  saccharate,  C4H804(C02)2HK, 
crystallises.  This  is  dissolved  in  a  little  potash,  and  precipitated  by  cadmium 
chloride.  The  precipitate  of  cadmium  saccharate  is  suspended  in  water  and 
decomposed  by  H2S,  the  CdS  filtered  off,  and  the  solution  of  saccharic  acid 
evaporated.  Saccharic  acid  forms  a  deliquescent  amorphous  mass,  soluble  in 
alcohol  and  in  water.  Its  salts  are  somewhat  similar  to  those  of  tartaric  acid, 
the  acid  salts  of  potassium  and  ammonium  being  sparingly  soluble.  Calcium, 
saccharate,  C4H804(C02)2Ca.Aq,  is  crystalline,  nearly  insoluble  in  water,  but  soluble 
in  acetic  acid.  The  stereochemistry  of  saccharic  acid  will  be  noticed  later. 

Mucic  acid,  C02H-[CHOH]4-C02H,  stereoisomeric  with  saccharic,  is  prepared  by 
oxidising  gum  arabic  or  milk  sugar  with  nitric  acid.  Milk  sugar  is  heated  with 
3  parts  of  nitric  acid  of  sp.  gr.  1.3  until  red  fumes  are  abundant  ;  the  heat  is  then 
removed,  when  the  acid  separates  as  a  granular  powder  sparingly  soluble  in  water 
and  alcohol.  The  mucates  differ  greatly  from  the  saccharates,  most  of  them  being 
insoluble  ;  the  acid  potassium  salt  is  more  soluble  than  the  normal  salt.  By 
boiling  mucic  acid  with  water  for  some  time,  it  is  converted  into  paramuclc  acid, 
which  is  isomeric  with  it,  but  more  soluble  in  alcohol.  Hydriodic  acid  reduces 
saccharic  and  mucic  acids  to  adipic  acid — 

C4H804(C02H)2  +  SHI  =  C4H8(C02H)2  +  4H20  +  4l.2. 

Pyromucic  acid,  or  furfurane  (L-monocarboxylic  acid,  C4H30'C02H,  is  a  pro- 
duct of  the  distillation  of  mucic  acid,  and  may  also  be  obtained  by  boiling  furfural 
(pyromucic  aldehyde,  p.  586)  with  silver  oxide  and  water.  It  forms  prismatic 
crystals  sparingly  soluble  in  cold  water,  soluble  in  hot  water,  alcohol,  and  ether. 
It  may  be  sublimed.  The  pyromucates  are  very  soluble. 

/  CH  =  C(C02H)v 
Meconic  acid,   CO^  >0,    hydroxypyrone     dicarboxylic    acid,   is 

xC(OH):C(CO2Hr 

extracted  from  opium  by  digesting  it  with  hot  water,  neutralising  the  solution 
with  calcium  carbonate,  and  adding  calcium  chloride,  which  precipitates  acid 
calcium  meconate,  HCaC7H07.Aq,  from  which  meconic  acid  may  be  crystallised  by 
dissolving  it  in  hot  dilute  HC1.  It  crystallises  (with  3H2O)  in  plates,  dissolving 
rather  sparingly  in  cold  water  and  ether,  easily  in  hot  water  and  alcohol.  When 
heated,  it  loses  C02,  and  becomes  comenic  acid,  C6H4O5,  and  when  further  heated, 
hydroxypyrone  (pyrocomenic  acid)  C5H5(OH)02.  Solution  of  meconic  acid  gives  a 
fine  red  colour  with  ferric  chloride,  not  bleached  by  mercuric  chloride  With 
silver  nitrate,  it  gives  a  white  precipitate  of  hydrodiargentic  meconate,  HAg2C2H07, 
but  if  a  drop  of  ammonia  be  added,  and  the  liquid  boiled,  the  precipitate  becomes 
bright  yellow nwrmal  silver  meconate,  Ag3C2H07.  Meconic  acid  is  closely  related,  by 


CITRIC   ACID.  623 

its  composition,  to  chelidonic  acid,  C7H406,  an  acid  obtained  from  celandine 
(CheUdonlum  majns),  which  belongs  to  the  same  botanical  order  as  the  opium 
poppy,  which  yields  meconic  acid. 

396.  Polybasic  acids.— Very  few  of  these  are  of  any  importance  Trlciii-- 
ballylic  acid,  CH2(C02H)'CH(C02H)-CH2(C02H),  may  be  obtained  by  heating 
citric  acid  with  hydriodic  acid.  It  may  also  be  built  up  from  glycerol,  C,H,(OH  ) 
by  first  converting  this  into  allyl  tribromide,  C3H5Br8  (p.  636),  and  heating  the  tri- 
bromide  with  alcohol  and  potassium  cyanide  to  obtain  tricyanhydrin,  or  allyl 
tricyanide,  C8H5(CN)8,  which  yields  potassium  tricarballylate  and  ammonia  when 
boiled  with  potash  ;  C3H?(CN)3  +  3KOH  +  3H20  =  C3H5(C02K)3  +  3NH3. 

The  calcium  salts  of  tricarballylic,  citric,  and  aconitic  acids  occur  in  the  deposit 
formed  in  the  stills  of  beet-sugar  manufactories.  Tricarballylic  acid  melts  at 
165°  C.  and  crystallises  in  rhombic  prisms,  which  are  easily  soluble  in  water  and 
alcohol. 

397.  Citric  acid,  or  hydroxytricarballylic  acid,  CH2(C02H)'C(OH) 
(C02H)'CH2(C02H),  the  most  important  polybasic  acid,  is  found  in 
many  fruits,  associated  with  malic?  and  tartaric  acid.  The  potassium 
and  calcium  salts  are  present  in  many  vegetables  and  in  the  indigo 
and  tobacco  plants.  The  acid  is  prepared  from  lemon  juice 

The  juice  is  heated  and  chalk  is  added  as  long  as  effervescence  occurs ;  this 
precipitates  part  of  the  acid  as  calcium  citrate,  leaving  the  rest  in  solution  as  an 
acid  salt  ;  this  is  precipitated  by  adding  milk  of  lime,  and  boiling.  The  calcium 
citrate  is  washed  with  boiling  water,  decomposed  by  exactly  the  required  quantity 
of  dilute  sulphuric  acid,  the  liquid  filtered  from  the  calcium  sulphate,  and 
evaporated  to  crystallisation.  It  is  sometimes  recommended  to  ferment  the  lemon- 
juice  with  yeast  for  two  days,  and  to  filter  before  adding  the  chalk. 

It  is  said  that  the  acid  can  also  be  obtained  industrially  by  fermenting  glucose 
with  a  particular  fungus. 

The  synthesis  of  citric  acid  from  acetone  is  by  the  following  steps  : — (i)  Acetone 
treated  with  chlorine  yields  dicfdoracetone,  CH2C1'CO'CH2C1,  which  (2)  heated  with 
strong  HCX  yields  "  dichloracetotie  cyanhydrin,  CH2C1'C(OH)(CN)-CH2C1 ;  on 
(3)  hydrolysis  this  gives  dichloracetonic  acid,  CH2C1-C(OH)(C02H)-CH2C1.  (4)  The 
two  Cl  atoms  are  now  exchanged  for  CN  by  treatment  with  KCN,  dicyanoacetonic 
acid  being  produced,  CH2CN-C(OH)(C02H)-CH2CN,  which  (5)  by  hydrolysis  yields 
citric  acid. 

Citric  acid  crystallises  in  rhombic  prisms  (with  iH20)  very  soluble  in 
water  and  fairly  so  in  alcohol,  but  little  in  ether ;  they  melt  at  100°  C., 
become  anhydrous  at  130°,  and  then  melt  at  153°.  Further  heated  to 
175°,  the  acid  loses  water  and  becomes  aconitic  add,  C3H3(C02H)3. 

By  further  heating,  the  aconitic  acid  becomes  aconitic  anhydride  which  then 
loses  C02  and  passes  into  the  anhydride  of  itaconic  acid  (ntethylene  suecinic  acid) 
(COOH)CH2-C(  :  CH2)(COOH),  which  crystallises  in  the  neck  of  the  retort.  The 
liquid  portion  of  the  distillate  contains  the  anhydride  of  citraconic  acid  (methyl 
maleic  acid]  isomeric  with  itaconic,  into  which  it  is  converted  by  heating  its  con- 
centrated solution  to  120°  C.  Oxidising  agents  convert  citric  acid  into  acetone  and 
its  derivatives.  When  dehydrated  by  phosphoric  or  sulphuric  acid,  it  also  yields 
acetone,  together  with  CO  and  C02  ;  C3H4(OH)(C02H)3=2C02  +  CO  +  H20  + 
CH3-CO-CH3  (acetone).  Fusion  with  potash  converts  it  into  acetate  and  oxalate— 
C3H4(OH)(C02H)3  +  4KOH  =  2(CH3'C02K)  +  (C02K)2  +  3H20. 

Solution  of  citric  acid,  mixed  with  excess  of  lime-water,  gives  no  precipitate 
in  the  cold,  distinguishing  it  from  tartaric  and  oxalic  acid  :  but  when  heated,  it 
deposits  calcium  citrate,  Ca3(C6H507)24Aq,  which  is  more  soluble  in  cold  than  in 
water,  but  it  is  insoluble  in  potash,  which  dissolves  calcium  tartrate  ;  ami 
chloride  and  acetic  acid  dissolve  it.  .      ,     .  . 

Magnesium  citrate,  Mg3(C6H307)v.i4Aq,  is  easily  soluble  in  water ;  mixed 
NaHC03,  citric  acid,  and  sugar,  and"  rendered  granular  by  moistening  with  alec 
and  drying,  it  forms  effervescent  citrate  of  magnesia. 

Ferric  citrate,  Fe2(C6H507)2.6Aq,  used  in  medicine,  forms  transparent  i 


624  KETONES. 

prepared  by  dissolving  ferric  hydroxide  in  citric  acid  and  evaporating.     Ferric- 
amtnonlo-cltrate,  Fe2(NH4)3(C6H507)3,  is  also  used  medicinally. 

Aconitic  acid,  C02H.CH  :  C(C02H)-CH2-C02H,  a  tribasic  acid  of  the  olefine  series, 
is  obtained  by  heating  citric  acid  in  a  retort  till  oily  drops  appear  in  the  neck,  and 
extracting  the  mass  with  ether,  which  leaves  the  unaltered  citric  acid  undissolved. 
On  evaporating  the  ether,  aconitic  acid  is  left  in  small  crystals,  easily  soluble  in 
water  and  alcohol.  It  is  distinguished  from  citric  acid  by  not  precipitating  when 
boiled  with  excess  of  lime  water.  Aconitic  acid  is  found  in  monkshood  {Aco-mtum 
napellus],  beet-root,  and  sugar-cane,  and  in  some  other  plants. 

398.  Trlmesic  acid,  or  i  :  3  :  $-be*senetriowboanflieaoia,  C6H3(C02H)3,  results  from 
the  oxidation  of  mesitylene  ;  it  sublimes. 

Mellitlc  acid,  C6(COOH)6,  is  a  hexabasic  acid  of  the  aromatic  series  (for  it  yields 
benzene  when  distilled  with  lime),  which  occurs  as  its  aluminium  salt  in  a  mineral 
melllte  or  honey-stone.  It  crystallises  in  fine  silky  needles. 

ACIDS  CONTAINING  NiTKOGEN. — See  Ammonia  Derivatives  emdCyanogen 
Derivatives. 

IV.  KETONES   OR   ACETONES. 

399.  The  relationship  between  an  aldehyde  and  a  ketone  has  already 
been  noticed  (p.  580) ;  both  contain  a  CO  group,  attached  in  the  former 
to  a  hydrocarbon  radicle  and  a  hydrogen  atom,  as  CH3'  CO'H,  and  in 
the  latter  to  two  hydrocarbon  radicles,  as  CH3'CO'CH3,  acetone.     Both 
may  be  regarded  as  formed  from  an  acid,  the  aldehyde  by  substituting 
an  H  atom,  the  ketone  by  substituting  a  hydrocarbon  radicle,  for  the 
OH  of  the  COOH  group.     Thus  both  may  be  formed  from  the  acid 
chloride,  e.g.,  CH3CO*C1 — the  aldehyde  by  action  of  nascent  hydrogen, 
the   ketone    by    action    of   the    sodium   compound   of   a   hydrocarbon 
radicle  : — 

CHg-CO-Cl  +  HH  =  CHg-CO'H  +  HC1 
CH3-CO-C1  +  CH3Na  =  CH3-COCH3  +  NaCl. 

It  has  already  been  shown  (p.  568)  that  the  ketones  are,  so  to  speak, 
the  aldehydes  of  the  secondary  alcohols,  into  which  they  are  converted 
by  nascent  hydrogen.  For  the  formation  of  ketones  from  esters  of 
ketonic  acids  see  p.  644. 

It  was  shown  at  p.  580  that  the  aldehyde  of  an  acid  can  generally  be 
obtained  by  distilling  a  mixture  of  a  calcium  salt  of  that  acid  with 
calcium  formate.  If  calcium  acetate  is  distilled  with  calcium  formate, 
acetic  aldehyde  is  produced — 

(CH3-CO-0)2Ca  4-  (H-COO)2Ca  =  2(CH3'CO'H)  +  2(CaOC02). 
But  if  calcium  acetate  be  distilled  with  calcium  acetate — that  is,  by 
itself — the  products  will  be  acetone  and  calcium  carbonate — 

(CH3-COO)2Ca  +  (CH3-COO)2Ca  =  2(CH3'COCH3)  +  2(CaOC02). 

Ketones  are  simple  or  mixed  accordingly  as  the  hydrocarbon  radicles 
attached  to  the  CO  group  are  the  same  or  different ;  thus,  by  distilling 
a  mixture  of  calcium  acetate  arid  propionate,  the  mixed  ketone 
acetone- propione  is  obtained — 

(CH3-COO)2Ca  +  (C2H5-COO)2Ca  =  2(CH3-COC2H5)  +  2(CaO-COJ. 

The  ketones  are  less  easily  oxidised  than  the  aldehydes  ;  for  instance, 
they  do  not  reduce  alkaline  silver  solutions.  By  more  powerful 
oxidants  they  are  generally  converted  into  twro  acids,  the  rupture  of 
the  molecule  occurring  at  the  CO  group.  Thus,  propione  CjHg'CO'CjHj, 
yields  propionic  acid,  C2H5'C02H,  and  acetic  acid,  CH3'C02H. 


ACETONE.  625 

As  in  the  aldehydes,  the  CO  group  is  unsaturated,  so  that  the  ketones 
yield  a  number  of  combinations  similar  to  those  obtained  with  the 
aldehydes.  Ketoximes,  R,C  :  NOH,  like  the  aldoximes  from  aldehydes, 
are  formed  by  reaction  of  ketones  with  hydroxylamine. 

The  oximes  show  a  number  of  cases  of  stereo-isomerism.  most  of  them,  both 
aldoximes  and  ketoximes,  existing  in  a  stable  and  an  unstable  (labile)  modifi- 
cation. This  has  been  explained  by  supposing  that  a  difference  exists  in  the 
relative  positions  of  the  radicles  attached  to  the  carbon  and  nitrogen 
respectively^/,  maleic  and  funiaric  acids).  This  difference  maybe  represented 

thus  :  and  •  •       (in  the  aldehydes  R'  is  H).     This  theory  is  supported 

N'OH          HO'N 

by  the  fact  that  one  of  the  two  aldoximes  nearly  always  loses  water  more  easily 
than  the  other,  showing  that  the  H  and  OH  are  probably  nearer  to  each  other  in 
this  aldoxime  than  in  its  isomeride.  The  syllables  syn-  and  anti-  are  used  to 
distinguish  the  forms,  the  first  being  syn-RK'-oxime  the  second  anti-RR'-oxime. 

With  phenylhydrazine  the  ketones  yield  hydrazones,  R2C:N-NHCGH5. 
Ketones  containing  a  methyl  group  combine  with  NaHS03  to  form 
sodium  hydroxysulphonates,  e.g.,  (CH3)2'C(OH)-S03lS"a.  By  the  action  of 
PCL,  the  0  of  the  CO  group  is  exchanged  for  01,  forming  chlorides  of 
the  type  R.,CC12  in  which  the  CL>  is  easily  exchanged  for  H2  to  form  a 
secondary  paraffin  hydrocarbon. 

From  their  constitution,  the  ketones  must  afford  many  cases  of  isomerism 
(metamerism)  ;  thus,  propione  and  methyl-propyl  ketone  have  the  same  ultimate 
composition  ;  so  have  methyl-butyl  and  propyl-ethyl  ketones  ;  methyl-amyl  ketone 
and  butyrone  form  another  pair.  Moreover,  each  ketone  of  the  acetic  series  is 
isomeric  with  the  aldehyde  of  the  acid  following  next  in  the  series  ;  thus,  acetic 
ketone,  (CH3).2CO,  is  isomeric  with  propionic  aldehyde,  C2H5-COH. 

400.  Acetone,  or  dinwthyl-ketone,  CH3*COtCH3,  or  pyro-acetic  spirit, 
is  obtained  among  the  products  of  distillation  of  wood  (p.  566),  and  may 
be  prepared  by  distilling  the  acetate  of  lead,  calcium,  or  barium,  the 
last  yielding  the  purest  product  (see  the  above  equation).  The  crude 
distillate  is  shaken  with  a  saturated  solution  of  NaHS03  and  the 
crystalline  compound  thus  formed  (see  above)  is  freed  from  the  mother- 
liquor  and  distilled  with  sodium  carbonate,  when  acetone  distils  over, 
mixed  with  water,  which  is  removed  by  fused  calcium  chloride. 

Acetone  is  a  colourless  fragrant  liquid,  of  sp.  gr.  0.80,  and  boiling  at 
56°. 3  C.  It  is  inflammable,  burning  with  a  luminous  flame.  It  mixes 
with  water,  alcohol,  and  ether.  On  adding  solid  KOH  to  its  aqueous 
solution,  the  acetone  separates  and  rises  to  the  surface.  It  is  a  good 
solvent  for  certain  resins  and  camphors,  and  is  also  used  for  making 
chloroform,  iodoform  and  sulphonal.  It  is  not  so  powerful  a  reducing- 
agent  as  aldehyde,  and  does  not  reduce  silver  nitrate.  "When  oxidised 
by  K0Mn,O8  or  by  K.,Cr.,07  and  H.,S04  it  yields  acetic  and  carbonic 
acids— CH3-CO-CH3  +  64  =  CH3-CO'OH  +  CO(OH)2. 

Acetone  is  formed  when  vapour  of  acetic  acid  ig  passed  through  a  red-hot  tube, 
and  when  starch,  sugar,  and  many  other  organic  bodies  undergo  destructive  distil- 
lation. It  occurs  in  the  urine  of  diabetic  patients. 

When  acted  on  by  dehydrating  agents,  such  as  sulphuric  or  hydrochloric  acid 
or  quicklime,  acetone  loses  the  elements  of  water,  and  yields  condensation-pro- 
duct*, richer  in  carbon  ;  thus,  two  molecules  of  (CH3).2CO,  losing  H20,  give 
(CH3)2C  :  CH-CO-CH3,  wesltyl  o.ride,  a  liquid  smelling  of  peppermint,  and  boiling 
at  130°  C.  Three  molecules  of  (CH3)2CO,  losing  2H20,  yield  [(CH3)2:C  :  CH]2CO, 
phot-one,  a  crystalline  solid,  smelling  of  geraniums,  and  boiling  at  196°  C.,  whilst  the 
loss  of  another  H00  gives  C«H10,  mesltylene  (p.  549). 

2   II 


626  PYRUYIC    ACID. 

Acetone  peroxide,  (C3H6O2)3,  is  formed  by  mixing  concentrated  solutions  of  H.20.2 
and  acetone.  It  forms  crystals,  melting  at  97°  C.,  insoluble  in  water  and  explosive. 

An  important  thio-derivative  of  acetone  is  obtained  by  heating  a  mixture  of 
acetone  and  mercaptan  with  HC1. 

(CHS)2CO  +  2C2H5SH  =  (CH3)2C(SC2H5)2  +  H2O. 

This  is  known  as  mercaptol  and  when  oxidised  by  permanganate  it  yields  svlpJtonal 
(acetonedlethylsulphom),  (CH3)2C(S02C2H5)2,  an  important  soporific  which  crystal- 
lises well  and  melts  at  126°  C. 

Met-hyl-ethyl  "ketom  may  be  obtained  by  the  reaction  between  acetyl  chloride  and 
zinc  ethide  ;  2(CH8'C6'C1)  +  Zn(C2H5)2  =  2(CH3-CO-C2H5)  +  ZnCl2.  It  boils  at  81°  C., 
and  is  present  in  small  proportion  in  commercial  acetone.  When  oxidised,  it  yields 
only  one  acid,  acetic  ;  CHS-CO-C2H5  +  03  =  2(CH8-CO-OH). 

Benzophenone  or  dlpKenyl  Itetotie,  (C6H5)2CO,  prepared  by  distilling  calcium  ben- 
zoate,  forms  stable  prisms  which  melt  at  46°  C.,  and  labile  rhombohedra  which 
melt  at  26°  C.  ;  the  labile  changes  into  the  stable  form  on  addition  of  a  trace  of  the 
latter.  Benzophenone  boils  at  307°  C. 

Acetophenone,  metliyl-plienyl  Itetone,  CH3*CO'C6H3,  from  calcium  acetate  and 
benzoate,  melts  at  20°  C..  boils  at  202°  and  is  used  as  an  hypnotic  Qiypnone). 

Jlethyl-nonijl  Itetone,  CH3'COC9H19,  is  the  chief  constituent  of  oil  of  rue,  from 
which  it  may  be  precipitated  by  NaHSO3.  It  may  be  obtained  artificially  by  dis- 
tilling calcium  acetate  with  calcium  rutate  (in.-p.  15°  ;  b.-p.  225°  C.). 

Naphthyl-plienyl  Itetone,  C10HyCOC6H5,  forms  a  dibromide,  which  is  useful  in 
optical  experiments,  on  account  of  its  high  refractive  power. 

401.  Ketone-alcohols,  ketone-aldehydes,  ketone-acids,  di- 
ketones. — It  was  shown  at  p.  574  that  these  compounds  may  be 
regarded  as  oxidation  products  of  polyhydric  alcohols  containing  a 
secondary  alcohol  group,  which  might  be  expected  to  become  a 
ketonic  group  on  oxidation  (p.  568)  while  the  primary  alcohol  group 
would  yield  the  aldehyde  or  acid  group.  Thus  from  a-propylene 
glycol,  CH3'CHOH-CH,OH,  would  be  obtained  the  ketone-alcohol, 
OH8-COCH,OH,the  ketone-aldehyde,CH3-C(>CHO,  and  the  ketone-acid, 
OHgCOCOOH,  and  from  /3-butylene  glycol,  CH3'CHOH-CHOH-CH3, 
the  diketone,  CH3'CO'CO'CH3.  All  these  compounds  share  with  the 
ketones  and  \  aldehydes  a  tendency  to  combine  and  to  undergo  nucleal 
condensation  ;  hence  many  are  of  great  value  in  synthetic  chemistry 
as  steps  to  more  complex  compounds. 

Isomerides  are  distinguished  as  a-  and  /3-  &c.,  as  indicated  on  page  596. 

Ketone-alcohols  or  hetols  are  exemplified  by  acetylocarbinol  or  acetol, 
CH3-COCH.2OH.  which  boils  about  150°  C.  and  is  obtained  by  cautious  oxidation 
of  d-propylene  glycol  with  bromine  water.  Several  of  the  sugars  are  ketols. 

Pyroracenilc  aldehyde,  or  methyl  f/lyo.ral.  CH.^COCHO.  is  the  type  of  the  ketone- 
aldehydes  ;  it  is  a  volatile  yellow  oil. 

Pyromcem'H'  a  eld  or  pyrurlc  acid,  CH3COCOOH,  is  the  typical  a-ketonic-acid. 
It  is  obtained  by  the  destructive  distillation  of  tartaric  or  racemic  acid  (p.  619),  as 
an  oxidation  product  of  ethylidene  lactic  acid.  CH3'CHOITCOOH,  and  by  hydro- 
lysing  acetyl  cyanide,  CH3COCN.  This  last  method,  the  hydrolysis  of  an  acidyl 
cyanide,  is  a  general  one  for  preparing  a-ketone-acids.  It  'is  a  colourless  liquid 
smelling  of  acetic  acid,  boiling  about  167°  C..  and  soluble  in  water.  It  shows  most 
of  the  reactions  of  a  ketone  and  an  acid  :  in  addition,  it  is  a  strong  reducing-agent, 
reducing  alkaline  silver  nitrate,  probably  because  the  CO  group  has  COOH  attached 
to  it  instead  of  the  second  hydrocarbon  radicle  of  a  ketone.  Baryta  water  converts 
it  into  uritic  acid,  a  dibasic  aromatic  acid.  With  nascent  H  it  yields  lactic 
acid. 

Aceto-acetlc  acid,  or  acetonecarboarylic  acid,  CH.,-COCH2COOH,  is  the  typical 
j3-ketone-acid,  all  of  which  are  very  unstable,  tending  to  break  down  into  C02,  from 
the  carboxyl  group,  and  the  corresponding  ketone.  Its  ethyl  salt  (xee  Ethereal 
Salts)  is  more  stable  than  the  acid  and  is  an  important  compound  for  synthetical 
work  ;  by  saponifying  this  salt  potassium  aceto-acetetate,  and  from  this  the  free 
acid  is  obtained.  It  is  a  liquid  soluble  in  water  and  decomposing  into  acetone  and 
COo  when  heated. 


ETHERS. 

Lt-ruluuc  acid,  CH,-CO-CHg-CHaCOOH,  is  the  type  of  the  7-ketone-acids.  which 
are  also  easily  broken  down  by  heat:  but  instead  of  losing  CO,  they  lose  HO 
yielding  y-lactones  (p.  607)  from  unsaturated  hydroxy-acids.  Thus,  levulinie  -.rid 
yields  y-lactones  from  angelic  acid  ; 

CH3C  :  CH-CH2COO  and  CH2  :  (>CH2-CH2Co6. 

Levulinie  acid  is  a  product  of  the  action  of  acids  on  various  carbohydrate* 
especially  levulose.  It  melts  at  32-5°  C.  and  boils  at  239°  C.,  dissolves  in  water 
and  is  used  in  calico-printing. 

PJtenylglyojpyliG  add  or  benzoyl  formic  add,  C6H6-CO'COOH,  is  produced  bv 
oxidising  mandehc  acid  and  by  hydrolysing  benzoylcyanide.  It  melts  at  65°  C 

Diacetyl,  OH3CO-COCHS,  is  the  simplest  a-diketone.*  It  is  made  by  hotting 
Lwnitrosoniethylacetone,  CH3-C(NOH)-CO-CH3  with  acid,  and  is  a  greenish-yellow 
liquid,  smelling  of  quinine  and  boiling  at  87°  C.  The  /3-diketones,  like  acetvlacetone 
CH3-COCHoCOCH3,  are  remarkable  for  forming  metallic  salts  (acetylwetonafe*) 
the  true  constitution  of  which  is  in  doubt.  The  7-diketones,  like  avetonylacetone. 
CH3-CO-CH.2'CH2-CO-CH3,  do  not  share  this  property,  but  are  important  because  of 
the  ease  with  which  they  pass  into  closed-chain  compounds  of  the  furfurane  or 
pyrrol  type  (</.f.) 

V.  ETHERS. 

402.  The  ethers  are  derived  from  the  alcohols  by  the  substitution  of  a 
hydrocarbon  radicle  for  the  hydrogen  in  the  OH  group ;  thus,  if  methyl 
alcohol,  CH3'OH,  be  treated  with  Na,  the  hydroxl  hydrogen  is  displaced 
by  sodium,  and  CH3'ONa,  or  sodium  methoxide,  is  obtained.  If  this  be 
acted  on  by  methyl  iodide— CH3-ONa  +  CH3I  =  CH3'0-CH3  +  NaI— the 
H  in  CH3OH  is  displaced  by  CH3,  and  methyl  ether,  CH3'OCH3,  is 
formed.  It  will  be  evident  that  a  similar  reaction  between  sodium 
methoxide  and  ethyl  iodide,  C2H.I,  would  furnish  the  mixed  ether, 
methyl-ethyl  ether,  CH3'OC2H5,  so  that  the  number  of  ethers  obtainable 
would  exceed  that  of  the  alcohols. 

Just  as  the  alcohols  are  comparable  with  the  metallic  hydroxides 
(p.  561),  albeit  far  less  prone  to  chemical  change,  so  the  ethers  may  be 
compared  with  the  metallic  oxides  deprived  of  most  of  their  chemical 
energy.  This  view  is  supported  by  a  second  general  method  of  pre- 
paring them,  namely,  by  heating  the  alkyl  halides  with  metallic  oxides, 
2CH3I-i-  Ag3O  =  (CH3)20  +  2AgI  ;  and  by  their  reaction  with  hot  hy- 
driodic  acid  to  yield  an  iodide  and  water,  as  the  alkali  oxides  do — 

K20  +  2HI  =  H20  +  KI ;  and  (CH3)20  +  2HI  =  H20  +  2CH3I. 

The  usual  method  for  obtaining  the  ethers  is  by  the  action  of  sul- 
phuric acids  on  alcohols,  as  will  be  explained  below. 

The  ethers  are  generally  insoluble  in  water,  and  lighter  and  more 
volatile  than  the  corresponding  alcohols.  They  are  almost  as  indifferent 
to  reagents  as  the  hydrocarbons  are,  and  probably  for  a  like  reason, 
viz.,  that  all  the  hydrogen  is  combined  with  carbon.  The  reaction  of 
the  ethers  will  be  gathered  from  those  of  ethyl  ether. 

It  will  be  remarked  that  the  ethers  derived  from  the  alcohols  of  the 
series  CWH2W+20  form  an  homologous  series  isologous  with  the  alcohols, 
that  each  ether  is  metameric  with  the  isologous  alcohol,  and  that  the 
ethers  containing  an  odd  number  of  carbon  atoms  are  mixed  ethers. 

*  By  the  now  system  of  nomenclature,  ketones  are  named  like  the  alcohols  (see  foot-note 
p.  568),  -on  being  substituted  for  -ol.  Thus,  CH3-CO'CH2-CH2-CH3  is  a-pentanon  (tin-  O  beiiiu 
attached  to  the  second  C  atom).  CH3-CO-CH2'CO-CH3  is 


628  ETHEPJFICATION. 


Ethers.  Alcohols. 


Methyl   .         .  .  CH3  "O  CH3 

Methyl-ethyl  .  .  CH3  '0-C2H5 

Ethyl      .         .  .  C2H5-OC2H5 

Ethyl-propyl  .  .  C2Hg-0'C3H7 

Propyl    .         .  .  C3H7-0'C3H7 


Ethyl      .  .  .  C0H5  -OH 

Propyl    .  .  .  C3H7  -OH 

Butyl      .  .  .  C4H9'OH 

Amyl      .  .  .  C5Hn'OH 

Caproic  .  .  .  C6H13'OH 


403.  Methyl  ether,  or  dimethyl  oxide,  CH3'0'CH3,  is  a  fragrant  inflammable  (/as 
prepared  by  adding  methyl  alcohol  (2  parts  by  weight)  to  cooled  strong  H2S04 
(3  parts)  and  heating  to  about  140°  C.,  keeping  up  a  supply  of  methyl  alcohol,  as 
in  the  preparation  of  ether  (q.r.),  the  reaction  being  the  same  as  in  the  preparation 
of  ether,  if  methyl  be  written  for  ethyl.  The  gas  may  be  stored  for  use  by  passing 
it  into  cooled  H2S04,  which  dissolves  600  volumes  of  it  and  gives  it  up  again  when 
mixed  with  water.  It  is  condensed  by  cold  or  pressure  to  a  liquid  boiling  at 
-21°  C.,  and  used  for  producing  cold.  Water  absorbs  about  37  times  its  volume  of 
the  gas. 

404.  Ether,  or  sulphuric  ether,  C2H5'OC2H5,  is  prepared  by  distilling 
alcohol  with  sulphuric  acid.  If  two  measures  of  alcohol  be  carefully 
added  to  one  measure  of  strong  sulphuric  acid,  and  the  mixture  distilled, 
ether  passes  over  together  with  water,  and  if  alcohol  be  added  from 
time  to  time,  a  small  quantity  of  sulphuric  acid  suffices  to  etherify  a 
large  quantity  of  alcohol.  The  alcohol  is  first  converted  into  hydrogen 
ethyl  sulphate,  sulphethylic  acid  or  ethylsulphuric  acid — 

S02(OH2)  +  C2H5-OH  =  S02(OH)(OC2H5)  +  HOH. 

When  this  is  heated  to  about  140°  C.  with  more  alcohol,  it  is  decom- 
posed into  ether  and  sulphuric  acid,  which  then  acts  in  the  same  way 
upon  a  fresh  quantity  of  alcohol — 

S02(OH)(OC2H5)  +  C2H5-OH  =  C2H6-OC2H5  +  S02(OH)2. 

Hence  the  process  has  been  termed  the  continuous  etherification  process 
and  is  carried  out  in  the  following  manner : — 

Alcohol  of  sp.gr.  0.83  is  carefully  added,  with  continued  shaking,  to  an  equal 
volume  of  strong  sulphuric  acid,  cooled  in  a  vessel  of  water.  When  the  mixture  is 
cold,  it  is  poured  into  a  retort  or  flask  (Fig.  276),  which  is  connected  with  a  reser- 
voir of  alcohol  and  a  well-cooled  condenser.  The  mixture  is  quickly  heated  till  it 
boils,  when  its  temperature  will  be  about  140°  C.  (284°  F.),  and  alcohol  is  then 
allowed  to  pass  in  slowly  from  a  siphon  tube  furnished  with  a  stop-cock,  and 
dipping  below  the  liquid  in  the  flask  ;  the  temperature  should  remain  as  nearly  as 
possible  at  140°  C.,  which  will  be  the  case  if  the  rate  of  flow  of  the  alcohol  is  so 
regulated  as  to  keep  the  mixture  at  the  same  level.  A  thermometer  is  fixed  in  the 
cork  with  its  bulb  in  the  liquid.  When  the  total  quantity  of  alcohol  used  amounts 
to  six  or  seven  times  that  originally  taken,  the  process  must  be  stopped,  because 
secondary  reactions,  attended  by  carbonisation,  have  used  up  much  of  the  sulphuric 
acid.  The  liquid  collected  in  the  receiver  contains  about  two-thirds  of  its  weight 
of  ether,  with  about  one-sixth  of  water,  an  equal  quantity  of  alcohol,  and  a  little 
sulphurous  acid.  It  usually  separates  into  two  layers,  of  which  the  upper  is  ether. 
The  whole  is  introduced  into  a  narrow  stoppered  bottle,  and  shaken  with  cold  water, 
added  in  small  portions,  as  long  as  the  layer  of  ether  on  the  surface  increases  in 
volume  ;  a  little  potash  is  then  added  to  fix  SO2,  and,  after  shaking,  the  upper 
layer  of  ether  is  drawn  off,  by  a  siphon  or  separator,  into  a  flask  containing  lumps 
of  fused  calcium  chloride,  to  remove  water  and  alcohol.  After  standing  for  some 
hours,  the  ether  is  distilled  off  in  a  water-bath  at  as  low  a  temperature  as  possible. 
To  free  it  entirely  from  water,  it  must  be  again  rectified  after  digestion  with 
powdered  quick-lime,  and  finally  with  bright  sodium,  till  no  more  hydrogen  bubbles 
are  visible.  Methylated  ether  is  prepared  from  methylated,  spirit,  and  is  much 
cheaper  than  pure  ether,  for  which  it  may  often  be  substituted. 

It  has  been  found  that  benzene  sulphonic  acid  (C6H5S03H)  may  advantageously 
be  substituted  for  the  sulphonic  acid,  as  it  will  etherify  about  100  times  its'weight 


PROPERTIES   OF  ETHER. 


629 


The  acid  is  melted  in  the  flask  and  alcohol  run  in  slowly,  the  tenner. 
kept  about  140°  C.  C6H5S03C2H5  is  first  formed  and  is  decomposed  by 
10!  into  C6H5S03H  and  (C2H5)20. 


of  alcohol, 
ture  being 
more  alcohol 

Theonj  of  etherljicatwn.— The  processdescribed  above  for  the  preparation  of  ether 
had  long  been  practised  before  a  satisfactory  explanation  of  it  was  arrived  at  One 
of  the  earliest  views  regarded  the  formation  of  ether  as  a  simple  removal  of 'water 
by  the  sulphuric  acid  from  the  alcohol,  which  was  then  believed  to  be  a  compound 
of  ether  and  water  ;  but  against  this  it  was  urged  that  the  water  was  not  retained 
by  the  acid,  but  distilled  over  with  the  ether,  and  that  the  same  acid  would  etherify 


Fig-.  276. — Continuous  ethcrincation. 

successive  additions  of  alcohol.  Passing  over  the  theory  of  catalytic  action,  or 
decomposition  by  contact,  which  was  a  mere  statement  of  the  facts  without  any 
real  explanation,  we  come  to  the  important  observation  that  the  first  product  of  the 
action  of  sulphuric  acid  on  alcohol  is  sulphethylic  acid,  which  is  decomposed,  when 
distilled  with  more  alcohol  at  140°,  into  ether,  water,  and  sulphuric  acid,  as  in  the 
equations  given  on  p.  628. 

Very  strong  evidence  that  the  above  equations  represent  the  reactions 
occurring  in  the  etherification  process  is  furnished  by  the  following 
experiment : — Amyl  aloohol,C5Hu*OH,  is  converted  by  sulphuric  acid 
into  sulphamylic  acid,  C5Hn'S04H,  which  is  heated  in  the  flask 
(Fig.  276),  whilst  ethyl  alcohol,  CaH5'OH,  is  allowed  to  flow  in  from  the 
reservoir ;  this  decomposes  the  sulphamylic  acid,  yielding  sulphuric 
acid,  and  amyl-ethyl  ether — 

C5Hn-S04H  +  C2H5-OH  =  C5Hn-0-C2H5  +  H2S04. 

If  the  process  is  continued  after  all  the  amyl-ethyl  ether  has  passed 
over,  only  ethyl  ether  is  obtained.  In  this  manner  any  mixed  ether  can 
be  prepared. 

405.  Properties  of  ether. — A  very  mobile  colourless  liquid  with  a  charac- 
teristic odour  ;  sp.  gr.  at  15°  C.  0.70.  It  boils  at-  35°  C.,  evaporates 
very  rapidly  in  air,  producing  intense  cold,  and  yielding  a  very  heavy 
vapour,  of  sp.  gr.  2.59,  which  is  very  inflammable,  and  renders  ether 
dangerous  in  unskilled  hands.  It  melts  at  113°  C.  It  is  sparingly 
soluble  in  water,  so  that,  when  shaken  with  it,  the  ether  generally  rises 
to  the  surface  on  standing,  rendering  it  very  useful  for  collecting  certain 
substances,  such  as  bromine  and  alkaloids,  from  large  bulks  of  aqueous 


630  EEACTIONS   OF  ETHER. 

solutions  into  a  small  bulk  of  ether.  Ten  volumes  of  water  dissolve  one 
volume  of  ether.  Thirty-four  volumes  of  ether  are  required  to  dissolve 
one  volume  of  water,  so  that  ether,  free  from  alcohol,  could  not  contain 
much  water,  but  commercial  ether  contains  alcohol,  which  enables  it  to 
take  up  a  larger  quantity  of  water.  Ether  and  alcohol  may  be  mixed 
in  all  proportions,  but  the  addition  of  much  water  generally  brings  the 
ether  to  the  surface.  Ether  is  much  used  in  laboratories  as  a  solvent, 
especially  for  fatty  substances  and  alkaloids,  and  by  the  photographer 
in  making  collodion. 

Ether  containing  water  becomes  turbid  when  shaken  with  OS,  and 
that  containing  alcohol  dissolves  sufficient  aniline  violet  to  become 
coloured  when  shaken  with  this  dye-stuff. 

The  properties  of  ether  admit  of  some  interesting  experiments. 

1.  If  a  little  ether  be  evaporated  by  blowing  upon  it  in  a  watch-glass,  with  a  drop 
of  water  hanging  from  its  convexity,  the  water  will  be  speedily  frozen.     A  thin 
beaker  containing  ether  may  be  frozen  to  a  wet  table  by  blowing  into  it  with  the 
bellows. 

2.  A  piece  of  tow,  wool,  or  sponge,  wetted  with  ether,  is  placed  at  the  upper  end 
of  a  sloping  trough  or  gutter  of  wood  or  metal,  over  six  feet  long  ;  a  match  applied 
at  the  lower  end  fires  the  train  of  vapour. 

3.  A  jug  is  warmed  with  a  little  hot  water,  emptied,  and  a  little  ether  poured  into 
it ;  the  vapour  may  be  poured  into  a  row  of  small  beaker-glasses,  each  of  which  is 
afterwards  tested  with  a  taper. 

4.  A  pneumatic  trough  is  filled  with  warm  water,  and  a  small  test-tube  filled 
with  ether  is  inverted  with  its  mouth  under  the  water,  and  quickly  decanted  up 
into   a  gas-jar  filled  with  warm  water,  when  it  will  be  vaporised,  and  may   be 
decanted  through  the  water  into  other  vessels,  and  treated  like  a  permanent  gas. 
Some  cold  water  poured  over  the  jar  containing  it  at  once  proves  its  condensable 
character. 

406.  Ether  is  also  produced  by  the  reactions  given  on  p.  627,  C2H5  being  substi- 
tuted for  CH3  in  the  equations.  Ethyl  iodide,  heated  with  a  small  quantity  of 
water,  under  pressure,  yields,  first  alcohol,  and  afterwards  ether — 

C2H5I  +  HOH  =  C2H5-OH  +  HI,  and  C2H5I  +  C2H5-OH  =  C2H5'OC2H5  +  HI. 

Other  acids  besides  sulphuric  are  able  to  produce  ether  from  alcohol,  especially 
those  which  ave  non-volatile  and  polybasic,  such  as  phosphoric,  arsenic,  and 
boric,  which  probably  act  in  the  same  way  as  sulphuric.  But  certain  salts, 
such  as  zinc  chloride  and  aluminium  sulphate,  also  generate  ether  from  alcohol, 
and  the  explanation  of  this  is  less  simple.  It  will  be  found  that  such  salts  are 
capable  of  decomposition  by  water,  with  formation  of  basic  salts  and  free  acid  ; 
thus,  ZnCl2  +  HOH  =  ZnCl-OH  +  HCl,  or  A12(S04)3  +  4HOH  =  A12S04(OH)4  +  2H2S04. 

If  these  reactions  occur  with  alcohol,  C2H5-OH,  instead  of  with  HOH.  the 
products  would  be  C2H5C1  instead  of  HC1,  and  C2H5'HS04  instead  of  H2804,  and 
either  of  these  would  react  with  the  excess  of  alcohol  to  produce  ether. 

Ether  may  be  converted  into  alcohol  by  heating  it  with  water  and  a  very  little 
sulphuric  acid,  in  a  sealed  tube,  at  180°  C.  The  ether  is  probably  converted  at 
first  into  sulphethylic  acid,  and  this  into  alcohol  and  sulphuric  acid,  the  etherifica- 
tion  reaction  (p.  628)  being  reversed. 

When  ether  is  acted  on  by  hydriodic  acid  gas,  in  the  cold,  it  yields  alcohol  and 
ethyl  iodide  ;  (C2H5)2O  +  Hi  =  C2H5'OH  +  C2H5I.  If  a  mi. red  ether,  such  as  ethyl- 
amyl  ether,  be  treated  in  this  wray,  the  radicle  containing  more  carbon  is  the  one 
converted  into  an  alcohol  ;  C2H5-6-C5Hn  +  HI  =  C5Hn-OH  +  C2H5L 

Ordinary  oxidising-agents  convert  ether  into  aldehyde  and  acetic  acid.  Ozonised 
oxygen  converts  it  into  formic,  acetic,  and  oxalic  acids  and  hydrogen  peroxide. 

When  ether  vapour  is  passed  over  heated  potash,  hydrogen,  marsh  gas,  and 
potassium  carbonate  are  formed,  potassium  acetate  being  probably  produced  in 
the  first  stage  of  its  reaction  ;  (C2H5)20  +  2KOH  +  H20  =  2KC2H302  +  4H2. 

Ether  enters  into  combination  with  several  metallic  chlorides  and  bromides, 
forming  crystalline  compounds ;  stannic  chloride  combines  with  two  molecules 
of  ether,  forming  SnCl4(C4H100)2  ;  aluminium  bromide  forms  Al2Br6(C4H100)2. 

Ether  is  inflamed  by  contact  with  chlorine  ;  but  if  it  be  very  well  cooled,  and 


ZEISEL'S   METHOD. 


63I 


light  be  excluded,  at  yields  a  series  of  substitution-products.  Monorhlorether 
dtehloretker  and  tetracUor  ether  are  known.  Per  chlorinated 'ether  ('  '1  0  re' 
c'm™hor  ^  f°rmati°n'  is  a  cl>Ystalline  body  (m.-p.  68°  C.)  smelling  like 

Distilled  with  PC15,  ether  yields  C2H5C1  and  POC13  but  no  HC1  (rf  p   <7Q) 

CHrOHUOV^  ^T^  alc0hols'-By  treating  monosodium^glycol 
<  2H4(OH)(0^a)  with  C^H5I,  as  in  the  general  reaction  (p.  627),  monoethul  ffLol 
ether  <\H4(OH)(OC2H5)  (b.-p.  127°  C.)  is  obtained.  If  disodium  glycol  be  similarly 
treated,  the  d.ethyl  ether  C2H4(OC2H5)2  (b.-p.  123°  C.)  is  obtained? 

.Regarding  the  formation  of  an  ether  as  the  abstraction  of  HOH  from  the  two 
OH  groups  of  two  molecules  of  an  alcohol,  glycol  might  be  expected  to  form  an 

CH.x 
internal   ether,  •      ^0.     This  compound,  ethylene  oxide,  is  produced  when  glycol 

\-S±lf) 

chlorhydrin  (p.  575)  is  distilled  with  potash  :— 

CH2OH  CH. 

CH2C1   +  KOH  =  CH>™  +  HOH. 
It  is  isomeric  with  ethyl  aldehyde,  boils  at  12-5°  C.  and  easily  passes  back  into  glycol 

/CH2x 

derivatives.     Trim  ethylene  oxide,  CH2^-      V),  boils    at    50°  C.  and  is  similarly 

CH2 


5(OH)3,  in 

-    ~  — 0 --  -   -  v — Jy     —  is  formed 

when  glycerine  is  distilled  with  CaCl2,  and  is  a  colourless,  inodorous  liquid,  boiling 
at  about  170°  C.,  and  of  sp.  gr.  1.16  ;  it  mixes  with  water.  Its  behaviour  with 
hydriodic  acid  is  analogous  to  that  of  ethyl  ether,  for  it  is  converted  into  glycerine 
and  glyceryl  tri-iodide,  C3H5I3. 

409.  Aromatic  Ethers. — these  may  be  either  the  true  ethers  corresponding 
with  the  aromatic  alcohols,  or  ethers  derived  from  phenols,  which,  it  will  be  re- 
membered, differ  from  the  alcohols  in  having  the  OH  group  attached  directly  to 
the  benzene  nucleus. 

Benzyl  ether,  (C6H5'CH2)00,  is  prepared  by  distilling  benzyl  alcohol  with  B203 
which  removes  the  elements  of  water,  2C6H5'  CH2OH-  HOH  =  (C6Hg-CH0).,0.  "it 
is  a  colourless  liquid  not  miscible  with  water,  and  boiling  at  296°  C. 

Dlphemjl  wide,  or  phenyl  ether,  C6H5-0'C6H5,  obtained  by  distilling  phenol  with 
aluminium  chloride,  forms  prisms,  fusing  at  28°  C.  and  boiling  at  252°  C.  It  smells 
like  the  geranium  leaf,  and  is  remarkable  for  its  stability  under  the  influence  of 
oxidising-  and  reducing-agents.  Water  does  not  dissolve  it,  but  alcohol  and  ether 
do  so. 

Phenyl- in ethyl  ether,  C6H5'0-CH3,  is  prepared  by  passing  methyl  chloride  through 
.sodium  phenol  at  200°  C.  It  is  a  fragrant  liquid,  of  sp.  gr.  0.991,  boiling  at  152°. 
This  ether  is  identical  with  AniWil,  obtained  by  distilling  anisic  acid  (p.  608) 
with  baryta.  Methyl  salicylate,  or  winter  green  oil,  C6H4(OH)'C02-CH3,  is  nieta- 
ineric  with  anisic  acid,  and  also  yields  phenyl-methyl  ether  when  distilled  with 
baryta.  Hydriodic  acid  heated  to  140°  C.  with  aniso'il,  in  a  sealed  tube,  converts 
it  into  phenol  and  methyl  iodide  ;  C6H5'OCH3  +  HI  — C6H5'OH  +  CH31. 

This  reaction  is  typical  of  the  method  commonly  employed  in  determining  the 
number  of  methoxy-groups  (OCH3)  in  the  molecule  of  a  compound.  It  is  known 
as  ZelseVs  method,  and  consists  in  boiling  a  known  weight  (0.3  gram)  of  the  substance 
with  fuming  hydriodic  acid  (10  c.c.)  in  a  flask  ^1  (Fig.  277)  through  which  a  gentle 
-current  of  C02  is  passed.  This  carries  the  CH3I  water  vapour  and  HI  through  the 
condensing-tube  B,  containing  a  number  of  aludels  shown  drawn  to  an  enlarged 
scale  at  C.  The  temperature  of  the  water-bath  D  is  regulated  to  ensure  that  the 
distillation  shall  not  be  too  rapid,  which  is  indicated  by  the  thermometer  J?  marking 
a  temperature  of  50°  C.  The  methyl  iodide  does  not  condense  at  this  temperature 
and  passes  through  the  absorption  flasks  E,  containing  water  and  red  phosphorus, 
where  it  leaves  the  HI  and  a  little  free  I  that  it  contains,  and  then  into  a  wash 
bottle  containing  an  alcoholic  solution  of  silver  nitrate.  Here  the  methyl  iodide 
is  decomposed  yielding  a  precipitate  of  Agl,  which  is  collected,  washed,  and 
weighed.  From  its  weight  that  of  the  CH3I  and  therefore  of  the  OCH3  in  the 
compound  taken,  is  calculated. 


632 


HALOGEN  DERIVATIVES  OF  HYDROCARBONS. 


The  methyl  ethers  of  the  phenols  are  formed  at  the  ordinary  temperature  when 
diazomethane,  CH2N2,  and  a  phenol  are  brought  in  contact,  e.;/..  C6H5OH  +  CH2N2=: 
C6H5OCH3  +  N2.  They  are  not  changed  when  heated  with  alcoholic  potash. 


Fig-.  277. — Apparatus  for  determining  methoxyl  «roups. 

Anetliol,  the  camphor-like  substance  in  oil  of  anise  is  i  :  4-propenyl-aniso'ilr 
CH3-CH  :  CH-C6H4-OCH3  ;  it  melts  at  22°  C.  and  boils  at  233°  C. 

Phenyl  ethyl  ether,  C6H5'0'C2H5,  or  pUenetoil  is  obtained  by  distilling  ethyl 
salicylate  with  baryta  ;  it  boils  at  172°  C. 


VI.  HALOGEN  DERIVATIVES. 

410.  Halogen  Compounds  from  Hydrocarbons. — (A)  Prom 
open-chain  hydrocarbons. — It  has  been  already  noticed  (p.  530) 
that  these  products  result  in  many  cases  from  the  direct  action  of  the 
halogens  on  the  hydrocarbons,  but  whilst  Cl  and  Br  react  thus  by 
metalepsis  with  hydrocarbons,  iodine  seldom  does  so  unless  an  absorbent 
for  HI  (e.g.,  HgO)  be  present ;  this  is  because  the  metalepsis  is  a 
reversible  reaction  (p.  309),  e.g.,  CH4  +  I2^:CH3I  +  HI. 


METHYL  CHLORIDE.  633 

Since  the  unsaturated  hydrocarbons  generally  combine  with  the- 
halogen  to  form  addition  products  (p.  534),  which  are  either  identical 
or  isomeric  with  the  halogen  substituted  saturated  hydrocarbons,*  some 
other  method  must  generally  be  resorted  to  in  order  to  prepare  halogen 
substitution-products  of  unsaturated  hydrocarbons.  Thus,  they  are 
obtained  either  by  treating  the  halogen  substituted  saturated  hydro- 
carbons with  reagents  which  will  remove  halogen  hydride,  or  by  only 
partially  saturating  still  more  unsaturated  hydrocarbons  with  halogen ; 
e.g.,  C2H4C12  -  HC1  =  C2H3C1 ;  C2H2  +  01,  =  C2H2C12. 

The  halogen  substitution- products  from  all  hydrocarbons  are  obtain- 
able by  the  interaction  of  the  alcohols  with  phosphorus  halides,  or,  what 
is  equivalent,  with  phosphorus  and  a  halogen.  Examples  will  be  met 
with  in  the  following  pages.  In  a  large  number  of  cases  the  mere 
treatment  of  an  alcohol  with  halogen  hydride,  particularly  in  the 
presence  of  a  dehydrating  agent,  will  produce  the  halogen  substitution- 
product,  the  reaction  being  of  the  type  R'OH  +  HX  =  EX  +  HOH. 

Methyl  choride,  or  monochloro-methane  CH3C1,  is  prepared  by  passing 
HC1  gas  into  a  boiling  solution  of  zinc  chloride  in  twice  its  weight  of 
methyl  alcohol,  contained  in  a  flask  connected  with  a  reversed  condenser. 
The  methyl  chloride  is  evolved  as  a  gas  which  may  be  washed  with  a 
little  water  to  remove  HC1,  dried  by  passing  over  calcium  chloride,  and 
condensed  in  tubes  cooled  in  a  mixture  of  ice  and  calcium  chloride 
crystals.  The  final  result  is  expressed  by  the  equation  CH3OH  +  HC1  = 
CH3C1  +  HOH.  The  action  of  the  zinc  chloride  is  little  understood. 
Methyl  chloride  is  an  inflammable  gas  of  ethereal  odour,  liquefied  by  a 
pressure  of  2^  atm.  at  o°  C.  Its  boiling-point  is  -  24°  C.  Water  dis- 
solves 4  vols.  of  the  gas  and  alcohol  35  vols. 

Methyl  chloride  may  also  be  prepared  by  distilling  methyl  alcohol  with  sodium 
chloride  and  sulphuric  acid.  It  is  made  on  a  large  scale,  for  use  in  freezing- 
machines,  from  the  trimethylamine  obtained  by  distilling  the  refuse  of  the  beet- 
sugar  factories  ;  this  is  neutralised  with  hydrochloric  acid,  and  heated  to  260°  C., 
when  it  is  decomposed  into  trimethylamine,  ammonia  and  methyl  chloride  ; 
3N(CH3)3HC1  =  2N(CHs)3  +  NHs  +  3CH3C1. 

Methyl  chloride  is  very  stable  ;  potash  decomposes  it  with  difficulty,  yielding 
methyl  alcohol  and  potassium  chloride.  It  is  used  in  the  preparation  of  some  of 
the  aniline  colours. 

Ethyl  chloride,  or  monochlor  ethane,  C2H5C1,  is  prepared  by  substi- 
tuting ethyl  for  methyl  alcohol  in  the  foregoing  prescription.  The 
purified  vapour  is  passed  into  95  per  cent,  alcohol  kept  cool  by  water. 
The  alcohol  absorbs  half  its  weight  of  ethyl  chloride,  which  may  be 
evolved  from  it  by  gently  heating,  and  purified  by  passing  through  a 
little  sulphuric  acid.  It  is  a  fragrant  liquid  of  sp.  gr.  0.92  and  boiling- 
point  1 2°. 5  C.  It  is  sparingly  soluble  in  water,  and  burns  with  a 
bright  flaire  edged  with  green.  Ethyl  chloride  is  formed  when  olefiant 
gas  and  HC1  are  heated  together  for  some  time. 

Methyl  lironnde,  CH3  Br,  is  prepared  by  acting  upon  methyl  alcohol  with  phos- 
phorus and  bromine  ;  3CH3OH  +  Brs  +  P  =  3CH8Br  +  P(OH)3.  Four  parts  of  methyl 
alcohol  are  poured  on  i  part  of  red  phosphorus  in  a  well-cooled  retort  witl 
reversed  condenser,  and  6  parts  of  bromine  are  gradually  added.  After  two  or  thret 

*  It  will  be  remembered  that  the  unsaturated  hydrocarbon  will  also  combine  directly  with 
halogen-hydrides  to  form  substituted  saturated  hydrocarbons.     It  is  to  be  noted  that  whe 
this  is  the  case  the  halogen  attaches  itself  to  the  carbon  atom  which  has  the  smallest  numl 
of  hydrogen  atoms  attached  to  it.     Thus,  from  propylene,  CH;,'  CHiCIta  and  jiU,  tu 
results  CH.j-  CHC1-  CH,,  isopropyl  chloride,  not  CH3'  CH2'  CHaCL 


634  ETHYL   IODIDE. 

hours,  heat  is  applied  by  a  water-bath,  and  the  vapour  condensed  by  a  freezing- 
mixture.  Methyl  bromide  boils  at  .-j.°.5,  burns  feebly,  and  smells  like  chloroform. 

Ethyl  bromide,  C2H5Br,  may  be  prepared  like  methyl  bromide,  using  16  parts  of 
absolute  alcohol,  4  parts  of  red  phosphorus,  and  10  parts  of  bromine.  It  is  a 
liquid  boiling  at  39°  C.  ;  sp.  gr.  1.419. 

Methyl  iodide,  CH3  I,  is  prepared  on  the  same  principle  as  the  bromide,  10  parts 
of  iodine  being  dissolved  in  4  parts  of  methyl  alcohol,  and  I  part  of  red  phos- 
phorus added  in  small  portions.  After  heating  in  a  water-bath  for  some  time, 
the  mixture  is  distilled.  The  methyl  iodide  is  the  lower  layer  of  the  distillate. 
It  has  a  pleasant  smell,  sp.  gr.  2.29,  and  boils  at  44°  C.  It  mixes  with  alcohol, 
but  not  with  water.  When  kept,  it  becomes  brown  from  separation  of  iodine. 
It  is  converted  into  CH3C1  gas  when  heated  with  HgCL,  dissolved  in  ether. 
Hydriodic  acid,  at  150°  C.,  converts  it  into  CH4.  Methyl  iodide  is  used  in  making 
aniline  dyes. 

Jletliyl  fluoride,  CH3F,  is  a  combustible  gas  obtained  by  heating  KF  with 
potassium  methyl  sulphate,  KCH3S04.  Ethyl  fluoride  boils  at  -48°  C. 

Ethyl  iodide,  C2H5I,  is  prepared  by  pouring  5  parts  of  absolute 
alcohol  on  one  part  of  red  phosphorus  in  a  retort,  adding  gradually 
10  parts  of  iodine  in  powder,  setting  aside  for  twelve  hours,  and 
distilling  in  a  water-bath  with  a  good  condenser.  Ethyl  iodide  mixed 
with  alcohol  distils  over,  leaving  phosphoric  acid  in  the  retort  (together 
with  somo  phosphethylic  acid  formed  by  its  action  on  some  of  the 
alcohol),  3C2H5OH  +  P  + 13  =  3C2H5I  +  P(OH)3.  The  distillate  is  sha.ken, 
in  a  stoppered  bottle,  with  about  an  equal  measure  of  water  and  enough 
soda  to  render  it  alkaline.  The  ethyl  iodide  collects  as  an  oily  layer  at 
the  bottom  ;  this  is  separated  from  the  upper  layer  by  a  tap-funnel  or 
pipette  or  siphon,  allowed  to  stand  with  a  little  fused  calcium  chloride 
in  coarse  powder,  to  remove  the  water,  and  distilled. 

Ethyl  iodide  has  a  pleasant  smell,  sp.  gr.  1.93,  and  boiling-point 
72°  C.  It  becomes  brown  when  kept,  especially  in  the  light,  iodine 
being  liberated,  and  butane  formed;  2C2H.I  =  C4H10  +  I2.  Ethyl  iodide 
is  sparingly  dissolved  by  water,  but  readily  by  alcohol  and  ether. 

Ethyl  iodide  is  a  very  important  reagent  in  organic  researches  for 
introducing  the  group  C,H5  into  the  places  of  other  radicles. 

The  monohalogen  substitution-derivatives  of  the  paraffins  higher  in 
the  series  than  ethane,  exist  in  isomeric  forms  exactly  analogous  to  the 
isomeric  alcohols  (p.  567),  a  halogen  being  substituted  for  OH. 

411.  Dihalogen  derivatives  of  ethane  can  obviously  exist  in  two 
modifications,  CH2X'CH,X,  or  ethylene  halides,  and  CH3'CHX2, 
ethylidene  halides/  The  "former  are  obtained  by  the  direct  addition 
of  halogen  to  ethylene,  and  since  by  judicious  treatment  with  moist 
silver  oxide  they  can  be  converted  into  glycol  haiogen-hydrins  (e.g., 
glycol  chlor-hydrin,  q.v.}  they  most  probably  have  the  formula  assigned 
to  them  above  ;  moreover,  they  may  be  prepared  from  the  glycols  by 
distillation  with  phosphorus  halides.  The  ethylidene  halides  can  be 
obtained  from  aldehyde  by  treatment  with  phosphorus  pentahalides 
(P-  579)- 

Ethylene  chloride,  etheiie  di chloride,  or  Dutch  liquid,  C2H4C12,  may  be  obtained 
from  glycol  by  distilling  it  with  PC15 — 

C2H4(OH)2  +  2PC15  =  C2H4C12  +  2POC13  +  2HC1  ; 

but  it  is  generally  prepared  by  allowing  equal  volumes  of  dry  ethene  gas  and  dry 
chlorine  to  pass  into  a  large  inverted  globe  or  flask,  the  neck  of  which  passes 
through  a  cork  into  a  receiver  for  the  condensed  liquid.  Ethene  dichloride 
smells  lather  like  chloroform  ;  its  sp.  gr.  is  1.28,  and  it  boils  at  84°  C.  ;  it  is  nearly 
insoluble  in  water,  but  dissolves  in  alcohol. 


CHLOROFORM. 


635 


EtJujUdene  chloride  CH3CH2C1,  is  best  prepared  by  the  action  of  COCL,  on 
CHg'CHO,  carbon  dioxide  being  liberated.  B-.p.  60°  C 

Ethylene  bromide,  or  ethene  dllromlde,  C2H4Br,,  is  prepared  a*  described  at 
p.  574.  It  resembles  the  dichloride,  but  its  sp.  gr.  is  2.16,  and  it  boils  at  m°  0 

Ethylem  iodide,  C,H4I2,  obtained  by  heating  iodine  in  olefiant  gas,  forms  silky 
needles,  which  may  be  sublimed  in  the  gas,  but  are  easilv  decomposed  into 
CoH4  and  I2. 

The  difference  in  the  stability  of  ethene  chloride,  bromide,  and  iodide  is  shown 
by  the  action  of  alcoholic  solution  of  potash,  which  converts  ethene  dichloride 
into  monocJt lorethene,  or  nnyl  clt lor'tde,  C,H4C1.2  +  KOH  =  C2H3C1  +  KC1  +  H.,0  :  whilst 
the  dibromide  yields,  in  addition  to  the  vinyl  bromide,"  a /quantity  of  acetylene; 
C2H4Br2  +  2KOH  =  C2H2  +  2KBr  +  H20  ;  and  the  di-iodide  is  much  more  easily  de- 
composed, giving  very  little  vinyl  iodide  and  much  acetylene. 

Metliylene  iodide,  CH2I2,  may  be  obtained  by  heating  iodoforin  with  strong  HI 
in  a  sealed  tube,  at  about  130°  C.,  for  some  hours  ;  CHIs-f  HI  =  CH2I0+I0.  It  is 
a  liquid  remarkable  for  its  high  specific  gravity,  3.328,  and  is  used  for  determin- 
ing the  specific  gravities  of  precious  stones.  It  boils  at  181°  C. 

412.  Chloroform,  or  tri-chloromethane,  CHC13,  the  anesthetic,  is  pre- 
pared by  distilling  i  part  of  alcohol  (sp.  gr.  0.834)  with  10  parts  of 
chloride  of  lime  and  40  parts  of  water,  at  65°  C.,  until  about  ij  part 
has  passed  over ;  the  distilled  liquid,  consisting  chiefly  of  water  and 
chloroform,  separates  into  two  la)ers;  the  chloroform  which  is  at  the 
bottom,  is  drawn  off,  shaken  with  strong  sulphuric  acid  to  remove 
some  impurities,  and  when  it  has  risen  to  the  surface  it  is  separated 
and  puritied  by  distillation  until  it  boils  regularly  at  61°  C.  (142°  F.). 
Chloroform  is  prepared  from  acetone  in  a  similar  manner. 

The  action  of  chloride  of  lime  on  alcohol  has  not  been  clearly  explained  ;  it 
might  be  expected  that  chloral  would  be  formed  at  first  by  the"  oxidising  and 
chlorinating  actions,  and  that  this  would  be  converted  into  chloroform  and 
calcium  formate  by  the  strongly  alkaline  calcium  hydroxide  in  the  chloride  of 
lime  (see  Chloral),  but  much  C02  is  given  oft',  causing  frothing  during  the  distil- 
lation. Probably  the  chloroform  is  produced  by  some  such  reaction  as  the 
following  :  3C,H6p  +  8Ca(OCl)2  =  2CHC13  +  SH20  +  C02  +  sCaCla  -f  3CaC03. 
Pure  chloroform  is  more  easily  prepared  by  decomposing  chloral  hydrate  with 
potash  or  soda. 

Chloroform  is  a  very  fragrant  liquid  of  sp.  gr.  1.50,  and  boiling-point 
6i°*5  C.  It  is  very  useful  in  the  laboratory  as  a  solvent,  and  is  much 
used  for  extracting  strychnine  and  other  alkaloids  from  aqueous  solu- 
tions. It  is  also  one  of  the  best  solvents  for  caoutchouc.  Chloroform 
is  very  slightly  soluble  in  water,  and  gives  it  a  sweet*  taste.  Alcohol 
dissolves  it  in  all  proportions,  and  it  is  nearly  as  soluble  in  ether.  Strong 
sulphuric  acid  does  not  affect  it,  and  it  is  not  coloured  by  pure  chloroform. 
Aqueous  solution  of  potash  does  not  decompose  it,  but  the  alcoholic 
solution  converts  it  into  potassium  chloride  and  potassium  formate ; 
CHC)3  +  4KOH  =  3KC1  +  HCOOK  +  2HOH.  If  Dutch  liquid  (C,H4C12) 
be  present  as  an  impurity  in  the  chloroform,  gaseous  chlorethylene 
(C,H3Ci)  is  evolved.  When  heated  with  alcoholic  potash  and  aniline,  it 
yie'lds  phenyl-carbamine  (q.v.),  the  powerful  odour  of  which  renders 
this  a  delicate  test  for  chloroform. 

Heated  with  alcoholic  solution  of  ammonia  in  a  sealed  tube  at  180°  C..  chloroform 
gives  ammonium  chloride  and  cyanide  ;  CHC13  +  5NH3  =  3NH4C1  +  NH4  'CN.  ^  When 
potash  is  present  a  similar  reaction  occurs  at  the  ordinary  temperature,  CHi.'l;,+ 
NH3  +  4KOH  =  KCN  +  3KC1  +  4H20.  Heated  with  potassium-amalgam,  chloroform 
evolves  acetylene;  2CHC13  +  3K2=C2H2  +  6KC1.  That  chloroform  is  really  a 
substitution-derivative  from  methane  is  shown  by  its  conversion  into  that  gas 
when  dissolved  in  alcohol  and  heated  with  zinc-dust  ;  by  the  formation  of 
tetrachloro-methane.  CC14,  by  the  action  of  chlorine  (in  presence  of  iodine)  upon 


636  IODOFOEM. 

chloroform,  and  by  that  of  dichloro-methane,  CH2C12,  by  the  action  of  zinc  and 
sulphuric  acid. 

When  chloroform  is  heated  with  sodium  ethoxide,  it  is  converted  into  ortho- 
formic  ether  ;  CHC13  +  3NaOC2H5  =  sNaCl  +  CH(OC2H5)3. 

lodoform,  CHI3,  or  tri-iodo-m ethane,  is  a  product  of  the  action  of 
iodine  upon  alcohol  in  an  alkaline  solution,  the  immediate  agent  being 
probably  a  hypo-iodite,  whilst  chloroform  is  produced  by  a  hypo-chlorite. 
To  prepare  it,  dissolve  32  parts  of  potassium  carbonate  in  80  parts  of 
water,  add  16  parts  of  alcohol  of  95  per  cent,  and  32  parts  of  iodine  ; 
heat  gently  till  the  colour  of  the  iodine  has  disappeared,  when  iodoform 
will  be  deposited  on  cooling. 

CH3-CH2OH  +  6KOH  +  I8  =  CHI3  +  HCOOK  +  5KI  +  H20. 

To  recover  the  iodine  left  as  KI,  the  nitrate  from  the  iodoform  is  mixed 
with  20  parts  of  HC1  and  2.5  parts  of  potassium  dichromate,  which 
liberates  the  iodine.  The  liquid  is  neutralised  with  potassium  carbonate, 
and  32  parts  more  of  that  salt  are  added,  together  with  6  parts  of 
iodine  and  16  of  alcohol  ;  the  operations  of  heating  and  cooling  are 
then  repeated. 

lodoform  is  deposited  in  yellow  shining  hexagonal  plates,  smelling  of 
saffron.  It  fuses  at  120°  0.,  and  may  be  sublimed  with  slight  decom- 
position. It  is  insoluble  in  water,  but  dissolves  in  alcohol  and  ether. 
When  boiled  with  potash,  it  is  partly  volatilised  with  the  steam,  and 
partly  decomposed,  yielding  potassium  iodide  and  formate.  The  pro- 
duction of  CHI3  on  adding  iodine  and  dilute  KOH  and  stirring,  is  a 
very  delicate  test  for  alcohol,  but  many  other  substances  also  yield  it. 
lodoform  is  used  in  medicine  and  surgery. 

&rotnaform,  CHBr3,  is  produced  when  bromine  is  added  to  an  alcoholic  solution 
of  potash.  It  has  a  general  resemblance  to  chloroform,  but  boils  at  151°  C.  Crude 
bromine  sometimes  contains  bromoform. 

ChJ/oriodoform,  CHIC12,  is  obtained  by  distilling  iodoform  with  HgCL2.  It  is  a 
yellow  liquid,  b.-p.  131°  C.  The  corresponding  Br  compound  has  been  prepared. 

Trichloi'opropane,  exists  in  several  forms.  The  commonest  of  these  is  glyceryl 
trichloride  or  trichlorhydrin.  CH2C1'CHC1'CH2C1 ;  it  is  obtained  by  the  action  of 
PC]5upon  glycerine,  C^H^OR^  +  ^PC^C^G^  +  ^Cl  +  ^POC^.  It  is  a  liquid 
of  pleasant  smell,  sp.  gr.  1.42,  and  boiling  at  158°  C.  It  is  sparingly  soluble  in 
water.  Tribromhydrin,  C3H5Br3,  is  a  crystalline  solid  ;  m.-p.  17°  C.  ;  b.-p.  220°  C. 
The  iodine  compound  corresponding  with  this  does  not  appear  capable  of  existing. 

413.  All yl  chloride,  CH2  :  CH'CH2C1,  is  obtained  by  distilling  allyl  alcohol  with 
PC13.  It  has  a  pungent  smell,  sp.  gr.  0.95,  and  boiling-point  46°  C.  ;  it  is  insoluble 
in  water.  Allyl  bromide  may  be  prepared  by  distilling  allyl  alcohol  with  KBr  and 
H2S04,  mixed  with  an  equal  bulk  of  water.  It  is  capable  of  combining  with 
bromine  to  form  f/lycerijl  or  allyl  tribromide,  C3H5Br3,  and  with  HBr  to  form 
CH2BrCH2'CH2Br,  trimetliylene  bromide.  Allyl  iodide,  C3H5I,  is  prepared  from 
glycerine  (200  parts)  by  adding  iodine  (135),  filling  the  retort  with  C02  and  adding, 
very  gradually,  vitreous  phosphorus  (40).  The  distilled  liquid  is  washed  with  a 
little  NaOH,  and  dried  with  CaCl2.  Probably,  glyceryl  tri-iodide  is  first  produced  ;. 
C3H5(OH)3  +  P  +  I3  =  C3H5I3+P(OH)3;  the  tri-iodide  is  then  decomposed  into 
C3H5I  and  I2.  Allyl  iodide  has  a  very  pungent  odour  of  leeks,  sp.  gr.  1.8,  and 
boiling-point  101°  C.  It  is  remarkable  for  combining  with  mercury,  shaken  with 
its  alcoholic  solution,  to  form  mercury  allyl  iodide,  Hg"C3H6I,  deposited  in  colour- 
less crystals,  which  become  yellow  in  light,  and  yield  Hgi2  and  C;5H5I  when  treated 
with  iodine.  Ag20,  in  presence  of  H20,  substitutes  OH  for  the  I,  producing. 
HgC3H5-OH,  mercury  allyl  hydroxide,  an  alkaline  base.  Bromine  converts  allyl 
iodide  into  tribromhydrin.  C3HgBrs. 

The  halogen propylenes — e.g..  a-ckloropropylene,  CH3*CH  :  CHC1, — isomeric  with 
the  allyl  halides,  exist  in  a  maleinoid  and  a  fumaroid  modification  (p.  616). 


CHLOEOBENZENE. 


637 


Propargyl  chloride,  CH  i  C-CH2C1,  is  obtained  by  acting  on  propargvl  alcohol 
with  phosphorus  chloride  ;  it  boils  at  65°  C. 

414.  (B)  Halogen  derivatives  of  closed-chain  hydrocarbons.— 
These  may  be  halogen  substitution  or  addition  products.  The  substitu- 
tion may  be  either  in  the  benzene  or  other  nucleus,  or  in  side-chains,  or 
in  both.  Thus,  while  only  i  compound  of  the  formula  C6H5X  exists, 
there  are  4  of  the  formula  C7H7X,  namely,  C6H4X'CH3(3)  andC6H.-CH  x! 
Again,  3  compounds  of  the  form  C6H4X2  are  known,  and  10  of  the  form 
C7H6X2,  viz.,  C6H3X2-CH3(6),  OflH4X-OHfX(3)  and  C6H5'CHX,. 

The  nucleal  substitution-products  are  more  stable  than  are  the  open- 
chain  hydrocarbon  substitution-products.  Thus,  C6H5C1  will  not  yield 
CGH.OH  when  treated  with  AgOH,  whilst  C2ELC1  yields  C2H5OH  by 
this  treatment.  But  the  side-chain  substitution-products  "behave  as 
open-chain  derivatives. 

The  direct  action  of  halogens  on  benzene  itself  produces  chiefly 
substitution-products.  In  the  case  of  its  homologues,  nucleal  sub- 
stitution occurs  if  the  action  be  allowed  to  proceed  in  the  cold, 
especially  in  the  dark  and  in  presence  of  iodine  ;  whilst  at  higher 
temperatures,  and  in  sunlight,  side-chain  substitution  occurs.  Thus, 
C6H4BrCH3  is  formed  when  Br  attacks  cold  toluene,  but  Cg 
if  the  temperature  is  higher. 

The  treatment  of  phenols  (or  alcohols)  with  phosphorus  halides,  and 
a  special  reaction  to  be  described  under  Diazo-compounds,  also  yield 
these  halogen  derivatives. 

C'Jdorolenzene  or  phenyl  chloride,  C6H5C1,  may  be  prepared  bypassing  Cl  into 
C6H6,  containing  3  per  cent,  of  A12C16,  until  the  calculated  gain  of  weight  is  observed; 
or  by  the  action  of  PClg  on  phenol  ;  C6H5OH  +  PC15  =  C6H5C1  +  POC13  +  HC1 ;  it  is 
a  colourless  liquid,  boiling  at  132°  C.  Bromobenzene  (b.-p.  155°  C.)  is  similarly 
prepared.  lodohenzene  (b.-p.  188°  C.)  may  be  obtained  by  heating  benzene  with 
iodine  and  HI03  (to  absorb  HI ;  p.  632)  at  200°  C.  By  dissolving  it  in  CHC13  and 
passing  Cl  through  the  solution  the  dichloride^  C6H5I :  C12  is  prepared  ;  this  is  of 
theoretical  importance,  since  the  iodine  in  it  is  trivalent ;  when  it  is  treated  with 
XaOH  it  yields  wdosobenzene,  C6H5I  :  0,  which  is  a  base  forming  salts  such  as 
C6H5I  :  OCr03;  when  heated  it  becomes  iodobenzene  and  iodo.fi/benzene,  C6H5IO.,, 
an  explosive  substance  presumably  containing  pentavalent  iodine. 

o-smd-p-C/ilorotoluenes,  C6H4C1'CH3,  are  obtained  by  passing  Cl  into  cold  toluene 
containing  iodine. 

Ben; ijl  chloride,  C6H5-CH2C1  (b.-p.  176°  C.),  lenzal  (ben;tjUdene)  chloride, 
C6H.5-CHC12  (b.-p.  213°  C.),  and  benzotrichlorlde,  C6H5'CC13  (b.-p.  213°  C.),  are 
obtained  by  chlorinating  boiling  toluene,  the  Cl  being  passed  into  the  liquid  until 
the  increase  of  weight  calculated  for  the  particular  compound  required,  has  been 
attained.  They  are  colourless  liquids  *  and  can  be  prepared  by  the  action  of  PC15 
on  the  corresponding  oxygen  compounds — viz.,  benzyl  alcohol,  benzoic  aldehyde, 
and  benzoic  acid — into  which  they  are  converted  by  hydrolysis.  They  are  inter- 
mediate products  in  the  manufacture  of  benzaldehyde  from  toluene  (p.  584). 

Two  of  each  of  the  monohalogen  tubstitwtion  product*  of  naphthalene  exist  (p.  552). 
0,-Chloro-naphthalene,  C10H7C1,  is  a  colourless  liquid  (b.-p.  263°  C.)  and  is  the  product 
of  passing  Cl  into  boiling  naphthalene.  fi-Cliloro-naphthaleue  crystallises  in  lamina? 
(m.-p.  61°  C.  ;  b.-p.  257°  C.),  and  is  obtained  by  treating  j8-naphthol.  C10H7'OH, 
with  PC15.  Ten  dichloro-naphthalenes  are  known.  When  naphthalene  is  chlori- 
nated in  the  cold,  the  addition-product,  naphthalene  tetracJtloride,  C10H8C14,  is 
formed  ;  this  crystallises  in  colourless  rhombohedra,  melts  at  182°  C.,  and  becomes 
C10H6C12  when  boiled  with  KOH.  Since  it  yields  phthalic  acid  and  not  a  chloro- 
phthalic  acid  when  oxidised,  all  the  Cl  atoms  must  be  in  the  same  benzene  nucleus, 
and  the  compound  must  have  the  orientation  i  :  2  :  3  : 4  (p.  552)- 

Anthracene  dlchlorlde,  C6H4  :  (CHC1)2  :  C6H4,  is  formed  when  chlorine  is  passed 

*  Benzyl  chloride  and  benzyl  bromide  have  a  tear-exciting  odour. 


638  CHLORAL. 

over  cold  anthracene,  whilst  at  a  high  temperature  y-chloranthracenf  (m.-p.  103°  C.) 
and  y-dichlorantkracene  (m.-p.  209°  C.)  are  produced  (p.  554)  as  yellow  needles. 

The  halogen  derivatives  from  other  condensed  benzene  nuclei  are  of  little 
importance. 

415.  Halogen  Compounds  from  Aldehydes  and  Acids.  — 
Chloral  or  tri-chlor aldehyde,  CC13'CHO,  prepared  by  passing  thoroughly 
dried  chlorine  into  absolute  alcohol,  which  must  be  placed  in  a  vessel 
surrounded  by  cold  water  at  first,  because  the  absorption  of  chlorine  is 
attended  by  great  evolution  of  heat.  The  passage  of  chlorine  is  con- 
tinued for  many  hours,  and  when  the  absorption  is  slow,  the  alcohol  is 
gradually  heated  to  boiling,  the  chlorine  being  still  passed  in  until  the 
liquid  refuses  to  absorb  it.  The  principal  reaction  is  represented  by  the 
equation,  CH:{-CH2'OH  +  4C12  =  5HC1  +  CC13'CHO  ;  but  the  HC1  attacks 
part  of  the  alcohol,  forming  ethyl  chloride  and  water.  On  cooling,  the 
product  solidifies  to  a  crystalline  mixture  of  the  compounds  of  water 
and  alcohol  with  chloral,  from  which  the  latter  may  be  obtained  by 
distillation  with  sulphuric  acid. 

On  the  large  scale,  chlorine  is  passed  into  alcohol  of  at  least  96  per  cent,  for  12 
or  14  days.  The  crude  product  is  heated  with  an  equal  weight  of  strong  H.2S04,  in 
a  copper  vessel  lined  with  lead.  HC1  escapes  at  first,  and  the  chloral  distils  over 
at  about  100°  C.  The  distillate  is  rectified,  and  mixed  with  water  in  glass  flasks, 
when  chloral  hydrate,  CC13'CHO.H20,  is  formed,  which  is  poured  into  porcelain 
basins,  where  it  crystallises. 

Chloral  is  a  liquid  of  sp.  gr.  1.5,  and  boiling-point  97°  C.  It  has  a 
pungent,  tear-exciting  odour,  and  irritates  the  skin.  Exposed  to  air,  it 
absorbs  water  and  forms  crystals  of  the  hydrate,  which  is  produced  at 
once  when  choral  is  stirred  with  a  few  drops  of  water,  heat  being 
evolved.  When  quite  pure  it  may  be  kept  unchanged,  but,  in  presence 
of  impurities,  especially  of  sulphuric  acid,  it  soon  becomes  an  opaque 
white  mass  of  metachloral,  which  is  insoluble  in  water,  alcohol,  and  ether. 
This  is  probably  formed  by  the  condensation  of  three  molecules  of 
chloral,  into  which  it  is  reconverted  at  180°  C.  It  will  be  remembered 
that  aldehyde  is  liable  to  a  similar  polymerisation.  Chloral  also  re- 
sembles aldehyde  in  forming  crystalline  compounds  with  NaHS03,  and  in 
giving  a  mirror  of  silver  with  silver  ammonio-nitrate.  With  ammonia 
it  forms  CC13'CH(NH.))(OH),  corresponding  with  aldehyde-ammonia. 
Zinc  and  HC1  substitute  H3  for  the  C13  in  chloral,  converting  it  into 
aldehyde.  Nitric  acid  oxidises  it  to  trichloracetic  acid,  CC1./  C02H,  which 
forms  deliquescent  crystals  and  boils  at  195°  C.  When  heated  with 
KCN  and  H20  it  yields  dichloracetic  acid  (b.-p.  191°  C.), 

CCL/CHO  +  KCN  +  H20  =  CHCL2'C02H  +  KC1  +  HCN. 
Potash  decomposes  it  easily;    CC13-CHO  +  KOH  =  CC13H  +  H-CO-OK. 
Chloral  is  formed  when  starch  or  sugar  is  distilled  with  HC1  and  Mn02. 

Chloral  hydrate,  CC13'CH(OH)2,  trichlorethylideneglycol,  forms  pris- 
matic crystals,  which  are  very  soluble  in  water  and  alcohol,  and  have 
the  odour  of  chloral.  It  fuses  at  57°  C.,  and  boils  at  97°,  but  is 
dissociated  into  chloral  and  steam,  which  recombine  on  cooling.  It  is 
employed  medicinally  for  procuring  sleep. 

Chloral  alcoholate,  CC13-CH(OH)(OC2H5),  formed  when  choral  is  dissolved  in 
alcohol,  crystallises  like  the  hydrate,  but  is  rather  less  soluble  in  water. 

Brumal,  obtained  by  action  of  Br  on  alcohol,  is  very  similar  to  chloral. 

Croton-chloral,  or  butyl  chloral,  CH3-CHC1-CC12-CHO,  is  wp-trithl&robvtynt 
aldehyde,  and  is  prepared  by  substituting  aldehyde  for  alcohol  in  the  preparation 


ACETYL  CHLORIDE. 

of  chloral,  when  croton-aldehyde  is  first  produced,  and  is  converted  into  butv! 
chloral ;  (i)  2CH,CHO  =  CH8-CH  :  CH'CHO  +  H20  ;  (2)  CH3'CH  :  CH-CHO  +  2CU 
CSH4C13'CHO  +  HC1.  It  is  an  oily  liquid  of  pungent  odour,  sp.  gr.  1.4,  and  boiliu"-- 
point  164°  C.  It  combines  with  water  to  form  a  hydrate  which  dissolves  in  hot 
water,  and  crystallises,  on  cooling,  in  plates  which  have  a  very  irritatino-  odour 
It  has  been  used  in  medicine. 

416.  Halogen    compounds    from    acids    by    substitution    of 
halogen    for   hydroxyl— Acidyl  halides. — These  bodies   have   th en- 
counter-parts among  inorganic  compounds  ;  thus,  nitrosyl  chloride,  NOC1, 
is  obtained  by  substituting  01  for  OH  in  nitrous  acid,  NO'OH ;  and,' 
in  acetic  acid,  CH3'CO'OH,  a  similar  exchange  gives  acetyl  chloride, 
CK/CO'Cl.     Thus  they  are  haloidanhydrides  (p.  191),  or  the  halides  of 
negative  radicles,  just  as  the  alkyl  halides  may  be  regarded  as  halides 
of  positive  radicles  and  compared  with  KC1. 

They  are  generally  prepared  by  the  action    of  phosphorus    halides 
on  the  acids. 

No  compound  of  this  kind  has  been  obtained  from  formic  acid. 

417.  Acetyl  chloride,  CH3'CO'C1,  or  acetic  chloride,  is  prepared  by 
distilling  acetic  acid  with  phosphorus  trichloride  ;  3CH3COOH  +  PC13  = 
3CH3-COC1  +  P203  +  3HC1.      To    5    parts  by  weight  of   glacial   acetic 
acid,  kept  cool,  are  gradually  added  4  parts  of  phosphorus  trichloride, 
and  the    mixture   distilled   on  a  water -bath.      The   distillate   may  be 
rectified   over    fused  sodium    acetate   to   remove  any  phosphorus   tri- 
chloride.    The  pentachloride  may  also  be  used, 

CH3-COOH  +  PC15  =  CH3-CO-C1  +  POC13  +  HC1. 

Acetyl  chloride  is  a  colourless  liquid,  which  fumes  in  air,  and  has 
an  irritating  odour;  its  sp.  gr.  is  i.n,  and  it  boils  at  55°  C.  Water 
decomposes  it  with  violence,  yielding  hydrochloric  and  acetic  acids  ; 
CH3-CO-C1  +  HOH  =  CH3-CO-OH  +  HC1.  If  alcohol  be  employed 
instead  of  water,  ethyl  acetate  is  produced  ;  CH3'  CO  •  01  +  C2H5-  OH  = 
CH3-  CO'  OC2H5  +  HC1.  This  mode  of  reaction  renders  acetyl  chloride 
a  most  useful  reagent  for  discovering  the  constitution  of  alcohols. 

Some  other  instructive  reactions  produce  acetyl  chloride,  such  as  that  between 
acetic  anhydride  (di-acetyl  oxide)  and  phosphorus  pentachloride  (C2H30).20  +  PC15  = 
2C2HoOCl  +  POOL  ;  or  between  phosphorus  oxychloride  and  sodium  acetate — 
POCl3  +  2CH3C06Na  =  2CH3COCl  +  NaP03  +  NaCl  ;  it  was  thus  that  acetyl  chloride 
was  first  made.  By  distilling  sodium  acetate  with  acetyl  chloride,  acetic  anhy- 
dride is  obtained— C.2H30-ONa  +  C2H30-Cl  =  (C2H30)20  +  NaCl.  By  careful  treat- 
ment with  sodium-amalgam  and  snow,  ethyl  alcohol  has  been  prepared  from 
acetyl  chloride  ;  aH3OCl  +  H4  =  C2H5OH  +  HCl. 

Acetyl  bromide,  OHg-CO'Br,  is  prepared  by  distilling  acetic  acid  with  bromine 
and  phosphorus  ;  it  resembles  the  chloride,  but  boils  at  81°  C.,  and  becomes  yellow 
when  kept.  Acetyl  iodide,  CHS!CO-I,  is  less  stable,  and  is  prepared  by  distilling 
acetic  anhydride  with  iodine ;  it  boils  at  108°  C. 

Benzoyf  chloride,  or  benzole  chloride,  C6H5-COC1,  is  prepared  by  distilling  benzoie 
acid  with  PClg.  It  is  a  pungent  smelling  liquid,  of  sp.  gr.  i.ii,  and  boiling-point 
199°  C.  It  is  decomposed  by  water,  but  more  slowly  than  is  acetyl  chloride, 
yielding  benzoie,  and  hydrochloric  acids.  It  may  also  be  obtained  by  the  action 
of  chlorine  on  bitter-almond  oil  (benzoie  aldehyde);  C6H6-CO-H  +  CI2— 
C5H5-COC1  +  HC1. 

When  hydroxy-acid*  are  distilled  with  PC15,  the  alcoholic  OH  groups  are  also 
exchanged  for  Cl.  Thus  lactic  acid  yields  a-chhrujtropionic  chlorxle  (I  art,// 
chloride),  CH,-CHC1-COC1.  Salicylic  acid  yields  I  :  2-chloroben:oic  chloride 
(salicylic  chloride).  With  water  these  chlorides  yield  HC1  and  the  corresponding 
chloro-acid. 

Sueelnyl  dichloride,  C2H4(COC1)2.  is  obtained  by  distilling  succinic  acid  with 


'640  ESTEES. 

PC15  ;  C.2H4(CO'OH>2  +  2PC15  =  C.2H4(COC1).2  +  2POC1,,  +  2HC1.  It  is  a  fuming  liquid, 
of  sp.  gi\  i  -39,  boiling  at  190°  C.  With  water  it  yields  HC1  and  succinic  acid,  but 
it  is  doubtful  whether  it  is  a  true  acid  chloride,  or  resembles  phthalyl  chloride  (r.v). 

Fumaryl  dichloride,  C.2H2(CO'C1)2,  is  the  product  of  the  distillation  of  fumaric 
acid,  C2H2(COOH).2,  and  of  its  isomeride,  maleic  acid,  with  phosphoric  chloride. 
It  boils  at"  1  60°  C.  Malic  acid  also  yields  fumaryl  dichloride  when  distilled  with 
PC15  ;  C.2HS(OH)(CO-OH)2+3PC15  =  C2H.2(CO-C1).2  +  3POC13  +  4HC]. 

Tartaric  acid,  C2H2(OH)2(COOH)2,  heated  with  phosphoric  chloride,  is  converted 
into  chloromaleic  chloride.  C2HC1(CO'C1)2,  an  oily  liquid  which  yields  crystals  of 
•chloromaleic  acid,  C2HC1(CO'OH)2,  when  decomposed  by  water. 

Phthalyl  dichloride  is  obtained  by  distilling  phthalic  acid,  C6H4(COOH)2,  with 
PC15.  It  is  a  yellow,  oily  liquid,  boiling  at  about  275°  C.  It  is  more  stable  than 
most  other  compounds  of  this  class,  being  slowly  decomposed  by  water  into  HC1 
;and  phthalic  acid.  Even  solution  of  NaOH  only  slowly  decomposes  it.  It  appears 

/CCU  /COC1 

to  have  the  constitution  C6H4<^        ^>0,  not    C6H4<^  ^       ,  since  nascent  H  con- 


verts  it  into  pht/ialide,  C6H4<^      2^>0,  a  lactone  from  i  :  2-hydroxymetliyllen:olc 

CO 

acid,  CH.2OH-C6H4-COOH. 

VII.  ETHEREAL  SALTS  OR  ESTERS. 

418.  These  compounds,  formed  by  the  substitution  of  a  hydrocarbon 
radicle  for  the    hydroxylic  hydrogen    in  an  acid,   are    numerous  and 
important.     They  correspond  in  composition  with  the  salts  formed  from 
.acids  by  substitution  of  metals  for  basic  hydrogen.     For  example  : 
,OK  /OCH3 


Potassium  sulphate,  SOo^        ;  methyl  sulphate,  S02<^ 


CH, 


Potassium  hydrogen  sulphate,  S00^        ;  methyl  hydrogen  sulphate.  SO.-/' 

XOH  "\)H 

Potassium  acetate,  CH3'COOK  ;  methyl  acetate,  CH3'CqOCH3. 

It  will  be  seen  that  the  ethereal  salts  of  the  organic  acids  consist  of  an  acidyl 
;group  and  a  hydrocarbon  radicle  united  by  an  oxygen  atom,  thus  resembling  the 
•ethers  ;  hence  the  name  esters,  or  compound  ethers. 

They  may  be  formed  (a)  by  heating  an  alcohol  with  an  acid, 
•whereby  water  is  eliminated  : 

(1)  CH3-OH  +  N02-OH     ^     NO.vOCHg  +  HOH. 

(2)  CH3OH  +  S02(OH),    <_     S02(OH)(OCH3 

(3)  CH3OH  +  CH3COOH     ^     CH3'COOCH3 

These  reactions  are  reversible  and  consequently  never  complete.  "With  polybasic 
acids  the  hydrogen  salts  are  generally  obtained. 

(b)  By  heating  a  chloranhydride  with  an  alcohol : 

(4)  CH3OH  +  CH3-COC1  =  CH3-COOCH3  +  HC1  ; 

•(c)  by  heating  a  halogen  derivative  of  a  hydrocarbon  with  the  silver 
salt  of  an  acid  : 

(5)  2CH3I  +  Ag2S04  =  (CH3)2S04  +  2AgI. 

The  ethereal  salts  exhibit  a  resemblance  to  the  metallic  salts  in  being 
decomposed  by  the  hydroxides  of  the  alkali-metals,  with  formation  of 
the  alcohol  corresponding  with  the  radicle  of  the  ethereal  salt,  and  of  a 
salt  of  the  alkali-metal ;  thus,  ethyl  acetate,  heated  with  potash, 


ALKYL  SULPHATES. 


641 


yields  ethyl  alcohol  and  potassium  acetate;  CH'COC.H  +KOH  = 
C,H/OH  +  CH3-C02K.  A  reaction  of  this  kind  is  termed  the  sapvni- 
fication  of  the  ethereal  salt,  because  the  formation  of  soap  is  effected  in 
a  similar  way  by  the  action  of  alkalies  on  the  fats  and  oils,  which  are 
ethereal  salts  formed  by  glycerine  with  the  higher  members  of  the  acetic 
series  of  acids. 

Many  of  the  ethereal  salts  are  volatile  liquids,  having  characteristic 
fruity  odours. 

When  treated  with  NH3  they  yield  an  alcohol  and  an  acid  amide  • 
CH3-COOCH3  +  NH3  =  CH3  •  CONH2  +  CH3OH.  Heated  with  water  or 
dilute  acids  they  are  hydrolysed  to  the  free  acid  and  the  alcohol- 
CH3-COOCH3  +  HOH  =  CH3-COOH  +  CH3-OH.  With  strong  halo-en 
acids  they  yield  the  free  acid  and  the  halide  of  the  hydrocarbon  radicle  • 
CH3-COOCH3  +  HC1  =  CH3-COOH  +  CH3C1. 

419.  Sulphuric  Esters.— Methyl  hydrogen  sulphate  or  sulphom-ethylic  acid, 
CH3HS04.— Methyl  alcohol  (i  weight)  is  slowly  added  to  strong  H2S04  (2  weights)' 
and  the  mixture  is  heated  to  boiling,  cooled,  and  neutralised  with  BaC03,  which 
precipitates  the  excess  of  H2S04  as  BaS04,  leaving  barium  mlphomethylate  in  solu- 
tion ;  this  is  evaporated  on  a  steam-bath,  and  finally  in  vacua,  when  square  tables 
of  Ba(CH3S04)2.2Aq.  crystallise.  By  adding  an, equivalent  of  H2S04  to  a  solution 
of  these,  the  barium  is  precipitated  and  the  solution  of  sulphomethylic  acid  mav 
be  concentrated  in  vacua  to  a  syrupy  liquid.  See  equation  2  above.  It  is  an 
unstable  compound,  decomposed  at  130°  C.  into  H2S04  and  methyl  sulphate, 
2CH3HS04  =  (CH3).2S04  +  H2S04,  and  by  boiling  with  water,  into  CH,OH  and  H2S04. 
Heated  with  an  alcohol,  it  gives  the  corresponding  mixed  ether,  CH3HS04  +  R'OH  = 
CH3-p-K  +  H2S04.  The  basic  hydrogen  in  CH3HS04  may  be  exchanged  for  a  metal 
forming  sulphoHiethylates,  which  are  all  soluble  in  water.  The  acid  is  also  formed 
by  gradually  adding  CH,OH  to  well-cooled  chlorosulphonic  acid  (a  chloranhydride, 
cf.  equation  4  above)  :  CH3OH  +  S02(OH)C1  =  HC1  +  CH3HS04. 

Methyl  sulphate,  (CH3)2S04,  is  prepared  by  gradually  adding  CH3OH  (i  weight) 
to  strong  H2S04  (8  weights)  and  distilling  the  mixture.  The  portion  which  distils 
at  150°  C.  is  shaken  with  water,  and  the  lower  layer  rectified  over  CaCl2.  Much  of 
the  CH3  group  is,  however,  broken  up  in  this  process.  A  better  result  is  obtained 
by  distilling  sulphomethylic  acid  at  130°  under  diminished  pressure.  It  is  a  liquid 
of  peculiar  odour,  sp.  gr.  1.32,  and  boiling-point  188°  C.  It  does  not  dissolve  in 
water,  but  is  slowly  decomposed,  yielding  methyl  alcohol  and  sulphomethylic  acid. 
Many  of  its  reactions  resemble  those  of  inorganic  salts  ;  thus,  if  distilled  with 
NaCl,  it  yields  methyl  chloride,  CH3C1,  and  Na^S04.  With  sodium  formate  it 
gives  methyl  formate  and  Na.2S04. 

Sulphethylic  or  ethyl-sulphuric  or  sulphovinic  acid,  HC2H5S04,  is  prepared  in  the 
same  way  as  sulphomethylic  acid,  employing  equal  weights  of  alcohol  and  sulphuric 
acid.  It  is  a  viscid  liquid,  very  similar  in  its  properties  and  reactions  to  sulpho- 
methylic acid.  The  sidp/iet/iylates  are  soluble  and  easily  crystallisable  salts, 
prepared  by  adding  the  metallic  carbonate  to  a  solution  made  by  heating  alcohol 
with  twice  its  weight  of  strong  H2S04,  and,  after  cooling,  diluting  with  water. 
The  solution  is  then  crystallised.  The  calcium  salt  is  Ca(C2H5S04)2.2Aq. 

Sulphethylic  acid  is  formed  when  ethylene  is  absorbed  by  H2S04  (p.  535). 

Etliyl  sulphate,  (C2H5)2S04,  is  obtained  by  the  reaction  between  ethyl  iodide 
and  Ag2S04in  a  sealed  tube  at  150°  C.  ;  2C2H5I  +  Ag2S04  =  2AgI  +  (C2H5)2S04.  It 
is  a  fragrant  liquid,  of  sp.  gr.  1.18,  and  boiling-point  208°  C.  It  does  not  mix 
with  water,  and  is  scarcely  decomposed  by  it  in  the  cold,  but  when  heated  with 
it  yields  alcohol  and  Sulphethylic  acid.  Heated  alone,  it  is  decomposed  into 
ethene  and  sulphuric  acid  ;  (C2H5)2S04  =  2C2H4  +  H2S04. 

Ethyl  sulphate  may  also  be  obtained  by  passing  vapour  of  SO.,  into  well-cooled 
ether  ;  S03  +  (C0H5)20  =  (C2H5)2S04.  It  is  obtained  as  a  secondary  product  in  the 
preparation  of  ether,  forming  the  bulk  of  the  liquid  called  heavy  oil  of  //•////•. 

Phenyl-mlphunc  add  is  unknown  ;  patassium  phenyhulphate,  S02'OC6He'OK,  is 
obtained  by  the  prolonged  action  of  KHS04  on  phenol  dissolved  in  potash  ; 
C6H5-OK  +  2S02OHOK^S02-OC6H5'OK  +  S02(OK)2  +  H20.  The  product  is  ex- 
tracted with  hot  alcohol,  from  which  it  crystallises  in  tables  soluble  in  water.  It 

2  3 


642  SWEET   SPIKIT   OF   NITRE. 

is  decomposed  by  exposure  to  moist  air,  or  by  boiling  with  water  or  dilute  HC1, 
yielding  phenol  and  KHS04  ;  S02;OC6H5'OK  +  HOH  =  HO-C6H5  +  S0.2-OH-OK. 

420.  Nitric  Esters. — The  type  is  etJujl   nitrate  or  nitric  ether,  prepared,   on  a 
small  scale  only  lest  explosion  occur,  from  C.2H5OH  and  HN03,  carefully  purified 
from  HN02.     80  grams  of  nitric  acid  of  sp.  gr.   i'4  are  heated  on  a  steam-bath, 
and  about  2  grams  of  urea  nitrate  are  added,  the  urea  of  which  decomposes  any 
nitrous  acid,  2HN02  +  CO(NH2)2  =  C02  +  N4  +  3H20.     After  a  time  the   mixture  is 
well  cooled  and  15  grams  more  urea  nitrate  are  added,  followed  by  60  grams  of 
alcohol  of  sp.  gr.  0.81.     By  fractional  distillation  dilute  alcohol  is  first  obtained,  and 
then  a  mixture  of  alcohol  and  nitric  ether,  from  which  the  latter  is  separated  by 
adding  water  containing  a  very  little  KOH  ;  the  lower  layer  is  draAvn  off,  dried 
with  calcium  chloride,  and  distilled,  C?H5OH  +  HN03  =  C2H5-N03  +  HOH.     The 
nitrous  acid  is  destoyed  because  it  rapidly  oxidises  the  alcohol  to  aldehyde  and 
other  products  which  react  very  violently  with  nitric  acid. 

Ethyl  nitrate  has  a  very  pleasant  smell,  and  sp.  gr.  i.i  ;  it  boils  at  86°  C.,  and 
its  vapour  explodes  when  heated,  from  the  sudden  disengagement  of  H20  and 
C02.  Water  dissolves  it  very  sparingly.  Alcoholic  solution  of  potash  converts 
it  into  KNOs  and  alcohol. 

421.  Nitrous    Esters.— Ethyl    nitrite,  C2H5N0.2,  is  the   chief   product  of    the 
action  of  nitric  acid  upon  alcohol,  until  it  becomes  very  violent,  the  nitric  radicle 
N03  being  reduced  to  the  nitrous  radicle  N02  by  the  conversion  of  part  of  the 
alcohol  into  aldehyde.     To  prepare  pure  ethyl  nitrite,  100  c.c.  of  a  solution  con- 
taining 46  grams  of  potassium  nitrite  are  mixed  with  50  c.c.  of  alcohol,  and  the 
mixture  allowed  to  run  slowly  into  a  cooled  mixture  of  50  c.c.  of  alcohol.  100  c.c. 
of  water,  and  75  grams  of  sulphuric  acid.     The  ethyl  nitrite  is  distilled  over  by  the 
heat  of  reaction,  and  is  condensed  b}r  ice.     It  is  purified  by  shaking  with  a  little 
dry  potassium  carbonate. 

Ethyl  nitrite  is  much  lighter  and  more  volatile  than  the  nitrate,  its  sp.  gr. 
being  0.95,  and  its  boiling-point  16°  C.  It  has  a  yellowish  colour,  and  a  pleasant 
odour  of  apples.  Like  many  other  nitrous  and  nitric  ethereal  salts,  it  may  be 
preserved  unchanged  if  perfectly  pure,  but  if  water  or  other  impurities  be  present, 
it  decomposes,  becoming  acid,  evolving  red  vapours,  and  bursting  the  bottle. 
Alcoholic  potash  converts  it  into  KN02  and  alcohol. 

The  spiritus  tct/teris  nitrosi,  or  sweet  spirit  of  nitre,  used  in  medicine,  is  made  by 
carefully  adding  2  measured  ounces  of  sulphuric  acid  to  a  pint  of  rectified  spirit, 
slowly  adding  2.\  measured  ounces  of  nitric  acid  to  the  cooled  mixture,  pouring  it 
upon  2  ounces  of  fine  copper  wire  in  a  retort  with  a  good  condenser,  and  distilling 
between  77°  C.  and  80°,  until  12  measured  ounces  have  distilled.  Half  an  ounce 
more  nitric  acid  is  then  poured  into  the  retort,  and  three  more  ounces  distilled 
over  ;  the  distillate  is  then  mixed  with  two  pints  of  rectified  spirit.  Hence  the 
sweet  spirit  of  nitre  consists  chiefly  of  spirit  of  wine,  holding  in  solution  ethyl 
nitrite,  aldehyde,  and  some  other  products  of  the  reaction.  The  proportion  of 
ethyl  nitrite  present  varies  greatly,  according  to  the  efficiency  of  the  condenser. 
Less  is  found  in  old  samples,  in  consequence  of  volatilisation  and  chemical 
change.  The  presence  of  aldehyde  is  shown  by  the  brown  colour  (aldehyde-resin) 
which  it  gives  when  shaken  with  alcoholic  potash.  Neglecting  secondary  changes, 
the  formation  of  the  ethyl  nitrite  in  the  above  process  may  be  represented  by 
C2H5-OH  +  HN03  +  H2S04  +  Cu  =  C2H5N02  +  CuS04  +  2H20. 

It  will  be  noticed  that  the  alkyl  nitrites  are  isomeric  with  the  nitro-paraffins. 

Amyl  nitrite,  C5H11N02,  may  be  prepared  by  distilling  amyl  alcohol  with  potas- 
sium nitrite  and  sulphuric  acid,  or  by  passing  N203  into  amyl  alcohol ;  it  is  a  yellow 
liquid  of  sp.  gr.  0.9,  and  boiling-point  96°  C.  It  has  a  remarkable  smell,  and  the 
peculiar  effect  of  its  vapour  when  inhaled  has  led  to  its  employment  in  medicine. 
The  vapour  of  amyl  nitrite  explodes  when  heated. 

422.  Esters   from    polyfoasic    acids    are    mainly    of    theoretical     importance, 
helping   to   settle   the   number   of   OH   groups  in   the   acid.     They  are  generally 
obtained  by  the   action  of  organic  acids  on  the  chloranhydrides,  such  as  POOL, 
PC13,  AsCl3,  BC13,   SiCl4,  &c.     Three  ethyl  phosphates,  PO(C2H5)3,  PO(OH)(CoH5).2 
and  PO(OH).2(OC2H5)  and  an  ethyl  metaphosj>/tate,  P(OC.2H5)3  are  known.     So" also 
ethyl  arsenite  As(OC.2H5)3,  b.-p.   166°  C.  ;  ethyl  borate  or  boric  ether,  B(OC.2H5)3, 
b.-p.  119°  C.,  which  burns  with  a  green  flame  ;  and  several  ethyl  silicates  or  silicic 
ethers,  such  as  Si(OC2H5)4,  (b.-p.  165°  C.),  which  burns  with  a  bright  flame  emitting 
clouds  of  Si02,  are  known.     Water  decomposes  them  into  alcohol  and  acid. 

Particularly  interesting  is  the  formation  of  ethereal  salts  of  acids  which  cannot 


ALKYL  ACETATES.  643 

exist  in  the  free  state.  Thus  ethyl  carbonate,  CO(OCoH5)0,  b.-p.  126°  C.,  is  obtained 
by  heating  silver  carbonate  with  ethyl  iodide  in  a  sealed  tube,  although  H.,CO.,  is 
unknown.  Potassium  ethyl  carbonate,  potassium  carbethylate  or  carbovi-nate 
CO(OC.2H5)(OK),  is  precipitated  in  crystals  when  C02  is  passed  into  a  cooled  solution 
of  KOH  in  absolute  alcohol. 

Again,  ethyl  orthocarbonate,  C(OC.2H5)4,  b.-p.  159°  C.,  formed  on  the  type  of 
orthocarbonic  acid  C(OH)4  (p.  261),  is  obtained  when  chloropicrin  is  treated  with 
sodium  ethoxide  in  alcohol,  CCl3N0.2  +  4C2HgONa  =  C(OC.,H5)4  +  3NaCl  +  NaN0.2. 

Xanthic  acid,  CS(OC2H5)(SH),  may  be  regarded  as  the  acid  ethyl  salt  of  sulpho- 
thiocarbonic  acid,  HO'CS'SH,*  which  is  not  known  in  the  free  state.  Xanthic 
acid  is  obtained  as  a  potassium  salt  by  saturating  alcohol  with  KOH  and  stirrin°- 
with  excess  of  CS.2  ;  C2H5-OH  +  CS.2  +  KOH  =  HOH  +  CS(OC2H5)(SK).  This  salt 
forms  colourless  crystals  with  a  faint  odour,  soluble  in  water  "and  alcohol,  but  not 
in  ether.  When  it  is  added  to  dilute  HC1  cooled  in  ice,  xanthic  acid  separates  as  a 
heavy  colourless  oily  liquid,  which  is  decomposed  at  24°  C.  into  alcohol  and  CS.2. 
The  characteristic  reaction  of  the  xanthates  is  that  with  cupric  sulphate,  which 
gives  at  first  a  dark -brown  precipitate  of  cupric  xanthate,  rapidly  decomposing  into 
a  yellow  oil  xantliogen  persulpkide,  and  bright  yellow  flakes  of  cuprous  .ranthate, 
the  reaction  being  apparently— 2(C2H50'CS2).2Cu  =  (C2HgO-CS2)2Cu2  +  2(C2H50-CS2). 

From  this  reaction  the  acid  was  named  (%av6os,  yellow). 

423.  Formic    "Ester*.— Methyl  formate,    HCOOCH.?,   is  obtained  by  distilling 
sodium   formate  with   KCH3S04  ;  HC02Na  +  KCH3S04  =  HC02CH3  +  KNaS04.     It 
is  isomeric  with  acetic  acid,  CH3C02H,  but  boils  at  32°  '5  C.     The  whole  of  its 
hydrogen  may  be  exchanged  for  chlorine,  yielding  C1C02CC13,  chloromethyl  formate, 
which  is  decomposed  by  heat  into  2COC12,  carbonyl  chloride. 

Ethyl  formate,  or  formic  ether,  HC02C2H5  (b.-p.  55°  C.)  is  prepared  by  distilling 
sodium  formate  (7  weights)  with  H2S04  (10)  and  alcohol  (6).  The  distillate  is  freed 
from  acid  by  shaking  with  a  little  lime,  and  redistilled.  It  is  a  fragrant  liquid, 
used  for  flavouring  rum.  It  dissolves  in  nine  times  its  weight  of  water.  Formic 
ether  is  also  prepared  by  heating  molecular  proportions  of  alcohol  and  oxalic  acid 
with  glycerine  for  some  time  in  a  flask  with  a  reversed  condenser,  and  distilling 
(see  p.  589). 

424.  Acetic   Esters. — Methyl   acetate,  CH3C02CH3    (b.-p.  57°  C.),    prepared  by 
distilling  methyl  alcohol  with  dried  lead  acetate  and  sulphuric  acid,  is  a  fragrant 
liquid,  lighter  than  water,  with  which  it  mixes  freely.     It  is  a  constituent  of  crude 
wood-spirit. 

Ethyl  acetate  or  acetic  ether,  CH3'COOC2H5. — Mix  50  c.c.  of  absolute  alcohol 
with  50  c.c.  of  strong  H2S04  and  heat  to  140°  C.  in  a  flask  with  a  good  condenser. 
Kun  in  through  a  tap  funnel  a  mixture  of  400  c.c.  of  alcohol  and  400  c.c.  of  glacial 
acetic  acid  at  the  rate  at  which  the  ethyl  acetate  distils.  Neutralise  the  distillate  with 
Na.2C03,  separate  and  shake  the  upper  layer  with  equal  weights  of  water  and  CaCl2  to 
extract  alcohol.  Separate,  dry  the  upper  layer  with  CaCl2,  and  distil. 

Ethyl  acetate  boils  at  77°  C.  and  smells  of  cider  ;  its  sp.  gr.  is  0.91  and  it  dis- 
solves in  ii  times  its  weight  of  water,  slowly  decomposing  into  CH3COOH  and 
C3H5OH.  It  mixes  readily  with  alcohol  and  ether,  and  is  useful  as  a  solvent  and  for 
flavouring.  Chlorine  converts  it  into  perchloracetic  ether,  CC13-C02'C2C15,  which 
smells  of  chloral. 

425.  Ethyl  aceto-acetate,  CH3CO-CH2C02C2H5  (see  aceto-acetic  acid,  p.  626),  is 
prepared  by  acting  on  ethyl  acetate  with  sodium,  treating  the  product  with  a  dilute 
acid,  diluting  with  saturated  brine  and  distilling  the  light  oil  which  separates.     It 
boils  at  181°  C.     The  simplest  equation  is — 

2CH3-C02C2H5  +  Na2  =  CH3COCHNaC02C2H5  +  C2H5ONa  +  H2. 
The  sodium  in  the  ethyl  sodacetoacetate  being  then  exchanged  for  H  by  the  dilute 
acid.  But  the  change  does  not  occur  between  pure  ethyl  acetate  and  Na  ;  some 
alcohol  must  be  present.  It  is  supposed,  therefore,  that  the  first  step  is  the  direct 
addition  of  sodium  ethoxide,  C.2H5ONa,  to  ethyl  acetate  producing  the  compound 
CH3C(OC.,H5)2(ONa).  This  is  a  derivative  of  the  hypothetical  ort/ioacetic  acid, 
CH'.SC(OH);!,  and  with  another  molecule  of  ethyl  acetate  yields  the  ethyl  sodaceto- 
acetate and  alcohol  which  reacts  with  more  sodium  to  repeat  the  cycle. 

Ethyl  acetoacetate  is  a  colourless  liquid,  smelling  of  hay.     It  is  sparingly  sc       le 

*  In  two-acids,  the  S  which  is  substituted  for  the  carbonyl  O  is  indicated  by  the  prefix 
mlpho-,  or   thion-,  the  prefix  thio-  being  confined    to   the  S  that  is   substituted 
hydroxyl O. 


644 


ETHYL  ACETO-ACETATE. 


in  water,  but  dissolves  in  alcohol,  the  solution  giving  a  violet  colour  with  Fe2Cl,;. 
and  a  green  crystalline  precipitate,  Cu(C6H9O3).2,  with  a  strong  solution  of  copper- 
acetate.  It  has  an  acid  bias,  for  alkalies  dissolve  it  and  acids  re-precipitate  it  from 
the  solutions  ;  but  alkali  carbonates  will  not  dissolve  it. 

Ethyl  acetoacetate  is  of  great  utility  in  synthetic  chemistry,  since  through  its- 
means  a  variety  of  complex  acids  and  ketones  can  be  synthesised.  This  is  rendered 
possible  by  two  facts :  (i)  When  ethyl  acetoacetate  is  heated  with  alkalies  it 
yields  either  a  ketone  (acetone)  or  an  acid  (acetic  acid)  according  to  the  con- 
centration of  the  alkaline  solution.  Thus,  with  dilute  aqueous  alcoholic  potash  the- 
reaction  is — 


C02C2H5  +  2KOH  =  CH3-CO'CH3  +  K2C03  +  C2H5OH, 
ited  alcoholic  potash  the  reaction  is — 


CH3-CO'CH2 
whilst  with  concentrated 
CH3-CO 

The  first  type  of  decomposition  is  called  hetonic  decomposition,  the  second  is  acidic- 
decomposition.  (2)  Only  one  of  the  two  inethylene  H  atoms  can  be  exchanged  for 
sodium,  but  when  ethyl  sodacetoacetate  is  treated  with  an  alkyl  iodide,  the  sodium 
is  exchanged  for  the  alkyl  group  ;  thus,  ethyl  ethylacetoacetate  may  be  prepared,. 
CH3-COCHNa-C02C2H5  +  C2H5I  =  CH3-CO'CHC2H5-C02C2H5  +  Nal.  By  treat- 
ing'this  with  Na,  ethyl  xodethylacetoacetate,  CH.5-CO-CNaC2H5-C02C2H5,  is  formed,. 
and  with  C2H5I  this  becomes  ethyl  diethylacetoacetate  CH3-CO-C(C2H5)2-C02C2Hg. 
Other  alkyl  radicles  may  be  substituted  instead  of  ethyl.  These  substituted 
acetoacetates  may  be  represented  by  the  general  formula  CH3'CO'CRR''C02C2H5r 
and  such  a  compound  yields  the  substituted  ketone  CH./CO-CHRR'  or  the 
substituted  acid  CHRR'-C02H  (together  with  acetic  acid),  accordingly  as  it  is  made 
to  undergo  the  ketonic  or  the  acidic  decomposition  described  above. 

Ethyl  acetoacetate  combines  with  phenylhydrazine  and  hydroxylamine  like  a 
ketone  (p.  615),  indicating  a  ketone  group.  By  reduction  it  yields  the  secondary 
alcoholic-acid,  CH3'CHOH'CH2-C02H  (ft-hydro.fi/butt/ric  acid).  It  is  a  fact,  howeverr 
that  in  many  respects  ethylacetoacetate  behaves  as  though  it  were  ethyl  fi-hydroxy.- 
isocrotonate,  CH3'COH  :  CH'C02C2H5.  This  is  explained  by  supposing  that  it  can 
exist  both  in  this  form  and  in  that  given  above,  under  the  influence  of  different 
reagents  (Tautotnerism.  See  Cyanic  Acid). 

When  ethyl  acetoacetate  is  heated  it  yields  dehydracetic  acid,  C8H804,  (6-meth>jl 
-^-acetopyronone).  which  forms  sparingly  soluble,  fusible  crystals,  unchanged 
by  the  strongest  acids,  but  hydrolysed  by  alkalies,  C8H804+3H00  =  C02  + 
CH3-CO'CH3  (iicetone)  +  2(CH3'C02H). 

Phenijl  acetate,  C6H5.C2H.}02  maybe  obtained  by  the  reaction,  C6H5-OH  +  C2H30'C1 
=  C6H5'OC2H30  +  HCi,  proving  that  phenol  contains  an  OH  group.  It  boils  at 
195°  C.  A  piece  of  hard  glass  tube  becomes  invisible  in  phenyl  acetate,  its  index 
of  refraction  for  light  being  the  same  as  that  of  the  liquid. 

One  of  the  amijl  acetates,  CH3'C02C5Hn,  is  sold  as  pear  essence;  and  is  prepared 
by  distilling  fusel  oil  with  acetic  and  sulphuric  acids  ;  boils  at  140°  C. 

426.  Esters     of    Higher    Fatty    Acids. — Ethyl,    fyityrate,     or     butyric     ether,. 
C3H7-C02C2H5,  prepared  by  distilling  butyric  acid  with  C2H5OH  and  H2S04  is  sold, 
dissolved  in  alcohol,  as  ananas  oil,  or  essence  of  pineapple,  which  it  resembles  in 
odour.     B.-p.  121°  C. 

Ethyl  pelargonate,  or  pelaryonic  ether,  C8Hll7'C02C2Hg,  prepared  from  oil  of  rue,, 
is  used  in  flavouring  as  quince  oil,  and  is  present  in  the  fruit. 

Ethyl  caprate,  or  capric  ether,  C9H19'C02C2H5  (b.-p.  187°  C.),  was  formerly  called 
cenanthic  ether,  because  it  is  found  in  old  wine.  It  is  made  by  distilling  wine-lees,. 
and,  when  pure,  is  a  colourless,  fragrant,  oily  liquid.  It  is  sold  for  flavouring. 

Amijl  ralerate,  C4H9'C02C5Hn,  or  apple  oil,  is  obtained  by  distilling  fusel  oil 
with  sodium  valerate  and  sulphuric  acid  ;  its  boiling-point  is  188°  C. 

The  ethyl  salts  of  acids  of  the  acetic  series  containing  more  than  ten  atoms  of 
carbon  are  generally  prepared  by  dissolving  the  acids  in  alcohol  and  passing  HC1 
into  the  solution  ;  probably  this  converts  the  alcohol  into  C2H5C1.  which  acts  upon 
the  acid  to  form  the  ethyl  salt  ;  this  is  deposited  in  crystals  from  the  alcoholic- 
solution.  Ethyl  pa  Imitate,  and  stearate  are  very  fusible  crystalline  solids-, 

427.  Cetyl  palmltate  (m.-p.  49°  C.)  and  ceri/l  cerotate  (m.-p.  81°  C.)     See  p.  570.^ 
Melissyl  palmitate,  or  myricin,  Cl5Rsl'C02C.]0B.6l.  forms  about  one-third  of  been;- 


ETHEREAL  SALTS.  645 

was,  the  colour,  odour,  and  tenacity  of  which  appear  to  be  due  to  the  presence  of 
about  5  per  cent,  of  a  greasy  substance  called  cerolein. 

428.  Aromatic  Esters.— Ethylbenzoate  or  ben:oicether,  C6H6'C02C2HB,  is  prepared 
by  dissolving  benzoic  acid  in  alcohol,  saturating  with  HC1,  distilling,  and  mixing 
the  distillate  with  water,  when  ethyl  benzoate  separates  as  a  fragrant  liquid  of  • 
sp.  gr.  1.05,  boiling  at  213°  C.     Benzyl  benzoate,  C6H5'C0.2C7H7,  is  a  crystalline 
substance,  contained  in  balsam  of  Peru  ;  m.-p.  20°  C. ;  b.-p.  323°  C.     Benzyl  ci/um- 
mate,  C8H7-C02C7H7,  (evrm&m&iri),  is  present  in  the  balsams  of  Peru  and  Tolu. 

Methyl  salicylate,  C6H4OH'C02CH3,  occurs  in  oil  of  winter-green,  extracted  from 
the  flowers  of  Gaulthena  procumbent,  and  was  one  of  the  first  vegetable  products 
prepared  artificially.  It  is  obtained  by  distilling  methyl  alcohol  with  sulphuric 
acid  and  salicylic  acid.  It  is  a  fragrant  liquid  of  sp.  gr.  1.2,  and  boiling-point 
224°  C.  Ferric  chloride  colours  it  violet.  On  treating  it  with  strong  solution  of 
soda,  in  the  cold,  it  yields  crystals  of  C6H4ONa-C02CH3.  When  this  is  heated 
with  methyl  iodide  in  a  sealed  tube,  it  gives  C6H4OCH3-C02CH3,  or  methyl  methyl- 
mallei/late,  an  oily  liquid.  If  this  be  saponified  by  potash,  it  yields  the  'potassium 
salt  of  methyl  salicylic  acid,  C6H4OCH3'C02H,  a  crystalline  acid  isomeric  with 
methyl  salicylate,  but  not  giving  the  violet  colour  with  ferric  chloride.  The 
ethyl  salicylate.  resembles  the  methyl  compound. 

Phenyl  salicylate,  C6H4OH'C02C6Hg,  is  prepared  by  the  action  of  POC13  on  a 
mixture  of  salicylic  acid  and  phenol,  2C6H4OH'COOH  +  2C6H3OH  +  POC13  = 
2C6H4OH-C02C6H5  +  HP03  +  3HC1 ;  it  crystallises  in  tables,  melts  at  43°  C.,  and  is 
used  as  an  anti-pyretic  under  the  name  of  salol. 

Cinnamijl  cinnamate,  or  styracin,  C8H7'C02-C9H9,  is  a  crystalline  ethereal  salt 
obtained  from  storax  by  treatment  with  soda. 

429.  Esters  from  Dibasic    Organic    Acids.— These    may   be   acid    or    normal, 
both  being  generally  obtained  by  distilling  the  anhydrous  acid  with  an  alcohol  and 
fractionating  the  distillate. 

Methyl  otalate,  (C02)2(CH3)2,  (b.-p.  163°  C.),  obtained  by  distilling  CH3OH  with 
an  equal  weight  of  H2SO4  and  oxalic  acid,  solidifies  in  scales  (m.-p.  51°  C.)  in  the 
receiver  ;  when  distilled  with  water  it  is  hydrolysed. 

Ethyl  oxalate,  or  o.ralic  ether,  (C02'C2H5)2,  is  prepared  by  boiling  equal  weights 
of  dried  oxalic  acid  and  absolute  alcohol  for  six  hours  in  a  retort  with  a  reversed 
condenser,  and  then  adding. water,  which  separates  the  oxalic  ether  as  a  fragrant 
liquid  of  sp.  gr.  1.09,  boiling  at  186°  C.  It  is  hydrolysed  by  boiling  with  water, 
and  saponified  by  potash.  If  mixed  with  one  equivalent  of  potash,  it  yields  pearly 
scales  of  potassium  oxalethylate  ;  (C02-C2H5)2  +  KOH  =  (C02)2KC2H5  +  C2H5'OH. 
By  decomposing  this  with  hydrofluosilicic  acid,  oj-alethylic  or  twaloe'tnic  acid, 
(C02)2HC2H5,  is  obtained,  but  it  is  easily  decomposed  by  water. 

By  the  action  of  sodium  on  an  ethereal  solution  of  ethyl  oxalate  and  acetate, 
the  sodium  derivative  of  ethtjl  o-i-alacetate  is  obtained  ;  this  has  the  formula 
C02C2H5-CO-CH2-C02C2H5,  and',  when  heated  with  dilute  H2S04  yields  pyniric  acid, 
(p/62~6). 

Ethyl  malonate,  or  malonic  ether,  CH2(C02-C2H5)2,  is  prepared  by  passing  HC1  gas 
into  absolute  alcohol,  containing  calcium  malonate  in  suspension — 

CH2(C02)2Ca  +  2(C2H5OH)  +  2HC1  =  CH2(C02'C2H5)2  +  CaCl2  +  2  HOH. 
After  some  hours'  standing,  the  liquid  is  boiled  on  a  steam-bath,  again  saturated 
with  HC1  gas,  the  alcohol  distilled  off,  the  liquid  neutralised  with  sodium  carbonate, 
and  mixed  with  water,  when  the  malonic  ether  separates  as  a  bitter  aromatic  liquid 
of  sp.  gr.  1. 068,  and  boiling-point  198°  C.  Its  application  for  the  preparation 
of  fatty  acids  has  been  already  noted  (p.  587). 

The' ethereal  salts  of  an  alcohol  radicle  may  be  converted  into  those  of  another 
alcohol  radicle  by  mixing  them  with  the  alcohol  in  question,  and  adding  a  small 
quantity  of  a  metallic  alkyl  oxide,  the  action  of  which  has  not  been  fully  explained. 
Thus,  methyl  oxalate  dissolved  in  ethyl  alcohol,  and  mixed,  in  the  cold,  with  a 
small  quantity  of  sodium  ethoxide,  C2Hg'ONa,  becomes  in  great  measure  converted 
into  ethyl  oxalate,  and,  conversely,  ethyl  oxalate  is  transformed  into  methyl 
oxalate  by  dissolving  it  in  methyl  alcohol,  and  adding  a  minute  quantity  of 
sodium  in  ethoxide. 

430.  Esters    from    Polyhydric    Alcohols.— Glijcol  esters    are  very    numerous, 
because  either  one  or  both  of  the  OH  groups  in  aH4(OH).2  may  be  exchanged,  and 
two  different  acid  radicles  may  be  introduced.    None  of  them,  however,  as  yet, 
possesses  any  practical  importance. 

431.  Glycerol  Esters    or  Propenyl  Salts.— These  compounds    are  even 


646  NITEOGLYCERINE. 

numerous  than  those  derived  from  glycol,  since  each  of  the  three  OH  groups  in 
C3Hg(OH);}  may  be  exchanged  for  a  different  acid  radicle. 

The  glyceryl  chlorides  are  known  as  cMorhydrlns.  a-Monochlorhydrin, 
CH2C1-CHOH:CH2OH,  and  a.-dlchlorhydrin,  CH2C1-CHOH-CH2C1,  are  prepared  by 
saturating  glycerol  with  HC1,  heating  for  several  hours  at  100°  C.,  neutralising  with 
Na.2CO:3,  and  extracting  with  ether.  On  fractionating  the  ethereal  solution  the 
dichlorhydrin  distils  first  (b.-p.  174°  C.).  They  are  liquids  heavier  than  water,  in 
which  the  mono-  is  more  soluble  than  the  di-chlorhydrin.  The  /3-chlorhydrins, 
CH2OH-CHC1-CH2OH  and  CH2OH-CHC1'CH2C1,  are  both  obtained  from  allyl 
alcohol,  the  former  by  action  of"HC10,  the  latter  by  action  of  Cl.  Tnchlorliydnn 
is  i  :  2  :  3-trichloropropane  (#./•.). 


EpiclilorJiydnn,  CH2'CH-CH2C1  is  obtained  by  treating  a-  or  /3-dichlorhydrin 
with  alkali,  which  removes  HC1.  It  is  a  mobile  liquid  smelling  of  chloroform  and 
insoluble  in  water  ;  sp.  gr.  1.2,  b.-p.  H7°C.  It  is  sometimes  used  as  a  solvent. 

Sulpliogly  eerie  acid,  C3H5(OH)2S04H.  is  formed  with  considerable  evolution  of 
heat,  when  glycerol  is  dissolved  in  strong  sulphuric  acid.  The  acid  may  be 
obtained  as  in  the  case  of  sulphethylic  acid.  It  is  only  known  in  solution,  being 
easily  decomposed  even  by  evaporation  in  'cacuo. 

432.  Nitroglycerine,  or  glyceryl  trinitrate,  C3H5(N03)3,  is  prepared 
by  the  action  of  nitric  acid  on  glycerine—  C3H6(OH)3  +  3(HN03)  = 
C3H5(N03)3  +  3H20.  It  is  a  heavy  oily  liquid,  of  sp.  gr.  1*6,  without 
smell,  very  explosive,  and  poisonous.  It  is  insoluble  in  water,  sparingly 
soluble  in  alcohol,  but  soluble  in  ether  and  in  methyl  alcohol.  When 
saponified  by  potash,  it  yields  glycerol  and  potassium  nitrate. 

On  a  large  scale  a  mixture  of  concentrated  HNOo  with  twice  its  volume  of  strong 
H2S04  is  placed  in  a  tank  lined  with  lead  and  cooled  by  water  circulating  in  leaden 
coils.  Glycerine  is  sprayed  into  the  acid,  care  being  taken  that  the  temperature 
does  not  rise  above  30°  C.  The  mixture  is  allowed  to  settle,  when  much  of  the 
nitroglycerine  floats  to  the  top  and  is  run  into  water  and  washed.  The  lower  layer 
is  then  run  into  water  to  separate  the  dissolved  nitroglycerine,  which  sinks  to 
the  bottom.  A  little  alkali  is  added  to  the  last  washing  water  to  remove  any  trace 
of  free  acid  remaining. 

This  oil  is  very  violent  in  its  explosive  effects.  If  a  drop  of  nitroglycerine  be 
placed  on  an  anvil  and  struck  sharply,  it  explodes  with  a  very  loud  report,  even 
though  not  free  from  water,  and  if  a  piece  of  paper  moistened  with  a  drop  of  it 
be  struck,  it  is  blown  into  small  fragments.  On  the  application  of  a  flame  or  of 
a  red-hot  iron  to  nitroglycerine,  it  burns  quietly  ;  and  when  heated  over  a  lamp 
in  the  open  air  it  explodes  but  feebly.  In  a  closed  vessel,  however,  it  explodes 
at  about  360°  F.  (182°  C.)  with  great  violence.  For  blasting  rocks,  the  nitro- 
glycerine is  poured  into  a  hole  in  the  rock,  tamped  by  filling  the  hole  with  water, 
and  exploded  by  the  concussion  caused  by  a  detonating  fuze  (see  below),  the  effect 
in  blasting  being  about  five  times  that  of  an  equal  weight  of  gunpowder,  and 
much  damage  has  occurred  from  the  accidental  explosion  of  nitroglycerine  in 
course  of  transport.  When  nitroglycerine  is  kept,  especially  if  it  be  not 
thoroughly  washed,  it  decomposes,  with  evolution  of  nitrous  fumes  and  forma- 
tion of  crystals  of  oxalic  acid  ;  and  it  may  be  readily  imagined  that,  should 
the  accumulation  of  gaseous  products  of  decomposition  burst  one  of  the  bottles  in 
a  case  of  nitroglycerine,  the  concussion  would  explode  the  whole  quantity. 

Nitroglycerine,  like  gun-cotton,  is  particularly  well  fitted  for  blasting,  because 
it  will  explode  with  equal  violence  whether  moisture  be  present  or  not,  but  it  has 
the  advantage  of  containing  enough  oxygen  to  convert  all  its  carbon  into  carbonic 
acid  gas.  On  the  other  hand,  it  is  very  poisonous,  and  is  said  to  affect  the  system 
seriously  by  absorption  through  the  skin,  and  the  gases  resulting  from  its  explosion 
are  exceedingly  acrid.  Again,  its  fluidity  prevents  its  use  in  any  but  downward 
bore-holes.  To  overcome  these  objections,  and  to  diminish  the  danger  of  trans- 
port. several  blasting  compounds  have  been  proposed,  of  which  nitroglycerine  is 
the  basis. 

Dynamite  is  composed  of  a  particularly  porous  siliceous  earth  (Kieselguhr), 
obtained  from  Oberlohe  in  Hanover,  impregnated  with  about  70  or  75  per  cent,  of 
nitroglycerine.  Kieselguhr  contains  63  per  cent,  of  soluble  silica,  about  18  of 
organic  matter,  1  1  of  sand  and  clay,  and  8  of  water.  It  is  incinerated  to  expel  the 


GLYCERYL  SALTS.  647 

organic  matter,  and  mixed  with  the  nitroglycerine  in  wooden  troughs  lined  with  lead 
When  used  in  solid  rock,  dynamite  is  six  or  seven  times  as  strong  as  blaatin*- 
powder. 

JoM'x  detonators  for  nitroglycerine  contain  7  parts  of  mercuric  fulminate  and 
3  parts  of  potassium  chlorate,  pressed  into  small  copper  tubes. 

masting  gelatine  is  made  by  dissolving  collodion-cotton  in  about  nine  times  its 
weight  of  nitroglycerine  ;  its  detonation  is  even  more  powerful  than  that  of  nitro- 
glycerine itself.  Gelatine-dynamite  consists  of  65  per  cent,  of  thinly  gelatinised 
nitroglycerine,  8.4  per  cent,  of  woodmeal,  26.25  potassium  nitrate,  and  0.35  per  cent. 
of  soda.  It  is  slow  in  detonation  and  is  an  excellent  blasting-agent, 

Cordite  is  made  by  Incorporating  58  parts  of  nitroglycerine  with  37  parts  of 
gun-cotton  ,  and  19.2  parts  of  acetone  ;  5  parts  of  vaseline  are  added  and  after 
this  has  been  mixed  the  compound  is  forced  through  dies,  so  that  it  assumes  the 
form  of  cords,  from  which  the  acetone  is  allowed  to  evaporate. 

Nitroglycerine  is  readily  soluble  in  ether  and  in  wood-naphtha,  but  somewhat 
less  so  in  alcohol  ;  it  is  re-precipitated  by  water  from  these  last  solutions.  It 
becomes  solid  at  40°  F.  (4.5°  C.),  a  circumstance  which  is  unfavourable  to  its  use 
in  mining  operations,  partly  because  it  is  then  less  susceptible  of  explosion  by 
the  detonating  fuse,  and  partly  because  serious  accidents  have  resulted  from 
attempts  to  thaw  the  frozen  nitroglycerine  by  heat,  or  to  break  it  up  with  tools. 
It  is  remarkable  that,  when  made  on  the  small  scale,  the  nitroglycerine  may  gene- 
rally be  cooled  down  to  o°F.  (-  1  8°  C.)  without  becoming  hard.  This  and  other 
observations  render  it  probable  that  some  other  substitution-product  is  occasionally 
mixed  with  it. 

Berthelot  finds  that,  in  the  formation  of  nitric  ether  by  the  action  of  nitric  acid 
upon  alcohol,  5800  heat  units  are  disengaged  for  each  molecule  of  nitric  acid 
entering  into  the  reaction,  whereas,  in  the  formation  of  nitroglycerine,  only  4300 
heat  units  per  molecule  of  nitric  acid  are  disengaged.  Less  energy  having  been 
converted  into  heat  in  the  latter  case,  more  is  stored  up  in  the  nitroglycerine, 
and  hence  its  formidable  effect  as  an  explosive.  In  the  formation  of  gun-cotton, 
each  molecule  of  nitric  acid  disengaged  11,000  heat  units,  to  which  Berthelot  attri- 
butes the  stability  and  inferior  explosive  effect  of  gun-cotton  in  comparison  with 
nitroglycerine. 

Nitroglycerine  is  reconverted  into  glycerine  by  alkali  sulphides  with  rise  of  tem- 
perature and  separation  of  sulphur  ;  C3J^(N03)3  +  3KHS  =  C3H5(OH)3  +  3KN02  +  S3. 
Compare  Gun-cotton. 

Gl  I)  eeryl-  phosphoric  or  pJutsplwytyeerie  acid,  C3H5(OH)2P02(OH).2,  is  formed  by 
the  action  of  metaphosphoric  acid  on  glycerol,  but  has  only  been  obtained  in 
solution.  It  is  a  product  of  decomposition  of  lecithin  («/.*'.). 

Glijcenjl  arxenite,  C3H5'As03,  is  obtained  by  dissolving  white  arsenic  in 
glycerol,  and  evaporating;  4C3H5(OH)3  +  As406  =  4C3H5As03  +  6HOH.  It  forms  a 


yellowish  glass,  fusing  at  50°  C.     It  is  sometimes  used  for  fixing  aniline  dyes. 

Glycenjl  lorate,  or  lorof/lyceride,  C3H5B03,  is  prepared  from  boric  acid  and 
glycerol  ;  it  is  also  a  transparent  glass,  dissolving  slowly  in  water,  and  has  been 
recommended  for  the  preservation  of  food. 

433-  By-  far  the  most  important  ethereal  salts  are  the  fats  and  oils 
which  are  mixtures  of  glyceryl  salts  of  the  fatty  acids,  also  called 
glycerides.  Like  other  esters  the  oils  arid  fats  are  easily  hydrolysed 
into  the  alcohol  (glycerol)  and  the  acid.  When  an  alkali  is  the  hydro- 
lytic  agent  the  alkali  salt  of  the  fatty  ucid,  a  soap,  is  obtained.  Thus 
when  tallow  is  saponified  it  yields  a  soap  composed  chiefly  of  alkali 
stearate  and  oleate,  from  the  stearin  (glyceride  of  stearic  acid)  and  olein 
(glycericle  of  oleic  acid)  of  which  it  is  mainly  composed  : 

(C17H,5COO)3C3H5  +  3NaOH  =  3C17H35COOXa  +  C3H.,(OH)3 
(C'X;COO)3aH0-  +  S^aOH  =  sC^COONa  +  C3H5(OH)3 
Palmitin,  the  glyceride  of  palmitic  acid,  the  chief  constituent  of  palm- 
oil,  is  the  other  principal  glyceride. 

Xonofonnin,  C,Hg(OH)0'C02H,  and  difi>raun,  C3H5(OH)(C02H)2,  are  produced 
when  oxalic  acid  is  heated  with  glycerol,  in  making  formic  acid- 

C3H5(OH)3  +  (C02H)2  -  C3H6(OH)2-C0.2H  +  C02  +  H20. 


648  SULPHONIC  ACIDS. 

Tri-acetin,  C3H5(C2H302)3,  is  present  in  cod-liver  oil,  and  may  be  obtained  by 
acting  on  glycerol  with  acetic  acid.  Tributyrin,  C3H5(C4H702)3,  occurs  in  butter. 

Tripalmitin  or  palmitin,  C3H5(C16H3102)3,  is  obtained  from  palm-oil  or  from 
Chinese  wax,  by  pressing  and  crystallising  from  alcohol.  It  fuses  at  46°  C. 

Tristearin  or  stearin,  C3H5(C18H3502)3,  prepared  by  repeatedly  recrystallising  the 
harder  natural  fats,  such  as  tallow,  from  their  solution  in  ether,  fuses  at  63°  C. 

Tri-olein  or  olein,  C3H5(C18H330.2)3,  is  obtained  by  cooling  olive-oil  to  o°  C..  press- 
ing out  the  liquid  part,  dissolving  this  in  a  little  alcohol,  again  freezing,  to 
separate  the  rest  of  the  stearin,  and  distilling  off'  the  alcohol.  Olein  is  less  easily 
decomposed  by  alkalies  than  are  palmitin  and  stearin,  and  is  left  unaltered  when 
olive-oil  is  treated  with  a  cold  concentrated  solution  of  NaOH,  which  converts 
the  palmitin  and  stearin  into  soaps  and  glycerol. 

The  three  glycerides,  palmitin,  stearin,  and  olein,  are  found  in  most  animal 
and  vegetable  fats.  Olive-oil  and  Chinese  wax  consist  almost  entirely  of  palmitin 
and  olein.  Palm-oil  contains  all  three.  Mutton  suet  is  chiefly  stearin,  with  a 
little  palmitin  and  olein.  Beef  suet  contains  more  palmitin  ;  these  constitute 
tallow.  Lard  has  a  similar  composition.  Human  fat  contains  more  palmitin. 
Goose  fat  and  butter  contain,  besides  the  above  glycerides,  those  of  volatile  acids, 
such  as  butyric,  capric,  caprylic,  and  caproic.  Coco-nut  oil  contains  trilaui-in, 


,OC,H5 


Palmitin,  stearin,  and  olein,  may  be  made  artificially  by  heating  glycerol  with 
the  corresponding  acids  ;  for  example  — 

C3H5(OH)3  +  3HC18H350.2  =  CaH^CjgHaBOak  +  3HOH. 

SULPHONIC  ACIDS. 

434.  The  ethereal  salts  of  sulphurous  acid  are  metameric  with  the 
compounds  known  as  the  sulphonic  acids  ;  thus,  both  ethyl  hydrogen 
sulphite  and  ethyl  sulphonic  acid,  have  the  empirical  formula  02H6S03. 
The  sulphonic  acids,  however,  differ  from  the  sulphites  in  that  when 
treated  with  reducing-agents  they  yield  the  corresponding  thio-alcohols; 
thus,  ethyl  sulphonic  acid,  C2H5S03H,  yields  mercaptan  (ethyl  thio- 
alcohol)  C2H5SH.  This  reaction  indicates  that  the  sulphur  in  ethyl 
sulphonic  acid  is  combined  directly  with  the  carbon  of  the  ethyl  group, 
for  there  can  be  no  doubt  that  the  S  in  mercaptan  is  so  combined. 
The  constitution  of  ethyl  sulphonic  acid,  is  therefore  probably 

/C2H5  A 

OJSx  ,  whilst  that  of  ethyl  hydrogen  sulphite  is  OS< 

X)H  \OH 

When  a  strong  solution  of  sodium  sulphite  is  heated  with  ethyl  iodide  at  140°  C., 
sodium  ethyl  sulphonate  and  sodium  iodide  are  produced;  Na2S03  +  C2H5I  = 
C2H5-S02ONa  +  NaI.  If  sodium  sulphite  were  a  salt  of  SO(OH)2,  viz.,  SO(ONa)2, 
this  reaction  would  be  expected  to  produce  ethyl  sodium  sulphite  SO(ONa)(OC2H5)f* 
Since  this  is  not  the  case,  Na-jSOg  must  have  the  constitution  S02(ONa)Na  ;  this 
constitutes  the  evidence  referred  to  on  p.  222. 

The  sulphonic  acids  bear  the  same  relationship  to  sulphuric  acid,  as  the 
carboxylic  acids  bear  to  carbonic  acid,  that  is,  they  contain  an  alcohol 
radicle  or  a  hydrocarbon  radicle  in  place  of  one  of  the  OH  groups.  They 
are  monobasic  acids  since  they  still  retain  one  OH  group.  By  partial 
reduction  they  generally  yield  sulphinlc  acids,  which  bear  the  same 
relationship  to  the  SO(OH)2  form  of  sulphurous  acid  as  the  sulphonic 
acids  bear  to  sulphuric  acid. 

The  sulphonic  acids  are  also  produced  by  oxidation  of  the  mercaptans. 

*  Ethyl  sulphite,  SO(OC2H5)2,  is  prepared  by  the  action  of  SOC12  on  alcohol.  When  heated 
with  one  equivalent  of  NaOH  it  yields  ethyl  sodium  sulphite;  when  this  is  treated  with  an 
acid  with  a  view  to  removing'  the  Na,  it  is  decomposed,  so  that  ethyl  hydrogen  sulphite  has 
not  been  prepared. 


NITRO-COMPOUNDS.  ^49 

Ethyl  sidphinic  acid  C2H5;SOOH,  is  obtained  as  a  zinc  salt  bv  the  action  of 
b02  on  a  cooled  ethereal  solution  of  zinc  ethide  ;  ZnfC0H  ^  +2SO  -ir  H  -?n  \  ?? 

rhR  ™self  is  s-r?py  li(rd-  li  mi«ht  S^S^WftS^ 

Srboxyl  m  tetravalent  sulphur  is  substituted  for  the  carbon  of  the 

Ethyl-mlphonic  acid  C2H5'S02-OH,  is  produced  when  ethyl-sulphinic  acid  mer- 
captan,  ethyl  polysulphides,  and  ethyl  sulphocyanate  are  oxidised  by  nitric  add  • 
also  from  C2H5I  and  Na2S03,  as  stated  above.  Ethyl-sulphonic  acid  isan  oily  l^uTd 
of  sp  gr.  1.3  and  may  be  crystallised  by  cooling.  It  forms  very  soluble  salts 
which  are  not  easily  decomposed  by  heat.  By  oxidation  with  HNO,  it  vields 
ethyl  hydrogen  sulphate. 

Ethionic  acid  baa  already  been  noticed  (p.  535).  It  is  a  mixed  ethereal  salt  and 
sulphonic  acid  from  glycol,  CH2(OS03H)'CH2(S03H).  By  hydrolysis  the  ethereal 
°  8  H2S°ad  i**1"0*1*  acid  ^r^- 


mm  p  m  lphonic  add, 

2(OH)-CH2(S03H).  being  produced. 

It  is  characteristic  of  closed-chain  compounds  (at  all  events  such  as 
contain  a  benzene  nucleus)  that  they  readily  yield  sulphonic  acids  when 
heated  with  strong  sulphuric  acid  (p.  549).  These  are  very  useful  for 
preparing  other  compounds,  e.g.,  phenols  (q.v.),  and,  on  account  of  their 
solubility,  for  use  as  dye-stuffs.  They  yield  chloranhydrides  (p  101} 
when  treated  with  PC15. 

When  benzene  is  warmed  with  H2S04  cone.,  benzene  sulphonic  acid,  C6H5-S02OH 
is  produced  ;  if  fuming  acid  be  employed  the  three  (chiefly  1:3)  benzene  di- 
sulphonic  acids,  C6H4(S02OH)2,  are  produced.  Naphthalene  may  be  similarly 
sulphonated  to  produce  isorneric  naphthalene  mono-  and  di-mlphomc  acids. 
Sulphonic  acids  of  most  benzene  hydrocarbon  derivatives  are  easily  obtainable  ; 
some  of  these  will  receive  passing  mention  later. 

NITRO-COMPOUNDS. 

435.  The  ethereal  salts  of  nitrous  acid  are  metameric  with  the 
nitre-substituted  hydrocarbons  ;  thus,  ethyl  nitrite,  C.,H5ON  :  0,  is 
metameric  with  nitro-ethane,  C2H5'NO,.  The  difference  In  constitution 
represented  by  these  two  formula  is  "justified  as  follows:  (i)  When 
an  ethereal  nitrite  is  treated  with  an  alkali,  it  is  readily  converted 
into  an  alcohol  and  an  alkali  nitrite  :  this  shows  that  the  compound 
is  a  true  ethereal  salt  of  nitrous  acid,  the  formula  for  which,  as  already 
shown  (p.  101),  is  probably  HON  :  O.  (2)  When  a  nitro-hydrocarbon 
is  treated  with  a  reducing-agent,  it  yields  an  amine  (e.g.,  C2H.'NH,),  a 
compound  which,  since  it  contains  only  C,  H,  and  N,  must  coutain  the 
N  attached  directly  to  carbon.  On  the  other  hand,  when  an  ethereal 
nitrite  is  treated  with  a  reducing-agent  it  yields  the  corresponding 
alcohol  and  ammonia  ;  since  the  alcohols  contain  O  attached  directly  to 
carbon,  the  ethereal  nitrite  probably  also  contains  0  attached  directly 
to  carbon,  in  which  case  the  N  is  probably  not  attached  directly  to 
carbon,  a  conclusion  confirmed  by  the  ease  with  which  the  C  and  N  are 
parted  in  these  compounds  by  sapooification.  The  nitro-com  pounds 
may  be  regarded  as  derived  from  nitric  acid  in  the  same  way  that  the 
sulphonic  acids  are  derived  from  sulphuric  acid. 

The  nitre-paraffins  are  produced  by  the  inter-action  of  silver  nitrite 
and  alkyl  iodides,  e.g.,  C2HJ  +  AgNO2  =  C2H3'N02  +  Agl.*  The  nilro- 

*  This  reaction  would  seem  to  show  that  silver  nitrite  is  derived  from  a  form  of  nitrous 
acid  in  which  H  was  attached  directly  to  X,  thus,  H  •  NO2.  It  may  be  that  nitrites  txist  in 
two  forms,  as  has  been  argued  for  sulphites  (p.  648).  It  is  necessary  to  add,  however,  that 
in  most  cases  much  ethereal  nitrite  is  produced,  tog-ether  with  the  nitro-paramn,  by  this 
method. 


650 


NITROBENZENE. 


hydrocarbons    of  the   benzene  series,  however,   result   from  the   direct 
action  of  nitric  acid  on  the  hydrocarbons  (p.  549). 

When  the  hydrocarbon  has  a  side-chain,  strong  nitric  acid  yields  a  nucleal  nit.ro- 
compound,  but  dilute  acid  introduces  the  nitro-group  into  the  side-chain.  While 
it  is  easy  to  introduce  one  or  two  nitro-groups  into  an  aromatic  nucleus,  the 
direct  introduction  of  the  third  is  difficult,  and  more  than  three  have  not  been 
introduced. 

The  nitro-paraffins  can  be  primary,  secondary,  or  tertiary  like  all  other  open- 
chain  hydrocarbon  substitution-products.  The  three  forms  have  the  same 
structure  as  the  three  forms  of  alcohols,  N02  being  substituted  for  OH  (p.  567). 
The  distinctive  behaviour  of  the  three  kinds  with  nitrous  acid  has  been  given  at 
p.  569.  The  primary  and  secondary  nitro-paraffins  contain  hydrogen  attached  to 
the  same  carbon  atom  as  that  to  which  the  N02  is  attached  ;  the  close  proximity 
of  the  N02  to  the  H  imparts  an  acid  character  to  the  latter,  so  that  this  may 
be  exchanged  for  metals,  such  compounds  as  CHg'CHNa'NOo  and  (CH3)2  :  CNa'N02 
being  produced  by  the  action  of  alcoholic  soda  on  the  nitro-paramn  ;  compare  the 
influence  of  two  COOH  group  on  a  CH2  group  (p.  587).  The  nitro-aromatic  com- 
pounds having  the  nitro-group  or  groups  in  the  nucleus  are  of  a  tertiary  character, 
but  when  the  group  or  groups  are  in  the  side-chain  all  three  kinds  may  exist.* 

Nitre-methane  boils  at  101°  C.  ;  hydrolysis  (by  strong  HC1  at  150°  C.)  converts 
it  into  formic  acid  and  hydroxylamine.  Nitro-ethane  boils  at  113°  C.  ;  it  gives  a 
blood-red  colour  with  ferric  chloride,  and  burns  with  a  luminous  flame.  Both  are 
heavier  than  water. 

Trichloronitromethane  or  chloropicrin  or  n'dro-chloroform,  CC13N02,  is  a  pro- 
duct of  the  joint  action  of  nitric  acid  and  chlorine  on  many  hydrocarbon 
derivatives.  It  is  best  obtained  by  heating  picric  acid  (</.<'.)  with  chloride  of 
lime,  when  it  distils  over  as  a  heavy  liquid  (sp.  gr.  1.69),  boiling  at  112°  C.  and 
possessed  of  a  tear-exciting  odour.  Nascent  H  reduces  it  to  -methylaniine,  HC1 
and  H20. 

Nitrobenzene,  C6H5'N02,  has  already  been  noticed  (p.  540).  It  is  prepared  on 
the  large  scale  by  slowly  running  a  mixture  of  1280  Ibs.  of  strong  HN03  and 
1790  Ibs.  of  strong  H2S04  into  1000  Ibs.  of  benzene  contained  in  a  cast-iron 
cylinder  well  cooled  by  water,  and  provided  with  an  agitator  ;  after  some  8  or 
10  hours  the  process  is  complete  and  the  product  is  washed  with  water.  If  the 
temperature  be  allowed  to  rise  above  50°  C.  during  the  preparation  of  nitro- 
benzene, the  three  dinitrobenzenes  are  produced.  Since  they  may  be  regarded 
as  being  formed  from  the  further  nitration  of  nitrobenzene,  it  is  only  in  accord- 
ance with  the  general  rule  (p.  547)  that  I  :  3-dinitrobenzene  is  the  chief  product  ; 
this  crystallises  in  pale  yellow  needles  and  melts  at  90°  C.  The  i  :  2-  and  i  ;  4- 
dinitrobenzenes  are  colourless  and  melt  at  116°  and  172°  C.  respectively.  The 
three  can  be  separated  by  fractional  crystallisation  from  alcohol.  They  yield 
the  corresponding  nitranitines,  C6H4(NH2)(N02),  and  dianudobenze.net  or  yhemjl- 
enediamlnes,  C6H4(NH2)2  when  reduced."  The"  i  :  2-derivative  differs  from  the 
others  in  the  comparative  ease  with  which  one  nitro-group  can  be  exchanged  for 
other  radicles  (<?.</.,  for  OH,  forming  i  :  2-nitrophenol,  C6H4(OH)(N02),  when  heated 
with  hot  alkalies). 

By  nitrating  toluene,  i  :  2-  and  i  :  ^-mtrotoluene,  C6H4(CH3)(N02),  are  mainly  pro- 
duced ;  the  former  is  a  liquid  boiling  at  223°  C.,  the  latter  a  solid  melting  at  54°  C. 
and  boiling  at  237°  C.  i  :  •$-Xitrotoluene  has  m.-p.  16°  C.,  and  b.-p.  230°  C. 

Trlnitrotertlarybutyltoluene,  (N02)3C6H(CH3)C(CH3)3[(N02)3  :  CH3  :  C(CH3)3=: 
2  :  4  :  6  :  I  :  3],  is  obtained  by  nitrating  various  butyltoluene  derivatives,  and  is  sold 
as  artificial  -tnuslt,. 

tk-Nitronaphthalene^  C10H7N02,  is  produced  by  boiling  naphthalene  in  glacial 
acetic  acid  with  strong  nitric  acid  ;  it  crystallises  in  yellow  prisms,  melts  at  61°  C. 
and  boils  at  304°  C.  It  is  used  for  making  dyes  and  for  destroying  the  fluorescence 
of  paraffin  oils  when  these  are  used  to  adulterate  vegetable  oils.  It  is  soluble  in 
alcohol  but  not  in  water. 

*  The  salts  of  the  primary  and  secondary  nitre-compounds  appear  to  be  derived  from  a 
tautomeric  form,  the  isonitro-compound,  e.g.,  CHyCHrNC^H  ;  for  when  treated  with  acids 
they  yield  a  free  iiitro-compouiid  which  at  first  shows  reactions  differing  from  those  of  the 
original  nitre-compound,  such  as  a  colouration  with  Fe2Cl6  ;  afterwards  it  resumes  the  usual 
properties. 


ZINC   ETHYL.  651 

Other  nitre-derivatives  will  be  considered  under  the  classes  of  bodies  from  which 
they  are  derived. 

VIII.   ORGANO-MINEKAL  COMPOUNDS. 

436.  The  importance  of  these  compounds  resides  mainly  in  the  light 
they  throw  upon  the  theory  of  valency  and  in  the  fact  that  many  of 
them  are  volatile  without  decomposition,  thus  yielding  evidence  of  the 
atomic  weight  of  their  elements  (p.  318).  They  maybe  regarded  as 
formed  on  the  type  of  the  chlorides  of  the  mineral  elements  by  the  sub- 
stitution of  hydrocarbon  radicles  for  the  chlorine.  Those  containing 
alkyl  groups  (alkides)  have  been  best  studied,  and  it  has  been  found 
that  in  the  case  of  the  compounds  from  the  more  electro-negative  ele- 
ments the  subtraction  of  one  or  more  alkyl  groups  from  the  saturated 
compound  yield  monovalent  or  polyvalent  radicles.  For  example,  tin 
methide,  Sn(CH3)4,  is  a  saturated  alkyl  derivative  of  Sniv ;  by  treatment 
with  iodine,  one  CH3  is  removed  and  Sn(CH3)3I  is  produced.  This  is 
the  iodide  of  a  monovalent  radicle,  Sn(CH3)3,  which  behaves  like  an 
alkali  metal,  forming  a  powerful  base,  Sn(CH3)3OH,  obtained  by  treating 
the  iodide  with  NaOH.  Like  other  monovalent  radicles,  such  as  CH3, 
Sn(CH3)3  cannot  exist  alone,  but  is  known  in  its  double  form,  Sn2(CH3)6, 
like  C9H6.  When  two  alkyl  groups  are  removed,  the  divalent  radicle, 
Sn(CH3)2,  is  produced ;  this  resembles  a  divalent  metal  and  forms  a 
base  Sn^CEy.jO ;  like  CH2  it  exists  alone  only  in  the  form  Sn2(CH3)4. 

The  most  important  method  of  producing  these  compounds  is  by 
the  action  of  metals  on  the  monohalogen  substituted  hydrocarbons. 
The  typical  case  is  that  of  zinc  ethide,  which  will  be  considered  first. 

Zinc  alkides. — Zinc  ethyl  or  zinc  ethide,  Zn(C2H5)2,  is  prepared  in 
accordance  with  the  equation  Zn.,  +  2C2H.I  =  Zn(C2H5)2  +  ZnI2. 


Fig.  278. — Preparation  of  zinc  ethyl. 

Fifty  grams  of  bright,  freshly  granulated  and  well-dried  zinc  are  placed  in  a 
flask  E  (Fig.  278)  connected  with  a  C02  apparatus  A,  the  gas  from  which  is 
by  strong  H0S04  in  bottles  B  and  C.     The  flask  is  also  connected  ™th  the  tube  , 
of  condenser  F,  the  other  end  of  which  is  sealed  by  mercury  in  D.     The  appai 
having   been  filled  with  C02,  the  cork  of  the  flask  is  removed,  and  25  gia 


652  PREPARATION  OF  ZINC   ETHYL. 

ethyl  iodide  (perfectly  free  from  moisture)  are  introduced,  the  cork  being  then 
replaced.*  C02  is  again  passed  for  a  short  time,  and  then  cut  off  by  closing  the 
nipper-tap  (T),  when  the  gas  escapes  through  the  mercury  seal  (G-).  A  gentle  heat 
is  then  applied  by  a  water-bath  to  the  flask  (E)  till  the  ethyl  iodide  boils  briskly, 
the  vapour  being  condensed  in  the  tube  (/),  and  running  back  into  the  flask.  In 
about  five  hours  the  conversion  is  complete,  and  the  iodide  ceases  to  distil.  The 
nipper-tap  (T)  is  again  opened,  and  a  slow  current  of  C02  is  passed,  the  position  of 
the  condenser  (F)  is  reversed  (Fig.  279),  and  the  tube  (/)  is  connected  by  the  cork 
(K)  with  the  short  test-tube  (0)  ;  the  longer  limb  of  a  very  narrow  siphon  (I)  of 
stout  tube  passes  through  a  second  perforation  in  the  cork  (K),  the  shorter  limb 


Fig.  279. — Collection  of  zinc  ethyl. 

passing  into  the  very  short  test-tube  (P),  the  cork  of  which  is  also  furnished  with 
the  short  piece  of  moderately  wide  tube  (L).  For  receiving  and  preserving  the 
zinc  ethyl,  a  number  of  small  tubes  are  prepared  of  the  form  shown  in  Fig.  280. 
The  long  narrow  neck  (R)  of  one  of  these  is  passed  down  the  short  tube  (L)  to  the 
bottom  of  P,  the  other  end  (N)  of  the  tube  being  connected  with  an  apparatus  for 
passing  dry  C02.  The  whole  of  the  apparatus  being  filled  with  this  gas,  the  nipper- 
tap  is  closed,  and  the  flask  (E)  heated  on  a  sand-bath,  so  that  the  zinc  ethyl  may 

distil  over,  a  slow  stream  of  car- 

„ if  bonic  acid  gas  being  constantly 

•**  —  passed  into  P,  the  excess  escaping 

through  L.     When  enough  zinc 
ethyl  has  collected  in   the  tube 
(0),  a  blowpipe  flame  is  applied 
Fig.  280.  to   the  narrow  tube  (N),  which 

is   drawn   off  and    sealed  ;   the 

siphon  tube  (I)  is  then  gradually  pushed  down,  so  that  its  longer  limb  may  be 
sufficiently  immersed  in  the  zinc  ethyl,  and  the  nipper-tap  (T,  Fig.  278)  is  opened, 
when  the  pressure  of  the  carbonic  acid  gas  forces  over  a  part  of  the  zinc  ethyl  into 
the  tube  (P).  By  heating  the  tube  (M)  with  a  spirit-lamp,  so  as  to  expel  part  of 
the  gas,  allowing  it  to  cool,  it  will  become  partly  filled  with  zinc  ethyl,  and  may  be 
withdrawn  and  quickly  sealed  by  the  blow-pipe.  The  spontaneous  inflammability 
of  the  zinc  ethyl,  and  its  easy  decomposition  by  water,  render  great  care  necessary 
in  its  preparation.  If  an  alloy  of  zinc  with  one-fourth  its  weight  of  sodium  be 
employed,  the  conversion  may  be  effected  in  an  hour. 

The  reaction  in  the  preparation  of  zinc  ethide  really  occurs  in  two  stages  ;  when 
the  ethyl  iodide  ceases  to  distil,  the  flask  contains  zinc-  iodo-et/tide,  ZnIC2H5, 
as  a  crystalline  solid,  decomposed  by  a  higher  temperature  into  zinc  ethide  and 
zinc  iodide  ;  2ZnIC2H5  =  Zn(C2H5)2  +  ZnI.  The  action  is  more  rapid  if  the  zinc  be 
polarised  by  copper.  To  effect  this,  CuO  is  reduced  by  heating  it  in  a  tube  in  a 
current  of  hydrogen  or  coal-gas,  and  10  grams  of  it  are  mixed  with  90  grams  of 
zinc-filings  in  a  300  c.c.  flask,  which  is  then  .heated  with  continual  shaking,  until 
the  mixture  forms  grey  granular  masses.  After  cooling,  87  grams  of  ethyl  iodide 
are  added,  and  the  mixture  heated  to  about  90°  C.  with  the  reversed  condenser, 

*  The  process  is  said  to  be  much  accelerated  if  about  g^th  of  zinc  ethyl  is  dissolved  in  the 
ethyl  iodide. 


BORON  AND  SILICON  ALKIDES. 


653 


till  no  more  liquid  distils  back,  which  requires  about  15  minutes  ;  the  rest  of  the 
operation  is  conducted  as  described  above,  using  a  sand-bath  or  an  oil-bath. 

Zinc  ethide  is  a  colourless  liquid  of  peculiar  odour,  sp.  gr.  1.18,  b.-p. 
1 1 8°  C.  In  contact  with  air,  it  inflames  spontaneously,  burning' with 
a  bright  greenish-blue  flame,  emitting  a  white  smoke  of  ZnO.  If  a  piece 
of  porcelain  be  depressed  upon  the  flame,  a  deposit  of  metallic  zinc  is 
formed,  surrounded  by  a  ring  of  oxide,  yellow  while  hot  and  white  on 
cooling.  Dissolved  in  ether  and  treated  with  oxygen,  it  yields  zinc 
ethoxide,  Zn(OC2H5)2,  a  white  powder.  Water  decomposes  it  readily, 
ethane  or  ethyl  hydride  being  evolved;  Zn(C2H5)9  +  H20  =  ZnO V 
2(C2H5'H).  When  NH3  is  passed  into  the  solution °of  zinc  ethide  in 
ether,  C2H6  is  evolved,  and  a  white  precipitate  of  zinc  amide  deposited— 
Zn(C2H5)2  +  2NH3  =  2(C2H5-H)  +  Zn(NH2)2. 

Zinc  ethide  and  ethyl  iodide,  dissolved  in  ether  and  heated  to  170°  C., 
yield  butane,  or  di-ethyl ;  Zn(C2H5)2  +  2C2ELI  =  ZnI2  +  2(C2H5)2.  Heated 
with  sulphur,  zinc  ethide  is  converted  into  zinc  mercaptide,  Zn(SC2H5)9, 
the  analogue  of  zinc  ethoxide  and  zinc  hydroxide.  Zinc  ethide  is  much 
used  in  organic  research,  especially  for  effecting  the  substitution  of  C  H 
for  Cl,  Br,  I,  or  OH. 

Dissolved  in  ether  and  heated  with  Na  in  a  sealed  tube,  zinc  ethide  exchanges 
one-third  of  its  Zn  for  Na,  forming  a  crystalline  compound  of  zinc  ethide  with 
sodium  ethide,  3Zn(C2H3)2  +  Na,2  =  2(Zn(C2H5)2-NaC2H5)  +  Zn.  When  this  is  treated 
with  dry  C02,  zinc  ethide  distils,  and  sodium  propionate  remains  ;  NaC2H5  +  COo  = 
C2H5-C02Na. 

Zinc  met/tide,  or  zinc  methyl,  Zn(CH3)2,  prepared  from  methyl  iodide,  like  zinc 
ethide,  which  it  resembles,  boils  at  46°  C.,  and  has  a  more  powerful  odour,  pro- 
ducing irritation.  It  is  more  energetic  in  its  reactions  than  zinc  ethide,  and  is 
decomposed,  with  inflammation  and  explosion,  by  water,  yielding  methane. 

437.  Boron  Alkides. — Boron  methide,  B(CH3)3,  formed  by  the  action  of  a  strong 
ethereal   solution   of    Zn(CH3)2    upon   ethyl  'borate,    2(C2H5)3B03  +  3Zn(CH3)2  = 
2B(CH3)3  +  3Zn(0'C2H5)2,  is  a  gas  with  an  intolerably  pungent,  tear-exciting  odour, 
liquefied  by  three  atmospheres  pressure.     When  issuing  very  slowly  into  the  air,  it 
undergoes  partial  oxidation,  with  phosphorescence,  but  when  it  comes  rapidly  into 
contact  with  air,  it  burns  with  a  green  flame,  remarkable  for  the  immense  quantity 
of  large  flakes  of  carbon  which  it  emits. 

Boron  ethide,  or  triborethijl,  B(C2H5)3,  is  prepared  bypassing  vapour  of  boron 
chloride  into  zinc  ethide  ;  2BCl3  +  3Zn(C2H5)2  =  2B(C2H5)3  +  3ZnClg.  It  is  a  colour- 
less liquid  of  irritating  odour,  and  insoluble  in  water.  Its  sp.  gr.  is  0.69,  and  it 
boils  at  95°  C.  It  inflames  spontaneously  in  air,  burning  with  a  green  flame,  and 
explodes  in  contact  with  pure  oxygen.  Water  slowly  converts  it  into  B(C2H5)2OH,. 
another  spontaneously  inflammable  liquid.  By  gradual  oxidation  in  air  it  becomes 
BC2H5(OC2H5)2,  decomposed  by  water,  into  alcohol  and  et/tyl-boricacid,BC2}is(OH)2, 
which  is  a  volatile  crystalline  body,  subliming  in  scales  like  boric  acid,  and  having 
a  very  sweet  taste  and  a  pleasant  smell  ;  it  is  very  soluble  in  water,  alcohol,  and 
ether. 

438.  Silicon   Alkides. — Silicon    methide,    Si(CH3)4,  produced  by  the   action   of 
SiCl4  upon  Zn(CH3)2,  is  a  liquid  lighter  than  water,  burning  in^air,  and  producing; 
a  white  smoke  of  silica.     It  is  stable  in  water,  and  boils  at  30°  C.    Silicon  ethide, 
or  Si(C2H5)4,  obtained  by  a  similar  process,  resembles  the  methide,  but  boils  at 
153°  C.     In  its  chemical  relations  it  resembles  the  paraffin  hydrocarbons,  and  is 
sometimes  called  silico-nonane,  the  ninth  member  of  the  paraffin  series,  CflH^,  in 
which  silicon  is  exchanged  for  an  atom  of  carbon.    When  acted  on  by  chlorine,, 
it   yields   SiC8HiqCl;  when   this  is  heated  with  potassium  acetate,  in  alcoholic 
solution,  it  yields  the  acetate  SiC8H19'C2H302,  and  by  heating  this  with  alcoholic 
solution  of  potash,  it  is  converted  into  silico-nonyl  alcohol,  SiC8H19'OH,  boiling  at 

I9By  acting  on  ethyl  orthosilicate,  Si(OC2H5)4,  with  zinc  ethide  and  sodium,  siliron 
triethyl  ethoxide  Si(C2H5)./OC2H5,  silicon  diethyl-diethoxide,  Si(C2H5)fc(OC2Hg)2,  and 


654  PHOSPHINES. 

silicon  et/iyl-triethoj'ide,  SiC.2H5(OC.2H5)3,  may  be  produced.  When  the  last  named 
is  heated  with  acetyl  chloride,  it  yields  silicon  ethyl  trichloride,  SiC2H5Cl3,  which 
is  converted  by  water  into  silico-2)ropionic  acid,  C.2H5-SiOOH,  a  solid,  feeble  acid. 
Silica-acetic  acid,  CH3'SiOOH,  is  also  known. 

439.  Phosphines. — These  compounds  being  formed  on  the  type  of 
PH3,  the  analogue  of  NH3,  are  primary,  secondary,  and  tertiary,  like 
the  alkylamines,  as  explained  in  the  next  section. 

Tri-ethyl  phosphine,  P(C2H5)3,  a  tertiary  phosphine,fis  prepared  by 
very  gradually  dropping  PC13  into  a  solution  of  zinc  ethide  in  ether, 
in  a  retort  connected  with  a  receiver  filled  with  C02 ;  a  very  violent 
action  occurs— 2PC13  +  3Zn(C2H5)2  =  sZnCL,  +  2P(C2H5)3.  The  upper 
layer  of  the  distillate  contains  the  excess  of  PC13  and  ether,  the  lower 
being  a  compound  of  ZnCl2  with  tri-ethyl  phosphine,  which  may  be 
separated  by  careful  distillation  with  KOH  in  a  retort  filled  with  H. 
It  is  also  obtained  by  heating  phosphonium  iodide  with  alcohol,  in 
a  sealed  tube,  to  180°  C. ;  PH4I  +  3C2H5OH  =  P(C2H5)3'HI  +  3HOH  ; 
the  hydriodide  is  distilled  with  KOH.  Tri-ethyl  phosphine  is  a 
liquid  of  strong  odour,  sp.  gr.  0.81,  and  b.-p.  127°  C.  It  behaves 
like  a  divalent  metal  of  the  calcium  group,  absorbing  "0  from  the  air, 
becoming  hot  and  exploding  below  100°  C.  It  forms  salts  with  the 
acids  and  its  oxide,  P(C2H5)30,  is  a  very  stable  crystalline  substance, 
obtained,  together  with  ethane,  by  distilling  tetrethyl  phosphonium. 
iodide  with  potash ;  P(0,H5)4I  +  KOH  =  P(C2H5)30  +  KI  +  C2H5'H.  The 
tetrethyl-phosphonium  iodide  is  obtained  by  heating  ethyl  iodide  with 
P  in  a  sealed  tube;  4.C2H5I  +  P2  =  P(C2H5)4I  +  PI3.  By  decomposing 
its  aqueous  solution  with  Ag20,  tho  tetrethyl  phosphonium  hydroxide, 
P(C2H5)4OH,  is  produced,  a  strongly  alkaline  substance,  which  may- 
be crystallised  and  is  comparable  with  the  hydroxides  of  the  alkali 
metals. 

The  primary  and  secondary  phosphines,  ethyl  phosphine  P(C2H5)H2, 
and  di-ethyl  phosphine,  P(C2H5)2H,  are  prepared  by  heating  PH4I  with 
C2H3I  and  ZnO,  in  a  sealed  tube  for  some  hours  ;  crystalline  compounds 
of  zinc  iodide  with  the  hydriodides  of  ethyl  phosphine  and  di-ethyl 
phosphine  are  first  formed  ; 

2PH4I  +  2C.,H5I  +  ZnO  =  H00  +  ZnI2  +  2(P(C.2H5)H0.HI),  and 
PH4I  +"C.2H5I  +  ZnO  =  "H20  +  ZnI2  +  P(C2H5)2H.HI. 

These  are  decomposed  by  distillation  with  water  out  of  contact  with 
air,  when  the  phosphines  distil  over. 

Ethyl  phosphine  is  a  feebly  basic  liquid,  boiling  at  25°  C.,  having  an  intolerable 
odour,  insoluble  in  water.  Di-ethyl  phosphine  is  also  liquid,  but  boils  at  85°  C., 
and  is  more  strongly  basic.  Both  compounds,  being  composed  upon  the  PC13 
model,  are  disposed  to  unite  with  other  bodies  to  form  compounds  upon  the  PCI, 
model.  When  oxidised  by  nitric  acid,  they  yield,  respectively,  ethyl  phosphinic. 
acid,  PO(C2H5)(OH)2,  and  di-ethyl  phosphinw  acid,  PO(C2H5)2OH,  composed  upon 
the  'model  of  orthophosphoric  acid,  PO(OH)3,  by  the  substitution  of  eth}rl  for 
hydroxyl. 

"Tri-ethyl  phosphine  combines  violently  with  methyl  iodide,  forming 
P(C.2H5)3CH3-I,  which  yields  an  alkaline  hydroxide  when  decomposed  with  water 
and  "silver  oxide. 

Tri-ethyl  phosphine  combines  with  sulphur,  evolving  heat,  and  forming 
P(C.2H5)3S,  which  crystallises  in  needles  from  solution  in  hot  water.  It  also  com- 
bines energetically  with  CS2,  forming  a  fine  red  crystalline  compound  soluble  in 
alcohol,  and  forming  a  test  for  CS2  in  coal  gas. 

The  methyl  phosphines  are  similar  to  the  ethyl  compounds  and  are  similarly 
prepared. 


KAKODYL. 

Phe.nylphosphlne  (phosphamlhw),  PH2'C6H5,  is  prepared  by  the  action  of  HI  on 
phosphenyl  chloride,  PC6H5C12  ;  it  is  a  liquid  of  intense  and  repellent  odour,  boils 
at  1 60°  C.,  and  absorbs  oxygen  from  the  air  to  form  the  soluble  crystalline  p/iem/l- 
phosphnie  oxide,  C6H5PH.20. 

Phospkenyl  chloride,  PC6H5CL2,  obtained  when  mercury  diphenyl  (C6H5)2Hg  is 
heated  with  PC13,  is  a  liquid  which  combines  with  Cl  to  form  crystals  of  the 
tetrach  loride,  PC6H5C14.  When  treated  with  water  it  yields  phenyl  h  yi>ophwphorou* 
acid  (phosphenylons  add),  C6H5'PHO(OH).  From  the  tetrachlorid'e,  phenyl  p/iox- 
phlnic  acid  (phosphenylic  acid],  C6H5'PO(OH)2,  is  similarly  prepared. 

Phosphenyl  chloride  arid  phenylphosphine  react  to  form  ph-oxnhoben~ene 
C6H5-P  :  P'C6H5,  the  analogue  of  azobenzene,  C6H5'N  :  N'C6H5. 

440.  Arsines.  While  the  alkyl  derivatives  of  NH3  and  PH3  are 
strongly  basic,  those  of  AsH3  are  not.  Moreover,  only  the  tertiary  and 
secondary  derivatives  are  known.  The  divalent  radicles  like  As(CH3).,, 
however,  give  rise  to  salt-forming  oxides,  and  the  radicles  themselves 
exist  in  double  form. 

Trimethyl  arsine,  As(CH3)3,  or  Kd.,  is  obtained  by  the  action  of  AsCl3 
on  zinc  methide.  It  is  a  strong-smelling  liquid,  boiling  at  about  70°  C., 
and  resembling  P(C2H5)3,  but  not  forming  salts  with  the  acids. 

Ar sen- dimethyl,  or  kakodyl,  As(CH3)2,  has  a  special  interest  as  hav- 
ing been  one  of  the  first  bodies  recognised  as  a  compound  radicle  capable 
of  behaving  like  an  elementary  substance.  The  formula  As(CH3)2  repre- 
sents only  one  volume  of  vapour,  so  that  it  must  be  doubled  to  represent 
a  molecule,  conveniently  termed  dikakodyl.  The  oldest  compound  of 
kakodyl  is  the  dikakodyl  oxide,  Kd20,  or  alcarsin,  or  arsenical  alcohol, 
named,  after  its  discoverer,  Cadet's  fuming  liquid,  and  obtained  by  dis- 
tilling a  mixture  of  equal  weights  of  white  arsenic  and  potassium  acetate — 

As406  +  8CH3C02K  =  2[As(CH3)2]20  +  4C02  +  4K2C08. 

The  distillate  has  a  strong  odour  of  garlic,  and  takes  fire  spontaneously, 
owing  to  the  presence  of  dikakodyl.  It  is  received  in  water,  when  it 
sinks  to  the  bottom;  sp.  gr.  1.46,  b.-p.  120°  C.  It  combines  with 
acids  to  form  salts,  and  dissolves  in  alcohol,  the  solution  giving,  with 
alcoholic  mercuric  chloride,  a  crystalline  precipitate  of  Kd.,0.2HgCl.,. 
By  distilling  this  precipitate  with  strong  HC1  in  a  retort  filled  with 
C02,  kakodyl  chloride,  KdCl  is  obtained  as  a  heavy  spontaneously 
inflammable  liquid,  of  terrible  odour.  When  this  is  heated  to  100°  C. 
with  zinc  in  an  atmosphere  of  C02,  a  compound  of  ZnCl2  with  kakodyl 
is  produced,  and  on  treating  this  with  water  dikakodyl  separates  as  a 
heavy  oily  liquid  which  boils  at  170°  C.  It  inflames  spontaneously  in 
air,  and  when  its  vapour  is  passed  through  a  tube  heated  to  400°  C.,  it 
is  decomposed — As2(CH3)4  =  2CH4  +  C2H4  +  As2.  When  slowly  oxidised 
by  air,  it  is  converted  into  Kd2O,  which  is  afterwards  converted,  in 
presence  of  water,  into  kakodylic  acid,  KdO'OH,  or  dimethyl-arsenic  acid, 
AsO(CH3)2-OH,  i.e.,  arsenic  acid,  AsO(OH)s,  in  which  two  OH  groups 
are  exchanged  for  (CH3)2.  This  acid  is  best  prepared  by  oxidising 
Kcl.,0  with  mercuric  oxide  in  presence  of  water — Kd20  +  2HgO  +  H20  = 
2Kd02H  +  Hg9.  It  crystallises  from  the  aqueous  solution,  and  is  a 
stable  acid. 

Sulphur  dissolves  in  dikakodyl,  forming  Kd2S,  a  colourless  liquid  of  unpleasant 
smell,  which  behaves  like  an  alkali  sulphide/  Kd2S2  is  a  solid  which  may.  be 
crystallised  from  alcohol. 

Kakodyl  cyanide,  KdCN,  prepared  by  distilling  kakodyl  chloride  with  mercuric 
cyanide,  forms  lustrous  prismatic  crystals,  m.-p.  37°  C.,  b.-p.  140°.  It  is  nearly 
insoluble  in  water,  but  dissolves  in  alcohol.  Its  vapour  is  very  poisonous. 


656  HEAVY  METAL   ALKIDES. 

Kaltodyl  trichloride,  As(CH:j)2Cl3,  is  composed  upon  the  model  of  AsCl5.  whilst 
the  chloride,  As(CH3)aCl,  is  formed  after  AsCl3.  The  chloride  ignites  in  Cl,  but, 
if  it  be  dissolved  in  CS2,  the  action  of  Cl  converts  it  into  crystals  of  the  trichloride. 
When  this  is  heated,  it  evolves  CH3C1,  and  a  heavy  irritating  liquid  distils,  which 
is  arsenmethyldichloride.  AsCH3C]2,  boiling  at  133°  C.,  andsoluble  in  water  without 
decomposition.  By  evaporating  the  solution  with  Na^CO.,,  and  extracting  the 
residue  with  alcohol  and  crystallising,  arsenmethyl  oxide,  AsCH30,  is  obtained.  The 
crystals  smell  like  assafcetida.  Mercuric  oxide  in  the  presence  of  water,  converts 
the  oxide  into  metJiyl-arsiiiic  acid,  AsCH30(OH)2. 

With  methyl  iodide,  dikakodyl  yields  kakodyl  iodide  and  tetrameth  yl-ar$onium 
iodide,  As2(CH3)4+2CH3I  =  As(CH3)2I  +  As(CH3)4I  ;  this  last,  when  decomposed  by 
moist  silver  oxide,  yields  the  corresponding  hydroxide,  As(CH3)4OH,  which  is 
strongly  alkaline,  and  may  be  crystallised. 

Dimethylarsine,  (CH3)2AsH,  is  a  spontaneously  inflammable  liquid  (b.-p.  36°  C.), 
obtained  by  the  action  of  Zn  and  HC1  on  an  alcoholic  solution  of  KdCl. 

The  ethyl  compounds  of  arsenic  are  in  every  respect  similar  to  the 
methyl  compounds. 

441.  Antimony  Alkides. — Antimony  forms    compounds  with  the  hydrocarbon 
radicles,  composed  upon  the  models  SbCl3  and  SbCl5. 

Stibio-trimethyl,  or  trimethyl  stibi'iie,  Sb(CH3)3,  is  prepared  by  distilling  in  a 
current  of  C02  methyl  iodide  with  the  potassium  antimonide  obtained  by  strongly 
heating  tartaVemetic  ;  3CH3I  +  K3Sb  =  3KI  +  (CH3)3Sb.  The  powdered  anti- 
monide must  be  mixed  with  sand  to  moderate  the  action.  The  product  is  a 
garlic-smelling  liquid,  of  sp.  gr.  1.52,  and  boiling  at  80°  C.  It  is  insoluble  in 
water,  but  dissolves  in  ether.  By  the  slow  action  of  air  it  is  converted  into 
Sb(CH3)30,  but  is  liable  to  take  fire.  It  combines  with  chlorine  and  iodine,  forming 
Sb(CH3)3Cl2  and  Sb(CH3)3I2,  which  may  be  crystallised,  and  are  formed  upon  the 
model  of  SbCl5.  Stibio-trimethyl  combines  at  once  with  methyl  iodide,  forming 
Sb(CH3)4I  as  a  white  solid,  crystallising  in  six-sided  plates  from  hot  water.  When 
decomposed  by  Ag20  in  presence  of  water,  it  yields  a  strong  alkali,  tetrameth  yl- 
stibonium  hydroxide,  Sb(CH3)4OH,  which  may  be  crystallised,  and  forms  crystal- 
Usable  salts. 

Stibio-pentamethyl,  Sb(CH3)5,  composed  on  the  model  of  SbCl5,  is  obtained  by 
distilling  stibio-trimethyl  iodide  with  zinc  methide. 

Stlbio-tri-etliyl,  or  tri-ethijl  stibine,  Sb(C2H5)»,  is  obtained  like  stibio-trimethyl  ; 
or  by  acting  on  antimonious  chloride  with  zinc  ethide  ;  2SbCl3  +  3Zn(C2H5j2=: 
2Sb(C2H5)3+3ZnCl2.  It  resembles  the  methyl  compound,  but  boils  at  158°  C.  It 
is  remarkable  for  behaving  like  a  metal ;  even  decomposing  hydrochloric  acid  and 
liberating  hydrogen;  Sb(C2H5)3  +  2HCl  =  Sb(C2H5)3Cl2  +  H2.  The  chloride  is  an 
oily  liquid  smelling  like  turpentine.  Its  salts  behave  like  those  of  the  alkalies. 

Bismuth  tri-ethyl,  Bi(C2H5)3,  is  prepared  by  acting  on  ethyl  iodide  with  an  alloy 
of  potassium  and  bismuth.  It  is  a  spontaneously  inflammable  liquid  which  is 
very  unstable,  depositing  bismuth  even  below  100°  C.,  and  exploding  at  150°. 
As  might  be  expected  from  the  non-existence  of  BiCl5,  bismuth  tri-ethyl  shows  no 
disposition  to  combine  directly  with  the  halogens,  its  derivatives  being  formed  on 
the  model  of  BiCl3. 

442.  Lead  Alkides. — The  compounds  of    lead  with    alcohol    radicles    are   not 
composed  upon  the  model  of  the  stable  chloride,  PbCl2,  but  upon  that  of  PbCl4, 
which  is  not  known  in  the  pure  state. 

Lead  tetrameth  yl,  Pb(CH3)4,  is  formed  by  the  action  of  zinc-methyl  upon  lead 
chloride;  2Zn(CH3)2  +  2PbCl2  =  2ZnC]2  +  Pb(CH3)4  +  Pb  ;  it  distils  at  110°  C.,  and 
has  the  sp.  gr.  2.03.  It  has  a  faint  odour,  is  unaffected  by  air,  and  is  insoluble  in 
water.  Heated  with  HC1— Pb(CH3)4  +  HCl  =  Pb(CH3)3Cl  +  CH4.  The  chloride  is 
crystalline,  and  may  be  sublimed  ;  by  reaction  with  KI  it  gives  colourless  crystals 
of  Pb(CH3)3I,  and  when  this  is  distilled  with  potash,  Pb(CH3)3'OH  is  obtained  as  a 
strongly  alkaline  body  smelling  like  oil  of  mustard. 

Lead  tetrethyl,  Pb(C2H5)4,  and  its  derivatives  resemble  the  methyl  compounds. 

Lead  tri-ethyl,  Pb(C2H5)3,  is  obtained  by  the  action  of  ethyl  iodide  upon  an  alloy 
of  sodium  and  lead.  This  combines  with  iodine  in  alcoholic  solution,  forming 
Pb(C2H5)3I,  which  yields  a  hydroxide,  like  the  corresponding  methyl  compound. 

443.  Mercury  Alkides. — Mercuric  met/tide,  Hg(CH3)2,  may  be  obtained  by  the 
reaction  between  mercuric  chloride  and  zinc  methide,  but  better  by   dissolving 


TIN  ALKIDES.  657 

one  part  of  sodium  in  one  hundred  parts  of  mercury,  and  adding  the  amalgam  by 
degrees,  to  methyl  iodide  mixed  with  one-tenth  of  its  volume  of  ethyl  acetate 
the  action  of  which  has  not  yet  been  explained.  On  distillation,  the  mercuric 
methide  is  obtained  as  a  colourless  liquid  which  is  one  of  the  heaviest  known  its 
sp.  gr.  being  3.07,  so  that  glass  floats  in  it.  It  is  unchanged  by  exposure  to  air, 
but  gives  otf  a  faint  odour  which  is  very  poisonous.  It  boils  at  95°  C  and  burns 
with  a  bright  flame.  With  strong  HC1,  Hg(CH3)2  +  HC1  =  HgCH.,Cl  +  CH3'H. 

Mercuric  ethide,  Hg(C2H5)2,  is  prepared  like  the  methide.  It  has  the  sp.  gr.  2.4, 
and  boils  at  159°  C.  Its  vapour  is  decomposed  at  200°  C.  into  Hg  and  butane, 
but  with  strong  H2S04  it  gives  ethane. 

Mercury  ethyl  chloride,  HgC2H5Cl,  is  obtained  by  acting  on  mercuric  ethide  with 
mercuric  chloride  dissolved  in  alcohol ;  Hg(C2H5)2  +  HgCl2  =  2HgC2H5Cl  :  this  shows 
it  to  be  composed  upon  the  mercuric  type,  HgCl2,  and  not  derived  from  the  mer- 
curous  compound  Hg2(C2H5)2,  corresponding  with  Hg2Cl2.  The  chloride  is  insoluble 
in  water,  but  crystallises  from  alcohol,  and  is  easily  sublimed.  Silver  oxide  con- 
verts it  into  the  mercury  ethyl  hydroxide,  HgC2H5OH,  a  caustic  alkaline  liquid 
which  blisters  the  skin.  The  iodide,  HgC2H5I,  obtained  by  treating  Hg(C2H5)2 
with  I2,  is  remarkably  stable,  crystallising  from  hot  caustic  soda,  almost  without 
decomposition.  It  is  hardly  soluble  in  water  or  alcohol. 

Mercury  diphenyl,  (C6H5)2Hg,  is  formed  when  Na-amalgam  acts  on  C6H5Br. 
It  is  a  crystalline  solid  (m.-p.  120°  C.),  subliming  almost  unchanged,  insoluble  in 
water,  and  sparingly  soluble  in  alcohol  and  ether,  but  soluble  in  benzene.  When 
heated,  in  a  sealed  tube,  with  HgCl2  and  alcohol,  it  yields  mercury -phenyl  chloride, 
HgC6H5Cl,  which,  with  silver  hydroxide,  yields  mercury -phenyl  hydroxide, 
HgC6H5'OH,  a  crystalline  strongly  alkaline  base. 

444.  Tin  Alkides. — Tin  tetrametJiide,  Sn(CH3)4,  composed    upon  the  model  of 
stannic  chloride,  SnCl4,  is  obtained  by  the  action  of  an  alloy  of  Sn,  Hg,  and  Na 
upon  CH3I.     It  boils  at  78°  C.    By  the  action  of  iodine,  one  CH3  group  is  removed, 
and  tin  trimetltyl  iodide,    Sn(CH8)3I,  obtained  ;  this,  acted  on  by  NaOH,  yields 
Sn(CH3)3OH,  a  sparingly  soluble,  crystalline,  volatile,  alkaline  base. 

When  CH3I  is  heated  to  160°  C.,  in  a  sealed  tube,  with  tin-foil,  tin  dimethyl 
iodide,  Sn(CH3)2I2  is  formed.  It  crystallises  in  yellow  prisms  soluble  in  water  ; 
NH3  gives  a  white  precipitate  of  the  base  Sn(CH3)20  with  the  solution. 

Tin  tetrethide,  or  stannic  ethide,  Sn(C2H5)4  (b.-p.  181°  C.),  prepared  by  distilling 
stannic  chloride  with  zinc  ethide,  is  remarkably  stable,  even  when  boiled  with 
sodium.  It  is  not  precipitated  by  H2S. 

Like  the  tetramethide,  it  yields  the  iodides  Sn(C2H5)2I2  and  Sn(C2H5)3I.  By 
treatment  with  Na  these  undergo  nucleal  condensation  yielding  a  mixture  of 
Sn2(C2H5)4  and  Sn2(C2H5)6,  which  may  be  separated  by  alcohol  in  which  the  former, 
stannous  ethide,  or  tin  dietliide,  is  insoluble.  It  is  a  liquid  of  sp.  gr.  1.56,  decom- 
posed when  heated ;  8n2(C2H5)4=Sn(C2H5)4  +  Sn.  It  is  an  unsaturated  compound, 
absorbing  oxygen  from  the  air,  and  forming  Sn(C2H5)20,  which  forms  crystalline 
salts,  like  Sn(C2H6)2(N03)2. 

Tin  he,rethide,  Sn2(C2H5)6.  boils  at  270°  C.,  decomposing  into  Sn(C2H5)4  and  Sn. 

445.  Aluminium  methide,  A1(CH3)3,  and  the  corresponding  ethide  are  obtained  by 
decomposing  mercuric  methide  and  ethide  by  Al.     They  are  spontaneously  inflam- 
mable liquids,  violently  decomposed  by  water,  yielding  A12(OH)6  and  methane  or 
ethane.     Their  vapour  densities  are  known. 

Maffoesiunt  methide,  Mg(CH3)2,  and  ethide  me  prepared  by  decomposing  CH3I  or 
CftHgl  with  Mg,  when  a  solid  iodide,  MgCH,I,  is  first  formed,  which  is  decomposed 
when  distilled  in  C02  ;  2MgCH3I  =  Mg(CH3)2  +  MgI2.  They  are  spontaneously 
inflammable  liquids,  yielding  Mg(OH)2  and  CH4  or  C2H6,  with  water. 

Organo-mineral  compounds  similar  to  those  which  have  been  described 
are  formed  by  other  alcohol  radicles  and  benzene  hydrocarbon  residues, 
and  mixed  compounds  are  obtainable. 

Thus,  Sn(CH3).>(C,H5)2  may  be  produced  by  the  action  of  zinc  methide 
upon  Sn(C2HA,Cl0 ;  and  Sn(CH8)3C9H5  is  formed  by  zinc  ethide  with 
Sn(OH8)801.  ° 


2  T 


658 


AMINES. 


IX.  AMMONIA-DERIVATIVES. 

446.  The  organic  compounds  classed  under  this  head  are  derived  from 
NH3  by  substitution  of  radicles  for   H,  and  are  in  many  cases  very 
nearly  related  to  the  organo -mineral  compounds,  since  such  compounds 
as  P(CH3)3,  As(CH3)3,  Sb(CH3)3,  B(CH3)3,  are  formed  upon  the  type  of 
PH3,  AsH3,  SbH3,  and  BH3,  which  are  nearly  allied  to  NH3 ;  but  the 
strongly  alkaline  character  of  ammonia  impresses  special  characters  upon 
the  bodies  derived  from  it.     These  may  be  divided  into — 

(1)  Amines  or  ammonia-bases,  formed  by  the  substitution  of  alcohol 
radicles  for  the   hydrogen  in  ammonia,  such  as  NH2'CH3,  NH(CH3)2, 
N(CH3)3.     This  class  also  includes  the  ammonium  bases,  formed  by  the 
substitution  of  alcohol  radicles  for  hydrogen  in  ammonium  hydroxide, 
NH4OH,   such  as  N(CH3)4OH.      All  these  are  basic,  many  of   them 
powerfully  so. 

(2)  A mides,  derived  from  ammonia  by  the  substitution  of  acid  radicles 
for  hydrogen,  such  as  NH2(CH3CO),  NH(CH3CO)2,  N(CHSCO)3.     These 
may  also  be  regarded  as  formed   from  acids  by  the  exchange  of   i,  2, 
or  3  OH  groups  from  the  COOH  groups  of  the  acid  for  (NH,)',  (NH)", 
and  N'"  respectively.     They  are  only  slightly  basic  compounds,   since 
the  acid  radicle  has  nearly  neutralised  the  basic  character  of  the  parent 
ammonia. 

(3)  Amido-acids,  derived  from  acids  by  the  substitution  of  (NH.,)'  for  H 
in  the  hydrocarbon  residue,  such  as  CH2(NH2)-COOH  from  CH3:COOH. 
These  are  both  basic  and  acid  in  character. 

A  compound  containing  the  group  NH2  is  known  as  an  amide,  one 
containing  NH  is  an  imide,  whilst  one  containing  N>  attached  to  carbon 
only,  is  a  nitrile. 

AMINES  OR  AMMONIA-BASES  AND  AMMONIUM-BASES. 

447.  These   are   called  p>*imary,  secondary,  tertiary,  or  quaternary ', 
accordingly  as  one,  two,  three,  or  four  atoms  of   H  in  NH3  have  been 
exchanged.     The  quaternary  bases  can  only  be  derived  from  NH4OH. 


Amines  or  ammonia  bases. 

Ammonium  -bases. 

Primary  or 
Amido-bases. 

Secondary  or 
Imido-bases. 

Tertiary  or 
Nitrile-bases. 

Quaternary 
bases. 

NH2R' 

NHB'a 

NHR" 

Nil', 

NR"' 

NR'4OH 

Amines  are  also  distinguished  as  monamines,  diamines,  and  triamines, 
accordingly  as  they  are  derived  from  one,  two,  or  three  molecules  of 
ammonia.  The  amines  in  the  above  table  are  examples  of  monamines, 
and  the  following  are  examples  of  the  other  two  classes : 


Diamines. 


Primary 

Secondary 

Tertiary 


N2H4R" 

N2H2R2"  ;  N2R2"R0' 

N3R3"  ;  N9R"R4' 


Triamines. 

N3H6B'" 

N3H3R'"R3'  ;  N-jH-j 
N-R3'"  ;  N3R"'R6'. 


PREPARATION  OF  AMINES. 


659 


The  secondary  and  tertiary  amines  may  be  either  simple  or  mixed, 
that  is  to  say,  the  radicles  H  may  be  either  the  same  or  different 

Generally  speaking  the  amines  share  the  properties  of  ammonia 
forming  crystalline  salts  with  acids,  which,  however,  differ  from  the 
ammonium  salts  in  being  soluble  in  alcohol.  The  amines  containing 
open-chain  radicles  are  somewhat  more  basic  than  NH3,  and  the  basicity 
increases  with  the  number  of  radicles,  NHR2  being  a  stronger  base  than 
NH2R,  and  NR3  stronger  than  either.  The"  amines  containing  aromatic 
radicles  may  have  the  NH,,  NH,  or  N  group  attached  either  to  the 
closed-chain,  like  NH2'C6H5  or  NH  :  (C6H5)2,  or  to  the  side-chain,  like 
NH/CH2-C6H.  and  NH  :  (CH2'C6H.)2  ;  those  of  the  latter  class  behave 
in  every  respect  like  the  fatty  amines,  but  those  in  which  the  nitrogen 
is  attached  to  the  closed-chain  show  slight  differences,  due  to  the  fact 
that  a  closed-chain  nucleus  is  always  somewhat  more  acidic  than  an  open- 
chain  nucleus  ;  thus,  phenylamine  (C6H5'NH2)  is  less  basic  than  ethyl- 
amine  (C2H.'NH2),  because  the  basic  properties  of  ammonia  have  been 
more  neutralised  by  phenyl  than  by  ethyl.  For  the  same  reason,  the 
nucleal  aromatic  amines  show  some  relationship  to  the  amides  and 
amido-acids  (p.  658)  ;  for  instance,  they  readily  undergo  the  diazo- 
reaction  (p.  680)  characteristic  of  amides  and  amido-acids.  Hence  some 
chemists  term  the  aromatic  amines  amido-compounds.  The  difference 
here  denned  is  precisely  similar  to  that  between  the  alcohols  and  phenols 
(see  Phenols). 

The  most  generally  applicable  method  for  preparing  the  amines 
consists  in  reducing  the  corresponding  nitro-compounds  with  nascent 
hydrogen.  Since  the  nitro-compoimds  are  more  easily  obtained  from 
closed-chain  than  from  open-chain  hydrocarbons,  this  method  is  most 
frequently  used  for  preparing  aromatic  amines  ;  C6H3N02  +  H6  = 
C6H5NH2+2H20. 

The  cyanides  of  hydrocarbon  radicles  are  convertible  into  amines  by 
treatment  with  nascent  H;  C2H5'CN  +  H4  =  C2H5-CH2'NH2. 

The  open-chain  amines  can  be  prepared  by  heating  the  hydrocarbon 
halides  with  ammonia  in  alcohol,  but  the  aromatic  amines  cannot 
be  similarly  produced  from  the  nucleal  halogen-substituted  benzene 
hydrocarbons.  For  example,  methylamine,  NH2CH3,  dimethylamine, 
NH(CH3)2,  and  trimethylamine,  N(CH3)3,  in  the  form  of  their 
hydriodides,  and  tetramethyl  ammonium  iodide,  N(CH3)4I,  are  all 
obtained  when  a  strong  solution  of  ammonia  in  alcohol  is  heated  with 
methyl  iodide  for  some  hours,  in  a  sealed  tube  at  100°  C.  The  re- 
actions which  occur  may  be  represented  by  the  following  equations 
(Me  =  CH3): 

(1)  NH,  +    Mel  =  NH2Me-HI  ; 

(2)  2NH3  +  2MeI  =  NHMeaHI  +  NH4I  ; 

(3)  3^H3  +  3MeI  =  NMe3'HI     +  2NHJ  ; 

(4)  4NH3  +  4MeI  =  NMe4I  +  3NH4I. 


The  NH4I  being  nearly  insoluble  in  alcohol  separates  at  once  and  the  hydriodides 
of  the  three  amines  crystallise  on  cooling,  leaving  the  NMe4I  in  solution.  They 
are  distilled  with  KOH  into  a  receiver  cooled  in  ice,  when  a  mixture  of  NMes, 
NHMe.,,  and  a  little  NH2Me  is  condensed,  much  of  the  last  escaping  as  gas  with 
the  NH3  from  the  NH4I.  Any  NMeJ  not  previously  separated  by  crystallisation 
remains  in  the  retort,  as  it  is  not  decomposed  by  KOH.  The  mixed  amines  are 
then  digested  with  ethyl  oxalate,  when  the  NMe3  is  not  acted  on,  and  may  be  dis- 
tilled off.  The  methylamine  is  converted  into  methyloxamide,  and  the  dimethyl- 
amine  into  ethyl  dimethyloxamate  (E  =  C2H3)  — 


660  DISTINCTION   BETWEEN  AMINES. 

CODE   CONHMe 

2NH.2Me  +  •     =  •       +  2EOH 
COOE   CONHMe 

COOE   CONMe., 
600E  -  COOE  • 

Water  at  o°  dissolves  the  last-named  compound,  and  leaves  the  methyloxamide 
undissolved.      On  distillation  with  potash,   the  methyloxamide  yields  potassium 
oxalate  and  methylamine  ;  (CONHMe)2  +  2KOH  =  (COOK2)  +  2NH2Me  ;  and  the 
ethyl  dirnethyloxamate  yields  potassium  oxalate,  dimethylamine,  and  alcohol  — 
C202(NMe2)(OE)  +  2KOH  =  (COOK)2  +  NHMe2  +  EOH. 

The  primary  and  secondary  amines  in  which  there  is  still  ammoniacal 
H  are  capable  of  many  of  the  reactions  of  NH3  ;  the  tertiary  amines, 
having  no  ammoniacal  H,  are  less  reactive. 

On  this  depend  the  reactions  which  distinguish  between  primary, 
secondary,  and  tertiary  amines.  The  amine  is  treated  with  nitrous  acid 
(or,  what  comes  to  the  same  thing,  NaNO2  is  added  to  a  strong  solution 
of  the  amine  hydrochloride).  A  primary  amine  yields  the  corresponding 
alcohol  with  evolution  of  nitrogen  ;  C2H5'NH2  +  HON  :  0  =  C9H5'OH  + 
N2  +  HOH.  (Of.  the  action  of  NH3  on  HNOr)  A  secondary  amine 
yields  a  nitrosamine,  which  separates  in  oily  drops  — 

(C2H5)2NH  +  HO'N  :  0  =  (C2H5)2N'NO  +  HOH. 
A  tertiary  amine  is  unchanged. 

A  primary  amine  can  also  be  distinguished  by  the  carlylamine  reaction. 
The  hydrochloride  is  warmed  with  chloroform  and  alcoholic  KOH  ;  the 
characteristically  disagreeable  odour  of  a  carbylamine  (q.v.)  is  Droduced  ; 


A  nitrosamine  can  be  further  recognised  by  Liebermann's  nitroso-reactlcni  ; 
the  suspected  compound  is  mixed  with  phenol  and  H2S04  cone.  A  nitroso- 
compound  gives  a  dark  green  solution,  becoming  red  when  diluted  and  blue 
when  made  alkaline. 

Another  method  of  investigating  the  constitution  of  an  amine,  is  to  heat  its 
alcoholic  solution  with  methyl  iodide  in  a  sealed  tube  ;  a  tertiary  amine 
yields  a  substituted  ammonium  iodide  by  direct  union  with  methyl  iodide  ; 
N(C0H5)3  +  CH3I  =  N(C2H5)3*CH3I  :  a  secondary  amine  yields  an  ammonium 
iodide  containing  two  methyl  groups'  ;  NH(C2H5)2  +  2CH3I  =  HI  +  N(C2H5)2(CH3)2I  ; 
a  primary  amine  yields  an  ammonium  iodide  containing  three  methyl  groups. 
NH2(C2Hg)  +  3CH3I  =  N(C2H5)(CH3)3I  +  2HL  See,  also,  Mustard-oil  reaction. 

With  organic  chloranhydrides  the  primary  and  secondary  amines  react  to 
form  amides  in  which  the  H  of  the  NH2  group  is  exchanged  for  hydrocarbon- 
radicles  (cf,  p.  667)  ;  thus,  with  acetyl  chloride,  methylamine,  NH2CH3  reacts 
to  form  acetmethylamide—CH9CO'Cl  +  NH0CH3  =  CH,CO-NHCHo  +  HC1  ; 
dimethylamine,  NH(CH3)2,  yields  acetdimefhylamide,  CH3CO'N(CH3)2.  The 
secondary  amines  also  react  with  inorganic  chloranhydrides  to  form  similar 
substituted  amides  (c.f.  p.  265)  ;  thus,  from  POC13  and  NH(CH3)2  is  obtained 
PO[N(CH3)2J3.  Primary  amines  are  apt  to  give  substituted  imides.  such  as 
CH3N  :  SO  from  NH2CH3  and  SOC12. 

448.  Monamlnes.  —  Simple  alkylamines  are  prepared  as  described 
above  for  methylamines.  Mixed  alkylamines  are  obtained  by  heating 
the  amine  of  one  radicle  with  the  iodide  of  another  (see  above).  The 
amines  of  methyl  and  ethyl  are  here  described  as  typical. 

Methylamine,  NH2CH3,  is  a  gas  (b.-p.  -  6°  C.)  resembling  ammonia, 
but  more  combustible  and  more  soluble  in  water  ;  in  this  it  surpasses 
all  gases,  one  volume  of  water  dissolving  1150  volumes  of  methylamine. 
The  solution  is  strongly  alkaline.  In  its  reactions  with  metallic  salts  it 
resembles  ammonia,  but  it  dissolves  aluminium  hydroxide  and  will  not 


TRIMETH  YLAMINE.  66 1 

dissolve  the  hydroxides  of  Cd,  Ni,  and  Co.  Its  behaviour  with  acids  and 
with  PtCl4  is  similar  to  that  of  ammonia. 

Heated  to  redness  it  yields  hydrocyanic  acid,  HCN,  and  NH.CN.  Potassium 
converts  it  into  potassium  cyanide— NH2CH3  +  K  =  KCN  +  H5.  Conversely 
methylamme  is  formed  by  the  action  of  nascent  hydrogen  on  hydrocyanic  acid; 
HCN  +  H4  =:  NH2CH3.  It  is  also  produced  by  distilling  methvl  isocyanate 
with  potash  (see  Cyanogen}.  Methylamine  occurs  in  the  fruit  of  Mercurialiarix 
(dog-mercury),  a  plant  of  the  order  EuphwUacece.  Several  of  the  alkaloids  yield 
it  when  distilled  with  potash. 

Dimethi/lamine,  NH(CH3)2,  is  a  gas  boiling  at  7°  C.,  and  resembling  methv- 
lamine.  It  has  been  found  in  wood-spirit  and  in  guano. 

Trimethylamine,  N(CH3)3,  is  obtained  on  a  large  scale  by  distilling 
the  vinasses  obtained  in  refining  beet-root  sugar,  which  corresponds  with 
the  molasses  from  cane-sugar,  but  is  not  tit  for  food.  It  contains 
sugar,  by  fermentation  of  which  alcohols  are  obtained,  and  substances 
containing  nitrogen,*  which  furnish  ammonia  and  amines  derived  from 
the  alcohols  when  distilled. 

By  neutralising  the  distillate  with  HC1,  the  hydrochlorides  of  ammonia,  trime- 
thylamine,  <fcc.,  are  obtained.  The  NH4C1,  being  less  soluble,  is  crystallised  out 
and  the  X(CH3)3HC1  is  distilled  with  lime,  when  trimethylamine  comes  off  as  a  gas 
which  may  be  absorbed  by  water.  The  solution  also  contains  dimethylamine, 
ethylamine,  propylamine,  and  butylamine.  It  has  been  used  for  converting  KC1 
into  K2C03,  by  a  process  resembling  the  ammonia-soda  process  (p.  315),  which 
depends  on  the  fact  that  NaHC03  is  less  soluble  in  water  than  is  NH4C1 ;  but 
KHC03  has  about  the  same  solubility  as  NH4C1,  so  that  trimethylamine,  whose 
hydrochloride  is  much  more  soluble,  is  substited  for  ammonia. 

Trimethylamine  boils  at  3.5°  C. ;  it  has  a  fish-like  smell,  is  inflam- 
mable, and  mixes  easily  with  water.  It  forms  salts  by  direct  com- 
bination with  acids,  like  ammonia.  It  is  not  unfrequently  found  in 
plants,  as  in  the  flowers  of  hawthorn,  pear,  and  wild  cherry,  and  in 
arnica  and  ergot  of  rye.  It  also  occurs  in  the  roe  of  the  herring,  and 
may  be  obtained  by  distilling  herring-brine  with  lime.  It  is  often 
found  in  the  products  of  distillation  of  animal  substances,  together  with 
amines  containing  other  alcohol -radicles.  Bones,  when  distilled,  yield 
trimethylamine,  methylainine,  ethylamine,  propylamine,  and  buty- 
lamine. The  putrefaction  of  flour  and  other  nitrogenous  substances 
furnishes  these  ammonia-derivatives.  The  hydrochloride  of  trimethyl- 
amine is  employed  for  making  methyl  chloride  on  the  large  scale,  as 
described  on  p.  633. 

449.  Tetramethylammonium  hydroxide,  N(CH3)4OH,  is  pre- 
pared by  decomposing  the  iodide  with  AgOH  ;  NMe4I  +  AgOH  = 
NMe4OH  +  AgL  The  iodide  (tetramethylium  iodide),  obtained  as 
already  described,  forms  prismatic  crystals,  and  may  be  purified  by 
crystallisation  from  water,  in  which  it  is  rather  sparingly  soluble. 
Evaporated  in  vacuo,  the  solution  of  the  hydroxide  yields  a  crystalline 
deliquescent  mass,  which  acts  like  a  caustic  alkali,  and  absorbs  C02  from 
the  air.  When  heated,  it  yields  methyl  alcohol  and  trimethylamine ; 
NMe4OH  =  NMe3  +  MeOH.  The  ammonium  bases  form  salts  with  acids 
in  the  same  way  as  the  alkali  hydroxides  ;  thus,  NMe4OH  +  HNO3  = 
NMe4N03  +  H90  ;  2NMe4OH  +  H2S04  =  (NMe4)2S04  +  2H?0.  These 
are  not  decomposed  by  potash,  even  on  boiling — a  distinction  between 
the  salts  of  amines  and  ammonium  bases. 

*  Particiilarly  bttaine  (Beta  vulgaris,  beet),  or  trimethyl  glijcocine,  C(CHSV  NH2CO2CH3. 


662  ETHYLAMINES. 

450.  The  ethylamines  may  be  prepared  by  the  action  of  ammonia  on 
ethyl  iodide  and  may  be  separated  from  each  other  in  the  same  way  as  the 
methylamines. 

They  are  prepared  on  a  large  scale  by  the  action  of  NH3  upon  the  impure  ethyl 
chloride  obtained  as  a  secondary  product  in  the  manufacture  of  chloral.  This  is 
heated  for  an  hour  in  a  closed  vessel  with  a  saturated  alcoholic  solution  of  NH3. 
The  volatile  matters  are  then  distilled  off,  and  the  hydrochlorides  crystallised  ;  on 
decomposing  these  with  strong  soda  solution,  the  three  ethylamines  form  an  oily 
layer  on  the  surface.  They  are  separated  as  described  under  the  methylamines. 

Ethylamine,  NH2C2H5,  is  an  ammoniacal  inflammable  liquid,  of  sp. 
gr.  0.696,  and  boiling-point  18.7°  0.  It  mixes  with  water  in  all  pro- 
portions. It  is  a  stronger  base  than  ammonia,  and  dissolves  alumina, 
though  it  does  not  easily  dissolve  cupric  hydroxide.  Its  salts  resemble 
those  of  ammonia,  e.g.,  NH,E.HC1,  (NH2E)2H2S04,  (NH2E.HCl)2PtCl4. 

Di-eth yla wine,  NH(C2H5)2,  is  also  an  auimoniacal  liquid,  boiling  at  56°  C.,  and 
mixing  easily  with  water.  Unlike  ethylamine,  it  does  not  dissolve  Zn(OH)2. 
When  its  hydrochloride  is  distilled  with  potassium  nitrite  and  a  little  water, 
ethylnitrpsamine  is  obtained  ;  this  contains  the  group  'NO  in  place  of  the  imido- 
hydrogen  atom,  (C0H5)2N>NO.  Di-ethylamme  nitrite  is  probably  first  formed 
and  then  decomposed— (C2H5)2NH.HONO  =  (C2H5)2N'NO  +  HOH.  Ethylnitro- 
samine  is  a  yellow  aromatic  liquid  insoluble  in  water,  of  sp.  gr.  0.95  and  b.-p.  177°  C. 
Nascent  H  reconverts  it  into  di-ethylamine— 2NE2NO  +  H4  =  2NE2H  +  H20  +  N20. 
When  it  is  dissolved  in  hydrochloric  acid,  and  HC1  gas  passed  into  the  solution,  it 
yields  nitrosyl  chloride  and  di-ethylamine  hydrochloride — 

NE2NO  +  2HC1  =  NE2H.HC1  +  NOC1. 

Tri-ethylamine,  N(C2H5)3,  differs  from  the  other  amines  in  having  a  pleasant 
smell,  and  being  sparingly  soluble  in  water.  It  boils  at  89°  C.  Its  reaction  is  strongly 
alkaline,  and  it  resembles  ammonia  in  its  action  upon  metallic  salts,  except  that  it 
dissolves  alumina,  and  scarcely  dissolves  silver  oxide,  which  is  readily  soluble  in 
ammonia. 

451.  Tetrethylammonium  hydroxide,  N(C2H5)4'OH,  is  prepared  like  the  methyl 
compound,  which  it  much  resembles,  but  crystallises  rather  more  easily.     In  its 
chemical  behaviour,  it  is  very  similar  to  potassium  hydroxide,  but  it  produces,  in 
chromic  salts,  a  precipitate  of  chromic  hydroxide,  which  does  not  dissolve  in  excess. 
When  heated  to  100°  C.,  it  does  not   yield  alcohol,  but  ethane,  water,  and  tri- 
ethylamine;    N(C2H5)4-OH  =  C2H4  +  H20  +  N(C2H5)3.     If   it    be  heated  with  ethyl 
iodide,    alcohol    and    tetrethylummonium    Iodide     are    formed  ;     KE4OH  +  EI  = 
EOH  +  NEJ.     The  iodide  may  be  obtained  by  the  combination  of  N(C2H5)3  with 
C2H5I,  just  as  NH4I  is  formed  by  NH3  and  HI,  the  combination  producing  heat. 
It  crystallises  in  cubes  like  the  alkali  iodides,  and  becomes  brown,  when  exposed 
to  air,  from  the  formation  of  the  tr iodide,  NE4I3.     It  is  very  soluble  in  alcohol  and 
in  water,  but  is  insoluble  in  solution  of  potash,  which  precipitates  it  from  the 
aqueous  solution,  but  without  decomposing  it.     When  heated,  tetrethylainmonium 
iodide   undergoes   dissociation,  like  ammonium  chloride,    yielding  ethyl  iodide, 
which  distils  over,  and  is  followed  by  tri-ethylamine,  these  afterwards  combining 
to  reproduce  the  iodide. 

By  heating  a  primary  amine,  NH2R',  successively  with  R"I,  KOH,  B'"I,  KOH 
and  Eivl,  a  mixed  quaternary  ammonium  iodide,  of  the  form  NB'B"B'"BivI,  may 
be  obtained.  The  importance  of  such  compounds  to  the  theory  of  stereoisomerism 
has  been  noted  at  p.  607. 

452.  CJdoramlnes  are  formed  from  primary  and  secondary  amines  by  action  of 
Cl  or  HC10  on  amines,  just  as  NC13  is  formed  from  NH3,  only  here  there  are  only 
one  or  two  H  atoms  to  be  exchanged  for  Cl.    lodaiulnes  and  broinainlnes  are  also 
known.- 

The  nitramines,  such  as  metliyUiitramine,  CH3NH'N02,  were  originally  supposed 
to  be  nitro-derivatives  of  the  primary  and  secondary  amines  in  which  N02  was 
substituted  for  the  ammoniacal  H.  This  view  has  been  traversed,  and  certain 
isomeric  forms  have  been  discovered. 

453.  Phenylamine,   or   aniline,    or    amidobenzene,    C6H5'NH2,    is 


PREPARATION  OF  ANILINE. 


663 


prepared  from   nitrobenzene,  C6H5-X09,  by  reducing  it  with  metallic 
iron  111  conjunction  with  acetic  or  hydrochloric  acid 

«Pe™t.on      The  aniline  is  purified  by  distillation,  and  the  iron  «!Staii?irtS 

thereto* 


4C6H0N02  +  4H20  +  Fe9  =  4C6H5NHa  +  3Fe-504. 

The  process  requires  care,  because,  if  the  action  becomes  too  violent,  benzene  and 
ammonia  are  produced  ;  C6H8-NOa  +  H8  =  C6H5'H  +  NH3  +  2H.,0. 

On  the  small  scale,  tin  is  more  convenient  than  iron.  Granulated  tin  is  placed 
in  a  retort  with  inverted  condenser,  and  covered  with  strong  HC1  ;  nitroben/ene 
is  added  m  small  portions,  and  when  the  action  has  moderated,  he  mixture  is 


Fig-.  281.—  Distillation  in  a  current  of  steam. 

boiled  till  all  the  nitrobenzene  has  disappeared  ;  C6HBN02  +  3SnCI2 
C6H5NH.2  +  3SnCl4  +  2H.20  ;  the  liquid  is  decanted  from  the  excess  of  tin,  when  it 
deposits,  on  cooling,  a  crystalline  compound  of  aniline  hydrochloride  with  stannic 
chloride  ;  (C6H?NH2HCl)2.SnCl4.  By  distilling  this  with  excess  of  potash  or  soda 
in  a  current  of  superheated  steam  the  aniline  is  set  free.  The  apparatus  for  this 
purpose  is  shown  in  Fig.  281.  The  steam  generated  in  the  boiler  passes  through 
the  coil  of  copper  tube,  which  is  heated  by  the  burner,  into  the  distillation  flask, 
carrying  the  aniline  with  it  through  the  ccmdenser. 

Nitrobenzene  may  also  be  converted  into  aniline  by  dissolving  it  in  alcohol, 
saturating  the  solution  with  NH3,  then  with  H<,S  gas  repeatedly,  as  long  as  the 
latter  is  acted  on;  C6H5N02  +  3H2S  =  C6H5NH2-f-2H20  +  S3.  The  liquid  is  de- 
canted from  the  S,  and  the  alcohol  and  ammonium  sulphide  distilled  off  in  a 
water-bath  ;  the  mixture  of  aniline  and  any  unaltered  nitrobenzene  is  treated 
with  HC1,  which  dissolves  only  the  aniline  ;  this  may  be  liberated  by  distillation 
with  potash. 

Since  commercial  benzene  contains  toluene  and  other  hydrocarbons,  the  aniline 
prepared  from  it  contains  toluidine  and  other  bases.  To  purify  it,  the  crude  aniline 
is  boiled  with  glacial  acetic  acid,  in  a  flask  with  a  reversed  condenser,  when  it  is 
converted  into  acetan'didp.,  C6H?-NH  *C2H3O.  This  is  distilled,  washed  with  c"irl>on 
bisulphide,  and  recrystallised  from  water  till  its  melting-point  is  115°  C..  when 
pure  aniline  may  be  obtained  from  it  by  boiling  with  NaOH  — 


(1)  NH.,-C6H5  +  CoH^O-OH  =  NH'C6H5-CoH.jO  +  HOH  ; 

(2)  NH:C6H5-C.2H36  +  NaOH  =  NH2'C6H;  +  NaO'C,H,0. 


664  PROPERTIES   OF  ANILINE. 

Aniline  was  originally  obtained  by  distilling  indigo,  either  alone  or 
with  caustic  alkalies,  and  was  named  from  anil,  the  Portuguese  name 
of  indigo.  It  is  also  found  in  coal  tar,  and  in  the  products  of  distilla- 
tion of  bones  and  peat. 

Properties  of  aniline. — Colourless  when  pure,  but  generally  of  a 
yellow  or  even  brown  colour,  having  a  characteristic  rather  ammoniacal 
smell;  sp.  gr.  1.03,  and  boiling-point  184°  C.  When  shaken  with 
water,  it  appears  almost  insoluble,  but  the  water  dissolves  about  ^th 
of  its  weight  of  aniline,  and  the  latter  about  ^V^n  °^  ^s  weight  of  water. 
It  is  easily  soluble  in  alcohol  and  ether,  which  collects  it  from  an 
aqueous  solution.  It  has  no  alkaline  reaction,  and  is  less  strongly  basic 
than  the  alky  lam  ines,  though  it  precipitates  hydroxides  of  Zn,  Al,  and  Fe. 
Most  of  its  salts  crystallise  easily.  The  hydrochloride,  C6H5'NH2.HC1, 
is  commercially  known  as  aniline-salt.  The  oxalate,  (C6H7N)2.H2C204, 
is  rather  sparingly  soluble  in  water.  Aniline  has  the  rare  property  of 
dissolving  indigo. 

Many  oxidising-agents  produce  intensely  coloured  products  with 
aniline.  The  usual  test  for  it  is  solution  of  chloride  of  lime  (bleach ing- 
powder),  which  gives  a  purple-violet  colour,  changing  to  brown. 
Solutions  of  aniline  give  a  bright  green  precipitate,  (C6H.NH2)2CuS04, 
with  CuS04.  By  Caro's  reagent  (a  persulphate  in  strong  H2S04)  aniline 
is  oxidised  to  nitrosobenzene,  C6H5'NO. 

Substitution  products  of  aniline  are  obtained  by  the  reduction  of  the  correspond- 
ing nitro-compounds ;  thus  i  :  2-chloronitro-benzene,  C6H4C1'N02,  will  yield 
i  :  2-chloramUne,  C6H4C1'NH2.  By  the  action  of  chlorine  or  bromine  water  on 
aniline,  the  trichloranuine*  and  tribromaniline*  are  produced,  the  latter  form  the 
white  precipitate  which  bromine-water  gives  with  aniline. 

Nitranilines,  or  nitrophenylamines,  C6H4N02*NH2,  are  obtained  by  the  partial 
reduction  of  the  dinitro-benzenes  with  NH4HS  (p.  663).  The  presence  of  the  acidic 
N02  or  Cl  greatly  reduces  the  basic  character  of  aniline.  Thus  dinitraniline  is 
neutral,  and  trinitraniline,  CfH^NOaVNHj,  is  acidic  in  properties. 

Aniline-sulphonic  acid,  or  I  :  ^•amidobenzenesulphonic  acid,  or  sulphanilie  t«-'xL 
C6H4(S03H)'NH2,  is  obtained  by  heating  aniline  with  twice  its  weight  of  fuming 
sulphuric  acid  at  180°  C.  until  S02  is  given  off.  When  the  liquid  is  diluted,  the 
acid  is  precipitated.  Sulphanilic  acid  is  the  parent  substance  of  several  dyes. 

454.  Alkylanilines. — Aniline,  being  a  primary  amine,  may  be  converted  into 
secondary  and  tertiary  amines  by  action  of  iodides  of  other  radicles.     Thus,  metlnjl- 
aniline,    C6H5'NHCH3,   and  dimethylaniline,   C6H5N(CH3)2,   are    obtained  by  the 
action  of   methyl   iodide  on  aniline,  or  by  heating  methyl  alcohol  with  aniline 
hydrochloride,   in  a  closed  vessel,   at   250°   C..   when  the  hydrochlorides  of  the 
methyl  bases,  and  water,  are  produced.     Dimethylaniline  is   also  prepared  on  a 
large  scale  by  the  action  of  methyl  chloride  on  a  heated  mixture  of  aniline  and 
caustic  soda — 

2CH3C1  +  C6H5NH2  +  2NaOH  =  C6H5N(CH3)2  +  2NaCl  +  2H20. 
They  are  liquids  boiling  at  about  190°  C.,  and  used  in  the  manufacture  of  certain 
aniline  dyes.  Such  alltylanilmes  are  more  basic  than  aniline,  and  behave  generally 
like  phenyl-substituted  open-chain  amines.  The  dialkylanilines,  however,  react 
with  nitrous  acid,  notwithstanding  that  they  are  tertiary  amines  (p.  660).  The 
products  are  iso-nitroso-derivatifes — i.e.,  the  NO  group  is  attached  directly  to  C  ; 
thus,  isoniti'oso-dimethylaniline  is  C6H4(NO)'N(CH3)2. 

455.  Diphenylamine,  GT phenylaniline,  NH(C6H5)2,  is  a  secondary  amine  obtained 
by  heating  aniline  hydrochloride  with  aniline  at  250°  C.,  in  a  closed  vessel  from 
which  the  NH3  is  allowed  to  escape  from  time  to  time — 

C6H5-NH2HC1  +  C6HB-NH2  =  NH(C6H5)2  +  NH3-HC1 ; 

the  excess  of  aniline  employed  decomposes  the  NH4C1,  so  that  a  mixture  of  aniline 
hydrochloride  and  diphenylamine  is  left  ;  on  adding  water,  the  latter  is  left  undis- 
solved.  It  is  a  crystalline  solid,  soluble  in  alcohol  and  ether,  and  having  feeble 
basic  properties.  It  melts  at  54°  C.  and  boils  at  310°  C.  When  acted  on  by  HN03t 


ANILINE-OIL,  66=; 

^ 

three  atoms  of  the  phenyl  hydrogen  are  exchanged  for  NO*  producing  kerauifn,- 
diphcnylamine,im(CjBL@K)&)v  an  acid  which  combines  with  ammonia  form  in  cr 
N(NH4)(C6H2(N02)3)2,  an  orange  dye,  aurantia. 

Diphenylamine  is  used  as  a  delicate  test  for  nitrous  acid,  with  which  it  gives  a 
deep  blue  colour  in  strong  sulphuric  acid. 

The  ammonia-hydrogen  in  aniline  may  be  evolved  by  dissolving  potassium  in 
the  base,  when  NHK>C6H5  and  NK2C6H5  are  produced.     By  acting  on  the  latter 
with  phenyl  bromide  (bromobenzene)  the  tertiary  amine,  triphenylamine,  N(CfiH.) 
is  produced  ;  NK2C6H5  +  2C6H5Br  =  N(C6H5)3  +  2KBr.  This  compound  is  not  basic  • 
it  is  insoluble  in  water,  but  may  be  crystallised  from  ether. 

456.  The   three  toluidines,  or   amido-toluenes,  C6H4CH3-NH,,,  are 
metameric  with  methyl-aniline  and  benzylamine.     They   are  prepared 
by  reducing  the  nitrotoluenes,  just  as  aniline  is  prepared  from  nitro- 
benzene.    Orthotoluidine  resembles  aniline;  sp.gr.  1.003,  and  boiling- 
point  197°  C.     It  becomes  pink  in  air.     Chloride  of   lime  gives  it  a 
brown  colour,  which  is  changed  to  red  by  acids.     Metatoluidine  is  a 
liquid  of  sp.  gr.  0.998,  and  boiling  at  199°  C.     Paratoluidine,  which 
forms  about  35  per  cent,  of  commercial  toluidine,  is  crystalline,  fusing 
at  45°  C.  and  boiling  at  198°  C.     It  is  sparingly  soluble  in  water,  and 
is  feebly  alkaline ;  alcohol  and  ether  dissolve  it.     It  is  not  coloured  by 
chloride  of  lime.    Its  basic  properties  are  weak.    Its  oxalate  is  insoluble 
in  ether,  which  dissolves  orthotoluidine  oxalate.     When  methylaniline, 
hydrochloride  is  heated  to  350°  0.,  it  is  converted  into  the  isomeric 
paratoluidine  hydrochloride  ;  C6H5-NHCHS,H01  =  C6H4(CH3)'NH2,HC1. 
This  migration  of  a  group  from  a  side-chain  into  the  nucleus  is  frequently 
noticed. 

Commercial  aniline-oil  is  never  free  from  toluidine,  so  that  it  gives  a  brown 
colour  with  chloride  of  lime,  as  well  as  the  violet  due  to  aniline.  Ether  extracts 
the  toluidine  brown,  which  becomes  pink  by  shaking  the  ethereal  layer  with  acetic- 
acid.  Aniline-oil  for  Hue  is  approximately  pure  aniline  ;  aniline-oil  for  red  contains 
equimolecular  proportions  of  aniline  and  orthotoluidine ;  aniline-oil  fur  safranine 
is  a  mixture  of  aniline  and  orthotoluidine  recovered  during  the  manufacture  of 
magenta. 

Commercial  toluidine  is  obtained  by  reducing  the  product  obtained  by  nitrating 
toluene  (p.  650).  and  consists  of  ortho-  and  para-toluidine.  The  latter  is  the 
stronger  base  of  the  two,  so  that  when  the  mixture  is  partially  saturated  with  H2S04 
and  distilled,  it  remains  in  the  retort  as  sulphate. 

457.  Xylidines,  C6H3(CH3)a-NH2.     These  are  six  in  number,  and  are  metameric 
with  dimethylaniline.      Commercial  xylidine    is    chiefly  amidoparaxijlen^  and  is 
prepared    by    heating   dimethylaniline    hydrochloride,     when    a    change    occurs 
analogous  to  that  involved  in  the  conversion  of  methylaniline  hydrochloride  into 
paratoluidine  hydrochloride  (r.«.)  ;  C6H5'N(CH3)2,  HC1  =  C6H3(CH3)2'NH2,  HC1.  It 
is  used  for  making  dyes. 

Ben:  ilia  mine,  C6H5'CH2NH0,  is  produced  by  the  action  of  benzyl  chloride  on  Mi3 
in  alcoholic  solution  ;  C6H5'CH2C1  +  NH3  =  C6H5'CH2NH2,  HC1.  By  distilling  the 
hydrochloride  with  KOH,  it  is  obtained  as  a  colourless  liquid,  boiling  at  187  . 
metameric  with  toluidine,  but  is  easily  soluble  in  water,  and  is  a  strongly  alkaline 
base.  lytieHzylam'tRe,  (C6H6'CHa)2NH,  and  tril>en;ylamine,  (C6H5'CH2)3N,  are 
formed  in  the  same  reaction  as  benzylamine. 

a-Naphthylamine,  or  naphtkalid'me,  C10H7;NH2,  or  amido-naphttwlrne,  prepar 
from  a-nitro-naphthalene  like  aniline  from  nitro-benzene,  forms  colourless  needles, 
smelling  of  mice  ;  m.-p.  50°  C.,  b.-p.  300°  C.     It  dissolves  sparingly  in  water,  but 
easily  in  alcohol,  and  forms  well-crystallised  salts,  which  give,  with  ferric  chloride, 
a  blue    precipitate,  changing   to  purple   o-vynaphthi/lamine,  C10H9NO.     It  i 
obtained   by  heating   aniline  with  pyromucic  acid,  C02  +  H20  being  eliminated. 
fl-naphthylamine  gives  no  colour  with  ferric  chloride. 

458.  Diamines.— The    commonest  open-chain    diamines  are   those 
which  are  derived  from  ethylene.     If  ethylene  diamine,  C2H4(NH2)2,  be 


666  PTOMAINES. 

regarded  as  glycol  in  which  NH2  is  substituted  for  OH,  it  will  be  seen 
that  alcohol-amines,  such  as  C2H4(OH)(NH2),  can  exist  ;  these  are 
monamines,  and  have  been  called  hydramines,  or  hydroxy  amines. 
Thus,  C2H4(OH)(NH2)  is  hydroxy-ethylamine.  The  diamines  are  diacid 
bases,  i.e.,  they  are  equivalent  to  2NH3  in  their  relation  to  acids. 


Etijlene  diamine,  CH2NH2CH2NH2  (b.-p.  ii6°C.).  Ethylene  bromide  is  heated 
with  an  alcoholic  solution  of  NH3  at  ioo°C.  ;  2NH3  +  C2H4Br2  =  C2H4(NH2)2.2HBr. 
The  hydrobromides  of  d't  ethylene  diamine,  N2H2(C2H4)2"  (b.-p.  145°  C.),  and  tri- 
etliylene  diamine,  N2(C2H4)3"  (b.-p.  210°  C.),  are  produced  at  the  same  time.  The 
three  diamines  are  liberated  by  KOH  and  fractionally  distilled. 

Ethylene  diamine  smells  feebly  of  ammonia,  but  dissolves  in  water  and  is 
alkaline.  It  is  also  formed  by  reducing  cyanogen  with  HC1  +  Sn  ;  CN  -CN  +  H8  = 
CH2NH2'CH2NH2.  Citrous  acid  converts  it  into  ethylene  oxide,  though  glycol 
is  probably  first  formed. 

xCH9'CH2\ 

Diet-hylene  diamine  has  the  structure  NH\  >NH  and   is  identical  with 

\prqr    .p  IT   / 
O±12  O±12 

piperasine  (see  Pyrazine)  which  is  used  as  a  remedy  for  gout,  since  it  readily  dis- 
solves uric  acid.     It  melts  at  104°  C.,  and  boils  at  145°  C. 

Hydroxy-ethylamine,  CH2OH'CH.,NH2,  is  obtained  by  the  action  of  ammonia  on 
ethylene  chlorhydrin;  C2H4(OH)C1  +  2NH3=C2H4(OH)NH2  +  NH4C1.  The  secon- 
dary monamine,  dihydroxy-et-kylamine,  (C2H4OH)2NH,  is  produced  at  the  same  time, 

PTT  'PIT 
and    when   this   is    dehydrated  it   yields  -morpholine,    O/  /NH,    a  base 

Cxi2°CH.2 
closely  allied  to  morphine. 

Two  important  animal  products  have  been  shown  to  be  ammonium 
bases  connected  with  the  hydramines  ;  these  are  choline,  which  occurs 
in  bile,  egg-yolk,  and  the  brain  ;  and  neurine,  which  is  also  obtained 
from  the  brain.  The  latter  is  typical  of  the  class  of  poisonous  substances 
resulting  from  decomposing  animal  matter,  and  known  as  ptomaines 
(Trrw/za,  a  corpse)  or  toxines. 

Clioline  is  kydroxyfltJiyl-trimffJtyl  amntO'niuin  hydroxide,  Js(C2H4OH)(CH3)3'OH, 
and  can  be  artificially  prepared  by  heating  ethylene  chlorhydrin  with  trimethyl- 
amine  in  aqueous  solution.  It  is  strongly  alkaline  and  crystallises  with  difficulty  ; 
it  is  not  poisonous,  but  when  oxidised  by  nitric  acid  it  yields  muse-urine  or 
hydroxycholine,  N[C2H3(OH)2](CH3)3'OH,  which  is  a  poisonous  base  found  in  the 
toad-stool,  Agaric-ids  muscarius. 

When  treated  with  hydriodic  acid,  choline  yields  the  iodine  derivative 
N(C2H4I)(CH3)3'I,  which  with  AgOH  yields  neurine  or  trimetliyl-'rinyl  ammonium 
hydroxide,  N(C2H3)(CH3)3'OH.  This  is  strongly  alkaline  and  poisonous,  but  has 
not  been  crystallised  ;  it  is  a  product  of  the  putrefaction  of  many  kinds  of 
animal  matter. 

Other  ptomaines,  beside  neurine  (from  flesh)  and  muscarine  (from  fish),  are 
neuridine,  C5H14N3  (from  flesh),  gadinine,  C6H17N02  (from  fish),  cadarerine,  or 
pentametliylene  diamine,  C5H16N2,  putrescine  or  tetra-methylene  diamine  C4H12N2, 
'inydine,  C8HnNO,  and  mydato&ine,  C6H13N02. 

'459.  Diamido-benzenes,  C6H4(NH2)2,  or  phenylene  diamines,  X2H4(C6H4)",  being 
disubstituted  benzenes,  exist  in  three  forms,  which  are  obtainable  by  the  reduction 
of  the  corresponding  dinitro-benzenes,  or  by  distilling  the  three  diamido-benzoic 
acids,  C6H3(NH2)2'C02H,  with  baryta.  They  are  diacid  bases.  Metaphenylene 
diamine  melts  at  63°  C.  and  boils  at  287°  C.  ;  it  is  very  soluble  in  water  and  gives 
a  yellow  colour  with  nitrous  acid  ;  it  is  used  for  the  estimation  of  small  quantities 
of  nitrites.  Tri-,  tetra-,  an  dpenta-amido-benze  ties  are  also  known. 

Dlamido-naphthalenes,  C10H6(NH2)2,  or  naphthijlene  diamines,  corresponding  with 
phenylene  diamine,  are  obtained  by  the  reduction  of  dinitronaphthalenes. 

460.  Diamidodiphenyl,  or  benzidine,  XH2'C6H4'C6H4>NH2,  is  produced  by  reducing 
the  corresponding  dinitro-derivative.  obtained  by  direct  nitration  of  diphenyl 
(P-  550)  5  ^  is  also  formed  by  the  intramolecular  change  of  hydrazo  -benzene  (q.  /•.), 
i\  product  of  the  reduction  of  azo-benzene.  and  is  generally  prepared  on  a  large 


AMIDES,  66? 

scale  from  this  source.  It  crystallises  in  colourless  plates,  melts  at  i22°C  dig 
solves  in  hot  water,  and  sublimes.  Its  sulphate,  C12H8(NH2)2.H2S04,  is"  very 
sparingly  soluble.  It  is  the  parent  substance  of  many  important  dyes  The  two 
NH2  groups  occupy  the  para-positions  with  regard  to  the  link  between 'the  ohenvl 
groups. 

(~1    TT 

Carbazole   is    imldlphenijl,     -6    4^NH;  lit    is    formed    by  passing   vapour    of 

C6H4 

diphenylamine  through  a  red-hot  tube  (C6H5)2NH  =  (C6H4)2NH  +  H2  (rf.  diphenyl) 
It  is  also  obtained  at  the  end  of  the  distillation  of  coal-tar,  and  as  a  secondary 
product  in  the  preparation  of  aniline.  It  crystallises  in  plates  (in.-p.  238°  C  • 
b.-p.  351°  C.),  sublimes  easily,  and  dissolves  in  alcohol  and  in  ether. 

AMIDES  AND  AMIO  ACIDS. 
461.  Amides  are  derived  from  NH3,  by  the  substitution  of  a  negative 

or  acid  radicle  for   hydrogen ;    thus,   in   acetamide,   CH3C^       2   the 

radicle  acetyl,  CH3CO,  has  been  substituted  for  one-third  of  the  H  in 
NH3.  The  amides,  like  the  amines  (p.  638),  may  be  primary,  secondary, 
or  tertiary,  accordingly  as  one,  two,  or  three  atoms  of  H  in  the  NH3 
group  have  been  exchanged,  and  they  may  be  monamides,  diamides,  or 
triamides,  accordingly  as  they  are  formed  upon  the  model  of  one,  two, 
or  three  ammonia  molecules. 

Amides  may  be  formed  from  ammonia  in  the  same  manner  as  amines, 
by  the  action  of  the  chloride  of  an  acid  radicle,  when  the  chlorine  removes 
the  ammonia-hydrogen,  CH3COC1  +  2NH3  =  CH3CONH2  +  NH3HC1 
(cf.  p.  660),  or  by  the  action  of  an  ethereal  salt,  when  the  hydrogen  is 
exchanged  for  the  acid  radicle,  CH3CO'OC2H5  +  NH3  =  CH3CONH2  + 
C2H3'OH.  Amides  may  also  be  formed  by  dehydrating  the  ammonium 
salts  of  the  acids,  by  heat  or  otherwise,  when  the  ammonia-hydrogen 
and  the  OH  group  of  the  acid  form  water,  leaving  the  NH2  group  in 
combination  with  the  acid  radicle,  CH3CQ'ONH4  =  CH3CO'NH2  +  H20. 
This  mode  of  formation  explains  the  characteristic  property  of  the 
amides  to  be  converted  by  hydrolysis  into  ammonia-salts,  CH3CO'NH2  + 


If  primary  or  secondary  amines  be  substituted  for  ammonia,  or  amine 
salts  for  ammonium  salts,  in  the  foregoing  reactions,  substituted  amines, 
such  as  ethylacetamide,  CH3CO'NHC2H,  and  acetanilide,  CH3CO'NHC6H5, 
are  formed. 

Nitrous  acid  converts  the  primary  amides  into  the  corresponding 
acids,  CH3CONH2  +  HON  :  0  =  CH3COOH  +  N2  +  HOH.  Dehydra- 
ting agents  convert  them  into  nitriles  (cyanides)  of  hydrocarbon  radicles  ; 
CH3CO-NH2  =  CH3'C  :  N  +  H20. 

The  amides  are  distinctly  basic,  forming  salts  with  acids,  but  far  less 
so  than  the  amines  owing  to  the  acid  radicles.  Indeed,  the  amidogen  H 
has  even  an  acid  character,  for  it  may  be  exchanged  for  metals. 

Monamides.— Formamide,  HCONH2,  obtained  by  distilling  ammonium  formate, 
or  by  saturating  ethyl  formate  with  NH3  and  heating  to  100°,  for  two  days,  in  a 
sealed  tube,  is  a  liquid,  boiling  at  193°  (1,  with  decomposition— 2(HCO'NH.,)  = 
HoO  +  CO  +  NHa  +  HCN .  Strong  KOH  converts  it  at  once  into  potassium  formate 


Acetamide,  CH3CO 
of  ammonium  acetate 


•NH2,  is  prepared  by  the  methods  mentioned  above.     Instead 
i,  a  mixture  of  NH4C1  with  dry  sodium  acetate  may  be  us.-d  in 


668  SACCHARINE. 

the  third  method.  It  crystallises  in  needles  smelling  of  mice,  fusing  at  82°  C.  and 
boiling  at  222°  C.,  soluble  in  water  and  alcohol,  but  sparingly  in  ether.  It  is  a 
weak  base,  forming  unstable  crystalline  salts.  Solution  of  acetamide  dissolves 
silver  oxide,  and  deposits  silver  acetamide,  C2H3O  -NHAg.  With  mercuric  oxide, 
crystals  of  mercuric  acetamide,  (C2H3ONH)2Hg,  are  obtained.  Boiling  with  water, 
especially  in  the  presence  of  acids  or  alkalies,  converts  acetamide  into  acetic  acid 
and  ammonia.  When  distilled  with  powerful  dehydrating  agents,  such  as  P205  or 
ZnCl2,  it  yields  acetonitrile,  or  methyl  cyanide,  CH3'CN. 

The  three   chloracetic   acids   yield   corresponding  amides — monochlor acetamide, 
WSL&Q&T&l^Awhl&ra*^^ 
all  crystalline  solids  with  high  boiling-points. 

Acetanilide,  CH3CO'NH(C6H5)  is  prepared  by  boiling  aniline  with  glacial  acetic 
acid  ;  it  forms  white  prisms,  soluble  in  hot  water,  melts  at  112°  C.  and  boils  at 
304°  C.  It  is  used  as  a  febrifuge  under  the  name  of  amtifebrlne.  The  methyl- 
acetanilide.  CH3CO.NCH3(C6H5),is  a  remedy  for  headaches  ;  it  is  called  ejcalgin  and 
melts  at  102°  C. 

Di-acetamide,  (CH3CO)2NH,  is  obtained  by  heating  acetamide  in  HC1  gas  ; 
2CH3CO-NH2  +  HC1  =  (CH3CO)2NH  +  NH4C1;  or  by  acting  on  acetamide  with 
acetyl  chloride;  CH3CO'NH.2+CH3CO-C1  =  (CH3CO)2NH  +  HC1.  It  is  a  feeble 
acid  and  forms  crystals  soluble  in  water,  melting  at  77°  C.  and  boiling  at  223°  O 

Tri-acetamide,  (>O2H80)8N  is  obtained  by  heating  acetonitrile  with  acetic  anhy- 
dride to  200°  C.  ;  CH3CN  +  (C2H30)20  =  (C2H30)3N.  It  maybe  crystallised  from 
ether,  and  is  neither  basic  nor  acid. 

The  amides  of  the  higher  fatty  acids  are  formed  when  their  glyceryl  salts,  such 
as  palmitine,  stearine.  and  oleine,  are  treated  with  strong  ammonia. 

Benzamide,  C6H5CONH2,  is  precipitated  when  benzoyl  chloride  is  treated  with 
NH3.  It  may  be  crystallised  from  hot  water  in  plates,  fuses  at  130°  C.,  and  boils 
at  288°  C.  It  is  soluble  in  alcohol  and  ether,  and  resembles  acetamide  in  its 
reactions  ;  it  forms  a  crystalline  compound  with  HC1,  and  its  aqueous  solution  dis- 
solves mercuric  oxide,  benzomercuramide,  C6H5CONHg,  being  produced. 

Glycolamide,  CH2(OH)CONH2,  from  ethyl  glycolate  and  NH3,  crystallises  in 
needles  (m.-p.  120°  C.),  dissolves  in  water,  and  is  easily  converted  by  alkalies  and 
acids  into  ammonia  and  glycollic  acid.  Glycolamide  is  also  formed  by  heating 
glycolide  in  ammonia  gas— 2NH3  +  (CH2'CO)202  =  2CH2(OH)CO-NH2. 

Lactamide,  C2H4(OH)CO'NH2,  from  NH3  and  ethyl  lactate  or  lactide,  forms 
crystals  which  fuse  at  74°  C.  and  volatilise  unchanged. 

462.  Sulphonamides    are     amides    from    sulphcnic     acids,    e.g.,    C6H5'S02NH2, 
benezene  sulponamide,    and  are  prepared    like   the    foregoing    amides    from    the 
corresponding  sulphonic  acid  derivatives.     The  compound  C6H4(C02H)-S02NH2, 
i  :  2-benzoic  sulphonamide,   is  of  some  importance    as  the   parent  substance   of 
saccharine,  the  sugar-substitute  made  from  toluene.     Saccharine  is  i  :  2-benzoic 

/C0\ 
sulpho-imide,  C6H4<^       /NH,  also  called  benzoic  sulphinide  and  2-anhydro  sulph- 

S02 

amine  benzoic  acid.  By  treating  toluene  with  sulphuric  acid  it  yields  o-  and  p- 
toluenesulphonic  acids,  CgH4(CH3)'S02OH  ;  these  are  oxidised  to  the  correspond- 
ing benzoic  sulphonic  acids,  C6H4(C02H)'S02OH,  which  by  treatment  with  PC15 
become  the  dichlorides,  C6H4(COC1)'S02C1.  Ammonia  converts  the  i  :  4-derivative 
into  C6H4(CONH2)'S02NH2,  which  is  insoluble  in  water,  and  the  I  :  2-derivative 
into  C6H4(C02NH4)-SO2NH2,  which  is  soluble;  when  an  acid  is  added  to  the 
solution  of  the  latter,  saccharine  is  precipitated.  It  is  said  to  be  500  times 
sweeter  than  cane  'sugar  ;  it  melts  at  224°  C.  It  is  sparingly  soluble  in  water,  but 
readily  in  alkalies  since  the  H  of  the  NH  group  is  exchanged  for  metals  to  form 
soluble  salts.  The  sodium  salt  is  the  commercial  saccharine. 

463.  Amidines. — It  is  possible  to  represent  the  primary  amides  by  two  formula?, 

0  OH 

K'Cf          and  E'C^        ;  the  two  amides  corresponding  with  these  formulae  do 
NH2,  NH 

not,  however,  appear  to  exist,  except  in  the  case  of  glycolamide.  Many  derivatives 
of  the  amides  exist  in  both  forms  ;  thus,  the  ethyl  acetamide  described  above  is 
CH3C(>NHC2H5,  but  the  compound  CH3C(NH)-OC2H5  is  also  known,  and  is  called 
acetimidoether.  By  acting  on  acetamide  with  PC15,  acetamldo-chloride,  CH3CC12'NH2, 
is  obtained ;  but  this  readily  loses  HC1,  and  passes  into  acetimido-chloride, 


UREA. 
CH3C(NH);«,  a  derivative  of  the  second  general  formula  given  above,  Cl  having 

x,NH 
Amidines,    R'C<        ,    may    be    regarded    as    derived    from    either    formula, 

-tlo 

although  the  fact  that  they  are  obtained  by  treating  the  imido-chlorides  with 
ammonia  (or  primary  amines)  seems  to  indicate  that  they  are  from  the  second 


formula  :  R-C(NH)-C1  +  NH2R  =  R-C(NH)-NHR  +  HC1.     The  amldoximet 

NH., 

may  be  regarded  as  derived  from  the  arnidines  ;  they  are  the  products  of  the 
action  of  hydroxylamines  on  the  cyanides  (nitrilea)  ;  thus,  hydrogen  cyanide  and 
hydroxylamine  yield  isuret  (methenyl-amidoxiine),  isomeric  with  urea  _ 
HCN  +  NH2OH  =  HC(N-OH)-NH2. 

464.  Diamides.—  Ox-amide,  CONH2'CONH2  is  best  prepared  by  shaking  ethyl 
oxalate  with  solution  of  ammonia,  when  the  mixture  becomes  hot  and  a  white 
crystalline  precipitate   of  oxamide   separates;   (COOC2H5)2  +  2NH3  =  (CONHo)2  + 
2(HOC2Hg).     If  an  alcoholic  solution  of  ammonia  be  employed,  or  if  ammonia  gas 
be  passed  into  ethyl  oxalate,  only  half  the  ethoxyl  (OC2H5)  is  exchanged  for  NH2, 
and  ethyl    oxamate   (jwa  methane),    COOC2H5'CONH2,   is    obtained.     Oxamide  is 
scarcely  dissolved  by  water,  alcohol,  or  ether,  and  is  a  perfectly  neutral  body.     It 
may  be  crystallised  in  needles  from  a  hot  saturated  solution  of  calcium  chloride. 
When  heated,  a  part  sublimes  unchanged.    A  red-hot  tube  decomposes  the  vapour, 
forming  hydrocyanic  acid  and  urea,  2(CONH2)2  =  HCN  +  CO(NH2)2  +  CO  +  C02  +  NH3. 
By  hydrolysis  it  yields  oxalic  acid  and  NH3. 

Oxamide  is  obtained  by  the  distillation  of  ammonium  oxalate,  showing  that  the 
ammonium  salt  of  a  dibasic  acid  yields  a  di-amide.  Since  it  contains  the  elements 
of  cyanogen,  it  is  not  surprising  to  meet  with  oxamide  in  many  reactions  of 
cyanogen  compounds  ;  it  can  be  formed  by  mixing  aqueous  solutions  of  hydro- 
cyanic acid  and  hydrogen  di-oxide  ;  2HCN  +  H202  =  2(CONH2)2.  The  reaction  of 
aldehyde  with  solution  of  cyanogen  also  produces  oxamide  ;  and  it  is  found  among 
the  products  of  the  action  of  nitric  acid  on  potassium  ferrocyanide.  The  oxida- 
tion of  potassium  cyanide  with  manganese  dioxide  and  dilute  sulphuric  acid  also 
forms  oxamide. 

Dimethyl  o.ramtde  (CONHCH3)2,  SLnddi-ethyl  oxamide  (CONHC2H5)2,  are  formed 
by  the  action  of  inethylamine  and  ethylamine  on  ethyl  oxalate.  They  crystallise 
from  hot  water.  By  acting  on  diethyl  oxamide  with  PC15,  a  remarkable  tertiary 
amine  has  been  obtained,  called  chloroxaletliyUne,  and  having  the  formula  C6H9C1N2  ; 
it  is  an  alkaline  liquid,  which  boils  at  217°  C.,  and  when  acted  on  by  hydriodic 
acid  and  red  phosphorus,  it  yields,  on  distillation  with  soda,  another  liquid  base, 
OJcaletlujliiie,  C6H10N2,  which  is  poisonous,  and  produces  the  same  symptoms  as 
atropine,  notably  the  dilatation  of  the  pupil  of  the  eye. 

465.  Suceitiainide,  C2H4(CONH2)2,  produced  like  oxamide,  crystallises  in  sparingly 
soluble  needles.     At  200°  C.  it  yields  ammonia  and  xuccinimide  ;  C2H4(CONH2)2  = 
NH3+r.2H4(CO).2NH.     This  body  is  also  formed   when  ammonium   succinate   is 
distilled.     It  is  crystalline,  and  soluble  in  water  and  alcohol.     By  mixing  the 
hot  alcoholic  solution  with  a  little  ammonia  and  silver  nitrate,  silver  succinimitlr, 
C.2H4(CO).2NAg,  is  obtained  in  crystals. 

The  unifies,  which  contain  the  group  NH  (imidogen),  exhibit  an  acid  character, 
allowing  the  H  of  this  group  to  be  exchanged  for  a  metal. 

466.  Carbamide,  or  urea,  CO(NH2)2,  is  the  diamide  of  carbonic 
acid,  CO(OH),,  and  is  produced  by  heating  NH3  with  ethyl  carbonate  at 
!8o°  C.—  CO(OC9H,)o  +  2NH3  =  CO(NHJ9  +  2HOC2H5  ;  by  treating 
NH3  with  car  bony  1  "chloride  (phosgene)—  COC12  +  4NH3  =  CO(NH2)3  + 
2NH4C1  ;  by  heating  oxamide  with  mercuric  oxide—  (CON  H,)2  +  HgO  = 
CO(NH,),  +  Hg  +  CO2;  or  by  heating  a  solution  of  CO  in  ammoniacal 
cuprous"  chloride—  CO  +  2NH3  +  Cu2Cl'2  =  CO(NH2)2  +  2HC1  +  Cu.  But 
the  best  process  for  preparing  it  is  to  heat  a  solution  of  ammonium 
isocyanate,  NH4'NCO,  which  is  metameric  with  urea—  CO  :  N'NH,  = 
CO(NH2)2.  (See  below.) 


670  AETIFICIAL   UEEA. 

Urea  is  the  chief  form  in  which  the  nitrogen  of  the  effete  tissues  is 
excreted  from  the  human  organism,  and  it  is  present  in  urine  to  the 
amount  of  about  1.4  per  cent,  by  weight. 

To  extract  it,  the  urine  is  filtered  to  separate  mucus,  evaporated  to  about  an 
eighth  of  its  bulk,  cooled  and  mixed  with  about  an  equal  volume  of  strong  HN03, 
which  must  be  quite  colourless,  showing  it  to  be  free  from  nitrous  acid,  which 
would  decompose  the  urea  ;  the  latter  is  precipitated  in  pearly  scales  of  urea 
nitrate,  which  is  nearly  insoluble  in  the  acid,  and  sparingly  soluble  in  water.  This 
is  collected  on  a  filter,  washed  with  ice-cold  water  till  the  washings  are  but  slightly 
coloured,  dissolved  in  boiling  water,  and  mixed  with  precipitated  BaC03,  rubbed 
to  a  cream  with  water,  as  long  as  a  fresh  addition  of  the  carbonate  causes  effer- 
vescence— 

2(NoH4COHN03)  +  BaC03  =  C02  +  2N2H4CO  +  H20  +  Ba(N03)2. 
After  filtering  from  the  excess  of  BaCO3,  the  liquid  is  evaporated  on  a  steam-bath, 
when  a  mixture  of  urea  and  barium  nitrate  is  obtained,  from  which  the  urea  may 
be  extracted  by  strong  alcohol,  and  crystallised  by  evaporation. 

Artificial  urea.  The  preparation  of  urea  without  having  resource  to 
urine  attracted  much  attention  as  one  of  the  earliest  examples  of  the 
artificial  formation  of  an  animal  product  from  mineral  sources.  The 
original  process  (Liebig  and  Wohler)  was  the  following :  56  parts  of 
well-dried  potassium  ferrocyanide,  are  mixed  with  28  parts  of  dried 
manganese  dioxide,  the  mixture  heated  to  dull  redness  in  an  iron  dish, 
and  stirred  until  it  ceases  to  smoulder.  The  cool  residue  is  treated 
with  cold  water,  filtered,  and  the  solution  (of  potassium  (iso)cyanate) 
decomposed  with  41  parts  of  crystallised  ammonium  sulphate.  It  is 
then  evaporated  to  dryness  on  a  steam-bath,  and  treated  with  strong 
alcohol  to  extract  the  urea. 

As  a  class  experiment,  a  strong  solution  of  potassium  isocyanate  may  be  mixed 
with  an  equal  volume  of  a  strong  solution  of  ammonium  sulphate,  and  divided  into 
two  parts,  one  of  which  is  boiled  for  a  minute,  and  cooled.  If  both  portions  be 
now  stirred  with  strong  (colourless)  nitric  acid,  the  first  will  simply  effervesce 
violently,  but  the  second  will  deposit  abundant  crystals  of  urea  nitrate. 

Urea  crystallises  in  long  prisms  resembling  nitre,  which  dissolve  in 
an  equal  weight  of  cold  water,  and  in  five  parts  of  cold  alcohol ;  it 
is  almost  insoluble  in  ether.  When  heated,  urea  fuses  at  132°  C.,  and 
evolves  much  ammonia  and  some  ammonium  cyanate.  If  kept  for 
some  time  at  150°  C.,  the  bulk  of  it  is  converted  into  biuret,  produced 
from  two  molecules  of  urea  by  the  loss  of  one  molecule  of  ammonia ; 
2CO(NH2)2  =  NH3  +  NH(CONH2)2.  When  the  temperature  is  raised 
to  170°  C.,  the  biuret  again  evolves  ammonia,  and  is  converted  into 
cyanuric  acid ;  3NH(CONH2)2  =  3NH3  +  2(CNOH)3. 

Urea  is  not  alkaline,  but,  like  many  amides,  it  is  a  weak  base,  and, 
though  a  diamide,  forms  salts  like  a  monacid  base  ;  these  are  acid  to 
litmus.  The  nitrate  and  oxalate  are  best  known  because  they  are 
sparingly  soluble,  and  are  obtained  as  crystalline  precipitates  when 
nitric  and  oxalic  acids  are  stirred  with  solution  of  urea. 

The  nitrate,  Avhen  heated,  evolves  a  very  pungent  smell,  and  is  decomposed  with 
almost  explosive  violence  at  150°  C.  Urea  o-ralate  crystallises  with  2Aq  ; 
(N2H4CO)2.H2C204.2Aq.  Urea  hydrochloride,  N2H4CO.HC1,  is  formed,  with 
evolution  of  heat,  when  HC1  gas  acts  on  dry  urea  ;  it  solidifies  to  a  crystalline 
deliquescent  mass,  which  is  decomposed  by  water. 

Urea,  like  many  other  amides,  forms  compounds  with  the  oxides  of  silver  and 
mercury.  The  compound  N2H4C0.3Ag20  is  obtained  as  a  grey  crystalline  powder 
when  silver  oxide  is  digested  in  solution  of  urea.  When  mercuric  oxide  is  treated 
in  the  same  way  the  compound  N2H4CO.HgO  is  formed  ;  on  adding  mercuric 


DERIVATIVES   OF   UREA.  671 

chloride  to  a  solution  of  urea  mixed  with  potash,  a  white  precipitate  of 
2X2H4C0.3HgO  is  obtained,  but  if  mercuric  nitrate  be  employed,  the  precipitate 
is  X2H4C0.2HgO.  The  formation  of  the  last  compound  is  the  basis  of  Liebio-'s 
method  for  the  determination  of  urea. 


Urea  also  forms  compounds  with  certain  salts  :  the  compound  X2H4CO.XaCl  An 
is  obtained  in  crystals  when  urine  is  evaporated  to  a  small  bulk.     When  strong 
solutions  of  urea  and  AgX03  are  mixed, -crystals  of  X2H4CO.AgXO3  are  deposited 
Bv  mixing  dilute  solutions  of  urea  and  mercuric  nitrate,  a  m-ecioitate  i*  forma 
having  the  formula  X2H4CO(HgO)2HX03. 

By  hydrolysis  urea  yields  ammonia  and  carbonic  acid,  hence  its  transformation 
into  ammonium  carbonate  when  urine  is  allowed  to  putrefy. 

Xitrous  acid  acts  on  urea,  as  on  amides  generally,  converting  the  XH2  into  OH, 
and  liberating^  N,  but  ^the  (HO)2CO  formed  is  at  once  decomposed  into  H20  and' 
C02 ;  (XH2)2CO  +  2HX02  —  X4+C02  +  3H20.  Hypochlorites  and  hypobromites 

(prepared   by   dissolving   Br  in  alkalies)   also  expel  all   the  nitrogen  as  gas 

(XH2)2CO  +  3XaOBr  +  2XaOH  =  X2  +  3H20  +  Xa^COs  +  3XaBr.  This  method  is 
sometimes  adopted  for  determining  urea  by  measuring  the  nitrogen.  The  nitrogen 
is  also  liberated  when  urea  is  boiled  with  potash  and  a  large  excess  of  potassium 
permanganate,  whereas,  in  most  other  amides,  the  bulk  of  the  nitrogen  is  oxidised 
to  nitric  acid.  When  chlorine  is  passed  into  fused  urea,  hydrochloric  acid  and 
nitrogen  are  evolved,  and  the  residue  is  a  mixture  of  cyanuric  acid  with  ammonium 
chloride— 3X.2H4CO  +  C13  =  HC1  +  X  +  (CX)3(HO)3  +  2XH4C1. 

By  boiling"  solution  of  urea  with  AgX03,  a  crystalline  precipitate  of  silver 
isocyanate  is  obtained  ;  X2H4CO  + AgX03  =  XH4X03  +  AgXCO. 

Urea  has  been  formed  by  passing  XH3  and  CO2  together  through  a  red-hot 
tube  ;  and  by  passing  a  mixture  of  benzene- vapour,  ammonia  and  air  over  red-hot 
platinum  wire. 

Although  most  of  the  derivatives  of  urea  behave  as  though  they  were  derived 
from  the  formula  CO(XH2)2,  there  are  certain  compounds  which  appear  to  be 
derivatives  of  a  pseudourea  of  the  form  XH:C(XH2)(OH). 

Biuret  or  alloplianamide,  XH(COXH2)2,  is  obtained  by  heating  urea  to  150°  C.as 
long  as  it  evolves  XH3  freely,  extracting  the  residue  with  cold  water,  which  leaves 
most  of  the  cyunuric  acid  undissolved,  precipitating  the  rest  by  lead  acetate, 
removing  the  lead  by  H2S,  and  evaporating  the  filtered  solution,  when  the  biuret 
crystallises  with  iH20.  It  is  soluble  in  alcohol.  Its  alkaline  aqueous  solution 
gives  a  fine  violet  colour  with  CuS04.  When  heated  in  HC1  gas,  biuret  is  con- 
verted into  guanidine  hydrochloride ;  XH(  COXH2)2  +  HC1  =  C02  +  C(XH)(XH2)2.HC1. 
Biuret  is  also  obtained  by  heating  ethyl  allophanate  with  XH3. 

Allophanic  acid  has  not  been  obtained  ;  when  liberated  from  its  salts,  it  decom- 
poses into  C02  and  urea  ;  XH2CO'XH'COOH  =  CO(XH2)2  +  C02.  Ethyl  allophanate 
is  formed  when  urea  is  acted  on  by  ethyl  chlorocarbonate  (prepared  by  saturating 
alcohol  with  carbonyl  chloride)  ;  CO(XH2)2  +  COCl-OC2H5  =  NH2CO-NH'COOCaHB  + 
HC1.  It  crystallises  in  prisms  soluble  in  water  and  alcohol. 

The  hydrogen  in  urea,  like  that  in  other  primary  amides,  may  be  exchanged  for 
radicles,  forming  so-called  compound  ureas.  Those  containing  positive  radicles, 
such  as  methyl  carbamide,  CO(XH2)(XHCH3),  and  dimethyl  carbamide,  CO(XHCH3)2, 
are  derived'  from  the  isocyanates  of  the  amines,  just  as  urea  is  derived  from 
ammonium  isocyanate.  Those  containing  acid  radicles,  such  as  acetyl  carbamide 
or  acetyl  urea,  CO(XH2)(XHC2H30),  obtained  by  the  action  of  acetyl  chloride  upon 
urea,  are  called  ureides.  Di-acetyl  carbamide  is  formed  when  acetamide  is  heated 


to  50°  C.  with  COC12  ;  2XH2C2H30  +  COC12  =  CO(XHC2H30)2  +  2HC1. 

The  action  of  XH.?  on  bromacetylurea,  NH2-CO'XHCH2BrCO,  produces  hydanto>n, 
which  is  a  reduction-product  of'alloxan  (//.r.).  The  Br  may  be  supposed  to  be 
exchanged  for  OH  by  the  action  of  the  ammonia  solution,  but  hydantom  appears 
to  be  an  internal  anhydride  of  the  glycolylurea  which  would  thus  be  formed, 
XH.2-CO-XH-CH2OHCO  giving  NHCO'NH-CH2CO  +  H20. 

Carbanilide,  or  diphenyl  vrea,  (NHC6H5)2CO,  is  prepared  by  heating  urea  with 
aniline  ;  (NH,),CO  +  2XH2C6H5  =  (XHC6H5)2CO  +  2NH3.  It  is  slightly  soluble  in 
water,  more  soluble  in  alcohol,  melts  at  235°  C.  and  boils  at  260'  C.  Carbanilide 
is  also  formed  when  aniline  is  acted  on  by  carbonyl  chloride. 

467.  Thiocarbumide  or  sulpho-urea,  CS(NH2)2,  is  the  amide  of  thiocarbomc  acid, 
CS(OH)2.  It  is  obtained  from  ammonium  (iso)thiocyanate,  OS  :  N'NH4,  just  as 
urea  is  obtained  from  the  isocyanate.  It  crystallises  easily  from  hot  water,  and 


672  AMIC  ACIDS. 

resembles  urea  in  its  chemical  reactions  ;  it  melts  at  169°  C.  PbO  abstracts  sulphur 
from  it,  converting  it  into  cyanamide  (</.v.).  Its  salts  appear  to  be  derived  from 
the  tautomeric  form  NH  :  C(NH2)(SH). 

T1iiocar~banHide,  or  dipheni/l  sulphurea,  is  formed  when  aniline  is  heated  with 
carbon  disulphide  ;  2NH2C6H5  +  CS2^CS(NHC6H5).2  +  H2S.  It  forms  colourless 
crystals,  insoluble  in  water,  soluble  in  alcohol  and  ether,  and  melts  at  154°  C. 

468.  Amic  Acids. — If  only  one  of  the  acid  hydroxyl  groups  of  a 
dibasic  acid  is  exchanged  for  NH2  an  amic  acid,  like  succinamic  acid, 
C2H4(CONH2)(COOH),  is  obtained.     These  acids  are  primary  amides, 
and  are  generally  obtained  by  heating  the  acid  ammonium  salts  of  the 
dibasic  acids,  just  as  the  normal  salts  yield  the  diamides.     Or  the  acid 
ethereal  salts,  like  ethyl  hydrogen  oxalate,  COOH-COOC2H5,  may  be 
treated  with  NH3. 

Oxamic  acid,  CONH2'COOH,  is  prepared  by  heating  ammonium  hydrogen 
oxalate  till  it  begins  to  give  off  C02  (see  above).  A  mixture  of  oxamide  and 
oxamic  acid  is  left,  from  which  water  extracts  the  acid.  Ammonium  oxamate  is 
formed  when  oxamide  is  boiled  with  solution  of  ammonia;  (CONH2)2  +  H20  = 
CONH2'COONH4.  On  adding  HC1,  the  oxamic  acid  is  obtained  as  a  crystalline 
precipitate,  sparingly  soluble  in  water,  alcohol,  and  ether,  and  converted  into 
hydrogen  ammonium  oxalate  by  boiling  with  water.  It  fuses  at  210°  C.,  and  de- 
composes, yielding  oxamide,  formic  acid,  and  water.  Treated  with  PC15,  it  yields 
oxlmide  (C02)  :  NH,  a  soluble  neutral  substance. 

469.  Carbamic  acid,  CO(NH«,)OH,  has  not  been  obtained  in  the  free 
state,   but  ammonium  carbamate  is  formed  when  ammonia  combines 
with  C02;    2NH3  +  C02  =  CO(NH2)(ONH4).      The  ammonium  salt   is 
best  prepared  by  saturating  absolute  alcohol   with   dry  ammonia  gas, 
and  passing  dry  C02  into  the  solution,  when  the  ammonium  carbamate 
crystallises.     It  is  soluble  in  water,  and  is   converted   into  ammonium 
carbonate  by  boiling  the  solution  ;  CO(NH2)'ONH4  +  H20  =  CO(ONH4)2. 
Ammonium  carbamate  sublimes   and    dissociates    below  100°  C.,  and 
when  heated,  in  a  sealed  tube,  to  135°  C.,  yields  urea  and   ammonium 
carbonate  ;  2CO(NH2)'ONH4  =  CO(NH2)2  +  CO(ONH4)2. 

When  ammonium  carbonate  is  distilled,  part  of  it  is  converted  into  the  car- 
bamate ;  CO(ONH4)2=CO-NH2(ONHi)  +  H20.  This  accounts  for  the  presence  of 
ammonium  carbamate  in  the  commercial  carbonate  (p.  355). 

Ethyl  carbamate,  wurethane,  CO(NH2)OC2H5,  is  formed  by  the  action  of  solution 
of  ammonia  upon  ethyl  carbonate  at  100°  C. — 

CO(OC2H5)2  +  NH3  =  CO(NH2)OC2H5  -f  HO'C2H5. 

It  forms  tabular  crystal's,  soluble  in  water,  alcohol,  and  ether,  melts  at  50°  C.,  and 
boils  at  184°  C.  Boiled  with  potash,  it  yields  the  carbonate,  alcohol,  and  ammonia  ; 
CO(NH2)OC2H5  +  2KOH^CO(OK)2  +  NH3  +  HO-C2H5.  Heated  with  ammonia,  it 
gives  alcohol  and  urea  ;  CO(NH2)OC2H5  +  NH3  =  CO(NH2)2  +  HO-C2H5. 

Thiocarbamic  acid,  CS(NH2)SH,  is  obtained  as  an  ammonium  salt 
by  acting  on  carbon  bisulphide  with  ammonia  in  alcoholic  solution  ; 
2NH3  +  CS2  =  CS(NH2)SNH4,  the  reaction  corresponding  with  that 
between  NH3  and  CO2.  The  ammonium  thiocarbamate  crystallises  in 
yellow  prisms.  When  decomposed  by  HC1,  it  yields  thiocarbamic  acid 
as  a  yellow  unstable  crystalline  body,  which  decomposes  spontaneously ; 
CS(NH2)SH  =  H2S  +  HSON  (thiocyanic  acid). 

470.  Gruanidines. — These  compounds,  which  are  of  much  importance 
on  account  of  their  physiological  significance,  are  amidines  (p.  668)  of 
carbonic  acid.      Guanidine  itself,  the  parent  substance,  is  also  called 
imido-urea,  since  it  may  be  regarded  as  containing  an  imodo-group  in 
the  place  of  the  oxygen  of  urea;  thus,  CO(NH,)2,  urea  ;  C(NH)(NHf)f 
guanidine.     The  guanidines  can  be  prepared  synthetically  by  heating 


GUANIDINE.  673 

the    hydrochloride  of   an  amine  with  cyanamide  dissolved  in  alcohol— 
e.g.,  CN-NH2  +  NH3,HC1  =  C(NH)(NH2)2,HC1. 

Guanidine,  or  carbon-diamide-imide,  C(NH)(NH2)8,  occurs  in  vetch 
seeds  and  sugar  beet.  It  was  so  called  because  originally  obtained  by 
the  oxidising  action  of  KC103  and  HC1  on  guanine,  a  feeble  base 
extracted  from  guano.  It  is  prepared  by  heating  ammonium  thio- 
cyanate  in  a  retort  at  190°  C.  for  several  hours.  A  portion  of  the 
thiocyanate  becomes  thiocarbamide,  which  then  reacts  with  the  re- 
maining ammonium  thiocyanate  yielding  guanidine  thiocyanate  • 
CS(NH2)2  +  NH3,CNSH  =  C(NH)(NH2)2,CNSH  +  H2S.  This  is  dissolved 
in  a  little  water  mixed  with  half  its  weight  of  potassium  carbonate,  and 
evaporated  to  dry  ness,  when  a  mixture  of  guanidine  carbonate  and 
potassium  thiocyanate  is  obtained.  This  is  boiled  with  alcohol,  which 
dissolves  the  thiocyanate,  and  leaves  guanidine  carbonate  (N3H5C)2.H2C03, 
which  may  be  recrystallised  from  water.  This  is  converted  into 
guanidine  sulphate,  (N3H5C)2.H2S04,  and  decomposed  by  baryta-water  ; 
the  filtrate  from  the  BaS04  is  evaporated  over  sulphuric  acid,  when 
guanidine  is  obtained  as  a  deliquescent  crystalline  substance,  which  is 
strongly  alkaline,  and  absorbs  C02  from  the  air.  It  is  a  strong  monacid 
base,  and  yields  well-crystallised  salts. 

Guanidine  nitrate,  N3H5C.HN03,  like  urea  nitrate,  is  sparingly  soluble  in  water, 
and  crystallises  in  plates.  Guanidine  is  soluble  in  alcohol.  Its  platinum  salt, 
(N3H5C.HCl)2PtCl4,  is  sparingly  dissolved  by  absolute  alcohol.  When  hydrolysed 
with  baryta-water,  guanidine  yields  urea  and  ammonia;  C(NH2)2NH  +  H20  = 
(NfL>)2CO  +  NH.V  Heated  with  strong  potash,  it  gives  potassium  carbonate  and 
ammonia  ;  C(NH2)2(NH)"  +  2KOH  +  H20  =  C(OK)20  +  sNH3.  Hot  dilute  H2S04 
converts  it  into  NH3  and  urea,  which  combine  with  the  acid. 

Guanidine  hydriodide  is  obtained  when  cyanogen  iodide  is  heated  with  alcoholic 
ammonia  in  a  sealed  tube  at  100°  C. ; 

I-CN  +  2NH3  =  C(NH)(NH2)2.HI. 

Xitroguanidine,  C(NH)(NH2)(NHN02),  is  obtained  by  nitrating  guanidine,  and 
yields  ainidoguanidine,  C(NH)(NH2)(NHNH2),  when  reduced.  This  compound  is 
of  interest  as  yielding  hydrazine,  NH3  and  C02,  when  hydrolysed,  Hydrazoic 
acid  (p.  107)  may  also  be  obtained  from  it  by  first  treating  it  with  nitrous  acid 
to  form  diazo-ffuanidine,  C(NH)(NH2)(NHN  :  N-OH),  and  hydrolysing  this. 
"^Dlphenyl  guanidine,  or  melaniline,  C(NH'C6H5)2NH,  is  a  crystalline  base  pro- 
duced by  the  action  of  cyanogen  chloride  on  aniline — 

Cl-CN  +  2NH2C6H5  =  C(NH-C6H5)2NH.HC1. 

AMIDO-ACIDS. 

471.  These  may  be  prepared  from  the  chloro-substituted  acids  by  treat- 
ment with  ammonia  ;  thus  amido-acetic  acid  results  from  the  action  of  am- 
monia on  monochloracetic  acid,  CH2C1'C02H  +  2NH3  =  CH2(NH2)-C02H 
+  NH3.HC1 ;  also  by  the  reduction  of  the  nitro-acids  or  the  cyano-acids 
by  nascent  hydrogen — 

CH2(N02)'C02H  +  H6  =  CH2(NH2)'C02H  +2H20. 
CH2(CN)-COOH  +  H4  =  CH2-CH2(NH2)-COOH.  ^ 

In  the  aromatic  group  the  nitro-acids  are  reduced  to  obtain  the  amido- 
acids.  They  are  metameric  with  the  amides  of  hydroxy-acids,  but  are 
distinguished  by  their  greater  stability  towards  hydrolysing  agents,  the 
amido-group  being  more  firmly  held  and  less  easily  evolved  as  NH3. 
Like  other  ammonia  derivatives  they  may  be  primary,  secondary, 
or  tertiary,  as  NH2(CH2COOH),  NH(CH2COOH)2,  N(CH2COOH)3, 
obtained  from  the  mono-  di-  and  tri-chloracetic  acids  respectively.  J  he 

2  u 


674  GLYCOCINE. 

open-chain  derivatives  may  be  a-,  /3-,  or  y-amido-acids,  like  other 
open-chain  substituted  acids.* 

By  action  of  nitrous  acid  the  NH2  group  is  converted  into  an  OH 
group,  as  in  the  case  of  the  amines  and  amides,  a  hydroxy-acid  being  pro- 
duced— CH2(NH2)-C02H  +  NOOH  =  CH2(OH)'C02H  +  1ST2  +  HOH. 
But  there  is  a  tendency  for  the  amido-acids  to  undergo  the  diazo-reaction 
(p.  106). 

When  heated  with  baryta  the  amido-acids  lose  C02  and  give  the  corre- 
sponding amines  -  CH2NH2'COOH  =  CH3NH2  +  C02. 

Just  as  the  a-hydroxy-acids  form  lactides  by  loss  of  water  from  both  the  COOH 
and  the  OH  groups  (p.  603),  so  the  amido-acids  are  converted  by  dehydrating 
agents  into  anhydrides  by  loss  of  water  from  the  NH2  and  COOH  groups  ;  thus 

OO*O  FT 

two    mols.   glycocoll,    CH2NH2-COOH,   yield    NH/  2\NH.     Further,    the 

XCH2'CO/ 

y-  and  S-amido-acids  yield  internal  anhydrides,  lactams,  corresponding  with  the 
lactones  (p.  607)  ;  y-amidcbwtyric  acid,  CH2NH2-CH2-CH2-COOH,  yields  y-lnttyro- 
lactam,  CH2NH-CH2'CH2CO. 

472.  Amidoformic  acid,  NH2'C02H,  is  identical  with  carbamic  acid. 

Glycocoll,  glycocine,  or  gli/cine,  is  amido-acetic  acid,  CH2(N"H9)C09H, 
and  is  prepared  by  heating  hippuric  acid  (benzoyl  amido-acetic)  for  half 
an  hour  with  4  parts  of  strong  HC1,  which  converts  it  into  benzoic  acid 
and  glycocine  hydrochloride  — 

CH2(NHC6H5CO)-C02H  +  HC1  +H20  =  C8H5C02H  +  CH2(NH2)C02H.HCL 
Hippuric  acid.  Benzoic  acid.       Glycocine  hydrochloride. 

The  solution  is  mixed  with  water  and  cooled,  when  most  of  the  benzoic  acid 
crystallises  out  ;  the  nitrate  is  evaporated  to  dryness  on  a  steam-bath,  the  glycocine 
hydrochloride  extracted  by  water,  boiled  with  lead  hydroxide,  filtered  from  the 
lead  oxychloride,  the  dissolved  lead  precipitated  by  H2S,  and  the  filtrate  evaporated. 
when  it  deposits  the  glycocine  in  transparent  rhombic  prisms,  easily  soluble  in 
water,  sparingly  in  alcohol,  and  insoluble  in  ether. 

Glycocoll  has  a  sweet  taste,  fuses  at  232°  0.,  evolving  ammonia  and 
methylamine.  Its  solution  gives  a  red  colour  with  Fe2Cl6,  and  a  blue 
with  CuS04  ;  if  this  blue  solution  be  mixed  with  potash  and  alcohol,  it 
deposits  blue  needles  of  the  formula  (NH2'CH2'C02)2Cu.Aq.  A  sparingly 
soluble  silver  salt,  NH2'CH2C02Ag,  may  also  be  obtained,  but  these 
compounds  do  not  behave  like  ordinary  salts  of  the  metals  (cf.  synthesis 
of  hippuric  acid).  Like  other  amido-acids,  glycocine  plays  the  part  of 
a  base  and  an  acid.  It  forms  hydrochlorides  containing,  respectively, 
one  and  two  molecules  of  glycocine,  and  the  latter  forms  a  crystalline 
platinum  salt.  Crystalline  compounds  of  glycocine  with  salts  are  also 
known. 

From  the  behaviour  of  the  metallic  and  other  derivatives  of  glycocoll, 
it  appears  probable  that  the  constitution  of  this  (and  of  other)  amido- 
acids  is  not  that  represented,  but  partakes  of  the  nature  of  an  intra- 


molecular  ammonia  salt  —  CH2<^ 

Glycocoll  can  also  be  prepared  by  heating  bromacetic  acid  with  ammonia,  and 
by  passing  cyanogen  into  a  boiling  saturated  aqueous  solution  of  hydriodic  acid  — 
C2N2  +  2lI20  +  5HI  =  CH2(NH2)-C02H  +  NH4I  +  I4. 

*  The  prefixes  amino-,  imhto-,  anilino-,  &c.,  are  now  often  substituted  for  aniido-,  imido-. 
anilido-,  &c. 


HIPPUKIC  ACID. 

Both  methods  afford  a  means  of  synthesising  glycocol,  which  derives  its  name  from 
the  fact  that  it  may  be  obtained  by  boiling  glue  (or  gelatine)  with  dilute  sulphuric 
acid  (sugar  of  gelatine  ;  y\vKvs,  sweet  ;  xoXXa,  give.) 

Sbrcosine,  or  methyl  glycocoll,  CH2(NHCH3)-C02H,  may  be  obtained  by  heating 
bromacetic  acid  with  methylamine  (in  place  of  ammonia,  which  yields  glycocine) 
.t  is  also  formed  when  the  creatine  extracted  from  flesh  is  boiled  with  baryta 
Caffeine  yields  it  under  similar  treatment.  Sarcosine  forms  prismatic  crystals 
very  soluble  in  water  and  of  sweet  taste.  It  is  sparingly  soluble  in  alcohol' 
insoluble  in  ether,  and  may  be  sublimed.  Its  reaction  is  neutral,  but  it  combines 
with  acids  and  bases. 

Betaine,  or  tri-methyl-glycocoll,  CH2[N(CH3)2]-C02CH3,  or  more  probably— 


is  found  in  the  juice  of  beet-root  (Beta  vulgaris),  and  may  be  formed  synthetically 
by  the  action  of  trimethylamine  on  chloracetic  acid  — 

CH2C1-C02H  +  N(CH3)3  =  CH2[N(CH3)2]-C02CH3  +  HC1. 

Betaine    hydrochloride    is  also  obtained  by  the    careful    oxidation   of    choline 
hydrochloride  — 

N(C2H4OH)  (CH3VC1  +  02  =  CH2[N(CH3)2]  -C02CH3,HC1.  +  H20. 
Betaine  is  soluble  in  water  and  alcohol,  arid  forms  salts  with  the  acids. 

Anilido-acetic  acid  or  phenylglycocine,  CH2(NHC6H5)-COOH,  prepared  from 
bromacetic  acid  and  aniline,  melts  at  127°  C.  It  is  important  as  the  parent  sub- 
stance of  artificial  indigo. 

Acetylglycocine,  or  aceturlc  acid,  CH2(NHCH3CO)'COOH,  from  acetyl  chloride 
and  silver  glycocine,  melts  at  206°  C. 

473.  Hippuric  acid,  or   benzoylglycocoll,    or   benzamidoacetic   acid, 
CH2(NHC6H5CO)'CO.,H,  is  prepared  from  the  urine  of  horses  or  cows 
(preferably  the  latter)  by  evaporating  it  to  about  an  eighth  of  its  bulk 
and  adding  an  excess  of  HC1.     On  standing,  long  prisms  of  hippuric 
acid  are  deposited,  which   may  be  decolorised  by  dissolving  in  boiling 
water  and  adding  a  little  chlorine-  water,  when  the  colourless  acid  will 
crystallise  out  on  cooling.     If  the  animal  has  undergone  much  exercise, 
or    the    urine    has    decomposed,  benzoic   acid    is    obtained  instead  of 
hippuric,  and  if  a  dose  of  benzoic  acid  is  taken,  it  is  found  as  hippuric 
acid  in  human  urine,  which  contains  naturally  but    a  minute    pro- 
portion. 

It  may  be  synthesised  by  heating  benzoyl  chloride  with  silver 
glycocoll  (of.  salts  of  glycocoll,  p.  674). 

CH2(NH2VC02Ag  +  C6H5COC1  =  CH2(NHC6H5CO)'C02H  +  AgCl  ; 
or  benzamide  with  chloracetic  acid  — 

CH2C1-C02H  +  C6H5CONH2  =  CH2(NHC6H5CO)'C02H  +  HC1. 

Hippuric  acid  crystallises  in  rhombic  prisms,  sparingly  soluble  in  cold 
water,  soluble  in  hot  water  and  in  alcohol,  but  insoluble  in  ether,  which 
distinguishes  it  from  benzoic  acid.  Like  benzoic,  it  dissolves  easily^  in 
ammonia,  and  is  precipitated,  in  feathery  crystals,  by  hydrochloric  acid  ; 
but  these  are  not  dissolved  on  adding  ether. 

The  more  complex  character  of  hippuric  acid  is  shown  by  the  action  of  heat  ; 
for,  whereas  benzoic  acid  sublimes  without  decomposition,  hippuric  assumes  a  red 
colour,  gives  a  small  sublimate  of  benzoic  acid  and  evolves  hydrocyanic  acid, 
benzamide,  C6H5CONH2,  and  benzonitrile,  or  pttenyl  cyanide,  C6H5'CN,  whicl 
smells  of  bitter  almonds. 

The  hippurate*  resemble  the  benzoates  ;  in  solution,  they  give  a  butt  precipiti 
with  ferric  chloride. 

474.  Glycocoll  may  be  regarded  as    the    parent    substance   of    two 
physiologically  important  compounds,  creatine  and  creatinine. 


676  CREATINE  AND   CREATININE. 

When  solutions  of  cyanamide  and  glycocoll  are  mixed,  glycocyamine,  or  guanl- 
doacetic  acid,  CH2[C(:NH)(NH2)(NH)]  •  C02H,  is  formed.  If  glycocoll  be  regarded 
as  an  amine,  NH2(CH2'C0.2H),then  the  formation  of  glycocyamine  is  only  in  accord 
with  the  general  method  for  producing  guanidines  (p.  672).  When  glycocyamine 
hydrochloride  is  heated  at  160°  C.  it  becomes  glycocyamidiiie  hydrochloride  by  loss 
of  water  — 


+  H20. 
NHCH2 

Creatine  and  creatinine  are  methylglycocyamine  and  methylglycocyarnidine 
respectively. 

Creatine,    or     methylglycocyamine    (/cpe'ay,    flesh),     C4H9N302,      or 

/NH, 

NH  :  C\  ,  is  obtained  from  chopped  flesh  by  soaking 

XN(CH3)-CH2-C02H 

it  in  cold  water,  squeezing  it  in  a  cloth,  heating  the  liquid  till  the 
albumin  coagulates,  straining,  adding  baryta  to  precipitate  phosphoric 
acid,  and  evaporating  the  filtrate  to  a  syrup  on  the  steam-bath  ;  on 
standing  for  some  hours  the  creatine  crystallises  out. 

It  may  also  be  prepared  from  Liebig's  extract  of  meat  by  dissolving  it  in  20  parts 
of  water,  adding  tribasic  lead  acetate,  filtering,  removing  the  excess  of  lead  by 
H2S,  and  evaporating  to  crystallisation.  Granular  crystals  of  creatine  are  some- 
times met  with  in  Liebig's  extract.  The  flesh  of  fowls  yields  0.32  per  cent,  of 
creatine,  that  of  cod-fish  0.17,  beef  0.07  per  cent. 

Creatine  forms  prismatic  crystals  (with  iH20)  easily  soluble  in  hot 
water,  but  very  sparingly  in  alcohol  and  ether.  It  is  neutral  in  reaction, 
but  behaves  as  a  feeble  monacid  base.  Creatine  nitrate,  C4H9N302.HNO3, 
crystallises  in  prisms.  When  the  solutions  of  its  salts  are  heated  above 
30°  C.,  they  are  converted  into  salts  of  creatinine,  a  stronger  base  con- 
taining H,  and  O  less  than  creatine.  When  boiled  with  baryta  water, 
creatine  is  hydrolysed  to  sarcosine  and  urea  — 

CH2[C(:NH)(NH2)(NCH3)]-C02H  +  H20  =  CO(NH2)2  +  CH2NH(CH3)'C02H. 

Creatine  has  been  prepared  synthetically  by  heating  cyanamide  with  an 
alcoholic  solution  of  sarcosine  or  methyl  glycocoll,  thus  settling  its  constitution. 
When  it  is  warmed  with  solution  of  sodium  hypobromite,  two-thirds  of  its  nitrogen 
is  liberated.  By  heating  creatine  in  aqueous  solution  with  mercuric  oxide,  it  is 
converted  into  oxalic  acid  and  methyl-guanidine,  C(NH)(NH2)(NHCH3). 

Creatinine,  or  methylglycocyamidine,  04H7N30,  or 

/NH  -  -CO 

NH  :  C<f  •      ,  is  prepared  by  heating  creatine  in  a  water-bath 

and  passing  a  current  of  pure  HC1  over  it  as  long  as  any  water  is 
formed.  The  hydrochloride  thus  obtained  is  dissolved  in  water,  decom- 
posed by  lead  hydroxide,  the  solution  filtered  and  slowly  evaporated, 
when  it  deposits  prismatic  crystals  of  C4H7N30.2Aq,  which  lose  water 
on  exposure  to  air,  becoming  opaque.  If  it  be  dissolved  in  cold  water, 
and  evaporated  in  vacua,  the  original  hyclrated  crystals  are  reproduced, 
but  if  it  be  dissolved  in  boiling  water  and  the  solution  evaporated,  it 
deposits  tabular  crystals  which  contain  no  water.  The  solution  of  these 
crystals  when  kept  for  some  time  at  60°  C.  deposits  the  prismatic 
hydrated  creatinine. 

Creatinine  is  much  more  soluble  in  water  than  creatine  is,  requiring 
about  1  2  parts  of  cold  water.  It  dissolves  in  about  i  oo  parts  of  cold 
alcohol.  It  has  an  alkaline  reaction,  and  is  a  strong  monacid  base.  It 


LEUCINE. 


is  characterised  by  forming  a  sparingly  soluble  crystalline  compound 
with  zinc  chloride,  (C4H7N30)2ZnCl2.  In  contact  with  water,  especially 
in  presence  of  bases,  creatmine  is  converted  into  creatine  by  hydration. 


Creatinine  does  not  appear  to  exist  as  such  in  flesh,  though  it  is  easily  produced 
from  it  by  the  dehydration  of  the  creatine.  A  substance  having  the  same  composi- 
tion as  creatinine  exists  in  considerable  quantity  <in  urine  (about  two  grams  in 
the  urine  of  twenty-four  hours),  but  its  properties  are  not  quite  the  same  as  those 
of  the  creatinine  prepared  from  the  creatine  of  flesh.  In  order  to  prepare  urinary 
creatinine,  the  urine  is  mixed  with  one-twentieth  of  its  volume  of  a  cold  saturated 
solution  of  sodium  acetate,  and  with  one-fourth  of  its  volume  of  a  cold  saturated 
solution  of  mercuric  chloride  ;  this  produces  an  amorphous  precipitate  which  is 
quickly  filtered  off,  and  the  filtrate  is  set  aside  for  forty>eight  hours,  when  it 
deposits  a  granular  precipitate,  appearing  in  spheres  under  the  microscope.  This 
precipitate  is  suspended  in  cold  water,  and  decomposed  by  H2S,  the  mercuric  sul- 
phide is  filtered  off,  and  the  acid  filtrate  evaporated  over  sulphuric  acid,  when  it 
leaves  crystals  of  the  hydrochloride,  C4H7N3O.HC1.  The  concentrated  aqueous 
solution  of  this  salt  is  decomposed,  in  the  cold,  with  lead  hydrate,  when  an  alkaline 
filtrate  is  obtained,  which  has  a  bitter  taste,  and,  by  spontaneous  evaporation, 
yields  prismatic  crystals  of  C4H7N30.2H20,  which  rapidly  become  opaque  and 
anhydrous  when  exposed  to  air.  If  heat  be  employed  during  the  preparation  of 
the  body,  tabular  crystals  of  C4H7N30  are  obtained,  which  are  unchanged  by 
exposure  to  air.  The  urinary  creatinine  requires  362  parts  of  cold  alcohol  to  dis- 
solve it,  while  flesh-creatinine  requires  only  102  parts.  It  is  a  more  powerful 
reducing-agent  than  creatinine  prepared  from  flesh-creatine. 

475.  Propionic  acid  can  give  rise  to  two  substituted  acids  (cf,  p.  580),  conse- 
quently there  are  two  amido-prdpionic  acids.    The  a-acid  is  called  alanine, 

CH3-CH(NH2)-C02H, 

prepared  by  the  action  of  ammonia  on  a-chloropropionic  acid.    It  dissolves  in 
water  and  becomes  ethylidene  lactic  acid  when  treated  with  nitrous  acid. 
Hutalanine,  which  occurs  in  the  pancreas  of  the  ox  is  a-afnido-isovaleric  acid, 
(CH8)2  :  CH'CH(NH2)-C02H. 

476.  Leucine,  or  a-amido-caproic  cwid,  CH3-[CH2]3>CH(NH2)<C02H, 
is  prepared  by  boiling  horn  shavings  (one  part)  with  sulphuric  acid 
(2^  parts)  and  water  (6J  parts)  in  a  reflux  apparatus,  for  twenty-four 
hours.     The  hot  liquid  is  neutralised  by  lime,  filtered,  and  evaporated 
to  about  one-  third  ;  it  is  then  carefully  neutralised  with  H2S04  and 
evaporated  till  crystals  of  leucine  and  tyrosine  are  deposited  on  cooling; 
by  recrystallisation  from  water  the  tyrosine  crystallises  first. 

Several  other  animal  substances  yield  leucine  and  tyrosine  when  boiled  with 
dilute  sulphuric  acid,  or  fused  with  potash.  The  elastlne  composing  the  cervical 
ligament  of  the  ox  yields  more  than  horn.  Leucine  also  occurs  extensively  in 
animals  and  vegetables.  It  is  found  in  the  liver,  spleen,  lungs,  and  pancreas  ;  also 
in  caterpillars  and  spiders  ;  in  the  white  sprouts  of  vetch,  in  yeast,  and  in  putre- 
fying cheese. 

Leucine  crystallises  in  pearly  scales,  moderately  soluble  in  water, 
slightly  in  alcohol,  and  insoluble  in  ether.  It  fuses  at  170°  C.,  and  may 
be  partly  sublimed,  though  much  of  it  decomposes,  yielding  amylamine  ; 
C5H10(NH9)-C09H  =  NH9-C5HU  +  C02.  Its  reaction  is  neutral,  but  it 
forms  compounds  both  with  acids  and  bases.  Hydriodic  acid  converts 
it  into  caproic  acid  and  ammonia  — 

C5H10(NH2)-C02H  +  2HI  =  CBHu-COaH  +  NH3  +  I2. 
With  nitrous  acid  it  yields  leucic  or  hydroxy  -caproic  acid— 

C5H10(NH2)'C02H  +  HN02  =  C5H10(OH)'C02H  +  N2  +  H20. 


6/8  TYEOSINE. 

Leucine  is  obtained  synthetically  from  ammonia  and  bromocaproic 
acid;  NH3  +  C5H10BrC62H  =  C3H10(NH2)-C02H  +  HBr  ;  also  by  the 
reaction  between  valeraldehyde-ammonia,  HCN,HC1  and  H20. 

C5H100'NH3  +  HCN  +  HC1  +  H20  =  C3H10(NH2)-COaH  +  NH3HC1. 

The  leucine  from  plants  appears  to  differ  from  that  from  animals,  • 
being  optically  active  and  existing  in  the  usual  three  modifications 
(p.  604). 

Tyrosine  (rvpds,  cheese)  or  ^-hydroxy-phenyl-amido-propionic  acid — 

CH2(C6H4OH)-CH(NH2)-C02H, 

is  obtained,  together  with  leucine,  when  albuminoid  or  gelatinoid  bodies 
are  boiled  with  dilute  sulphuric  acid  or  fused  with  potash.  It  crystal- 
lises in  needles,  which  are  sparingly  soluble,  even  in  hot  water,  sparingly 
soluble  in  alcohol,  and  insoluble  in  ether.  It  melts  at  235°  C.,  and  is 
laevo-rotatory.  Like  leucine,  it  behaves  both  as  a  feeble  acid  and  a 
feeble  base.  When  its  aqueous  solution  is  boiled  with  mercuric  nitrate 
it  gives  a  yellow  precipitate,  which  becomes  red  when  boiled  with  nitric 
acid  containing  nitrous  acid.  With  chlorine,  it  yields  chloranil,  06C1402, 
and  with  fused  potash,  NH3,  and  potassium  parahydroxy-benzoate  and 
acetate ; 
C6H4OH-C2H3NH2-C02H  +  2KOH  =  NH3  +  C6H4OH'C02K  +  CH3-C02K  +  H2. 

477.  Amido-succinamic  acid,  CH2CONH2'CHNH2C02H,  or  asparagine,  is  found 
in  the  shoots  of  asparagus  and  of  other  plants  grown  in  the  dark.     It  is  of  very 
frequent  occurrence  in  plants,  being  found  in  marsh-mallow,  vetches,  peas,  beans, 
mangold-wurzel,  lettuces,  potatoes,  chestnuts,  and  dahlia  roots.     It  may  be  ex- 
tracted from  the  expressed  juices  of  the  plants  by  boiling  to  coagulate  the  albumin, 
filtering,  and  evaporating  to  a  syrup,  when  the  asparagine  crystallises,  on  standing, 
in  rhombic  prisms  (with  iH20)  which  may  be  recrystallised  from  boiling  water. 
It  is  nearly  insoluble  in  alcohol  and  ether.     It  behaves  as  a  weak  acid  and  a  weak 
base.     By  ferments,  asparagine  is  converted  into  ammonium  succinate  ;  by  nitrous 
acid  into  malic  acid — 

.  C2H3NH2(CO-NH2)(CO-OH)  +  2HX02=  C2H3OH(CO'OH)(CO-OH)  +  N4  +  2H20. 
From  this  reaction  it  was  formally  inferred  that  asparagine  was  the  amide  of 
malic  acid,  with  which,  however,  it  is  only  isomeric.  Ordinary  asparagine  is 
laevo-rotatory ;  the  dextro-form  has  been  found  in  the  mother-liquor  from  crude 
asparagine,  and  is  much  sweeter  than  ordinary  asparagine.  A  solution  of  the  two 
in  equal  proportions  is  inactive,  but  the  asparagines  are  deposited  from  it  in 
crystals,  which  are,  respectively,  right-  and  left-handed.  The  isomeric  derivatives 
from  each  kind  retain  the  optical  properties  of  their  source.  When  asparagine  is 
boiled  with  acids  or  alkalies, it  is  converted  into  l-am'idosucclnlc  or  aspartie  acid — 

C2H3NH2(CO-NH2)(CO-OH)  +  H20  =  C2H3NH2(CO'OH)(CO-OH)  +  NH3. 
Aspartie  acid  is  sparingly  soluble  in  cold  water  and  alcohol,  but  may  be  crystal- 
lised from  hot  water.  Nitrous  acid  substitutes  OH  for  the  NH2  in  aspartie  acid, 
converting.it  into  malic  acid.  Aspartie  acid  is  found  in  the  molasses  from  beet- 
root juice,  and  occurs  among  the  products  of  the  action  of  sulphuric  acid  and  of 
zinc  chloride  upon  albuminous  substances. 

478.  Amidobenzoic acids,  C6H4(NH2)-C02H.     Of  these  the  I  :  2-acid  or  anthranilic 
acid  is  of  importance,  being  an  oxidation  product  of  indigo.     It  is  prepared  by 
reducing  I  :  2-nitrobenzoic  acid  ;  it  sublimes  in  needles,  melts  at  145°  C.  and  dis- 
solves in  hot  water  ;  the  solution  tastes  sweet  and  fluoresces  blue. 

Methyl  anthranilate  (m.-p.  25°'5  C.)  in  dilute  solution  smells  of  orange-blossom 
oil  (iieroli  oil'),  of  which  it  is  a  constituent. 

/COv 

The  internal  anhydride  or  lactam,  anthranil,  C6H4<^        \  might  be  expected  to 

be  formed  by  dehydration  of  anthranilic  acid,  this  being  a  i :  2-derivative  (cf.  p.  674) ; 
it  cannot  be  so  obtained,  however,  but  is  a  product  of  the  reduction  of  i  :  2-nitro- 
benzaldehyde.  It  dissolves  in  alkalies  to  form  salts  of  anthranilic  acid.  By 


TAURINE.  679 

treating  it,  or  anthranilic  acid,  with  COC12,  isatoic  anhydride,  C6H4/ C  °'? 

NH'CO'  ' 

oxidation-product  of  indigo,  is  obtained. 

Amidophenylacetic  acids,  C6H4(NH.2)-CH.,COoH,  are  obtained  by  reducing  the 
corresponding  nitre-acids,  but  only  the  -HI-  and  j>-  acids  are  known  in  the  free 

pTT 

.state  ;  attempts  to  prepare  the  I  :  2-acid  produce  oxindol,  C6H,/      ^CO,  which 

XNHX 

is  an  internal  anhydride  or  lactam  of  the  acid  (p.  674).     The  same  .happens  in  the 
case   of   i  :  2-emidopkettylglyv&ylic  acid  or   isatic  acid,   C6H4(NH2)-CO-C02H,  a 

CO 

ketonic  acid  ;  in   this  case  the  anhydride  is  a   lactim,  isatin,  C6H4/      \OOH. 

These  compounds  are  closely  related  to  indigo  and  will  receive  further  attention  in 
connection  with  that  substance. 

479.  Amidosulphonic  Acids. — Taurine,  amido-ethyl-sulphonic  acid, 
or  amido-isethionic  acid,  C2H4(NH2)S03H,  is  a  decomposition-product  of 
taurocholic  acid  (q.v.)  and  is  prepared  by  boiling  ox-gall  with  dilute 
HC1,  evaporating  to  dryness  on  the  steam-bath,  and  treating  the  residue 
with  absolute  alcohol,  which  leaves  the  taurine  undissolved.     This  is 
dissolved  in  water,  from  which  it  crystallises  in  large  four-sided  prisms 
sparingly  soluble  in  cold  water,  and  insoluble  in  alcohol  and  ether.     It 
fuses  at  240°  C.  and  is  decomposed.     It  has  no  acid  reaction,  but  it 
forms  salts  with  bases.     When  fused  with  KOH,  it  yields  the  acetate 
and  sulphite  of  potassium — 

C2H4(NH2)-S03H  +  sKOH  =  CH3'COOK  +  K2S03  +  NH3  +  H20  +  H2. 
Nitrous  acid  substitutes  OH  for  the  NH2,  producing  isethionic  acid. 

Synthesis  of  taurine  : — C2H4  is  absorbed  by  S03,  the  product  dissolved  in  water, 
neutralised  with  NH3,  and  evaporated  to  crystallisation  ;  C2H4+S03  +  H20  +  NH3  = 
CoH4OH-SO.}NH4  (ammonium  isethionate).  When  this  is  heated  to  220°  C.,  it  yields 
taurine— C2H4OH  -S03NH4  =  C2H4NH2.S03H  +  H20. 

Taurine  may  also  be  synthesised  by  converting  ethene  into  glycol-chlorhydrin, 
HO'CoH4-Cl,  heating  this  with  K2S03  to  obtain  potassi umisethionate— 

HO-C2H4-C1  +  K2S03  =  HO-C2H4-S03K  +  KC1 ; 
distilling  the  isethionate  with  phosphoric  chloride — 

HO-C2H4'S03K  +  PC15  =  P02C1  +  HC1  +  KC1  +  Cl'CaH4-S02Cl  (isethionic  chloride]  ; 
heating  this  with  water — 

C1'C2H4-S02C1  +  HOH  =  HC1  +  C1-C2H4-S02'OH  (chlor-etlbtjlsul^honic  acid)  ; 
and  heating  this  to  100°  C.  with  ammonia  in  a  sealed  tube — 

C1'C2H4-S02-OH  +  2NH3  =  NH3HC1  +  NH2-C2H4-S02'OH  (taurine}. 

Some  taurine  exists  as  such  in  the  bile  ;  it  has  been  found  in  the  kidneys,  lungs, 
and  muscles.    When  solution  of  taurine  is  evaporated  with  potassium  cyanate,  it 
yields  potassium  tauro-carbamate,  NH2CONH-CH2'CH2S03K  ;  tauro-carbamic  a. 
is  found  in  the  urine  when  taurine  is  taken  internally ;  it  forms  crystj 
.soluble  in  water. 

Amidobenzemsulphoriic  acid  (see  p.  664). 

DlAZO-   AND    AZO-COMPOUNDS. 

480.  Diazo- Compounds. — It  has  been  already  noticed  that  the  amines 
of  open-chain  hydrocarbons  show  no  tendency  to  undergo  the  diazo- 
reaction  described  on  p.  106,  whereas  the  amines  of  closed-chain  nydi 
carbons"  readily  do  so  at  low  temperatures.      It  thus  happens    that 
diazo-compounds  of  the  type  R'N  :  N'X,  where  R  is  a  positive  and  X  a 


680  DIAZO-COMPOUNDS. 

negative  radicle,  are  only  known  when  R  is  a  radicle  containing  a  ben- 
zene ring. 

There  is,  however,  a  tendency  for  the  amido-acids  of  the  open-chain  series  to 
undergo  the  diazo-reaction,  although  the  diazo-acids  produced  appear  to  be 
differently  constructed  from  the  true  diazo-coinpounds,  and  have  only  been 
isolated  as  ethereal  salts  or  as  amides. 

Diazoacetic  acid,    ••\CH'C02H,   has  not  been   isolated,  but  ethyl  diazoacetate, 

N2CH-C02C2H5,  is  precipitated  as  a  yellow  oil  when  the  hydrochloride  of  ethyl 
amidoacetate  (ethyl  glycocoll)  is  dissolved  in  a  little  water  and  treated  with 
sodium  nitrite  ;  it  boils  at  143°  C.  and  is  decomposed  by  acids  with  evolution  of 
nitrogen,  which  becomes  explosively  rapid  if  the  acid  be  strong  ;  it  reduces  hot 
Fehling's  solution  (p.  619).  When  it  is  slowly  dissolved  in  strong  ammonia  it  is 
converted  into  diazoacetamide,  N2CH-CONH2,  which  is  soluble  in  water  and  forms 
crystals  :  it  detonates  when  suddenly  heated.  When  attacked  by  halogens  ethyl 
diazoacetate  exchanges  its  nitrogen  for  two  atoms  of  halogen  ;  this  indicates  that 
its  constitution  differs  from  that  of  diazobenzene,  for  instance. 

By  reduction,  ethyl  diazoacetate  yields  NH3  and  glycocoll,  but  an  intermediate 
product  is  a  salt  of  hydraziacetic  acid  which  yields  a  hydrazine  salt  and  glyoxylic 
acid  when  treated  with  an  acid. 

Strong  NaOH  saponifies  and  polymerises  ethyl  diazoacetate  yielding  the  sodium 

salt  of  lisdiazoacetic  acid,  COoH'CH/  \CH'COoH,  formerly  called  triazoacetic 

XN  :W 

acid.  The  acid  crystallises  in  orange  red  tables  (with  2H20)  and  gives  a  charac- 
teristic red  colour  with  nitric  acid.  When  heated  with  dilute  acids  it  is  hydrolysed 
to  oxalic  acid  and  hydrazine  ; 

C02H-CH[N4]CH-C02H  +  2H2S04  +  4H20  =  2(N2H4,H2S04)  +  2(COOH)2. 

Nx 

Diazomethane^    ••^>CH2,  is  obtained  by  treating  various  nitroso-derivatives  of 

methylamine  such  B&  nitrosomethylurethane,  with  alkalies  : — CO(NCH3-NO)OC2H54- 
NaOH  =  CH2N2  +  H20  +  CO(ONa)(OC2H5).  When  solutions  of  KCN  and  KHSOa 
are  mixed  and  allowed  to  remain  for  some  days,  potassium  amidomethane-disul- 
phonate,  (S03K)2  :  CHNH2,  crystallises.  If  the  mixture  is  warmed  and  then  acidified 
the  corresponding  hydrogen  potassium  salt,  (S03K)(S03H)  :  CHNH2,  is  obtained  ; 
this  yields,  when  treated  with  KN02,  potassium  diazometh'ane  disulphonate, 

/N 
(S03K)2C^..,  the  best  source  of  hydrazine  (p.  106).     Diazomethane  is  a  yellow, 

odourless,  poisonous  gas,  yielding  methylhydrazine  when  reduced.  Diazoetbane 
has  also  been  prepared. 

At  moderately  high  temperatures  the  aromatic  amines  react  with 
nitrous  acid  just  as  the  fatty  amines  do,  the  NH3  being  exchanged  for 
OH  ;  C6H5NH2  +  ON'OH  =  C6H5OH  +  N2  +  HOH.  But  at  low  temper- 
atures, particularly  when  a  salt  of  the  aniine  is  employed,  the  diazo- 
compound  is  formed  as  an  intermediate  product — 

C6H5-NH2,HN03  +  ON'OH  =  C6H5'N  :  N'N03  +  2HOH. 
Aniline  nitrate.  Diazobenzene 

nitrate. 

The  salts  of  diazo-compounds  are  usually  prepared  in  aqueous  solution, 
since  they  are  only  used  as  transition-products  in  the  preparation  of 
other  compounds  (v.i.),  or  for  the  production  of  azo-compounds.  The 
amido-compound  (amine)  is  dissolved  in  a  dilute  acid,  the  solution  cooled 
in  ice,  and  the  calculated  quantity  of  sodium  nitrite  added. 

For  preparing  the  crystalline  salts,  arnyl  nitrite  is  the  best  nitrite  and  the 
reaction  should  be  effected  in  absolute  alcohol  ;  the  amine  and  the  amyl  nitrite 


REACTIONS   OF  DIAZO-COMPOUNDS,  68 1 

are  dissolved  in  the  alcohol,  and  an  acid  is  added  to  the  cooled  solution  ;  after  a 
few  minutes  the  diazo-salt  crystallises  and  may  be  washed  with  alcohol  and  ether  • 
C6H5-NH2,HC1  +  C5HnN02  -  C6H5'N  :NC1  +  C5Hn'OH  +  HOH. 

Diazobenzene  nitrate  is  best  prepared  by  passing  N203  (p.  98)  into  a  thin  paste 
of  aniline  nitrate  and  water,  cooled  by  ice  and  salt,  until  KOH  no  longer  precipi- 
tates aniline.  A  brown  product  is  filtered  off,  and  alcohol  added  to  the  filtrate 
when  the  nitrate  separates  in  colourless  needles.  These  are  soluble  in  water' 
but  insoluble  in  ether  and  sparingly  soluble  in  alcohol.  At  90°  C.,  or  when  struck 
it  detonates  with  extreme  violence. 

By  decomposing  diazobenzene  nitrate  with  potash,  the  compound  C6H5N2'OK, 
diazobenzene  pctassoxide,  is  obtained,  in  which  the  potassium  may  be  exchanged  for 
other  metals,  producing  unstable  and  sometimes  explosive  compounds.  By  acting 
on  the  potassium  compound  with  acetic  acid,  dlazobenzene  hydroxide,  C^jNyOH, 
is  obtained  as  a  very  unstable  liquid. 

Dlazobenzene  butyrate  is  said  to  be  identical  in  chemical  behaviour  and  physio- 
logical  effect,  with  tyrotoxicon,  a  poison  which  has  been  isolated  from  decom- 
posing milk. 

The  diazo-bases,  e.g.,  C6H5'N  :  N'OH,  have  never  been  isolated  owing 
to  their  instability. 

The  value  of  the  diazo-compounds  in  effecting  chemical  syntheses  will 
be  appreciated  from  the  following  typical  reactions  when  it  is  re- 
membered that  the  conversion  of  an  aromatic  hydrocarbon  into  a 
nitro-derivative,  this  into  an  amido-derivative,  and  the  amido-  into  a 
diazo-derivative  (diazotising),  is  easily  performed. 

(1)  For  the  diazo-group  may  be  substituted  a  hydroxyl  group  by 
warming  the  compound  with  water,  a  phenol  being  produced ; 

C6H5-N  :  N-C1  +  HOH  =  C6H5'OH  +  N2  +HC1. 

(2)  The  diazo-group  may  be  exchanged  for  a  halogen  or  cyanogen, 
producing  a  halogen  substituted  hydrocarbon  or  a  cyanide.     This  is  best 
effected  by  warming  the  diazo-compound  with  the  corresponding  cuprous 
salt  (Sandmeyer's  reaction).    The  cuprous  salt  forms  a  double  compound 
with  the  diazo-salt  which  decomposes  with    the    re-formation  of    the 
cuprous  salt ;  C6H5'N  :  NCl,Cu2Cl2  =  C6H5'C1  +  N2  +  Cu2Cl2. 

The  cuprous  salt  need  not  be  pre-formed  ;  thus,  to  produce  cyanobenzene 
(phenyl  cyanide,  C6H5CN),  diazobenzene  chloride  may  be  treated  with  a  mixture  of 
copper  sulphate  and  potassium  cyanide  (potential  cuprous  cyanide,  p.  675). 
Similarly,  nitre-benzene  may  be  formed  when  the  diazobenzene  chloride  is  treated 
with  KX02  and  freshly  precipitated  Cu20  (potential  cuprous  nitrite).  Finely 
divided  metallic  copper  will  frequently  cause  the  separation  of  nitrogen  and  the 
attachment  of  the  acid  radicle  to  the  benzene  nucleus  in  a  diazo-salt. 

The  cyanides  can  be  converted  into  acids  by  hydrolysis  (p.  587),  so 
that  acids  may  be  synthesised  through  Sandmeyer's  reaction. 

(3)  For  the  diazo-group  hydrogen  may  be  substituted,  the  hydro- 
carbon being  formed,  by  boiling  the  compound  with  alcohol — 

C6H5-N  :  XC1  +  C2H5OH  =  C6H5'H  +  N2  +  HC1  +  CH3'CHO. 

The  above  reactions  conclusively  show  that  diazobenzene-compounds 
must  contain  the  C6H.  group  ;  that  the  nitrogen  atoms  are  linked  in 
the  manner  represented,  is  concluded  from  the  fact  that  diazobenzene 
salts  yield  phenylhydrazine  salts  (p.  684)  when  reduced. 

C6H5'X  :  NCI  +  H4  =  C6H5'XH-NH2,HC1. 

On  the  other  hand,  the  behaviour  of  solutions  of  the  diazo-salts  indicate  that 
they  are  ionised  by  solvents  in  the  same  sense  as  the  ammonium  salts.  Hence  it 
is  probable  that  they  are  really  quaternary  ammonium  derivatives,  or  ******** 


682  AZO-COMPOUNDS. 

P  TT 

mlts  of  the  form  /NssK,  corresponding    with     tetramethylium     chloride, 

Cl  x 

3\N==(CH3)3,  for  example. 

or 

The  salts  like  C6H5N2rOK  are  apt  to  pass,  when  heated,  into  an  unstable  form 
which  cannot  be  coupled  readily  to  make  an  azo-compound  when  treated  with  an 
aniine  or  phenol,  as  the  normal  salts  can.  These  isodiazo-salts  have  been  supposed 
to  be  really  salts  of  the  nitrosamines,  of  the  form  C6H5NK*NO. 

481.  Diazo-amido-compounds.  —  When    it    is    attempted   to    prepare     a    diazo- 
compound   in  the  absence  of  an   acid,   a    diazo-amido-compound  is    obtained  ; 
probably,  one  portion  of  the  amine  is  diazotised  and  immediately  combines  with 
another  portion.     Thus,  diazoamidobenzene,  C6H5'N  :  N'NH'C6H5,  is  prepared  by 
passing  N203  into  a  cooled  solution  of  aniline  in  alcohol  ;  diazobenzene  hydroxide 
may    be    supposed    to    be    first    formed    and    then    to    combine   with    aniline  ; 
C6H5-N  :  N-OH  +  NH2-C6H5  =  C6H5-N  :  N'NHC6H5  +  HOH.     It  is  also  prepared  by 
the    interaction    of    diazobenzene   chloride    and   aniline,    HC1    being   liberated, 
C6H5N  :  NC1  +  C6H6NH2=C6H5N  :N-NHC6H8  +  HC1  ;  by  substituting  other  primary 
(or  secondary)  amines  for  aniline,  other  diazo-amido-compounds  are  formed,  and 
if  two  molecular  proportions  of  diazobenzene  chloride  to  one  of  the  amine  be  used,  a 
disdiazo-amido-compouiid  is  produced:   2C6H5N  :  NCl  +  NH2CfiHg=[C6H5N  :  N]0  : 
NC6H6  +  2HC1. 

Diazo-amidobenzene  crystallises  in  yellow  prisms  (m.-p.  96°  C.),  and  is  not  basic  ; 
like  most  other  diazo-amido-compounds,  it  readily  undergoes  an  intra-molecular 
transformation  when  in  solution,  becoming  the  corresponding  amido-a~o-compound, 
C6H5'N  :  N'C6H4(NH2)  (v.i.).  This  is  particularly  liable  to  happen  in  the  presence 
of  an  amine,  so  that  during  the  preparation  of  diazo-amido-benzene  the  excess  of 
aniline  may  cause  the  change.  The  diazo-amido-compounds  are  readily  split  up 
into  diazobenzene  compounds  and  aniline,  so  that  they  show  most  of  the  reactions 
of  the  former  compounds. 

482.  Azo-Compounds.  —  When  a  nitro  -compound  is  reduced  in  acid 
solution  the  corresponding  amido-derivative  is  immediately  produced, 
but  when  the  liquid  is  alkaline  there  are  formed,  in  the  case  of  the 
aromatic  nitro-compounds,  three  intermediate  products,  derived  from  two 
molecules    of    the    nitro-compound.      Thus,  nitro-benzene    in  alkaline 
solution  will  yield  azoxybenzene,  azobenzene  and  hydrazobenzene,  accord- 
ing to  the  reducing  capacity  of  the  agent  employed. 


C6H5N02                    C6HBNv  C6H5N                    C6H5NH 

I  >0  ||                              | 

C6H5N02                    C6HBir  C6H5N                    C6H5NH 

2  mols.  Nitro-benzene.         Azoxybenzene.  Azobenzene.  Hydrazobenzene. 


formed  when  nitrobenzene  is  reduced  by  alcoholic  potash,  but 
is  best  prepared  by  oxidising  azobenzene  by  chromic  acid  in  acetic  acid.  It 
crystallises  in  yellow  needles  (m.-p.  36°  C.),  insoluble  in  water,  but  soluble  in 
alcohol. 

Azo-compounds  may  be  symmetrical,  like  azobenzene,  or  mixed,  like 
benzeneazometkane,  C6H5']Sr  :  N'CH3  ;  the  latter  kind  are  produced  by 
oxidation  of  the  corresponding  hydrazines. 

Azobenzene,  C6H5N  :  NC6H5,  is  produced  when  an  alcoholic  solution  of 
nitrobenzene  is  treated  with  sodium  amalgam  or  with  zinc-dust  andNaOH. 
It  is  readily  obtained  by  dissolving  nitrobenzene  in  alcohol,  adding  an 
equal  weight  of  KOH,  and  distilling,  when  the  alcohol  is  oxidised  to 
acetic  acid,  and  the  nitrobenzene  reduced  to  azobenzene.  At  the  end 
of  the  distillation  it  comes  over  as  a  dark  red  oil,  which  solidifies  after 
a  time  to  a  crystalline  mass  ;  it  is  insoluble  in  water,  but  may  be 


AZO-DYESTUFFS.  683 

crystallised  from  alcohol  or  ether  in  beautiful    red  tables  resembling 
K0Cr2O7;  it  melts  at  68°  C.  and  boils  at  293°  C. 

Azobenzene  is  also  formed  when  aniline  is  oxidised  with  KMn04.  It  forms 
.substitution  products  like  benzene  does.  Alkaline  reducing-agents  convert  it  into 
hydrazobenzene,  but  acid  reducing-agents  convert  it  into  aniline. 

483.  Azo-dyestuffs.— Since  the  dyeing  of  a  fabric  involves  the  formation  of  an 
insoluble  coloured  substance  in  the  fibre,  it  is  essential  that  a  dyextuff  shall  be 
capable  of  combining  either  with  the  fibre  itself  or  with  some  substance  (a  mordant) 
previously  fixed  in  the  fibre,  to  form  an  insoluble  compound  (the  dye).  Most  dyestuffs 
are  capable  of  forming  dyes  with  wool,  and  to  a  smaller  extent  with  silk,  without 
the  intervention  of  a  mordant  ;  the  dyes  thus  produced  are  termed  substantive  dyes. 
With  cotton,  on  the  other  hand,  a  mordant  is  nearly  always  requisite,  the  dye 
obtained  being  called,  in  this  case,  an  adject I  ce  dye.  It  will  be  seen  that  since  a  dye- 
stuff  must  enter  into  some  form  of  chemical  combination  before  it  can  become  a  dye, 
it  must  be  a  substance  possessed  of  a  certain  amount  of  chemical  activity.  Thus  it 
happens  that  those  substances  which  have  been  found  to  be  successful  dyestuffs  are 
generally  either  acid  or  basic  in  character  ;  this  observation  has  proved  of  great 
value,  since  it  has  shown  that  although  a  compound  may  be  useless  as  a  dyestuff 
it  may  become  useful  if  it  be  treated  in  such  a  manner  that  the  necessary  acidity 
or  basicity  be  imparted  to  it.  It  is  possible  to  impart  acidity  to  an  organic  com- 
pound by  the  introduction  of  certain  radicles,  such  as  OH  or  S02OH,  and  basicity 
by  introducing  the  NH2  radicle.  It  is,  of  course,  only  certain  organic  compounds* 
which  can  be  converted  into  dyestutt's  by  the  introduction  of  such  groups  ;  these 
compounds  are  called  chromogem,  whilst  the  groups  that  lend  them  their  dyeing 
capacity  are  called  auxochromes.  An  acid  auxochrome  yields  an  acid  dyestuff, 
capable  of  being  fixed  by  a  basic  mordant  (alumina,  &c.)  ;  whilst  a  basic  auxo- 
chrome yields  a  basic  dyestuff,  capable  of  being  fixed  by  an  acid  mordant  (tannin). 
That  a  dyestuff  must  be  soluble  in  water  hardly  needs  stating  ;  it  will  be  equally 
obvious  that  a  dyestuff  need  not  be  itself  a  coloured  substance,  although  the  in- 
soluble compound  which  it  forms  in  the  fibre  must  be  coloured. 

Azobenzene  is  a  highly  coloured  substance,  but  is  at  the  same  time  both  chemi- 
cally indifferent  and  insoluble  in  water,  so  that  it  is  not  a  dyestuff.  It  is,  however, 
a  ctiromogen,  for,  by  the  introduction  of  the  OH  or  NH2  group,  compounds  are 
produced  which  are  either  dyestuffs  (when  soluble  in  water)  or  become  dyestuffs 
when  rendered  soluble  by  conversion  into  sulphonic  acids. 

The  dwzo-dyestuff*  are  compounds  containing  the  *N  :  N€  group  and  are  made 
by  diazotising  an  amido-compound  and  combining  the  product  with  an  amido-  or 
hydroxy-compound  (a  "dyestuff  component"). 

Amido-azo-oomptntnd*  are  produced  by  the  intramolecular  change  of  diazo- 
amido-compounds  (p.  682),  especially  in  presence  of  the  salt  of  an  ainine  which, 
hoAvever,  is  not  consumed.  The  change  generally  produces  an  amido-azo- 
compound  in  which  the  amido-group  is  in  the  para-position  to  the  azo-group,  hence 
if  an  aromatic  amine  is  used  to  prepare  the  diazo-amido-compound,  the  para- 
position  to  the  amido-group  should  be  unoccupied. 

p-Aniido-azobenzene  is  prepared  by  heating  diazo-amidobenzene  (10  grams)  with 
aniline  hydrochloride  (5  grams)  and  aniline  (25  grams)  at  45°  C.,  dissolving 
out  the  amiline  with  acetic  acid  and  crystallising  the  residue  from  HC1.  The 
hydrochloride  thus  formed  is  in  steel-blue  needles  and  was  formerly  sold  as 
aniline  yellow,  a  dyestuff.  The  base,  liberated  by  NH:?  from  the  hydrochloride, 
forms  yellow  needles  and  melts  at  127°  C.  By  sulphonation  it  yields  a  mixture  of 
mono- and  di-sulphonic  acids,  known  as  acid  yellow  or  fast  yellow.  It  is  largely  used 
for  making  indulines  (#.r.).  By  reduction,  amido-azobenzene  yields  aniline  and 
paraphenylenediamine. 

plniethylantidobetizenesidphoHlG   acid  is   prepared  from  diazo-benzenesulpnc 
acid  chloride  and  dimethylaniline — 

C6H4(S03H)-N:  N-C1  +  C6H5'N(CH3)2  =  C6H4(S03H)-N :  N'C6H4N(CH3)2  4-  I 
The  sodium  salt  is  -methyl  orange  (tropaeulin  O,  helianthin  or  orange  III.),  ui 
the  laboratory  as  an  indicator. 

2  :  4-])iamidoa:oben.ene,  C6H5'X  :  N'C6H3(NH2)2,  is  made  by  the  action  o 
•diazobenzene  chloride  on  metaphenylene-diamine— C6H5N  :  JSU  <-/6tl4(iNJi2).2  — 
O6H5-N :  N-C6H3(NH2)2  +  HC1.  It  melts  at  117°  C.  and  its  hydrochloride  is  an  or 

*  Almost  always  such  as  contain  one  or  more  benzene  nuclei,  and  a  special  group,  like  the 
<Jiazo-group,  called  a  chroinophore. 


684  HYDEAZINES. 

yellow  dyestuff  called  chrysoldlne.  The  4  :  ^'-diamido-azobenzene,  NH2'C6H4*N  :  N 
•C6H4'NH2  gives  rise  to  the  red  basic  dyestuffs,  the  azylines,  which  are  the  tetra- 
alkyl  derivatives  of  the  above  compound  and  are  obtained  by  diazotising  a  dialkyl-jw- 
phenylenediainine  and  combining  the  product  with  a  dialkylaniline — 

NE2-C6H4-N:  N-C1  +  C6H5NK2  =  NK2-C6H4'N :  N'C6H4-NK2  +  HC1. 

Bismarck  'brown  (phenylene  brown,  Manchester  brown)  is  the  hydrochloride  of  a 
mixture  of  bases  prepared  by  the  action  of  nitrous  acid  on  metaphenylendiamine  ; 
it  consists  largely  of  the  hydrochloride  of  triamido-azobenzene,  C6H4(NH2)-N  :  N 
•C6H3(NH2)2,  formed  by  diazotising  one  NH2  in  the  metaphenylene-diamine  and 
combining  the  diazo-compound  with  another  mol.  of  the  diamine. 

Hydroxyazo-compounds  are  prepared  by  the  interaction  of  a  diazo-chloride  and  a 
phenol.  Thus  hydt'oxyazo-benzene  is  prepared  from  diazo-benzene  chloride,  and 
phenol  ;  C6H5'N  :  N'Cl  +  C6H5OH  =  C6H5'N  :  N'C6H4(OH)  +  HC1.  They  are  also 
formed  by  an  intra-molecular  change  of  the  azoxy-compounds,  just  as  the  amidoazo- 
result  from  the  diazoamido-compounds. 

Dihydroxyazobenzenesulphonic  acid,  C6H4(S03H)'N  :  N  'CgH^OH)^  is  prepared 
from  the  chloride  of  diazobenzenesulphonic  acid  and  resorcinol  (cf.  methyl 
orange).  Its  sodium  salt  is  resorcin  yellow. 

Diazo-dyestuffs. — These  contain  the  'N  :  N-  group  twice,  and  are  of  three  kinds, 
(i)  The  two  N2  groups  may  be  attached  to  the  same  benzene  nucleus  which  also 
contains  the  auxouhrome  (OH  or  NH2).  For  instance,  by  the  reaction  of  diazo- 
benzene  chloride  on  resorcinolazobenzene,  resorcinoldisazobenzene  is  obtained — 
C6H5N2C1  +  C6H5N2C6H3(OH)2  =  C6H5'N  :  N'C6H2(OH)2'N  :  N'C6H5  +  HC1.  (2)  The 
two  N2  groups  may  be  attached  to  the  same  benzene  nucleus  and  the  auxochrome 
to  another  nucleus.  Biebrich  scarlet  is  a  dyestuff  of  this  type  made  by  diazotising 
amidoazobenzene  disulphonic  acid  to  produce 

C6H4(S03H)-N  :  N'C6H3(S03H)-N  :  N'Cl, 
which  is  then  combined  with  /3-naphthol,  producing 

C6H4(S03H)-N  :N'C6H3(S03H)-N  :N'C10H6(OH). 
(3)  The  two  N2  groups  may  be  attached  to  different  nuclei.  To  this  class  belong 
the  numerous  benzidlne  dyestuffs  or  tetrazo-dyest'itjfs,  which  are  valuable  as  substan- 
tive dyestuffs  for  cotton,  most  others  requiring  a  mordant.  Congo-red  serves  as  a 
type;  benzidine,  NH2 *C6H4  -  C6H4'NH2  (p.  666)  is  diazotised  to  tetrazodijpkenyl 
chloride,  C1N  :  N'C6H4-C6H4'N  :  NCI,  which  is  then  combined  with  a-naphth  ij- 
laminesulphonic  acid,  C10H6(SO3H)'NH2  to  form  congo-red,  the  formula  for  which  is 
NH2-(S03Na)C10H5-N  :  N'C6H4-C6H4-N  :  N'C10H5(S03Na)-NH2. 


DERIVATIVES  OF  HYDRAZINE  AND  HYDROGEN  NITRIDE  (DIAZOIMIDES). 

484.  Hydrazines. — These  bases  are  derived  from  hydrazine  (p.  106), 
H2N'NH2,  by  substituting  a  hydrocarbon  radicle  for  H.  They  may  be 
primary,  B/NH'NH2,  or  secondary,  E,2:N'NH2,  and  symmetrical, 
KHN'NHR  (hydrazo-compounds),  or  asymmetrical,  RHN'NH2  (hydra- 
zine compounds).  When  R  is  an  alkyl  radicle,  the  hydrazines  are  best 
prepared  by  the  action  of  reducing-agents  on  the  nitrosoamines ; 
R2 :  N-NO  +  H4  =  R2 :  N'NH2  +  H20.  But  the  alkyl  hydrazines 
are  of  very  little  importance  at  present.  When  R,  is  an  aromatic 
radicle,  the  hydrazines  are  best  prepared  by  the  reduction  of  the 
diazo-compounds.  The  reaction  of  the  hydrazines  with  compounds 
containing  ketonic  or  aldehydic  oxygen  has  been  already  noticed 
(PP-  583^25). 

Phenylhydrazine,  C6H3*NH'NH2,  is  prepared  by  dissolving  aniline 
(i  part  by  weight)  in  strong  HC1  (20  parts),  cooling  by  adding  ice,  and 
slowly  adding  an  ice-cold  solution  of  NaN02  (0.75  parts),  in  water 
(4  parts).  The  aniline  hydrochloride  is  thus  converted  into  di-azoben- 
zene  chloride  (p.  680).  A  solution  of  stannous  chloride  (4.5  parts)  in 
an  equal  weight  of  HC1  is  now  carefully  added  ;  this  converts  the 


PHENYLHYDRAZINE.  685 

diazobenzene  chloride  into  phenylhydrazine  hydrochloride,  which  is 
precipitated — 

C6H5N  :  N-C1  +  4HC1  +  2SnCl2  =  C6H5-NH'NH2,HC1  +  2SnCl4. 

The  precipitate  is  washed  with  a  mixture  of  alcohol  and  ether, 
dissolved  in  a  little  water,  and  decomposed  by  strong  NaOH,  when  the 
hydrazine  separates  as  an  oily  layer,  which  is  freed  from  water  by 
distilling  with  potassium  carbonate. 

Phenylhydrazine  is  thus  obtained  as  a  colourless  aromatic  liquid  of 
sp.  gr.  1.091,  and  boiling-point  241°  C.  It  solidifies  in  a  freezing 
mixture  to  tabular  crystals,  fusing  at  23°  C.  It  is  sparingly  soluble 
in  cold  water,  but  dissolves  in  alcohol  and  ether.  Phenylhydrazine  is 
a  strong  reducing-agent  and  absorbs  oxygen  from  air,  becoming  brown. 
It  reduces  alkaline  cupric  solution,  even  in  the  cold,  precipitating  yellow 
cuprous  hydroxide,  and  evolving  nitrogen,  while  aniline  and  benzene 
are  found  in  the  solution.  This  is  a  general  reaction  for  identifying 
hydrazines,  and  may  also  be  employed  for  diazo -compounds  by  boiling 
their  aqueous  solutions  with  KHS03,  to  reduce  them  to  hydrazines,  and 
adding  potash  and  alkaline  cupric  solution.  It  also  reduces  mercuric 
oxide  in  the  cold,  forming  nitrogen,  aniline,  benzene,  and  mercury- 
diphenyl.  It  is  a  monacid  base,  and  forms  crystalline  salts.  Solution 
of  phenylhydrazine  hydrochloride,  mixed  with  sodium  acetate,  forms  a 
general  test  for  aldehydes  and  ketones,  with  which  it  forms  insoluble  oily 
or  crystalline  compounds  (hydrazones,  p.  625,  see  also  osazones),  thus 
precipitating  them  from  their  aqueous  solutions ;  by  warming  these 
compounds  with  HC1  they  are  reconverted  into  their  parent  substances. 
When  heated  with  nascent  hydrogen  phenylhydrazine  yields  C6H5NH2 
and  NH3,  a  fact  which  settles  its  constitution,  as  well  as  that  of  the 
other  hydrazines.  It  is  used  technically  for  making  antipyrine  (q.v.) 

Sodium  dissolves  in  phenylhydrazine  evolving  H  and  forming  C6H5NaN'NH2. 

Hydrazine  yields  derivatives  on  the  same  lines  as  NH3  does,  but  as  it  has  four 
H  atoms  and  two  N  atoms,  the  latter  allowing  of  dissymmetry,  the  number  of  such 
derivatives  is  even  greater  than  that  obtainable  from  NH3.  Moreover,  the  hydra- 
zine derivatives  have  a  remarkable  tendency  to  undergo  internal  condensation, 
yielding  nitrogen  ring  compounds  (cf.  antipyrine).  The  following  are  the  leading 
types  : 

(i)  Asymmetrical  and  secondary  hydrazines  ;  hydra  zonluni  and  azonlum  com- 
pounds, corresponding  with  the  amines.  Hydrazobenzene  or  sym-diplienyl-hydm- 
zine,  C6H5HN-NHC6H5  (p.  684),  is  prepared  by  dissolving  azobenzene  in  alcohol, 
passing  NH3,  and  afterwards  H2S  till  the  solution  is  colourless. 

C6H5N  :  NC6H5  +  H2S  =  C6H5HN'NHC6H5  +  S. 

On  adding  water,  the  hydrazobenzene  is  precipitated,  and  may  be  crystallised  from 
alcohol.  It  forms  colourless  tables  (m.-p.  131°  C.)  becoming  orange  in  air,  from 
production  of  azobenzene,  and  smelling  of  camphor.  A  convenient  method  of 
converting  azobenzene  into  hydrazobenzene  is  to  boil  its  alcoholic  solution  with 
zinc-dust  until  it  is  colourless. 

When  heated,  hydrazobenzene  is  decomposed  into  azobenzene  and  aniline— 

2(C6HBHX-NHC6H6)  =  C6H5N'NC6H5  +  2(C6H5'H2N). 

When  dissolved  in  hydrochloric  or  sulphuric  acid,  it  is  converted  into  its  meta- 
meride  benzidine,  NH2C6H4'C6H4NH2  (p.  666).  This  change  recalls  that  of  a  diazo- 
amido-compound  into  an  amido-azo-compound  (p.  682)  and  like  the  latter  only 
occurs  when  the  4-positions  in  the  benzene  rings  are  free.  Thus  o-  or  m-Ayaraxo- 
toluene  yields  tolidine  by  this  intramolecular  change  (lenzidim  munition), 
but  in  tf-hydrazotoluene  only  one  of  the  NH  groups  shifts  (semidme  migration), 
producing  C7H7NHC7H6NHa,  in  which  NH2  is  in  the  2-position.  These  changes 
may  also  be  compared  with  that  of  methylaniline  into  paratoluidme  (p.  665),  and  n 


686  CYANOGEN   COMPOUNDS. 

should  be  noted  that  all  migrations  of  this  type  tend  to  produce  a  compound  of 
more  basic  properties. 

Examples  of  other  hydrazines  of  this  class  are  a-  and  fi-ethylphenylhy&razine, 
C6H5N(C2H5)-NH2  and  C6H5HN-NHC2H5.  The  former  combines  with'  C2H5Br 
forming  diethylphenylhydrazonvum  bromide,  C6H5N(C2H5)2BrNH2,  while  afi-dlethyl- 
phmylhydrazine,  C6H5iST(C2H5)-NHC2H5,  combines  with  C2H5Br  to  form  the 
azonium  compound,  C6H5N(C2H5)2BrNHC2H5. 

(2}  Plienylhydrazones.  —  Already  noticed  (p.  685). 

(3)  Hydrazldes.  —  These  are  acidyl  derivatives  corresponding  with  the  amides  and 
prepared  analogously.    For  example,  a.-acetylphenylhydrazide,  C6H5N(CH3CO)'XH.,. 
from  sodium  phenylhydrazine  and  acetyl  chloride  (m.-p.  124°  C.). 

Semicarbazide,  NH2CO'NH'NH2,  may  be  regarded  as  the  hydrazide  of  carbamic 
acid,  and  is  obtained  by  heating  urea  with  hydrazine  sulphate  at  100°  C.  It  gives 
rise  to  many  derivatives,  combining  with  aldehydes  and  ketones  as  phenylhydrazine 
does  ;  the  products  are  called  semlcarbazones. 

(4)  Hydrazido-acids  are    like  amido-acids    and    are   either   symmetrical,   e.y., 
C6H5NH-NH-CH2COOH,  or  asymmetrical,  e.g.,  C6H5N(NH2)'CH2COOH. 

.  (5)  Hydrazidines  (amidoazones)  are  analogues  of  the  amidines  (p.  668),  the  NH 
group  of  the  latter  having  been  exchanged  for  the  phenylhydrazone  group,  pro- 

x,N-NHC6H5 
ducing  compounds  of  the  type,  RC\  .    When  the  NH2  group  is  exchanged 


for  the   diazobenzene  group,  formaziil-deriratives  are  obtained,  RC\ 

\\:NC6H5 

which  are  highly  coloured  and  may  be   viewed  as  azo-dyestuffs,  prepared  from 
diazobenzene  and  phenylhydrazones. 

(6)  Tetrazones  are  produced  when  two  mols.  of  a  secondary  hydrazine  are  oxidised 
with  HgO— 

2C6H5N(CH3)'NH2  +  02  =  C6H5N(CH3)'N  :  N<CH,)KC^. 

485.  Diazoimides.  —  The   derivatives   of  hydrogen  nitride,    or    azoimide,    HN3 
(p.  107),  are  also  called  diazoimides,  or  tr'tazo-compounds.   They  are  obtainable  by  the 
action  of  NH3  on  the  diazo-perbromides.     Thus,  when   diazobenzene  bromide  is 
brominated,    C6H5'N  :  NBr  +  Br2  =  C6H5-NBrNBr2  ;     when   the  perbromide    is 

treated  with   ammonia,  C6H5'NBrNBr2  +  NH3  =  3HBr  +  C6H3'X<(^    (phenyl- 

azoimide).    When  heated  with  alcoholic  potash  the  dm\tro-pUenylazo\m\de  yields 
dinitrophenol  and  potassium  nitride,  KN3. 

Benzoyl  azoimide,  C6H5CON3,  formed  when  benzoyl-hydrazhle,  C6H5CO'NH'NH2. 
is  diazotised,  yields  sodium  benzoate  and  sodium  nitride  when  boiled  with 
NaOH. 

X.  CYANOGEN  AND  ITS  COMPOUNDS. 

486.  In  the  beginning  of  the  eighteenth  century,  a  manufacturer  of 
colours  at  Berlin  accidentally  obtained  a  blue  powder  when  precipitating 
sulphate  of  iron  with   potash.     This  substance  was  used  as  a  colour 
under  the  name  of  Prussian  blue,  for  several  years,  before  any  explana- 
tion of  its  production  was  attempted,  or  even   before  the  conditions 
under  which  it  was  formed  were  exactly  determined.     It   17  24  it  was 
shown  that  Prussian  blue  could  be  prepared  by  calcining  dried  animal 
matters  with  potashes,  and  mixing  the  aqueous  solution  of  the  calcined 
mass,  first  with  sulphate  of  iron  and  afterwards  with  hydrochloric  acid  ; 
but  the  most  important  step  towards  the  determination  of  its  composi- 
tion was  made  by  Maquer,  who  found  that,  by  boiling  it  with  an  alkali, 
Prussian  blue  was  decomposed,  yielding  a  residue  of  red  oxide  of  iron, 
and  a  solution  which  reproduced  the  blue  when  mixed  with  a  salt  of 
iron  ;  hence  he  inferred  that  the  colour  was  a  compound  of  the  oxide  of 
iron  with  an  acid  for  which  the  alkali  had  a  more  powerful  attraction  — 


CYANOGEN.  687 

a  belief,  confirmed  in  1782,  by  Scheele's  observations,  that  when  an 
alkaline  solution  prepared  for  making  the  blue  was  exposed  to  the  air, 
or  to  the  action  of  carbonic  acid,  it  lost  the  power  of  furnishing  the 
colour,  but  the  escaping  vapour  struck  a  blue  on  paper  impregnated 
with  oxide  of  iron.  Scheele  also  prepared  this  acid  in  a  pure  state,  and 
it  soon  after  obtained  the  name  of  prussic  acid. 

In  1787,  Berthollet  found  prussic  acid  to  be  composed  of  carbon, 
hydrogen,  and  nitrogen,  but  he  also  showed  that  the  power  of  the  alka- 
line liquor  to  produce  Prussian  blue  depended  upon  the  presence  of  a 
yellow  salt  crystallising  in  octahedra,  and  containing  prussic  acid, 
potash,  and  oxide  of  iron,  though  the  latter  was  so  intimately  bound 
up  with  the  other  constituents  that  it  could  not  be  separated  by  those 
substances  which  are  usually  employed  to  precipitate  iron. 

Porrett,  in  1814,  applying  the  greatly  increased  resources  of 
chemistry  to  the  investigation  of  this  subject,  decomposed  Prussian 
blue  with  baryta,  and  subsequently  removed  the  baryta  from  the  salt 
thus  obtained  by  means  of  sulphuric  acid,  when  he  obtained  a  solution 
of  the  acid,  which  he  named  ferruretted  chyazic  acid. 

In  1815,  Gay-Lussac,  having  boiled  Prussian  blue  (or  prussiate  of 
iron,  as  it  was  then  called)  with  red  oxide  of  mercury  and  water,  and 
crystallised  the  so-called  prussiate  of  mercury,  exposed  it,  in  the  dry 
state,  to  the  action  of  heat,  and  obtained  a  gas  having  the  composition 
CN",  which  was  called  cyanogen*  in  allusion  to  its  connection  with 
Prussian  blue.  It  was  then  seen  that  the  substance  which  had  been 
called  ferruretted  chyazic  acid  contained  iron  and  the  elements  of 
cyanogen,  whence  it  was  called  ferrocyanic  acid,  and  its  salts  were 
spoken  of  as  ferrocyanates.  Robiquet  first  obtained  this  acid  in  the 
crystallised  state,  having  the  composition  C6H4N6Fe ;  and  since  it  was 
found  that,  when  brought  in  contact  with  metallic  oxides,  it  exchanged 
the  H,  for  an  equivalent  quantity  of  the  metal,  according  to  the  equa- 
tion, H4-C6N6Fe  +  2M//0  =  M/'C6N6Fe  +  2H20,  it  was  concluded  that 
the  C6N6Fe  composed  a  distinct  group  or  radicle,  which  was  named 
ferrocyanogen  (Fey),  the  acid  being  called  hydro- 
ferrocyanic  acid,  and  the  salts  ferrocyanides. 

487.  Cyanogen  and  Cyanides. — Cyanogen, 
(CN)9  or  NC'CX,  is  obtained  by  heating  mercuric 
cyanide  in  a  glass  tube  or  retort  (Fig.  282),  and 
collecting  the  gas  over  mercury  ;  Hg(ON)2  = 
Hg  +  (CN)2 ;  the  metallic  mercury  collects  in 
globules  on  the  cool  glass.  The  whole  of  the 
cyanogen  is  not  obtained,  part  being  converted 
into  a  brown  solid  called  paracyanogen,  which  is 
left  behind.  This  is  polymeric  with  cyanogen,  Fig-  282. 

into  which  it  may  be  converted  by  a  high  tempe- 
rature.    By  heating  together  solutions  of  potassium  cyanide  and  CuS04). 
cyanogen  is  evolved  ;  2CuS04  +  4KCN  =  Cu2(CN)2  +  (ON),  +  2K2S04. 

Cyanogen  is  identified  by  its  remarkable  odour,  and  by  its  burning 
with  a  pink  flame  edged  with  green.  Its  sp.  gr.  is  1.806  (air  =  i),  and 
it  may  therefore  be  collected  by  displacement  of  air.  It  is  easily 
liquefied  by  a  pressure  of  4  atmospheres  at  15°  C.  and  ij  atmosphere 

*  From  Kvai'eos,  blue. 


688  REACTIONS   OF  CYANOGEN. 

at  o°  C.  Liquid  cyanogen  has  sp.  gr.  0.87,  and  solidifies  to  a  crystal- 
line mass  at  -34°  C.  and  boils  at  -21°  C.  Water  dissolves  about 
4  volumes  of  cyanogen,  yielding  a  solution  which  soon  deposits  a  brown 
flocculent  substance  termed  azulmic  acid.  C4N5H50.  The  solution  is 
then  found  to  contain  ammonium  salts,  especially  carbonate,  formate, 
and  oxalate,  together  with  urea. 

The  first  reaction  between  cyanogen  and  water,  on  standing,  probably  resembles 
that  between  chlorine  and  KOH  in  the  cold.  viz..  C12  +  2KOH  =  KC1  +  KC10  +  H20  ; 
the  reaction  in  the  case  of  cyanogen  being  (CN)2  +  H20  =  HCN  +  H(CN)0,  producing 
hydrocyanic,  HCN,  and  cyanic,  HCNO,  acids.  The  cyanic  acid  yields  NH4HC03 
by  reaction  with  water;  HCNO  +  2H20  =  NH4HC03.  Hydrocyanic  acid,  with 
water,  yields  ammonium  formate;  HCN  +  2H20  =  HCO2NH4.  Cyanogen,  with 
water,  yields  ammonium  oxalate;  (CN)2  +  4H2O=:C204(NH4)2.  Cyanic  acid, 
with  ammonia,  yields  urea;  HCNO  +  NH3  =  (NH2)2CO.  The  azulmic  acid 
appears  to  result  from  a  reaction  between  cyanogen,  ammonia,  and  water ; 
2(CN)2  +  NH3  +  H20  =  C4HgN50  ;  it  may  be  prepared  by  passing  cyanogen  into 
dilute  ammonia,  and  heating  in  a  closed  vessel.  When  dry  ammonia  gas  acts 
upon  cyanogen  gas,  a  black  substance  is  produced,  which  is  called  hydrazulmin  ; 
2NH3  +  2(CN)2  =  C4H6N6.  This  appears  to  be  azulmanride,  for,  when  acted  on  by 
water,  it  yields  azulmic  acid  and  ammonia  ;  C4H6N6  +  H20  =  C4H5N50  +  NH3. 

In  most  of  its  reactions,  cyanogen  exhibits  the  mutability  which  is 
generally  observed  in  organic  groups,  but  in  some  cases  it  exhibits  a 
stability  which  allows  it  to  be  compared  with  the  halogens.  Thus, 
alkali  metals  take  fire  in  cyanogen  when  gently  heated,  producing  their 
respective  cyanides ;  K2  +  (CN)2  =  2KCN  ;  cyanogen,  acting  on  solution 
of  potash,  yields  potassium  cyanide  and  cyanate ;  (CN)2+2KOH  = 
KCN  +  KCNO  +  H20,  just  as  chlorine  yields  chloride  and  hypochlorite. 
Cyanogen  combines  with  H,  under  influence  of  the  silent  electric 
discharge,  to  form  hydrocyanic  acid,  H(CN),  which  forms  cyanides  by 
exchanging  its  hydrogen  for  metals,  just  as  hydrochloric  acid  forms 
chlorides  ;  but  the  cyanides  of  potassium  and  sodium  are  much  less 
stable  compounds  than  the  corresponding  chlorides.  When  boiled  with 
water,  the  alkali  cyanides  are  converted  into  alkali  formates,  the 
nitrogen  being  evolved  as  NH3,  and  the  carbon  converted  into  the 
COOH  group  ;  KCN'"  +  2H20  =  KCO"(OH)'  +  NH3. 

The  facility  with  which  the  ON  group  is  transformed  by  hydrolysis  into 
the  C02H  group,  is  of  very  great  importance  in  organic  research,  since  it 
is  often  easy  to  introduce  the  ON  group  into  an  organic  molecule,  and, 
by  afterwards  converting  it  into  CO2H,  to  effect  the  synthetical  forma- 
tion of  an  organic  acid,  as  has  been  already  explained  (p.  587). 

Cyanogen  is  produced  in  small  quantity  by  the  direct  union  of 
carbon  and  nitrogen  at  the  extremely  high  temperature  of  the  electric 
spark,  but  to  produce  it  in  quantity,  one,  at  least,  of  its  elements  must 
be  in  the  form  of  a  compound  ;  thus,  if  ammonia  be  passed  over  red-hot 
charcoal,  hydrogen  cyanide  is  produced  ;  NH3  +  C  =  HCN  +  H2  ;  again, 
if  acetylene  is  mixed  with  nitrogen  and  "  sparked,"  hydrogen  cyanide  is 
formed,  C2H2  +  N2  =  2  HCN.  If  one  of  the  alkali  metals  be  present, 
nitrogen  is  much  more  easily  converted  into  cyanogen ;  potassium 
cyanide  may  be  obtained  by  passing  nitrogen  through  an  iron  tube  con- 
taining a  heated  mixture  of  charcoal  and  potassium — N2  +  C2  +  K2  = 
2 KCN.  In  place  of  the  costly  potassium,  the  materials  for  making  it, 
viz.,  potassium  carbonate  and  charcoal,  may  be  used  (see  below).  A 
better  yield  is  obtained  by  employing  a  compound  of  nitrogen  with 


YELLOW  PRUSSIATE   OF  POTASH.  689 

carbon,  such  as  refuse  horn  or  cuttings  of  hides  and  old  leather,  which 
are  rich  in  nitrogen. 

On  a  large  scale,  potassium  cyanide  is  made  in  this  way,  but  as  it 
cannot  be  crystallised  easily,  it  is  converted  into  the  ferrocyanide, 
which  is  the  source  whence  all  cyanogen  compounds  are  obtained. 

488.  Potassium  ferrocyanide,  K4FeC6N6.3Aq  or  4KCN.Fe" 
(CN)2.3Aq,  yellow  prussiate  of  potash,  is  manufactured  by  meltino- 
potashes  (crude  K2C03)  mixed  with  iron  filings  in  an  iron  vessel,  and 
adding  any  cheap  material  containing  carbon  and  nitrogen,  such  as  old 
leather.  Sometimes  the  animal  matter  is  distilled  for  the  sake  of  the 
ammonia  which  it  will  yield,  and  the  remaining  charcoal,  still  rich  in 
nitrogen,  is  used  for  making  ferrocyanide.  The  fused  mass  is  heated  with 
water  in  open  boilers,  when  a  yellow  solution  is  obtained,  which,  after 
evaporation,  deposits  truncated  pyramidal  crystals  of  potassium  ferro- 
cyanide. 

The  chemistry  of  this  process  is  somewhat  abstruse,  but  is  generally 
explained  as  follows  :  (  i  )  The  carbon  containing  nitrogen  decomposes 
the  potassium  carbonate  at  a  high  temperature,  producing  potassium 
cyanide  and^CO;  K2C03  +  C4  +  N2  =  2KCN  +  3CO.  (2)  Sulphur,  derived 
from  the  animal  matters,  and  partly  from  potassium  sulphate  present  as 
an  impurity  in  the  potashes,  combines  with  iron  to  form  ferrous  sulphide. 
(3)  On  treating  the  fused  mass  with  water,  the  ferrous  sulphide  is 
dissolved  by  the  KCN,  yielding  potassium  sulphide  and  ferrocyanide  ; 
FeS  +  6KCN  =  K4Fe(CN)6  +  K3S. 

It  has  been  suggested  to  avoid  the  presence  of  K2S  in  the  liquor  (which  hinders 
crystallisation)  by  melting  pure  K2C03  with  animal  charcoal,  extracting  the 
KCJST  from  the  residue  by  treatment  with  water,  and  digesting  with  finely  ground 
spathic  iron  ore  (FeC03)  ;  FeC03  +  6KCN  =  K4Fe(CN)6+K2C03. 

The  ferrocyanide  dissolves  in  twice  its  weight  of  boiling  and  in  four 
times  its  weight  of  cold  water,  but  is  insoluble  in  alcohol.  The  aqueous 
solution  assumes  a  darker  yellow  colour  when  exposed  to  air  for  some 
time,  oxygen  being  absorbed  and  potassium  ferricyanide  (see  below) 
produced  in  small  quantity.  The  neutral  solution  then  becomes  slightly 
alkaline  from  formation  of  potash. 

Crystallised  ferrocyanide  does  not  lose  water  till  60°  C.,  when  it  gradually  be- 
comes white  and  opaque.  At  100°  C.  it  may  be  dried  completely,  though  with 
difficulty,  unless  finely  powdered  and  heated  in,  a  current  of  dried  air.  When  the 
undried  salt  is  moderately  heated,  it  evolves  ammonia  and  hydrocyanic  acid, 
and  becomes  brown.  The  thoroughly  dried  salt  does  not  evolve  ammonia,  but 
fuses  at  a  high  temperature,  evolving  nitrogen,  and  leaving  a  residue  of 
potassium  cyanide  andiron  carbide  ;  K4C6N6Fe  = 


Nearly  all  acids  decompose  the  ferrocyanide,  evolving  hydrocyanic 
acid,  and  producing  compounds  containing  cyanogen  and  iron,  which 
become  blue  when  exposed  to  air,  from  the  formation  of  Prussian  blue 
and  similar  compounds.  It  is  for  this  reason  that  the  yellow  crystals 
become  blue  and  green  when  exposed  to  the  air  of  a  laboratory. 
Oxidising-agents  convert  the  ferrocyanide  into  ferricyanide,  as  will  be 
seen  later.  With  a  large  number  of  metallic  salts,  the  ferrocyann 
gives  precipitates,  so  that  it  is  an  indispensable  test.  It  is  also  largely 
employed  in  the  manufacture  of  colours,  and  in  dyeing  and  calico- 
printing.  The  constitution  and  chemical  relations  of  the  ferrocyamd* 
will  be  better  understood  later  in  the  history  of  cyanogen  compounds. 

/•»    •v 


690  PRUSSIC  ACID. 

Hydrogen  cyanide,  hydrocyanic,  or  prussic  acid,  H.C  :  N  (or 
HCy),  is  prepared,  in  aqueous  solution,  by  distilling  potassium  ferro- 
cyanide  (prussiate  of  potash)  with  dilute  H2S04.  50  grammes  of  the 
crystallised  ferrocyanide  are  dissolved  in  200  cubic  centimetres  of  warm 
water  in  a  flask  or  retort  connected  with  a  good  condenser.  20  c.c.  of 
strong  sulphuric  acid  are  diluted  with  60  c.c/of  water,  cooled,  and  added 
to  the  solution  of  ferrocyanide ;  heat  is  applied  by  a  ring-burner  to 
avoid  bumping,  until  about  140  c.c.  of  liquid  has  passed  into  the  receiver. 

The  potassium  ferrocyanide  gives  up  half  of  the  cyanogen,  ON,  as 
hydrocyanic  acid,  leaving  the  remainder  combined  with  the  iron  and 
half  of  the  potassium  as  potassio-ferrous  ferrocyanide,  K2Fe".Fe"(CN)6, 
a  yellow  ealt  which  quickly  becomes  blue  when  exposed  to  air,  oxygen 
being  absorbed,  and  Prussian  blue,  or  ferric  ferrocyanide,  Fe"'4.3Fe"(CN)6, 
produced.  The  following  equation  represents  the  preparation  of  hydro- 
cyanic acid  ;  2K4FeCy6  +  6H2SO4  =  6HCy  +  K2Fe"2Cy6  +  6KHS04. 

Hydrocyanic  acid  is  generally  used  diluted,  but  it  may  be  obtained  anhydrous 
by  gently  heating  the  diluted  acid  in  a  retort  connected  with  a  condenser  cooled 
by  iced  water,  and  receiving  the  distillate  in  a  bottle  cooled  in  ice  and  con- 
taining fused  calcium  chloride  in  coarse  powder.  This  bottle  is  afterwards 
placed  in  a  water-bath  connected  with  a  receiver  cooled  in  ice  and  salt,  and 
gently  heated,  when  the  pure  hydrocyanic  acid  distils  over.  The  anhydrous 
HCy  may  also  be  obtained  by  passing  dry  H2S  gas  into  a  long  tube  filled  with 
mercuric  cyanide  and  connected  with  a  receiver  cooled  in  ice  and  salt ;  the 
operation  must  be  stopped  when  an  inch  or  two  of  mercuric  cyanide  remains 
undecornposed,  to  avoid  contamination  of  the  HCy  with  H2S  ;  HgCy2  +  H2S  = 
HgS  +  2HCy. 

Properties  of  hydrocyanic  acid. — A  colourless  liquid,  sp.  gr.  0.7,  which 
evaporates  rapidly,  so  that  a  few  drops  in  a  watch-glass  are  solidified 
by  the  cold  of  evaporation,  the  freezing-point  being  -  12°  C.  The  acid 
boils  at  25°  C.,  and  its  vapour  burns  with  a  purple  flame.  The  smell 
of  the  vapour  is  quite  characteristic,  and  is  compared  by  some  to  a  faint 
odour  of  almonds ;  it  generally  produces  a  sensation  of  dryness  at  the 
back  of  the  throat.  The  inhalation  of  the  vapour,  unless  largely 
diluted  with  air,  is  very  dangerous,  and  an  extremely  small  quantity  of 
the  acid  taken  internally  generally  kills  immediately.  When  the  pure  acid 
is  mixed  with  an  equal  volume  of  water,  a  contraction  ensues,  amounting 
to  about  one-twentieth  of  the  total  volume,  and  cold  is  produced.  The 
aqueous  acid  is  decomposed  when  exposed  to  light,  depositing  a  brown 
substance,  whilst  ammonia  formate  and  other  products  are  found  in 
solution  ;  HCN  +  2H20  =  H'C02NH4.  A  trace  of  sulphuric  acid,  which 
generally  splashes  over  in  preparing  prussic  acid,  prevents  this  decom- 
position. Acids  and  alkalis,  when  boiled  with  the  acid,  convert  the 
HCN  into  formic  acid  and  ammonia. 

The  acid  properties  of  HCy  are  very  feeble ;  it  hardly  reddens  litmus, 
and  does  not  destroy  the  alkaline  reaction  of  the  alkalies  or  their 
carbonates.  The  salts  formed  by  displacing  its  hydrogen  by  alkali- 
metals  are  easily  decomposed  by  water  and  carbonic  acid,  and  therefore 
smell  of  HCy,  but  the  cyanides  formed  by  many  of  the  metals  are  very 
stable  bodies. 

Although  HCy  is  so  much  more  easily  liquefied  than  HC1,  its  vapour 
continually  escapes  even  from  a  weak  aqueous  solution,  so  that  the 
strength  is  diminished  every  time  the  stopper  is  removed  from  the 
bottle ;  it  thus  happens  that  the  weak  prussic  acid  (2  per  cent.)  dis- 


POTASSIUM  CYANIDE.  69! 

pensed  by  the  druggists,  is  sometimes  found  to  have  become  nearly  pure 
water. 

Hydrocyanic  acid  is  found  in  laurel-water,  and  in  water  distilled 
from  the  kernels  of  many  stone-fruits,  such  as  peach,  apricot,  and 
plum.  In  these  cases  it  appears  to  be  produced  from  amygdalin  (see 
p.  584). 

Hydrocyanic  acid  is  produced  synthetically  by  passing  a  succession  of 
electric  sparks  through  a  mixture  of  nitrogen  with  an  equal  volume  of 
acetylene,  this  being  itself  produced  by  carbon  intensely  heated  in 
hydrogen  (p.  100).  HCy  is  also  found  among  the  products  of  distilla- 
tion of  coal,  and  occurs  in  imperfectly-purified  coal-gas. 
N  Tests  for  hydrocyanic  acid.— Silver  nitrate  produces  a  white  precipitate  of 
silver  cyanide,  AgCN,  which  is  dissolved  by  boiling  with  strong  nitric  acid,  and 
precipitated  in  microscopic  needles,  AgCN.2AgN03,  on  cooling.  Prussian-blue 
test  :  Add  potash  in  slight  excess,  to  form  KCy  ;  then  add  ferrous  sulphate 
solution  (which  always  contains  ferric  sulphate).*  to  form  potassium  ferro- 
cyanide  :  6KCy  +  Fe"S04=K4Fe"Cy6  +  KjSO^  ;  this  acts  on  the  ferric  sulphate, 
and  produces  ferric  ferrocyanide,  or  Prussian  blue:  3K4Fe"Cy6  +  2Fe"'2(S04)3 
=  Fe'"4(Fe"Cy6)3  +  6K2S04.  But  the  excess  of  potash  decomposes  the  blue;  to 
correct  this,  add  excess  of  hydrochloric  acid  to  neutralise  the  potash,  the  blue 
will  then  be  visible.  SulpJwcya tilde  test :  Add  yellow  ammonium  sulphide  (which 
contains  some  disulphide),  to  form  ammonium  sulphocyanide  ;  HCN  +  (NH4)2S2= 
NH4CNS  +  NH4HS  ;  evaporate  till  the  smell  of  ammonium  hydrosulphide  has 
disappeared,  and  add  ferric  chloride,  which  will  produce  the  blood-red  colour  of 
ferric  sulphocyanide,  bleached  on  adding  mercuric  chloride.  A  very  fugitive 
purple  colour  is  due  to  ammonium  thiosulphate  produced  by  the  action  of  air, 
and  does  not  indicate  HCy. 

Potassium  cyanide,  KCN,  or  KCy,  is  prepared  by  fusing,  in  an  iron 
crucible,  a  mixture  of  well-dried  potassium  ferrocyanide  (8  parts)  with 
dried  K2C03  (3  parts);  K4Cy6Fe  +  K2003  =  5KCy  +  KCyO  +  Fe  +  C02. 
As  soon  as  the  escape  of  C02  has  ceased,  and  the  metallic  iron  has  sub- 
sided, the  clear  fused  mixture  of  cyanide  and  cyanate  of  potassium  is 
poured  into  an  iron  mould.  The  presence  of  cyanate  does  not  interfere 
with  most  of  the  uses  of  the  cyanide ;  its  quantity  may  be  diminished 
by  adding  some  powdered  charcoal  to  the  mixture. 

A  purer  product  is  obtained,  though  less  economically,  by  fusing  the  dried  ferro- 
cyanide alone  (see  above),  and  crystallising  the  product  by  dissolving  in  hot  alcohol. 
The  purest  potassium  cyanide  is  made  by  passing  vapour  of  hydrocyanic  acid 
into  solution  of  potash  in  absolute  alcohol,  when  the  cyanide  is  deposited  in  small 
octahedral  crystals. 

Potassium  cyanide,  as  met  with  in  commerce,  is  in  white  opaque  lumps,  and  con- 
tains about  98  per  cent,  of  cyanide,  the  rest  being  cyanate  and  carbonate.  When 
exposed  to  air,  it  deliquesces,  and  smells  of  hydrocyanic  acid  and  ammonia,  the 
former  being  produced  from  the  cyanide,  and  the  latter  from  the  cyanate,  by  tho 
action  of  water — 

(i)  KCN  +  H20  =  KOH  +  HCN.         (2)  KCNO  +  2H20  =  NH3  +  KHCOa. 

It  dissolves  very  readily  in  water,  yielding  a  strongly  alkaline  solution, 
which  evolves  HCy  and  NH3  when  boiled,  and  becomes  a  solution 
of  potassium  formate;  KCN  +  2H20  =  NH3  +  HC02K.  When  the 
commercial  cyanide  is  boiled  with  moderately  strong  alcohol,  the 
cyanide,  together  with  a  little  cyanate,  is  dissolved,  and  may  be 
crystallised  from  the  solution,  while  the  carbonate  is  left  undissolved. 
Potassium  cyanide  fuses  at  a  low  red  heat,  becoming  very  fluid  ;  it  then 

*  It  is  well  either  to  shake  with  air  or  to  add  a  drop  of  ferric  chloride  to  ensure  the 
presence  of  ferric  salt. 


692  CYANIDES. 

absorbs  oxygen  from  the  air,  forming  cyanate.  This  disposition  to 
combine  with  oxygen  causes  it  to  act  as  a  powerful  reducing-agent 
upon  metallic  oxides  ;  tin-stone  is  assayed  by  fusing  it  with  potassium 
cyanide,  when  a  button  of  tin  collects  at  the  bottom  of  the  fused  mass ; 
Sn02  +  2KCy  =  Sn  +  2KCyO.  When  heated  with  KN03  or  KC103,  it 
causes  a  violent  explosion,  from  evolution  of  C02  and  N. 

Pure  potassium  cyanide  is  alkaline,  but  does  not  effervesce  with  acids,  like  the 
commercial  cyanide.  Solution  of  potassium  cyanide  dissolves  silver  chloride  and 
iodide,  which  leads  to  its  use  in  electro-plating  and  in  photography,  while  its  pro- 
perty of  dissolving  silver  sulphide  is  useful  in  cleaning  gold  and  silver.  It  is  one 
of  the  most  dangerous  poisons.  It  is  also  used  in  gold-extraction  (p.  514),  for  which 
purpose  it  may  be  made  by  heating  K4FeCy6with  sodium  ;  K4FeCy6  +  Na2  =  4KCy  + 
2NaCy  +  Fe.  The  product  is  a  mixture  of  the  two  cyanides  which  is  as  effective  as 
pure  KCN. 

Potassium  cyanide  is  sometimes  obtained  in  considerable  quantity  from  the  blast- 
furnaces of  iron-works  being  formed  from  the  potassium  carbonate  in  the  ash 
of  the  fuel. 

Ammonium  cyanide,  NH4CN,  may  be  sublimed  in  cubes  by  heating  a  mixture 
of  mercuric  cyanide  and  ammonium  chloride.  It  dissociates,  at  36°  C.,  into 
NH3  and  HON.  It  is  very  soluble  in  water  and  alcohol,  and  smells  of  hydro- 
cyanic acid  and  ammonia.  When  kept  it  becomes  brown,  azulmin  being  produced 
(p.  688). 

The  cyanides  of  barium,  strontium,  and  calcium  are  less  soluble  than  the  alkali 
cyanides,  and  are  easily  decomposed  by  carbonic  acid.  Zinc  ci/anide,  ZnCy2,  is 
precipitated  by  KCy  from  ZnS04  ;  it  dissolves  in  KCy,  forming  ZnCy2(KCy).2 
which  crystallises  in  octahedra.  Nlcltel  cyanide,  NiCy2,  obtained  in  a  similar  way, 
forms  a  pale  green  precipitate,  readily  soluble  in  excess,  forming  NiCy2(KCy)2, 
from  which  hydrochloric  acid  re-precipitates  the  nickel  cyanide — 

NiCy2(KCy)2  +  2HC1  =  NiCy2  +2KC1  +  2HCy. 

If  the  solution  of  nickel  cyanide  in  potassium  cyanide  be  heated  with  mercuric 
oxide,  nickel  oxide  is  precipitated:  NiCy2(KCy)2  +  HgO  =  HgCy.2(KCy)2  +  NiO. 
This  reaction  is  important  in  quantitative  analysis.  Nickel  cyanide  is  remarkable 
for  its  insolubility  even  in  boiling  hydrochloric  acid. 

489.  Cobalt  cyanide,  CoCy2,  is  precipitated  of  a  reddish-brown  colour  when 
potassium  cyanide  is  added  to  cobalt  nitrate  ;  it  dissolves  easily  in  excess  of 
potassium  cyanide,  forming  jtotaxshtm  coba Itocyanide,  K4(CoCy6),  which  may  be 
obtained  in  red  deliquescent  crystals  by  adding  alcohol.  This  compound  corre- 
sponds with  potassium  ferrocyanide,  K4(FeCy6),  but  is  far  less  stable  ;  when 
exposed  to  air,  or  boiled  with  water,  it  undergoes  oxidation,  the  cobaltous  com- 
pound being  converted  into  a  cobaltic  compound,  the  potassium  cobalt  icijunide — 
2K4(Co"Cy6)  +  0  +  H20  =  2K3(Co'"Cy6)  +  2KOH.  The  potassium  cobalti- 
cyanide  is  a  pale  yellow  salt,  its  solution  being  nearly  colourless,  so  that  the  brown 
solution  formed  at  first  when  KCy  in  excess  is  added  to  a  cobalt  salt  gradually 
becomes  pale  yellow  when  boiled  in  contact  with  air.  This  solution,  when  mixed 
with  hydrochloric  acid  in  excess,  yields  hydro-cobalticyanic  acid,  H3CoCy6.  which 
is  soluble,  forming  a  distinction  between  cobalt  and  nickel.  When  both  metals 
are  present,  the  addition  of  HC1  to  the  solution  in  excess  of  KCy  produces  a 
yellowish-green  precipitate  of  nickel  cobalt  icij  a  nide,  Ni3(CoCy6)2,  which  is  decom- 
posed by  boiling  with  potash,  the  nickel  being  precipitated  as  hydroxide,  and  the 
cobalt  passing  into  solution  as  potassium  cobalticyanide;  Ni3(CoCy6)2  +  6KOH  = 
3Ni(OH)2  +  2K3CoCy6.  The  solution  of  potassium  cobalticyanide  is  not  decom- 
posed by  digestion  with  HgO  (to  precipitate  the  NiO),  but  a  solution  of  mercurous 
nitrate  gives  a  white  precipitate  of  mercurous  cobalticyanide,  Hg3Co2Cy6,  which  is 
converted  into  oxide  of  cobalt  when  heated  in  air. 

The  potassium  cobalticyanide  may  be  obtained  in  crystals  ;  it  is  analogous  to. 
and  isomorphous  with,  the  potassium  ferricyanide,  to  be  presently  described. 
nydrocobaltici/anic  add  fa  prepared  by  mixing  a  strong  solution  of  the  potassium- 
salt  with  sulphuric  acid  and  alcohol,  when  K2S04  is  precipitated,  and  the  solution 
yields  colourless  crystals  of  H6(CoCy6)2.H20,  which  is  a  very  stable  and  powerful 
acid.  Potassium  cobalticyanide  gives,  with  ferrous  salts,  a  white  precipitate  of 
ferrous  cobalticyanide,  Fe2(CoCy6)3;  and  with  cobalt  salts  a  red  precipitate  of 


PRUSSIAN  BLUE.  693 

,anlde,  Co"3(Co'"Cy6).2.i4Aq,  which  loses  its  water  at  200°  C.,  and 

490.  Cyanogen  and  iron-Fe>>r<>i(S  cyanide,  Fe(CN)2,  or  FeCv*  is  obtained 
(apparently  m  combination  with  some  KCy)  as  a  red-brown  precipitate  bv  addin- 
potassium  cyanide  to  a  ferrous  salt ;  it  dissolves  when  boiled  with  an  excess  of  the 
cyanide,  and  the  solution,  when  evaporated,  deposits  vellow  crystals  of  potassium 
ferrocyamde-FeCy2  +  4KCy  =  K4FeCy6.  This  might  be  regarded  as  4KCv.FeCv,, 
but  the  iron  cannot  be  detected  by  any  of  the  tests  for  that  metal  •  thui 
ammonium  sulphide,  which  produces  a  black  precipitate  in  ferrous  salts  does  not 
change  the  ferrocyanide ;  moreover,  the  K4  may  be  exchanged  for  hvdrozen  or 
for  other  metals  without  affecting  the  iron  and  cyanogen,  leading  to  the  con- 
clusion that  the  group  FeCy6  contains  the  iron  in  a  state  of  intimate  association 
with  the  cyanogen,  so  that  its  ordinary  properties  are  lost.  Again,  the 
ferrocyanide  is  not  poisonous,  so  that  it  cannot  be  believed  to  contain  potassium 
cyanide. 

Hydrogen  ferrocyanide,  or  hydroferrocyanic  add,  H4FeCy6,  is  prepared  by 
mixing  a  cold  saturated  solution  of  potassium  ferrocyanide  with  an  equal  volume 
of  strong  hydrochloric  acid.  It  forms  a  white  crystalline  precipitate,  soluble  in 
water,  but  not  in  HC1.  If  it  be  drained,  dissolved  in  alcohol,  and  ether  added,  it 
may  be  obtained  in  large  crystals.  It  is  a  strong  acid.  When  exposed  to  air,  it 
absorbs  oxygen,  and  evolves  hydrocyanic  acid,  leaving  a  residue  of  Prt/wiati  Uue  or 
ferric  ferrocyanide.  Fe4(FeCy6)3.  The  acid  is  decomposed  by  boiling  its  solution, 
into  hydrocyanic  acid  and  ferrous  ferrocyanide,  Fe2(FeCy6),  which  is  white,  but 
becomes  blue  when  exposed  to  air  ;  3H4FeCy6  =  1 2HCy  +  Fe.,(FeCy6).  These  changes 
are  applied  to  produce  blue  patterns  in  calico-printing. 

Hydroferrocyanic  acid  is  tetrabasic,  its  four  atoms  of  hydrogen  admitting  of 
displacement  by  a  metal  to  form  a  ferrocyanide.  The  group"  FeCy6,  ferrocyanogen, 
Fey  or  Cfy,  is  a  tetrad  group,  consisting  of  ferrous  iron,  which  is  diad,  Fe",'  and  six 
monad  cyanogen  groups,  (CN)',  leaving  four  vacant  bonds. 

Prussian  blue  or  ferric  ferrocyanide,  Fe'"4Fcyiv3,  (Fey  =  FeC6N6),  is 
prepared  by  adding  potassium  ferrocyanide  to  a  solution  of  ferric  chloride, 
or  ferric  sulphate ;  2Fe2Cl6  +  3K4Fcy  =  Fe4Fcy3  +  1 2KC1.    When  washed 
and  dried,  it  is  a  dark-blue  amorphous  body,  which  assumes  a  coppery 
lustre  when  rubbed.     It  cannot  be  obtained  perfectly  free  from  water, 
always  retaining  about  20  per  cent.  (Fe4Fcy  +  12  Aq).     On  heating,  the 
water  decomposes  it,  hydrocyanic  acid  and  ammonia  being  evolved,  and 
ferric  oxide  left.     The  water  appears  essential  to  the  blue  colour,  for 
strong  sulphuric  acid  converts  it  into  a  white  powder,  becoming  blue 
again  on  adding  water.     Strong  hydrochloric  acid  dissolves  Prussian 
blue,  forming  a  brown   solution,  which  gives  a  blue  precipitate  with 
water.     Oxalic  acid  dissolves  it  to  a  blue  solution,  used  as  an  ink. 
Some  ammonium  salts,  such  as  acetate  and  tartrate,  also  dissolve  it. 
Alkalies  destroy  the  blue  colour,  leaving  ferric  hydroxide  and  a  solution 
of    an  alkali  ferrocyanide  ;    Fe4Fcy3+  I2KOH  =  2Fe2(OH)6  +  3K4Fcy. 
This  is  turned  to  account,   in  calico-printing,  for  producing  a  buff  or 
white  pattern  upon  a  blue  ground.     The  stuff  having  been  dyed  blue 
by  passing,  first  through  solution  of  a  ferric  salt,  and  afterwards  through 
potassium  ferrocyanide,  the  pattern  is  discharged  by  an  alkali,  which 
leaves  the  brown  ferric  hydroxide  capable  of  being  removed  by  a  dilute 
acid,  when  the  stuff  has  been  rinsed,  so  as  to  leave  the  design  white. 
Prussian  blue  is  present  in  large  quantity  in  many  black  silks,  and  may 
be  extracted  by  heating  with  hydrochloric  acid,  and  precipitating  the 
brown  solution  with  water. 

Soluble  Prussian  Uue,  or  potaxsio-ferric  ferrocyanide,  K2Fe'"2(Fcy)iv2,  is  formed 
when  solution  of  ferric  chloride  or  sulphate  is  poured  into  potassium  ferrocyanide, 
so  that  the  latter  may  be  present  in  excess  during  the  reaction  ;  FegCLj- al^Fcy * 
K2Fe.2Fcy2  +  6KCl.  This  blue  is  insoluble  in  the  liquid  containing  saline  matter 


694  RED  PRUSSIATE   OF  POTASH. 

but  dissolves  as  soon  as  the  latter  has  been  removed  by  washing.  The  addition  of 
an  acid  or  a  salt  re-precipitates  it.  By  decomposing  soluble  Prussian  blue  with 
ferrous  sulphate,  a  blue  precipitate  of  ferroso-ferric  ferrocyanide,  Fe"Fe'"2Fcy2.  is 
obtained,  which  is  erroneously  called  Turnbull's  blue  (ferrous  ferricyanide}. 

Potassio-ferrous  ferrocyanide,  K2Fe"Fcy,  is  obtained  as  a  white  precipitate  when 
a  solution  of  ferrous  salt  quite  free  from  ferric  salt,  such  as  a  solution  of  ferrous 
hydrosulphite  (p.  237)  made  by  dissolving  iron  in  H2S03,  is  added  to  potassium 
ferrocyanide  quite  free  from  ferricyanide;  FeS04  +  K4Fcy  =  K2S04  +  K2FeFcy. 
The  precipitate  is  snow-white,  and  remains  so  for  some  time  at  the  bottom  of  the 
liquid,  but  if  it  be  exposed  to  air,  it  eagerly  absorbs  oxygen  and  becomes  blue  ; 
6K2FeFcy  +  03  =  3K4Fcy  +  Fe4Fcy3  +  Fe203.  Oxidising-agents,  such  as  chlorine- 
water  and  nitric  acid,  change  it  at  once  into  Prussian  blue.  When  potassium 
ferrocyanide  is  added  to  ordinary  ferrous  sulphate,  some  Prussian  blue  is  always 
formed  from  the  ferric  sulphate  present  in  the  ordinary  salt.  In  making  the  Prussian 
blue  of  commerce,  this  precipitate  is  oxidised  by  solution  of  chloride  of  lime  (p.  183), 
and  afterwards  washed  with  dilute  HC1,  to  remove  Fe203. 

Calcium  chloride  gives,  with  potassium  ferrocyanide,  a  white  crystalline 
precipitate  of  potassio-calcium  ferrocyanide,  K2CaFcy,  which  is  insoluble  in  acetic 
acid,  but  dissolves  in  HC1,  and  is  reprecipitated  by  ammonia.  Potass w-barium 
ferrocyanide,  K2BaFcy.3Aq,  is  similar.  Manganese  ferrocyanide,  Mn2Fcy,  and  :inc 
ferrocyanide,  Zn2Fcy,  are  white  precipitates.  When  potassium  ferrocyanide  is 
added  to  a  zinc-salt  mixed  with  excess  of  ammonia,  a  white  crystalline  precipitate 
of  ammonio-zinc  ferrocyanide  is  obtained.  Nickel  ferrocyanide,  Ni2Fcy,  is  a  pale 
green  precipitate.  Cobalt  ferrocyanide,  Co2Fcy,  forms  a  pale  blue-green  precipitate. 
Uranic  ferroctjanide,  U4Fcy3  (?),  is  a  rich  brown-red  precipitate.  Cupric  ferro- 
cyanide, Cu2Fcy,  is  also  obtained  as  a  brown-red  precipitate  by  adding  potassium 
ferrocyanide  to  cupric  sulphate  ;  it  forms  the  colour  known  as  Hatchctfs  brown. 
Its  formation  is  a  delicate  test  for  copper,  a  very  dilute  solution  giving  a  pink 
colour  with  the  ferrocyanide. 

Silver  ferrocyanide,  Ag4Fcy,  is  obtained  as  a  white  precipitate  from  silver 
nitrate  and  potassium  ferrocyanide  ;  it  is  insoluble  in  dilute  nitric  acid,  like 
silver  chloride,  but  it  is  also  insoluble  in  ammonia,  which  is  the  case  with  few 
silver  salts.  When  boiled  with  nitric  acid  it  is  converted  into  the  red-brown 
xilrer  ferricyanide,  which  is  soluble  in  ammonia.  When  silver  ferrocyanide  is 
boiled  with  ammonia  (or  KOH),  it  deposits  metallic  silver  and  ferric  oxide,  leaving 
silver  cyanide  and  ammonium  (or  potassium)  cyanide  in  solution — 

2Ag4FeCy6  +  6NH3  +  3H20  =  Ag2  +  Fe203  +  6AgCy  +  6NH4Cy. 

Ferric  cyanide,  Fe2Cy6,  is  very  unstable.  When  KCy  is  added  to  ferric  chloride, 
the  solution  soon  becomes  turbid,  depositing  ferric  hydroxide  and  evolving  HCy  ; 
Fe2Cy6  +  6H20  =  Fe2(OH)6  +  6HCy. 

Potassium  ferricyanide,  or  red  prussiate  of  potash,  K3Fe'"C6N6,  or 
3KCN.Fe"'(CN)3,  is  prepared  by  the  action  of  chlorine  upon  potassium 
ferrocyanide  ;  K4Fe"Cy6  +  Cl  =  K3Fe'"Cy6  +  KC1.  Chlorine  is  passed 
into  the  solution  of  ferrocyanide  until  a  little  of  the  solution  tested 
with  ferric  chloride  no  longer  gives  a  blue  precipitate.  On  the  small 
scale,  chlorine-water  may  be  added  to  the  ferrocyanide.  The  yellow 
colour  is  changed  to  greenish-yellow,  and  the  solution,  when  evaporated 
and  cooled,  deposits  dark-red  prisms  of  the  ferricyanide.  It  is  very 
soluble  in  water,  yielding  a  dark  yellowish-green  solution,  but  is  nearly 
insoluble  in  alcohol.  The  aqueous  solution  is  slowly  decomposed  by 
exposure  to  light,  depositing  a  blue  precipitate,  and  becoming  partly 
converted  into  ferrocyanide.  If  the  solution  be  mixed  with  acetic  acid, 
and  heated,  it  deposits  a  blue  precipitate,  a  reaction  which  is  turned  to 
account  in  dyeing.  An  alkaline  solution  of  potassium  ferricyanide  acts 
as  a  powerful  oxidising-agent,  becoming  reduced  to  ferrocyanide ; 
2K3Fe'  "Cy6  +  2KOH  =  2K4Fe"Cy6  +  H20  +  O.  Such  a  solution  converts 
chromic  oxide  into  potassium  chromate,  and  bleaches  indigo,  whence  it 
is  used  as  a  discharge  in  calico-printing,  for  white  patterns  on  an  indigo 


FEERICYANIDES. 


69- 

ground.     Potassium  ferricyanide  is  also  reduced  to  ferrocyanide  when 
boiled  with  potassium  cyanide  — 


2K3Fe'"Cy6  +  2KCN  +  2H20  =  2K4Fe"Cy6  +  HCN  +  NH3  +  CO,. 
Hydrogen  ferricyanide,  or  hydroferricyanic  acid,  H3Fe'"Cy6,  is  obtained  by  de- 
composing lead  ferricyanide  with  H2S04,  not  in  excess.  It  may  be  crystallised  in 
brown  needles  by  evaporation  in  vacua.  Its  solution  is  decomposed  by  boiling, 
with  evolution  of  HCy  and  separation  of  a  blue  precipitate.  Hydroferricyanic  acid 
is  tribasic,  the  3  atoms  of  hydrogen  being  displaced  by  metals  to  form  ferri- 
cyanides. 

*  Ferrous  ferricyanide,  or  TurnbulVs  blue,  Fe"3Fe'"2Cy12.—  Whilst  potassium  ferro- 
cyanide gives  a  light  blue  precipitate  with  common  FeS04,  the  ferricyanide  gives  a 
dark  blue  precipitate,  resembling  Prussian  blue.  This  contains  the  same  proportions 
of  iron  and  cyanogen  as  the  ferroso-ferric  ferrocyanide,  Fe"Fe'"2  (Fe"Cy6)2,  and  it 
is  sometimes  regarded  as  identical  with  it,  on  the  supposition  that  the"  ferrous 
sulphate  reduces  the  ferricyanide  to  ferrocyanide.  Ferric  salts  give  no  precipitate 
with  the  ferricyanide,  but  only  a  dark  brown  solution,  probably  containing  ferric 
ferricyanide,  which  yields  a  blue  precipitate  of  ferrous  ferricyanide  with  reducing- 
agents  such  as  H2SO3,  and  is  used  as  a  test. 

Lead  ferricyanide,  Pb3Fe2Cy12.i6Aq,  is  deposited  in  red-brown  crystals  on  mixing 
strong  solutions  of  lead  nitrate  and  potassium  ferricyanide.  Silver  ferricyanide, 
Ag6Fe2Cy12,  has  been  already  mentioned  as  a  red-brown  precipitate  formed  by 
boiling  the  ferrocyanide  with  dilute  nitric  acid.  Cold  potash  converts  it  into 
black  Ag20  and  potassium  ferricyanide  ;  on  boiling,  the  black  changes  to  pink  ; 
3Ag20  +  K6Fe2Cy12  =  6AgCy  +  6KCy  +  Fe203.  The  pink  precipitate  is  a  compound 
of  AgCy  with  silver  ferricyanide,  which  may  also  be  obtained  by  boiling  silver 
ferricyanide  with  silver  oxide;  Ag6Fe2Cya2  -f  3Ag20  =  Fe203  +  i2AgCy,  which  com- 
bines with  undecomposed  silver  ferricyanide.  On  continuing  to  boil  the  silver 
ferricyanide  with  potash,  the  pink  precipitate  again  becomes  black,  for  the  potas- 
sium cyanide  reduces  the  silver  ferricyanide  to  ferrocyanide,  which  is  ultimately 
decomposed  by  the  silver  oxide,  with  separation  of  metallic  silver  — 

(1)  2Ag6Fe2Cy12  +  4KCN-f  4H20  =  3Ag4FeCy6  +  K4FeCy6  +  2HCN  +  2C02  +  2NH3  ; 

(2)  4Ag4FeCy6  +  2Ag20  =  Ag^e^y^  +  i2AgCy  +  2FeO  +  Ag2. 

In  the  preparation  of  K3FeCy6,  if  an  excess  of  chlorine  be  employed,  the  liquid 
when  evaporated  deposits  a  precipitate  of  Prussian  green,  which  appears  to  be  a 
compound  of  ferric  ferrocyanide  and  ferricyanide,  2Fe4Fcy3.FeFcy,  for,  when 
boiled  with  potash,  it  yields  5  molecules  of  ferric  hydroxide,  3  molecules  of 
potassium  ferrocyanide,  and  i  molecule  of  potassium  ferricyanide. 

491.  Nitroprussides.  —  When  potassium  ferricyanide  is  acted  on  by  a 
mixture  of  NaN02  and  acetic  acid,  it  is  converted  into  potassium  nitro- 
prusside,  K4Fe2Cy]0(NO)2,  probably  according  to  the  equation  — 

K6Fe2Cy12  +  4HN02  =  K4Fe2Cy10(NO)2  +  2HCy  +  H20  +  KN03  +  KN02. 
If  HgCl2  be  added  to  the  solution,  HgCy2  crystallises,  and,  on  further 
evaporation,  red  prisms  of  sodium  nitroprusside  are  deposited  — 

K6Fe2Cy12  +  4NaN02  +2HA  +  HgCl2  = 
Na4Fe2Cy10(NO)2  +  HgCy2  +  2KC1  +  2KA  +  KN02  +  KN03  +  H20. 

Sodium  nitroprusside,  Na4Fe2Cy10(NO)r4Aq,  is  prepared  by  a  process 
founded  upon  the  above  reactions  (Hadow). 

332  grains  of  potassium  ferricyanide  are  dissolved  in  half  a  pint  of  boiling  water 
and  800  grains  of  acetic  acid  'are  added.  Into  this  hot  solution  is  poured  a 
cold  solution  containing  80  grains  of  sodium  nitrite  and  164  grams  of  mercuric 
chloride  in  half  a  pint  of  water.  The  solution  is  kept  at  60  C.  for  some  hours, 
until  a  little  no  longer  gives  a  blue  coloration  with  ferrous  sulphate  (a  HI 

)dium  nitrite  and  acetic  acid  may  be  added  if  necessary).     The  mixture  is  then 
.iled  down  till  it  solidifies  to  a  thick  paste  on  cooling  ;  this  is  squeezed  in  linen 
to  drain  off  the  solution  of  potassium  acetate  ;  the  mass  is  dissolved  m  boili] 
water,  and  allowed  to  cool,  when  most  of  the  mercuric  cyanide  crystallises.    < 
concentrating  the  red  filtrate,  and  cooling,  crystals  of  sodium  mtroprus 
obtained,  and  may  be  purified  by  recrystallisation. 


696  CYANIDES. 

Sodium  nitroprusside  was  originally  prepared  by  boiling  ferrocyanide  with  nitric 
acid  (Playfair).  Potassium  ferrocyanide,  in  powder,  is  dissolved  in  twice  its 
weight  of  strong  HN03  (1.42)  mixed  with  an  equal  volume  of  water  ;  effervescence 
occurs,  from  escape  of  C02  and  N,  and  the  odours  of  (CN)2,  HCN  and  cyanic  acid 
may  be  distinguished.  When  the  salt  has  dissolved,  the  solution  is  heated  on  a 
steam  bath  till  it  no  longer  gives  a  blue  with  FeS04.  It  is  then  allowed  to  cool, 
when  KN03  crystallises,  and  the  solution  is  boiled  with  excess  of  Na^COg  and 
filtered  ;  the  nitrate  when  evaporated  deposits  crystals  of  nitroprusside. 

Sodium  nitroprusside  is  very  soluble  in  water  ;  the  solution  deposits 
a  blue  precipitate  when  exposed  to  light.  When  its  solution  is  rendered 
alkaline  by  soda,  and  boiled,  the  NO  group  exerts  a  reducing  action, 
ferrous  hydroxide  being  precipitated, and  sodium  ferrocyanide  and  nitrite 
remaining  in  solution.  Alkali  sulphides  have  also  a  reducing  effect 
upon  the  solution,  producing  a  fugitive  violet-blue  co)our,  even  in  very 
weak  solutions,  rendering  sodium  nitroprusside  a  most  delicate  test 
for  sulphur  in  organic  compounds,  which  yield  sodium  sulphide  when 
fused  with  sodium  carbonate.  The  sulphur  in  an  inch  of  human 
hair  may  be  detected  by  this  test.  The  higher  (yellow)  alkali  sul- 
phides should  be  reduced  by  warming  with  KCN"  solution.  Alcoholic 
solutions  of  nitroprusside  and  sulphide  of  sodium  yield  a  purple  oily 
compound  soon  decomposing  into  ammonia  and  several  cyanogen  com- 
pounds. 

With  silver  nitrate,  sodium  nitroprusside  gives  a  buff  precipitate  of  silrer 
nitroprusside,  Ag4Fe2Cy10(NO)2,  and  by  decomposing  this  with  HC1  the  Injdro- 
nitroprussic  acid,  H4Fe2Cy10(NO)2,  may  be  obtained,  by  evaporation,  in  racuo,  in 
red  deliquescent  prisms  (with  iH20).  It  is  very  unstable. 

Potassium  carbonyl  ferrocyanide.  K3FeCOCy5  is  obtained  by  heating  a  solution 
of  K4FeCy6  with  CO. 

492.  Chromic  cyanide,  Cr2Cy6,  is  a  pale  green  precipitate  produced  by  KCy  with 
chrome  alum  ;  heated   with   excess   of   KCy,    it   yields  2)otassium  chromicyanide, 
K6Cr2Cy12,  which  may  be  obtained  in  yellow  prisms. 

Manganous  cyanide,  MnCy2,  is  probably  contained  in  the  greenish  precipitate 
by  KCy  in  manganous  acetate  ;  an  excess  of  KCy  dissolves  it  to  a  colourless 
solution,  from  which  alcohol  separates  blue  crystals  of  potassium  manganocyanide, 
K4MnCy6.3Aq,  isomorphous  with  the  ferrocyanide.  When  exposed  to  air,  the 
solution  of  the  manganocyanide  absorbs  oxygen,  and  deposits  red  prisms  of 
potassium  mangani  cyanide,  KgMn2Cy12,  isomorphous  with  the  ferricyanide. 

Cuprous  cyanide,  Cu2Cy2,  is  obtained  as  a  white  precipitate  by  boiling  cupric 
sulphate  with  KCy,  when  cupric  cyanide,  CuCy2,  is  first  formed  as  a  brown  pre- 
cipitate, which  evolves  cyanogen  when  boiled.  Cuprous  cyanide  dissolves  in 
KCy.  and  the  solution  yields  colourless  crystals  of  potassium  cupro-cyanide, 
K2Cu'2Cy4,  which  gives  a  precipitate  of  plumbic  cupro-cyanide,  PbCu2Cy4,  with  lead 
acetate.  By  decomposing  the  lead  salt  with  H2S,  a  solution  of  the  corresponding 
acid,  H2Cu2Cy4,  is  obtained,  but  this  soon  decomposes  into  2HCy  and  Cu2Cy2. 

493.  Silver  cyanide,  AgCy,  is  obtained  as  a  white  precipitate  when  hydrocyanic 
acid  or  a  cyanide  is  added  to  silver  nitrate.     Its  insolubility  in  water  renders  its 
formation  a  very  delicate  test  for  HCy  (in  the  absence  of  other  acids  forming 
insoluble  silver  salts)  and  an  accurate  method  of  estimating  its  quantity. 

Silver  cyanide  is  not  altered  by  sunlight  like  silver  chloride,  and  is  dissolved 
when  boiled  with  strong  nitric  acid,  which  does  not  dissolve  the  chloride.  The 
nitric  solution,  when  cooled,  deposits  flocculent  masses  of  minute  needles  of  the 
composition  AgCy.2AgNO3,  which  detonate  when  heated. 

Silver  cyanide,  when  heated,  fuses,  evolves  cyanogen,  and  leaves  a  residue  of 
silver  mixed  with  silrer  paracyamde,  AgC3N3.  Silver  cyanide  dissolves  in  ammonia 
like  the  chloride,  but  the  latter  is  deposited  in  microscopic  octahedra,  while  the 
cyanide  forms  distinct  needles  ;  a  mass  of  silver  cyanide,  moistened  with  ammonia 
and  warmed,  becomes  converted  into  needles.  Potassium  hydroxide  does  not 
decompose  silver  cyanide.  Potassium  cyanide  readily  dissolves  silver  cyanide, 
forming  KAgCy2,  which  may  be  crystallised  in  six-sided  tables.  It  is  used  in 
electro-plating. 


PLATINOCYANIDES.  697 

Mercuric  cyanide,  HgCy.2,  is  prepared  by  dissolving  precipitated  HgO  in  excess 
of  solution  of  HCN,  and  evaporating,  when  the  cyanide  is  deposited  in  four-sided 
prisms,  which  dissolve  in  eight  parts  of  cold  water,  and  are  insoluble  in  alcohol  For 
its  behaviour  when  heated  see  p.  687.  It  is  one  of  the  most  stable  of  the  cyanides, 
scarcely  allowing  the  cyanogen  to  be  detected  by  the  ordinary  tests.  Dilute 
H.2y04  and  HN03  do  not  decompose  it,  but  HC1  liberates  HCy.  KOH  and  NH,  do 
not  precipitate  its  solution. 

Mercuric  cyanide  dissolves  mercuric  oxide  when  boiled,  giving  an  alkaline 
solution,  which  deposits  needles  of  mercuric  oacycyanide,  JAg^OCy.^  When  solutions 
of  mercuric  cyanide  and  silver  nitrate  are  mixed,  the  solution  becomes  acid,  and, 
on  stirring,  deposits  fine  needles  containing  Ag.Hg.N03.Cy2.2Aq.  The  acid 
reaction  of  the  solution  proves  that  some  of  the  mercuric  cyanide  has  become 
converted  into  mercuric  nitrate  ;  the  same  salt  may  be  obtained  by  dissolving 
silver  cyanide  in  mercuric  nitrate.  Neither  mercuric  cyanide  nor  silver  nitrate 
is  precipitated  by  excess  of  ammonia,  but  a  mixture  of  the  two  salts  gives  an 
abundant  precipitate,  containing  HgCy.27AgCy.2HgO,  which  explodes  when 
heated.  The  crystalline  salt  is  probably  AgCy.CyHgN03.2Aq,  containing  HgCy.,, 
in  which  N03  is  substituted  for  Cy.  Other  crystalline  compounds  of  the  same  kind 
are  formed  by  HgCy.2  ;  such  as  NaCy.CyHgCl  and  KCy.CyHgl.  A  potassio- 
mercuric  cyanide,  KCy.CyHgCy.CyK,  "may  be  obtained  "in  "fine  crystals,  which 
may  be  decomposed  by  mercuric  chloride,  yielding  HgCL2.HgCy2  or  Hg"Cy'Cr. 

Mercuric  cyanide  was  originally  prepared  by  Scheele,  when  he  discovered  that 
prussic  acid  could  be  prepared  from  Prussian  blue.  This  was  boiled  with  mercuric 
oxide  and  water  till  the  blue  colour  had  disappeared;  Fe4(Cy6Fe)3  +  9HgO  — 
9HgCy.2-r2Fe.203  +  3FeO.  The  filtered  solution  was  mixed  with  sulphuric  acid, 
shaken  with  iron  filings,  which  precipitated  the  mercuiy,  and  distilled  to  obtain 
hydrocyanic  acid  ;  HgCy2  +  H2SO4  +  Fe  =  2HCy  +  FeS04  +  Hg. 

Mercuric  cyanide  may  be  directly  obtained  from  potassium  ferrocyanide  by 
boiling  it  with  mercuric  sulphate  (2  parts)  and  water  (8  parts) — 


2K4FeCy6  +  ;HgS04  =  6HgCy2  +  4K2S04  +  Fe2(S04)3  +  Hg. 

The  mercurous  cyanide  is  not  known  ;  when  mercurous  nitrate  is  decomposed 
by  potassium  cyanide,  a  solution  of  mercuric  cyanide  is  formed,  and  metallic  mer- 
cury is  precipitated  ;  Hg2(N03)2  +  2KCy  =  HgCy2  +  Hg  +  2KN03. 

Gold  cyanides. — Potassium  aurocyanide,  2KAu'Cy2,  is  obtained  by  dissolving 
gold  in  KCN  solution  (p.  514),  or  by  dissolving  fulminating  gold  (p.  518)  in  hot 
water  containing  pure  potassium  cyanide.  The  filtered  solution  deposits  colourless 
crystals  of  the  aurocyanide,  which  are  very  soluble  in  hot  water.  Aurmis  cyanide, 
AuCy,  is  obtained  as  a  crystalline  precipitate  by  adding  HC1  to  solution  of  the 
aurocyanide  of  potassium. 

Potassium  aurlcyanlde,  KAu'"Cy4,  is  prepared  by  mixing  hot  strong  solutions 
of  gold  trichloride  and  potassium  cyanide.  It  forms  colourless  tables  (with  iH20). 
With  AgN03  a  precipitate  of  silver  aurlcyanlde,  AgAuCy4,  is  obtained,  and  if  this 
be  treated  with  HC1,  avoiding  excess,  the  silver  is  precipitated  as  AgCl,  and  the 
solution,  evaporated  in  vacuo,  yields  crystals  of  auric  cyanide,  AuCy3.3Aq. 

Both  aurocyanide  and  auricyanide  of  potassium  are  used  in  electro-gilding. 

494.  Platinum  cyanides. — The  cyanides  of  platinum  have  not  been  prepared  in 
a  pure  state,  but  the  salts  known  as  platinocyanides  exceed  the  ferrocyanides  in 
the  force  with  which  they  retain  the  platinum  disguised  to  the  ordinary  tests. 
When  KCN  is  strongly  heated  on  platinum  foil,  the  metal  is  attacked,  and  an 
orange-coloured  mass  is  produced.  Spongy  platinum  is  slowly  dissolved  by  a 
boiling  solution  of  KCN,  and  if  mixed  with  the  solid  cyanide,  and  heated  to  6 
in  steam,  pota&xiuvi platlnocijan\de  is  formed — 

Pt  +  4KCy  +  2H20  =  K2Pt"Cy4  +  2KOH  +  H2. 

When  solutions  of  potassium  cyanide  and  platinic  chloride  are  boiled  together 
till  colourless,  the  platinocyanide  is  found  in  solution — 

PtCl4  +  6KCN  +  4H20  =  K2Pt(CN)4  +  4^C1  +  2NH3  +  H2C204. 
Or  the  ammonio-platinic  chloride  may  be  boiled  with  pptash  and  a  strong  solution 
of  potassium  cvanide  until  no  more  ammonia  is  evolved.  hWiHo  \ 

Potassium  platinocyanide  is  also  prepared  by  dissolving  platmous  chloride  m 
solution  of  potassium  cyanide;  PtCl2  +  4KCy;=K2PtCy4  +  2KU.  it  .allies 
in  prisms  (with  3HoO),  which  are  yellow  by  transmitted,  light,  and  reflect  a  blue 
colour.  They  are  very  soluble  in  water.  The  solution  is  colourlebs,  and  gives  a 


698  CHLOEIDE   OF  CYANOGEN. 

characteristic  blue  precipitate  with  mercurous  nitrate.  CuSO4  also  gives  a  blue 
precipitate,  and  if  this  be  decomposed  by  aqueous  H.2S,  it  yields  a  solution  of 
kydroplatinocyanic  acid,  H2PtCy4,  which  crystallises  from  ether  in  red  prisms  (with 
5H20)  with  a  blue  reflection. 

Barium  platinocyanide,  BaPtCy44Aq,  is  prepared  by  decomposing  the  cupric 
salt  with  baryta.  It  is  dichroic.  being  green  when  looked  at  along  the  primary 
axis  of  the  crystal,  and  yellow  across  it.  It  is  remarkable  for  its  property  of 
becoming  luminous  when  exposed  to  the  Rb'ntgen  rays,  in  which  respect  it  re- 
sembles, but  excels,  many  other  platinocyanides. 

Magnesium,  platinocyanide,  MgPtCy4.7Aq,  obtained  by  decomposing  the  barium 
salt  with  MgS04,  crystallises  in  large  prisms,  deep  red  by  transmitted  light,  but 
when  viewed  by  reflected  light,  the  sides  of  the  prisms  exhibit  a  brilliant  beetle- 
green,  and  the  ends  a  deep  blue  or  purple  colour.  When  the  red  salt  is  gently 
warmed,  even  under  water,  it  becomes  bright  yellow,  from  production  of 
MgPtCy4.6Aq,  which  may  be  obtained  in  crystals  from  the  solution  at  71°  C. 
Heated  at  100°  C.,  the  yellow  salt  becomes  white  MgPtCy4.2Aq,  and  at  about  i8o°C. 
it  again  becomes  yellow,  and  is  then  anhydrous.  If  a  little  of  the  yellow  anhydrous 
salt  be  placed  on  the  powdered  red  salt  (with  7Aq),  it  abstracts  water  from  it,  and 
converts  it  into  the  yellow  salt  with  6Aq,  while  it  is  itself  changed  to  the  white 
salt  with  2Aq,  so  that  a  white  layer  is  formed  between  two  yellow  layers.  The 
yellow  salt  may  also  be  obtained  by  crystallisation  from  alcohol. 

When  the  platinocyanides  are  attacked,  in  solution,  by  oxidising-agents,  such 
as  chlorine,  bromine,  or  nitric  acid,  new  salts  are  formed,  which  have  a  coppery 
lustre,  and  act  as  oxidising-agents  in  alkaline  solutions,  like  the  ferricyanides. 
These  were  formerly  called  platinicyanides,  but  were  shown  by  Hadow  to  contain 
chloro-,  bromo-,  &c.,  platinocyanides.  When  chlorine  is  passed  into  a  hot  solution 
of  potassium  platinocyanide,  it  deposits,  on  evaporation,  colourless  crystals  of 
the  chloroplatinocyanide,  K.2PtCy4Cl2.2Aq.  When  these  are  treated  with  a  strong 
solution  of  the  platinocyanide,  they  are  converted  into  copper-red  needles  of 
5K2PtCy4.K2PtCy4Cl2.3H2O.i8Aq.  This  compound,  when  boiled  with  potash, 
yields  the  platinocyanide  and  potassium  hypochlorite — 

5K2PtCy4.K2PtCy4Cl2  +  2KOH  =  6K2PtCy4  +  KOC1  +  KC1  +  H20. 

495.  Cyanogen  Halides. — Cyanogen  chloride,  C  !  N'Cl,  is  prepared 
by  the  action  of  chlorine  upon  moist  mercuric  cyanide,  in  the  dark ; 
HgCy2  + 2Cl2  =  HgCl2  +  2CyCl.  On  gently  heating,  the  cyanogen 
chloride  passes  off  in  vapour,  and  may  be  condensed  in  a  tube  sur- 
rounded with  a  freezing-mixture.  It  is  a  colourless  liquid,  boiling  at 
15°  C.,  and  yielding  a  vapour  which  irritates  the  eyes,  causing  tears. 
When  exposed  to  light,  or  treated  with  acids,  it  polymerises  into 
cyanuric  chloride,  Cy3013,  which  fuses  at  146°  and  boils  at  190°  C. 
This  has  also  an  irritating  effect  on  the  eyes.  It  is  sparingly  soluble  in 
cold  water,  and  is  decomposed  by  boiling  water,  yielding  cyanuric  acid; 
Cy3cl3  +  3H20  =  Oys(OH)3  +  3HC1.  Both  these  chlorides  may  be  obtained 
by  the  action  of  chlorine  on  hydrocyanic  acid. 

In  practice  cyanogen  chloride  is  generally  required  in  solution  which  is  best 
prepared  by  dissolving  260  grams  of  KCN  and  90  grams  of  crystallised  ZnS04  in 
8  litres  of  water,  and  passing  Cl  until  the  ZnCy2  at  first  thrown  down  is  nearly 
redissolved. 

Cyanogen  bromide,  CyBr,  is  obtained  in  crystals,  mixed  with  KBr,  when  bromine 
is  gradually  added  to  a  strong  well-cooled  solution  of  KCy.  On  gently  heating, 
it  sublimes  in  crystals,  which  are  very  volatile  and  cause  tears.  When  heated  in 
a  sealed  tube,  it  becomes  Cy3Br3.  It  melts  at  52°  C.  and  boils  at  61°  C. 

Cyanogen  iodide.  Cyl.  is  prepared  by  dissolving  iodine  in  a  warm  strong  solution 
of  KCy,  when  a  crystalline  mass  of  KI  and  Cyl  is  obtained  on  cooling,  from  which 
the  Cyl  may  be  extracted  by  gently  heating  or  by  treatment  with  ether.  It 
crystallises  easily  in  colourless  needles  or  tables,  which  are  sparingly  soluble  in 
water,  very  volatile,  and  have  a  tear-exciting  odour.  It  sometimes  occurs  in 
commercial  iodine,  from  which  it  may  be  sublimed  in  a  tube  or  flask  plunged  in 
boiling  water.  When  heated  to  100°  C.,  in  a  sealed  tube,  with  alcoholic  ammonia, 
it  yields  hydriodide  of  guanidine,  CNI  +  2NH3  =  CN3H5.HI. 


NITRILES. 


496.  Cyanides  of  Hydrocarbon  Radicles,  or  Acid  Nitriles.—  The 
term  nitrile  was  originally  applied  to  the  final  product  of  the  removal 
of  water  from  an  ammonium  salt  (cf.  p.  667),  the  amide  being  the 

intermediate  product.     Thus,  when  the  group  C/  ,  characteristic 


of  the  organic  ammonium  salts,  loses  i  mol.  H20,  it  passes  into  the 
C^  group  of  the  amides,  and  when  this  loses  i  mol.  H,0,  it 

becomes  C=N,  the  nitrile  group.  It  was  later  found  that  the  nitriles 
are  identical  with  the  cyanides  of  the  hydrocarbon  radicles. 

Hence  there  are  two  general  lines  on  which  these  compounds  may  be 
prepared,  viz.,  (i)  by  reactions  which  produce  cyanides,  such  as  (a)  by 
heating  the  iodide  of  a  hydrocarbon  radicle  with  KCN  in  alcoholic 
solution,  CH3I  +  KCN  =  KI  +  CH3-CN,  or  (b)  by  distilling  an  alkali 
alkyl  sulphate  with  KCN,  KCH3S04  +  KCN  =  CHyCN  +  K2S04  ;  (2)  by 
dehydrating  ammonium  salts  or  amides  by  distillation"  with  P80., 
CH3-CONH2  -  H20  =  CH3-CN. 

The  ease  with  which  the  CIS"  group  reverts  to  the  COOH  group  when 
the  cyanides  or  nitriles  are  hydrolysed  and  the  importance  thus  attach- 
ing to  these  compounds  in  synthetic  chemistry  have  been  dwelt  upon 
already  (p.  688).  When  an  acid  is  the  hydrolytic  agent  the  ammonium 
salt  is  produced  CH3-CN  +  2HOH  =  CH3-COONH4;  but  when  it  is  an 
alkali  the  NH3  is  evolved,  CH3'CN  +  HOH  +  KOH  =  NH3  +  CH3-COOK. 
The  reaction  shows  that  of  two  possible  formulae  for  the  cyanide, 
H3C'C  •  N  and  H3C'N  I  C,  the  former  must  be  correct,  since  the 
hydrolysis  does  not  part  the  C  atoms,  which  must  therefore  be  directly 
united  in  the  cyanide.  The  action  of  nascent  hydrogen  on  the  cyanide 

<**j 
. 

JN  -tlo 

Cyanogen  itself  is  oxalonitrile,  and  may  be  obtained  by  dehydrating 
ammonium  oxalate  COONH4-COONH4  =  CN'CN  +  4H20.  Hydrocyanic 
acid  is  formonitrile,  obtained  from  ammonium  formate;  HCOONH4  = 
HCN  +  2H20. 

Methyl  cyanide,  or  acetonitrile,  CH3'CN,  prepared  as  above,  is  a 
volatile  liquid  of  pleasant  odour  boiling  at  8i°.6  C.  Its  sp.  gr.  is  0.8, 
and  it  is  soluble  in  water  and  alcohol. 

The  tendency  for  the  nitrogen  in  the  C  :  N  group  to  become  pentavalent,  leads 
to  the  formation  of  crystalline  compounds  of  CH3CN  with  Br2,  HBr  and  HI,  &c. 
Certain  chlorides  also  combine  with  methyl  cyanide  to  form  crystalline  volatile 
substances,  decomposed  by  water  ;  such  compounds  are  formed  with  PC13,  SbCl5, 
and  SnCl4.  When  methyl  cyanide  is  acted  on  by  sodium,  part  of  it  is  decomposed 
with  violent  evolution  of  methyl  hydride,  and  the  remainder  is  polymerised  to 
form  cyanmethlne  (CH3)3(CN)3,  an  organic  base,  soluble  in  water,  and  having  a 
very  bitter  taste.  It  forms  prismatic  crystals,  which  may  be  sublimed. 

An  instructive  reaction  yielding  methyl  cyanide  is  that  between  diazomethane 
and  HCN  ;  CH0  :  N2  +  HCN  =  CH3CN  +  N2.  This  illustrates  the  application  of  diazo- 
methane in  the"  formation  of  a  number  of  organic  compounds. 

Methyl  cyanide  is  present,  in  small  quantity,  in  coal-naphtha,  and  in  the  c 
tillate  from'  beet-sugar  refuse. 

Ethyl  cyanide,  or  pnyw-nitrlle,  C2H5'CN,  is  similarly  obtained.  It  resembles 
methyl  cyanide,  except  in  being  less  soluble  in  water,  and  in  boiling  at  95  L/. 


700  CAEBAMINES. 

combines  with  HC1  to  form  a  sparingly  soluble  crystalline  compound,  which 
absorbs  water  from  the  air,  and  yields  propionic  acid  and  ammonium  chloride. 

Sodium  acts  on  ethyl  cyanide  in  the  same  way  as  on  CH3*CN  :  one  part  is  decom- 
posed, with  evolution  of  butane  (di-ethyl) — 2C2H5CN  +  Na2  =  C4H10  +  2NaCN. 
The  remainder  is  polymerised  to  cyanetldne  (C2H5)3(CN)3. 

Phenyl  cyanide,  or  benzonitrile,  C6H5'CN,  also  called  cyanohenzene,  may  be 
prepared  by  dehydrating  ammonium  benzonate.  also  by  distilling  potassium 
benzenesulphonate  with  KCN  (or  well-dried  K4FeCy6)  ;  C6H5'S03K  +  KCN  = 
CfiH5'CN  +  K2S03.  It  is  a  colourless  liquid  smelling  of  bitter  almonds  ;  sp.  gr. 
1.023,  Boiling  at  191°  C.  By  hydrolysis  it  becomes  ammonium  benzoate.  Nascent 
hydrogen  converts  it  into  benzylamine,  C6H5CH2'NH2.  Its  formation  from 
diazobenzene  has  already  been  noticed  (p.  681). 

Benzyl  cyanide,  C6H5'CH2'CN,  or  phenyl-acetonitrile,  is  obtained  by  heating 
benzyl  chloride  with  potassium  cyanide  and  alcohol.  It  occurs  in  the  essentail  oils 
of  nasturtium  and  cress.  When  boiled  with  alkalies,  it  yields  ammonia  and  frfienyl 
acetic  (or  a-toluic)  acid,  C6H5-CH2-C02H. 

497.  Isocyanides,  Isonitriles,  or  Carbylamines  (Carbamines). 
— These  compounds  are  isomeric  with  the  cyanides  of  the  hydrocarbon 
radicles,  but  differ  from  them  in  being  much  less  easily  attacked  by 
alkalies  and  in  yielding  formic  acid  and  an  amine  of  the  hydrocarbon 
radicle  when  hydrolysed  by  acids,  methyl  isocyanide,  for  example, 
yielding  methylamine,  H3C'NH2,  and  formic  acid,  HCOOH.  This 
reaction  shows  that  the  C  atoms  in  the  isocyanide  are  not  united 
directly,  but  through  the  N  atom  ;  in  other  words,  the  second  of  the 
two  possible  formulae  given  above  for  the  cyanide,  H3C'N  I  C,  must  be 
ascribed  to  the  isocyanide.*  The  formation  of  two  carbon  compounds 
on  hydrolysis  is  easily  explained  on  this  assumption  ;  CH3*NC  +  2HOH  = 
CH3-NH2  +  HCOOH. 

The  isocyanides  are  obtained  in  small  proportion  together  with  the 
cyanides  when  the  iodides  of  the  hydrocarbon  radicles  are  heated  with 
KCN,  but  they  are  almost  the  sole  products  when  AgCN  is  substituted 
for  the  KCN.  The  iodide  and  AgCN  are  heated  in  a  sealed  tube  with 
ether  at  140°  C.,  when  a  crystalline  compound  of  the  isocyanide  with 
AgCN  is  formed  ;  this  is  distilled  with  water  and  KCN,  whereupon  the 
isocyanide  distils  ;  CH3I  +  2  AgCN  =  CH3'NC,  AgCN  +  Agl ; 

CH3-NC,AgCN  +  KCN  =  CH3«NC  +  KCN,AgCN. 

The  term  carbamine  refers  to  the  idea  formerly  entertained  that  the 
isocyanides  were  amines  in  which  carbon  is  substituted  for  hydrogen  ; 
thus,  methyl  carbamine,  NC'CH3,  might  be  regarded  as  methylamine, 
NH2CH3,  in  which  C"  is  substituted  for  H2.  Their  connection  with 
the  amines  is  illustrated  by  the  fact  that  they  can  be  prepared  by 
the  action  of  chloroform  and  alcoholic  potash  on  the  amines ;  e.g., 
CH3-NH2  +  CHC13  +  3KOH  =  CH3-NC  +  3KC1  +  3HOH. 

The  isocyanides  often  accompany  the  cyanides  of  the  alcohol-radicles,  especially 
when  prepared  by  distilling  the  acid  ethereal  salts,  such  as  potassium  ethylsulphate, 
with  potassium  cyanide.  For  this  reason  the  cyanides  of  alcohol-radicles  were 
formerly  described  as  having  an  offensive  smell,  which  is  really  characteristic 
of  the  isocyanides  mixed  with  them. 

Methyl  isocyanide  or  methyl  carbamine,  H3ONC,  is  prepared  as  described  above. 
It  is  lighter  than  water  (sp.  gr.  0.76)  and  moderately  soluble  in  it.  It  has  an 
extremely  unwholesome  smell,  and  boils  at  59°  C.  Methyl  carbamine  is  slightly 
alkaline  ;  it  combines  with  HC1  gas.  forming  a  crystalline  hydrochloride,  which  is 
decomposed  by  water  into  formic  acid  and  methylamine  hydrochloride ; 
H3C-NC.HC1  +  2H20  =  H3ONH2-HC1  +  HC02H. 

*  According-  to  Nef  the  isocyauides  must  be  regarded  as  containing  bivalent  carbon, 
H-.C-NiC. 


TAUTOMERISM. 

Ethyl    m-i/amde,   or  ethyl    carbarn  ine,   H5C2'NC,    prepared   like  the  methyl 
compound,  boils  at  79    C.,  and  has  a  repulsive  odour  like  that  of  hemlock 
is  lighter  than  water,  and  slightly  alkaline.    When  heated  with  water  at  180°  C   for 
some  hours  it  is  converted  into  ethylatnine  formate  ; 

H5C2-NC  +  2H20  =  H5C2-NH2.HC02H. 

Heated  alone  in  a  sealed  tube  at  230°  C.,  it  is  metamerised  into  propionitrile  ; 
HsC2-:NC  =  HgC2-CN.  Ethyl  carbamine  torms  a  crystalline  salt  with  HC1  from 
which  very  strong,  well  cooled  potash  separates  an  oily  layer  of  eth.,1  for,,,  amide  ; 
CN  C2H5  +  H.2O  =  ICO  NHC2H5.  Glacial  acetic  acid  also  converts  ethyl  carbamine 
into  ethyl  formamide,  producing  acetic  anhydride  and  much  heat  _ 

CN-C2H5  +  2(C2H3OOH)  =  HCO-NHC2H5  +  (C2H30)20. 

Phenyl  isocyanide,  or  phenyl  carbamine,  H5C6'NC,  is  prepared  by  mixing  aniline 
with  a  saturated  alcoholic  solution  of  potash,  and  gradually  adding  chloroform  ; 
the  distillate  is  treated  with  oxalic  acid  to  remove  aniline,  with  potash  to  remove 
water,  and  re-distilled.  Phenyl  carbamine  has  a  very  terrible  odour  ;  it  is  green 
by  transmitted  light,  and  shows  a  blue  reflection,  "it  begins  to  boil  at  166°  C., 
but  soon  decomposes,  being  converted,  at  230°  C.,  into  an  odourless  liquid  which 
crystallises  on  cooling.  When  heated,  in  a  sealed  tube,  at  200°  C.,  phenyl 
carbamine  slowly  metamerises  into  phenyl  cyanide,  or  benzonitrile,  H5C6'CN. 
Treated  with  acids,  it  yields  formic  acid  and  salts  of  phenylamine  (aniline)  "• 
H5C6'NC  +  2H20  =  H5C6-NH2  +  HC02H. 

498.  Tautomerism.  —  It  has  been  seen  that  the  cyanides  of  alcohol- 
radicles  exist    in  two  forms,  as    though  they  were  derived,  from  two 
hydrocyanic  acids,  H'C=N  and  H'N=C.     It  will  be  seen  later  that 
derivatives  of  cyanamide  also  appear  to  be  derived  from  two  isomerides, 
H9N'C  :  N    and    HN  :  C  :  NH.       Two    hydrocyanic    acids    or     two 
cyanamides,  however,  have  never  been  prepared.     It  is  the  case  with 
a   large  number   of  substances  that,   although  they  do   not   exist   in 
isomeric  forms,  they  behave  in  different  reactions  as  if  they  had  two 
structural  formulae,  either  of  which  could  be  assumed  according  to  the 
conditions.     Such  compounds  are  said  to  possess  tautomeric  structures. 
The  derivatives  of  one  form  (the  stable  form)  are  generally  more  stable 
than  those  of  the  other  (the  labile  form  or  pseudoform). 

Tautomerism  is  generally  connected  with  the  migration  of  a  H  atom,  as  will  be 
seen  from  the  above  examples.  It  is  very  common  among  ketonic  compounds,  in 
which  the  grouping  -CH  :  COH'  occurs,  this  tending  to  become  'CH./CO  (ef.  ethyl 
acetoacetate,  p.  643)  ;  the  former  is  the  hydroxtjl-  or  enol-  form,  while  the  latter 
is  the  lieto-  form.  Cf.  also  lactanis  and  lactims  (pp.  674,  679),  and  (iinidhtrx  (p.  698). 

From  the  fact  that  the  chief  product  of  the  action  of  CH3I  on  KCN  is  methyl 
cyanide,  it  may  be  supposed  that  potassium  cyanide  is  a  salt  of  H'C  •  N.  Silver 
cyanide,  on  the  other  hand,  must  be  a  salt  of  H'N  j  C.  for  the  chief  product  of 
its  reaction  with  methyl  iodide  is  methyl  isocyanide. 

499.  Hydroxy-   and   Thio-Cyanogen  Compounds.—  Cyanuric 
acid,  Cy3(OH)3,  is  obtained  by  heating  urea  till  the  melted  mass  solidifies  ; 

(CN)3(OH)3.     The  residue  is  washed  with  water, 


dissolved  in  KOH,  and  the  cyanuric  acid  precipitated  by  adding  HC1. 
A  better  yield  is  obtained  by  passing  dry  chlorine  over  urea  kept  in 
fusion  by  a  gentle  heat—  3CO(NH2)2  +  C13  -  2NH4C1  +  HC1  +  N  + 
(CN)3(OH)3.  The  residue  is  washed  with  cold  water,  and  crystallised 
from  hot  water.  Cyanuric  acid  crystallises  in  prisms  containing  2Aq. 
It  is  insoluble  in  alcohol.  It  is  a  tribasic  acid.  It  is  probable  that 
cyanuric  acid  is  a  closed-chain  compound,  and  it  may  be  represented  by 

- 


either     of     the      tautomeric       formulae     C(OH)<      C/QO\/    '     or 


702  CYANIC  ACID. 


x 

CCX'  /NH,  derivatives  (the  cyanuric  esters,  e.g.,  C3lSr303(CH3)3) 

NH'CO 
of  both  forms  being  known. 

Trisodium  cyanurate,  (CN)3(ONa)3,  is  insoluble  in  hot  solution  of  soda  and  forms 
a  crystalline  precipitate  on  heating  solution  of  cyanuric  acid  mixed  with  excess  of 
soda.  Barium  cyanurate,  Cy303HBa,  is  obtained  as  a  crystalline  precipitate  by 
dissolving  cyanuric  acid  in  NH3,  and  stirring  with  BaCl2.  It  has  a  great  tendency 
to  deposit  on  the  lines  of  friction  by  the  stirring-rod.  The  most  characteristic 
test  for  cyanuric  acid  is  ammoniacal  CuS04,  which  gives  a  violet  crystalline 
precipitate  containing  Cy6(OH)4'02'Cu(NH3)2.  Stiver  cyanurate,  Cy3(OAg)3  is 
obtained  as  a  crystalline  precipitate  by  adding  ammonium  cyanurate  to  silver 
nitrate. 

500.  Cyanic  acid,  CyOH,  is  prepared  by  distilling  cyanuric  acid 
(dried  at  ioo°C.),  and  condensing  in  a  receiver  surrounded  by  a  freezing- 
mixture  ;  Cy3(OH)3  =  3CyOH.  The  cyanic  acid  is  a  colourless  liquid,  of 
sp.  gr.  1.14  at  o°  C.,  which  smells  rather  like  acetic  acid.  It  cannot  be 
kept,  for  when  the  receiver  is  taken  out  of  the  freezing-mixture  the 
acid  becomes  turbid,  and  presently  begins  to  boil  explosively,  being 
entirely  converted  in  a  few  minutes  into  a  white  hard  solid,  known  as 
cyamelide,  which  is  a  polymeride  of  cyanic  acid,  into  which  it  is  recon- 
verted by  distillation.  When  cyanic  acid  is  mixed  with  water,  heat  is 
evolved,  and  the  liquid  becomes  alkaline  ;  CN'OH  +  2H2O  =  NH4'HC03. 
A  compound  of  HC1  and  CNOH  is  obtained  as  a  fuming  liquid  by 
acting  on  a  cyanate  with  dry  HC1  gas. 

It  is  doubtful  whether  cyanic  acid  is  HOC  :  N  (the  nitrile  of  car- 
bonic acid)  or  HIS"  :  C  :  0  (carbimide).  The  former  would  be  cyanic 
acid  and  the  latter  isocyanic  acid.  At  one  time  it  was  supposed  that 
derivatives  of  both  were  known,  but  the  compounds  formerly  called 
esters  of  cyanic  acid  have  been  shown  to  have  a  different  constitution. 

Potassium  cyanate.  —  The  compound  formerly  so  called  is  probably  the 
isocyanate,  K'N  :  C  :  0,  since  it  has  been  found  to  give  rise  to  alkyl 
isocyanates  when  heated  with  potassium  alkyl  sulphates.  It  is  formed 
when  the  cyanide  is  oxidised  by  fusion  in  contact  with  air  or  with 
metallic  oxides. 

It  may  be  prepared  by  oxidising  potassium  ferrocyanide  with  potassium  di- 
•chrornate.  Four  parts  of  perfectly  dried  K4FeCy6  are  intimately  mixed  with  3  parts 
of  K2Cr207  ;  the  mixture  is  thrown,  in  small  portions,  into  a  porcelain  or  iron  dish, 
heated  sufficiently  to  kindle  it.  When  the  whole  has  smouldered  and  blackened, 
it  is  allowed  to  cool,  introduced  into  a  flask,  boiled  with  strong  alcohol,  and  filtered 
hot  ;  the  isocyanate  crystallises  out  on  cooling,  and  the  mother  liquor  may  be 
employed  to  extract  a  fresh  portion. 

Potassium  isocyanate  is  also  prepared  by  passing  cyanogen  chloride 
into  well-cooled  potash;  CN'C1  +  2KOH  =  KCNO  +  KC1  +  H20.  It 
crystallises  in  plates  ;  it  is  decomposed  b}'  moist  air  into  KHC03  and 
ammonia;  K'NC  :  0  +  2H20  =  KHC03  +  NH3.  It  is  very  soluble  in 
water,  but  the  solution  soon  decomposes,  especially  if  heated  — 
sK-NC  :  0  +  4H20  =  CO(OK)2  +  CO(ONH4)2.  If  the  freshly  pre- 
pared solution  be  mixed  with  dilute  acetic  acid,  a  crystalline  precipitate 
of  potassium  dihydrogen  cyanurate  is  obtained;  3  KNCO  +  2HA  = 
KH0C3N303+  2KA.  Solution  of  potassium  isocyanate  effervesces  with 
acids  evolving  C02,  together  with  some  pungent  vapour  of  cyanic  (or 
isocyanic)  acid,  and  leaving  an  ammonium  salt  in  solution. 

Ammonium  cyanate,  NH4-0'CN,   or  O  :  C  :  N(NH4)  is  prepared  by 


POTASSIUM  SULPHOCYANIDE.  703 

mixing  vapour  of  cyanic  acid  with  ammonia  gas  in  excess,  when  it 
is  deposited  in  minute  crystals,  which  effervesce  with  acids,  evolving 
C02.  The  cyanate  or  isocyanate  is  also  formed  when  potassium  iso- 
cyanate is  decomposed  by  ammonium  sulphate.  By  employing  strong 
solutions  and  cooling  artificially,  the  bulk  of  the  potassium  sulphate 
may  be  crystallised  out.  The  isocyanate  has  not  been  crystallised,  for, 
when  its  solution  is  evaporated,  it  metamerises  into  urea  •  NH  *NC  -0=' 
(NH2)2CO  (p.  670). 

501.  Thiocyanic  acid,  HSCN  (sulphocyanic),  is  obtained  by  decom- 
posing mercuric  thiocyanate  with  hydrogen  sulphide.  It  is  a  colourless 
pungent  liquid,  boiling  below  100°  C.,  being  then  decomposed  into 
hydrocyanic  and  persulphocydnic  acids;  sCySH  =  HCy  +  Cy2S3H2.  It 
mixes  with  water,  but  the  solution  soon  decomposes — 

3HSCN  +  6H20  =  CS2  +  H2S  +  NH4HC03  +  (NH4)2C03. 
Thiocyanic  acid  and  the  thiocyanates  give  an  intense  blood-red  colour 
with  ferric  salts,  producing  ferric  thiocyanate ;  the  red  is  bleached  by 
HgCl2,  which  distinguishes  it  from  ferric  acetate  and  meconate. 

Potassium  thiocyanate,  or  sulphocyanide,  KCSN,  may  be  obtained  by 
direct  fusion  of  potassium  cyanide  with  sulphur,  or  by  boiling  sulphur 
with  solution  of  the  cyanide. 

It  is  best  prepared  by  fusing  dried  potassium  ferrocyanide  (3  parts),  potassium 
carbonate  (i  part),  and  sulphur  (2  parts),  at  a  low  red  heat,  in  a  clay  crucible. 
The  cooled  mass  is  extracted  by  hot  water,  evaporated,  and  the  residue  boiled  with 
alcohol,  which  deposits  the  thiocyanate  on  cooling.  KCy  is  formed  by  the  reaction 
between  the  ferrocyanide  and  the  carbonate  (p.  691),  and  combines  with  the  sulphur. 

Potassium  thiocyanate  forms  prismatic  crystals,  which  are  deliquescent 
and  very  soluble  in  water,  producing  great  reduction  of  temperature. 
It  fuses  easily,  becoming  a  dark  blue  colour,  which  fades  on  cooling ;  it 
burns  when  heated  in  air,  potassium  sulphate  being  produced.  When 
hydrochloric  acid  is  added  to  a  strong  solution  of  potassium  thio- 
cyanate, a  yellow  precipitate  of  persulphocyanic  acid  is  obtained ; 
this  may  be  crystallised  from  hot  water,  and  yields  a  yellow  precipi- 
tate of  lead  per  sulphocyanate,  PbCy2S3,  with  lead  nitrate.  When  heated 
with  sulphuric  acid  mixed  with  an  equal  volume  of  water,  potassium 
thiocyanate  yields  carbon  oxysulphide,  an  offensive  gas  which  burns 
with  a  blue  flame  ;  KSCN  +  2H2S04  +  H20  =  KHS04  +  NH4HS04  +  COS. 

Potassium  -isothhcyanate,  K'NCS,  is  said  to  be  obtained  by  heating  persulpho- 
cyanic acid  with  alcoholic  solution  of  potash.  The  crystals  are  soluble  in  water  ; 
the  solution  does  not  give  the  red  thiocyanate  reaction  with  ferric  salts.  It  is  con- 
verted into  normal  thiocyanate  by  boiling  or  fusing.  Sodium  thiocyanate  occurs 
in  saliva. 

Perthiocyanoyen,  or  ineiidosulphocyanogen,  C3N3S3H,  is  obtained  as  a  yellow  pre- 
cipitate when  potassium  thiocyanate  is  heated  with  potassium  chlorate  and  hydro- 
chloric acid.  It  is  used  in  dyeing  (canarln). 

Ammonium  t/tior//(jnate  is  prepared  by  acting  on  carbon  bisulphide  (7  parts  by 
weight)  dissolved  in  alcohol  (30  parts)  with  strong  ammonia  (30  parts).  After 
standing  for  a  day  or  two,  with  occasional  shaking,  until  all  the  CS2  has  dissolved, 
the  red  solution  is  distilled  down  to  one-third  of  its  bulk,  when  it  becomes  colour- 
less, filtered  if  necessary,  and  allowed  to  crystallise  ; 

CS2  +  4NH3  =  CNS-NH4  +  (NH4)2S. 

It  is  also  made  on  a  large  scale  by  boiling  sulphur  with  the  solution  of  ammonium 
cyanide  from  the  gasworks.  It  crystallises  like  the  potassium  salt,  and  is  very 
soluble  in  water,  producing  great  cold.  When  heated,  it  fuses  easily,  and  at 
170°  C.,  is  metamerised  into  tMooarbamide  (p.  671). 


704  CYANOGEN  DEEIVATIVES. 

Leadth'toeyanate,  Pb(CyS)2,  forms  a  yellow  crystalline  precipitate. 

Silver  thioeyanate,  AgCyS,  is  a  white  precipitate,  very  insoluble  in  water  and  in 
nitric  acid,  and  sparingly  soluble  in  ammonia. 

Mercuric  thioeyanate,  Hg(CyS)2,  is  a  crystalline  precipitate  formed  on  stirring- 
mercuric  chloride  with  an  alkali  thioeyanate.  It  attracted  much  notice  formerly 
as  the  toy  called  Pharaoh's  serpent,  which  was  a  small  cylinder  of  the  thioeyanate 
mixed  with  gum,  which  burnt  when  kindled,  evolving  mercury  and  other  vapours, 
and  swelling  to  a  bulky  vermiform  mass  of  mellone. 

Cuprous  thioeyanate,  Cu2(CyS)2,  precipitated  by  potassium  thioeyanate  from  a 
cuprous  salt,  is  very  insoluble  in  water  and  in  cold  dilute  acids,  so  that  copper  is 
sometimes  precipitated  in  this  form  in  quantitative  analysis. 

502.  Cyanogen   sulphide.   Cy2S,  is    obtained   by  decomposing   cyanogen  iodide, 
dissolved  in  ether,  with   silver  thioeyanate;  CyI  +  AgCyS  =  Cy2S  +  AgI.     It  is  a 
crystalline,  fusible,  volatile  solid,  soluble  in  alcohol  and  ether,  but  decomposed  by 
water  ;  potash  converts  it  into  cyanate  and  thioeyanate. 

Phosphorus  tricyanide,  Cy:5P,  is  sublimed  in  tabular  crystals  from  a  mixture  of 
silver  cyanide  and  phosphorus  trichloride,  heated  in  a  sealed  tube  at  140°  C.  for 
some  hours,  and  distilled  in  a  current  of  C02.  It  inflames  at  a  very  low  tempera- 
ture, and  is  decomposed  by  water  into  hydrocyanic  and  phosphorous  acids  ; 
Cy.,P  +  3HOH  =  3CyH  +  P(OH)3. 

Cyanamide,  H2N'CN,  which  also  behaves  as  carbodiitwide,  NH  :  C  :  NH,  may  be 
obtained  by  fusing  urea  with  sodium— (NH2)2CO  +  Na  =  H.2N  -ON  +  NaOH  +  H.  The 
mass  is  dissolved  in  water,  ammonia  added  in  excess,  and  silver  nitrate,  which 
gives  a  yellow  precipitate  of  Ag2N'CN  ;  this  is  washed,  dried,  covered  with  ether, 
and  decomposed  byH2S,  when  Ag2S  and  H2N'CN  are  produced,  the  latter  dissolv- 
ing in  the  ether,  from  which  it  may  be  crystallised. 

Cyanamide  may  also  be  prepared,  like  other  amides,  by  acting  on  NH.,,  dissolved 
in  ether,  with  gaseous  CNC1  ;  NH3  +  CN;C1  =  H2N'CN  +  NH4C1. 

Another  reaction  which  furnishes  it  is  that  between  thiourea  (p.  671)  and  mer- 
curic oxide  ;  (NH2)2CS  +  HgO  =  H2N'CN  +  HgS  +  H20.  It  forms  crystals  soluble  in 
water,  alcohol,  and  ether,  and  melting  at  40°  C.  HC1  passed  into  its  ethereal 
solution  gives  crystals  of  H2N'CN,2HC1.  Hydrolysis  converts  it  into  urea,  and 
H2S  into  thio-urea.  With  NH3  it  yields  guanidine.. 

Dicyanimlde,  HN(CN)2,  is  produced  by  the  action  of  potash  on  solution  of 
potassium  cyanate  ;  3KOCN  +  H20  =  (KO)2CO  +  KOH  +  HN(CN2.)  On  neutralising 
the  solution  with  HN03  and  adding  AgN03,  a  precipitate  of  AgN(CN)2  is  obtained. 
Potassium  isocyanate,  K'NCO,  does  not  yield  dicyanimide. 

The  amides  of  cyanuric  acid  are  (i)  melamine  or  cyanuramide,  C3N3(NH.2)3r 
obtained  by  the  action  of  NH3  on  cyanuric  chloride,  (2)  ammeline,  C3N3(NH2).,OH, 
produced  \>\  boiling  melamine  with  HC1,  and  (3)  ammelide,  C3N3NH2(OH)2,  formed 
by  boiling  melamine  with  KOH.  Melamine  crystallises  from  water,  but  the  others, 
are  insoluble. 

When  NH4SCN  is  heated,  it  loses  NH3  and  H2S,  and  is  converted  successively 
into  melam,  C6H9Nn,  melem,  C6H6N10,  and  mellone,  C6H3N9,  white  amorphous  com- 
pounds. Potassium  mellonide,  C9K3N13,  is  formed  when  KSCN  is  heated  out  of 
contact  with  air,  CS2  being  evolved ;  this  crystallises  with  3Aq  and  yields  a  corre- 
sponding silver  salt  and  free  acid. 

Chrysean,  [CN'CH(SH)]2NH,  is  obtained  by  covering  potassium  cyanide  with 
water,  in  a  flask,  and  saturating  with  H2S  gas  ; 

4KCN  +  5H2S  =  C4H5S2N3  +  2K2S  +  NH4HS. 

It  crystallises  from  boiling  water  in  golden  needles,  soluble  in  alcohol,  ether,  acids, 
and  alkalies.  Its  alcoholic  solution  is  red,  and  changes  to  a  fugitive  green  on 
adding  a  little  alkali. 

503.  Alltyl  cyanurates  and  isocyanates. — The  compounds  recently  described  as 
alkyl  cyanates  are  proved  to  be  esters  of  imido-carbonic  acid.     By  the  action  of 
CNC1  on  sodium  alkyloxides,  products  are  obtained  which  rapidly  polymerise  to 
alkyl  cyanurates— e.g.,  3Cl'CN  +  3CH3ONa  =  3NaCl  +  (CH3)303C3N3. 

Methyl  isocyanate,  or  methyl  carbimlde,  H3C'NC:0,  was  formerly  regarded  as  the 
normal  cyanate,  being  obtained  by  distilling  potassium  methyl  sulphate  with 
potassium  cyanate  ;  KCH3S04  +  K'O  •  CN  =  H3ONC  :0  +  K2S04.  It  is  also  obtained 
by  oxidising  methyl  isocyanide  with  mercuric  oxide  ; 

H3C'NC  +  HgO  =  H3C-NC:0  +  Hg. 
It  is  a  volatile  liquid  (b.-p.  44°  C.)   with  a  suffocating  odour.     When  distilled 


OIL  OF  MUSTARD.  705 

with  potash  it  yields-  methylamine,  showing  that  the  methyl  is  attached  to  the 
S  n°xreR  /rn^\  A6  comP.ound  is  the  isocyanate:  H3ON  :  CO  +  2KOH  = 
?Tt  P  T?P  t<?  °(VH  ^R'TRrR  ^converts  methyl  ^cyanate  into  «,«%*  ««« 
(H3L  JNb  .  U  +  JSH3  =  NH2-NHCH3-CO)  resembling  urea  itself 

m^W%™^%'^W<>£**a™*d  by  the  action  of  water  on  methyl  iso- 

cyanate ;  -  - 


Ethyl  isocyanate,  or  ethyl  carUmide,  H5C2'NC  :  0,  is  prepared  like  the  methyl 
compound,  which  it  resembles.  Its  sp.  gr.  is  0-9  and  it  boils  at  60°  C  It  yields 
ethylamine  when  distilled  with  potash,  and  triethylamine  with  sodium  ethoxide  • 
H5C2-NC  :  0  +  2(C2H5-ONa)  =  (H5C2)3N  +  CO(ONa)2. 


Ai  i?*yl  Ur™'  (NHC2H5)2CO,  and  Methyl  urea 

5)2-CO,  have  been  obtained. 
Methyl-ethyl  urea,  NHCH3'NHC2H5-CO,  is  formed  by  the  action  of  methylamine 
ethyl  isocyanate  ;  H5C2'NC  :  0  +  NH2CH3  =  (NHCH3)NHC2H3'CO. 


on  23  323 

504.  The  isothiocyanates  of  the  hydrocarbon  radicles  are  called 
mustard  oils  or  thiocarbimides. 

Allyl  isothiocyanate,  H5C3'NCS,  is  the  essential  oil  of  mustard, 
obtained  by  grinding  black  mustard  seeds  with  water  and  distilling.  It 
does  not  exist  in  the  seed,  but  is  produced  by  the  decomposition  of 
potassium  myronate  contained  in  the  seed,  induced  by  a  peculiar  ferment 
called  myrosin,  which  decomposes  the  myronate  into  the  essence  of 
mustard,  glucose,  and  KHSO4  ;  K010H18NS,010  =  H5C3'NCS  +  C6H1206  + 
KHS04.  The  seed  yields  about  0-5  per  cent,  of  the  oil. 

The  potassium  myronate  may  be  obtained  from  ground  mustard  by 
rendering  the  myrosin  inactive  by  boiling  alcohol,  and  then  extracting 
the  myronate  with  cold  water.  The  solution  is  evaporated  to  a  small 
bulk  and  mixed  with  alcohol,  which  precipitates  the  potassium 
myronate.  The  free  acid  is  not  known,  being  very  unstable. 

Myrosin  is  prepared  by  extracting  ground  white  mustard  with  cold 
water,  evaporating  the  nitrate  to  a  syrup  below  40°  C.,  and  adding 
alcohol  in  small  quantity,  when  the  myrosin  is  precipitated.  It  some- 
what resembles  albumin,  being  coagulated  and  rendered  inactive  by 
heat.  Its  aqueous  solution,  when  added  to  potassium  myronate, 
causes  it  in  a  few  minutes  to  smell  of  mustard  and  become  acid  ;  it 
also  becomes  turbid  from  the  separation  of  small  globular  cells  like 
those  of  yeast.  Myrosin  occurs  in  other  plants  than  mustard,  such 
as  the  radish,  rape,  cabbage,  and  swede,  all  belonging  to  the  same 
natural  order  as  mustard  (Cruciferce).  Mignonette  root  furnishes  phenyl 
ethyl  mustard  oil,  or  phenyl  ethyl  isothiocyanate. 

%  Essential  oil  of  mustard  has  sp.  gr.  1.017,  and  boils  at  150°  C.  It  is  insoluble  in 
water,  but  dissolves  in  alcohol  and  ether.  It  is  the  cause  of  the  pungent  odour 
of  mustard  paste  and  of  its  power  to  redden  and  irritate  the  skin.  It  is  slowly 
decomposed  by  light,  depositing  a  yellow  precipitate.  When  heated  with  water 
at  100°  C.  for  some  time  it  loses  sulphur  and  becomes  crotono-mtrile,  C3H5-CN, 
which  is  present  in  considerable  quantity  in  commercial  mustard  oil.  When 
mustard  oil  dissolved  in  alcohol  is  acted  on  by  HC1  and  Zn,  it  yields  allylamine  : 
H5C3-NCS  +  H4  =  H5C3'NH2  +  HCHS  (thhformaldehyde).  By  mixing  mustard  oil 
with  ammonia  and  passing  ammonia  gas,  allijl-thw-urea,  or  MtMMMMMM, 
NH2-NH(CoHB)-CS,  is  obtained,  forming  prismatic  crystals  soluble  in  water, 
alcohol,  and  ether,  and  having  a  bitter  taste.  It  is  a  weak  base.  Whenheated  witj 
lead  hydroxide,  it  loses  H2S,  and  becomes  allyl-cyanamide,  NHGA^i  ™luch 
afterwards  polymerises  into  sinamine,  or  trl-allyl  melamine,  (1  iO3U6)3CO. 
This  is  a  strongly  alkaline  base. 

If  allyl  bromide  be  decomposed  by  ammonium  thiocyanate,  at  a  low  tem- 
perature, alliil  thiocyanate,  H,CS'SCN,  is  formed,  which  has  no  smell  of  mustard. 
When  this  is  heated,  it  boils  at  i6i°C.,  but  the  boiling-point  soon  falls,  and  •< 
strong  smell  of  mustard  is  perceived.  When  the  boiling-point  has  re 


706  MERCUEIC   FULMINATE. 

150°  C.,  the  whole  distils  over  as  allyl  isothiocyanate,  H5C3'NCS,  or  mustard  oil. 
Allyl  thiocyanate,  decomposed  by  potash,  yields  potassium  thiocyanate  and  allyl 
alcohol  ;  H5CS  -SON  +  KOH  =  H5C3'OH  +  K-SCN  ;  allyl  isothiocyanate  gives  allyl- 
amine  ;  H5C3:NCS  +  4KOH  =  H6C3-NH2  +  K2S  +  CO(OK)2  +  H20. 

Mustard  oil  is  also  obtained  artificially  by  distilling  allyl  iodide  (p.   636)  with 

th 


potassium  thiocyanate;  C3H5I  +  KSCN  =  C3H8-NCS  +  KI.  When  ethyl  iodide  is 
treated  in  the  same  way,  ethyl-  thiocyanate,  C2H5'SCN  is  obtained.  To  obtain 
the  ethyl  isothiocyanate,  or  ethyl  mustard  oil,  or  ethyl  tlitocarbimide,  C2H5'NCS, 
ethylamine  dissolved  in  alcohol  is  digested  with  carbon  bisulphide,  "distilled 
nearly  to  dryness.  and  the  residue  in  the  retort  boiled  with  solution  of  HgCl2.  All 
primary  amines  yield  the  corresponding  mustard  oils  when  treated  in  this  manner, 
and,  since  the  odour  is  quite  characteristic,  the  treatment  with  CS2  iand  HgCl2  is 
known  as  the  mustard-oil  tent  for  primary  lases. 

The  mustard-oil  reaction  is  easily  explained.  When  C02  is  combined  with  dry 
NH3,  ammonium  carlamate  is  formed;  C02  +  2NH3  =  CO(ONH4)(NH2).  If  CS2  be 
substituted  for  C00  (the  CS2  employed  in  alcoholic  solution),  ammonium  tkioearba- 
mate  is  produced—  CS2  +  2NH8  =  CS(SNH4)(NH2). 

When  ethylamine  is  used  instead  of  ammonia,  the  product  is  etht/l  ammonium, 
ethyl-thiocarbamate  ;  CS2  +  2NH2(C2H5)  =  CS-SNH3(C2H5)NH(C2H5).  On  decompos- 
ing this  with  mercuric  chloride,  it  yields  the  corresponding  mercuric  salt,  which 
is  decomposed,  by  boiling  with  water,  into  ethyl  isothiocyanate.  mercuric  sulphide 
and  hydrogen  sulphide  ;  Hg(CS-S'NHC2H6)2  =  HgS  +  H2S  +  2C2H5NCS.. 

Butyl  isothiocyanate,  C4H9'NCS,  is  the  essential  oil  of  scurvy-grass,  another 
cruciferous  plant,  and  is  sometimes  sold  as  mustard  oil.  but  it  has  a  higher 
boiling-point,  160°  C. 

505.  Fulminates.  —  The  salts  known  as  fulminates  are  prepared  from 
the  fulminates  of  mercury  and  silver,  obtained  when  those  metals  are 
treated  with  nitric  acid  and  alcohol.  It  is  still  doubtful  what  is  their 
constitution,  but  the  latest  researches  seem  to  show  that  they  are  salts 
of  the  acid  C  :  N*OH,  which  may  be  regarded  as  the  oxime  (p.  625)  of 
C  0  —  carbyloxim  e  . 

Mercuric  fulminate  (C  :  N'0)2Hg,  is  prepared  on  a  small  scale,  with 
safety,  by  carefully  observing  the  following  directions  :  —  Dissolve 
1.6  grm.  of  mercury  in  14  c.c,  of  ordinary  concentrated  nitric  acid 
(sp.  gr.  1.42)  in  a  half-pint  beaker,  covered  with  a  dial-glass  ;  the  dis- 
solution may  occur  in  the  cold,  or  may  be  accelerated  by  gently  heating. 
The  solution  contains  Hg(NO3)2,  HN03  arid  HN02.  When  all  the 
mercury  is  dissolved,  remove  the  beaker  to  a  distance  from  any  flame 
and  pour  into  it,  at  arm's  length,  17.5  c.c.  of  alcohol  (sp.  gr.  0.87). 
Very  brisk  action  soon  begins,  and  the  fulminate  separates  as  a  crystal- 
line precipitate  ;  dense  white  fumes  pour  over  the  sides  of  the  beaker, 
having  the  odours  of  nitrous  ether  and  aldehyde;  they  also  contain 
mercury  compounds  and  HCN,  and  are  very  poisonous.  When  red 
fumes  begin  to  appear  abundantly,  some  water  is  poured  in  to  stop 
the  action  (which  occupies  only  two  or  three  minutes),  and  the  ful- 
minate is  collected  on  a  filter,  washed  with  water  as  long  as  the  washings 
taste  acid,  and  dried  by  exposure  to  air. 

On  a  large  scale  the  preparation  is  carried  out  under  sheds.  At  Montreuilr 
300  grams  of  mercury  are  dissolved  in  3  kilos  of  colourless  HN03,  of  sp.  gr.  1.4  in 
the  cold.  The  solution  is  transferred  to  a  retort,  and  2  litres  of  strong  alcohol  are 
added.  In  summer  no  heat  is  required,  and  the  vapours  are  condensed  in  a  receiver 
and  added  to  a  fresh  charge.  When  the  action  has  ceased,  the  contents  of  the  retort 
are  poured  into  a  shallow  pan,  and,  when  cold,  the  fulminate  is  collected  in  a  conical 
earthen  vessel  partially  plugged  at  the  narrow  end.  It  is  washed  with  rain-water, 
and  drained  until  it  contains  20  per  cent,  of  water,  being  stored  in  that  state. 

Mercuric  fulminate,  thus  prepared,  has  a  grey  colour  from  the  presence  of 
finely  divided  mercury,  and  sometimes  contains  mercuric  oxalate.  It  may  be 
purified  by  dissolving  it  in  100  parts  of  boiling  water,  which  leaves  the  metal 


CAP  COMPOSITION. 


70? 


and  the  oxalate  undissolved,  and  deposits  the  fulminate  on  cooling  in  lustrous 
white  prisms.  It  should  not  be  kept  in  a  Btofbered  bottle,  as  it  would  easily 
detonate  by  friction  between  the  stopper  and  the  neck  of  the  bottle.  The  blow 
of  a  hammer  causes  it  to  detonate  sharply  with  a  bright  flash  and  grey  fumes  of 
mercury  ;  HgC2N202  =  Hg  +  2CO  +  N2.  It  is  also  d&onated  by  being  touched  with 
a  wire  heated  to  195°  C..  or  by  an  electric  spark,  or  by  contact  with  strong  sulphuric 
or  nitric  acid.  Its  sp.  gr.  being  4.4,  a  small  volume  of  it  evolves  a  large  volume  of 
gas  ;  according  to  the  above  equation,  the  gas  and  vapour  would  occupy  more  than 
1340  times  the  volume  of  the  solid,  at  the  ordinary  temperature,  and  the  volume  at 
the  moment  of  detonation  would  be  much  greater,  because  the  fulminate  evolve* 
403  units  of  heat  (per  unit)  in  its  decomposition,  and  this  would  expand  the  evolved 
gases  and  greatly  increase  their  mechanical  effect.  It  is  estimated  that  a  pressure 
of  48,0x30  atmospheres  is  thus  produced. 

Fulmlnlc  add,  C  :  N'OH,  is  isomeric  with  cyanic  acid,  and  was  long  supposed  to 
contain  the  cyanogen  group.  It  is  doubtless  obtained  when  fulminates  are  treated 
with  HC1,  when  a  smell  of  HCN  is  perceived  although  none  is  to  be  detected ; 
but  the  fulminic  acid  immediately  combines  with  the  HC1,  forming  chlorofttrmojrlme, 
C1HC  :  N'OH,  an  indication  that  the  carbon  is  unsaturated,  as  in  CO.  This  oxiim- 
rapidly  breaks  up  into  formic  acid  and  hydroxylamine  hydrochloride  ;  C1HC  :N'OH 
+  2H20  =  NH2OH.HC1  +  HCOOH.  Thus  these  two  compounds  and  mercuric 
chloride  are  the  products  of  the  action  of  strong  HC1  on  mercuric  fulminate  ;  by 
precipitating  the  mercury  by  H2S  and  evaporating~the  solution,  hydroxylamine  hydro- 
chloride  may  be  crystallised,  and  this  is  one  of  the  best  methods  for  preparing  this 
salt. 

Mercuric  fulminate  is  formed  when  HgCl2  is  added  to  sodium  nitromethane, 
CH2  :  NO'ONa,  water  being  formed.  This  confirms  the  above  constitution,  but  it 
must  be  added  that  the  behaviour  of  the  fulminate  with  halogens  indicates  the 
presence  of  a  CN  group.  With  Cl  it  yields  HgCl.2.  CNC1  and  CC13NO2  (chlorpicrin), 
and  with  Br  the  reaction  is  similar,  but  dibromonitro-aceto-nltrile,  Br2  (N02)C'CN,  is 
an  intermediate  product.  Again,  NH3  converts  the  fulminate  into  urea  and 
guanidine,  as  though  it  contained  an  isocyanic-group  (see  Isocyanates). 

Cap  composition.—  The  explosion  of  mercuric  fulminate  is  so  violent  and  rapid 
that  it  is  necessary  to  moderate  it  for  percussion-caps.  For  this  purpose  it  is 
mixed  with  potassium  nitrate  or  chlorate,  the  oxidising  property  of  these  salts 
possibly  causing  them  to  be  preferred  to  any  merely  inactive  substances,  since  they 
would  tend  to  increase  the  temperature  of  the  flash  by  burning  the  carbonic  oxide 
into  carbon  dioxide,  and  would  thus  ensure  the  ignition  of  the  cartridge.  In  the 
military  caps,  in  this  country,  potassium  chlorate  is  always  mixed  with  the 
fulminate,  and  powdered  glass  is  sometimes  added  to  increase  the  sensibility  of 
the  mixture  to  explosion  by  percussion.  Antimony  sulphide  is  sometimes  substi- 
tuted for  powdered  glass,  apparently  for  the  purpose  of  lengthening  the  flash  by 
taking  advantage  of  the  powerful  oxidising  action  of  potassium  chlorate  upon 
that  .compound  (p.  186).  Since  the  composition  is  very  liable  to  explode  under 
friction,  it  is  made  in  small  quantities  at  a  time,  and  without  contact  with  any 
hard  substance.  After  a  little  of  the  composition  has  been  introduced  into  the 
cap,  it  is  made  to  adhere  and  waterproofed  by  a  drop  of  solution  of  shell-lac  in 
spirit  of  wine. 

If  a  thin  train  of  mercuric  fulminate  be  laid  upon  a  plate,  and  covered,  except 
a  little  at  one  end,  with  gunpowder,  it  will  be  found,  on  touching  the  fulminate 
with  a  hot  wire,  that  its  explosion  scatters  the  gunpowder,  but  does  not  inflame 
it.  On  repeating  the  experiment  with  a  mixture  of  10  grains  of  the  fulminate 
and  15  grains  of  potassium  chlorate,  made  upon  paper  with  a  card,  the  explosion 
will  be  found  to  inflame  the  gunpowder. 

By  sprinkling  a  thin  layer  of  the  fulminate  upon  a  glass  plate,  and  firing  it  with 
a  hot  wire,  the  separated  mercury  may  be  made  to  coat  the  glass,  so  as  to  give 
all  the  appearance  of  a  looking-glass. 

Although  the  effect  produced  by  the  explosion  of   mercuric  fulminate  is  very 
violent  in  its  immediate  neighbourhood,  it  is  very  slightly  felt  at  a  distance,  am 
the  sudden  expansion  of  the  gas  will  burst  firearms,  because  it  does  not 
time  for  overcoming  the  inertia  of  the  ball,  though,  if  the  barrel  escape  desti 
tion,  the  projectile  effect  of  the  fulminate  is  found  inferior  to  that  ot  po^ 
It  has  been  proved  by  experiment  that  the  mean  pressure  exerted  by  the  explosi< 
of  mercuric  fulminate  is  very  much  lower  than  that  produced  by  gun-cotton,  and 
only  three-fourths  of  that  produced  by  nitroglycerine.     Its  great  pressure 


708 


FULMINATES. 


to  its  instantaneous  decomposition  into  CO,  N,  and  Hg  vapour  within  a  space  not 
-sensibly  greater  than  the  volume  of  the  fulminate  itself,  which  volume  being  very 
-small,  on  account  of  the  high  density  of  the  fulminate,  the  escaping  gases  exert 
an  enormous  pressure  at  the  moment  of  explosion.  This  detonating  property  of 
mercuric  fulminate  renders  it  exceedingly  useful  for  effecting  the  detonation  of 
-gun-cotton  and  nitroglycerine.  Berthelot  finds  that  even  such  stable  gases  as 
^acetylene,  cyanogen,  and  nitric  oxide  are  decomposed  into  their  elements  by  the 
•detonation  of  mercuric  fulminate.  CS2  is  similarly  decomposed  (p.  239). 

Silver  fulminate,  (CN)2(OAg)2  (?),  is  prepared  'in  a  similar  way  to  the  mercury 
'salt.  0.65  gram  of  silver  is  dissolved,  by  gently  heating,  in  5  c.c.  of  ordinary 
strong  HN03  (sp.  gr.  1.42)  and  3.5  c.c.  of  water.  As  soon  as  the  silver  is  dissolved, 
the  lamp  is  removed,  and  14  c.c.  of  alcohol  (sp.  gr.  0.87)  are  added.  If  the  action 
does  not  start  shortly,  a  very  gentle  heat  may  be  applied  until  effervescence  begins, 
when  the  fulminate  will  be  deposited  in  fine  needles,  and  may  be  further  treated 
like  the  mercuric  salt.  In  some  cases  a  little  red  HN03  is  necessary  to  start  the 
action.  It  may  also  be  obtained  as  a  crystalline  precipitate  by  warming  solution 
of  AgN03  with  HN03  and  alcohol  until  effervescence  begins. 

Silver  fulminate  is  far  more  dangerous  than  mercuric  fulminate,  and,  if  stored 
dry,  should  be  wrapped  up,  in  small  portions,  in  paper.  Even  if  wet,  it  is  not  safe, 
in  a  glass  bottle.  When  dry,  it  should  be  lifted  with  a  slip  of  card. 

Silver  fulminate  crystallises  in  shining  prisms,  and  is  mere  soluble  in  boiling 
water  (36  parts)  than  is  mercuric  fulminate  ;  it  detonates  sharply  when  pressed  with 
a  hard  body,  or  when  heated  a  little  above  100°  C.  When  'touched  with  a  hot 
wire  upon  a  piece  of  glass  or  thin  metal,  it  gives  a  sharp  report  and  shatters  the 
plate,  whilst  mercuric  fulminate  emits  a  dull  sound,  and  does  not  shatter  unless 
closed  in.  Silver  fulminate  is  used  in  toy  crackers,  such  as  the  pull  crackers, 
where  it  is  mixed  with  powdered  glass  to  increase  the  friction,  and  the  throw- 
down  crackers,  where  it  is  twisted  up  in  thin  paper  with  some  fragments  of  quartz- 
pebble.  It  is  occasionally  mixed  with  mercuric  fulminate  in  detonating  tubes,  to 
raise  the  note  of  the  report. 

Warm  ammonia  dissolves  silver  fulminate,  and  deposits,  on  cooling,  crystals  of 
silver-ammonium  fulminate,  NH40'CN'0'NCAg,  which  is  even  more  violently 
explosive,  and  is  dangerous  while  still  moist.  A  similar  compound  is  formed  with 
mercuric  fulminate.  Potassium  chloride,  added  to  a  hot  solution  of  silver  ful- 
minate, removes  only  half  the  silver  as  precipitated  chloride,  and  the  solution 
deposits  shining  plates  of  silver-potassium  fulminate,  KOCN'O'NCAg,  which  is 
very  explosive.  By  the  careful  addition  of  HN03  the  K  may  be  exchanged  for  H, 
and  the  silver  hydrogen  fulminate,  HO'CN'ONCAg,  obtained,  which  dissolves 
easily  in  boiling  water  and  crystallises  on  cooling  ;  by  boiling  with  silver  oxide, 
it  is  converted  into  silver  fulminate,  or,  with  mercuric  oxide,  into  silver-mercury 
fulminate. 

Zinc  and  copper  fulminates  may  be  obtained  by  decomposing  moist  mercuric 
fulminate  with  those  metals  ;  they  are  soluble,  crystalline,  and  explosive. 

Sodium  fulminate  is  obtained  by  the  action  of  sodium  amalgam  on  an  aqueous 
solution  of  mercuric  fulminate.  On  evaporating  over  lime  and  sulphuric  acid,  the 
sodium  salt  is  deposited  in  prisms  (with  2H20),  which  explode  when  rubbed.  A 
crystalline  compound  of  single  molecules  of  sodium  fulminate  and  mercuric 
fulminate,  and  4Aq,  has  been  obtained. 

Fulminuric  or  isocyanuric  acid,  HO'NC(OONH)2,  is  obtained  as  a  potassium 
salt  by  boiling  mercuric  fulminate  with  potassium  chloride.  On  adding  silver 
nitrate,  the  sparingly  soluble  silver  fulminurate  crystallises  out,  and  by  decompos- 
ing this  with  H2S,  and  evaporating  the  filtrate,  a  solution  of  the  acid  is  obtained  ; 
it  crystallises  with  difficulty,  and  is  soluble  in  alcohol. 


XI.  PHENOLS. 

506.  The  phenols  are  hydroxy-benzenes,  naphthalenes,  &c.,  derived  from 
aromatic  hydrocarbons  by  substituting  hydroxyl  for  the  nucleal  hydrogen 
atoms,  e.g.,  phenol,  C6H5'OH ;  orcinol,  C6H3CH3<(OH).> ;  pyrogallol, 
C6H3(OH)3 ;  naphthol,  C10H/OH.  If  the  hydroxyl  is  introduced  into  the 
methyl  group  instead  of  the  phenyl  group  in  the  homologues  of  benzene 


CARBOLIC  ACID.  yOo 

(p  548),  an  alcohol  is  produced;  thus,  C6H5'CH2(OH)  is  benzyl  alcohol, 
whereas  C6H4(OH)-CH3  is  methyl  phenol  or  cresol. 

Phenols  are  distinguished  from  alcohols  in  combining  more  readily 
with  alkalies,  which  caused  them  originally  to  be  mistaken  for  acids 
The  phenolic  hydroxyl  is  more  acidic  in  character  than  the  alcoholic 
hydroxyl,  C6H5,  £c.,  being  more  negative  (acidic)  than  alcohol  radicles  ; 
it  is  less  acid,  however,  than  the  carboxylic  hydroxyl  contained  in  the  true 
acids.  Thus  sodium  phenoxide,  C6H.'ONa,  is  formed  when  phenol  is 
dissolved  in  NaOH,  but  phenol  does  not  dissolve  in  Na2C03.  Again, 
they  do  not  yield  aldehydes  (or  ketones)  and  acids  when  oxidised,  being 
comparable  in  this  respect  with  the  tertiary  alcohols  ;  and  when  attacked 
by  HN03  and  H2S04,  they  yield  substitution-products,  whereas  the 
alcohols  yield  ethereal  salts;  thus,  phenol  yields  tri-nitrophenol  orpicrio 
acid,  C6H2(NO,)3-OH,  and  phenol- sulphonic  acid,  C6H4(OH)-S02'OH. 
The  phenols  have  a  great  tendency  to  produce  coloured  products  of  oxi- 
dation, and  ferric  salts  generally  colour  them  intensely. 

The  phenols  are  frequently  products  of  the  dry  distillation  of  com- 
plex organic  substances,  e.g.,  coal.  They  are  alsn  obtained  by  fusing 
the  sulphonic  acids  with  alkalies  ;  thus  benzenesulphonic  acid  yields 
phenol;  C6H.-S02OK  +  KOH  =  C6H.'OH  +  K2S03.  The  formation  of 
phenols  through  the  diazo-reaction  has  been  already  noticed  (p.  68 1). 
Another  general  method  sometimes  employed  is  the  distillation  of 
aromatic  hydroxy-acids  either  alone  or  with  lime  (see  Pyrogallol). 

The  halogen-substituted  benzenes  are  not  attacked  easily  by  alkalies,  but  when 
they  contain  nitro-groups  they  more  readily  exchange  Cl  for  OH,  forming  nitro- 
phenols  ;  thus  C6H4(N0.2)C1  yields  C6H4(N0.2)OH.  The  greater  the  number  of 
nitro-groups  the  more  readily  this  change  occurs.  The  same  remarks  apply  to  the 
amido-  and  nitramido-  benzenes. 

Monohydric  Phenols,  (i)  Monohydroxybenzenes. — Phenol, or 
phenic  acid,  or  carbolic  acid  or  hydroxybenzene,  C6H5'OH,  is  extracted 
from  that  portion  of  the  heavy  oil  of  coal-tar  which  boils  between 
150°  C.  and  200°  C. 

This  is  allowed  to  cool,  when  it  deposits  crystals  of  naphthalene,  and  is  then 
well  stirred  with  caustic  soda  of  sp.  gr.  1.34.  On  standing,  two  layers  are  formed, 
the  upper  consisting  of 'the  higher  homologues  of  benzene,  and  the  lower  of  an 
aqueous  solution  of  sodium  phenoxide.  This  is  diluted  with  water,  and  exposed 
to  air,  when  tarry  oxidation-products  separate,  and  the  liquid  is  neutralised  by 
successive  additions  of  H.2S04,  which  first  precipitates  more  tarry  matters,  then 
cresol  and  other  homologues  of  phenol,  and  finally  phenol  itself  as  a  light  oil.  It 
is  purified  by  fractional  distillation,  the  portion  distilling  between  180°  C.  and 
190°  C.  being"  collected  and  artificially  cooled,  to  crystallise  the  phenol. 

Phenol  is  present  in  small  quantity  in  urine,  and  in  the  trunk,  leaves,  and  cones 
of  the  Scotch  fir.  It  may  be  produced  by  the  action  of  hydrogen  peroxide  on 
benzene;  C6H5-H  +  HO-OH  =  C6H5-OH  +  HOH.  Benzene  may  also  be  directly 
oxidised  to  phenol  by  mixing  it  with  aluminium  chloride  and  passing  oxygen  gas. 
Benzenesulphonic  acid,  when  distilled  with  fused  potash,  yields  phenol— 
C6H5-S02-OH  +  KOH  =  C6H5'OH  +  KH803. 

Properties  of  phenol— Phenol  crystallises  in  needles,  often  several 
inches  long,  which  smell  strongly  of  coal-tar.  It  fuses  at  43°  C.  and 
boils  at  183°  C.  Fused  phenol  is  slightly  heavier  than  water 
(sp.  gr.  1.084  at  o°  C.).  It  dissolves  in  15  parts  of  water  at  20°  C.,  and 
easily  in  alcohol  and  ether.  It  becomes  pink  or  brown  when  kept,  from 
the  presence  of  some  impurity.  When  two  molecules  of  phenol  (198 
parts)  are  heated  with  one  molecule  (18  parts)  of  water,  and  cooled  to 


710  PROPERTIES   OF   PHENOL. 

4°  C.,  six-sided  prisms  of  phenol  aquate,  (C6H5-  OH)2Aq,  are  obtained, 
which  fuse  at  16°  C.  (61°  F.).  The  commercial  carbolic  acid  crystals 
generally  consist  of  the  aquate,  and  soon  become  liquid  when  the  bottle 
is  placed  in  warm  water.  It  has  a  great  tendency  to  remain  super- 
fused  after  cooling,  solidifying  suddenly  on  opening  the  bottle.  The 
homologues  of  phenol,  which  accompany  it  in  coal-tar,  do  not  form 
crystalline  aquates.  Carbolic  acid  blisters  the  skin  immediately  ;  it 
is  very  poisonous,  and  arrests  fermentation  and  putrefaction,  so  that  it 
is  largely  used  as  an  antiseptic.  MacDougaUs  disinfectant  is  a  mixture 
of  phenol  with  calcium  sulphite.  Calvert's  disinfecting  powder  consists 
of  clay,  with  12  or  15  per  cent,  of  phenol. 

When  phenol  vapour  is  passed  through  a  red-hot  tube,  it  yields 
benzene,  toluene,  xylene,  naphthalene,  anthracene,  and  phenanthrene. 
The  aqueous  solution  of  phenol  gives  a  purple-blue  colour  with  ferric 
chloride.  With  ammonia  and  chloride  of  lime,  it  gives  a  blue  colour. 
With  the  mixture  of  mercuric  nitrate  and  nitrous  acid  obtained  by 
dissolving  mercury  in  cold  nitric  acid,  it  gives  a  yellow  precipitate, 
which  dissolves  with  a  dark-red  colour  in  nitric  acid. 

Sulphuric  acid  (concentrated^,  to  which  6  per  cent,  of  potassium 
nitrite  has  been  added,  gives  a  brown  colour,  changing  to  green  and 
blue,  when  gently  heated  with  phenol.  This  is  Liebermanris  general 
reaction  for  identifying  phenols. 

Bromine  water  added  to  an  aqueous  solution  of  phenol  produces  a 
pale  yellow  precipitate  of  tribromophenol,  C6H2Br3<  OH,  which  redissolves 
until  the  bromine  is  in  excess.  This  a  fiords  an  excellent  qualitative  and 
quantitative  test  for  phenol.  If  the  precipitate  be  warmed  with  water 
and  sodium  amalgam,  sodium  phenoxide  is  produced,  which  gives  the 
smell  of  phenol  when  heated  with  dilute  sulphuric  acid. 

507.  By   passing  phenol   vapour   over   heated   zinc-dust,    it   is   converted   into 
benzene;  C6H5'OH  +  Zn  =  C6H6+ZuO.     This  is  a  general  method  for  the  conversion 
of  phenol*  into  the  corresponding  hydrocarbons. 

Phenol  forms  a  crystalline  compound  with  CO2,  which  is  only  stable  under 
pressure,  and  may  be  obtained  by  heating  salicylic  acid  in  a  sealed  tube  at 
260°  C.  ;  C6H4(OH>C02H  =  C6H5-OH,C02. 

Potassium-  and  sodium-  phenol,  or  phenolates,  C6H5'OK,  C6H5'OXa,  are  soluble 
crystalline  bodies  obtained  by  heating  phenol  with  hydroxide  or  carbonate  of  the 
alkali  (see  p.  709). 

508.  Phenol  is  not  attacked  by  acids,  as  alcohol  is,  yielding  ethereal  salts,  but 
corresponding   phenyl   compounds   are   obtained   by   indirect    processes.      When 
phenyl    is   heated  with  PC15,    it  yields  cJdorobenzene  and  phenyl  ortliophosphate  ; 
the    formation    of     chlorobenzene    proves     the     existence    of     OH    in    phenol  ; 
C6H5'OH  +  PC15  =  POC13  +  C6H5-C1  +  HC1.     The  phenyl  orthophosphate  results  from 
the  action  of  more  phenol  on  the  POC13  ;  POC1S  +  3C6H5OH  +  PO(C6H50)3  +  3HC1. 

Phenyl  hydrosulj)hide,or  thiophenol,  w phenyl  mercaptan,  C6H5'SH,  is  formed  by 
the  action  of  phosphoric  sulphide  on  phenol  — 

8C6H5OH  +  P.2S5  =  2C6H3SH  +  2(C6H5)3P04  +  3H2S. 

It  has  an  offensive  odour,  and  boils  at  169°  C.  Its  extra-radicle  hj'drogen  may  be 
exchanged  for  metals,  as  usual  with  mercaptans.  With  mercuric  oxide,  it  yields 
mercuric  t/tio-p/ienol.  (C6H5S)2Hg.  When  mixed  with  ammonia  and  exposed  to  air, 
phenyl  hydrosulphide  is  converted  into  dlphenyl  disulphide.  a  crystalline  solid  : 
2C6H5SH  +  0  =  (C6H5)2S2  +  H20.  Dlphenyl  sulphide,  (C6H5)2S,  is  obtained  by  distil- 
ling sodium  benzene  sulphonate  with  P2S5.  It  is  an  offensive  liquid,  boiling  at 
about  292°  C.  Nitric  acid  converts  it  into  dlphemjUulpJione  or  sulp/iobenzide, 
(C6H5)2S02,  which  is  also  produced  by  the  action  of  sulphuric  anhydride  on 
benzene  ;  2C6H5H  +  2S03  =  (C6H5)2S02  +  H2S04. 

509.  Chloro phenols,  C6H4C1'OH.  and  the  corresponding  bromine  and  iodine  sub- 
stitution-products, are  obtained  by  the  action  of  those  elements  on  phenol. 


PICRIC  ACID. 
NitrophenoU  ,   C6H4(N02)OH,  dinitrophenoU, 


Nitropheno  ,  C6H4(N02)OH,  dinitrophenoU,  C^NO^/  OH,  and  tnnltronhenol 
C6H2(N02V  OH,  are  produced  when  nitric  acid  acts  on  phenol.  The  last  is  known 
as  picric  (ic  id  (v.i.). 

By  reducing  nitrophenols  with  tin  and  HC1,  the  N02  group  is  converted  into  the 
NH2  group,  and  amido-phenols  are  produced.  Dinitro-  and  trinitro-phenols  admit 
of  a  partial  conversion  of  the  N02  groups,  so  that  anrido-nitrophenoh  are  formed 
The  antipyretic  p/ienacetine  is  a  derivative  of  i  :  4-amido-phenol  and  has  the 
formula  C6H4(OC2H5)(NHCH3CO),  p-acetamidophenetml. 

510.  Picric  or  carbazotic  acid,  or  trinitrophenol,  C6H2(N03)3'OH,  is 
best  prepared  by  dissolving  phenol  (i  part)  in  strong  sulphuric  acid 
(i  part)  and  adding  the  solution  of  phenolsulphonic  acids  thus  ob- 
tained to  strong  nitric  acid  (3  parts)  by  degrees.  When  the  violent 
action  is  over  the  mixture  is  heated  on  the  water-bath  as  long  as  much 
red  gas  is  disengaged.  On  cooling,  a  crystalline  mass  of  picric  acid  is 
obtained,  which  is  purified  by  dissolving  in  boiling  water,  filtering,  and 
crystallising.  It  is  deposited  in  yellow  plates  or  prisms,  which  are 
sparingly  soluble  in  cold  water,  but  more  easily  on  heating,  imparting  a 
bright  yellow  colour  to  a  large  volume  of  water;  alcohol  dissolves 
it  readily.  Its  solution  has  an  intensely  bitter  taste  (whence  its 
name),  and  stains  the  skin  and  other  organic  matters  yellow,  which  is 
turned  to  account  in  dyeing  silk  and  wool.  When  heated,  the  crystals 
fuse  at  122°  C.,  with  partial  sublimation,  and  explode  slightly  at  a 
higher  temperature,  in  consequence  of  the  sudden  formation  of  gas  and 
evolution  of  heat  by  the  action  of  the  N02  upon  the  C  and  H.  This 
nitration  of  phenol  into  picric  acid  may  be  represented  by  the  equation 
—  C6H5-  OH  +  3(HO'N02)  .  C6H,(NOf)8OH  +  3HOH. 

Picric  acid  is  one  of  the  very  few  acids  which  form  sparingly  soluble  potassium 
salts  ;  a  cold  saturated  aqueous  solution  of  picric  acid  is  even  a  better  test  for 
potassium  than  is  tartaric  acid,  giving,  especially  on  stirring,  a  yellow  adherent 
crystalline  precipitate  of  potassium  picrate,  C6H2(N02)3OK.  This  salt  explodes 
violently  when  heated  or  struck,  and  has  been  used  as  an  explosive.  Ammonium 
picrate  is  also  a  very  explosive  salt.  Picric  acid  precipitates  several  of  the  alkaloids. 
An  alcoholic  solution  of  picric  acid  forms  crystalline  compounds  with  several 
hydrocarbons  in  alcoholic  solution,  particularly  with  benzene,  naphthalene,  and 
anthracene.  Keducing-agents,  such  as  glucose,  in  alkaline  solutions,  convert 
picric  acid  into  picramic  acid,  C6H2(N02)2(NH2)OH,  which  forms  red  salts. 
Gently  heated  with  solution  of  chloride  of  lime,  picric  acid  yields  chloropicrin,  or 
kitrochloroform,  C(N02)C13,  recognised  by  its  pungent  tear-provoking  odour. 

Picric  acid  is  a  very  common  product  of  the  action  of  nitric  acid  upon  organic 
substances  ;  indigo,  silk,  and  many  resins  furnish  it  in  considerable  quantity, 
especially  the  fragrant  red  resin  known  as  Botany  Bay  gum,  obtained  from  one  of 
the  grass-trees  of  New  South  Wales,  which  is  sometimes  used  for  preparing  picric 
acid.  It  is  said  that  picric  acid  is  used  as  a  hop-substitute  in  beer  ;  its  presence 
would  be  shown  by  the  fast  yellow  colour  imparted  to  a  thread  of  white  wool 
soaked  in  the  warm  liquid. 

The  constitution  of  picric  acid  is  expressed  by  the  orientation  [OH  :  (NO2)3- 
1:2:4:6];  this  follows  from  the  fact  that  it  can  be  obtained  by  oxidising 
symmetrical  trinitrobenzene  with  potassium  ferricyanide,  a  change  which  results 
in  the  substitution  of  an  OH  for  a  hydrogen  atom.  A  little  consideration  will 
show  that  this  hydroxyl  group  can  only  take  up  a  position  between  two  mtro-groups 
if  the  trinitrobenzene  is  the  symmetrical  one  (p.  547). 

51  1.  Picramlc  acid,  or  2-amido-  w-dinitrop/ienol,  C6H2(N02)2(NH2)OH,  is  prepared 
by  reducing  ammonium  picrate  in  alcoholic  solution  by  passing  hydrogen  sulphide, 
evaporating   to  drvness,  and  decomposing  the  ammonium  picramate  with  acel 
acid;C6H2(N02),-ONH4;3H,S  =  C6H2(N02).2(NH2)ONH4  +  2H20  +  S3.    TheplcrAnic 
acid  crystallises  in  red  needles,  which  fuse  at  165°  C.     It  is  soluble  in  water  and 
alcohol,  forming  red  solutions,  which  become  blood-red  on  adding  an  alkali. 
change  of  the  yellow  colour  of  potassium  picrate  to  the  dark  red  of  potassi 
picramate  by  the  action  of  a  reducing-agent  in  the  presence  of  excess  of  potash, 


712  NAPHTHOLS. 

is  employed  in  the  examination  of  urine  for  the  detection  and  estimation  of 
glucose,  which  easily  converts  the  picrate  into  picramate  when  heated.  The 
picramates  of  potassium  and  ammonium  form  dark-red  crystals. 

512.  Phetwl-sulphonic,  C6H4(OH)S02OH,  and  dimlphonic,  C6H3(OH)(S02OH).2, 
acids,  are  obtained  by  dissolving  phenol  in  strong  sulphuric  acid,  S02OH'OH. 
Orthophenolsulphonic  acid  rapidly  changes  by  migration  of  the  OH  group,  into 
the  para-acid  when  warmed.  The  antiseptic  aseptol  is  a  solution  of  phenol- 
sulphonic  acid. 

The  sodium  salt  of  di-lodo-{parci)phenolsulplionic  acid,  C6H2I2OH'S02OH,  has 
lately  been  introduced  under  the  name  of  sozoldol  as  an  antiseptic  ;  it  is  said  to 
be  as  effective  as  iodoform,  and  has  no  smell. 

513.  Cresols,  or  methyl-phenols,  or  hydroxy  toluenes,  C6H4(CH3)OH, 
accompany  phenol  in  coal-tar.  The  coal-tar  kreasote  is  a  mixture  of 
phenol  and  cresol.  The  cresols  may  be  prepared  by  dissolving  the  cor- 
responding toluidines  in  sulphuric  acid,  adding  potassium  nitrate,  and  dis- 
tilling by  steam  ;  C6H4(CH3)NH2  +  HN02  =  C6H4(CH3)OH  +  2H2O  +  N2. 

Orthocresol  is  solid,  fuses  at  31°  C.,  and  boils  at  188°  C.  Metacresol 
is  liquid,  and  boils  at  201°  C.  Paracresol  is  solid,  fusing  at  36°  C., 
and  boiling  at  198°  C. ;  they  are  metameric  with  benzyl  alcohol, 
C6H5*  CH2-  OH.  Paracresol  occurs  in  urine,  and  is  a  product  of  the 
putrefaction  of  albumin ;  its  dinitro-derivative  is  a  yellow  dye,  Victoria 
orange.  Meta-  and  para-cresol  give  a  blue  colour  with  ferric  chloride. 

The  presence  of  the  OH  group  in  the  cresols  protects  the  methyl  group  from 
the  easy  oxidation  which  characterises  the  methyl  group  of  the  toluenes.  But 
the  substitution  of  a  radicle  for  the  H  of  the  OH  group  destroys  the  protective 
influence,  and  the  methyl  cresols  C6H4(CH3)-OCH3  are  easily  oxidised  to  methoxy- 
benzoic  acids,  C6H4(COOH)'OCH3. 

Creoline  and  It/sol  are  sold  as  disinfectants  ;  they  are  solutions  of  crude  cresol 
in  soap  and  water. 

Methylisopropylphenols. — Thymol  [CH3 :  CH(CH3)2  :  OH  =  i  14:3]  occurs  in  oil 
of  thyme.  Carracrol  [CH3  :  CH(CH3)2  :  OH—  I  :  4  :  2]  exists  in  the  oil  of  Origanum 
hlrtum,  and  is  obtained  by  heating  camphor  with  iodine. 

514.  (2)  Monohydroxynaphthalenes. — Naphthols,   C]0H7'OH,   are  prepared  from 
naphthalenesulphonic    acids  or  naphthylamines    by  the    reactions   described   on 
pp.  68 1,  709.     a-^Yap/tthol  melts  at  94°  C.  and  boils  at  280°  C.  ;  fi-Xaphtliol  melts 
at  122°  C.  and  boils  at  286°  C.     The  latter  is  the  more  soluble  in  water,  and  is 
used  as  an  antiseptic.*     The  naphthols  are  true  phenols,  but  they  resemble  the 
alcohols  more  nearly  than  the  benzene  phenols  do.     They  give  rise  to  a  number  of 
important    dyestuffs,  which    are  chiefly  nitro-derivatives    and    diazo-derivatives. 
Thus,  dinitro-a-naphthol,  C10H5(NO2)2'OH,  is  Martins'  yellow  or  na-phthalene  yellow, 
and  the  sodium  yalt  of  its  sulphonic  acid  is  naphthol  yellow,  or  fast  yellow.     The 
photographic     developer     eilionogen     is     sodium      amido-fi-naplithol     sulphonate, 
C10H5(OH)(NH2)(S03Na). 

NaphthoUulphonic  acids  are  very  numerous  and  a  large  number  has  been  prepared 
both  for  settling  the  constitution  of  naphthalenes  and  for  use  as  dyestuffcomponents 
(p.  683),  for  which  purpose  the  most  important  are  the  I  :  4-monosulphonic  acid, 
C10H6(OH)-SO3H,  (Neville  and  Winther's  acid)  and  the  2:3:6-  and  2  :  6  :  8- 
disulphonic  acids,  CIOH5(OH)(S03H)2,  (R.  and  G.  acids). 

515.  Dihydric    Phenols.   Dihydroxybenzenes. — Pyrocatechol, 
i  :  2-C6H4(OH)2,  obtained  by  fusing  potassium  phenol-sulphonate  with 
potash,  C6H4(OH)Sp2OK  +  KOH  =  C6H4(OH)2  +  K2SO3,  is  found  among 
the  products  of    distillation   of  catechu,  an  astringent  body  extracted 
by  boiling  water  from  the  inner  bark  wood  of  Acacia  catechu  and  used 
in  tanning.     Kino,  a  similar  extract  from  certain  varieties  of  Ptero- 
carpus,  an  Indian  tree  of  the  same  botanical  order,  also  furnishes  it ;  as 

*  Betol,  or  fi-naphthyl  salicylatf,  CeH4(OH)  •  COOC10H7,  is  used  iu  medicine  like  phenyl 
salicylate  (salol). 


PYROCATECHOL. 

do  most  vegetable  extracts  which  contain  tannin.  The  leaves  of  the 
Virginia  creeper,  a  plant  of  the  vine  order,  contains  pyrocatechol.  It 
is  present  in  crude  pyroligneous  acid  distilled  from  wood,  and  is  said  to 


is  very  soluble  in  water,  alcohol,  and  ether.  It  is  a  reducing-agent, 
precipitating  Cu,O  from  alkaline  cupric  solutions  on  warming,  and 
reducing  silver  nitrate  in  the  cold.  In  presence  of  alkalies  it  absorbs 
oxygen  from  the  air,  becoming  brown.  With  ferric  chloride,  it  gives  a 
green  colour,  changed  to  red  by  alkalies.  Nitric  acid  oxidises  it  to 
oxalic  acid.  It  has  weak  acid  properties,  and  was  formerly  called 
oxyphenic  acid. 

Guaiacol,  or  methylpyrocatechol,  C6H4(OH)OCH3,  may  be  obtained  by  distilling 
guaiacum,  a  resinous  exudation  from  the  West  Indian  tree  called  lignum  ri*<9< 
The  distillate  is  dissolved  in  ether,  and  mixed  with  alcoholic  potash,  which  pro- 
duces a  crystalline  mass  of  potassium  guaiacol,  which  is  washed  with  ether  and 
decomposed  by  dilute  sulphuric  acid.  It  is  also  produced  by  heating  to  180°  C.  a 
mixture  of  pyrocatechol,  potassium  methyl  sulphate,  and  potash — 

C6H4(OH)2  +  KCH3S04  +  KOH  =  C6H4(OH)OCH3  +  K2S04  +  HOH. 
Beech-wood  kreasote  also  contains  it.  Guaiacol  forms  colourless  crystals,  m.-p. 
28°  C.  and  b.-p.  203°  C.  It  mixes  sparingly  with  water,  but  easily  with  alcohol 
It  gives  an  emerald-green  colour  with  ferric  chloride,  and  acts  as  a  reducing-agent 
in  alkaline  solutions.  When  heated  with  hydriodic  acid,  it  yields  methyl  iodide 
and  pyrocatechol  ;  C6H4(OH)OCH3  +  HI  =  C6H4(OH)2  +  CH3L  It  has  the  properties 
of  a  weak  acid.  When  potassium  guaiacol  is  heated  with  methyl  iodide,  it  yields 
veratrol  or  methyl  guaiacol ;  C6H4'OK-OCH3  +  CH3I  =  C6H4(OCH3)2  +  KL  Veratrol 
is  an  aromatic  liquid,  which  may  also  be  obtained  by  heating  with  baryta  the 
veratric  (dlmethyl-protocatechuic)  acid,  extracted  from  sabadilla  seeds  ; 
C6H3(OCH3)2-C02H  +  BaO  =  C6H4(OCH3)2  +  BaC03. 

Wood-tar  kreasote  contains  phenol,  cresol,  phlorol,  C6H3(CH3)0'OH,  guaiacol,  and 
creosol,  C6H3(OCH3)(CH3)OH.  This  last  is  obtained  from  that"  portion  of  the  tar 
which  distils  at  221°  C.,  by  dissolving  it  in  ether,  and  adding  very  strong  KOH, 
which  precipitates  potassium-creosol,  from  which  creosol  is  separated  by  H2S04. 
It  is  an  aromatic  liquid,  which  yields  acetyl-creosol,  C6H3(OCH3)CH3(OC2HS0), 
when  treated  with  acetyl  chloride,  and  this,  when  oxidi&ed  by  permanganate, 
becomes  acetijl-ranillic  acid,  C6H3(OCH3)C02H(OC2H3O),  from  which  vanillic  acid 
may  be  obtained  by  treatment  with  XaOH. 

516.  Resorcinol,  i  :  3-C6H4(OH)2,  was  named  from  resin,  being 
obtained  from  several  bodies  of  that  class,  and  orcin,  with  which  it  is 
homologous.  It  is  now  prepared  on  a  large  scale  for  the  manufacture 
of  colours  by  the  action  of  caustic  alkalies  on  benzene-disulphonic  acid. 

This  acid  is  prepared  by  gradually  adding  benzene  (4  parts)  to  fuming 
sulphuric  acid,  sp.  gr.  2244  (is  parts),  gently  heating  for  some  hours,  and 
finally  at  275°  C.  ;  C6Hfi  +  2H2S04  =  C6H4(S02'OH)2  +  2H20.  The  I  :  3-benze*+ 
d'mdphanie  acid  forms  a  deliquescent  crystalline  mass  on  cooling.  This  is 
dissolved  in  a  large  quantity  of  water,  neutralised  with  lime,  and  strained  from  the 
calcium  sulphate  formed  by  the  excess  of  sulphuric  acid.  The  solution  of  calcium 
benzene-disulphonate  is  decomposed  by  Na2C03,  the  precipitated  CaC03  filtered 
off,  the  solution  evaporated  to  dryness,  and  the  residue  of  sodium  benzene- 
disulphonate  fused  with  2^  times  its  weight  of  caustic  soda,  at  270°  C.,  for  eight  or 
nine  hours;  C6H4(S02-ONa)2  +  2NaOH  =  C6H4(OH)a  +  2S03Na*  The  fused  mass  u 
dissolved  in  hot  water,  and  boiled  with  HC1  till  all  the  S02  is  expelled.  The 
resorcinol  is  then  extracted  from  the  cooled  aqueous  solution  by  agitation  with 
ether,  and  is  obtained  in  crystals  when  the  ether  is  distilled  off. 

Resorcinol  is  obtained  in  considerable  quantity  by  distilling  extract  of  Jirazil- 
wood,  a  dye  made  by  boiling  the  wood  of  Ctesalplnht  fcasiliensi*  with  water,  and 
evaporating  the  solution.  It  was  originally  prepared  by  fusing  with  potash  the 


714  ORCIN. 

gum-resin  known  as  galbanum.  obtained  in  Turkey  and  the  East  Indies  as  an 
exudation  from  the  Galbanum  officinale,  an  umbelliferous  plant.  Other  gum-resins 
obtained  from  plants  of  the  same  order  also  yield  resorcinol  when  fused  with 
potash  ;  such  as  ammoniacuni,  assafcetida,  sagapenum,  all  more  or  less  foetid- 
smelling  medicinal  bodies  imported  from  the  East.  When  these  gum-resins  are 
distilled  alone,  they  yield  vmbelliferone,  C9H6O3,  or  C6H4(CHO)2CO,  which  is  con- 
verted into  resorcinol  when  fused  with  potash. 

Resorcinol  crystallises  in  prisms  or  tables  which  fuse  at  118°  C.,  and 
boil  at  276°  C.,  but  may  be  sublimed  at  a  much  lower  temperature. 
It  has  a  sweet  taste,  and  is  easily  soluble  in  water,  alcohol,  and  ether. 
Its  solution  gives  a  violet  colour  with  ferric  chloride.  Exposed  to  air, 
it  absorbs  oxygen  and  becomes  brown.  Ammoniacal  copper  and  silver 
solutions  are  reduced  when  heated  with  it.  The  most  characteristic 
test  for  resorcinol  consists  in  heating  it  with  phthalic  anhydride, 
(p.  617),  dissolving  in  dilute  sulphuric  acid,  and  adding  ammonia,  when 
a  splendid  green  fluorescence  is  produced,  due  to  the  formation  of 
resorcin-phtkalein,  or  fluorescein  (q-v.^). 

The  resorcinol  of  commerce  sometimes  contains  thioresorclnol,  C6H4(SH)2,  which 
may  be  obtained  by  reducing  benzenedisulphonlc  chloride,  C6H4(S02C1)2,  with  tin 
and  hydrochloric  acid  ;  it  melts  at  179°  C. 

Styphnlc  acid,  or  trinitroresorcin,  C6H(N02)3(OH)2,  so  named  from  its  astringent 
taste  (<TTi>(f>vos)  is  prepared  from  resorcinol  just  as  picric  acid  is  prepared  from 
phenol,  and  by  the  action  of  nitric  acid  on  those  gum  resins  which  yield  resorcinol 
on  fusion  with  potash.  Styphnic  acid  forms  yellow  six-sided  prisms  or  tables, 
sparingly  soluble  in  cold  water,  but  dissolving  in  alcohol  and  ether.  It  fuses  at 
J75°  C.,  and  explodes  when  strongly  heated,  though  it  sublimes  when  heated 
gradually.  It  is  a  dibasic  acid,  and  forms  salts  which  are  more  explosive  than  the 
picrates.  Ferrous  sulphate  and  lime-water  give  a  green  colour  with  styphnic 
acid,  and  a  blood-red  with  picric  acid. 

Dinitroso-resorcinol,  C6H2(NO)2(OH)2.  produced  by  the  action  of  nitrous  acid  on 
a  solution  of  resorcinol,  is  a  dyestuff  known  as  fast  green  or  solid  green. 

Hydroquinone,  or  quinol,  is  the  third  (1:4)  dihydroxybenzeue  ;  it 
will  be  considered  under  quinone. 

517.  Orcin,  or  orcinol,  or  1:3:  $-dihydroxiitoluene,  C6H3CH3(OH)2, 
is  prepared  from  certain  lichens,  which  are  used  by  dyers  for  preparing 
the  colours  known  as  litmus,  cudbear,  and  archil ;  such  as  Lecanora  tar- 
tarea,  or  rock-moss,  Roccella  tinctoria,  or  orchella  weed,  and  others.  The 
lichens  are  boiled  with  lime  and  water  for  some  time,  the  solution  filtered, 
evaporated  to  one-fourth,  treated  with  C02  to  precipitate  the  lime,  and 
shaken  with  ether  to  extract  the  orcin.  Some  orcin  appears  to  exist 
ready  formed  in  the  lichens,  but  the  greater  part  of  it  is  formed  by  the 
action  of  the  lime  and  water  upon  certain  acids,  which  may  be  extracted 
from  the  lichens  by  lime  in  the  cold,  and  obtained  as  gelatinous  preci- 
pitates by  adding  HC1.  Thus,  orsellinic  acid,  C6H2CH3(OH)2002H, 
when  boiled  with  lime,  yields  carbon  dioxide  and  orcin,  C6H3CH3(OH)2. 

Erythric  acid,  C^H^O^,  yields  orcin  and  erythrite  (p.  578)  ;  erernic  acid, 
C17H1607,  from  the  lichen  Erernia  prunastri,  yields  orcin  and  ererninic  acid, 
C9H1004. 

Lecanoric  acid.  CI6H14CVH20,  when  boiled  with  water,  yields  two  molecules  of 
orsellinic  acid,  C8H804. 

Orcin  is  also  produced  by  the  action  of  fused  potash  on  aloes,  the  juice  of  a 
plant  of  the  Liliaceous  order  (dragon's  blood,  obtained  from  the  same  order,  yields 
phloroglucol).     Orcin  may  be  prepared  from  toluene,  C6H5'CH3,  by  converting  it 
into  (ortho)chlorotoluenesulphonic  acid,  and  fusing  this  with  excess  of  potash — 
C6H3C1(CH3)-S03H  +  2KOH  =  KC1  +  KHS03  +  C6H3CH3(OH)2. 

Orcin  crystallises  in  colourless  six-sided  prisms  (with  iH20),  melting 


PYROGALLOL.  7:5 

at  58°  C.,  or  when  anhydrous  at  107°,  and  boils  at  289°  C\  It  tastes 
sweet  and  dissolves  in  water,  alcohol,  and  ether ;  ferric  chloride  colours 
it  violet. 

It  forms  a  crystalline  compound  with  a  molecule  of  ammonia  and  when  its 
.solution  in  ammonia  is  exposed  to  air,  it  absorbs  oxygen,  becoming  purple,  and 
yielding  with  acetic  acid  a  red  colouring-matter,  orcein,  C7H802t-NH3  +  03  = 
2H20  +  C7H7N03.  This  substance  is  the  chief  colouring-matter  of  the  dyes  pre- 
pared from  lichens,  by  mixing  them  with  lime  and  urine  (to  furnish  ammonia), 
and  exposing  them  to  the  air  for  some  weeks.  The  colour  is  pressed  out  and 
made  into  cakes  with  chalk  or  plaster  of  Paris. 

Orcein  is  sparingly  soluble  in  water,  but  dissolves  easily  in  alcohol  and  in 
.alkaline  liquids,  yielding  purple  solutions  which  are  reddened  by  acids,  orcein 
being  precipitated. 

518.  Trihydric  Phenols.  Trihydroxybenzenes.— Pyrogallin, 
or  pyrogallol,  1:2:  3-C6H3(OH)3,  formerly  called  pyrogallic  acid,  is  a 
phenol  obtained  by  heating  gallic  acid — 

C6H2(OH)3-C02H  =  C6H3(OH)3  +  C02. 

To  prepare  it,  gallic  acid  is  heated  with  2\  parts  of  water  in  a  digester  (autorlure) 
at  2io°-220°  C.  for  half  an  hour.  The  solution  thus  obtained  is  decolorised  by 
animal  charcoal  and  crystallised. 

Pyrogallol  maybe  sublimed  from  nut-galls  heated  to  about  215°  C..  when  the 
tannin  is  decomposed  into  pyrogallol  and  carbon  dioxide  ;  C13H907-C02H  +  H20  = 
2C6H3(OH)3  +  2COo.  It  may  be  obtained  synthetically  by  fusing  chloro2>henol- 
-sulphonic  add  (i  12:3)  with  potash — 

C6H3C1(OH)S03H  +  2KOH  =  C6H3(OH)3  +  KC1  +  KHS03. 

Pyrogallol  crystallises  in  line  needles,  which  are  felted  together  in 
light  white  tufts.  It  fuses  at  132°  C.  and  boils  at  210°  C.  It  is  very 
soluble  in  water  (2^  parts),  alcohol,  and  ether.  When  its  solution  is 
mixed  with  an  alkali,  it  at  once  absorbs  oxygen  from  the  air,  becoming 
brown,  and  forming  a  carbonate,  acetate,  and  other  products,  a  little 
carbonic  oxide  being  evolved.  A  mixture  of  potash  and  pyrogallin  is 
employed  to  absorb  oxygen  in  gas  analysis.  Pyrogallin  is  a  strong 
reducing-agent,  precipitating  silver  and  mercury  in  the  metallic  state ; 
its  action  on  silver-salts  renders  it  useful  in  photography  and  in  hair- 
dyeing. 

A  pure  ferrous  salt  gives  no  colour  with  pyrogallin,  but  a  trace  of  ferric  salt 
causes  a  blue  coloration,  while  a  pure  ferric  salt  gives  a  red  colour.  When  heated 
with  phthalic  anhydride,  it  yields  pyrogallol  phthalein,  or  gallein,  C^H^O-.  which 
is  used  as  a  red  dye.  When  chlorine  is  passed  through  a  cooled  solution  of  i>yn>- 
gallol  in  acetic  acid,  triehloro-pyrogalUl^  C6C13(OH)3,  is  obtained,  and  may  !>«• 
crystallised  in  needles,  melting  at  177°  C. 

Phloroglucol.    1:3:5  -C6H3(OH)3,   was  first  obtained  from  a  glucoside  called 
phlorizin,  existing   in  the  bark  of  the  apple-tree  ;  the  glucol  refers  to  its  swtvt 
taste.     It  is  also  made,  like  resorcinol,  by  fusing  certain  vegetable  extracts  and 
gum-resins  with  caustic  potash.     It  is  thus  obtained  from  gamboge,  the  irsiii..u> 
juice  of   Ganilwf/ui  t/ufta  (Ceylon),   from  dragon's  Mood,  the  resin  of  Drae&na 
draco,  from  kino  (p.  712),  catec/w,  and  from  the  yellow  dye-wood,  futtie.     The 
residue  of  the  preparation  of  extract  of  fustic  is  fused  with  potash  and  a  lit 
water,  dissolved  in  water,  acidified  with  sulphuric  acid,  and  shaken  with  ether, 
which  extracts  phloroglucol  and  protocatechuic  acid  :  the  ether  is  distilled  ott, 
and  the  aqueous  solution  of  the  residue  mixed  with  lead  acetate  to  precipitate 
the  protocatechuic  acid.     The  lead  is  precipitated  by  H2S,  and  the  phloroglin 
again  extracted  by  ether.     It  may  also  be  prepared  by  fusing  resorcinol  (I  par 
with  soda  (6  parts)  until  the  mass  has  a  light  chocolate  colour,  when  it 
as  above,  omitting  the  separation  of  protocatechuic  acid. 

Phloroglucol  is  formed  by  fusing  i  :  3  :  $-benze>te-tn><ulp1ionir  <«-id,  C6H3(MVUrt)3, 
with  soda,  or  better  by  hydrolysing  1:3:  5-triamido-benzene  with  HC1. 


716  INOSITE. 

It  crystallises  in  prisms  with  2Aq,  which  it  loses  at  100°  C.  It  fuses  at  218°,  and 
may  be  sublimed  ;  it  dissolves  easily  in  water,  alcohol,  and  ether,  and  reduces 
alkaline  cupric  solution.  Ferric  chloride  gives  a  violet  colour.  Its  solution  in 
hydrochloric  acid  stains  wood  violet-red,  and  is  an  excellent  test  for  woody  tissue. 
Alkaline  solutions  of  phloroglucol  are  oxidised  by  air,  and  become  brown. 
When  dissolved  in  ammonia,  it  yields  a  crystalline  base;  C6H3(OH)3  +  NH3  = 
H2O  +  C6H3NH2(OH)2  (phloramtne).  Other  phenols  do  not  so  readily  exchange  OH 
for  NH2. 

When  phloroglucol  is  dissolved  in  acetic  acid  and  treated  with  potassium  nitrite, 
at  a  low  temperature,  it  yields,  on  addition  of  excess  of  potash  and  alcohol,  green 
needles  of  a  very  explosive  body,  which  is  the  potassium  salt  of  tri-nitroso-pliloro- 
glucol,  C603(NOK)?.  When  this  is  gradually  added  to  a  mixture  of  nitric  and 
sulphuric  acids,  it  is  converted  into  trinitro-phloroglucol,  C6(N02)3(OH)3,  which 
crystallises  in  yellow  explosive  prisms,  and  dyes  wool  and  silk  yellow  like  picric 
acid.  It  is  a  tribasic  acid,  and  forms  three  series  of  coloured  salts. 

In  most  of  its  reactions,  phloroglucol  behaves  as  symmetrical  tri-hydroxyben- 
zene  ;  but  in  the  remainder  it  behaves  as  a  triketone,  yielding,  for  instance,  a 
trioxime,  C6H6(N'OH)3,  with  hydroxylamine  (p.  625).  From  this  it  seems  probable 
that  phloroglucol  exists  in  tautomeric  forms  (p.  701),  namely, 

/XC(OH)-CHX  /CO-CH- 

CHf  ^C(OH)  and  CH  /  ~>CO. 

XC(OH):CHX  "XCO-CH/ 

The  first  of  these  would  represent  a  trihydroxybenzene  (the  enol  form)  containing 
a  tertiary  benzene  ring,  and  the  latter  a  triketone  of  hexamethylene,  containing  a 
secondary  benzene  ring. 

1:2:4  -Trihydroxybenzene  is  called  hydroxyhydroquinone. 

51 8ft.  Inosite,  C6Hi206  +  2H20.  This  compound  was  formerly  included  among 
the  sugars  under  the  name  ot~Jiesh-svgar,  but  inasmuch  as  (i)  it  does  not  behave 
as  a  reducing  agent  (see  Su-gars),  (2)  it  yields  a  hexanitrate,  C6H6(ON02)6,  when 
dissolved  in  strong  HN03,  and  (3)  it  is  converted  into  benzene  and  tetriodophenol 
when  heated  at  170°  C.  with  HI,  it  is  now  known  to  be  a  cyclohexane  derivative, 
probably  he&ahydroasy-cyclohexane)  C6H6(OH)6.  It  is  obtained  from  the  juice  of 
beef  ;  the  chopped  heart  or  lung  of  the  ox  is  exhausted  with  water,  the  liquid 
pressed  out,  mixed  with  a  little  acetic  acid,  and  heated  to  boiling.  The  liquid 
filtered  from  the  coagulated  albumin  is  mixed  with  lead  acetate,  filtered,  and  basic 
lead  acetate  added  ;  this  precipitates  a  lead  compound  of  inosite,  2C6H1206.5PbO, 
which  is  to  be  suspended  in  water  and  decomposed  by  H2S.  when  the  inosite 
passes  into  solution.  The  lead  sulphide  is  filtered  off,  the  solution  evaporated 
on  the  water-bath,  to  a  syrup,  and  mixed  with  ten  volumes  of  alcohol  and  one  of 
ether,  when  the  inosite  is  precipitated.  It  forms  prismatic  crystals,  which  are 
sweet  and  soluble  in  6  parts  of  water.  It  is  but  slightly  soluble  in  weak  alcohol, 
and  insoluble  in  absolute  alcohol  and  in  ether.  The  crystals  effloresce  in  air,  and 
become  anhydrous  at  100°  C.  Inosite  is  optically  active,  occurring  in  the  usual 
modifications.  It  undergoes  lactic  fermentation  and  is  oxidised  by  nitric  acid 
to  oxalic  acid.  Inosite  may  be  identified  by  moistening  it  with  dilute  nitric 
acid,  evaporating  almost  to  dryness,  and  adding  ammoniacal  calcium  chloride, 
which  produces  a  rose  colour.  Inosite  solution  mixed  with  a  drop  of  mercuric 
nitrate  gives  a  yellow  precipitate,  which  becomes  red  when  heated. 

The  proportion  of  inosite  obtained  from  flesh  is  very  small  ;  many  vegetables 
contain  it  more  abundantly.  The  unripe  French  bean  yields  0.75  per  cent,  of 
inosite  ;  walnut-leaves  in  August,  0.3  per  cent.  It  is  also  present  in  the  leaves  of 
ash  and  vine  ;  grapes  contain  it,  so  that  inosite  is  found  in  wine.  Unripe  peas, 
asparagus,  and  dandelions  contain  inosite.  From  these  vegetables  it  may  be  ex- 
tracted as  from  flesh.  It  has  been  found  in  urine  in  cases  of  Bright's  disease. 

He.jcahydro,ry-benzene,  C6(OH)6,  has  been  obtained  by  a  circuitous  process.  It  is 
crystalline,  sparingly  soluble  in  cold  water,  alcohol,  and  ether ;  the  solutions 
absorb  oxygen,  becoming  violet,  and  reduce  silver  nitrate.  It  is  converted  into 
benzene  by  distillation  with  zinc-dust. 

He.r,ahydro,i-ydlphenyl,  C6H2(OH)3'C6Ho(OH):?,  is  the  parent  of  the  quinone 
fioei'ulignone,  O  :  C6H2(OCH3)2'C6H2(OCH3)2 :  0,  which  is  obtained  during  the  refining 
of  crude  acetic  acid  from  wood  by  K2Cr.2O7  ;  it  is  soluble  in  ordinary  solvents,  but 
crystallises  from  phenol  in  blue  needles.  It  was  formerly  called  cedrlret  in  allusion 
to  its  interlaced  crystals,  (cedria,  pitch  ;  rate,  a  net).  Tin  and  HC1  convert  it  into 


QUINONE. 

kydrocoerulignone,  HO.C6H2(OCH3)2-C6H2(OCH3)2-OH,  which  is  colourless,  and 
yields  hexahydroxydiphenyl  when  boiled  with  HC1.  Hexahvdroxvdiphenvl 
dissolves  in  potash  with  a  blue  colour. 


XII.  QUINONES. 

519.  QUINONES  are  formed  from  aromatic  hydrocarbons  by  the 
substitution  of  (O,)"  for  H2,  and  are  therefore  products  of  oxidation. 

Quinone,  C6H4(02)",  or  benzoquinone,  may  be  obtained  by  heatino- 
benzene  with  chromyl  chloride,  when  HC1  is  evolved  and  a  brown  solid 
compound  produced  ;  this  is  decomposed  by  water  with  formation  of 
quinone,  which  remains  dissolved  in  the  excess  of  benzene — 

(1)  C6H6  +  2CrOoCl2  =  2HC1  +  C6H4(Cr02Cl)0  ; 

(2)  C6H4(Cr02Cl)2  +  H20  =  C6H4(O2)"  +  Cr203  +  2HC1. 

Many  benzene  derivatives  also  yield  quinone  when  oxidised.  It  is  best 
prepared  by  oxidising  aniline  with  potassium  dichromate  and  sulphuric 
acid. 

One  part  of  aniline  is  dissolved  in  a  mixture  of  8  parts  of  sulphuric  acid  with 
30  parts  of  water,  and  3^  parts  of  powdered  potassium  dichromate  are  slowly 
added  to  the  cooled  solution,  which  is  then  heated  for  some  hours  at  about  35°  0. 
After  cooling,  the  liquid  is  shaken  with  ether,  which  extracts  the  quinone,  and 
leaves  it  in  golden  yellow  crystals  when  evaporated. 

It  is  also  obtained  when  quinic  acid  is  oxidised  with  manganese  dioxide  and 
sulphuric  acid;  C6H7(OH)4C02H  +  02=C6H4(0)2"  +  C02  +  4H20.  Many  plant- 
extracts  yield  quinone  when  thus  treated. 

Quinone  crystallises  very  easily  in  yellow  prisms  or  plates,  which  sub- 
lime even  in  the  cold,  and  fuse  at  n6°C.,  emitting  a  characteristic 
odour,  and  subliming  in  long  golden  needles  in  the  presence  of  steam. 
It  is  sparingly  soluble  in  cold  water,  but  dissolves  in  hot  water,  and 
crystallises  on  cooling ;  alcohol  and  ether  dissolve  it.  Its  solution  stains 
the  skin  brown.  Quinone  acts  as  an  oxidisiiig-agent,  liberatiog  iodine 
from  hydriodic  acid,  and  becoming  converted  into  hydroquinone,  or 
quinol,  C6H4(OH)2,  which  is  i  :  4  -  dihydroxybenzene. 

In  many  reactions  quinone  behaves  like  a  diketone  ;  for  instance, 
with  hydroxylamine  it  yields  both  a  monoxime,  0  :  C6H4  :  N*OH,  and  a 
dioxime,  HON  :  C6H4  :  N'OH  (cf.  p.  625).  The  formula 


has  therefore  been  proposed  (by  Fitlig)  for  quinone. 

It    has    been   pointed    out,   however,   that    if    quinone    contain    true    ketone 
groups,   it  should    yield    a    secondary    alcohol    HOHC<f  ^>CH'OH   when 

reduced,  instead  of,  as  is  actually  the  case,  the  quasi-tertiary  alcohol,  hydroquinone, 
C-OH.*     Moreover,  when   substituted  quinones  react  with  PC18. 


each  of  the   0  atoms   is  exchanged  for  one   Cl  atom  instead  of  two,  as  would 
be   expected  if  the  0  were  doubly  linked  to   carbon.     These  considerations  I 

*  A«ainst  this  argument  it  may  be  urged  that  a  ketone  may  give  rise  to  a  tertiary  alcohol 
by  redaction,  as,  for  example,  in  the  formation  of  piuacoue  from  acetone  (p.  575). 


7i8 


CHLOBANIL. 


Graebe  to  the  "  peroxide  "  formula,  C^- — Q-0 — -^C  for  quinone.     Fittig's  formula, 
is,  however,  preferred. 

That  the  oxygen  atoms  in  quinone  occupy  the  i  :  4-position  is  shown 
by  its  easy  conversion  into  i  :  4-dihydroxybenzene,  and  by  the  fact 
that  its  dioxirne  yields  i  :  4-diamidobenzene  when  reduced. 

Qulnonemonoxlme  appears  to  be  identical  with  the  compound  obtained  by  the 
action  of  nitrous  acid  on  phenol,  nitroso-phenol,  C6H4(OH)NO,  also  obtained  by 
treating  nitrosobenzene,  C6H5NO,  with  NaOH. 

Hydroquinone  is  a  constant  product  of  the  action  of  reducing-agents  on  quinone, 
and  is  best  prepared  by  passing  S02  through  a  warm  saturated  solution  of  quinone, 
when  it  is  deposited  in  six-sided  prisms,  which  fuse  at  169°  C.,  and  sublime  in 
monoclinic  tables,  so  that  hydroquinone  is  dimorphous.  It  is  moderately  soluble 
in  water,  and  easily  in  alcohol  and  ether.  Hydroquinone  is  distinguished  from 
other  dihydroxybenzenes  (p.  712)  by  the  action  of  oxidising-agents,  such  as  Fe2Cl6, 
which  converts  it  into  fine  green  metallic  prisms  of  green  liydroqulnone,  or  quin- 
hydrone,  C6H402'C6H4(OH)2,  also  obtained  by  mixing  aqueous  solutions  of  quinone 
and  hydroquinone.  This  is  sparingly  soluble  in  cold  water,  but  dissolves  in  hot 
water  to  a  brownish-red  solution,  which  deposits  the  splendid  green  crystals  on 
cooling.  It  dissolves  in  alcohol  and  ether  with  a  yellow  colour.  It  is  readily 
dissociated  into  quinone  and  hydroquinone.  Hydroquinone  occurs  among  the 
products  of  distillation  of  the  succinates,  and  has  been  produced  from  ethyl 
succinate  by  the  following  steps  :  Ethyl  succinate,  C2H4(CO2C2H5)2,  acted  on  by 
sodium,  yields  ethyl  succinyl  succinate,  C2H4'C2H2(CO)2'(C02'C2H5)2  ;  when  this  is 
treated  with  bromine,  hydrogen  is  abstracted,  leaving  ethyl  quinol-dicarbo.vylatet 
C6H402(CO./C2H5)2.  The  acid  obtained  from  this  ethereal  salt,  qulnol-dlcarbu.xylic 
acid,  C6H4O2(C02H)2,  crystallises  in  needles,  and  yields  a  blue  colour  with  ferric 
chloride.  When  distilled,  it  yields  hydroquinone,  C6H4(OH)2,  and  2CO2.  As  ethyl 
succinyl  succinate  may  also  be  obtained  by  the  action  of  sodium  on  ethyl  bromaceto- 
acetate,  hydroquinone  may  be  built  up  from  acetic  acid.  It  is  used  as  a  photo- 
graphic developer. 

Tetrachloroquinone,  or  chloran'd,  C6C14(02)",  is  a  frequent  product  of  the  action  of 
chlorine  or  of  a  mixture  of  KC103  and  HC1  upon  aromatic  compounds,  such  a& 
phenol,  aniline,  salicin,  and  isatin.  It  may  be  prepared  from  quinone  by  the  action 
of  KC1O3  and  HC1.  but  more  cheaply  from  phenol,  by  mixing  it  with  potassium 
chlorate  (4  parts)  and  adding  it  gradually  to  hydrochloric  acid  diluted  with  an 
equal  volume  of  water.  The  mixture  is  gently  heated,  and  more  chlorate  added, 
when  a  yellow  mixture  of  tricJiloroqulnone,  C6HC13(02)",  and  tetrachloroquinone  is 
precipitated.  This  is  treated  with  sulphurous  acid,  which  reduces  the  quinones  to 
hydroquinones.  The  tetrachlorohydroquinone,  C6C14(OH)2,  is  insoluble  in  water, 
whilst  the  trichlorohydroqulnone,  C6HC13(OH)2,  dissolves.  The  former  is  then 
oxidised  by  strong  nitric  acid,  which  converts  it  into  chloranil.  This  body,  which 
is  used  in  colour-making,  is  yellow,  insoluble  in  water,  and  sparingly  soluble  in 
alcohol ;  ether  and  benzene  dissolve  it,  and  deposit  it  in  yellow  crystals  which 
may  be  sublimed.  It  is  unattacked  even  by  concentrated  acids.  Potash  dissolves 
it  with  a  purple  colour,  and  yields  purple  crystals  of  potassium  chloranilate  ; 
C6C1402  +  4KOH  =  2KC1  +  2H20  +  C6C12(OK)202.  By  dissolving  the  sparingly  soluble 
potassium  salt  in  hot  water,  and  adding  HC1,  a  red  crystalline  body  is  precipi- 
tated, which  is  chloranlllc  acid,  C6Cl2(OH]2O2.Aq.  It  is  soluble  in  water,  with  a 
violet  colour,  but  sulphuric  or  hydrochloric  acid  precipitates  it  from  the  aqueous 
solution.  Bromanil,  C6Br4(02)",  has  also  been  obtained  from  phenol. 

//°  //NGl 

Quinone  chlorimides,  C6H4x^          and  C6H4/         ,  are  obtained  by  the  action  of 

^NCl  ^NCl 

chloride  of  lime  on  i  :  4-amidophenol  and  I  :  4-diamidobenzene  respectively. 

By  reaction  of  quinonechlorimide  with  phenols,  indophenols  are  obtained  ;  these 
are  also  formed  by  the  oxidation  of  a  mixture  of  phenol  and  a  p-amidophenol. 
The  typical  indophenol  is  0  :  C6H4  :  N;C6H4-OH. 

Quinonechlorimide  and  a  dialkylaniline  react  to  form  an  indoaniline.  These 
compounds  are  dyestuffs  and  are  manufactured  by  oxidising  a  mixture  of  a 
paraphenylenediamine  and  a  phenol.  Thus  phenol  blue,  0  :  C6H4  :  N'C0H4'N(CH3)2, 


ANTHRAQUINONE. 

is  made  by  oxidising  a  mixture  of  «.s-dimethylparaphenylenediamine  and  phenol 
By  hydrolysis  with  H.2S04  it  yields  quinone  and  the  original  diamine. 

By  substituting  an  aniline  for  the  phenol  in  the  foregoing  reaction,  an  \,nl«  «/;///? 
is  produced.  Phenylene  blue,  NH  :  C6H4  :  N'C6H4'NH2,  is  the  compound  obtained 
when  a  mixture  of  paraphenylenediamine  and  aniline  is  oxidised 

Naphthoquinones,  C10H6(02)".—  <L-Naphthoqulnone  [0  :.0  =  i  :  4]  is  a  truey^/v/- 
quinom,  possessing  the  characteristic  yellow  colour,  volatility  and  pungent  odour 
of  these  quinones,  and  being  reduced  to  naphthohydroquinone,  C10H6(OH)2.  It  is 
prepared  by  dissolving  naphthalene  (i  part),  C10H8,  in  glacial  acetic  acid  (6  parts) 
and  oxidising  with  chromic  anhydride  (3  parts),  dissolved  in  glacial  acetic  acid 
(2  parts).  The  mixture  is  boiled,  and  distilled  after  adding  more  water,  when  the 
naphthoquinone  passes  over  with  the  steam.  It  is  insoluble  in  water,  sparingly 
soluble  in  cold  alcohol,  but  dissolves  in  hot  alcohol  and  in  ether,  crystallising  in 
yellow  tables,  which  fuse  at  125°  C.,  and  sublime  below  100°.  Alkalies  dissolve 
it,  and  it  is  oxidised  by  strong  nitric  acid  into  phthalic  acid,  CeH^CO.^H)^ 

B-Napkthoqmnone,  [0  :  0  =  i  :  2],  is  an  example  of  an  oi-tlio-tiit'mone,  possessing  the 
red  colour,  the  non-volatility  and  the  lack  of  odour  characteristic  of  these.  It  is 
obtained  by  oxidising  i  :  2-derivatives  of  naphthalene. 

/C0\ 
520.  Anthraquinone,  C6H4/^      ^>C6H4,  is   prepared  by  dissolving 

anthracene,  C14H10,  in  glacial  acetic  acid,  and  adding  chromic  anhydride 
to  the  hot  solution  ;  on  adding  water,  the  anthraquinone  is  precipitated 
and  may  be  purified  by  sublimation  ;  it  has  no  quinone  odour.  It  sub- 
limes in  yellow  needles,  which  are  sparingly  soluble  in  alcohol  and  ether, 
but  dissolve  in  hot  benzene  and  in  nitric  acid.  It  fuses  at  285°  C.  and 
boils  at  382°  C.  Potash  does  not  dissolve  it,  but,  when  fused  with 
KOH,  it  yields  potassium  benzoate.  Sulphurous  acid  does  not  con- 
vert it  into  a  hydroquinone,  nor  does  hydriodic  acid,  but  the  latter 
reduces  it  to  anthracene  ;  as  intermediate  products  of  the  reduc- 
tion there  are  obtained  the  secondary  alcohols,  hydroxyanthranol, 

CO  --  v  XCH(OH)X 

D.H/  >C«H4,  and  anthranol,  C,H4<  >C6H4.       Hence 

IX 


anthraquinone  is  more  nearly  a  true  diketone  (diphenylenediketone)  than 
is  benzoquinone. 

Anthraquinone  may  be  synthetically  prepared  by  heating  phthalyl 
dichloride  with  benzene  and  zinc-dust  ; 

orvf^i  r^o 

C6H4<  +  C6H6  +  Zn  =  C6H4/      >C6H4  +  ZnCl,  +  H2. 

CO'Cl  CO 

This  synthesis  shows  that  the  CO  groups  must  be  attached  to  one  of  the  benzene 
rings  in  the  ortho-position  to  each  other.  That  this  is  the  case  also  with  the 
other  benzene  ring  is  seen  from  the  fact  that  when  bromanthraquinone,  C8H3Br 
(CO)0C6H4  (synthesised,  as  above,  from  bromophthalyl  chloride,  C6H3Br(COCl)2),  is 
oxidised,  the  product  is  phthalic  acid,  not  broniophthalic  acid,  showing  that  the 
brominated-ring  has  been  removed,  and  that  the  CO  groups  must  have  been 
attached  to  the  non-brominated-ring  in  the  ortho-position. 

Anthraquinone  is  chiefly  important  as  the  source  of  arti6cial  alizarin. 
521.  Alizarin,  or  i  :  2-dihydroxyanthraquinone*  C6H4(CO)3 
C6H,(OH),,  may  be  prepared  from  anthraquinone  by  treating  it  with 
bromine,  which  converts  it  into  dibromanthraquinone,  C6H,(CO).,C6H2Br2, 
and  when  this  is  heated  to  about  180°  C.  with  potash,  it  yields  potassium 
alizarate,  C6H4(CO)2C6H2(OK)2  ;  from  the  aqueous  solution  of  this, 
hydrochloric  acid  precipitates  alizarin. 

*  Anthracene  derivatives  are  orientated  similarly  to  those  of  naphthalene  (p.  554). 


720  ALIZARIN. 

Alizarin,  one  of  the  chief  vegetable  dyes,  was  formerly  obtained  ex- 
clusively from  madder,  the  root  of  Rubia  tinctorum,  imported  from  the 
South  of  France  and  the  Levant.  It  does  not  occur  ready  formed  in 
the  plant,  but  is  produced  by  the  decomposition  of  ruberythric  acid, 
C26H28O14,  which  may  be  extracted  from  madder  root  by  cold  water,  and 
crystallises  in  yellow  prisms.  When  the  root  is  allowed  to  ferment,  or 
is  treated  with  H2S04,  the  ruberythric  acid  is  hydrolysed  into  alizarin 
and  glucose,  C26H28O14+  2H<JO  =  C14H804  +  2C6HJ2O6.  Alizarin  is  pre- 
pared on  a  large  scale  from  anthraquinone  by  converting  it  into  the 
sulphonic  acid  and  fusing  this  with  caustic  soda. 

The  anthraquinone  is  made  by  treating  anthracene,  in  leaden  tanks,  with  potas- 
sium dichromate  and  diluted  sulphuric  acid,  the  reaction  being  completed  by 
boiling.  The  anthraquinone  is  dissolved  in  strong  sulphuric  acid  and  re-precipi- 
tated by  water,  which  retains  the  impurities  in  solution.  After  being  washed  and 
dried,  it  is  heated  for  eight  or  ten  hours  at  160°  C.  with  fuming  sulphuric  acid  in 
an  iron  pot,  being  constantly  stirred  ;  on  diluting  with  water,  any  unaltered 
anthraquinone  is  precipitated,  and  anthraquinone  mono-  and  di-sulphonic  acids, 
C6H4(CO)2C6H3(S03H),  and  C6H3(S03H)(CO)2C6H3(SO3H),  remain  in  solution. 

The  mixed  sulphonic  acids  are  neutralised  with  lime,  and  the  calcium  salts  are 
decomposed  by  sodium  carbonate.  The  concentrated  solution  of  the  sodium  salts 
is  heated  with  caustic  soda  and  a  little  sodium  chlorate,  in  a  closed  iron  boiler, 
at  about  i8o°C.  for  twenty-four  hours,  when  a  purple  solution  is  obtained,  con- 
taining the  alizarate  and  anthrapurpurate  of  sodium.  The  sodium  anthraquinone 
monosulphonate  is  first  decomposed  by  the  NaOH  yielding  sodoxyanthraquinone  — 

C6H4(CO)2C6H3-S03Na  +  2NaOH  =  C6H4(CO)2C6H3(ONa)  +  SOgNa^  +  H20. 
The  sodoxyanthraquinone  is  then  oxidised,  by  the  oxygen  from  the  chlorate,  in 
presence  of  the  excess  of  NaOH,  into  sodium  alizarate — 

C6H4(CO)2C6H3(ONa)   +  O  +  NaOH  =  C6H4(CO)2C6H2(ONa)2  +  H20. 
The  sodium  anthraquinone  disulphonate  yields  sodium  dnthrapvrpurafa — 

C6H3(S03Na)(CO)2C6H3(S03Na)  +  ;NaOH  = 
C6H3(ONa)(CO)2C6H2(ONa)2  +  2Na2S03  +  4H,-0. 

The  solution  is  run  into  dilute  sulphuric  acid,  when  a  mixture  of  alizarin  and 
anthrapurpurin  is  obtained  as  a  yellow  precipitate. 

Alizarin  forms  orange  prisms  (with  3H20)  very  sparingly  soluble  in 
water,  but  easily  soluble  in  alcohol  and  ether,  and  becomes  red  when 
dried.  It  fuses  at  about  290°  C.,  and  may  be  sublimed.  It  dissolves 
in  strong  H2S04  with  a  deep-red  colour,  and  is  precipitated  by  water. 
It  acts  like  a  dibasic  acid,  dissolving  in  alkalies  to  purple  solutions, 
which  give  purple-blue  precipitates  with  salts  of  alkaline  earths.  The 
insolubility  and  the  brilliant  colours  of  the  alizarates  are  of  great  value 
in  dyeing  and  calico-printing.  Alizarin  gives  red  precipitates  (madder 
lakes)  with  salts  of  Sn  and  AJ,  and  a  dark  violet  with  salts  of  iron. 

That  alizarin  is  an  adjacent  dihydroxyanthraquinone  follows  from  the  fact 
that  it  can  be  synthesised  from  phthalic  anhydride  and  i  :  2-dihydroxybenzene 
(pyrocatechol)  in  the  presence  of  sulphuric  acid  at  i5o°C.  That  the  OH  groups 
occupy  the  I  :  2  (or  3  :  4  or  i'  -.2'  or  3'  :  4',  all  these  being  the  same  in  value  as 
I  :  2)  position  follows  from  the  fact  that  alizarin  yields  two  mono-substitution  pro- 
ducts in  which  the  substituent  is  in  the  same  ring  as  the  OH  groups  ;  if  the  hydroxyl 
groups  occupied  the  2  :  3-positions  this  would  not  be  possible,  since  the  positions 
i  and  4,  which  would  then  be  vacant,  are  of  the  same  value. 

Anthrapurpurin,  C6H3-OH-(CO)2'C6H2(OH)2,  is  formed  as  above  mentioned  in 
the  preparation  of  alizarin,  and  may  be  obtained  by  oxidising  alizarin  with  Mn02 
and  H2S04.  It  resembles  alizarin,  but  fuses  at  a  higher  temperature  (330°  C.), 
and  is  more  soluble  in  water.  The  colours  of  its  metallic  salts  are  more  brilliant 
than  those  given  by  alizarin,  so  that  its  presence  in  the  artificial  dye  is  ad- 
vantageous. 


ANILINE  DYES.  y2I 

PurpurinoTi  :  2  :  4-tri-hydroxy-anthraquinone,  C6H4(CO)2C6H(OH)3,  is  isomeric 
with  the  preceding,  and  is  found  accompanying  alizarin  in  old  madder  root,  and 
may  be  separated  from  it  by  boiling  with  alum,  which  dissolves  only  the  purpurin 
It  may  also  be  obtained  by  oxidising  natural  alizarin  with  Mn<X  and  H0SCh 

Flavo-purpurin,  C6H3OH(CO)2C6H2(OH)2,  is  sometimes  formed  in  the  manu- 
facture of  alizarin.  It  crystallises  in  golden  needles  soluble  in  alcohol. 

Tetrahydroxy-anthraquinone,  anthrachrysone,  C6H2(OH)?(CO)2C6H,(OH)9,  or 
alizarine-bordeaux,  is  obtained  by  heating  I  :  3  :  5-dihydroxybenzoic  acid. 
C6H3(OH)2-COOH,  with  H2S04,  which  abstracts  the  elements7  of  ^"5  from  two 
molecules  of  the  acid. 

Hexa-hydroxy-anthraquinone,  C6H(OH)3(CO)2C6H(OH)3,  rufigallic  acid,  or 
alizarine  cyamne  (seep.  610),  is  prepared  by  heating  gallic  acid  with  H2S04,  which 
removes  the  elements  of  2H2Ofrom  two  molecules  of  gallic  acid,  C6H2(OHVCOOH. 
It  is  used  as  a  red  dye. 

All  these  anthracene  derivatives  yield  that  hydrocarbon  when  heated  with  zinc- 
dust. 

C6H4-CO 
522.    Plienanthraquinone,    •         •    ,    is    prepared    by    oxidising    phenanthrene 

C6H4*CO 

(P-  554)  with  chromic  acid.      It   crystallises   in  orange-yellow  needles,  melts  at 
198°  C.,  and  dissolves  in  hot  alcohol.     It  is  an  ortho-quinone  giving  most  of  the 
reactions  of  a  diketone. 
Coerulignone  (p.  716)  is  a  derivative  of  the  quinone  of  diphenyl. 

TRIPHENYLMETHANE  DYESTUFFS. 

These  compounds  include  the  majority  of  the  colouring-matters 
commonly  called  the  aniline  dyes.*  Although  they  are  amido-  or 
hydroxyl  derivatives,  consideration  of  them  has  been  postponed  until 
now  because  they  contain  a  benzene  nucleus  to  which  other  groups 
are  attached  in  a  manner  similar  to  that  in  which  the  oxygen 
atoms  of  quinone  are  linked  to  the  benzene  ring  (quinonoid 
structure). 

When  three  amido-groups  or  three  hydroxyl-groups  are  introduced  into  triphenyl- 
methane,  CH(C6H5)3  (p.  551),  compounds  are  produced  which  are  colourless,  but 
readily  become  coloured  when  oxidised  and  treated  with  an  acid.  For  example,. 
triamido-triphenylmethane,  CH(C6H4NH2)3,  is  a  colourless  substance  ;  when 
oxidised  it  becomes  triamidotriphenyl  carbinol,  C(OH)(C6H4NH2)3,  which  is  also  a. 
colourless  substance,  and  yields  colourless  salts  (with  one  equivalent  of  acid) 
when  treated  with  cold  acids,  but  coloured  salts  when  treated  with  warm  acids. 
The  latter  salts  are  dyestuffs  ;  they  are  formed  from  the  carbinol  by  loss  of  a 
molecule  of  water,  and  since  the  only  oxygen  in  the  carbinol  is  that  of  the  alcoholic 
group,  OH,  it  must  be  supposed  that  this  group  forms  water  with  the  hydrogen  of 
the  acid.  This  loss  of  the  OH  group  entails  the  conversion  of  the  ordinary  benzene 
linking  of  one  of  the  benzene  rings  into  the  quinonoid  linking,  the  change  being 
accompanied  by  a  development  of  colour,  just  as  the  conversion  of  the  ordinary 
linking  of  hydroquinone  (colourless)  into  the  quinonoid  linking  of  quinone,  develops 
a  colour.  HO'C6H4-OH  becoming  0  :  06H4  :  0.  The  following  equation  will  make 
the  change  more  clear  :  — 


HC1,NH2-C6H4-C(OH)(C6H4-NH2)2  =  C1NH2  :  C6H4  :  C(C6H4'NH2)2  +  H20. 
Triamidotriphenylcarbinol  hydro-  Coloured  salt  f 

chloride  (colourless).  (Pararosaniline  chloride). 

The  foregoing  reactions  are  typical  of  the  behaviour  of  every  triphenylmethane 

*  It  is  here  only  possible  to  call  attention  to  some  typical  "  aniline  dyes  "  ;  for  information 
as  to  the  chemical  constitution  of  dyes  of  trivial  names,  the  student  must  consult  a  work  on 
dyestuffs. 

t  A  simpler  view  of  the  constitution  of  this  salt  is  that  it  is  that  of  an  ethereal  chloride, 
derived  from  the  carbinol  by  exchange  of  OH  for  Cl  ;  (C6H4-  NH2)8C  •  Cl.  This  view  is  not 
regarded  as  t-  instantiated. 

2  Z 


722  ROSANILINE   SALTS. 

dyestuff ;  that  is  to  say,  each  may  be  obtained  by  oxidising  a  derivative  of 
triphenylmethane  and  treating  the  product  with  a  warm  acid.  The  parent 
triphenylmethane  derivative  is  called  the  leuco-base  of  the  dyestuff ;  the  carbinol 
into  which  it  is  converted  by  oxidation  is  called  the  colour-base  of  the  dyestuff  ; 
whilst  the  coloured  salt  is  the  dyestuff  itself.  Thus,  triamidotriphenylmethane 
is  called  leuco-pararosaniline  ;  triamidotriphenyl  carbinol  is  pararosamline  base, 
whilst  the  coloured  salt  with  the  quinonoid  linking  is  pararosanlline  chloride. 
The  converse  changes  are  possible  ;  that  is  to  say,  by  treating  the  dyestuff  with  a 
caustic  alkali  the  colour-base  is  precipitated,  and  if  this  be  treated  by  reducing- 
agents  (nascent  hydrogen)  it  yields  the  leuco-base. 

The  triphenylmethane  dyestuffs  are  classified  into  derivatives  of : — 
(i)  Diamido-tripheni/lmethane,  06H5*CH(C6H4<NH2)2 ;  the  type  of  these 
is  malachite  green.  (2)  Triamidotriphenylmethane,  CH(C6H4'NH2)3; 
the  type  of  these  is  rosaniline  (magenta).  (3)  Trihydroxytriphenyl- 
methane,  CH(C6H4-OH)3 ;  the  type  of  these  is  aurin.  (4)  Triphenyl- 
methane carboxylic  acid,  CH(C6H5)2(C6H4*C02H) ;  the  type  of  these  is 
eosin. 

Malachite  green  or  tetramethyl-i  :  ^-diamido-triphenylmethane  chloride — 

C1N(CH3)2  :  C6H4  :  C(C6H5)[C6H4-N(CH3)2]. 

The  leuco-base  of  this  dyestuff  is  prepared  by  heating  benzaldehyde  with 
dimethylaniline  and  zinc  chloride  (to  act  as  a  dehydrating  agent) — 

C6H5-CHO  +  2C6H5-N(CH3)2  -  C6H5-CH[C6H4'N(CH3)2]2  +  H20. 

The  leuco-base  is  oxidised  by  Pb02  (when  it  yields  the  corresponding  carbinol  or 
colour-base,  see  above)  in  the  presence  of  HC1  (to  produce  the  colour-salt).  The 
dyestuff  is  then  precipitated  by  zinc  chloride  and  sold  in  the  form  of  a  double 
zinc-salt. 

Bosaniline  salts  constitute  the  bulk  of  the  dyestuff  known  as 
magenta  (fuchsine).  They  are  formed  by  the  action  of  acids  on 
rosaniline-base,  which  is  triamidotolyldiphenyl  carbinol — 

NH2-C6H3(CH3)-C(OH)(C6H4-NH2)2. 

The  chloride,  C1NH2  :  C?H3(CH3)  :  C(C6H4-NH2)2,  nitrate  and  acetate  are 
the  most  common  salts  in  the  market.  They  are  prepared  by  heating 
aniline  oil  for  red  (p.  665),  which  should  contain  equi-molecular  pro- 
portions of  aniline,  orthotoluidine  and  paratoluidine,  with  an  oxidising- 
agent  (arsenic  acid  or  nitrobenzene  *  is  generally  used) ; 

C6H4(CH3)-NH2  /C6H3(CH3)-NH2 

NH2-C6H4-CH3  +  +  03  =  NH2-C6H4-C(OH)<  +2H20. 

C6H5-NH2  XC6H4-NH2 

The  rosaniline  base  made  in  this  way  is  converted  into  the  chloride 
by  adding  hydrochloric  acid,  and  this  salt  is  precipitated  by  adding 
common  salt.  When  recrystallised,  rosaniline  salts  form  bronze-green 
crystals  which  are  sparingly  soluble  in  cold  water,  but  more  readily  ii 
hot  water,  to  a  red  solution.  When  the  hot  solution  is  mixed  with 
ammonia  and  filtered  quickly  the  rosaniline  base  crystallises  from  th< 
.  filtrate  in  colourless  plates  which  become  red  in  air,  from  absorption  of 
C02>  Reducing-agents  bleach  the  red  solution  with  formation  of 
leucaniline,  NH2-C6H3(CH3)-CH(C6H4'NH2)2,t  the  leuco-base  of  rosani- 
line. 

*  This  oxidising-ag'ent  is  now  more  common  than  any  other.  When  it  is  employed,  HC1 
and  iron  filings  form  a  part  of  the  charge,  so  that  the  nitrobenzene  is  first  reduced  to  aniline 
(which  enters  into  the  reaction),  and  the  ferric  chloride  formed  by  its  reduction  is  the  imi 
diate  oxidant. 

f  When  diazotised  (p.  681),  and  heated  with  alcohol,  leucaniline  yields  metatolyldiphenyl- 
methane,  C6H4(CH3)  •  CH(C6H5)2,  (cf.  p.  681),  showing  that  leucauiline,  and  therefore  rosani- 
line  must  be  a  derivative  of  this  hydrocarbon. 


AURIN  AND   EOSIN.  723 

Pararosaniline  or  triamidotriphenol  carbinol,  C(OH)(C  H  -NH  ) ,  i« 
prepared  by  oxidising  a  mixture  of  paratoluidine*  (i  mol.)  aid  aniline 
(2  mols.)  in  the  same  way  as  is  described  for  rosaniline.  The  salts  are 
red  dyestuffs,  like  the  rosaniline  salts. 

In  both  oxidations  it  may  be  supposed  that  the  paratoluidine  is  oxidised  to  »- 
amidobenzaldehyde,  which  then  condenses  with  the  orthotoluidine  and  aniline  (in 
the  case  of  rosaniline)  or  with  the  aniline  alone  (in  the  case  of  pararosaniline). 

Many  derivatives  of  pararosaniline  and  rosaniline,  containing  methyl,  ethyl  and 
phenyl  groups  in  place  of  the  amido-hydrogen  atoms,  are  prepared  by  heating 
pararosaniline  or  rosaniline  chloride  with  alkyl  or  phenyl  halides  ;  these  are  also 
used  as  dyestuffs,  the  shade  produced  by  them  becoming  more  blue  as  successive 
alkyl  or  phenyl  groups  are  introduced,  Thus  pentamethyl-pararowniline  is  known 
as  methyl  violet,  and  triphenyl-rosaniline  chloride  as  aniline  blue.  The  combination 
of  tetramethylrosaniline,  which  is  saturated  with  methyl  groups,  with  methyl 
chloride  or  iodide,  produces  a  green  dyestuff  known  as  iodine  green. 

Aurin. — When  pararosaniline  base  is  diazotised  (p.  68 1),  the  three 
NH2  groups  are  converted  into  diazo-groups,  and  when  the  resulting 
compound  is  boiled  with  water  it  yields  trihydroxytriphenyl  carbinol, 
(C6H4-OH)3C'OH,  (cf.  p.  681).  This  compound  is  very  unstable  and 
loses  a  molecule  of  water,  becoming  aurin,  0  :  C6H4  :  C(C6H4OH)2,  com- 
parable in  structure  with  pararosaniline  chloride.  It  crystallises  in 
green  needles  which  dissolve  in  alkalies  to  a  red  solution,  but  are 
precipitated  again  by  acids.  Thus  aurin  behaves  as  an  acid  substance, 
as,  indeed,  is  to  be  anticipated  from  the  presence  of  phenolic  OH 
groups.  It  will  be  noticed  that,  whilst  pararosaniline  is  a  type  of  basic 
dyestuffs,  tending  to  combine  with  acid  mordants,  aurin  is  a  type  of 
acid  dyestuffs  tending  to  combine  with  basic  mo7'dants. 

Rosolic  acid  bears  the  same  relation  to  rosaniline  as  aurin  bears  to 
pararosaniline. 

Eosin. — Triphenylmethane-carboxylic  acid  (see  above),  or  rather  its 
hydroxy-derivative  triphenyl  carbinol- 1: 2 -carboxylic  acid — 

(C6HB)a(C6H4-COOH)C-OH, 

gives  rise  to  the  dyestuffs  of  this  class.  Diphenylphthalide  is  the  lactam 
(p.  674)  of  this  alcohol  acid  ;  it  may  also  be  regarded  as  derived  from 
phthalic  anhydride  by  substituting  (C6H5)2"  for  0",  for  it  is  prepared  by 
the  interaction  of  phthalyl  chloride  and  benzene  in  presence  of  A12C16 — 


Diphenylphthalide. 

By  substituting  phthalic  anhydride  for  the  chloride,  a  phenol  for  the 
benzene  and  a  dehydrating  agent  for  the  A12C16  in  this  reaction,  the 
eosin  dyestuffs  are  obtained. 

Thus,  phenol-phthalein  is  obtained  when  phthalic  anhydride  is  heated  with  two 
molecular  proportions  of  phenol  and  ZnCl2 — 

/C0\  C(C6H4'OHk 

C6H4<(      >0  +  206H5OH  -  C6H4< CQ __>0  4-  H20. 

CO 

The  mass  is  dissolved  in  an  alkali  and  the  phenophthalein  precipitated  by  an  acid. 
Its  alkali  salts  are  pink  in  solution,  and  are  decomposed  by  the  feeblest  acids 

*  Its  prefix  appears  to  have  been  given  to  pararosaniline  on  account  of  the  fac^that  para- 
toluidine is  used  in  its  manufacture.     Since  it  has  been  recognised. that  paratoluidine  n 
necessary  for  rosaniline,  the  name  has  lost  its  significance. 


724  CARBOHYDRATES. 

p.  709),  so  that  phenolphthalein  is  useful  as  an  indicator  in  acidimetry.  It  can 
hardly  be  termed  a  dyestuff. 

It  has  been  supposed  that  phenolphthalein  may  behave  as  dikydroaryphthalein, 
C6H4(COC6H4OH)2.  As  this  does  not  import  a  quinonoid  structure  into  its  consti- 
tution, it  has  also  been  suggested  that  the  salts  of  phenolphthalein  are  from  the 

pseudoform  COOH'CfiH4<^  6    4       .     The  ease  with  which  the  salts  are  decomposed 

\J8H4:0 

by  all  acids  seems  to  show,  however,  that  they  are  derived  from  phenolic,  not 
carboxylic  groups. 

.C[(C6H3'OH)20]X 
Fluor 'esc&in,  C6H4<^  ^0,  is  formed  when   phthalic   anhydride  is 

OO 

heated  with  resorcinol,  2  mols.  H20  being  liberated.  It  forms  red  crystals  and  dis- 
solves in  dilute  alkalies,  giving  a  solution  which  is  red  with  a  green  fluorescence  ; 
this  is  also  noticeable  on  the  dyed  fabric,  hence  the  dyestuff  is  frequently  mixed 
with  others  for  producing  a  fluorescent  green. 

Eosin  itself  is  a  tetrabromo-derivative  of  fluorescein,  and  is  made  by  brominating 
the  latter  in  acetic  solution.  It  dissolves  in  alkalies,  giving  a  deep  red  solution 
which  fluoresces  green  when  diluted. 

XIII.  CARBOHYDRATES. 

523.  It  has  been  already  indicated  (p.  584),  that  this  group  of  organic 
compounds  is  only  a  temporary  one  in  chemical  classification,  and  that 
it  will  be  broken  up  so  soon  as  the  true  constitution  of  the  compounds 
which  it  now  comprises  is  understood.     Indeed,  it  is  already  on  the 
eve  of    extinction,  since  several   of    the    sugars,  formerly  the  typical 
members  of  the  group,  have  been  shown  to  be  either  aldehyde-alcohols 
or  ketone-alcohols. 

Originally,  the  compounds  belonging  to  this  class  were  such  as  contain 
hydrogen  and  oxygen  in  the  proportion  to  form  water,  combined  with 
six  atoms,  or  some  multiple  of  six  atoms,  of  carbon.  This  is  still  true 
for  a  majority  of  the  compounds  of  the  class,  but  it  is  necessary  now  to 
describe  several  substances  which  do  not  fall  in  with  the  above  defini- 
tion, among  the  carbohydrates. 

The  carbohydrates  may  be  divided  into  two  groups  :  (i)  the  Sugars, 
and  (2)  the  Starches  and  Celluloses. 

The  group  of  sugars  contains  compounds  which  are  comparable  in  taste  and 
other  properties  with  the  substance  commonly  called  sugar.  The  molecular 
formulae  for  the  sugars  may  be  said  to  be  known  in  almost  all  cases,  and  it  is 
found  that  whilst  a  number  of  them,  such  as  glucose,  C6H1206,  correspond  with 
the  general  formula,  CK(H20)K,  others,  such  as  cane-sugar,  C12H220n,  correspond 
with  the  general  formula.  Cw(H20)w_i.  The  molecular  formulae  for  the  starches 
and  celluloses  are  not  known  ;  but  the  percentage  composition  of  these  compounds 
indicates  that  their  molecular  formula  is  (C6H1005)W.  As  may  be  expected,  the 
compounds  Cw(H20)w_i  yield  the  compounds  CM(H20)W  when  decomposed  by 
hydrolysis,  and  the  compounds  (C6H1005)M  undergo  a  similar  change. 

The  above  considerations  have  given  rise  to  a  classification  of  the  carbo- 
hydrates into  (i)  saccharifies  or  monoses,  CM(H2O)M  ;  (2)  disaccharides  or  saccharo- 
bioses,  C^H^OH ;  (3)  trisaccharides  or  saccharotrioses,  C18R^0IQ  ;  (4)  polyBaccharide$^ 
(C6H1005)W. 

THE  SUGARS. 

524.  These  may   be    subdivided   into  glucoses  (aldoses  and  ketoses)j 
having  the  general  formula  CW(H20)M,  disaccharides  (formerly  sucroses) 
or   saccharo-bioses,  having    the    formula    C12H22On,   and    trisaccharides 


GLUCOSES. 


725 


or  saccharo-trwses,  having  the  formula  C18H32016.*  The  sugars  of  the 
second  and  third  classes  are  converted  into  sugars  of  the  first  class  by 
hydrolysis.  The  type  of  the  sugars  of  the  first  class  is  grape-sugar 
that  of  the  second  cane-sugar,  whilst  that  of  the  third  is  rafftnose.  " 

Since  the  sugars  contain  asymmetric  carbon  atoms,  they  give  rise 
to  a  large  number  of  optically  active  stereo-isornerides  (p.  542). 

525.  The  Glucoses. — These  are  named  according  to  the  number 
of  carbon  atoms  which  they  contain— e.g.,  triose,  C3H603 ;  tetroses,  C4H804 ; 
pentoses,  C5H1005 ;  hexoses,  C6H1206 ;  heptoses,  C7H14O7,  &c.  In  constitu- 
tion they  are  either  aldehyde-alcohols  or  aldoses  (containing  the  group 
•CH(OH)-CHO),  or  ketone-alcohols  or  ketoses  (containing  the  group 
•COCH2OH),  and  accordingly  behave  as  reducing-agents  and  yield 
hydrazones  just  as  other  compounds  containing  the  aldehyde  or  the 
ketone  group  do. 

The  glucoses  must  be  regarded  as  the  first  oxidation-products  of 
polyhydric  alcohols,  the  most  important  of  which  have  been  mentioned 
(P-  577)-  The  aldoses  would  be  formed  by  oxidation  of  the  primary 
alcohol  group,  and  the  ketoses  by  oxidation  of  the  secondary  group. 
All  the  glucoses  have  asymmetric  carbon  atoms,  and  each  exists  in  two 
stereoisomeric  forms,  the  d-  and  the  I-  form,  and  in  a  third,  externally 
compensated  or  racemic,  inactive  (d  + 1)  form  t  (p.  605). 

526.  Thus  the  simplest  aldose  would  be  gly collie  aldehyde,  CH2OH'CHO,  from 
glycol ;  glycerol  yields  both  an  aldose,  glycerose  (aldotriose),  CH2OH'CHOH'CHO 
(p.  584)  and  a  ketose,  dihydroxyacetone  (ketotriose),  CH2OH*COCH2OH. 

(1)  Tetroses. — Erythrose,  obtained  by  the  oxidation  of  erythritol  (p.  578)  by  the 
action  of  dilute  nitric  acid,  is  probably 'a  mixture  of  the  aldotetrose, 

CH2OH-[CHOH]2-CHO, 
and  the  ketotetrose,  CH2OH-CHOH-CO'CH2OH.     A  d-  and  an  I-  form  are  known. 

(2)  Pentoses. — The  aldopentoses,  CH2OH'[CHOH]3'CH2OH  are  alone  known  at 
present.     They  are  natural  sugars,  occurring  in  many  plants.    They  resemble  the 
aldohexoses  (v:i.)  in  their  general  behaviour  except  that  they  are  not  fermented  by 
yeast.     Other  characteristics  are  that  they  yield  furfural  (p.  586)  or  its  homologues 
when  distilled  with  dilute  acids,  and  that  they  give  a  red  colour  with  phloro- 
glucinol  and  HC1. 

Eight  optically  active  and  four  externally  compensated  aldopentoses  are  possible 
(p.  621).  I- Arabinose,  the  chief  member  of  the  class,  is  prepared  by  boiling  with 
dilute  H2S04  gum  arabic  and  other  gums  which  yield  little  mucic  acid  when 
oxidised  by  HN03.  It  crystallises  in  sweet  prisms,  melts  at  160°  C.  and  is  strongly 
dextro-rotatory.f 

By  reduction  it  yields  the  pentatomic  alcoholiarabitol,  CH2OH-[CHOH]3-CH2OH. 
Xylose  (from  wood-gum,  straw,  and  jute),  and  ribose  are  isomerides  of  arabinose. 
Rhamnose  (from  quercitrin)  and  fucose  (from  sea-weed)  are  methyl  arabinose, 
C5H9(CH3)05. 

(3)  Hexoses,  C6H1206.— These  are  the  compounds  which  were  origin- 
ally called  glucoses.     They  are  widely  distributed  in  nature,  but  are 
mainly  found  in  unripe  fruit,  the  chief  being  dextrose,  or  grape-sugar, 
and  Isevulose,  or  fruit-sugar ;  they  are  produced  by  the  hydrolysis  of 
the  disaccharides  and  poly sacchar ides,  the  change  being  effected  both 
by  enzymes  and  by  dilute  acids  or  alkalies.     d-Glucose,  d-mannose, 

*  According  to  one  system  of  nomenclature  the  termination  -ose  is  employed  to  designate 
sugars  of  the  first  class,  and  the  termination  -on  to  indicate  sugars  of  the  second  class.  T, 
CfiH12Ofi  is  hexose,  whilst  C12HoQOn  is  dihexon. 

t  Much  confusion  is  engendered  by  Fischer's  custom  of  naming  the  sugars  d-  and  J- with- 
out reference  to  their  actual  rotation,  but  according  to  the  way  in  whjch  they  a 
from  each  other. 


726  GBAPE-SUGAR. 

d-galactose,  and  d-fructose  are  fermented  by  yeast,  yielding  alcohol.  A 
few  have  been  synthesised,  and  the  constitution  of  nearly  all  has  been 
settled  (see  below). 

(a)  -Aldohexoses,  CH2OH-[CHOH]4'CHO.— The  substance  commonly 
called  glucose,  grape-sugar  or  dextrose  is  d-glucose,  there  being  also 
an  ^-glucose  and  a  (d  +  Q-glucose.  It  is  the  aldehyde  of  sorbitol  (p.  5  79). 

d-Glucose  is  the  crystallised  sugar  found  in  honey,  raisins,  and  many 
other  fruits  ;  it  is  almost  always  accompanied  by  Isevulose,  a  keto- 
hexose,  which  is  far  more  difficult  to  crystallise.  Dextrose  is  also 
found  in  small  quantity  in  several  animal  fluids,  and  in  the  liver,  and 
it  is  abundant  in  urine  in  cases  of  diabetes. 

Dextrose  may  be  obtained  from  honey  by  mixing  it  with  cold  alcohol 
to  dissolve  the  Isevulose,  which  forms  about  one-third  of  its  weight,  and 
leaves  about  an  equal  quantity  of  dextrose,  which  may  be  dissolved  in 
boiling  alcohol  and  crystallised.  To  extract  it  from  fruits,  they  are 
crushed  with  water,  strained,  the  liquid  boiled  to  coagulate  albumin, 
filtered,  evaporated  to  a  syrup,  and  set  aside  for  some  days,  when  crystals 
of  dextrose  are  deposited.  Fresh  fruits  contain  chiefly  Isevulose,  which 
is  gradually  converted  into  dextrose. 

Dextrose  is  also  a  product  of  the  hydrolysis  of  glucosides  (q.v.),  and 
di-  and  poly-saccharides  (cane-sugar,  starch,  &c.). 

From  cane-sugar  it  is  best  prepared  by  heating  a  mixture  of  250  c.c.  of  alcohol 
(sp.  gr.  0.823)  with  10  c.c.  of  strong  HC1  to  45°  C.  and  adding  80  grams  of  finely 
powdered  cane-sugar  in  small  doses.  When  the  sugar  has  entirely  dissolved,  the 
whole  is  set  aside  for  a  week  and  stirred  to  induce  crystallisation.  The  crystals  of 
dextrose  are  drained  from  the  solution  containing  laevulose  and  washed  with 
alcohol. 

Commercial  glucose  or  starch-sugar  is  made  by  heating  starch  with  diluted  sul- 
phuric acid,*  which  first  converts  it  into  dextrin  and  finally  into  ^-glucose, 
(C6H1005)W  +  %H20  =  rcC6H1206. 

Water  containing  about  1.5  per  cent,  of  H2S04  is  heated  to  boiling  and  a  hot 
mixture  of  starch  and  water  is  allowed  to  flow  gradually  into  it.  The  mixture  is 
boiled  for  half  an  hour,  neutralised  with  chalk,  and  concentrated  by  evaporation, 
when  it  deposits  crystals  of  calcium  sulphate.  The  clear  syrup  is  drawn  off  and 
evaporated  in  a  vacuum-pan  till  it  is  strong  enough  to  crystallise,  some  glucose 
from  a  previous  batch  being  added  to  promote  crystallisation.  The  glucose  thus 
obtained  contains  about  70  per  cent,  of  ^-glucose  and  also  maltose,  dextrin,  and 
some  calcium  salts  of  organic  acids  ;  it  may  be  purified  by  washing  with  strong 
alcohol  mixed  with  3  per  cent,  of  HC1,  and  afterwards  with  commercial  absolute 
alcohol. 

When  crystallised  from  an  aqueous  solution,  dextrose  forms  six-sided 
scales  (with  iH20)  ;  these  fuse  at  86°  C.,  and  become  anhydrous  at 
110°  C. ;  it  crystallises  from  alcohol  at  30°  C.  in  small  anhydrous 
needles,  which  melt  at  146°  C.  It  is  less  sweet  than  cane-sugar,  and 
can  be  directly  fermented  by  yeast  (p.  561).  Glucose  dissolves  in  1.2 
parts  of  cold  water,  in  50  parts  of  cold,  and  in  5  parts  of  boiling, 
alcohol  (sp.  gr.  0.837).  When  heated  to  170°  C.,  it  is  converted  into 
dextrosan  (glucosan),  C6H1005,  a  nearly  tasteless  substance,  convertible 
into  glucose  by  dilute  acids.  When  boiled  with  caustic  potash,  glucose 
gives  a  dark  brown  solution,  being  ultimately  converted  into  humus- 
like  acids.  In  presence  of  alkalies,  glucose  acts  as  a  strong  reducing- 
agent.  If  a  solution  of  glucose  be  mixed  with  CuS04,  and  KOH  be 
gradually  added,  the  blue  precipitate  of  cupric  hydroxide  produced  at 

*  Care  should  be  taken  that  the  sulphuric  acid  is  free  from  arsenic,  lest  the  latter  pass 
into  the  glucose  and  thence  into  the  beer  brewed  therefrom. 


FEUIT-SUGAE. 

first  dissolves  in  excess  of  potash  to  a  fine  blue  solution ;  if  this  be 
gently  heated,  a  yellow  precipitate  of  cuprous  hydroxide  is  produced 
which  becomes  red  cuprous  oxide  when  boiled  ;  a  little  metallic  copper 
is  precipitated  at  the  same  time,  and  the  glucose  is  oxidised  to  a  number 
of  organic  acids.  Glucose  precipitates  metallic  silver  when  warmed 
with  ammonia-nitrate  of  silver,  and  metallic  mercury  from  HefCN^ 
mixed  with  KOH. 

Solution  of  glucose  mixed  with  NaCl  deposits  crystals  of  2C6H12Ofi  NaCl  H  0 
which  is  sometimes  deposited  from  diabetic  urine.  Glucose  is  not  so  easily 
blackened  by  H2S04  as  is  sucrose,  but  forms  an  unstable  compound  with  it.  With 
alkaline  earths  dextrose  combines  to  form  compounds  like  C6H1206.CaO,  which  are 
precipitated  by  alcohol.  Other  reactions  will  be  discussed  under  Constitution  of  the 
Sugars. 

Dextrose  rotates  the  plane  of  polarisation  to  the  right  hand,  but  a 
solution  which  has  been  kept  for  some  hours  has  only  half  the  effect  of 
a  freshly  made  solution,  a  phenomenon  known  as  bi-rotation,  and 
probably  due  to  the  formation  of  hydrates. 

Glucose  is  used  by  brewers  and  distillers  for  making  alcohol,  and  by 
confectioners  ;  dyers  and  calico-printers  use  it  to  reduce  indigo. 

d-Mannose  is  obtained,  together  with  Isevulose,  by  the  cautious  oxidation  of 
mannitol  (p.  578),  with  platinum  black  or  nitric  acid.  It  may  be  prepared  by 
boiling  seminine,  the  reserve-cellulose  of  many  seeds,  with  dilute  H2S04 ;  it  is 
sometimes  called  seminose.  Mannose  has  not  been  crystallised  ;  it  is  very  soluble 
in  water,  and  its  solution  is  dextro-rotatory  ;  a  I  and  a  (d  +  I)-  form  are  also 
known. 

d-Galactose  is  obtained,  together  with  ^-glucose,  when  milk-sugar  and  some 
varieties  of  gum  arabic  are  boiled  with  dilute  H2S04.  To  prepare  it,  milk-sugar  is 
boiled  for  six  hours  with  four  parts  of  water  containing  5  per  cent,  of  H2S04. 
The  solution  is  precipitated  by  baryta,  filtered,  evaporated  to  a  syrup,  and  induced 
to  crystallise  by  adding  a  few  crystals  of  dextrose.  The  crystals  are  washed  with 
alcohol  of  80  per  cent.,  and  recrystallised  from  hot  alcohol  of  70  per  cent.  It 
crystallises  in  rhombic  prisms,  which  are  less  sweet  than  cane-sugar,  and  melts  at 
1 66°  C.  It  is  not  very  soluble  in  cold  water,  and  is  insoluble  in  absolute  alcohol. 
Galactose  is  also  obtained  by  hydrolysing  galactitol,  C9H1807,  a  crystalline  substance 
extracted  by  alcohol  from  yellow  lupines.  I-  and  (d  +  Z)-galactose  are  known. 

The  guloses  and  taloses  are  artificial  aldohexoses.  Methylhexose  or  rhamnohexose, 
C6H11(CH3)06,  has  also  been  prepared. 

(b)  Ketohexoses,  CH2OH-[CHOH]3-CO'CH2OH.—  d-Fructose  is  the 
most  important  of  these.  It  is  commonly  known  as  fruit-sugar  or 
Isevulose,  and  is  prepared  by  heating  cane-sugar  with  water  and  a  very 
little  sulphuric  acid  on  a  water-bath  for  half  an  hour,  removing  the 
acid  by  barium  carbonate,  and  evaporating  to  a  syrup.  This  syrup 
contains  invert-sugar^  a  mixture  of  equal  weights  of  dextrose  and 
Isevulose,  which  mixture  deposits  crystals  of  dextrose  when  exposed  to 
light.  To  obtain  pure  Isevulose,  it  is  mixed  with  water,  cooled  in  ice, 
and  stirred  with  calcium  hydroxide,  which  precipitates  a  sparingly 
soluble  lime  compound  of  Isevulose.  This  is  suspended  in  water  and 
decomposed  by  C02 ;  the  filtrate  from  the  calcium  carbonate  is  then 
evaporated  on  a  water-bath.  The  syrup  is  washed  with  cold  alcohol 
and  set  aside  in  a  cold  place,  when  the  Isevulose  crystallises. 

Lasvulose  is  much  sweeter  than  dextrose,  rivalling  cane-sugar  in  this 
respect.  It  does  not  ferment  so  readily  as  dextrose,  so  that  when  invert- 
sugar  is  mixed  with  yeast,  the  dextrose  is  the  first  to  disappear.  It  also 
reduces  alkaline  cupric  solutions  (p.  6 1 9)  less  readily.  Lsevulose  rotates 
the  plane  of  polarisation  of  light  to  the  left,  whence  its  name,  but  a 


728  SYNTHESIS   OF   SUGARS. 

dextro-  (I)  and  an  inactive  (d  +  I)  laevulose  also  exist.  It  forms  two 
crpstalline  compounds  with  lime,  C6H1206.Ca0.2Aq  and  C6Hl206.3CaO, 
dissolving  respectively  in  137  and  333  parts  of  cold  water. 

When  heated  to  170°  C.,  laevulose  is  converted  into  Icevulosan,  C6H1005, 
which  is  dextro-rotatory.  "When  heated  with  alkalies  it  is  partly  con- 
verted into  d-glucose  and  cZ-mannose. 

527.  (4)  Heptoses,  C7H1407,  octoses,  CgHigOg,  and  nonoses,  C9H1809.—  It  has  been 
found  possible  to  produce  a  glucose  containing  x  carbon  atoms  from  one  containing 
fc-i  carbon  atoms  by  treating  the  latter  with  hydrocyanic  acid,  whereby  it  is  con- 
verted into  a  cyanohydrin  (p.  582)  just  as  any  other  aldehyde  or  ketone  would  be. 
This  cyanohydrin  is  convertible  into  a  carboxylic  acid  by  hydrolysis  ;  this  may 
be  reduced  to  a  new  sugar  by  sodium  amalgam  ;  thus,  dextrose  yields  the  cyano- 
hydrin CH2OH-[CHOH]4-CH(OH)-CN,  which  is  converted  into  dextrose-carloxylic 
acid  (gluco-heptonic  acid),  CH2OH-[CHOH]5-C02H,  by  hydrolysis,  and  when  this 
acid  is  reduced  it  yields  glucoheptose,  CH2OH-[CHOH]5-CHO.     By  these  means 
each  glucose  may  be  made  to  yield  a  heptose,  which,  in  its  turn,  may  be  converted 
into  an  octose  and  a  nonose  ;  consequently  the  possible  number  of  these  sugars  is 
very  large.     They  have  not  been  found  in  nature. 

528.  Synthesis  of  the  Glucoses.  —  The  key  to  the  synthetical  production  of  the 
glucoses  was  phenylhydrazine.     Like  other  aldehydes  and   ketones  the  glucoses 
form  hydrazones  when  heated  with  a  solution  of  phenylhydrazine  hydrochloride 
and  sodium  acetate  (p.  685).     Thus  the  aldohexoses  form  the  hydrazones 

CH2OH-[CHOH]3-CHOH-CH  :  N'NC6H5, 
while  the  hydrazones  from  the  ketohexoses  have  the  form 

CH2OH-[CHOH]3-C(  :  N'NHC6H5)-CH2OH. 

When  an  excess  of  phenylhydrazine  is  used,  the  hydrazones  lose  H2  on  account  of 
the  tendency  for  C6H5NH'NH2  to  absorb  H2  and  become  C6H5NH2  and  NH3 
(p.  685).  This  converts  the  aldose  hydrazone  into  a  ketonic  compound  and  the 
ketose  hydrazone  into  an  aldehydic  compound  — 

CH2OH-[CHOH]3'CO-CH  :  N'NHC6H5 
CH2OH-[CHOHJ3-C(  :  N'NHC6H5)-CHO. 

These  immediately  combine  with  a  second  molecule  of  phenylhydrazine  to  form 
osazones,  both  of  which  have  the  formula, 

CH2OH-[CHOH]3-C(  :  N'NHC6H5)-CH  :  N'NHC6H5. 

Thus  the  aldoses  and  ketoses  yield  the  same  osazones  except  in  so  far  as  these  may 
differ  stereochemically. 

The  hydrazones  are  generally  soluble  in  water,  but  the  osazones  are  bright 
yellow,  sparingly  soluble,  and  easily  crystallised.  Thus  their  formation  is  often 
the  best  method  of  identifying  a  known  sugar  or  of  isolating  a  new  one. 

For  this  latter  purpose  the  osazone  is  dissolved  in  cold  strong  HC1  ;  it  is  thus 
converted  into  the  corresponding  osone,  a  ketone-aldehyde  ; 
CH2OH-[CHOHJ3'C(  :  N'NHC6H5)-CH  : 
=  CHOH-CHO 


The  red  liquid  which  is  formed  deposits  phenylhydrazine  hydrochloride  ;  it  is 
filtered  and  neutralised  with  PbC03  ;  the  lead  compound  of  the  osone  remains  in 
solution  ;  it  is  precipitated  by  baryta  and  the  precipitate  decomposed  by  H.2S04. 
To  convert  the  solution  of  the  osone,  thus  obtained,  into  a  sugar  it  is  reduced  by 
means  of  zinc  and  acetic  acid  ; 

CH2OH-[CHOH]3-CO'CHO  +  H2=CH2OH-[CHOHJ3-CO-CH2OH. 

When  dextrose  is  treated  in  this  way  it  is  converted  into  lasvulose. 

529.  Formaldehyde  is  the  first  step  in  synthesising  glucoses  from  their  elements. 
Treated  with  lime-water,  it  is  polymerised  to  a  mixture  of  sugars,  termed  formose  ; 
a  similar  mixture  (methylenitan)  is  obtained  from  trioxymethylene  (p.  581)  in  like 
manner.  Two  sugars,  a-  and  (3-acrose,  have  been  isolated  from  this  mixture  and 
also  from  the  mass  obtained  by  treating  glycerose  (p.  584)  with  alkalies.  They  are 
separated  by  taking  advantage  of  the  greater  solubility  of  /3-acrosazone,  than  of 
o-acrosazone,  in  ethyl  acetate. 

The  glucose  recovered  from  ct-acrosazone  in  the  manner  described  above  appears 
to  be  identical  with  (d-  +  ^-fructose,  which  by  fermentation  with  yeast  is  converted 


CONSTITUTION  OF  GLUCOSES.  729 

into   Z-fructose,   the  ^-constituent   having  been  used  by  the  yeast  (see  D  606) 
This  Z-fructose  is  dextro-rotatory  (see  foot-note,  p.  f*c\    »»*  J^t  X™^:™': 


reduction  yield  first  I-  and  <*-mannose  anYthenT 

nn°Se        °Ugh  the  Phenylhyd^ine  reactions  they  yield  I-  and  I 


fructose 


When  I-  and  d-  mannonic  acids  are  heated  with  quinoline  they  are  converted 
into  I-  and  d-  glucomc  acids,  which  are  stereo-isomeric  with  them.     By  reduction 
°nlaCleld  *~  and  ^gluCOSe  Cdextrose^    Thus  a  number  of  hexoses 


has 

It  will  be  observed  that  the  monocarboxylic  acids  derived  from  the  polyhydric 
alcohols  are  useful  transition  products  in  the  syntheses,  as  they  readily  lend  them- 
selves  to  resolution  by  means  of  their  salts  with  the  alkaloids. 

Through  these  acids  also  it  is  possible  to  pass  from  the  pentoses  to  the  hexoses 
and  vice  versa.  Thus  Z-arabinose  combines  with  HCN  as  any  other  aldehyde  does 
(p.  582),  forming  the  cyanohydrin  CH2OH-[CHOH]3-CH(OHYCN,  which  by 
hydrolysis  yields  Z-mannonic  acid,  the  CN  becoming  COOH  as  usual.  Again  by 
oxidising  d-gluconic  acid  with  H2O2  in  presence  of  ferric  acetate  it  yields 
d-arabinose  ;  or  by  treating  d-glucoseoxime,  CH2OH[CHOH]4'CH  :  N(OH)  with 
acetic  anhydride  and  sodium  acetate,  it  yields  a  pentacetyl  derivative  which 
becomes  d-arabinose  when  treated  with  HC1. 

530.  Constitution  of  the  Glucoses.—  The  molecular  weight  of  many  of  the  sugars 
has  been  settled  by  Raoult's  method  (p.  3  19).  That  the  hexoses  (the  same  arguments 
apply  to  the  pentoses)  are  alcoholic  aldehydes  or  ketones  is  shown  by  the  following 
reactions  : 

When  heated  with  acetic  anhydride  and  sodium  acetate  the  hexoses  yield 
pentacetyl-derivatives,  C6H70(OCH3CO)5,  showing  that  they  contain  5  alcoholic 
hydroxyl  groups  (p.  578)  and  are  pentahydric  alcohols.  Five  out  of  the  six 
atoms  of  oxygen  are  thus  disposed  of  :  that  the  sixth  must  be  present  either  as  an 
aldehyde  or  as  a  ketone  group,  is  shown  by  the  fact  that  these  sugars  give  a  number 
of  the  reactions  which  characterise  aldehydes  and  ketones.  In  the  aldohexoses 
this  remaining  oxygen  atom  must  be  present  as  an  aldehyde  group,  for  on  oxida- 
tion these  sugars  yield  acids  containing  the  same  number  of  carbon  atoms,  which 
would  not  be  the  case  if  the  sugars  were  ketones  (p.  624).  Thus,  the  dextroses 
yield  first  gluconic  acids,  CH2OH-[CHOH]4'CO2H,  and  then,  by  further  oxidation, 
saccharic  acids,  C02H-[CHOH]4-C02H  ;  the  mannoses  yield  mannonic  acids  and 
manno-saccharic  acids,  stereo-isomeric  with  the  above  acids  ;  whilst  the  galactoses 
yield  galactonic  and  mucic  acids,  also  stereo-isomeric  with  the  preceding  acids. 
Moreover,  when  reduced  by  sodium  amalgam  these  sugars  yield  hexahydric 
alcohols  ;  e.g.,  the  mannoses  yield  mannitols,  the  dextroses  sorbitol,  and  the 
galactoses  dulcitol.  This  behaviour  on  reduction  shows  that  the  sugars  are  certainly 
open-chain  compounds,  for  the  above-named  alcohols  are  all  convertible  into  normal 
hexane  by  hydriodic  acid.  The  rule  already  referred  to  as  guiding  us  in  the 
interpretation  of  chemical  constitution,  namely,  that  one  carbon  atom  cannot  hold 
more  than  one  hydroxyl  group,  may  be  applied  to  these  sugars,  when  it  becomes 
evident  that  the  five  hydroxyl  groups  must  be  attached  to  five  separate  carbon 
atoms,  forming  one  primary  and  four  secondary  alcohol  groups  ;  the  sixth  carbon 
atom  may  constitute  the  aldehydic  carbon. 

The  ketonic  character  of  the  ketohexoses  follows  from  the  fact  that  wtien  oxidised 
they  yield  two  acids  (p.  624).  Thus,  the  lasvuloses  yield  trihydroxybutyric  acids, 
CH2OH-[CHOH]2-CO2H,  and  glycollic  acid,  CH2OH  C02H.  By  reduction,  these 
sugars  yield  mannitol.  The  position  of  the  ketone  group  in  the  open-chain  repre- 
senting the  Isevuloses  may  be  said  to  be  settled  by  the  following  facts.  When 
Isevulose  is  treated  with  HCN  it  yields  a  cyano-hydrin  which  is  almost  certain  to 
contain  the  group  :C(OH)(CN)  in  place  of  the  group  :CO  (p.  582)  ;  when  this 
cyano-hydrin  is  hydrolysed  it  yields  a  corresponding  carboxylic  acid  which  is 
equally  certain  to  contain  the  group  :C(OH)(COOH)  ;  when  this  acid  is  reduced  by 
hydriodic  acid,  it  yields  methylbutylacetic  acid,  the  structure  of  which  shows  that 
the  carbonyl  carbon  of  the  original  laevulose  must  have  had  one  carbon  atom 
attached  to  it  on  the  one  hand  and  four  carbon  atoms  attached  to  it  on  the  other 
hand.  The  following  equations  will  make  this  apparent  : 


73°  STEREOISOMERISM. 


(  i  )  CH2OH  -[CHOH]3-  ^O-CHgOH  +  HCN  =  CH2OH-[CHOH]3'  6r(OH)(CN)  'CH2OH 
(2)  CH2OH-[CHOH]3-6'(OH)(CN)-CH2OH  +  2HOH  = 

CH2OH-[CHOH]3-6'(OH)(COOH)-CH2OH  +  NH3 

(3)  CH2OH-[CHOH]3-6'(OH)(COOH)-CH2OH  +  i2HI  = 

CH3-[CH2]3'6'H(COOH)-CH3  +  I12  +  6H20. 


CH3-[CH2]3-CH(COOH)'CH3  or         '  >CH'COOH  is  methylbutylacetic  acid. 

CUtf 

When  dextrose  is  submitted  to  a  similar  series  of  reactions  it  yields  normal  hep- 
tylic  acid,  CH3-[CH2]4-CH2-COOH,  showing  that  the  aldehyde  group  is  at  the  end 
of  the  open-chain,  a  position,  indeed,  which  is  the  only  possible  one  for  the 

0 
•C^H  group. 

531.  Keference  must  now  be  made  to  the  stereoisomerism  of  compounds  con- 
taining a  number  of  asymmetric  carbon  atoms,  as  do  these  polyhydroxy-alcohols, 
aldehydes,  ketones  and  acids. 

It  was  shown  at  p.  621,  that  a  compound  containing  two  asymmetric  carbon 
atoms  can  exist  in  four  stereo-chemical  modifications,  when,  as  in  the  case  of 
tartaric  acid,  each  carbon  atom  is  attached  to  the  same  groups,  that  is,  when  the 
compound  is  of  the  type  abcC  —  Cabc.  Two  of  these  are  optically  active,  one 
inactive,  by  internal  compensation  and  one  inactive  by  external  compensation. 

In  the  case  of  a  compound  of  the  type  abcC  —  Ca'b'c'  there  can  be  no  inactivity 
by  internal  compensation.  A  little  reflection  will  show  that,  instead,  there  will  be 
four  optically  active  isomerides,  one  in  which  abc  and  a'Vc'  are  both  arranged  to 
cause  dextro-rotation,  one  in  which  they  are  both  arranged  to  cause  Isevo-rotation, 
and  two  in  which  they  are  oppositely  arranged.  In  addition  there  will  be  two 
externally  compensated,  inactive  forms. 

Now  the  pentahydric  alcohols,  CH2OH-CHOH'CHOH-CHOH-CH2OH,  and  the 
corresponding  dicarboxylic  acids,  have  two  asymmetric  carbon  atoms  (printed  in 
heavy  type)  and  are  of  the  form  abcC  —  Cabc.  Hence,  like  tartaric  acid,  they  occur 
in  a  d-form,  an  Z-form,  an  externally  compensated  or  d  +  Z-form,  and  an  internally 
compensated  or  i-form.  There  is,  however,  a  fifth,  viz.,  a  second  internally  com- 
pensated form  ;  for  although  the  central  carbon  atom  is  not  asymmetric,  being 
balanced  on  either  side,  it  has  an  H  and  an  OH  attached  to  it,  the  positions  of 
which  may  be  reversed. 

The  aldopentoses,  CH2OH-CHOH-CHOH'CHOH-CHO,  and  the  corresponding 
monocarboxylic  acids.  CH2OH[CHOH]3COOH,  have  3  asymmetric  carbon  atoms. 
Each  of  these  should  give  rise  to  a  +  and  a  -  form,  and  since  the  nature  of  the 
whole  compound  will  depend  on  which  carbon  atoms  have  their  attached  groups 
in  the  +  form,  and  which  have  them  in  the  -  form,  there  should  be  as  many  aldo- 
pentoses as  there  are  ways  of  writing  +  or  -  three  times,  e.g.,  +  +  +,  -  -, 
+  —  +,-  +  -,  and  so  on.  This  number  is  eight,  so  that  there  are  8  optically 
active  isomerides.  As  the  aldopentoses  are  of  the  type  abcG  —  Ca'b'c',  there  are  no 
internally  compensated  forms,  but  by  combining  pairs  of  the  optically  active  forms, 
four  racemic  or  externally  compensated  forms  are  possible. 

The  hexahydric  alcohols,  CH2OH-CHOH'CHOH-C  HOH'CHOH'CH2OH,  and 
corresponding  dicarboxylic  acids,  have  four  asymmetric  carbon  atoms,  so  that  the 
number  of  optically  active  isomerides,  should  be  discoverable  by  finding  the 
number  of  ways  of  writing  +  and  -  four  times.  This  will  be  found  to  be  16. 
But  these  alcohols  are  of  the  type  abcC—Cabc,  wherefore  those  forms  in  which  the 
+  and  -  are  similarly  arranged,  but  in  opposite  order,  e.g.,  +  -  +  -,-  +  -+, 
are  identical,  reducing  the  essentially  different  ways  of  writing  +  and  -  to  10, 
two  of  which  represent  internally  compensated  molecules,  leaving  8  active 
isomerides.  In  addition  there  should  be  four  racemic  forms. 

Now  the  aldohexose  formula,  CH2OH'C  HOH-CHOH'CHOH-CHOH'CHO, 
also  contains  four  asymmetric  carbon  atoms,  and  is  of  the  type  abcC  —  Ca'b'c',  so 
that  all  1  6  isomerides  exist,  none  of  which  is  internally  compensated.  Besides 
these  there  should  be  8  racemic  forms.  At  present  1  1  of  the  optically  active  forms 
are  known,  viz.,  d-  and  Z-mannose,  d-  and  Z-glucose,  d-  and  Z-gulose,  d-  and  Z-galac- 
tose,  d-  and  Z-idose,  and  ^-talose. 

The  ketohexoses,  CH2OH'C  HOH'C  HOH-CHOH-CO'CH2OH,  contain  3  asym- 
metric carbon  atoms  and  are  of  the  type  abcC  —  Ca'b'c'  ;  stereoisomerism  among 
them,  therefore,  is  similar  to  that  among  the  aldopentoses. 


CANE-SUGAR. 

It  has  been  found  to  be  possible  to  orientate  those  carbon  atoms  which  have  a 
+  arrangement  of  groups  and  those  which  have  a  -  arrangement  in  the  glucosee 
but  for  a  description  of  the  arguments  employed,  the  student  must  be  referred 
the  chemical  dictionaries. 

532.  The  Disaccharides.— The  members  of  this  class  of  sugars  are 
characterised  by  being  converted  by  hydrolysis  into  two  molecules  of 
glucoses  (hence  the  synonym,  saccharo-bioses)* 

Cane-sugar  or  sucrose,  Gl2R2fllv  is  not  found  only  in  the  sugar- 
cane, but  in  many  other  plants,  such  as  beetroot,  sorghum,  maize,  barley, 
almonds,  walnuts,  hazel-nuts,  coffee-beans,  and  madder  root.  It  occurs 
also  in  the  sap  of  the  maple,  lime,  birch,  and  sycamore,  as  well  as  in  the 
juices  of  many  fruits  ;  in  these,  it  is  generally  accompanied  by  invert- 
sugar  (v.i.).  During  the  early  period  of  vegetation,  it  appears  that 
grape-sugar  and  fruit-sugar  are  formed,  and  that  these  become  cane- 
sugar  during  the  ripening.  The  green  sugar-cane  contains  much  dextrose 
and  laevulose,  which  are  afterwards  converted  into  sucrose.  Honey  con- 
tains cane-sugar  and  invert-sugar,  in  varying  proportions,  depending 
on  the  food  of  the  bees. 

To  extract  sugar  from  plants,  they  should  be  cut  up,  dried  at  a  tem- 
perature not  exceeding  100°  C.,  and  boiled  repeatedly  with  alcohol  of 
sp.  gr.  0.87,  which  deposits  the  sugar  in  crystals,  on  cooling. 

On  the  large  scale,  sugar  is  manufactured  by  crushing  the  cane  between  rollers, 
when  an  acid  juice  is  obtained,  containing  about  20  per  cent,  of  sucrose  ;  this  is 
neutralised  by  lime,  to  prevent  inversion  of  the  sugar,  and  heated  to  coagulate 
the  albumin.  This  is  skimmed  off  the  surface,  and  the  syrup  is  evaporated  till 
it  is  strong  enough  to  crystallise.  About  half  the  sugar  is  thus  obtained  in  brown 
crystals  (moist  sugar'),  the  remainder  being  partly  extracted  as  an  inferior  sugar 
(foots  sugar')  by  another  evaporation,  and  partly  left  as  uncrystallisable  sugar  in 
the  molasses  or  treacle.  To  refine  the  raw  sugar,  it  is  dissolved  in  water,  decolor- 
ised by  filtering  through  a  thick  bed  of  animal  charcoal,  and  evaporated  at  60°  C. 
(140°  F.)  in  a  copper  vacuum-pan  connected  with  an  air-pump,  since  a  higher 
temperature  would  invert  the  sugar.  It  may  then  be  obtained  in  large  crystals, 
sugar-candy,  or,  by  stirring,  in  minute  crystals  which  are  drained  in  conical 
moulds,  and  washed  with  a  saturated  solution  of  sugar  till  they  form  white  loaf- 
sugar. 

Sugar  is  extracted  by  a  similar  process  from  the  juice  of  the  white  beetroot. 
The  juice  contains  about  10  per  cent,  of  sugar,  about  half  of  which  is  obtained  in 
a  crystallised  state. 

A  larger  yield  of  crystallisable  sugar  has  been  obtained  from  cane  and  beet 
juice  by  the  strontia  process,  which  consists  in  precipitating  the  sugar  from  the 
boiling  solution  by  adding  strontium  hydroxide  ;  the  precipitate,  Cl2R^Ou(SrO^ 
is  washed  with  hot  water,  and  afterwards  suspended  in  boiling  water  and  allowed 
to  cool,  when  most  of  the  strontia  is  deposited  as  hydroxide,  and  the  remainder  is 
precipitated  from  the  solution  by  C02. 

Sometimes  the  potassium  salts  which  are  present  in  the  molasses,  and  hinder 
crystallisation,  are  precipitated  in  the  form  of  alum  by  adding  aluminium  sulphate. 

533.  Properties  of  Sucrose. — It  crystallises  in  monoclinic  prisms,  which 
are  insoluble  in  absolute  alcohol,  but  dissolve  to  almost  any  extent  in 
boiling  water.      100  parts  of  saturated  syrup  at  20°  C.  contain  67  of 
sugar ;  the  solution  of  sugar  is  dextro-rotatory.     When  boiled  with 
dilute  acids  it  is  hydrolysed  to  a  mixture  of  equal  weights  of  dextrose 
(d-glucose)  and  tevulose  (d-f  ructose),  CI2H22On  +  H20  =  C6H1206  +  C6H1206. 

*  In  one  system  of  nomenclature,  they  are  termed  dipentons,  dihexom,  &c.,  according-  as  the 
glucoses  produced  by  the  hydrolysis  are  pentoses  or  hexoses.  Thus,  arabinon,  C10H18Oft 
(from  gum),  is  a  dipenton,  since  it  yields  two  molecules  of  arabinose  by  hydrolysis ;  cane- 
sugar  is  a  dihexon,  since  it  yields  dextrose  and  lasvulose  by  hydrolysis. 


732  COMPOUNDS   OF  SUGAR. 

This  mixture  is  known  as  invert-sugar,  since  it  is  Isevo -rotatory  (the 
laevo-rotation  of  leevulose  being  greater  than  the  dextro-rotation  of 
dextrose).  It  is  prepared  for  the  use  of  brewers  (see  foot-note,  p.  726). 
Sucrose  fuses  at  160°  C.  (320°  F.),  and  does  not  crystallise  on  cooling. 
If  kept  melted  for  some  time,  it  is  converted  into  a  mixture  of  dextrose 
and  Icevulosan ;  C12H22OH  =  C6H1206  +  C6H1005.  If  this  be  dissolved 
in  water,  and  yeast  added,  the  dextrose  ferments,  but  the  Isevulosan  is 
unaltered.  When  further  heated,  but  below  190°  C.  (374°  F.), 
sucrose  loses  2H2O  and  becomes  brown,  yielding  caramelan,  C12H]809, 
an  amorphous,  brittle,  very  deliquescent  body,  colourless  when  pure,  and 
not  capable  of  reconversion  into  sugar.  Commercial  caramel,  used  for 
colouring  liquids,  is  a  mixture  of  this  with  other  bodies  formed  at 
higher  temperatures,  and  is  usually  made  by  heating  starch-sugar.  It 
is  bitter.  Cane-sugar  does  not  reduce  Fehling's  solution  unless  boiled 
with  it  sufficiently  long  to  effect  the  inversion  of  the  sugar. 

When  sugar  is  melted  in  a  little  water  (barley-water  was  formerly  used),  it 
cools  to  a  glassy  mass  (barley-sugar*)  enclosing  a  little  water  ;  this  dissolves  some 
of  the  sugar  and  deposits  it  in  crystals,  until  in  course  of  time  the  whole  mass  is 
opaque  and  crystalline.  Heated  with  water  at  160°  C.,  sucrose  yields  formic 
acid,  carbon  dioxide,  and  charcoal.  At  280°  C.  some  pyrocatechin  is  produced. 
Dilute  acids,  even  carbonic,  convert  sucrose  into  dextrose  and  Isevulose,  slowly  in 
the  cold,  and  quickly  on  heating. 

Fused  with  potash,  sucrose  gives  the  potassium-salts  of  oxalic,  formic,  acetic, 
and  propionic  acids,  together  with  acetone. 

Sucrose  acts  as  a  reducing-agent ;  if  ammonio-nitrate  of  silver  is  added  to  its 
solution,  followed  by  sodium  hydroxide,  a  mirror  of  silver  is  deposited  on  heating. 
The  antiseptic  properties  of  sucrose  are  well  known  :  a  strong  syrup  arrests  fermenta- 
tion. Weak  solution  of  sucrose,  in  contact  with  yeast,  is  first  converted  into 
dextrose  and  lasvulose,  and  then  into  alcohol  aad  carbon  dioxide  (see  p.  562). 
Sugar  absorbs  ammonia  gas,  forming  C12H21(NH4)0U,  which  decomposes  again  on 
exposure  to  air. 

Sucrose  behaves  like  a  weak  acid  to  strong  bases.  Sodium  sucrate,  C12H21NaOn, 
is  precipitated  when  strong  caustic  soda  is  added  to  an  alcoholic  solution  of 
sugar.  Slaked  lime  is  easily  dissolved  by  solution  of  sugar  ;  if  equal  molecules 
of  sugar  and  lime  be  dissolved  in  cold  water,  and  alcohol  added,  a  precipitate  of 
CaO.C^HsoOn,  is  obtained,  but  if  an  excess  of  lime  be  employed,  the  precipitate, 
is  2CaO.C]12H22011.  When  the  solution  of  either  of  these  is  boiled,  it  deposits 
3CaO.  C12HijOu,  which  requires  more  than  100  parts  of  cold  water  and  200  parts 
of  boiling  water  to  dissolve  it,  but  dissolves  readily  in  solution  of  sugar.  All 
these  compounds  are  decomposed  by  C02. 

If  strontium  hydroxide  be  added  to  a  boiling  solution  containing  15  per  cent, 
of  sucrose,  the  compound  2SrO.Cj2H2.jOn,  separates  as  a  granular  precipitate, 
and  when  2.5  molecular  weights  of  the  hydroxide  have  been  added,  the  precipi- 
tation of  the  sugar  is  nearly  complete.  If  the  precipitate  be  stirred  with  boiling 
water,  it  decomposes,  on  cooling,  forming  sugar  and  strontium  hydroxide. 

Iron  is  much  corroded  by  sugar,  in  the  presence  of  air,  the  metal  being  dis- 
solved as  ferrous  sucrate,  C12H20Fe"011  (?),  which,  in  contact  with  air  and  mois- 
ture, deposits  ferric  hydroxide,  and  is  reconverted  into  sugar,  which  attacks  a 
fresh  portion  of  the  iron.  Lead  is  also  attacked  and  dissolved  by  sugar  solution, 
especially  when  heated.  On  boiling  lead  hydroxide  with  solution  of  sugar,  it  is 
dissolved,  and,  as  the  solution  cools,  it  deposits  diplumbic  sucrate,  C12H]8Pb2Ou.Aq, 
as  a  white  powder,  which  loses  its  water  at  100°  C.  The  sugar  may  be  completely 
precipitated  in  this  form.  Triplumbic  sucrate,  C12H16Pb3On,  is  precipitated  when 
soda  is  added  to  a  mixture  of  solutions  of  lead  acetate  and  sugar  ;  it  may  be 
crystallised  in  needles  from  sugar  solution. 

Many  metallic  oxides  form  compounds  with  sugar  which  are  readily  soluble  in 
alkalies,  so  that  the  addition  of  sugar  to  solutions  of  copper  and  iron,  for  example, 
prevents  their  precipitation  by  alkalies.  If  solution  of  sucrose  be  mixed  with  cupric 
sulphate,  and  potash  gradually  added,  a  blue  precipitate  of  Cu(OH)2  is  formed, 
which  dissolves,  when  more  potash  is  added,  to  a  deep-blue  liquid,  which  may  be 


MILK-SUGAR.  733 


heated  to  boiling  without  change,  but  if  long  boiled  or  kept,  deposits  cuprous  oxide 
or  hydroxide  as  a  red  or  yellow  precipitate. 

When  a  solution  containing  sugar  with  one-fourth  of  its  weight  of  common 
sat  is  allowed  to  evaporate  spontaneously,  it  deposits  deliquescent  rhombic 
prisms  of 


^^n... 

Strong  sulphuric  acid  converts  dry  sucrose  into  a  brown  mass,  but  if  water  be 
present,  or  if  heat  be  applied,  the  mixture  froths  up  and  blackens,  evolving  CO 
C02,  and  S02  gases.  Dilute  sulphuric  and  hydrochloric  acids,  when  boiled  with 
sugar,  convert  it  into  a  brown  substance,  partly  soluble  in  alkalies,  and  containing 
about  63  per  cent,  of  carbon  (sugar  contains  42).  Formic  acid  (containing  only 
26  per  cent,  of  carbon)  is  found  in  the  solution.  Strong  nitric  acid  dissolves 
sucrose,  and  converts  it,  on  heating,  into  oxalic  and  saccharic  acids.  When 
heated  with  dilute  nitric  acid,  it  yields,  besides  these,  acetic,  tartaric,  hydrocyanic, 
and  carbonic  acids,  with  evolution  of  N,  NO,  and  N203.  A  cold  mixture  of  strong 
nitric  and  sulphuric  acids  converts  sugar  into  a  resinous  mass,  which  is  insoluble 
in  water  and  soluble  in  alcohol.  It  explodes  when  heated  or  struck,  and  appears 
to  be  sucro-tetra-nitrate,  C12H1807(N03)4. 

534.  Milk-sugar  or  lactose  (lactobiose),  CI2H22On  +  H20,  is  prepared 
by  evaporating  the  whey  of  milk  to  a  syrup,  and  setting  it  aside  in  a 
cold  place  to  crystallise.  The  commercial  product  is  generally  crystal- 
lised round  strings  or  slender  wooden  rods.  It  is  purified  by  dissolving 
it  in  water  and  precipitating  by  alcohol.  The  crystals  lose  their  water 
of  crystallisation  at  130°  C.  Lactose  is  much  less  sweet  and  less 
soluble  than  sucrose,  requiring  6  parts  of  cold  and  2.5  parts  of  hot 
water.  It  is  insoluble  in  alcohol  and  ether.  By  rapidly  boiling 
the  aqueous  solution,  lactose  may  be  obtained  in  anhydrous  crystals, 
which  dissolve  in  3  parts  of  cold  water,  but  quickly  deposit  in  the 
hydrated  form.  Cow's  milk  contains  about  4.7  per  cent,  of  milk- 
sugar. 

Lactose  is  a  much  stronger  reducing-agent  than  sucrose,  and  precipi- 
tates cuprous  oxide  when  gently  heated  with  alkaline  cupric  solution  ; 
a  fine  mirror  of  silver  is  deposited  when  silver  nitrate  is  mixed  with 
ammonia,  potash,  and  lactose,  and  gently  warmed.  Milk-sugar  also 
differs  from  cane-sugar  in  becoming  brown  when  heated  with  potash. 
It  is  dextro-rotatory  and  shows  bi-rotation.  When  boiled  with  diluted 
acids,  it  is  hydrolysed  to  dextrose  (^-glucose)  and  galactose.  Yeast 
causes  a  similar  change,  subsequently  fermenting  the  dextrose  to 
alcohol  (as  in  koumiss).  Putrefaction  -ferments,  such  as  old  cheese, 
ferment  milk-sugar  to  lactic  acid  (see  p.  603).  It  is  unchanged  by 
heating  to  100°  C,  with  solution  of  oxalic  acid,  which  inverts  sucrose. 
When  oxidised  by  nitric  acid,  it  yields  mucic  and  saccharic  acids.  By 
reduction  with  sodium-amalgam,  lactose  yields  mannite,  dulcite,  iso- 
propyl  alcohol,  and  secondary  hexyl  alcohol.  In  its  behaviour  with 
bases  milk-sugar  resembles  cane-sugar. 

Maltose,  C12H22On  +  H2O,  is  formed  by  the  action  of  malt  upon  starch, 
and  was  formerly  mistaken  for  dextrose,  but  it  is  less  soluble  in  alcohol, 
more  dextro-rotatory,  and  does  not  reduce  a  weak  acetic  solution  of 
cupric  acetate.  To  prepare  maltose,  starch  (100  parts)  is  ground  up 
with  water  (450  parts)  and  gelatinised  by  heating  on  a  water-bath  ;  after 
cooling,  crushed  malt  (7  parts)  is  added,  and  the  mixture  kept  at  about 
65°  C.  (149°  F.)  for  an  hour.  The  malt  (germinated  barley)  contains 
an  albuminoid  substance  termed  diastase,  which  acts  like  a  ferment  upon 
the  starch,  causing  it  to  undergo  hydrolysis  into  maltose  and  dextrin— 

3C6H1005  (starch)  +  H20  =  C^H^On  (mattose)  +  C6H1006  (dextrin). 


734  STARCH. 

The  mixture,  which  has  now  become  much  more  liquid,  is  boiled,  filtered, 
evaporated  to  a  syrup  on  a  water- bath,  and  boiled  with  alcohol,  which 
leaves  the  dextrin  undissolved,  and,  on  standing  for  some  days,  deposits 
the  maltose  in  crusts  of  fine  needles,  which  become  anhydrous  at  100°  C. 
Maltose  is  easily  fermented  by  yeast,  yielding  alcohol  and  carbon  dioxide; 
C12H220U  +  H20  =  4C2H60  +  4CO2.  Boiling  with  dilute  acids  converts 
it  into  glucose;  C12H220U  +  H2O  =  206H1206.  It  reduces  the  alkaline 
cupric  solution  when  warmed,  but  not  the  acetic  solution. 

Trehalose,  or  my  cose,  C^H^O-u  +  2H20,  is  found  in  the  trekala  manna,  or  nest- 
sugar,  of  Persia,  an  edible  substance  produced  by  an  insect  from  the  tree  on  which 
it  lives.  It  is  also  found  in  the  ergot  of  rye  and  in  certain  edible  fungi,  whence  its 
name  of  mycose.  Alcohol  extracts  it  from  the  manna.  It  crystallises  in  prisms 
which  have  a  sweet  taste,  and  fuses  at  100°  C.,  losing  their  water  at  130°  C.  It  is 
soluble  in  water  and  in  hot  alcohol,  but  not  in  ether.  It  is  more  strongly  dextro- 
rotatory than  cane-sugar. 

535.  The  constitution  of  the  disaccharides  is  not  yet  known  ;  all  that  can  be 
said  is  that  they  are  probably  anhydrides  formed  from  two  molecules  of  glucoses, 
since  they  break  up  into  these  by  absorption  of  water.     The  two  molecules  may  be 
of  the  same  glucose  (as  in  the  case  of  maltose)  or  of  different  glucoses  (as  in  the 
case  of  cane-sugar).     Cane-sugar  and  milk-sugar  yield  octacetyl-derivatives  when 
treated  with  acetic  anhydride  and  sodium  acetate,  showing  that  they  are  octohydric 
alcohols.     It  will  be  noticed  that  maltose  is  the  only  disaccharide  which  is  directly 
fermentable  with  yeast  and  directly  reduces  Fehling's   solution.     Maltose  and 
lactose  yield  osazones,  showing  that  they  are  aldehydic. 

536.  Trisaccharides. — These  yield  three  molecules  of  hexoses  when  hydrolysed. 
Rajfinose,   or.  melitose,  C18H32016  +  5H20,   is   the  chief   constituent   of   Australian 
manna,  an  exudation  from  Eucalyptus  mannifera,  and  occurs  in  cotton  seeds  and 
sugar-beets.     It  crystallises  in  fine  needles.     It  is  but  slightly  sweet,  and  dissolves 
in  water  and  alcohol.     Melitose  does  not  reduce  alkaline  cupric  solution,  and  is 
dextro-rotatory.     Diluted  acids  and  yeast  convert  it  into  ^-fructose  and  melibiose, 
C^H^O-u,  which  subsequently  breaks  up  into  dextrose  and  galactose. 

Melezitose,  CjgH^Ojg  +  2H20,  is  extracted  by  alcohol  from  the  manna  exuding 
from  the  larch.  Its  crystals  lose  H20  at  100°  C.  and  are  sweet  enough  to  be  used 
as  a  substitute  for  sugar.  It  does  not  easily  reduce  alkaline  cupric  solution,  and  is 
dextro-rotatory.  It  is  converted,  though  not  easily,  into  dextrose  by  boiling  with 
dilute  acids. 

THE  STABCHES  AND  CELLULOSES  (POLYSACCHARIDES). 

537.  Starch,  or  amylose,  (C6H10O5)K,  differs  from  the  sugars  in  being 
insoluble  in  cold  water,  and  therefore  tasteless,   and  in  not  forming 
crystals,  but  having  an  organised  structure  visible  under  the  microscope, 
which  is  not  seen  in  any  artificial  product  of  the  laboratory.     It  is  an 
indispensable  constituent  of  all  plants  (except  fungi),  and  is  stored  up 
in  their  seeds  and  tubers,  for  the  nourishment  of  the  young  shoots. 

To  obtain  starch  on  the  small  scale,  flour  (which  contains  about  60  per 
cent.)  is  mixed  with  cold  water  to  a  stiff  dough,  which  is  tied  up  in  fine 
muslin  and  well  kneaded  in  a  basin  of  distilled  water,  when  the  grains 
of  starch  pass  through,  leaving  the  tenacious  gluten  in  the  muslin.  The 
milky  fluid  is  left  to  settle  for  a  few  hours,  the  bulk  of  the  water 
poured  off,  the  starch  collected  on  a  filter,  and  dried  by  exposure  to 
air. 

On  the  large  scale,  in  England,  starch  is  commonly  made  from  rice,  which 
contains  about  80  per  cent.  The  rice  is  soaked  for  24  hours  in  water  containing 
about  0.3  per  cent,  of  caustic  soda  ;  it  is  then  washed,  ground  into  flour,  and  again 
soaked  for  two  or  three  days  in  a  fresh  alkaline  solution  ;  the  starch  is  allowed  to 
settle,  and  the  alkaline  liquid,  holding  the  gluten  in  solution,  is  drawn  off.*  The 

*  The  gluten  is  sometimes  precipitated  by  sulphuric  acid,  and  used  as  a  feeding-stuff. 


KINDS  OF  STAECH. 

starch  is  then  stirred  up  with  water,  the  heavier  woody  fibre  allowed  to  subside 
and  the  milky  liquid  run  off  into  another  vessel,  where  it  deposits  the  starch 
Ihis  is  transferred  to  drainers  where  it  partly  dries,  and  the  drying  is  finished  by 
gradual  application  of  heat ;  this  splits  the  starch  into  roughly  prismatic  fragments 
which  still  retain  about  18  per  cent,  of  water.  Commercial  starch  is  glneralh' 
coloured  blue  by  a  little  ultramarine  or  smalt,  in  order  to  correct  the  yellow  tint  of 

Being  possessed  of  an  organised  structure,  starch  varies  in  external 
aspect,  according  to  the  plant  from  which  it  is  obtained.  When 
powdered  starch  is  examined  by  the  microscope,  it  appears  in  grains 
resembling  some  of  those  in  Fig.  283  :  the  largest  are  those  of  potato- 
starch  (P),  about  ^  inch  in  the  longer  diameter ;  the  smallest  are 
those  of  rice  (B),  about  ^^  inch  in  diameter:  wheat-starch  (W)  has 
nearly  spherical  granules,  T^w  inch  in  diameter ;  (A)  is  the  starch  of 
arrowroot,  from  Maranta  arundinacea,  a  tropical  plant.  When 


Fig.  283. 

moistened  with  water  and  viewed  under  a  microscope,  provided  with  a 
polariser  and  analyser,  starch  granules  behave  like  doubly  refracting 
crystals,  exhibiting  a  black  cross  when  the  planes  of  polarisation  of  the 
polariser  and  analyser  are  at  right  angles,  which  becomes  white  when 
the  analyser  is  turned  through  an  angle  of  90°  ;  this  is  best  seen  in  the 
starch  of  potato,  Indian  corn,  and  tons  le  mois  (from  Canna  coccinea  of 
the  Arrowroot  order).  The  starch  granules  are  composed  externally  of 
starch  cellulose,  or  farinose,  and  internally  of  granulose,  and,  perhaps, 
other  isomeric  bodies. 

Cold  water  does  not  attack  starch,  unless  the  cell-walls  are  broken  by 
trituration,  when  a  part  of  the  granulose  dissolves,  yielding  a  solution 
strongly  dextro-rotatory  and  coloured  blue  by  iodine,  which  gives  a 
violet  colour  to  farinose.  When  starch  is  heated  with  water  to  about 
50°  0.,  the  granules  begin  to  burst,  which  is  completed  at  about 
70°  C. ;  the  granulose  then  dissolves  to  a  viscous  liquid,  becoming  a 
jelly  on  cooling  and  a  gummy  mass  when  dried.  The  cell-wall  may  be 
dissolved  in  the  cold  by  strong  alkalies,  acids,  and  zinc  chloride. 
Heated  with  glycerine  at  190°  C.,  starch  is  dissolved,  and  if  the  solution 
be  mixed  with  alcohol,  soluble  starch  is  precipitated,  and,  while  moist, 
may  be  dissolved  by  water  or  weak  alcohol.  Its  strong  aqueous 
solution  becomes  a  jelly  on  standing. 

The  conversion  of  starch  into  maltose  and  dextrin  by  the  action  of 
diastase  has  already  been  mentioned.  Other  enzymes,  notably  the 
ptyalin  of  the  saliva,  effect  a  similar  change. 

The  aqueous  solution  of  starch  is  precipitated  by  alcohol,  by  baryta  and  lime, 
and  by  ammoniacal  lead  acetate,  which  gives  C6H1005.PbO.  For  the  behaviour 
of  starch  with  iodine,  see  p.  194.  When  boiled  with  diluted  sulphuric  or  hydro- 
chloric acid,  starch  is  converted  into  d-glucose,  maltose  and  dextrin  (p.  726). 

When  starch  is  heated  with  acetic  anhydride,  it  yields  an  insoluble  compound, 


73^  BRITISH   GUM. 

which  may  be  represented  as  C12H14O4(C2H302)6.  This  yields  starch  and  potassium 
acetate  when  saponified  by  potash,  showing  that  starch  is  a  hexahydric  alcohol,. 
C12Hi404(OH)6.  Strong  sulphuric  acid  dissolves  starch  in  the  cold,  apparently 
forming  a  soluble  sulpho-acid.  When  heated,  carbonisation  occurs. 

Heated  at  about  205°  C.  for  some  hours,  starch  becomes  brownish  and  soluble  in 
cold  water,  having  been  converted  into  the  isomeric  compound  dextrin.  This 
conversion  of  starch  into  a  soluble  form  is  important  in  the  preparation  of  food. 
In  toasting  bread  a  portion  of  the  starch  becomes  dextrin,  which  is  dissolved  in 
toast  and  water.  Further  heated,  starch  is  carbonised  and  yields  products  of 
destructive  distillation  resembling  those  from  sugar. 

538.  Dextrin,  or  British  gum,  C6H10O5,  is  prepared  by  moistening 
starch  with  one-third  of  its  weight  of  weak  nitric  acid  (0.66  per  cent.), 
drying  it  in  air,  and  heating  to  115°  C.     There  are  several  varieties, 
e.g.,  erythro-dextrin,  coloured  red  by  iodine- water :    and  achro-dextrin,, 
not  coloured  by  iodine.     The  erythro-dextrin  is  formed  at  first  when 
starch  is  boiled  with  diluted  sulphuric  acid,  so  that  the  blue  starch- 
reaction  with  iodine  gives  place  to  a  red,  and  finally  ceases.    Commercial 
dextrin  gives  a  violet  colour  with  iodine,  because  it  contains  unaltered 
starch ;  and  erythro-dextrin ;  it  is  sweet  from  the  presence  of  glucose. 
It  may  be  purified  by  dissolving  in  water  and  precipitating  by  alcohol. 

Dextrin  dissolves  when  soaked  in  water,  and  is  left  on  evaporation  as 
a  transparent  mass.  Its  solution  has  twice  the  dextro-rotatory  power  of 
dextrose.  Pure  dextrin  does  not  reduce  Fehling's  solution  ;  commercial 
dextrin  does,  though  not  so  quickly  as  glucose.  It  shows  aldehydic 
properties,  and  when  boiled  with  dilute  H2S04,  or  HC1,  it  is  converted 
into  dextrose.  Nitric  acid  oxidises  it  to  oxalic  acid,  while  ordinary  guin 
yields  mucic  acid.  Heated  with  acetic  anhydride,  it  yields  an  acetyl- 
compound  isomeric  with  that  from  starch  (see  above),  which  is  converted 
into  the  dextrin- derivative  at  160°  C.  Dextrin  is  used  by  calico- 
printers  for  thickening  their  colours ;  it  is  used  for  adhesive  stamps,  for 
confectionery,  and  for  stiffening  surgical  bandages. 

Inulin,  (C6H1005)6'H20,  was  first  obtained  from  elecampane  root  (Inula  helenium), 
an  aromatic  medicinal  plant.  It  is  also  found  in  the  roots  of  the  dahlia,  and  in  the 
Jerusalem  artichoke,  which  belong  to  the  same  sub-order  (Corymbiferce),  and  in 
the  roots  of  dandelion  and  chicory,  belonging  to  the  Cichoracetc  ;  all  being  plants 
of  the  natural  order  Composites.  It  may  be  extracted  from  dahlia  roots,  which 
contain  10  per  cent.,  by  boiling  with  water,  which  deposits  the  inulin  in  minute 
spheres  on  cooling.  It  'is  not  coloured  blue  by  iodine,  and  does  not  reduce  Fehling's 
solution.  It  is  insoluble  in  alcohol.  Solution  of  inulin  is  laevo-rotatory.  When 
boiled  with  dilute  sulphuric  acid,  it  yields  laevulose.  It  also  differs  from  starch  in 
being  unchanged  by  diastase.  It  melts  at  160°  C. 

Glycogen,  or  animal  starch,  (C6H1005)W,  occurs  in  the  liver,  blood,  flesh,  yolk  of 
egg,  and  oysters,  where  it  is  said  to  amount  to  9.5  per  cent,  of  the  dried  fish.  It  is 
most  abundant  in  the  liver  during  active  digestion,  and  disappears  quickly  after 
death,  being  converted  into  dextrose  by  fermentation.  To  prepare  glycogen,  the 
minced  liver  is  extracted  with  water  as  long  as  it  runs  off  milky  ;  the  albumin  is 
coagulated  by  boiling,  and  the  filtrate  mixed  with  alcohol,  which  precipitates  the 
glycogen  ;  it  is  purified  by  boiling  with  weak  acetic  acid  to  remove  albuminoids, 
again  precipitating  with  alcohol,  and  washing  with  ether  to  remove  traces  of  fat. 
When  dried  over  CaCl2,  glycogen  has  the  formula  (C6H1005)2.H2O  ;  it  loses  the  H20 
at  100°  C.  It  is  an  amorphous  powder  like  starch,  swelling  in  water,  and  yielding 
a  turbid  solution  on  heating.  The  solution  is  strongly  dextro-rotatory,  and  gives 
a  wine-red  colour  with  iodine.  Glycogen  does  not  reduce  Fehling's  solution,  and 
is  not  fermented  by  yeast.  Diastase  converts  it  into  maltose  and  dextrin,  as  it  does 
starch  (p.  733).  It  is  converted  into  dextrose  when  boiled  with  dilute  H2S04  or 
HC1,  or  when  placed  in  contact  with  saliva  or  pancreatic  juice. 

539.  Gums. — The  carbohydrates  of  this  group  resemble  dextrin  in 
yielding  viscous  solutions  in  water,  in  being  precipitated  by  alcohol,  and 


GUMS.  737 

in  conversion  into  sugars  by  boiling  with  dilute  acids  :  but  the  gums 
have  a  marked  acid  tendency,  though  they  do  not  form  well-defined 
salts.  Moreover,  the  gums  yield  mucic  acid  when  oxidised  by  nitric  acid 

Arabin,  or  arabic  acid,  2C6H1005  +  H20,  occurs  in  gum  arable,  an 
exudation  from  various  tropical  acacias.  It  is  extracted  by  dissolving 
the  gum  m  water,  acidifying  with  HC1,  and  adding  alcohol,  which 
precipitates  it  in  white  flakes  ;  or  the  acid  solution  may  be  dialysed 
(p.  278),  when  the  aqueous  solution  of  arabin  remains  in  the  dialyser. 
The  pure  aqueous  solution  is  not  precipitated  by  alcohol,  but  the 
presence  of  a  minute  quantity  of  a  base  or  a  salt  determines  the  preci- 
pitation. The  aqueous  solution  has  an  acid  reaction,  and,  on  evapora- 
tion, leaves  a  vitreous  mass,  which  loses  water  above  120°  C.,  yielding 
metarabin  isomeric  with  dextrin.  This  does  not  dissolve  in  water,  but 
increases  greatly  in  bulk.  Arabic  acid  decomposes  alkali  carbonates, 
and^  the  composition  of  its  salts  indicates  the  formula  C^H^O^  or 
-^-2^36^-64^33-  ^  appears  to  occur  in  gum  arabic  as  arabates  of  calcium, 
magnesium,  and  potassium,  since,  when  incinerated,  the  gum  leaves 
about  3  per  cent,  of  ash  containing  those  metals. 

Arabin  gives  a  characteristic  reaction  with  CuS04,  followed  by  KOH,  which 
produces  a  blue  precipitate,  insoluble  in  excess,  and  neither  blackened  nor  reduced 


by  boiling,  but  collecting  into  a  blue  mass,  leaving  the  liquid  colourless. 
arabin  is  boiled  with  dilute  H2S04  it  is  converted  into  arabinose  or  gum- 

' 


When 

-sugar^ 

(p.  725)  ;  substances  which  yield  pentoses  on  hydrolysis  are'  known  as 
pentosans. 

Gum  Senegal,  obtained  from  similar  sources,  is  used  by  calico-printers  to  thicken 
their  colours.     It  is  darker  in  colour  than  gum  arabic,  but  also  consists  essentially 
of  arabin. 
Metarabin,  or  cerasin,  C^H^Ojo,  is  found  in  the  gum  of  the  cherry-tree  and 


,  ,     ^ 

beech-tree  (wood-gum},  probably  as  calcium  metarabate,  which  remains  undissolved 
after  the  calcium  arabate  which  accompanies  it  has  been  extracted  by  water  ;  when 
heated  with  lime-water,  it  is  converted  into  calcium  arabate,  which  dissolves.  It 
is  also  found  in  the  residue  of  beet-root  from  which  the  juice  has  been  expressed. 
By  hydrolysis  it  yields  xylose  (p.  725),  and  is  therefore  a  pentosan. 

Bassorin,  very  similar  to  cerasin,  occurs  in  Bassora  gum  and  in  gum  tragacanth^ 
the  exudation  from  Astragalus  tragacantha,  a  Papilionaceous  plant.  These  gums 
do  not  dissolve  in  water  like  gum  arabic,  but  swell  up  immensely  by  absorption 
of  water,  and  form  a  mucilage.  When  boiled  with  dilute  acids  it  is  converted 
into  dextrose.  A  substance  very  similar  to  bassorin  is  formed  in  the  ropy  or 
viscous  fermentation  of  saccharine  liquids.  The  mucilaginous  liquids  obtained  by 
boiling  linseed  (linseed  tea),  quince-seed,  and  marshmallow  root  with  water,  contain 
bassorin,  or  some  allied  body. 

Gelose,  orparabin,  C^H^Ojj,  forms  the  greater  part  of  Ceylon  moss  (Gracilaria 
lichenoides)  and  China  moss  (#.  spinosa),  sea-  weeds  which  are  used  for  making 
soups  and  jellies.  Carrots  and  beet  also  contain  gelose.  When  dissolved  in  as 
much  as  500  parts  of  hot  water,  it  sets  to  a  jelly  on  cooling.  It  also  differs  from 
the  other  bodies  of  this  group  by  dissolving  in  dilute  acids  and  being  precipitated 
by  alkalies.  When  long  heated  with  alkalies  it  is  converted  into  arabin.  It  does 
not  appear  to  yield  a  sugar  when  boiled  with  dilute  acids. 

540.  Cellulose,  (C6H10O5)12,  is  the  substance  which  composes  the  walls 
of  plant-cells,  and  is  left  undissolved  after  the  matters  contained  in 
and  encrusting  the  cells  have  been  removed  by  various  solvents. 
Hence,  white  filter-paper,  prepared  cotton-wool,  and  well-washed  linen 
consist  of  nearly  pure  cellulose.  To  purify  these  they  are  digested 
successively  with  dilute  KOH,  dilute  HC1,  water,  alcohol,  and  ether  ; 
the  encrusting  substances  of  the  cellulose  are  thus  removed. 

When  pure,  cellulose  is  white,  opaque,  exhibits  an  organised  structure, 
is  infusible  and  insoluble  in  all  ordinary  solvents.  It  may  be  dissolved 


73$  CELLULOSE. 

by  Schweitzer's  reagent,  a  solution  of  cupric  hydroxide  in  ammonia. 
The  cellulose  is  precipitated  in  flakes  on  addition  of  an  acid.  When 
contact  with  the  Schweitzer's  reagent  is  sufficiently  brief  to  attack  the 
superficial  fibres  only,  and  the  cellulose  fabric  is  then  pressed  and  dried, 
it  becomes  impervious  to  water ;  in  this  way  the  green  waterproof 
coverings  known  as  Willesden  paper  are  manufactured.  Chlorine,  in 
presence  of  moisture,  slowly  attacks  cellulose,  so  that  paper  becomes 
brittle  if  the  excess  of  bleach  be  not  killed  by  an  antichlore  (p.  221). 
Iodine  does  not  give  a  blue  colour  with  pure  cellulose,  but  the  cellular 
tissue  of  plants  is  often  blued  by  it,  from  the  presence  of  a  little 
starch.  Ferric  oxide  slowly  oxidises  cellulose,  and,  since  the  ferrous 
oxide  is  repeatedly  oxidised  again,  a  continual  oxidation  and  corrosion 
of  the  cellulose  is  kept  up,  as  may  be  seen  from  the  effect  of  iron-mould 
on  linen  and  of  rusty  nails  on  wood. 

Strong  sulphuric  acid  converts  dry  cellulose  into  a  gummy  mass 
which  dissolves  in  the  acid  with  very  little  colour  in  the  cold.  If  this 
solution  be  immediately  poured  into  water,  it  yields  a  gelatinous 
precipitate,  but  after  digestion  for  some  hours  with  the  acid,  a  clear 
solution  is  formed  in  water,  and  if  this  be  largely  diluted  and  boiled, 
the  cellulose  is  converted,  first  into  dextrin,  and  then  into  dextrose, 
which  may  be  obtained  as  a  syrup  by  neutralising  the  acid  liquid  with 
chalk,  filtering,  and  evaporating.  By  fermenting  this  dextrose,  the 
curious  transformation  of  rags  into  alcohol  may  be  accomplished. 
Cotton-wool  dissolves  in  a  mixture  of  sulphuric  acid  with  one-fourth 
its  weight  of  water,  and,  on  dilution,  a  precipitate  of  amyloid  is 
obtained,  which  is  isomeric  with  cellulose,  but  is  coloured  a  fugitive 
blue  by  iodine. 

By  immersing  unsized  paper  in  a  cold  mixture  of  strong  sulphuric 
acid  with  half  its  volume  of  water,  it  becomes  converted  externally 
into  amyloid.  This  is  turned  to  account  for  making  vegetable  parch- 
ment, which  is  five  times  as  strong  as  paper,  and  is  waterproof. 
After  immersion  in  the  acid,  the  paper  is  thoroughly  washed  with 
water  and  finally  with  weak  ammonia.  A  strong  solution  of  zinc 
chloride  affects  the  paper  in  the  same  way.  The  parchment  paper  is 
translucent ;  it  may  be  boiled  in  water  without  disintegration ;  it 
receives  many  useful  applications,  as  for  luggage  labels  which  are  not 
easily  torn  or  destroyed  by  rain,  as  a  substitute  for  bladder  in  tying 
over  preserves,  &c.,  and  for  making  dialysers. 

"When  cellulose  is  left  for  twelve  hours  in  H2S04  of  sp.  gr.  1.453,  or  in  HC1  of  sp. 
gr.  1.16,  it  is  converted  into  a  brittle  mass  of  hydro-cellulose,  C12H22011(?),  which  is 
more  easily  oxidised  than  cellulose,  and  dissolves  in  hot  potash.  This  is  applied 
for  dissolving  the  cotton  from  old  fabrics  containing  wool,  the  latter  being  left  as 
shoddy.  Dry  rot  is  ascribed  to  a  similar  change  in  the  wood  caused  by  acid 
substances  generated  in  its  fermentation. 

Cellulose  swells  up  and  becomes  gummy  when  in  contact  with  strong  potash  or 
soda  ;  on  heating  to  160°  C.  with  strong  potash,  it  dissolves,  and  the  solution, 
when  acidified,  yields  a  precipitate  isomeric  with  cellulose,  but  easily  soluble  in 
alkalies.  If  calico  be  soaked  for  half  an  hour  in  very  strong  potash  or  soda,  and 
washed  with  alcohol,  it  is  converted  into  C^B^K^O-u,  or  C^H^N^O^  (inercerisa- 
tion).  Both  compounds  are  decomposed  by  CO2.  When  treated  with  CS2  they 
form  thio-carbonates  which  are  soluble  in  water ;  the  solution  coagulates  spon- 
taneously, and  immediately  on  the  addition  of  salt  solution,  the  coagulum  being 
regenerated  cellulose.  Viscose  is  the  viscid  solution  of  these  thiocarbonates,  and  is 
applied  for  producing  a  glaze  of  cellulose  on  fabrics.  When  cellulose  is  boiled  with 


PYROXYLIN. 

potash  of  ep.  gr.  1.5  it  dissolves  to  a  brown  solution  which  deposits  brown  flakes 
(ulmicacid)  when  acidified  ;  but  on  prolonged  heating,  the  colour  disappears  and 
carbonate  oxalate  formate  and  acetate  of  potassium*  are  found  in  solution  By 
heating  cellulose  with  fused  potash,  abundance  of  potassium  oxalate  is  obtained 

(S6G   LstEal'lC  CtClCLjm 

Cellulose  was  the  name  originally  given  to  the  constituent  of  plants  which 
remains  after  treatment  with  reagents  that  may  be  supposed  to  remove  all  other 
constituents.  It  is  now  realised  that  this  residue  when  obtained  from  different 
plants  is  not  necessarily  the  same  substance.  Modern  workers  have  distinguished 
between  cotton  cellulose,  jute  cellulose,  and  straw  cellulose.  The  first  of  these  is 
characterised  by  its  resistance  to  chlorine,  by  the  fact  that  it  yields  no  furfurol 
when  distilled  with  acid,  and  by  being  precipitated  unchanged  from  its  solution  in 
a  mixture  of  CS2  and  NaOH  solution.  Jute  cellulose  is  somewhat  attacked  by 
chlorine,  yields  some  3-5  per  cent,  of  furfurol  when  distilled  with  acid,  and  is 
decomposed  by  NaOH  and  CS2.  Straw  cellulose  absorbs  a  considerable  proportion 
of  chlorine,  yields  some  15  percent,  of  furfurol,  and  is  coloured  red  by  aniline  salts  : 
it  also  is  decomposed  by  NaOH  and  CS2. 

For  the  detection  of  cellulose  in  the  microscopic  examination  of  tissues,  advan- 
tage is  taken  of  its  conversion  into  amyloid  by  zinc  chloride,  and  of  the  bluing  of 
this  by  iodine.  The  reagent  is  prepared  by  dissolving  6  per  cent,  of  KI  in  solu- 
tion of  ZnCl2  of  sp.  gr.  1.8,  and  adding  as  much  iodine  as  will  dissolve. 

By  heating  cellulose  with  8  parts  of  acetic  anhydride  in  a  sealed  tube  at  180°  C., 
it  may  be  converted  into  hexacetyl  cellulose,  or  cellulose  hexacetate — 

C12H20010  +  6(CH3CO)20  =  C12H1004(OCH3CO)6  +  6(CH3COOH). 

Cellulosetetr acetate  is  made  by  heating  cellulose  at  uo°C.  with  zinc  acetate  solu- 
tion and  treating  the  cooled  mass  with  acetyl  chloride.  It  dissolves  in  chloroform, 
from  which  it  may  be  obtained  in  films  by  evaporation. 

Oxy  cellulose  is  the  name  given  to  the  product  of  aldehydic  nature  obtained  by 
the  action  of  various  oxidising-agents  on  cellulose. 

541.  Action  of  nitric  acid  on  cellulose. — Cold  dilute  nitric  acid  (sp.gr. 
1.2)  does  not  act  on  cellulose  in  the  form  of  filter-paper,  and  scarcely 
when  heated  to  100°  C.  Acid  of  1.42  corrodes  it,  producing  amyloid  and 
malic  acid,  and,  on  boiling,  suberic  and  oxalic  acids.  Cotton,  linen,  or 
paper,  soaked  for  two  or  three  minutes  in  the  strongest  nitric  acid  and 
washed,  resembles  parchment,  and  is  waterproof  and  very  combustible, 
having  become  partly  converted  into  cellulose  hexanitrate,  or  pyroxylin 
(gun-cotton) ;  C12H1404(OH)6  +  6(HON02)  =  C12H1404(ON02)6  +  6HOH. 
This  change,  which  is  analogous  to  the  conversion  of  alcohol  into  the 
ethereal  salts,  is,  like  that  conversion,  much  facilitated  by  the  presence 
of  strong  sulphuric  acid,  which  may  either  act  simply  as  a  dehydrating- 
agent  or  may  form  an  intermediate  sul phonic  acid. 

If  pure  dry  cellulose  (prepared  cotton- wool)  be  steeped  for  some  time 
in  a  cold  mixture  of  equal  molecular  weights  of  the  strongest  nitric 
and  sulphuric  acids,  and  afterwards  thoroughly  washed,  and  dried  by 
exposure  to  air,  it  has  the  composition  of  cellulose  hexanitrate  above 
given,  retaining  the  organised  structure  of  the  original  cotton,  but 
being  somewhat  harsher  to  the  touch,  and  becoming  highly  electrified 
when  drawn  through  the  dry  hand. 

Pyroxylin  is  insoluble  in  water,  alcohol,  and  ether,  either  separately 
or  mixed,  but  it  dissolves  in  acetic  ether  and  in  ethereal  solution  of 
ammonia.  It  is  not  oxidised  by  potassium  permanganate,  as  cellulose 
is,  so  that  it  may  be  used  for  filtering  its  solution.  When  moderately 
heated,  it  burns  more  rapidly  than  gunpowder,  and  it  is  detonated  by 
the  blow  of  a  hammer  or  by  the  rapid  vibration  caused  by  a  smart 
detonation  in  its  vicinity.  Pyroxylin  dissolves  in  strong  sulphuric  acid, 
and  the  solution  is  not  blackened  by  heat.  Strong  nitric  acid  also 


740  GUN-COTTON. 

dissolves  it  when  heated,  but  it  is  reprecipitated  by  strong  sulphuric 
acid  or  by  water.  Strong  potash  dissolves  it  with  formation  of  potas- 
sium nitrate,  nitrite,  and  oxalate,  together  with  glucose  and  some  other 
organic  bodies.  The  formation  of  potassium  nitrate  would  be  expected 
if  pyroxylin  be  a  nitrate  of  cellulose. 

Potassium  hydrosulphide,  in  alcoholic  solution,  reconverts  pyroxylin  into  cellu- 
lose, potassium  nitrite  being  found  in  solution — 

C12H1404(0'N02)6  +  6KHS  =  C12H1404(OH)6  +  6KN02  +  S6. 
This  shows  that  pyroxylin  is  not,  as  was  formerly  supposed,  the  trinitro-cellulose 
C6H7(N02)305,  since,  in  that  case,  the  N02  group  would  be  reduced  to  the  NH2 
group,  and  an  amido-compound  would  be  formed  (p.  659). 

A  strong  aqueous  solution  of  ferrous  chloride  containing  HC1  also  converts 
pyroxylin  into  cellulose,  with  evolution  of  nitric  oxide — 

C12H1404(0-N02)6  +  i2FeC!2  +  I2HC1  =  C12H1404(OH)6  +  6Fe2Cl6  +  6NO  +  6H20. 
This  would  be  the  result  expected  from  cellulose  hexanitrate.  Iron  filings  and 
acetic  acid  reduce  pyroxylin  to  cellulose,  the  nascent  hydrogen  converting  the 
N03  group  into  NH3 — 

C12H1404(N03)6  +  H48  =  C12H1404(OH)6  +  6NH3  +  I2H20. 

Pyroxylin  behaves  like  a  nitrate  when  shaken  with  mercury  and  strong  sulphuric 
acid,  evolving  the  whole  of  its  nitrogen  as  nitric  oxide. 

542.  The  following  proportions  may  be  recommended  for  preparation  of  gun- 
cotton  on  a  small  scale  : — Dry  1000  grains  of  pure  nitre  (p.  338)  at  a  very 
moderate  heat,  place  it  in  a  dry  retort  (Fig.  73),  pour  upon  it  10  drachms  (by 
measure)  of  strong  sulphuric  acid,  and  distil  until  6  drachms  of  nitric  acid  have 
passed  over  into  the  receiver.  Dry  some  pure  cotton-wool,  and  weigh  out  30 
grains  of  it.  Mix  2.\  measured  drachms  of  the  nitric  acid  with  an  equal  volume 
of  strong  sulphuric  acid  in  a  small  beaker.  Allow  the  mixture  to  cool,  immerse 
the  cotton-wool  in  separate  tufts,  pressing  it  down  with  a  glass  rod,  cover  the 
beaker  with  a  glass  plate,  and  set  it  aside  for  fifteen  minutes.  Lift  the  cotton 
out  with  a  glass  rod,  throw  it  into  at  least  a  pint  of  water,  and  wash  it  thoroughly 
in  a  stream  of  water  till  it  no  longer  tastes  acid  or  reddens  blue  litmus-paper. 
Dry  the  cotton  by  exposure  to  air  or  to  a  very  moderate  heat. 

Gun-cotton  is  manufactured  from  the  waste  cuttings  from  spinning-machines 
(cotton-waste),  which  is  first  thoroughly  cleansed.  One  part  of  nitric  acid  (sp. 
gr.  1.52)  and  3  parts  by  weight  (or  2.45  by  volume)  of  sulphuric  acid  (sp.  gr.  1.84) 
are  placed  in  separate  stoneware  cisterns  with  taps,  and  allowed  to  run  simul- 
taneously, in  slow  streams,  into  another  stoneware  cistern  furnished  with  a  tap 
and  an  iron  lid,  through  a  second  opening  in  which  an  iron  stirrer  is  moved 
to  mix  the  acids  thoroughly.  The  mixture  is  set  aside  for  several  hours  to  become 
perfectly  cool. 

A  quantity  of  the  mixed  acids  is  drawn  off  into  a  deep  stoneware  pan  standing 
in  cold  water,  and  provided  with  a  perforated  iron  shelf,  upon  which  the  cotton 
may  be  drained.  The  well-dried  cotton  is  immersed,  a  little  at  a  time,  in  the 
acid,  and  stirred  about  in  it  for  two  or  three  minutes  with  an  iron  stirrer.  It  is 
then  placed  upon  the  perforated  shelf,  and  the  excess  of  acid  squeezed  out  with 
the  stirrer.  Enough  acid  is  drawn  from  the  cistern  to  make  good  that  which  has 
been  absorbed  by  the  cotton,  and  more  cotton  is  treated  in  the  same  way.  Since 
a  considerable  rise  of  temperature  is  produced  by  the  action  of  the  nitric  acid 
upon  the  cotton,  it  is  necessary  to  keep  the  pan  surrounded  with  cold  water.  A 
large  proportion  of  the  cotton  is  doubtless  converted  into  gun-cotton  in  this 
preliminary  immersion  in  the  mixed  acids  ;  but  in  order  to  convert  the  remainder, 
it  is  necessary  to  allow  the  cotton  to  remain  in  contact  with  the  acid  for  a  much 
longer  period,  so  as  to  ensure  its  penetration  into  every  part  of  the  minute  twisted 
tubes  of  the  fibre. 

The  skeins  are  next  transferred  to  a  jar  with  a  well-fitting  cover,  in  which  they 
are  pressed  down  and  completely  covered  with  the  mixed  acids,  of  which  from 
10  to  15  times  the  weight  of  the  cotton  will  be  required,  according  to  the  close- 
ness with  which  the  skeins  are  packed  in  the  jar.  The  jar  is  placed  in  cold  water, 
and  the  cotton  allowed  to  remain  in  the  acid  for  about  twelve  hours. 

The  skeins  are  then  removed,  with  the  aid  of  an  iron  hook,  to  a  centrifugal 
extractor,  which  is  a  cylinder  made  of  iron  gauze,  through  which  the  bulk  of  the 


EXPLOSION   OF  GUN-COTTON.  74! 

acid  is  whirled  out  by  the  rapid  rotation  of  the  cylinder  upon  an  axle.  In  order 
to  wash  away  the  remainder  of  the  acid,  the  cotton  is  plunged,  suddenly,  to  avoid 
rise  of  temperature,  into  a  cascade  of  water,  and  is  then  drained  in  the  centrifugal 
extractor,  and  again  rinsed  in  much  water.  It  is  next  reduced  to  pulp  in  a  rag 
engine  such  as  is  employed  in  paper-mills.  The  pulp  is  thoroughly  washed  by  being 
well  stirred  by  a  poaching '-engine  for  about  forty-eight  hours  in  a  stream  of  warm 
water,  so  as  to  remove  every  trace  of  acid,  which  is  assisted  by  rendering  the  water 
alkaline  with  a  little  lime  or  carbonate  of  soda  or  with  ammonia.  The  pulp  is 
then  drained,  moulded  into  discs  or  any  other  required  form,  condensed  bv 
hydraulic  pressure  until  it  has  at  least  the  same  specific  gravity  as  that  of  water 
and  dried  upon  heated  plates.  As  it  leaves  the  hydraulic  press,  the  cotton  contains 
about  one-fifth  of  its  weight  of  water,  so  that  it  may,  if  required,  be  cut  up  or  bored 
without  danger  of  explosion. 

543.  When  a  mass  of  the  gun-cotton  wool  is  exploded  in  an  unconfined  state,  the 
explosion  is  comparatively  slow  (though  appearing  to  the  eye  almost  instantaneous), 
since  each  particle  is  fired  by  the  flame  of  that  immediately  adjoining  it,  the  heated 
gas  (or  flame)  escaping  outwards,  so  that  some  time  elapses  before  the  interior  of 
the  mass  is  ignited.  But  when  the  gun-cotton  is  enclosed  in  a  strong  case,  so  that 
the  flame  from  the  portion  first  ignited  is  unable  to  escape  outwards,  and  must 
spread  into  the  interior  of  the  mass,  this  is  ignited  simultaneously  at  a  great  number 
of  points,  and  the  decomposition  occurs  far  more  rapidly  ;  a  given  weight  of  cotton 
being  thus  consumed  in  a  much  shorter  time,  a  far  higher  temperature  is  produced, 
and  the  ultimate  results  of  the  explosion  are  much  less  complex,  as  would  be  ex- 
pected from  the  well-known  simplifying  effect  of  high  temperatures  upon  chemical 
compounds. 

If  a  tuft  of  gun-cotton  wool  be  placed  at  the  bottom  of  a  tall  glass  cylinder 
and  inflamed  by  a  heated  wire,  it  will  be  seen  that,  immediately  after  the  explosion, 
the  gas  within  the  cylinder  is  colourless,  but  soon  becomes  red,  showing  that  NO 
was  present  among  the  products,  and  became  converted  into  N02  by  the  oxygen 
of  the  air.  The  water  formed  by  the  combustion  of  the  hydrogen  converts  the  N02 
into  HJSI02  and  HN03  (p.  101),  and  hence  the  acid  character  of  the  moisture  deposited 
in  the  barrel  of  a  fowling-piece  in  which  gun-cotton  cartridges  are  employed. 
A  little  HCN  can  be  detected  among  the  products  of  combustion  of  loose  gun- 
cotton. 

Berthelot  estimates  the  pressure  produced  by  the  detonation  of  gun-cotton, 
compressed  to  a  density  of  i.i,  at  24,000  atmospheres,  or  about  160  tons  per 
square  inch,  being  only  half  the  pressure  assigned  by  him  to  the  detonation  of 
mercuric  fulminate. 

If  a  piece  of  compressed  gun-cotton  be  kindled  with  a  hot  wire,  it  burns  rapidly 
away,  producing  a  large  volume  of  flame,  but  without  any  explosive  effect.*  In 
order  that  gun-cotton  fired  in  this  manner  might  be  used  for  destructive  purposes, 
it  was  found  necessary  to  confine  it  in  strong  cases,  so  that  the  flame  of  the  por- 
tion first  ignited  should  be  employed  in  raising  the  temperature  of  the  rest  to  the 
exploding-point. 

The  unconfined  gun-cotton,  however,  can  be  made  to  explode  or  detonate  with 
most  destructive  violence,  by  exploding  in  contact  with  it  a  detonating  fuze,  con- 
sisting of  a  little  tube  of  quill  or  thin  metal  charged  with  a  few  grains  of  mercuric 
fulminate.  Such  detonation  can  be  communicated  along  a  row  of  pieces  of  com- 
pressed cotton  placed  at  short  distances  from  each  other.  This  sympathetic 
explosion  is  by  no  means  confined  to  gun-cotton,  but  exists  in  the  case  of  nitro- 
glycerine, and  even  gunpowder.  The  modus  operandi  of  the  detonating  fuze 
appears  to  consist  in  the  influence  of  vibratory  motion,  and  the  nature  of  the 
motion  necessarily  depends  upon  the  nature  of  the  explosive.  That  it  is  not  a 
result  of  the  action  of  heat  is  proved  by  the  circumstance  that  wet  gun-cotton  may 
be  exploded  by  a  detonating  fuze,  so  that  torpedoes  may  be  charged  with  a 
mixture  of  gun-cotton  pulp  and  water,  containing  15  per  cent,  of  the  latter,  if  a 
small  charge  of  dry  gun-cotton  be  placed  in  contact  with  the  fuze.  It  has  been 
found  that  the  wet  gun-cotton  is  more  easily  detonated  when  in  a  frozen  state. 

*  Too  much  stress,  however,  should  not  be  laid  upon  this  as  rendering  gun-cotton  maga- 
zines safer  in  case  of  fire  than  gunpowder  magazines.     The  experiment  with  gunpowder 
mentioned  at  p.   342  shows  that  if  all  the  particles  of  an  explosive  be  raised  at  once  t< 
nearly  the  inflamiug-point,  the  first  particle  which  inflames  will  cause  the  detonation  o 
remainder.     Since  the  inflaming-point  of  gun-cotton  is  low,  the  above  conditi 
easily  fulfilled  in  a  conflagration. 


742  COLLODION. 

The  very  destructive  effect  of  the  gun-cotton  exploded  in  this  way  is,  of  course, 
due  to  the  sudden  manner  in  which  the  whole  mass  is  resolved  into  gaseous  pro- 
ducts. When  heat  is  the  cause  of  the  explosion,  it  must  be  comparatively  slow, 
for  gun-cotton  transmits  heat  slowly,  but  the  vibration  caused  by  detonation  is 
transmitted  with  the  velocity  of  sound,  and  the  explosion  becomes  rapid  in  pro- 
portion. 

544.  Gun-cotton  is  more  easily  exploded  than  gunpowder  ;  the  latter  requires  a 
temperature  of  at  least  600°  F.  (316°  C.),  whilst  gun-cotton  may  explode  at  277°  F. 
(136°  C.),  and  must  explode  at  400°  F.  (204°  C.).  It  is  very  difficult  to  explode 
gunpowder  by  percussion,  even  between  a  steel  hammer  and  anvil ;  but  gun-cotton 
invariably  detonates  in  this  way,  though  the  explosion  is  confined  to  the  part 
under  the  hammer.  The  explosion  of  gun-cotton  is  approximately  represented  by 
the  equation,  C12H1404(N03)6  =  500  +  7C02  +  H8  +  3H20  +  N6,  and  is  attended  by  the 
evolution  of  1071  heat-units  per  unit  weight,  but  by  no  smoke,  a  most  important 
advantage  in  mines,  the  atmosphere  of  which  is  sometimes  rendered  almost 
intolerable  by  the  smoke  of  gunpowder  used  in  blasting  ;  but  death  has  been 
caused  by  the  carbonic  oxide  generated.  The  absence  of  residue  from  the  gun- 
cotton  prevents  the  fouling  of  guns,  and  renders  it  unnecessary  to  sponge  them 
after  each  discharge,  for  the  amount  of  incombustible  mineral  matter  present  in 
the  cotton  is  very  small  (from  I  to  2  per  cent.),  and  is  entirely  scattered  by  the 
explosion. 

Nitrated  cellulose  is  the  main  constituent  of  several  modern  sporting  powders 
such  as  E.  C.  sporting  powder,  E.  C.  rifle  powder ,  and  Schultze's  powder. 

545.  Soluble  pyroxylin,  or  collodion  cotton,  is  a  mixture  of  cellulose 
nitrates  lower  than  the  hexanitrate — e.g.,  the penta-,  tetra-,  tri-,  and  di- 
nitrates.  It  is  the  product  of  the  action  upon  cellulose  of  a  mixture  of 
HNO3  (i  mol.)  and  H2S04  (i  mol.)  slightly  diluted  with  water 
(if  mols.).  It  differs  from  pyroxylin  in  being  soluble  in  a  mixture  of 
ether  with  one-seventh  of  alcohol,  yielding  a  viscous  solution,  which 
leaves  the  transparent  collodion  film  when  evaporated.  It  is  much  less 
rapidly  combustible  than  pyroxylin. 

In  order  to  prepare  the  soluble  cotton  for  collodion,  3  measured  ounces  of 
ordinary  HN03  (sp.  gr.  1.429)  are  mixed  with  2  ounces  of  water  in  a  pint  beaker. 
Nine  measured  ounces  of  strong  H2S04  (sp.  gr.  1.839)  are  added  to  this  mixture, 
with  continual  stirring.  A  thermometer  is  placed  in  the  mixture,  which  is 
allowed  to  cool  to  140°  F.  ;  100  grains  of  dry  cotton-wool,  in  ten  separate  tufts,  are 
immersed  in  the  mixture  for  five  minutes,  the  beaker  being  covered  with  a  glass 
plate.  The  acid  is  then  poured  into  another  beaker,  the  cotton  squeezed  with  a 
glass  rod,  and  thrown  into  a  large  volume  of  water  ;  it  is  finally  washed  in  a  stream 
of  water  till  it  is  no  longer  acid,  and  dried  by  exposure  to  air. 

Collodion  balloons. — These  balloons  may  be  made  in  the  following  manner  : — ' 
Six  grains  of  collodion-cotton,  prepared  according  to  the  above  directions,  are 
dissolved  in  a  mixture  of  i  drachm  of  alcohol  (sp.  gr.  0.835)  and  2  drachms  of 
ether  (sp.  gr.  0.725)  in  a  corked  test-tube.  The  solution  is  poured  into  a  dry 
Florence  flask,  which  is  then  turned  about  slowly,  so  that  every  part  of  its 
surface  may  be  covered  with  the  collodion,  the  excess  of  which  is  then  allowed  to* 
drain  back  into  the  tube.  Air  is  then  blown  into  the  flask  through  a  long  glass 
tube  attached  to  the  bellows  as  long  as  any  smell  of  ether  is  perceptible.  A  pen- 
knife blade  is  carefully  inserted  between  the  flask  and  the  neck  of  the  balloon, 
which  is  thus  detached  from  the  glass  all  round  ;  a  small  piece  of  glass  tubing  is 
introduced  for  an  inch  or  two  into  the  neck  of  the  balloon,  so  that  the  latter  may 
cling  round  it.  Through  this  tube  air  is  drawn  out  by  the  mouth,  until  one-half 
of  the  balloon  has  left  the  side  of  the  flask  and  collapsed  upon  the  other  half  ;  by 
carefully  twisting  the  tube,  the  whole  of  the  balloon  may  be  detached  and  drawn 
out  through  the  neck  of  the  flask,  when  it  must  be  quickly  untwisted,  distended  by 
blowing  through  the  tube,  tied  with  a  piece  of  silk,  and  suspended  in  the  air  to  dry. 
The  average  weight  of  such  balloons  is  2  grains. 

Celluloid,  or  artificial  ivory,  or  xylonite,  used  for  combs,  billiard-balls,  &c.,  is 
essentially  compressed  collodion-cotton  mixed  with  camphor  and  zinc  oxide. 

When    collodion-cotton  is  kept  for   some   time,  especially  if   at   all   damp,  it 


SALICIN. 

undergoes  decomposition,  filling  the  bottle  with  ™H  f,,™ 
verted  into  a  gummy  mass,  whA  contains  oSte  ac?d  '       * 

546.  Tunicin,  C^05,  or  animal  cellulose,  is  prepared  from  the  outer  covering  or 
,nantle  of  the  mollusks  belonging  to  the  class  Tuntata.  The  manUe  is  LnTbofled 
with  hydrochloric  acid  and  potash,  in  succession,  and  the  residue  wSdwHh 
water,  alcohol  and  ether.  Tunicin  is  left  as  a  translucent  mas^s  so^ 
Ambling  cellulose  in  properties  that  it  is  believed  by  some  cheS  to 


XIV.  GLUCOSIDES. 

547-  The  compounds  belonging  to  this  class  arecapable  of  conversion 
into  a  sugar  and  some  other  compound  by  the  action  of  acids,  alkalies 
and  certain  ferments,  the  change  being  generally  the  result  of  hydrolysis' 
(p.  265).  They  are  chiefly  found  in  plants,  and  generally  yield  products 
of  decomposition  belonging  to  the  aromatic  group.  Some  of  them  have 
been  already  noticed.* 

Salicin,  C6H1105;0-C6H4CH2OH,  is  extracted  from  willow-bark 
(&ahx)  by  boiling  it  in  water,  removing  the  colouring-matter  and  tannin 
from  the  solution  by  boiling  with  lead  hydroxide,  precipitating  the 
excess  of  lead  by  H2S,  and  evaporating  the  filtered  liquid,  when  the 
salicin  crystallises  in  needles  which  may  be  recrystallised  from  alcohol 
It  forms  bitter  colourless  prisms  (m.-p.  188°  C.)  soluble  in  about  30  parts 
of  cold  water,  in  less  alcohol,  but  not  in  ether.  It  is  readily  distin- 
guished by  the  bright  red  colour  which  it  gives  with  strong  sulphuric 
acid,  which  detects  it  when  applied  to  the  inner  bark  of  the  willow. 
With  emulsin  (p.  566)  or  saliva,  its  aqueous  solution  yields  glucose  and 
salicyl-alcohol  or  saligenin  : 

C13H1807  +  H20  =  C6H1206  +  C6H4(OH)-CH2-OH. 
The  saligenin  gives  a  blue  colour  with  ferric  chloride. 

Salicin  is  occasionally  administered  as  a  febrifuge,  and  is  a  common 
adulteration  of  quinine. 

When  solution  of  salicin  is  boiled  for  some  time  with  dilute  sulphuric  or  hydro- 
chloric acid,  it  yields  an  amorphous  precipitate  of  saliretln,  a  product  of  the 
decomposition  of  saligenin  — 

2C7H802  (saligenin)  =  H20  +  C14H1403  (saliretiri). 

Sulphuric  acid  and  potassium  dichromate  convert  salicin  into  oil  of  spiraea 
(p.  586).  Fused  with  potash,  it  yields  potassium  salicylate.  Dilute  nitric  acid 
converts  salicin  into  helicln:  C13H1807  +  0  =  C13H1607  +  H20.  This  is  also  a  gluco- 
side,  yielding  glucose  and  oil  of  spiraea  when  hydrolysed  by  ferments  or  acids  ; 
C13H1607  +  H20  =  C6H1206  +  C7H602.  Strong  nitric  acid  converts  salicin  into  nltro- 
salicyUc  acid,  C6H3(OH)(N02)C02H.  When  acted  on  by  chlorine,  salicin  yields 
substitution-products  containing  one,  two,  and  three  atoms  of  chlorine,  and  these, 
when  boiled  with  dilute  acids,  yield  the  corresponding  chlorosaligenins. 

Populin,  or  benzoyl-salicin,  C13H17(C7H50)07  +  2H20,  is  a  sweet  crystalline  body 
existing,  together  with  salicin,  in  the  bark  and  leaves  of  the  aspen  (Populus  tremula), 
a  tree  of  the  Willow  order,  and  may  be  extracted  in  the  same  way  as  salicin. 
When  boiled  with  Ba(OH)2,  it  yields  salicin  and  benzoic  acid  (which  becomes 
barium  benzoate)  ;  C13H17(C7H50)07  +  H20  =  C13H1807  +  C7H60'OH.  Boiled  with 
dilute  acids,  it  is  converted  into  benzoic  acid,  saliretin,  and  glucose.  It  is 
obtained  artificially  by  fusing  salicin  with  benzoic  anhydride  — 

C13H1807  +  (C7H50)20  =  C13H17(C7H60)07  +  C7H6OOH. 

*  They  will  probably  be  shown  to  be  ethereal  alcohol  derivatives,  for  several  compound*, 
closely  resembling  glucosides  in  behaviour,  have  been  synthesised  by  dissolving  sugars  in 
alcohols  and  saturating  with  hydrogen  chloride.  In  this  way,  methyl  alcohol  and  glucose 
have  yielded  methylglucoside,  C6Hn(OCH3)O5. 


744  AMYGDALIN. 

Arbutin,  C12H1607,  is  found  in  the  leaves  of  the  bear-berry  (Arbutus  uva  ursi), 
an  astringent  plant  of  the  Heath  order,  sometimes  used  medicinally,  and  in  Pyrola 
umbellata,  also  a  medicinal  plant  of  the  closely  allied  Winter-green  order.  It  may 
be  prepared  like  salicin,  and  crystallises  in  bitter  needles  from  its  aqueous  solution. 
Emulsin  or  dilute  acids  decompose  it  into  glucose  and  hydroquinone — 
C12H1607  +  H20  =  C6H1206  +  C6H4(OH)2. 

Phlorizin,  C21H24010  (<£Xoi6y,  bark,  and  pifa,  roof),  is  extracted  by  hot  alcohol 
from  the  root-bark  of  the  apple,  pear,  plum,  and  cherry  tree.  It  crystallises  from 
hot  water  in  bitter  needles  with  2Aq.  When  boiled  with  dilute  acids,  it  yields 
glucose  and  phloretin  ;  CZ1H240W  +  H20  =  C6H1206  +  C15H1405.  When  exposed  to  air 
in  the  presence  of  ammonia,  it  is  converted  into  a  fine  purple  colouring-matter, 
phlorizein,  021H30N2013  =  ( CaH^O^  +  2NH3  +  08) .  It  melts  at  1 08°  C . 

Qlycyphyilin,  C21IT2409,  is  a  crystalline  substance  allied  to  phlorizin,  extracted 
from  the  leaves  of  Sniilax  glycyphylla,  an  Australian  plant  of  the  Sarsaparilla  order. 
It  is  sparingly  soluble  in  cold  water,  but  dissolves  in  hot  water  and  in  alcohol. 
Its  solution  tastes  like  liquorice.  It  does  not  reduce  alkaline  copper  solutions, 
and  is  not  precipitated  by  normal  lead  acetate,  though  it  is  by  the  basic  acetate. 
When  boiled  with  dilute  sulphuric  acid,  it  yields  phloretin  and  rhamnose  (p.  725) — 
CjaHjaO.  +  H20  =  C15H1405  +  C5H9(CH3)05. 

Hesperidin,  C^H^O^,  is  contained  in  the  fruit,  leaves,  and  stalks  of  the  orange- 
tree  and  other  members  of  the  same  family  ;  it  is  resolved  by  acids  into  glucose 
and  hesperitin,  C16H1406. 

JB»CUlin,  C15H1609,  is  extracted  by  boiling  water  from  the  bark  of  the  horse- 
chestnut  (&sculus  hippocastanum),  sometimes  used  as  a  febrifuge.  The  infusion 
of  the  bark  is  mixed  with  lead  acetate,  to  precipitate  the  tannin  and  colouring- 
matter,  filtered,  the  excess  of  lead  precipitated  by  H2S,  and  the  filtered  solution 
evaporated,  when  aesculin  crystallises  in  colourless  needles  containing  ^Aq, 
sparingly  soluble  in  cold  water,  but  readily  in  hot  water  and  in  alcohol.  The 
aqueous  solution  is  slightly  bitter,  and  has  a  strong  blue  fluorescence,  destroyed 
by  acids  and  restored  by  alkalies.  Emulsin  and  boiling  dilute  acids  convert 
assculin  into  glucose  and  cssculetin,  a  dihydroxycoumarin  (p.  611) — 

Ci5Hi609  +  H2°  =  C6H1206  +   C9H604. 

jEsculetin  exists,  in  small  quantity,  in  horse-chestnut  bark.  Paviin  or  fraxin, 
C16H18010,  accompanies  assculin  in  horse-chestnut  bark.  It  is  more  soluble  in  ether 
than  is  aesculin,  and  has  a  green  fluorescence.  Fraxin  is  obtained  in  larger  quantity 
from  the  bark  of  the  ash  (JFraxinus  excelsior),  which  is  also  febrifugal.  Trees  of 
the  genus  Pavia,  belonging  to  the  same  order  as  horse-chestnut  (soap-worts),  yield 
more  paviin  than  aesculin. 

548.  Amygdalin,  C20H27NOn,  is  extracted  from  bitter  almonds,  the 
kernels  of  the  fruit  of  Amygdalus  communis,  of  which  one  variety 
yields  the  sweeet  almond,  containing  no  amygdalin.  The  almonds  are 
pressed  to  extract  the  fixed  oil  (not  the  essential  oil,  but  a  glyceride), 
and  the  bitter-almond  cake  is  boiled  with  alcohol,  from  which  the  amyg- 
dalin crystallises  in  pearly  scales  which  dissolve  in  water,  and  crystallise 
from  it  in  prisms  with  3Aq.  Amygdalin  may  also  be  extracted  from 
the  kernels  of  peaches  and  nectarines,  both  fruits  of  varieties  of  ainyg- 
dalus.  It  is  also  present  in  the  leaves  and  kernels  of  several  species  of 
cherry,  and  the  bitter-almond  oil  formed  from  it  confers  the  flavour 
upon  cherry- brandy,  noyau,  ratafia,  and  maraschino.  The  production 
of  glucose,  hydrocyanic  acid,  and  benzoic  aldehyde,  by  the  action  of 
emulsin  on  solution  of  amygdalin,  has  been  already  noticed  (p.  584). 
When  long  boiled  with  baryta,  it  yields  ammonia  and  the  barium  salt  of 
amygdalic  acid,  C20H280,3.  This  acid  is  a  glucoside,  for  when  boiled 
with  dilute  acids  it  is  converted  into  glucose  and  mandelic  acid  (p.  609) — 
C20H28013  +  2H20  =  2C6H1206  +  C8H803. 

Daphnin,  C15H1609,  isomeric  with  aesculin,  is  obtained  from  the  bark  of  Daphne 
mezereitm,  used  as  a  remedy  for  toothache.  Dilute  acids  convert  it  into  glucose 
and  daphnetin,  a  dihydroxy-coumarin  (p.  591)  ;  CigH1609  +  H20  =  C6H12O6  +  C9H604. 


BITTER  PRINCIPLES. 

,£S£ftJ^^ 

amorphous  bodies,  which  yield  glucose,  and,  respectively,  convolrulinol  C  H   O 
Ktdjalapinol,  C16H30O3,  when  hydrolysed  by  acids  or  emulsin.     Turpethin  Somerir 
with  jalapin,  is  extracted  from  the  roots  of  Convolvulus  turpethum  also  used  as 
purgative. 

Helleborein  CXH^OWJ  is  the  narcotic  poison  from  the  root  of  black  Mlebore  a 
plant  of  the  Buttercup  order.  It  crystallises  in  needles,  which  dissolve  easily  in 
water,  but  sparingly  m  alcohol. 

Digitalin  is  the  poisonous  glucoside  extracted  from  the  seeds  of  the  foxelove 
(Digitalis  purpurea)  It  is  crystalline,  sparingly  soluble  in  water  and  ether,  but 
dissolves  in  alcohol  and  chloroform.  Strong  sulphuric  and  hydrochloric  acids 
dissolve  it  with  a  green  colour.  Its  formula  is  not  known. 

Saponin,  C32H54018,  is  found  in  the  soap-wort,  in  the  root  of  the  clove-pink  which 
belongs  to  the  same  natural  order  (Ca,ryophyllacea\  in  the  pimpernel,  and  'in  the 
fruit  of  the  horse-chestnut.  It  may  be  extracted  by  boiling  alcohol,  which 
deposits  it  as  an  amorphous  powder  on  cooling.  It  is  soluble  in  water,  and  its 
solution  lathers  like  soap.  This  leads  to  the  use  of  decoctions  containing  it,  such 
as  that  of  the  soap-nut  of  India,  for  cleansing  delicate  fabrics.  The  dry  powder 
of  saponin  causes  sneezing. 

Coniferin,  Cl6K^08.2Aq,  crystallises  from  the  gummy  liquid  found,  in  the  spring, 
between  the  inner  and  outer  barks  of  coniferous  trees.  In  contact  with  water  and 
emulsin,  it  yields  glucose  and  coniferyl  alcohol— 

CieHsA  +  H20  =  C6H1206  +  C10H1203. 

The  latter  is  a  crystalline  body,  soluble  in  ether,  and  smelling  of  vanilla.  When 
distilled  with  potassium  dichromate  and  sulphuric  acid,  it  yields  acetic  aldehyde 
and  vanillin  ;  C10H1203  +  0  =  C2H40  +  C8H803  (p.  586). 

Quercitrin,  C^H.^O^,  is  the  colouring-matter  of  quercitron  bark,  and  is  also  found 
in  horse-chestnut  flowers,  and  in  grape-vine,  sumach  and  catechu.  It  may  be 
extracted  from  quercitron  bark  by  alcohol,  the  tannin  precipitated  by  solution  of 
gelatine,  and  the  filtrate  evaporated.  Quercitrin  forms  yellow  crystals,  sparingly 
soluble  in  water.  Dilute  sulphuric  acid  converts  it  into  rhamnose  and  quercetin; 
CggHgaOao  +  H20  =  2CSH9(CH3)05  +  C24H16On.  This  last,  also  called  flavin,  is  found  in 
heather,  in  tea,  and  in  the  root  bark  of  apple  and  other  trees.  It  is  a  yellow 
crystalline  body,  which  is  sparingly  soluble  in  water  and  more  soluble  in  alcohol. 
It  may  be  sublimed  in  yellow  needles.  Rutin,  which  occurs  in  rue  and  in  capers, 
much  resembles  quercitrin. 

Antiarin,  C^H^Og.aAq,  is  the  principle  of  the  Javanese  arrow-poison,  upas- 
antiar,  the  juice  of  Antiaris  toxicaria,  a  large  tree  of  the  Bread-fruit  tribe.  It  may 
be  crystallised  from  the  alcoholic  extract  of  upas,  and  is  soluble  in  water  and 
ether.  With  acids,  it  behaves  like  a  glucoside. 

549.  Bitter  Principles. — Picrotoxin,  C^H^O^,  is  a  narcotic  poison  contained  in 
Cocculus  indicus,  the  fruit  of  Anamirta  paniculata,  a  tropical  trailing  shrub  of  the 
order  Menispermacece.  The  fruit  has  been  sometimes  used  as  a  hop-substitute  by 
brewers.  Picrotoxin  may  be  extracted  from  the  seeds  by  boiling  with  alcohol, 
from  which  it  crystallises  in  needles  ;  it  is  sparingly  soluble  in  water,  and  soluble 
in  ether  ;  it  is  a  mixture  of  picrotoxinin,  C15H1606  +  H20,  and  picrotin,  C15H807. 
Quassiin,  C^H^Ojo,  is  another  crystalline  bitter  principle,  extracted  by  alcohol  from 
quassia  chips,  the  wood  of  Picrasma  excelsa  (bitterwood).  This  is  also  said  to  be 
used  as  a  hop-substitute,  and  is  not  poisonous,  except  to  flies.  It  is  administered 
as  a  tonic.  Water  dissolves  it  sparingly,  but  acquires  a  bitter  taste.  Calumbin, 
CaHaaO?,  is  a  substance  of  the  same  kind,  extracted  from  calumba  root  (Cocculux 
palmatus). 

Santonin,  C15H1803,  is  the  bitter  principle  of  the  seeds  of  Artemisia  santonica 
(worm-seed)  and  of  Artemisia  absinthium  (wormwood)  ;  it  may  be  extracted  from 
absinthium  by  mixing  it  with  lime  and  boiling  with  weak  alcohol ;  the  solution  is 
evaporated  and  the  residue  boiled  with  acetic  acid,  which  deposits  colourless 
prisms  of  santonin,  which  become  yellow  when  exposed  to  light.  It  is  insoluble 
in  water,  but  dissolves  in  alcohol  and  ether  ;  it  is  dissolved  by  alkalies,  yielding 
santonates,  e.g.,  sodium  santonate,  NaC15H1904,  from  which  santonic  acid,  HC15H1904, 
may  be  obtained  by  shaking  with  HC1  and  ether  ;  thus  it  appears  to  be  a  lactone. 
It  contains  a  ketonic  group.  Santonin  is  moderately  poisonous,  and  affects  the 
perception  of  colours,  rendering  violet  invisible  ;  it  is  contained  in  the  liqueur 
known  as  creme  d 'absinthe,  or  Wermuth.  Gentianin,  C14H]005,  is  extracted  by  ether 


746  CHLOEOPHYLL. 

from  the  roots  of  the  yellow  gentian,  used  as  a  bitter  and  tonic.  It  forms  yellow 
needles,  sparingly  soluble  in  water,  but  freely  in  alcohol  and  ether  :  also  soluble 
in  alkalies,  with  a  strong  yellow  colour. 

Elaterin  (efXarTj/nos,  driving  away,  in  allusion  to  its  drastic  quality),  G^H^O^  is 
the  active  principle  of  the  drug  elaterium,  obtained  from  the  juice  of  the  squirting 
cucumber  (Momordica  elateriurri).  It  is  crystalline,  insoluble  in  water,  but  soluble 
in  alcohol  and  ether.  It  admits  of  sublimation.  Kosine,  C^H^O^,  is  the  active 
principle  of  Kousso,  an  Abyssinian  plant  used  as  a  vermifuge  ;  it  crystallises  in 
yellow  needles,  which  are  insoluble  in  water,  but  soluble  in  ether  and  alcohol. 
Aloin,  C17H1807,  is  a  crystalline  bitter-sweet  substance  extracted  from  aloes,  the 
dried  juice  of  various  species  of  aloe. 

Glycyrrhizic  acid  (formerly  called  glycyrrhizin),  C^H^NO^,  is  extracted  from 
dried  liquorice  root  ( Glycyrrhiza  glabra)  by  dilute  acetic  acid ;  alcohol  is  added 
and  the  nitrate  evaporated  to  a  syrup.  It  is  amorphous  and  has  a  sweet  taste. 

Cantharidin,  C10H1204,  is  extracted  from  the  Spanish  fly  and  other  insects.  It 
is  a  bitter  substance,  melting  at  218°  C.  and  subliming.  It  blisters  the  skin. 

550.  Vegetable  Colouring-Matters. — Notwithstanding  the  great 
variety  and  beauty  of  the  tints  exhibited  by  plants,  comparatively 
few  yield  colouring-matters  which  are  sufficiently  permanent  to  be 
employed  in  the  arts,  the  greater  number  of  them  fading  rapidly  as 
soon  as  the  plant  dies,  since  they  are  unable  to  resist  the  decomposing 
action  of  light,  oxygen,  and  moisture,  unless  supported  by  the  vital 
influence  in  the  plant ;  some  of  them  even  fade  during  the  life  of  the 
plant,  as  may  be  seen  in  some  roses  which  are  only  fully  coloured  in 
those  parts  which  have  been  screened  from  the  light.  Diligent  re- 
search has  disclosed  the  constitution  of  many  of  the  vegetable  colouring- 
matters,  such  as  those  of  the  madder  and  indigo  plants ;  these  are 
considered  under  the  classes  of  compounds  to  which  they  belong. 
Those  which  are  described  here  are  still  under  investigation,  and 
little  is  yet  known  of  their  chemistry  save  that  many  are  glucosides. 

Chlorophyll  (from  ^Xwpdc,  green;  ^vXXoi/,  a  leaf),  the  abundant  green 
colour  of  plants,  has  not  been  obtained  in  a  pure  state,  because  it 
neither  crystallises  nor  volatilises.  The  want  of  exact  knowledge  of 
the  chemistry  of  this  body  is  especially  felt,  because  its  physiological 
importance  to  plants  is  of  the  highest  order.  It  is  evidently  active 
in  constructing  the  tissues  of  the  plant  from  carbonic  acid,  water, 
ammonia,  &c.,  derived  from  the  air  and  soil.  It  may  be  extracted  from 
the  leaves  of  plants  by  boiling  with  alcohol,  ether,  or  benzene. 

The  alcoholic  extract  of  the  leaves  is  allowed  to  stand  for  some  time,  then 
filtered  and  shaken  with  one  volume  of  ether  and  two  volumes  of  water.  The 
ethereal  layer,  which  contains  all  the  chlorophyll,  is  shaken  with  water  as  long 
as  the  latter  reduces  Fehling's  solution  ;  it  is  then  allowed  to  evaporate,  the 
chlorophyll  remaining  as  a  bright  green  residue.  When  this  is  dissolved  in  alcohol, 
and  boiled  with  dilute  H2S04  or  HC1,  the  solution  gives  the  glucose  reaction  with 
Fehling's  solution,  rendering  it  probable  that  chlorophyll  is  a  glucoside.  Chloro- 
phyll dissolves,  in  cold  strong  sulphuric  acid,  to  a  green  solution  which  gives  a 
dark  green  precipitate  on  dilution,  and  the  nitrate  gives  the  glucose  reaction. 

An  alcoholic  solution  of  chlorophyll  is  very  unstable  in  air,  especially 
when  exposed  to  light,  but  gives  rise  to  two  stable  colouring-matters, 
phylloxanthin  and  phyllocyanin  when  treated  with  acids ;  the  precipitate 
obtained  is  dissolved  in  ether  and  the  solution  is  shaken  with  strong 
HC1,  which  dissolves  the  phyllocyanin  and  settles  as  a  bright  blue  layer 
below  the  ethereal  solution  of  the  phylloxanthin,  which  is  yellowish- 
green.  The  phyllocyanin  yields  a  remarkably  stable  bright  green 
colouring-matter  with  copper,  the  production  of  which  is  probably  the 


VEGETABLE   COLOURING-MATTERS.  747 

cause  of  the  improved  colour  of  preserved  vegetables  which  have  been 
treated  with  a  small  dose  of  a  copper  salt. 

When  distilled  with  zinc-dust  chlorophyll  yields  pyrrol,  and  the  same  result  has 
been  obtained  with  the  colouring-matter  of  the  blood ;  thus  these  two  substances 
so  mysteriously  essential  to  life,  appear  to  be  offspring  of  the  same  chemical 
parent, 

Iron  is  said  to  be  an  essential  constituent  of  chlorophyll ;  if  iron  be 
absent  from  the  plant's  food,  chlorophyll  is  not  developed. 

The  blue  colouring-matter  contained  in  many  flowers,  such  as  the  violet,  has 
been  named  cyanin.  Acids  redden  it,  and  hence  only  those  flowers  which  have  a 
neutral  juice  are  blue  ;  red  flowers  yielding  an  acid  juice.  The  colouring-matter 
of  grapes  and  of  red  wine  appears  to  be  cyanin. 

551.  Saffron  is  a  yellow  colouring-matter,  obtained  from  the  flowers  of  Crocus 
sativus,  which  are  purple,  with  yellow  anthers.    When  these  are  dried  and  pressed 
into  cakes  they  form  the  saffron  of  commerce,  which  has  an  agreeable  odour.    It 
is  chiefly  imported  from  Spain,  and  is  often  adulterated.     It  gives  up  to  water  and 
alcohol  a  yellow  amorphous  glucoside,  termed  polychroite.     Annatto,  or  arnotto, 
is  another  yellow  colouring-matter,   which  forms  the  pulp  round  the  seeds   of 
Biaca  orellana,  a  West  Indian  shrub.     It  is  used  for  colouring  butter  and  cheese. 
The  colouring  principle  has  been  called  Usein  ;  it  is  sparingly  soluble  in  water,  but 
dissolves  in  alcohol  and  in  alkalies  ;  acids  reprecipitate  it  without  much  change 
of  colour. 

Turmeric  is  the  root  of  an  East  Indian  plant,  the  Curcuma  longa,  and  is  used  in 
curry.  It  contains  a  crystalline  yellow  body,  curcumin,  C21H.^O&  which  may  be 
extracted  by  boiling  benzene.  It  is  insoluble  in  water,  but  dissolves  in  alcohol 
with  a  green  fluorescence.  Alkalies  dissolve  it,  forming  red  salts,  from  which  acids 
precipitate  it  of  a  yellow  colour.  Paper  dyed  with  turmeric  is  used  as  a  delicate 
test  for  alkalies,  which  turn  it  brown.  When  acted  on  by  boric  acid  and  strong 
sulphuric  acid,  it  is  converted  into  rosocyanin,  which  crystallises  in  green  needles 
dissolved  by  alcohol,  with  a  red  colour,  which  is  changed  to  deep  blue  by  alkalies. 
Turmeric-paper  is  used  in  testing  for  boric  acid  (p.  274). 

Weld  is  the  Reseda  luteola,  a  plant  of  the  Mignonette  order,  the  leaves  of  which 
give  a  yellow  solution  when  boiled  with  water.  The  hot  decoction,  mixed  with 
alum  and  chalk,  gives  a  yellow  precipitate,  which  is  used  in  paper-staining.  It 
contains  a  crystalline  yellow  body,  luteolin,  C15H1006,  sparingly  soluble  in  water, 
but  dissolved  by  alcohol  and  by  alkalies.  It  sublimes  in  yellow  needles. 

Fustic  is  a  yellow  dyestuff,  of  which  there  are  two  kinds.  Old  fustic  is  the 
wood  of  a  tree  of  the  Mulberry  order  (Mvru*,  or  Madura  tinctorla),  grown  in  the 
West  Indies.  Young  fustic  is  the  wood  of  Rhus  cotinus,  or  Venice  sumach,  from 
Italy  and  the  South  of  France.  When  old  fustic  is  boiled  with  water,  the  solution 
deposits  yellow  needles  of  morin,  C13H806,  soluble  in  alcohol.  The  mother-liquor 
of  morin,  when  evaporated,  yields  maclurin  or  moritannic  acid  (p.  61 1). 

Gamboge  is  a  yellow  gum-resin,  originally  obtained  from  Camboja  in  Asia,  and 
is  exuded  by  certain  species  of  Guttiferge.  It  contains  about  30  per  cent,  of  a 
yellow  gum,  soluble  in  water,  and  70  per  cent,  of  resin  soluble  in  alcohol  and 
alkalies,  called  gambodic  acid. 

Purree  (pwri),  or  Indian  yellow,  imported  from  India  and  China,  and  said  to  be 
the  dried  excrement  of  buffaloes  fed  on  mango  leaves,  is  a  compound  of  magnesia 
with  euxanthin  (or  euxanthic  acid),  C19H16010.  By  extracting  it  with  hydrochloric 
acid  and  alcohol,  the  euxanthin  is  obtained  in  yellow  prisms,  sparingly  solub  e  in 
water,  soluble  in  alcohol,  ether,  and  alkalies.  When  heated,  it  yields  a  yellow 
crystalline  sublimate  of  euxanthone,  C13H804.  On  fusion  with  potash,  euxanthone 
yields  hydroquinone,  and  nitric  acid  converts  it  into  trinitroresorcm,  wni< 
oppose  the  idea  that  purree  is  of  animal  origin. 

552.  Safflower,  which  yields  rouge,  consists  of  the  dried  flowers  vttarthamus 
tinctorius,  cultivated  in  Egypt.     It  contains  a  yellow  substance,  which  may  De 
extracted  by  water,  and  a  red  colour,  carthamin,  C14H1607,  which  may  be  dissolved 
out  by  sodium  carbonate,  and  precipitated  by  acetic  acid.     Alcohol  dissolves  i 

a  red  solution.     It  is  used  in  dyeing,  but  soon  fades  when  exposed  to  light. 
Carotin,  C^O,  is  a  red  substance,  found  in  small  crystals  m  the  cell 
carrot.     It  crystallises  from  alcohol  in  cubes  of  agreeable  odour. 


748  SHELLAC. 

Santalin,  C15H405,  is  the  colouring-matter  of  red  sanders  wood  (Pterocarpus  santa- 
linus),  from  which  it  may  be  extracted  by  alcohol,  which  deposits  it  in  red  crystals 
insoluble  in  water,  but  giving  violet  solutions  with  alkalies. 

Haematoxylin.  C16H1406.3H20,  is  extracted  from  logivood  (Hcematoxylon  campe.chi- 
anum),  which  grows  at  Cam  peachy  in  the  Bay  of  Honduras,  by  boiling  the  chips 
with  water.  It  is  deposited  from  the  solution  in  yellow  needles,  which  are  soluble 
in  water,  alcohol  and  ether.  It  resembles  the  phenols  by  dissolving  in  alkalies  to 
a  purple  solution,  which  absorbs  oxygen  and  forms  a  red  colouring-matter,  hcema- 
tein,  C16H1206,  sparingly  soluble  in  cold  water,  which  may  also  be  obtained  by 
oxidising  hasmatoxylin,  in  ethereal  solution,  with  nitric  acid.  Reducing-agents, 
such  as  sulphurous  acid,  convert  it  into  haematoxylin.  When  fused  with  potash, 
haematoxylin  yields  pyrogallol.  It  contains  five  OH  groups. 

Potassium  chromate  gives  an  intense  black  colour  with  infusion  of  logwood, 
which  has  been  used  as  an  ink,  but  is  fugitive.  Logwood  boiled  with  distilled 
water  gives  a  yellow  solution,  but  with  common  water  it  gives  a  fine  purple-red, 
from  the  production  of  hasmatein  by  the  oxidation  of  the  htematoxylin  in  presence 
of  the  calcium  carbonate  in  the  water.  The  solution  of  logwood  is  sometimes 
used  as  an  indicator  in  alkalimetry. 

Brazilin,  C16H1405,  is  contained  in  Brazil  wood  ( Ccesalpiniea  brasiliensis)  ;  peach- 
wood  (C.  echinata),  and  Sappan  wood  (O.  sappan) — all  dyewoods  from  the  same 
botanical  sub-order  as  logwood.  Brazilin,  when  quite  pure,  forms  colourless 
crystals,  and  yields  colourless  solutions  in  air-free  water  and  alcohol ;  but  it  soon 
becomes  yellow  by  oxidation,  and  dissolves  in  alkalies  with  a  fine  red  colour, 
which  is  bleached  by  reducing-agents.  It  contains  four  OH  groups. 

553.  Lac  is  a  red  dye  extracted  from  the  resinous  exudation  of  certain  tropical 
trees  of  the  Fig  tribe,  punctured  by  an  insect  (Coccus).  In  its  crude,  natural 
state,  encrusting  the  small  branches,  it  is  known  as  stick-lac,  and  has  a  deep  red 
colour  ;  when  broken  oft'  the  branches  and  boiled  with  water  containing  sodium 
carbonate,  it  gives  a  red  solution,  from  which  the  colouring-matter  is  precipitated 
as  a  lake  by  adding  alum,  and  made  into  cubical  cakes  for  the  market.  The 
resinous  matter  (about  68  per  cent.)  left  undissolved  by  sodium  carbonate,  is 
termed  seed-lac ;  this  is  melted,  strained  through  a  cloth,  and  allowed  to  solidify 
in  thin  layers,  when  it  forms  shell-lac,  which  is  much  used  in  the  manufacture  of 
sealing-wax  and  varnishes.  The  lacquer  applied  to  brass  is  named  after  this  resin, 
being  an  alcoholic  solution  of  shell-lac,  sandarach,  and  Venice  turpentine.  Indian 
ink  is  made  by  mixing  lamp-black  with  a  solution  of  100  grains  of  lac  in  20  grains 
of  borax  and  4  ounces  of  water. 

Carmine  owes  its  colour  to  carminic  acid,  C^H.^O^,  a  glucoside  extracted  by 
boiling  water  from  the  cochineal  insect,  which  is  found  upon  a  species  of  cactus  in 
Mexico  and  Peru.  Carmine-lake  is  precipitated  by  alum  and  potassium  carbonate 
from  the  aqueous  extract  of  the  cochineal  insect.  The  acid  itself  is  an  amorphous 
purple  solid,  easily  soluble  in  water  and  alcohol,  and  sparingly  in  ether.  It  dis- 
solves unchanged  in  strong  sulphuric  acid. 


XV.  ALBUMINOID  COMPOUNDS. 

554.  Under  this  head  are  classed  several  nitrogenous  products  of 
animal  and  vegetable  life,  which  are  not  crystalline  or  volatile.  They 
resemble  each  other  very  closely  in  composition,  containing  from  50  to 
55  per  cent,  carbon,  21  to  25.5  oxygen,  15  to  18  nitrogen,  6.7  to  7.3 
hydrogen,  and  0.4  to  i  .7  sulphur.  If  the  sulphur  be  regarded  as  essential 
to  the  formula,  the  mean  of  these  numbers  would  give,  approximately, 
the  formula  C,3]H210N35044S.  Concerning  the  constitution  of  these  com- 
pounds very  little  is  known.  They  are  generally  Isevo-rotatory. 

It  has  become  customary  among  physiologists  to  distinguish  between  proteids* 
and  albuminoids.  The  former  term  is  applied  to  such  compounds  as  resemble 
albumin,  or  white  of  egg,  in  properties,  whilst  the  albuminoids  are  typified  by 
gelatine.  The  two  classes  of  compounds  dift'er  mainly  in  the  fact  that  the 

*  A  name  originally  given  to  compounds  supposed  to  be  derived  from  a  primary  source, 
protein  (Trpumiov,  pre-eminence). 


ALBUMIN. 

majority  of  the  proteids   are  coagulated   by  heat.      In  what  follows,  only  a  few 
of  the  more  important  proteids  and  albuminoids  will  be  described,  since  it  is  i 
possible  in  a  general  text-book  to  enter  into  details  of  the  modern  classification  o 
these  compounds. 

Albumin,  or  white  of  egg,  C72H1]3N18022S,*  may  be  extracted  from  its 
aqueous  solution  contained  in  the  egg,  by  stirring  it  briskly  to  break  up 
the  membrane,  adding  a  little  acetic  acid  to  neutralise  the  soda  present 
in  the  white,  filtering,  placing  for  twelve  hours  on  a  dialyser  (p.  278)  to 
separate  the  sodium  chloride  and  acetate,  evaporating  the  contents  of 
the  dialyser  below  50°  0.,  powdering  the  residue,  and  treating  with 
ether  to  extract  fatty  matters.  The  albumin  so  prepared  is  an  amorphous 
solid,  of  sp.  gr.  i.3i.t  When  heated,  it  swells  up,  carbonises,  and 
evolves  offensive  alkaline  vapours,  usually  leaving  a  slight  alkaline  ash, 
containing  a  trace  of  calcium  phosphate,  which  is  very  difficult  to 
separate  completely  from  the  albuminoids. 

In  cold  water,  albumin  slowly  softens  and  dissolves,  like  gum  ;  if  this 
solution  be  heated  to  about  70°  0.,  the  albumin  is  converted  into  an 
insoluble  form,  becoming  a  white,  soft  solid,  as  in  boiled  eggs,  if  the 
albumin  amounts  to  12  per  cent.,  and  a  nocculent  precipitate  if  the 
solution  be  diluted.  The  coagulated  albumin  is  not  easily  dissolved  by 
acids  or  alkalies,  and  is  believed  to  be  the  anhydride  of  soluble  albumin, 
for  if  it  be  heated  in  water  in  a  sealed  tube  to  above  150°  C.,  it  is  dis- 
solved to  a  reddish  liquid,  which  behaves  like  a  solution  of  ordinary 
albumin,  but  is  not  coagulated  by  heat.  Raw  white  of  egg  is  inodorous, 
and  does  not  blacken  silver;  but  after  boiling  it  smells  of  H3S,  and 
blackens  silver,  showing  that  it  suffers  some  decomposition  during 
coagulation.  When  dried,  coagulated  albumin  forms  a  translucent 
brittle  mass,  which  becomes  white  and  opaque  in  water.  Soluble 
albumin,  completely  dried  below  50°  C.,  may  afterwards  be  heated  to- 
100°  C.,  without  becoming  insoluble. 

Alcohol  precipitates  albumin  from  its  solution,  and  the  soluble  is 
converted  into  the  insoluble  form  by  digestion  with  strong  alcohol.  It 
is  also  precipitated  by  shaking  with  ether  or  turpentine. 

In  many  reactions  albumin  resembles  the  amido-compounds,  as  in  playing  the 
part  of  a  weak  acid  and  a  weak  base.  Strong  potash  added  to  a  solution  of  albumin 
precipitates  a  gelatinous  compound  of  potash  and  albumin,  which  is  soluble  in 
boiling  water,  and  gives,  with  metallic  salts,  precipitates  containing  albumin  and 
metallic  oxides.  Acids  coagulate  the  solution  of  potash-albumin. 

The  mineral  acids,  except  ortho-  and  pyro-phosphoric  acids,  precipitate  a  solution 
of  albumin,  the  precipitate  being  a  compound  of  the  acid  with  albumin,  but  the 
organic  acids,  except  picric,  do  not.  as  a  rule,  precipitate  it.  Many  of  the  compounds 
of  albumin  and  acid  have  been  proved  to  have  a  definite  composition.  Nitric  acid 
has  long  been  employed  as  a  test  for  albumin  (in  urine,  for  example),  since  it  forms 
a  precipitate  even  in  a  very  weak  solution,  but  if  the  liquid  be  mixed  with  a  very 
minute  quantity  of  the  acid,  the  flocculent  precipitate  formed  at  first  disappears  on 
shaking,  and  the  clear  acid  liquid  is  not  precipitated  by  boiling.  The  same  thing 
is  observed  with  sulphuric  and  hydrochloric  acids. 

To  obtain  definite  compounds  of  albumin  with  the  acids,  beaten  white  of  egg 
is  placed  in  a  dialyser  suspended  upon  the  surface  of  the  very  diluted  acid  for 
about  24  hours,  when  the  acid  passes  through  the  dialyser  and  combines  with  the 
albumin.  The  products  are  nearly  colourless  jellies  soluble  in  hot  water. 

The  reagents  commonly  employed  for   precipitating   albumin   are  nitric     3id, 

*  The  simplest  formula  for  crystallised  albumin  is  said  to  be  C720H1134N218SBO348. 
f  It  is  stated  that  by  adding  a  saturated  solution  of  ammonium  sulphate  to  egg  albumin  v 
filtering  and  evaporating  the  filtrate,  crystals  of  albumin  may  be  obtained. 


750  SERUM  ALBUMIN. 

mercuric  chloride,  potassium  ferrocyanide,  and  picric  acid.  Of  these,  nitric  and 
picric  acids  precipitate  all  the  above  compounds  of  albumin  with  the  acids  ; 
potassium  ferrocyanide  precipitates  all  except  the  metaphosphate,  citrate,  and 
oxalate  ;  mercuric  chloride  only  precipitates  the  hydrochloride  and  the  meta- 
phosphate. 

Strong  hydrochloric  acid  gives  with  albumin  a  precipitate  which  dissolves  in 
excess,  and  gives  a  purplish  solution  when  boiled  in  contact  with  air.  Strong 
nitric  acid  colours  coagulated  albumin  yellow  ;  alkalies  dissolve  the  yellow  mass  to 
an  orange  liquid,  from  which  acids  precipitate  yellow  flakes  (xantho-proteic  acid). 
Albumin  also  gives  a  fine  red  colour  with  mercuric  nitrate  containing  nitrous 
acid  (Mi lion's  test;  prepared  by  dissolving  mercury  in  twice  its  weight  of  nitric 
acid,  in  the  cold,  and  adding  twice  its  bulk  of  water).  When  boiled  with  moder- 
ately dilute  sulphuric  acid,  albumin  yields  leucine  and  tyrosine  (p.  678).  With 
solution  of  potash,  on  boiling,  it  also  gives  leucine  and  tyrosine,  evolves  one-third 
of  its  nitrogen  as  ammonia,  and  its  sulphur  is  converted  into  potassium  sulphide, 
which  gives  a  black  precipitate  on  adding  a  salt  of  lead.  When  heated  with 
baryta-water  to  150°  C.,  it  evolves  part  of  its  nitrogen  as  ammonia,  and  barium 
carbonate  is  formed  in  the  same  ratio  to  the  ammonia  as  when  urea  is  heated 
with  baryta  ;  this  has  led  to  the  conclusion  that  albumin  contains  one-fifth  of  its 
nitrogen  in  a  form  nearly  allied  to  urea,  and  that  it  is  probably  a  complex  ureide 
(p.  671).  When  oxidised  by  potassium  permanganate,  it  yields  benzoic  acid. 
Boiled  with  a  mixture  of  potassium  permanganate  and  potash,  it  evolves  the  whole 
of  its  nitrogen  as  ammonia,  whilst  with  potash  alone  it  only  gives  off  one-third  of 
its  nitrogen. 

The  putrefaction  of  the  albuminoids  gives  rise  to  the  ptomaines  or  toxines ; 
p.  666.  Such  poisonous  products  are  also  formed  by  the  bacilli  of  diseases  like 
diphtheria,  and  it  is  upon  the  introduction  into  the  system  of  antidotes  (anti- 
toxines),  derived  from  animals  that  have  been  able  to  survive  the  poisons,  that  the 
principle  of  inoculation  depends. 

555.  The  gastric  juice  dissolves  coagulated  albumin  digested  with  it 
at  about  37°  C.,  and  the  solution  is  not  precipitated  by  potassium  ferro- 
.cyanide,  nor  coagulated  by  heating.  In  this  condition  it  is  said  to  have 
been  peptonised,  or  converted  into  peptone  (neTr™,  to  digest).  The  con- 
stituent of  the  gastric  juice  which  effects  this  change  is  termed  pepsin, 
and  may  be  precipitated  from  the  juice  by  alcohol.  It  resembles  albu- 
min in  composition,  but  is  much  less  putrescible.  When  dissolved  in 
dilute  hydrochloric;  acid,  also  present  in  the  gastric  juice,  it  yields  a 
mixture  which  peptonises  most  albuminoids  if  digested  at  about  40°  C. 
The  pepsin  prepared  from  the  stomach  of  the  pig  and  other  animals  is 
sometimes  administered  medicinally  to  assist  digestion. 

The  action  of  pepsin  and  HC1  on  albuminoids  is  hydrolytic  and  occurs  in  several 
etages,  the  successive  products  between  the  original  compound  and  peptone  being  a 
syntonin  or  acid-albumin  and  an  albumose  or  propeptone. 

Serum  albumin  forms  nearly  8  per  cent,  of  the  serum  of  blood,  and  is  found  in 
other  liquid  secretions.  It  may  be  prepared  by  precipitating  the  diluted  serum 
with  lead  acetate,  suspending  the  washed  precipitate  in  water,  and  decomposing 
it  with  C02  ;  the  filtered  liquid  is  then  evaporated  below  50°  C.  It  appears  to 
contain  less  sulphur  than  ovalbumin  (egg  albumin)  in  the  ratio  of  1.2  :  1.6,  but 
rather  more  oxygen  (23.1  : 22.4).  In  properties  it  very  closely  resembles  oval- 
bumin, but  it  is  not  coagulated  by  ether,  and  gives  precipitates  with  nitric  and 
hydrochloric  acids,  which  are  more  easily  dissolved  by  excess  than  are  those  of  egg 
albumin.  It  is  more  powerfully  leevo-rotatory  than  egg  albumin. 

Vegetable  albumin  is  the  substance  which  is  precipitated  by  heat  from  the  juices 
of  plants,  and  from  their  infusions  in  cold  water.  It  has  not  been  obtained  pure  in 
the  soluble  condition.  It  appears  to  contain  less  sulphur  even  than  serum  albumin 
contains. 

Globulin,  or  serum  globulin,  is  very  like  albumin,  but  is  insoluble  in  pure  water  ; 
it  dissolves  in  a  very  weak  solution  of  salt,  and  in  very  weak  acids  and  alkalies. 
It  dissolves  in  water  saturated  with  oxygen,  and  is  precipitated  by  carbon  dioxide. 
This  gas  precipitates  it  in  a  granular  form  from  the  serum  of  blood  ;  saturation  of 


FIBRIN.  75 ! 

the  serum  with  salt  also  precipitates  it.     Crystallin  is  found  in  the  aqueous  humour 
and  crystalline  lens  of  the  eye. 

Myosin  (/tus,  a  muscle)  separates  from  muscle  plasma  (the  liquid  contained  in 
living  muscle)  after  death,  producing  rigor  mortis.  Chopped  flesh  is  triturated  to 
a  pulp  with  common  salt,  9  parts  of  water  are  added  for  i  of  salt,  the  whole 
digested  for  some  time  at  24°  C.,  pressed  through  linen  and  filtered  ;  the  myosin  is 
precipitated  on  adding  much  water  or  salt. 

556.  Fibrin  is  the  albuminoid  which  separates  from  the  blood  when 
this  has  been  shed  from  the  animal,  causing  the  coagulation  or  clotting 
of  the  blood  plasma.    It  appears  to  be  formed  from  jibrinogen — a  soluble 
albuminoid  existing  in  the  plasma— by  a  ferment  (thrombin)  contained 
in  the  white  blood  corpuscles.    Human  blood  yields  about  0.25  per  cent, 
of  fibrin,  which  resembles  myosin,  but  is  not  dissolved  by  solution  of 
salt.     It  may  be  obtained  from  freshly  drawn  blood  by  whipping  it 
with  a  bunch  of  twigs,  when  the  fibrin  adheres  to  them  in  threads  which 
become  nearly  white  when  washed,  and  may  be  freed  from  fat  by 
alcohol  and  ether.     If  the  blood  be  not  stirred  when  freshly  drawn,  it 
forms  a  red  clot,  caused  by  the  coagulation  of  the  fibrin,  and  the  en- 
tanglement in  it  of  the  red  blood  corpuscles ;  if  the  clot  be  cut  up  and 
washed  in  a  cloth,  the  corpuscles  and  blood  serum  may  be  washed  away 
and  the  fibrin  left.     If   7   measures  of  blood  be  drawn  into  a  vessel 
containing  i  measure  of  a  cold  saturated  solution  of  Na2S04,  the  fibrin 
wrill  remain  in  solution,  whilst  the  blood-globules  will  be  deposited  on 
standing.     The  clear  yellow  solution  containing  albumin,  globulin,  and 
fibrinogen  is  largely  diluted  with  water,  when  fibrin  is  precipitated. 

Fibrin  forms  elastic  strings  which  dry  into  a  yellow  horny  mass.  When  fresh, 
it  readily  absorbs  oxygen,  and  evolves  C02  ;  when  moist  it  decomposes  H202, 
evolving  0.  It  is  insoluble  in  water,  alcohol,  solution  of  salt,  and  in  cold  very 
dilute  HC1  (o.i  per  cent.),  but  this  dissolves  it  at  60°  C.  Solution  of  nitre  at  40°  C. 
also  dissolves  it.  When  heated  for  some  time  with  water  at  72°  C.,  it  becomes 
insoluble  in  dilute  acids  and  salts,  but  dissolves  in  alkalies.  Boiled  for  many  hours 
with  water,  one-fifth  of  it  may  be  dissolved,  yielding  a  solution  having  some  of  the 
properties  of  gelatine.  Heated  with  water  at  120°  C.  for  some  hours,  it  is  almost 
entirely  dissolved.  The  solution  of  fibrin  in  weak  HC1  is  precipitated  by  neutralisa- 
tion and  by  saline  solutions.  The  precipitate  always  contains  a  little  calcium 
phosphate.  Fibrin  soaked  in  weak  potash  becomes  gelatinous  and,  if  heated  to 
60°  C.,  dissolves  to  a  solution  resembling  that  of  albumin.  Fibrin  is  hardened  and 
rendered  non-putrescible  when  soaked  in  solution  of  tannin.  Moist  fibrin  soon 
begins  to  putrefy  when  exposed  to  air,  and  becomes  fluid  in  a  week  ;  the  products 
of  putrefaction  resemble  those  from  albumin. 

Fibrinogen  may  be  precipitated  from  blood  plasma  by  a  solution  of  salt  which  is 
semi-saturated,  and  can  in  this  way  be  separated  from  the  serum  globulin. 

Fibrin  from  blood  contains  more  nitrogen  than  the  albumin  of  serum  (17.4  : 15.6) 
and  a  little  less  oxygen  (21.8  :  23.1).  It  does  not  appear  that  blood-fibrin  and  flesh- 
fibrin  are  identical. 

557.  Casein  is  the  chief  constituent  of  the  curd  of  milk,  and  differs 
from 'the  other  albuminoids  in  not  coagulating  spontaneously  or  on 
heating.     It  exists  in  milk  as  a  soluble  compound  with  a  little  potash 
or  soda,  and  is  separated  as  curd  when  the  alkali  is  neutralised  either 
by  adding  an  acid,  or  by  the  formation  of  acid  (lactic)  by  the  decom- 
position of  milk-sugar  caused  by  spontaneous  fermentation. 

It  is  prepared  by  precipitating  diluted  milk  with  acetic  acid  and  washing  the 
precipitate  with  water,  alcohol,  and  ether  in  succession,  to  remove  soluble  matte 
and  fat ;  it  is  further  purified  by  dissolving  in  weak  soda  and  precipitating  : 
acetic  acid.     Coagulated  casein  is  characterised  by  the  facility  with  which 
dissolved  by  weak  alkaline  solutions,  yielding  a  liquid  upon  the  surface  Of  WW 
when  boiled,  an  insoluble  pellicle  forms,  like  that  produced  on  the  surface  ot  b 


752  CASEIN. 

milk.  Coagulated  casein  may  also  be  dissolved  by  acetic  or  oxalic  acid,  but  sul- 
phuric or  hydrochloric  acid  reprecipitates  it,  these  acids  forming  compounds  with 
casein  which  are  insoluble  in  the  acids,  but  soluble  in  water.  If  skimmed  milk  be 
carefully  evaporated  to  dryness,  and  the  fat  extracted  from  the  residue  by  ether, 
the  casein  is  left  in  the  soluble  form  mixed  with  milk-sugar,  and  may  be  dissolved 
in  water  or  in  dilute  alcohol. 

A  distinctive  property  of  casein  is  its  coagulation  by  rennet,  the 
mucous  membrane  of  the  stomach  of  the  calf,  a  small  quantity  of  which 
or  of  its  solution  in  brine,*  coagulates  the  casein  in  a  large  quantity  of 
milk  ;  the  coagulation  does  not  appear  to  depend  upon  the  formation  of 
lactic  acid,  but  upon  a  specific  action  of  the  rennet ;  the  curd  thus 
produced  contains  calcium  and  magnesium  phosphates,  and  is  not  easily 
soluble  in  sodium  carbonate.  The  casein  of  milk  is  more  readily 
coagulated  by  acids  and  by  rennet  when  the  milk  is  warmed  ;  hence 
milk  which  has  undergone  very  slight  fermentation  is  curdled  when 
heated,  but  if  fresh  milk  be  heated  to  boiling,  the  decomposition  will  be 
prevented.  The  casein  of  milk  is  precipitated  by  some  neutral  salts, 
such  as  sodium  chloride  or  magnesium  sulphate,  and  even  by  an  excess 
of  sodium  carbonate. 

At  the  present  time,  the  condition  in  which  casein  exists  in  milk  and  the  cause 
of  its  coagulation  by  rennet  are  subjects  of  much  discussion.  Some  chemists  claim 
that  the  milk  contains  caseinogen,  which  is  precipitated  by  acids,  and  differs  from 
casein  into  which  it  is  converted  by  rennet.  According  to  Hammarsten,  caseinogen 
is  only  coagulated  by  rennet  when  it  contains  earthy  phosphates,  which  combine 
with  the  casein  produced  and  precipitate  it.  A  solution  of  casein  free  from  lime 
salts  is  not  precipitated  by  rennet,  but  the  precipitation  occurs  on  adding  a  lime 
salt,  even  though  the  rennet  has  been  made  inactive  by  heating  the  casein  solution 
containing  it. 

The  general  chemical  behaviour  of  casein  resembles  that  of  albumin.  It  contains 
a  little  less  sulphur  than  albumin  and  fibrin  contain,  and  phosphorus  appears  to 
be  an  essential  constituent  (0.85  per  cent.). 

Casein  combines  with  slaked  lime  to  form  a  hard  insoluble  mass,  so  that  a  mix- 
ture of  cheese  with  lime  is  sometimes  used  as  a  cement  for  earthenware.  The  curd 
of  milk,  washed  and  dried,  is  used  by  calico-printers,  under  the  name  of  lactarine, 
for  fixing  colours.  If  it  be  dissolved  in  weak  ammonia,  mixed  with  one  of  the 
aniline  dyes,  printed  on  calico,  and  steamed,  the  colour  is  left  as  an  insoluble  com- 
pound with  the  casein.  By  treating  coagulated  casein  with  formaldehyde  it 
becomes  similar  to  horn,  for  which  it  is  substituted  in  making  combs  and  the 
like. 

Legumin,  or  vegetable  casein,  is  found  in  peas,  beans,  and  most  leguminous  seeds. 
If  dried  peas  be  crushed  and  digested  for  some  time  in  warm  water,  a  turbid 
liquid  is  obtained,  holding  starch  in  suspension  ;  this  is  allowed  to  settle,  the  super- 
natant liquid  precipitated  by  acetic  acid,  and  the  legumin  purified  from  fat  by 
washing  with  alcohol  and  ether.  It  closely  resembles  casein,  its  solution  forming 
a  pellicle  when  heated,  and  being  coagulated  by  rennet.  In  composition  it  differs 
somewhat  from  casein,  containing  about  I  per  cent,  more  nitrogen,  and  only  about 
half  as  much  sulphur.  When  boiled  with  dilute  sulphuric  acid,  legumin  yields 
much  less  leucine  than  albumin  and  fibrin  furnish,  and  very  little  tyrosine  ;  but 
it  gives  more  aspartic  acid  and  glutamic  acid,  C3H5(NH2)(C02H)2,  homologous 
with  aspartic  acid. 

Gluten  is  the  tough,  sticky  substance  which  is  left  when  flour  is  made  into  dough, 
tied  up  in  muslin,  and  kneaded  in  water  as  long  as  any  starch  passes  through.  It 
speedily  putrefies  when  exposed  to  the  air,  and  dries  up  to  a  brittle,  horny  mass  at 
100°  C.  When  fresh  gluten  is  boiled  with  dilute  alcohol,  a  portion  is  left  undissolved, 
and  has  been  named  vegetable  fibrin,  as  it  forms  a  tough  elastic  mass.  It  dissolves 
in  very  dilute  HC1  and  in  dilute  alkalies,  and  is  precipitated  by  acetic  acid  and  by 
salts.  When  the  alcoholic  solution  cools,  it  deposits  white  flakes  of  mucedin, 

*  The  active  principle  (lab  or  chymosin)  of  the  rennet  nauy  be  obtained  from  rennet 
extract  by  saturating  it  with  salt,  when  the  lab  will  rise  to  the  surface. 


GELATINE. 

and  on  adding  water  to  the  nitrate,  glladin  is  precipitated.     These  substances- 
resemble  legumm  in  composition,  but  contain  twice  as  much  sulphur 

It  has  been  asserted  that  gluten  does  not  exist,  as  such  in  flour,  but  is  produced 
from  the  proteids  in  the  flour  by  the  action  of  water,  which  may  enable  a  ferment 

to  effect  the  conversion. 

558.  Gelatine. — This  substance  is  so  called  from  gelu,  ice,  because  its- 
solution  in  hot  water  becomes  a  transparent  jelly  on  cooling.  It  con- 
tains 50  per  cent.  C,  25.7  0,  17.7  N,  and  6.6  H,  numbers  which 
approximate  to  C42H66N13016,  but  its  molecular  formula  has  not  been 
determined,  because  it  cannot  be  converted  into  vapour,  and  does  not 
form  well-defined  compounds  with  other  bodies.  It  may  be  obtained 
by  digesting  bones  in  cold  dilute  hydrochloric  acid,  till  the  calcium 
phosphate  and  other  salts  are  dissolved,  leaving  a  residue  of  the  same 
form  as  the  bone,  but  of  a  soft,  flexible  character.  This  is  termed  ossein, 
and  has  the  same  composition  as  gelatine,  into  which  it  is  converted  by 
long  boiling  with  water,  especially  under  pressure,  a  solution  being 
obtained  which  becomes  a  jelly  on  cooling,  and  leaves  a  brittle,  trans- 
parent mass  (glue)  when  dried.  Gelatine  does  not  fuse  when  heated,  but 
swells  up  and  decomposes,  yielding  very  offensive  alkaline  vapours,  con- 
taining ammonia  and  compound  ammonias  (methylamine,  &c.),  pyrrol, 
and  its  derivatives,  toluene,  naphthalene,  ammonium  cyanide,  water,  &c. 
DippeVs  oil,  obtained  by  distilling  bones,  contains  these  products, 
together  with  others,  in  the  formation  of  which  the  fat  of  the  bones 
takes  part,  such  as  the  cyanides  of  the  fatty  acid  series  (propionitrile, 
&c.),  pyridine  bases,  phenol,  and  aniline. 

Gelatine  softens  and  swells  in  cold  water,  but  does  not  dissolve ;  hot 
water  dissolves  it,  and  the  solution  gelatinises  on  cooling,  even  when  it 
contains  only  i  per  cent.  Continued  boiling  of  the  solution  destroys 
the  tendency  to  gelatinise.  Gelatine  is  insoluble  in  alcohol,  which  pre- 
cipitates it  in  white  flakes  from  its  aqueous  solution.  It  is  also  precipi- 
tated by  tannin,  which  combines  with  it  to  form  an  insoluble  non- 
putrescible  compound.  Mercuric  chloride  also  precipitates  solution  of 
gelatine.  If  gelatine  solution  be  mixed  with  potassium  dichromate,  the 
jelly  formed  on  cooling  becomes  insoluble  on  exposure  to  light,  which 
is  turned  to  account  in  photography  ;  the  action  probably  consists  in  an 
oxidation  of  the  gelatine.  Acetic  acid  dissolves  gelatine  (liquid  glm) ; 
alkalies  also  dissolve  it.  When  boiled  with  strong  alkalies  or  with  di- 
luted sulphuric  acid  for  a  long  time,  it  yields  leucine  and  glycocine 
(sugar  of  gelatine).  Heated  with  sulphuric  acid  and  potassium  dichro- 
mate or  manganese  di-oxide,  gelatine  yields  numerous  products  of 
oxidation,  among  which  are  found  many  of  the  fatty  acids,  with  their 
corresponding  aldehydes  and  cyanides,  with  benzoic  acid,  bitter-almond 
oil,  &c. 

Gelatine  may  also  be  obtained  by  the  action  of  water  at  a  high  temperature  on 
skin,  sinews,  and  connective  tissue.    Isinglass  is  very  similar  to  gelatine  and  i 
prepared  from  the  air-bladder  of  fish,  especially  of  the  sturgeon.     It  differs  from 
gelatine  in  being  liable  to  settle  in  flocks  when  stirred  up  with  water  ;  hence  _ 
application  as  a  "  fining"  for  beer,  for  which  purpose  it  is  made  into  an  emulsn 
by  treatment  with  sulphurous  acid  (cutting}.     Glue  is  made  from  the  refuse  and 
parings  of  hides,  after  being  cleansed  from  hair  and  blood  by  steeping  in  lime- 
water,  and  exposed  to  the  air  for  some  days  to  convert  the  lime  into  carbonate,  and 
prevent  the  injurious  effect  of  its  alkaline  character  -upon  the  gelatine, 
then  boiled  with  water  till  the  solution  gelatinises  firmly  on  cooling,  when  il 
run  off  into  another  vessel,  kept  warm  to  allow  the  impurities  to  settle  down,  af 

3  B 


754  MUCIN. 

which  it  is  allowed  to  set  in  shallow  wooden  coolers.  The  jelly  is  cut  up  into  slices 
and  dried  upon  nets  hung  up  in  a  free  current  of  air.  Spring  and  autumn  are 
usually  selected  for  drying  glue,  since  the  summer  temperature  would  liquefy  it,  and 
frost  would,  of  course,  split  it  and  render  it  unfit  for  the  market.  Size  is  made  in 
a  similar  manner,  but  finer  skins  are  employed,  and  the  drying  is  omitted,  the  size 
being  used  in  the  gelatinous  state.  The  best  size  is  made  from  parchment  cuttings. 
Moist  gelatine  easily  putrefies,  becoming  very  offensive  :  for  this  reason  size  is  often 
treated  with  sulphurous  acid. 

Clwndnn  (x&vfyos,  cartilage)  is  prepared  by  the  action  of  water  at  a  high 
temperature  on  the  cartilages  of  the  ribs  and  joints,  and  resembles  gelatine  in 
composition  and  properties,  but  contains  less  N  and  a  small  quantity  of  S.  The 
aqueous  solution  of  chondrin  is  precipitated  by  acetic  acid,  by  alum,  and  by  lead 
acetate,  which  do  not  precipitate  gelatine.  When  boiled  with  dilute  sulphuric  acid, 
it  yields  leucine,  but  no  glycocine.  Boiled  with  hydrochloric  acid,  it  gives  a 
solution  which  reduces  Fehling's  solution  like  glucose. 

Sericin,  or  silk-gelatine,  ClgH?5N508,  is  the  so-called  gum  extracted  from  silk  by 
boiling  with  water  ;  it  resembles  gelatine,  but  is  precipitated  by  basic  lead  acetate, 
and,  when  boiled  with  sulphuric  acid,  yields  leucine,  tyrosine,  and  amldogly eerie 
acid  (serin),  C2H3(OH)(NH2)C02H.  (Cystine,  C3H7N02S,"found  in  some  rare  urinary 
calculi,  appears  to  be  a  sulphur  derivative  of  serin.) 

Keratin  forms  the  chief  part  of  horns,  claws,  nails,  feathers,  hair,  and  wool, 
and  remains  when  these  have  been  treated  with  all  ordinary  solvents.  It  is 
softened  by  long  boiling  with  water,  and  is  dissolved  when  heated  with  water 
under  pressure.  It  swells  up  and  gradually  becomes  soluble  in  strong  alkalies 
and  in  acetic  acid,  especially  on  boiling.  It  contains  more  sulphur  than  do  the 
albuminoids.  Fibroin  from  silk,  and  spongln  from  sponge,  are  similar  bodies. 

CJiitin,  C18H30N2012,  is  the  chief  constituent  of  the  shells  of  lobsters,  crabs  and 
beetles,  and  is  left  after  exhausting  them  with  water,  alcohol,  ether,  acetic  acid,  and 
alkali.  It  is  a  white  translucent  substance,  soluble  in  cold  strong  H2S04  to  a  solu- 
tion which  yields  glucose  when  diluted  ;  the  change  appears  to  be  a  hydrolysis,  4'H20 
being  absorbed  to  produce  ghieosamlne,  C6Hn(NH2)05,  (2  mols.)  and  acetic  acid 
(3  mols.). 

Mucin  is  the  substance  which  gives  the  viscous  character  to  bile,  saliva,  and 
some  other  animal  secretions,  and  to  the  slime  of  the  snail.  To  prepare  it,  snails 
are  cut  up,  triturated  with  sand  to  a  pulp,  boiled  with  water,  filtered  while  hot, 
and  precipitated  by  excess  of  acetic  acid  ;  the  precipitated  mucin  is  washed  with 
weak  acetic  acid  as  long  as  the  washings  are  precipitated  by  tannic  acid,  indi- 
cating peptone.  Dry  mucin  is  unaffected  even  by  hot  water.  Moist  mucin  swells 
up  in  a  remarkable  manner  in  water,  but  does  not  dissolve  ;  a  little  acid  causes  it 
to  separate  in  flocks  which  do  not  easily  dissolve  in  an  excess  of  acid.  Alkalies 
dissolve  it  and  acids  reprecipitate  it.  Mucin  dissolves  in  a  strong  solution  of 
salt,  and  is  precipitated  again  by  water.  Alcohol  coagulates  mucin  into  flocks. 
Acid  solutions  of  mucin  are  not  precipitated  by  potassium  ferrocyanide  (unlike 
albumin).  Boiling  dilute  acids  dissolve  mucin,  converting  it  into  a  substance 
having  the  properties  of  glucose  and  another  which  resembles  albumin.  The 
composition  of  mucin  has  not  been  well  established  ;  it  contains  the  same 
elements  as  albumin,  but  much  less  nitrogen. 

Nuclein  is  contained  in  the  nuclei  of  pus-globules,  in  the  blood  globules  of 
birds  and  snakes,  in  yolk  of  egg,  in  brain,  and  in  milk.  It  stands  apart  from 
other  proteids,  by  containing  about  2  per  cent,  of  phosphorus,  in  actual  organic 
combination  (and  not  as  calcium  phosphate,  which  so  constantly  accompanies  the 
albuminoids).  In  extracting  it,  advantage  is  taken  of  its  insolubility  in  the 
digestive  fluids.  Pus-globules  are  treated  with  warm  alcohol,  which  removes 
lecithin,  and  afterwards  with  a  pepsin  solution  made  from  extract  of  pig's  stomach, 
and  containing  I  per  cent,  of  strong  HCL  The  insoluble  residue  consists  of 
nuclein.  Pus-globules  are  obtained  by  treating  the  discharge,  or  the  bandages  to 
which  it  adheres,  with  a  mixture  of  i  part  of  a  saturated  solution  of  sodium  sul- 
phate and  9  parts  of  water,  when  the  serum  remains  in  solution,  and  the  pus- 
globules  sink  and  may  be  washed  by  decantation  ;  if  these  be  digested  with  cold 
dilute  HC1  and  afterwards  shaken  with  a  mixture  of  ether  and  water,  the  nuclei 
remain  as  a  fine  powder  at  the  bottom.  Nuclein  is  remarkable  for  its  insolubility 
in  all  ordinary  solvents,  it  appears  to  have  an  acid  character,  and  dissolves  in 
sodium  carbonate  or  acetate,  the  solution  in  the  latter  giving  precipitates  with 
salts  of  zinc,  copper  and  lead.  It  is  of  considerable  importance  in  the  chemistry 


HEMOGLOBIN. 


the  group  C.,H5  (glyceryl),  and  probably  the  mdSl^^Jm^T  ^  11t.cont^1J18 
and  a  phosphorised  group,  N(CH,)3  C2H4(PO  V)  wlv  £?  f  ^  ?leiC  a°'d8' 
N(CH3)  -C  H3-OH  (p.  666).  A  variation  ffai^  jftSUj^^ft 

Lecithin  may  be  prepared  from  the  substance  of  the  brain  by  exhausting  it 
with  ether,  treating  the  residue  with  alcohol,  and  cooling  the  alcohoHc  *o  ution 
in  ice,  when  a  mixture  of  lecithin  and  cerebrin  is  deposited  On  trattai 
with  ether,  the  lecithin  is  dissolved,  and  may  be  purified^^po^^^ 
redissolvmg  m  alcohol,  adding  an  alcoholic  solution  of  platinfc  chforide  and 
decomposing  the  platinum  salt  (C42H84NP08HCl)2.PtCl4,  withH2S  on  e?a^atiSg 
the  nitrate,  the  lecithin  is  obtained  as  a  fusible  crystalline  body,  insofuWe  if 
water  and  sparing  y  soluble  in  cold  alcohol  and  ether.  It  combines  both  wi  h 
bases  and  acids.  When  boiled  with  acids  or  with  potash  or  baryta  i  vSds 
neurme,  phosphoglyceric  acid,  C3H5(OH)2.P02(OH)2,  palmitic  and  oleic  acids 

.Cerebrin  obtained  from  brain  as  above  described,  is  a  white  powder  which 
swells  up  like  starch  when  boiled  with  water.  It  yields  a  substance  resemblin- 
glucose  when  boiled  with  dilute  acids.  The  formula  of  cerebrin  or  metric 
1*  ^  8°metimeS  Called'  aPPears  to  be  CwHgsNOs.  It  is  also  found  in  pus- 


The  so-called  pratagon  appears  to  be  a  mixture  of  lecithin  and  cerebrin. 

560.  Haemoglobin.  —  The  colouring-matter  contained   in   the   red 
globules  of  arterial  blood  is  called  oxyhcemoglobin,  and  resembles  albumin 
in  composition,  except  that  it  contains  only  0.4  per  cent,  of  sulphur 
and  0.43  per  cent,   of  iron.     To  extract  it  from   blood,  the  fibrin  is 
separated  by  whipping  (p.    751),  and  the  defibrinated  blood  is  mixed 
with  ten  volumes  of  a  solution  containing  3  per  cent,  of  NaCl.     This 
prevents  the  coagulation  of  the  albuminoids,  and  the  red  globules  sub- 
side after  a  day  or  two  ;  the  clear  liquid  is  poured  off,  and  the  globules 
shaken  with  water  and  an  equal  volume  of  ether,  which  dissolves  the 
envelopes  of  the  globules,  and  allows  the  colouring-matter  to  pass  into 
the  water.     The  aqueous  layer  is  separated,  cooled  in  ice,  one-fourth  of 
its  volume  of  alcohol  added,  and  the  cooling  carried  to  -  5°  C.,  when  the 
oxyhsemoglobin   crystallises  in  forms  which  vary  in  different  animals. 
That  obtained  from  the  blood  of  men,  oxen,  sheep,  pigs,  and  rabbits  is 
not  easily  crystallised,  the  best  for  this  purpose  being  the  blood  of  dogs, 
guinea-pigs,  hedgehogs,  and  rats.     The  crystals  contain  oxygen  in  a 
loosely  combined  form,  which  they  evolve  when  exposed  in  a  vacuum, 
especially  if  warmed,  becoming  thus  converted  into  hcemoglobin,  which 
again  absorbs  oxygen  on  exposure  to  air  ;  this  change  is  attended  with 
production  of  a  much  brighter  red  colour,  and  with  a  difference  in  the 
action  on  transmitted  light,  for  if  white  light  be  allowed  to  pass  through 
the  solution  of  oxyhsemoglobin  contained  in  a  test-tube  placed  before 
the  slit  of  a  spectroscope  (p.  328),  the  green  of  the  spectrum  is  seen  to 
be  crossed  by  two  broad  black  bands,  which  are  also  seen  when  arterial 
blood  is  employed,  whilst  the  solution  of  haemoglobin  exhibits  only  one 
band  in  the  middle  of  the  green,  which  is  seen  when  venous  blood  is 
employed.     This  difference  in  the  absorption-spectrum  is  best  shown  by 
reducing  the  solution  of  oxyhaemoglobin  with  a  little  ferrous  sulphate, 
mixed  with  tartaric  acid  and  ammonia  in  excess.     The  oxygen  of  oxy- 


756  BILE. 

haemoglobin  is  also  displaced  by  passing  hydrogen  or  C02,  haemoglobin 
being  left,  and  the  colour  changing  from  red  to  purple. 

Oxyhsemogoblin,  when  shaken  with  CO,  parts  with  its  oxygen  and 
absorbs  an  equal  volume  of  CO,  its  colour  changing  to  purple  ;  the 
absorption-spectrum  exhibits  two  dark  bands,  which  are  situated  further 
from  the  sodium-line  (D)  and  nearer  to  the  blue  of  the  spectrum  than 
is  the  case  with  haemoglobin.  This  is  turned  to  account  in  cases  of 
poisoning  by  carbonic  oxide.  The  compound  of  haemoglobin  and  CO 
may  be  obtained  in  bluish-red  four-sided  prisms.  When  solution 
of  oxy haemoglobin  is  heated  above  70°  C.,  it  is  decomposed  into 
albumin,  which  coagulates,  and  another  red  colouring-matter,  termed 
haematin. 

Hcematin,  C34H34N4Fe05,  is  formed  when  oxyhasmoglobin  is  decomposed  by 
acids.  If  a  solution  of  that  substance,  mixed  with  a  little  NaCl,  is  evaporated 
over  sulphuric  acid  to  a  syrup,  mixed  with  15  times  its  volume  of  glacial  acetic 
acid,  and  heated  on  a  steam-bath  for  several  hours,  it  yields,  on  cooling,  flat 
rhombic  prisms  of  hasmatin  hydrochloride  (formerly  known  as  hcemin,  or  blood- 
crystals)  of  a  dark,  violet-red  colour,  and  metallic  lustre,  containing  single  mole- 
cules of  hasmatin  and  HC1.  The  formation  of  these  crystals  is  employed  for  the 
identification  of  blood-stains,  the  suspected  matter  being  placed  on  a  microscope 
slide,  a  little  sodium  chloride  added,  and  glacial  acetic  acid  allowed  to  run  under 
the  cover-glass  ;  on  heating  till  bubbles  appear,  and  cooling,  the  dark  red  hasmin 
crystals  become  visible.  Hasmatin  is  a  magnetic  substance,  while  oxyhasmoglobin 
and  carbonic  oxide  haemoglobin  are  diamagnetic. 

561.  Bile  Constituents. — The  chief  colouring-matter  of  the  bile  is  bilirubin, 
C16H18N203,  which  is  accompanied  by  bilifuscin,  C16H20N204,  and  biliprasin, 
CjgH^NaOg.  These  may  be  extracted  from  gall-stones,  in  which  they  exist  in  com- 
bination with  calcium.  The  powdered  calculi  are  boiled  with  alcohol  and  ether  to 
extract  the  cholesterin,  and  with  dilute  HC1  to  remove  the  lime.  After  washing 
and  drying,  the  residue  is  boiled  with  chloroform,  which  extracts  bilirubin  and 
bilifuscin  ;  the  chloroform  is  distilled  off  and  the  residue  boiled  with  alcohol,  which 
dissolves  the  latter.  The  original  residue,  un dissolved  by  chloroform,  contains 
biliprasin,  which  may  be  extracted  by  boiling  with  alcohol. 

Bilirubin  crystallises  from  chloroform  in  dark-red  prisms,  insoluble  in  water 
and  alcohol,  but  soluble  in  alkaline  liquids,  and  imparting  a  yellow  colour  to  a 
very  large  volume  of  solution.  It  appears  to  have  acid  properties.  Its  alkaline 
solutions  absorb  oxygen  and  become  green,  yielding  a  green  precipitate  of  bili- 
verdin,  C]6H18N204,  on  addition  of  an  acid.  Bilifuscin  and  biliprasin  are  obtained 
as  very  dark  green  amorphous  bodies,  insoluble  in  water.  The  alkaline  solutions 
of  the  biliary  colouring-matters,  when  treated  with  nitric  acid,  yield  successive 
tints  of  green,  blue,  violet,  red,  and  yellow,  which  serve  to  indicate  the  presence 
of  bile  in  other  secretions. 

Olyoooholic  acid,  C24H3904<NH'CH2C02H,  exists  in  bile  as  a  sodium  salt,  together 
with  the  sodium  salt  of  taurocholic  acid,  C24H3904-NH'CH2CH2S03H.  To  extract 
them,  ox-gall  is  mixed  with  bone-black  to  a  paste,  which  is  dried  on  the  steam-bath 
and  digested  with  absolute  alcohol,  which  dissolves  the  sodium  salts  together  with 
cholesterin  and  cholin.  Ether  is  then  added,  to  precipitate  the  sodium  salts. 
These  are  dissolved  in  water,  and  decomposed  by  dil.  .H2S04,  which  precipitates 
the  glycocholic  acid,  at  first  amorphous,  but  changing  into  colourless  needles.  It 
is  sparingly  soluble  in  water,  but  dissolves  in  alcohol,  though  not  in  ether.  The 
alkali  salts  are  very  soluble  and  sweet.  It  is  characterised  by  its  behaviour  with 
solution  of  sugar  and  strong  H2S04,  which  give  a  purple-red  colour  (Pettenltofer 's 
test  for  bile).  It  is  an  amido-acid,  and  yields  ohologlycholic  acid,  C^H^NO^  when 
treated  with  nitrous  acid.  When  boiled  with  alkalies,  glycocholic  acid  is  hydro- 
lysed  into  glycocine  (amido-acetic  acid)  and  cholic  acid;  C26H43N06  +  H00  = 
CH2(NH2)  -C02H  +  C^opg.  Boiling  with  dilute  HC1  effects  the  same  change"  but 
converts  the  cholic  acid  into  dy  sly  sin,  C24H3603,  an  amorphous  precipitate,  which 
becomes  potassium  cholate  when  boiled  with  alcoholic  KOH. 

Taurocholic  acid  is  not  precipitated  by  normal  lead  acetate,  which  precipitates 
the  glycocholic  acid  from  ox-gall,  and  the  filtrate  gives  a  precipitate  of  lead 
taurocholate  on  adding  basic  lead  acetate.  When  this  is  suspended  in  water  and 


CHOLESTERIN. 

decomposed  by  H2S  a  solution  of  the  acid  is  obtained,  which  may  be  concen- 
trated and  mixed  with  ether,  when  the  acid  separates  as  a  syrup  which  deposits 
needle-  ike  crystals.  Dog's  bile  yields  more  taurocholic  acid  than  that  of  the  ox 
Taurocholic  acid  dissolves  readily  in  water  and  alcohol.  It  is  decomposed,  like 
glycochohc  acid  by  boiling  with  alkalies  or  acids,  but  it  yields  taurine,  CQH,NSO, 
instead  of  glycocme  ;  C.26H45NS07  +  H20  =  C2H7NS03  +  C24H4005. 

Cholesterin,  or  cholesterol,  C^H^OH,  is  a  crystalline  alcohol  found  in  bile,  and 
composing  the  chief  part  of  gall-stones  or  biliary  calculi,  from  which  it  may  be 
extracted  by  boiling  with  alcohol,  which  deposits  the  cholesterin  in  transparent 
lustrous  plates  on  cooling.  It  is  insoluble  in  water,  but  soluble  in  ether  •  fuses  at 
145  C.  and  sublimes  at  200°  C.  It  is  unchanged  by  boiling  with  potash,  and 
yields  ethereal  salts  when  heated  with  the  fatty  acids  in  sealed  tubes.  HC1  con- 
^61S  ^^iocholesteryl  chloride,  C^H^Cl,  and  ammonia  into  cholester  «,„;,«>. 
^26H43'NH-2-  When  dissolved  in  petroleum  and  treated  with  sodium  it  evolves 
hydrogen  and  forms  crystalline  C26H43'ONa.  When  moistened  with  strong  HNO, 
and  dried,  cholesterin  gives  a  yellow  residue  which  becomes  red  with  NH3.  Strong 
HC1  and  a  little  Fe2Cl6  give  a  violet-blue  colour  with  cholesterin  on  evaporation. 
Cholesterin  occurs  in  the  blood,  in  brain,  in  yolk  of  egg,  in  cod-liver  oil,  and  in 
muslt,  the  dried  secretion  of  the  musk  deer.  It  is  also  found  in  sheep's  wool 
together  with  isocholesterin,  having  the  same  composition,  but  crystallising  in 
needles  which  melt  at  138°  C.  Cholesterin  can  absorb  over  100  per  cent,  of  water, 
and  in  this  condition  is  used  as  an  emollient  (lanolin). 


Phytosterin,  CggH^O,  is  a  similar  substance  found  in  peas  and  other  seeds,  and 
in  olive  oil. 

XVI.  HETEROCYCLIC  COMPOUNDS. 

562.  Nearly  all  the  compounds  hitherto  considered  have  been  hydro- 
carbons or  derivatives  thereof.     There  remains  a  class  of  substances 
having  closed-chain  nuclei,  composed  not  of  carbon  alone,  as  are  the 
benzene  and  naphthalene  nuclei,  for  example,  but  containing  one  or 
more  atoms  of  N,  O  or  S  as  member  or  members  of  the  closed  chain. 
Thus   they  are    not   strictly  derivatives  of    hydrocarbons.      In  other 
respects  they  might  have  been  considered  under  the  preceding  classes, 
for  they  are  hydrides,  alcohols,  acids,  &c.,  derived  from  these  heterocyclic 
nuclei  instead  of  from  open-chain  nuclei  or  from  carbocydic  nuclei  (like 
the  benzene  nucleus). 

A  few  compounds  which  are  strictly  within  this  class  have  already 
been  described,  such  as  succinic  anhydride  and  the  various  lactones. 
These  are,  however,  more  of  the  nature  of  open-chain  derivatives  than 
are  those  that  remain  to  be  discussed.  A  number  of  the  three  and  four 
membered  heterocyclic  compounds  have  also  received  passing  notice  — 
e.g.,  ethylene  oxide,  trimethylene  oxide,  diazo-methane,  &c.  The  five- 
and  six-membered*  rings  of  this  kind,  together  with  the  condensed 
nuclei  corresponding  with  naphthalene,  £c.,  will  now  receive  attention. 

563.  Five-membered  heterocyclic  compounds.  —  The  prototypes 
of  these  are  furfurane,  thiophen,  and  pyrrol,  which  are  believed  to 
possess  constitutions  expressed  by  the  following  formulae  :— 

CH  :  CH,        CH  :  CHX       CH  :  CH, 

>0-          /s-         /NIL 
CH  :  CH/       CH  :  CH/       CH  :  CH/ 

Furfurane.  Thiophen.  Pyrrol. 

They  resemble  benzene  in  that  they  yield  derivatives  similar  to  those 
of  that  of  hydrocarbon,  and  show  little  disposition  to  form  addition- 

«  As  in  the  case  of  the  carbocyclic  compounds,  7,  8,  &c.,  membered  rings  are  little  known. 


75$  THIOPHEN. 

products  with  the  halogens.  In  fact,  the  arguments  which  lead  to  the 
closed-chain  formula  for  benzene  (p.  541)  are  equally  applicable  to  these 
compounds. 

Eloquent  of  their  constitution  is  their  formation  from  y-diketones, 
such  as  acetonylacetone  (p.  647) ;  by  dehydration  this  compound  yields 
i  :  4-dimethylf urfurane. 

CH2-  CO  •  CH3  CH :  C(CH3\ 

-     H20     =      •  >0. 

CH2-  CO  •  CH3  CH :  C(CH3)/ 

With  P2S5  it  yields  i  :  4-dimethylthiophen,  and  with  NH3  i  :  4-di- 
methyl  pyrrol. 

Two  classes  of  mono-substitution  products  are  known  from  these  compounds — 
the  a-derivatives,  which  contain  the  substituent  attached  to  a  carbon  atom 
adjacent  to  the  0,  S  or  1ST,  and  the  /^-derivatives,  in  which  a  hydrogen  atom  of  one 
of  the  far  carbon  atoms  has  been  displaced.  A  third  class  is  possible  in  the  case 
of  pyrrol,  for  the  H  of  the  NH  group  can  be  substituted.  The  possible  di- 
derivatives  are  more  numerous  than  in  the  case  of  benzene  ;  their  orientation  is 
expressed  by  numbering  the  near  carbon  atoms  i  and  4,  and  the  far  atoms 
2  and  3  ;  or  by  numbering  the  N,  0  or  S  atom  i  and  the  C  atoms  2,  3,  4,  5  suc- 
cessively. A  reaction  common  to  all  three  compounds  is  the  blue  colour  produced 
by  their  reaction  with  isatin  ($.f.)  and  strong  H2S04. 

Furfurane,  C4H40,  together  with  several  of  its  derivatives,  is  found  in  the  first 
runnings  of  the  distillation  of  wood-tar.  It  is  made  artificially  by  distilling 
pyromucic  acid  with  lime.  Pyromucic  acid  is  itself  obtained  by  the  destructive 
distillation  of  mucic  acid  (p.  622),  thus— 

CHOH-CHOH-COOH     CH  :  C(C02H\ 

=   •          >0  +  3HOH  +  C00. 
CHOH-CHOH-COOH     CH  :  CH— 

This  indicates  the  constitution  of  pyromucic  acid,  and  since  this  acid  yields 
furfurane  when  distilled  with  lime  it  is  probably  furfurane-carboxylic  acid  (just 
as  benzoic  acid,  which  yields  benzene  on  distillation  with  lime,  is  benzene- 
carboxylic  acid).  Thus  the  constitution  of  furfurane  is  settled. 

Furfurane  is  a  colourless  liquid,  smelling  of  chloroform,  insoluble  in  water  am 
boiling  at  32°  C.  Its  aldehyde  (furfural)  and  carboxylic  acid  (pyromucic  acid) 
have  been  already  considered. 

Uvinic  acid  or  pyrotritartaric  acid,  C4H(CH3)20'C02H,  found  among  theproduci 
of  the  destructive  distillation  of  tartaric  acid,  is  «-a1-dimethylfurfurane-/3-carboxylic 
acid  ;  it  is  also  produced  together  with  vritie  acid  (5:1:  $-methylpkthalic  acid)  by 
heating  pyrotartaric  acid  with  baryta  water.  It  melts  at  I35°C.  and  deconi] 
into  C02  and  dimethylfurfurane. 

TMophen,  C4H4S,  its  homologues  and  substitution-derivatives,  are  remarkable  for 
their  similarity  to  benzene,  its  homologues  and  derivatives  respectively ;  thus  with 
a  large  number  of  benzene  derivatives  there  are  corresponding  thiophen  derivativ 
of  approximately  the  same  boiling-point.  Thiophen  and  its  homologues  accompany 
benzene  and  its  homologues  in  coal-tar,  commercial  benzene  containing  about  0.6 
percent,  of  thiophen.  To  separate  it  the  benzene  is  shaken  with  about  10  per  cent, 
of  strong  H2S04,  which  extracts  the  thiophen  as  a  sulphonic  acid.  Or  the  benzene 
may  be  heated  with  mercuric  acetate,  which  forms  a  complex  precipitate  with  the 
thiophen,  decomposable  by  HC1  into  thiophen  and  HgCl2. 

The  thiophen  passes  over  when  the  sulphonic  acid  is  distilled  with  steam  ;  it  is 
colourless  liquid  (sp.  gr.  1.06)  which  smells  of  benzene,  boils  at  84°  C.  and  yields 
blue  colour  when  mixed  with  isatin  and  strong  H2SO4  ;  this  reaction — due  to  the 
formation  of  indophenin,  C12H7NOS — serves  to  detect  thiophen  or  its  homologues  in 
benzene. 

Several  fatty  compounds  yield  thiophen  when  heated  with  P2S3  ;  sodium  succinate, 
for  example — 

CH2-COONa  CH  :  CH, 

gives       •  j>S. 

CHyCOONa  CH  :  CH/ 

Derivatives  of  selenophen,  C4H4Se,  are  also  known. 


Pyrrol, 


INDOL. 
is  a  secondary  amine  and 

'^,^'1     /"_       .X       *• 


fatty  acids  and  benzene  hydrocarbons  a  ml 

'  which 


pyirol  treated  with 

There  are  3  mono-substitution  products  from       rrol,  because  the  H  in  the 


lodopyrroli  C4I4NH,  is  an  odourless  substitute  for  chloroform 
Several  hydrojtyrroU  and  their  derivatives  are  known  ;  pyrrollne  is 

4    6         ;  ' 


29 

564  Condensed  Nuclei  from  the  Five-membered  heterocyclic  Compounds  —These 
are  believed  to  consist  of  one  or  two  benzene  nuclei  condensed  with  a  furfurane 
thiophen,  or  pyrrol  nucleus,  just  as  naphthalene  consists  of  two,  and  anthracene  of 
three  benzene  nuclei  condensed  together.  They  are  probably  represented  by  the 
following  formulae  — 


CH 

^0 


Benzofurfurane. 


GE 


C«H, 


-C6H4 


Dibenzofurfuraue. 


>CH(a) 
8  / 
Beuzothiophen. 

C6H4  -  C6H4 


Dibenzothiophen. 


Beuzopyrrol. 


C«H 


Those  derived  from  one  benzene  nucleus  are  formed  by  treating  the  corre- 

CH  *  CHC1  PH 

spending  chloro-styrolene  with  alkali,   C6H4/  '    gives   C6H4(^      ^CH, 

XH  X 

where  X  =  0,  S  or  NH. 

Benzofurfurane  or  coumarone  is  a  product  of  the  action  of  alcoholic  KOH  on 
coumarin  (p.  611)  ;  it  is  found  in  coal-tar  and  boils  at  177°  C.  Countarilic  acid  is 
its  a-carboxylic  acid. 

Benzothlophen  melts  at  31°  C.  and  boils  at  221°  C. 

Benzopyrrol  or  indol  is  the  most  important  member  of  the  group,  as  it  is  constitu- 
tionally the  parent  substance  of  indigo.  It  may  be  obtained  by  distilling  reduced 
indigo  (<?.r.)  with  zinc  dust,  and  by  reducing  o-nitro-cinnaniic  aldehyde  with  Zn 
and  KOH— 


C6H4 


CH-CHO 


/X 
H7  -  C6H/     3CH  +  3H20. 


It  crystallises  in  colourless  prisms  (m.-p.  52°  C.)  of  disagreeable  odour,  and  may  be 
distilled  in  a  vacuum  or  with  steam.  It  is  soluble  in  water  and  has  weak  basic 
properties,  forming  a  sparingly  soluble  hydrochloride.  A  shaving  of  deal  moistened 
with  HC1  and  exposed  to  its  vapour  gives  the  pyrrol  red  colour.  The  hydrochloric 
solution  is  coloured  red  by  potassium  nitrite.  Indol  is  produced  by  the  action 
of  the  peculiar  ferment  of  the  pancreatic  juice  upon  the  albumin  of  blood  or  eggs, 
and  the  indican  occasionally  present  in  the  urine  appears  to  be  formed  from  it. 

Many  derivatives  of  indol  are  known,  but  only  the  most  important  can  receive 
notice  here.     The  orientation  of  the  substitution  derivatives  is  expressed  by  the 


760 


INDOXYL. 


letters  a,  /3,  n  in  the  pyrrol  ring  (cf.  formula  above)  and  by  the  numbers  I,  2,  3,  4 
in  the  benzene  ring  ;  or  by  numbering  the  N  atom  i  and  the  C  atoms  successively 
2  and  3  in  the  pyrrol  ring,  and  4,  5,  6,  7  in  the  benzene  ring.  Py-i,  2,  3  and 
Bz-i,  2,  3,  4  are  obvious  variations. 

The  alkylindols  are  obtained  by  heating  phenylhydrazones  of  aldehydes  or 
ketones  with  HC1  or  ZnCl2,  uucleal  condensation  occurring  with  evolution  of  NH3. 
Thus,  p-methylindol  or  sltatol  is  formed  when  propionic  aldehyde  phenylhydrazone 
is  so  treated — 

C6H5NH'N  :  CH'CH2-CH3  =  C6H4/        ^CH  +  NH3. 

Skatol  is  also  a  product  of  the  pancreatic  fermentation  of  albumin,  and  is  the 
chief  constituent  of  the  volatile  portion  of  human  excrement  (cr/:ar6s,  of  dung).  It 
crystallises  from  hot  water  in  colourless  plates,  melts  at  95°,  boils  at  263°  C.,  and 
has  a  faecal  odour.  Skatol  is  found  among  the  products  of  the  distillation  of 
strychnine  with  lime,  and  in  the  wood  of  Celtis  reticulosa,  a  plant  of  the  Nettle- 
tree  order. 

Indoxylic  acid  is  fi-hydroxymdol-ai-car'boxylic  acid,  and  is  obtained  as  its  ethyl 
salt  by  heating  ethyl  o-phenylglycocinecarboxylate  with  sodium  ethoxide — 

/COOEt  /C(OH) 

C6H4/  =  C6H4/  \0-COoEt  +  EtOH. 

xNH-CH2C02Et  XNH — / 

The  free  acid  is  obtained  by  heating  the  ethyl  salt  with  fused  NaOH.  dissolving 
in  water  and  precipitating  by  acid  ;  when  heated  with  alkali  and  air  it  yields  indigo. 
It  is  sold  as  indopJwr  for  cotton  printing,  since  it  is  readily  converted  into  indigo 
by  oxidation  on  the  fibre. 

Indoxyl  is  fi-hydroxyindol  and  is  produced  by  heating  indoxylic  acid,  which 
loses  CO^  also  by  heating  indigo  with  KOH  in  absence  of  air.  It  is  an  oily  liquid, 
soluble  in  water  to  a  yellow  fluorescent  solution.  In  alkaline  solution  it  is  easily 
oxidised  to  indigo,  2C8H7ON  +  02  =  (C8H5ON)2  +  2H2p. 

The  indoxyl  derivatives  are  either  from  /3-hydroxyindol  or  the  pseudo-form — viz., 


/C(OH) 
'\NH 


or  C6H4 


,00 


NCHg,  respectively.     The  indogenides  are  deriva- 


tives of  the  latter  form  in  which  the  =CH2  group  has  condensed  with  a  =00 
group  of  an  aldehyde  or  ketone  to  form  a  =0  =  0=  nucleus. 

Indoxyl  occurs  in  the  form  of  potassium,  indoxyl-sulplionate  in  the  urine  (urine- 
indicari)  of  herbivora. 

OTT 

a.-MethyUndolin,  C6H4/      ^CH'CHo,  is  a  liquid  boiling  at  227°  C.,  obtained  by 

XNHX 

reducing  a-methylindol  with  Sn  and  HOI  ;  by  carrying  the  reduction  further,  with 
HI  and  P,  0-propylaniline  is  produced.  It  will  be  seen  that  this  compound  is  a 
methyl-derivative  of  dihydroindol,  which  does  not  exist  ;  the  oxygenated  dihydro- 
indols,  however,  are  known  and  are  closely  related  to  indigo.  They  are  called 
indolinones  and  are  lactams  of  amidophenylacetic  acid  and  its  homologues  (p.  679). 
They  are  also  obtained  by  heating  the  phenylhydrazides  (p.  686)  of  the  acids  with 
lime  (see  oxindol). 

Oxindol,  or  a-indoUnone,  has  been  already  noticed  (p.  679)  ;  it  is  produced  when 
acetylphenylhydrazide  is  heated  with  lime — 

,CH^ 

C6H3NH-NH-COCH3  =  C6H4/        XCO  +  NH3. 

XNHX 

It  melts  at  120°  C.  and  is  easily  oxidised  to  diox'mdol  or  fi-hydroxyoxyindol^  which 
in  its  turn  may  be  oxidised  to  isatin. 
ret  nn 

,  is  prepared  by  oxidising  indigo  with 


nitric  or  chromic  acid.  It  crystallises  in  orange-coloured  prisms  (m.-p.  201°  C.), 
soluble  in  boiling  water  and  alcohol.  When  heated,  it  sublimes  with  partial 
decomposition.  It  dissolves  in  KOH  to  a  violet  solution,  and  is  precipitated  again 
by  acids.  AgN03  added  to  the  potash  solution  gives  a  carmine-red  crystalline 


INDIGO.  76! 

precipitate  of  silrer  imtin  C8H4AgN02.  Isatin  forms  crystalline  compounds  with 
NaHb03  (like  the  aldehydes  and  ketones).  It  yields  aniline  when  distilled  with 
strong  KOH.  With  chlorine  it  yields  chlorisatin  and  dichhrrimtin,  also  formed 
when  chlorine  acts  on  indigo.  When  these  are  distilled  with  KOH,  they  yield 
mono-  and  di-chloraniline.  Keducing  agents  convert  isatin  into  hydro-iaatin  or 
isatide,  C16H12N204,  and  then  into  dioxindol  and  oxindol. 

Isatin  is  also  produced  by  treating  Q-nitrophenylpropiolic  acid  with  alkali— 

/C  :   C-COOH  XCOK 

ceH4\  =  C6H4/       \CO  +  C02. 

Isatin  condenses  with  indoxyl  under  action  of  alkalies  to  form  the  isogenide  (r.  *.) 
indirubin,  an  isomeride  of  indigo  ; 


/CO  /C6H4  GO  C6H 

<NH>CH2  +   °C<CO>H  =   C6<NH>    : 
Indoxyl.  Isatin.  Indirubin. 


4v 
:    <CO>H 


CO 

Isatin  reacts  with  PC15  in  benzene,  yielding  isatin  chloride,  C6H4/      )>CC1,  the 

formula  for  which  supports  the  second  formula  given  above  for  isatin.    When  this 
chloride  is  reduced  it  yields  indigo-blue. 

565.  Indigotin  or  indigo  blue,  C16H10N202,  is  prepared  from  Indigo- 
fera  tinctoria  and  ccerulea,  plants  of  the  same  natural  order  (Leguminosse) 
as  those  furnishing  the  dye-woods  described  on  p.  747,  and  like  the 
colours  obtained  from  those,  it  does  not  exist  as  such  in  the  plant,  but 
is  a  product  of  alteration  of  a  nearly  colourless  substance  termed  indican. 
Woad  (I  satis  tinctoria),  a  crucifer,  also  yields  indigo. 

Indican  may  be  extracted  from  the  leaves  and  twigs  of  the  plant  by 
digestion  with  cold  alcohol,  which  leaves  it,  when  evaporated,  as  a 
brown,  bitter,  syrupy  liquid.  It  appears  to  be  a  glucoside  of  indoxyl 
and  is  hydrolysed  by  fermentation  or  by  boiling  dilute  acids  into  indoxyl 
and  a  glucose  called  indiglucin.  The  indoxyl  is  rapidly  oxidised  by  the 
air  into  indigotin,  which  forms  a  blue  precipitate  — 

C8H6ON(C6HU05)  +  H20  =  C6H1206  +  C8H7ON 
Indican.  Indoxyl. 

C6H4<  °°  >CH2  +  H2C<C°  >C6H4  +  02  =  C6H4<°  }  >C  :  C<°  D  >C6H4  +  2H20. 
XNIT  XNET  XNHX        XNHX 

Indoxyl.  Indoxyl.  Indigotin. 

For  the  preparation  of  indigo  on  the  large  scale,  the  plants  are  cut  just  before 
they  blossom,  chopped  up,  covered  with  cold  water,  and  allowed  to  ferment  for 
twelve  or  fifteen  hours,  when  the  indican  is  hydrolysed  as  explained  above.  As 
soon  as  a  blue  scum  appears  upon  the  surface,  a  little  lime  is  added,  and  the  yellow 
liquid  is  run  into  shallow  vats  and  well  beaten  with  sticks  to  promote  the  action 
of  air,  which  oxidises  the  indoxyl.  The  indigo-blue  is  precipitated  and  collected, 
on  calico  strainers,  to  be  pressed  and  cut  up  into  cakes.  As  purchased,  indigo-blue 
contains  about  half  its  weight  of  indigotin  ;  it  may  be  purified  by  boiling,  first,  with 
acetic  acid,  which  extracts  a  substance  termed  indigo-yluten,  then  with  weak 
potash,  to  extract  indigo-brown,  and,  lastly,  for  some  time  with  alcohol,  wni< 
removes  indigo-red. 

Indigotin  may  be  prepared  from  commercial  indigo  by  boiling  it  with 
aniline,  or  heating  it  with   melted  paraffin  ;  both  solvents  deposit  the 
indigotin  in  dichroic,  rhombic  crystals  on  cooling.     From  hot  turpen- 
tine it  crystallises  in  blue  tables  and  from  fused  phthahc  anhydrid 
needles 


762  ARTIFICIAL  INDIGO. 

When  commercial  indigo  is  carefully  heated,  it  is  converted  into  a 
violet  vapour,  the  sp.  gr.  of  which  settles  the  molecular  formula  for  the 
compound.  The  vapour  condenses  in  dark  blue  needles,  with  a  coppery 
reflection.  The  best  indigo-blue  floats  upon  water. 

Indigotin  is  insoluble  in  water,  alcohol,  ether,  and  diluted  acids  and 
alkalies.  Strong  sulphuric  acid  and,  more  easily,  fuming  sulphuric  acid, 
dissolve  it,  forming  indigotin-monosulphonic  acid,  C16H9(SO2'OH)N202, 
and  indigotin-disulphonic  or  sulphindylic  acid,  C^ 


On  adding  water,  a  blue  precipitate  of  the  mono-acid  is  obtained,  which  is  soluble 
in  pure  water  and  in  alcohol.  It  in  mono-basic,  audits  concentrated  solution  gives 
a  purple  precipitate  of  the  potassium  salt  on  addition  of  potassium  acetate.  The 
precipitate  produced  by  K2C03  in  the  solution  of  indigo  in  H2SO4  is  known  as 
indigo-carmine,  and  consists  chiefly  of  potassium  sulphlndylate  ;  it  is  soluble  in 
water.  The  sulphonic  acids  of  indigo  are  bleached  by  zinc-dust,  being  converted 
into  the  corresponding  acids  of  indigo-white,  which  become  blue  again  when  shaken 
with  air.  Sulphindylic  or  sidphindigotic  acid  is  used  in  dyeing  Saxony  blue 
cloth. 

Indigo-white  (leucindigo  or  hydrindigotin)  is  prepared  by  shaking 
powdered  indigo  with  2  parts  of  ferrous  sulphate,  3  parts  of  slaked  lime, 
and  200  parts  of  water,  in  a  stoppered  bottle  placed  in  warm  water,  till 
the  indigo  has  dissolved  to  a  yellow  liquid,  when  the  calcium  sulphate  and 
ferroso-ferric  hydroxide  are  allowed  to  subside,  and  the  clear  solution 
drawn  off  into  dilute  hydrochloric  acid  in  a  vessel  from  which  air  has 
been  expelled  by  C02.  The  hydrindigotin  is  precipitated  in  white  flakes, 
which  quickly  become  blue  indigo  when  exposed  to  air.  Other  reducing- 
agents  are  sometimes  substituted  for  ferrous  sulphate  in  preparing  the 
dyer's  indigo-vat.  A  mixture  of  indigo,  madder,  potassium  carbonate, 
and  lime,  left  to  ferment,  gives  an  alkaline  solution  of  reduced  indigo. 
Hydrosulphites  (p.  237)  and  lime,  or  zinc-dust  and  alkali,  are  also 
employed  for  this  purpose,  and  it  has  been  suggested  to  apply  electro- 
lysis for  the  reduction.  When  linen  and  cotton  are  immersed  in  the 
indigo-vat  and  exposed  to  air,  the  indigo-white  is  oxidised  to  indigo- 
blue,  which  is  precipitated  upon  the  fabric.  Hydrindigotin  precipi- 
tated by  acids  from  its  alkaline  solutions  becomes  crystalline  after  a 
time  ;  it  is  soluble  in  alcohol  and  ether.  It  probably  is  of  the  same 
form  as  indigotin,  but  containing  OH  groups  in  place  of  the  O  atoms. 

When  indigo  is  heated  with  dilute  HN03,  it  is  oxidised  into  isatin, 
which  gives  a  yellow  solution,  and  sulphindylic  acid  is  sometimes  em- 
ployed as  a  test  for  HNO3.  By  fusion  with  KOH  it  is  converted, 
first  into  potassium  anthranilate,  and  afterwards  into  aniline,  which 
distils. 

566.  Artificial  indigo.  —  The  unremitting  skill  and  labour  which  have 
been  concentrated  during  the  last  20  years  on  the  attempt  to  make 
indigo  from  materials  the  cost  of  which  would  be  comparable  with  that 
of  cultivating  the  indigo  plant,  have  at  length  succeeded.  It  may  now 
be  said  that  indigo  is  made  from  coal,  wood  and  air,  and  that  the 
cultivation  of  the  plant  is  a  doomed  industry. 

Naphthalene  and  ammonia  from  coal,  acetic  acid  from  wood  and 
oxygen  from  air  are  the  immediate  raw  materials  for  the  manufacture  ; 
sulphuric  acid,  chlorine,  mercury  and  alkali  are  used  as  agents,  but 
these  may  be  recovered  and  returned  to  the  process. 

The  naphthalene  is  oxidised  to  phthalic  anhydride,  which  is  con- 
verted by  NH3  into  phthalimide.  When  the  latter  compound  is 


MANUFACTURE   OF  INDIGO. 


acid.     This  acid  is  heated  with 


The  operations  are  as  follows  •  — 

•i^£*^$3^f^£SSSA  ft**  •* 

ot  100  Der  r.fint.  at.™™  o-fh r«~  ir  meitui\  with  sulphuric  acid 


ulphateand  aids  the  reaction  ;  the 


ph^altofd     thallC  a"hydride  !S  treated  With  NH.«»d«  P"—™  -hen  it  becomes 


. 

(4)  The  solution  of  alkali  anthranilate  thus  obtained  is  boiled  for  « 

(5)  This  acid  is  heated  with  NaOH  in  a  closed  vessel  at  200°  C.  until  the  orange 
colour  no  longer  increases  in  intensity. 

Jli  ™6,pfH  >hl  mas}f'  c,ontai.ni/?g  indoxyl,  is  quickly  cooled,  dissolved  in  water  and 
?JUh,S         +     T1§  :  i  th?.solu^n  to  Precipitate  indigo  ;  if  the  precipitate  is  too 
crystalline  it  is  dissolved  in  sulphuric  acid  and  precipitated  by  adding  water. 
The  following  equations  explain  the  chemistry  of  these  processes  :— 
CH  :  CH  co 


CH  :CH  CO 

/CON  CO 

(2)  C6H4<co^O  +  NH3  =  C6H4/      \NH  +  H20. 

(3)  C6H4<^\NH  +  NaOCl  +  3NaOH  =  C6n4/C<  °Na+  XaCl  +  Na.2C03 


(4)    C6H4/  +  CH.C1-COOH  +  Na.CO,  =  C6HC°°Na 


NH-CH2-COONa 
NaCl  +  C02  +  H20. 


(6)  The  equation  for  the  oxidation  of  indoxyl  has  been  given  above. 

It  is  probable  that  the  process  will  shortly  be  simplified,  for  it  has  been  found 
that  the  product  obtained  by  heating  anthranilic  acid  with  a  polyatomic  alcohol  or 
a  carbohydrate  and  KOH  yields  indigo  when  treated  with  water  and  oxidised. 

Another  promising  method  consists  in  heating  phenylglycocine,  made  from  ani- 
line and  mono-chloracetic  acid,  with  sodamide. 

567.  It  is  proposed  to  synthesise  indigo  from  aniline  by  first  heating  it  with  CS2 
to  produce  thiocarbanilide  (p.  672)  ;  the  aqueous  solution  of  this  is  to  be  heated 
with  white  lead  and  KCN,  of  which  the  former  appropriates  the  S,  while  the  latter 
introduces  a  cyanogen  group,  the  product  being  a  hydrocyaMOOarbodi^henylvm&de^ 
which  becomes  a  thioamide  by  treatment  with  (NH4)2S.  The  thioamide  is  to  be 
heated  with  strong  H2S04  to  produce  the  anilide  of  isatin.  and  this  is  to  be  reduced 
with  (NH4)2S  when  it  yields  aniline  and  indigo  :  — 
C6H5NH\  C6H5NH\  C6H6NH\  /CO  \ 

>CS  ;  >C'CN  ;  >C'SNH2  ;  C6H4<         >C:NC',1  1:,. 

CeH^H/  C6H5N^  C6H5N  ^  \\HX 

Thiocarbanilide.       Cyanogen  derivative.  Thioamide.  Isatiu  anilide. 


764  ANTIPYEINE. 

568.  Other  methods  of  synthesising  indigo  are  now  only  of  academic  interest* 
either  because  the  yield  is  too  small  or  because  the  raw  materials  are  too  costly. 

From  aniline  it  has  been  synthesised  by  heating  the  base  with  chloracetic  acid  to 
produce  phenylglycocine,  which  yields  indigo  when  heated  with  fused  NaOH  and 
afterwards  treated  with  air.  The  fusion  converts  the  phenylglycocine  into 
indoxyl. 

From  benzaldehyde  the  synthesis  is  byway  of  dissolving  I  :  2-nitrobenzaldehyde 
in  acetone  and  adding  NaOH,  whereupon  indigotin  is  precipitated.  It  is  probable 
that  the  first  action  of  the  acetone  and  soda  is  to  convert  the  I  :  2-nitrobenzalde- 
hyde  into  I  :  2-nitrophenyl-lactomethyl  Itetone  ;  CQH4(NO2)-CHO  +  CH3-CO'CH3  = 
C6H4(N02)-CH(OH)-CH2-CO-CH3.  This  then  breaks  up  into  indigotin,'  acetic  acid 
and  water  under  further  action  of  NaOH  ;  2[C6H4(N02)-CH(OH)-CH2-CO'CH3]  = 
C16H10N202  +  2CH3-C02H  +  2H20.  The  ketone  has  been  sold  as  its  NaHS03  compound 
(p.  625),  under  the  name  indigo  salt  for  printing  on  the  fabric,  which  is  then  im- 
mersed in  a  bath  of  caustic  soda. 

When  cinnamic  acid  is  treated  with  nitric  acid,  it  is  converted  into  nitro- 
cinnamic  acid.  This  combines  directly  ,  with  two  atoms  of  bromine,  to  form 
dibromo-nitro-pkenyl-propionic  acid,  C6H4(N02)'CHBr-CHBrC02H.  When  this 
is  treated  with  caustic  soda,  two  molecules  of  HBr  are  removed,  producing  the 
sodium  salt  of  nitrophenylpropiolic  acid,  C6H4(N02)'C  :  OC02H.  By  heating  this 
with  an  alkali  and  a  reducing-agent,  it  is  converted  into  indigotin. 

569.  Dibenzofurfurane  (p.  759)  is  identical  with  diplienylene  oxide  and  is  obtained 
by  distilling  phenol  with  PbO.     It  melts  at  81°  and  boils  at  288° C. 

Dibenzothiophen  is  diplienylene  sulphide,  obtained  by  heating  phenyl  sulphide  ; 
m.-p.  97°,  b.  p.  333°  C. 

Dibenzopyrrol  is  identical  with  carbazole  (p.  667). 

570.  Azoles. — Within  the  last  few  years  a  large  class  of  compounds  has  been  dis- 
covered the  members  of  which  are  regarded  as  derived  from  furfurane,  thiophen 
and  pyrrol  by  substitution  of  a  trivalent  N  atom  for  a  trivalent  CH  member  of  the 
ring,  and  are  known  as  mono-,  di-  or  tri-azoles  accordingly  as  i,  2,  or  3  of  the  CH 
members  have  been  exchanged  for  N. 

By  one  system,  theazoles  are  distinguished  by  the  prefixes/wro-,  tkio-,&ad.pyrr6a 
to  indicate  the  parent  ring,  also  by  the  numbers  2,  3,  4,  or  5,  or  the  letters  «,  «1?  b, 
or  Z>!,  to  show  which  of  the  four  CH  members  has  or  have  been  exchanged.  By 
another  system  they  are  classified  as  oxazoles,  thiazoles,  and  pyrazoles,  accordingly 
as  they  are  allied  to  furfurane,  thiophen,  and  pyrrol  respectively.  Condensed  azole 
nuclei,  distinguished  by  the  prefix  beJizo,  are  also  known  (cf.  furfurane,  <kc.,  p.  757). 
Generally  speaking,  the  azoles  are  products  of  condensation  of  aldehydes  or 
ketones  with  substitution-derivatives  of  NH3  or  N2H4,  or  H2NOH. 

CH:N 
Pyrazole  or  pyrro-2-azole,     •  ^X^H,  is  produced  by  combining  acetylene 

CH  :  GW 

with  diazomethane  (p.  680),  but  better  by  distilling  3:4:  ^jyrazole-tricarboxylic 
acid,  made  by  condensing  ethyl  diazoacetate  with  ethyl  acetylenedicarboxylate  and 
saponifying.  It  is  a  feeble  base,  melts  at  70°  C.  and  boils  at  187°  C. 

The  substituted  pyrazoles  are  nucleal  condensation  products  from  the  hydrazones 
of  /3-diketones.  Thus  benzoylacetone-hydrazone  yields  1:3:  ^-dlphenylmethyl-2- 
pyrazole  : — 

C6H5-C-CH2-CO-CH3         C6H5-C-CH  :  C-CH3 

+   H20. 

N NHC6H5  N N-C6H5 

By  reduction  with  Na  in  alcohol  the  pyrazoles  yield  dihydropyrazoles  derived 

CH2-CH2, 
from  •  >NH,  and  called  pyrazolines. 

CH:N   7 
Pyrazolones  are  lietodihydropyr azoles,  and  are  important  as  including  the  febri- 

CMe-NMe, 
fuge  antipyrine  which    is    1:2:  '\-phenyldimethylpyrazolone,    ••  \NC6H5, 

CH— CO  7 

prepared  by  first  heating  ethyl  aceto-acetate  with  phenylhydrazine  to  produce 
phenylmethylpyrazolone,  which  is  then  heated  with  CH3I  in  CH3OH  to  introduce 
the  second  CH.,  group  ;  the  alcohol  is  distilled  and  the  antipyrine  precipitated  by 
NaOH.  Antipyrine  crystallises  in  white  plates,  melts  at  114°  C.,  dissolves  fairly 


AZOLES. 

easily  in  cold  water  and  is  a  strong  base  ;  its  salicylate  is  sold  as  taUovrine  and 
the  homologue  in  which  tolyl  takes  the  place  of  phenyl,  as  tolypyrine  ' 

Another  very  complex  pyrazolone  derivative  is  the  yellow  dyestuff  'tartra-lne 
The  tetrahydropyrazoles  are  called  pyrazolidines,  and  the  corresponding  keto- 
denvatives  are  py>-azolido)tes.     They  are  unimportant. 

OFT 

The  indazoles  are  benzopyrazoles  from  the  isomeric  forms  C6H4/.    \NH  and 

,CH, 
C6H4^       /N>  and  are  so  called  by  analogy  with  indol,  the  name  given  to  benzo- 

pyrrol.  Indazole  itself  has  the  first  form  and  is  made  by  heating  o-cinnamic- 
hydrazide. 

N :     CH 
The  glyoxalims   are   pyrrol-azote,    .  ^>NH,    obtained    by  condensing 

OTT  .    OTT/ 
vyJjL  .   V^XX 

a-diketones  with  NH3.  Several  of  them,  particularly  lophin  (triphenylglyoxaline) 
phosphoresce  when  decomposed  by  caustic  alkali.  Lyndine,  used  as  a  remedy  for 
gout  because  of  the  high  solubility  of  its  urate,  is  a  methyldihydroglyoxaline. 

Isoxazole    or    furo-2-azole,    and    thiazole    or    thio-^-azole,     •  \0,    and 

/^ITT    .    OTJ/ 

V^Jl  .   vyXl 

N     :  CH, 

>S  respectively,  yield  a  number  of  derivatives.     The  amidothiazoles,  made 

PTT  •  PTT' 
\  j  n  .  \_j±i 

by  condensing  chloracetone  with  thiourea,  behave  like  aniline  and  may  be  diazo- 
tised  to  produce  thiazole  dyestuffs. 

The  true  diazoles  and  triazoles  of  the  pyrrol  type  have  sometimes  been  mis- 
called triazoles  and  tetrazoles  respectively,  the  prefix  referring  to  the  total  number 
of  N  atoms. 

CFT  •  TsT 
Thus,  pyrro-2  :  $-diazole,  •         '  \N[H,  has  been  called  osotriazole.    Its  derivatives 

CH:NX 
are  obtained  by  distilling  the  osazones  of  ortho-diketones. 

CH  :  K  N  :  CH. 

Pyrro-2  :  5  :  ^-triazole  may  be  either  •  %NH  or  .  ^>NH,  and  is  also 

known  as  tetrazole. 

The  derivatives  of  these  compounds  as  also  those  of  the  corresponding  oxy-  and 
thio-compounds  are  at  present  of  theoretical  interest  only 

571.  Six-membered  heterocyciic  compounds. — The  most  impor- 
tant members  of  this  class  are  the  substances  pyridine,  quinoline  and 
acridine.  These  may  be  regarded  as  analogous  in  constitution  to  ben- 
zene, naphthalene  and  anthracene  respectively,  containing,  in  each  case, 
N  in  place  of  CH.  This  will  be  clear  from  the  following  formulae  :— 

H  c  c  c  c 

n/  \H       K/      9      \H       HC        9~~N — c        CH 


H 
Pyridine.  Quinoline.  Acridine. 

Their  behaviour  towards  reagents  indicates  that  they  are  closed-chain 
compounds  (c/.  benzene,  p.  527),  and  a  study  of  their  substitution- 
products  shows  that  the  number  of  position-isomerides  which  has  been 
prepared  is  in  accord  with  that  prophesied  from  the  above  formulae. 


766  PYKIDINE. 

An  inspection  of  the  formulas  shows  that  there  should  be  three  isomeric  mono- 
substituted  pyridines,  seven  isomeric  mono-substituted  quinolines  and  five  mono- 
substituted  acridities.  The  orientation  is  expressed  similarly  to  that  of  the 
corresponding  hydrocarbons,  the  N  in  pyridine  and  quinoline  being  i. 

By  another  system  of  orientation  for  pyridine,  position  2  =  a,  6  =  a',  3=/3,  5=/3', 
and  4  =  7  ;  for  quinoline  2  =  a,  3  =  /3,  4  =  7. 

572.  Pyridine  bases.  —  The  destructive  distillation  of  bones  yields 
ammonia  and  other  bases,  produced  by  the  decomposition  of  the  bone- 
gelatine,  or  ossein,  which  forms  about  30  per  cent,  of  the  bones,  and 
contains  about  18  per  cent,  of  nitrogen.  These  bases  form  an  homo- 
logous series,  of  which  pyridine  is  the  first  member  ;  many  of  them  are 
also  found  in  coal-tar.  They  are  liquids  of  disagreeable  odour,  and  are 
tertiary  monamines  (p.  658).  They  may  be  extracted  from  the  offensive 
oil  known  as  DippeVs  animal  oil,  obtained  by  distilling  bones,  by 
shaking  it  with  warm  dilute  H2S04,  which  dissolves  the  bases  as 
sulphates,  and  yields  them  up  on  adding  alkali.  They  are  separated  by 
fractional  distillation.  Their  solubility  in  water  decreases  with  the 
increase  of  C  atoms  and  is  generally  greater  in  cold  water  than  in  hot. 


Pyridine  .  .  C5H5N  ...  115°  C. 

Picoline  .  .  C6H7N  ...  130 

Lutidine  .  .  C7H9N  ...  142 

Collidine  .  .  C8HnN...  179 


Parvoline  .  .  C9H13N  ...  188°  C. 

Coridine  .  .  C10H15N  ...  211 

Kubidine  .  .  CnH17N  ...  230 

Viridine  .  .  C12H]9N  ...  251 


Pyridine  bases  are  often  present  in  commercial  ammonia,  and  cause 
it  to  become  pink  when  neutralised  with  hydrochloric  acid. 

Like  other  tertiary  amines  the  pyridines  combine  with  alkyl  iodides  to  form 
alkylpyridinium  iodides,  e.g.,  C5H5N'CH3I,  and  when  these  are  heated  they  become 
alkyl-substituted  pyridines,  e.g.,  C5H4(CH3)N'HI,  a  behaviour  similar  to  that  of 
alkylanilines  (p.  664). 

Pyridine  is  a  colourless  liquid  which  is  soluble  in  water  ;  it  forms  a  deliquescent 
hydrochloride,  C5H5N'HC1,  the  solution  of  which  is  precipitated  by  HgCl2,  K4FeCy6 
and  PtCl4.  By  the  action  of  sodium  in  alcohol,  pyridine  is  hydrogenised  to  liexa- 
hydro-pyridine,  C5Hn]Sr,  which  is  identical  with  piperidine  (r.-/.)  and  may  be 
reconverted  into  pyridine  by  heating  at  300°  C.  with  H2S04 — 

C6HnN  +  3H2S04  =  C5H5N  +  3S02  +  6H20. 

This  conversion  of  pyridine  into  piperidine  establishes  the  constitution  of  the 
former,  that  of  the  latter  being  known.  Pyridine  is  obtained  by  heating  amyl 
nitrate  with  P205,  which  removes  the  elements  of  water  ;  C5HnN03  =  3H20  +  C5H5N. 
It  is  also  formed  when  a  mixture  of  hydrocyanic  acid  and  acetylene  is  passed 
through  a  red-hot  tube,  HCN  +  2C2H2  =  C5H5N.  Like  benzene,  pyridine  resists 
oxidation  in  high  degree. 

Pyridine  has  been  suggested  as  a  remedy  for  asthma  ;  on  the  Continent  it  is  used 
for  denaturing  alcohol. 

The  alkylpyridines  may  be  obtained  by  distilling  the  aldehyde-ammonias,  either 
by  themselves  or  with  aldehydes  or  ketones.  Thus  acrolein-ammonia  yields 
^-methylpyridine  {picoline),  which  is  also  obtained  by  heating  glyceryl  tribromide 
in  a  sealed  tube  at  250°  C.  with  alcoholic  NH3  ;  2C3H5Br3  +  NH3  =  6HBr  +  C6H7N. 


The  alkylpyridines  are  readily  oxidised  to  pyridinecarboxylic  acids. 

//  ydroxy-py  ridin 
they  are  really  phenolic  or  ketonic  compounds  (pyridones  ;  cf.  phloroglucol,  p.  716). 


The  hydroxy -pyridines  behave  in  a  manner  which  leaves  it  doubtful  whether 


Hexahydropyridine  or  piperidine,  C5HnN,  obtained  by  reducing  pyridine  with 
Na  and  boiling  alcohol,  or  electrolytically,  maybe  regarded  as  pentamethylencimlde, 
for  it  is  obtained  by  distilling  the  hydrochloride  of  pentamethylene  diamine  — 
CH.-OH.-NH,  m  CH  /CH2-CH  + 

XCH2-CH2'NH2  XCH2'CH/ 

It  is  a  secondary  amine,  boiling  at  106°  C.,  smelling  of  pepper  and  NH3,  soluble  in 
water  and  forming  crystalline  salts  (cf.  piperine).  It  combines  with  alkyl  iodides 
to  form  alkylpiperidinium  iodides. 


QUINOLINE. 

573.  Quinoline  bases  -These  may  be  regarded  as  benzo-pyridrnes. 
They  occur  in  bone  oil  and  in  coal-tar,  and  are  products  of  the  distilla 
tion  of  many  alkaloids  with  KOH.     They  form  an  homologous  series 
qmnolme    being   the   lowest    member  :—  Quinoline,    CHN-    levidin, 
C9H6(CH3)N  ;  cryptidine,  C9H5(CH3)9N. 

The  qumolme  bases  are  synthetically  prepared  (Skraup's  method) 
by  heating  aniline  and  its  homologues  with  glycerine,  a  debydrating- 
agent  (cone.  H2S04)  and  an  oxidant  (nitrobenzene/  ; 

H  CH°H 


C6H4  +  >CH(OH)  +  0  =  C6H4/ 

XXH2       CH2(OH/  x   N  :  CH 

This  synthesis  shows  that  the  N  atom  in  quinoline  must  be  attached  to  a  benzene 
nucleus  ;  that  it  occurs  in  a  pyridine  ring  is  proved  by  the  fact  that  when  quino- 
Hn£  ^/?^ij?d.  "7th  KMn0^'  5:6-pyridine  dicarboxylic  acid  (f/uhw/i/tir  ami). 
G6H3(CO2H)2N,  is  formed  (cf.  the  deduction  drawn  concerning  the  constitution  of 
naphthalene  from  the  oxidation  of  the  hydrocarbon  to  phthalic  acid). 

Quinoline,  or  cliinoUne,  is  prepared  by  the  action  of  H2S04  (50  parts)  and  nitro- 
benzene (12  parts)  upon  aniline  (19  parts)  and  glycerine  (60  parts).  The  mixture 
is  cautiously  heated  at  130°  C.  in  a  flask  with  a  reflux  condenser,  the  lamp  being 
removed  when  the  reaction  begins  ;  it  is  then  again  heated  for  three  hours,  and 
distilled  with  lime,  when  quinoline  distils  over  together  with  aniline  ;  the  latter  is 
converted  into  phenol  by  the  diazo-reaction  (p.  681)  and  the  mixture  again  dis- 
tilled with  alkali  when  quinoline  passes  over.  It  is  a  colourless  liquid  of  tarry 
smell,  of  sp.  gr.  1.09  and  boiling-point  239°  C.  It  is  sparingly  soluble  in  water,  and 
is  a  tertiary  amine  ;  it  forms  a  sparingly  soluble  chromate.  It  combines  with  alkyl 
iodides  to  form  alkylquinotinium  iodides  which,  when  heated  with  potash,  yield 
blue  dyestuffs  termed  cyanines,  used  in  orthochromatic  photography.  Quinolinic 
derivatives  are  very  numerous  ;  a  few  only  can  be  considered. 

2-HcthylquinoUne  or  quinaldine  (b.-p.  247°  C.)  is  synthesised  by  boiling  paral- 
dehyde  and  aniline  with  HC1.  By  substituting  other  aldehydes  for  paraldehyde, 
the  reaction  becomes  a  general  one  for  preparing  alkylquinolines.  ^-Methylquiiw- 
line  or  lepidine  boils  at  257°  C.  Both  occur  in  coal-tar  and  the  CH3  group  in  each 
shows  a  remarkable  tendency  to  react  with  aldehydic  and  ketonic  compounds. 
Quinaldine  combines  in  this  manner  with  phthalic  anhydride,  forming  qu'uto1iiu> 
yellow,  a  dyestuff,  (C9H6N)CH  :  (C202)C6H4. 

Carbostyril    is    2-Jiydrojcy  -quinoline  and   is  prepared  by  dehydrating   o-amido- 

/CH  :  CH-C02H  CH  :  CH 

cinnamic  acid,  C6H4<  '     =  C8H,<  •  +H20,  and  by  tivatin- 

XNH2  x  N  :  C(OH) 

acetamidobenzaldehyde  with  NaOH.     It  melts  at  199°  C. 

The  tetrahydroquinolvnes,  C9HnIsr,  are  produced  by  reducing  the  quinolines  with 
nascent  H.  They  behave  like  fatty  amines,  readily  forming  nitroso-  and  di;i/.<>- 
derivatives.  That  obtained  by  reducing  carbostyril  boils  at  224°  C.  and  yields  with 
methyl  iodide  the  compound  kairolin,  C9H10N'CH3,  the  hydroxy-derivative  of  which 
is  Itairine,  C9H9(OH)N-CHS  ;  these  two  substances  and  thaliine,  C9H9(OCH3)NH 
are  used  as  substitutes  for  quinine. 

574.  Isoquinolines  yield  4  :  5-pyridine-dicarboxylic  acid   when  oxidised,  showing 

CH:CH 

that  the  N  atom  is  in  the  2-position  of  the  naphthalene  ring,  C6H4/          •     . 

XCfl  :N 

Isoquinoline  accompanies  the  quinoline  from  coal-tar  and  is  separated  therefrom 
by  fractionally  crystallising  the  sulphates.  It  melts  at  23°  C.  and  boils  at  24O'5°  C. 
When  a  mixture  of  it  with  quinaldine  is  treated  with  benzotrichloride,  quinoline  red, 
a  dyestuff  used  in  making  orthochromatic  photographic  films,  is  obtained  (cf.  method 
of  making  malachite  green,  p.  722). 

Napkthoquinoline,  C13H9N,  and  anthraquinoline,  C17HnN,  are  obtained  by  sub- 
stituting naphthylamine  and  amidoanthracene,  respectively,  for  aniline  in  8knnp'l 
reaction  (see  above).  When  m-  or^-phenylenediamine  is  the  amine  used,  a  j>lientin- 
throline,  C12H8N2J  is  the  product.  These  compounds  are  bases  similar  to  quino- 
line and  of  complex  constitution  which  cannot  be  discussed  here.  Alisorifie  l>h>r 


768 


LAUTH'S   VIOLET. 


is  a  dihydroxyanthraquinoline  obtained  by  applying  Skraup's  reaction  to 
w-amidoalizarin. 

C6H4-CH 
Phenanthridine,  •         ••    ,  bears  the  same  relationship  to  phenanthrene  (p.  554), 

C6H4-N 

that  quinoline  bears  to  naphthalene,  and  is  obtained  by  heating  benzylideneaniline* 
C6H5CH  :  NC6H5.  It  melts  at  104°  C. 

575.  Acridine  bases. — Acridine,  C13H9lSr,  occurs  in  crude  anthracene,  from  which 
it  is  extracted  by  dilute  acids,  yielding  a  fluorescent  solution  ;  potassium  bichro- 
mate precipitates  it.     It  forms  colourless  needles,  readily  sublimes  and  has  a  very 
irritating  vapour.     It  is  a  feebler  base  than  pyridine  and  quinoline,  but,  like  these, 
combines  with  alkyl  iodides  to  form  acridlnium  derivatives.     The  synthesis  that 
establishes  the  constitution  of  acridine  is  from  diphenylamine  and  formic  acid  by 
heating  with  ZnCl2  ;  formt/ldiphenylamine  is  first  formed  and  then  loses  H20  : — 

CHO  CH 

C6H5X   ^    ^H,  =  C6H4/^   \C6H4  +  H20. 

The  dyestuff  chrymniline  or  phosphine,  obtained  as  a  by-product  in  making  aniline, 
is  meso-p-amidop/ienyl-2-amidoacridine.  Acridine  yellow  and  benzqflavine  are  also 
dyestuffs  of  this  series. 

576.  Azines. — Just  as  the  azoles  (p.  764)  may  be  regarded  as  derived  from  the 
N-,  0-,  and  S-  five-membered  heterocyclic  rings,  by  substituting  an  N  atom  for  a 
CH  group,  so  the  azines  are  derived  by  a  similar  substitution  from  the  six-membered 
heterocyclic  rings.     They  are  either  oxazines.  thiazines,  or  diazines  (also  triazines 
and  tetr azines)  accordingly  as  they  contain  0  and  N,  S  and  N,  or   N  alone.     They 
are  further  distinguished  by  the  prefixes  ortho-,  meta-,  and  para-  accordingly  as  the 
0  and  N,  S  and  N,  or  N  and  N  are  in  the  I  :  2,  I  :  3  or  I  :  4  positions  to  each  other 
respectively.     Very  few  of  these  numerous  compounds  can  be  mentioned  here. 

0 
Phenoxazine  is  a  dibenzoparoxazine,  C6H4/        \C6H4,  produced  by  heating    o- 

NH 

amidophenol  with  pyrocatechol  ;  it  melts  at  148°  C.  and  only  deserves  notice  as  the 
progenitor  of  the  dyestuffs  resorujine,*  0  :  C6H3  :  [NO]  :  C6H3OH,  obtained  by 
heating  resorcinol  with  nitrosophenol  and  an  oxidant  to  remove  H2,  and  gallo- 
cyanine,  a  more  complex  derivative  made  by  heating  gallic  acid  with  nitrosodi- 
methylaniline  ;  the  former  dyes  red,  the  latter  violet. 

NH 
To   the  dibenzoparathiazines  belongs  thio-diphenylamine,  C6H4<^       \C6H4,  the 

product  of  heating  diphenylamine  with  sulphur.  It  melts  at  180°  C.  and  is  the 
parent  substance  of  the  diphenylamine  dyes ;  thus,  by  oxidising  paraphenylene- 
diamine  in  presence  of  H2S  is  obtained  LautWs  violet  or  thionine, 

NH2-C6H3/N^C6H3  :  NH. 

S 

The  tetramethyl  derivative  of  this  thionine  is  methylene  blue,  N(CH3)2'C6H3  :  [NS] 
:  C6H3 :  N(CH3)2C1,  obtained  by  treating  dimethylaniline  hydrochloride  with 
sodium  nitrite  and  reducing  the  isonitroso-dimethylaniline  (p.  664)  with  H2S  ;  the 
dlmethyl-para-plienylenedianiirie,  C6H4(NH2)'N(CH3)2,  thus  produced  is  then 
oxidised  by  Fe2Cl6  in  presence  of  the  excess  of  H2S  ;  the  blue  solution  is  next  satu- 
rated with  NaCl,  and  ZnCl2  is  added  to  precipitate  the  ZnCl2  compound  of  the  dye- 
stuff,  which  forms  bronze-green  crystals,  soluble  in  cold  water  to  a  fine  blue  liquid, 
from  which  the  colour  is  fixed  on  cotton  with  a  tannin  mordant.  The  produc- 
tion of  methylene  wliite,  C12H7(CH3)4N3S,  by  the  action  of  reducing-agents  has  led  to 
the  use  of  methylene  blue  for  measuring  the  reducing  power  of  different  portions 
of  the  body.  The  formation  of  the  blue  is  one  of  the  most  delicate  tests  for  H2S 
in  solution  ;  the  liquid  to  be  tested  is  mixed  with  excess  of  HC1,  a  little  dimethyl- 
para-phenylene  diamine  sulphate  added,  followed  by  a  drop  of  Fe2CL. 

CH:N-CH 
The  simplest  metadlazine  is  pyrimidine,  •  ••    ,  a  soluble  base  melting  at 

CH  :  CH-N 

*  It  will  be  noticed  that  thes3  dyestuffs  are  represented  as  containing'  quinonoid  linking 
(p.  721). 


INDULINES  AND   SAFRANINES.  769 

21°  C.  and  boiling  at  124°  C.     The  pyrimidines  are  obtained  by  heating  fl-diketon 
with  amidmes  ;  they  are  also  products  of  the  polymerisation  of  alkyl  cyanides  bv 
150    C.,  and  were  originally  called  cyanalkines.      Thus  «*«*«***«£ 


(CH3CN)3,  from  methylcyamde  is  constitutionally  dimetkylamidopyrim&iw  \  it  is 
a  crystalline  base  having  a  bitter  taste  and  soluble  in  water. 

CH  •  N 
The  lenzonietadiazines  are  derivatives  of  quinazoline,  C6H4/        '  •         not  it- 

XN     :CH5 

self  known  ;  its  a-methyl  derivative  is  produced  by  treating  o-amidobenzaldevhde 
with  NH3  ;  it  melts  at  35°  C.  and  boils  at  238°  C.  " 

The  paradlazines  are  derived  from  pyrazine,  •  ..    ,  obtained  bv  distilling 

CH :  N-CH 

amidoacetaldehyde  with  HgCl2  solution.  It  melts  at  55°  and  boils  at  115°  C.,  but 
sublimes  at  the  ordinary  temperature  and  smells  of  heliotrope.  Hexahydropyra- 
zine,  C4H10N2,  is  called  piperazlne  from  its  analogy  to  piperidine;  it  is  a  remedy  for 
gout. 

N  •  C  FT 
Quinoxaline  is  a  lenzoparadiazine,  C6H4/        J    ,  obtained  by  heating  glyoxal 

N  :  CH 
CHOCHO.  with  orthophenylenediamine  ;  m.-p.  27° ;  b.-p.  229°  C. 

Phenazine  is    a    dilenzoparadiazine,   C6H4/ .  \C6H4,   obtained  by  condensing 

o-phenylenediamine  with  pyrocatechol,  2H20  and  H2  being  lost.  It  crystallises  in 
yellow  needles,  melting  at  171°  C.  Several  important  dyestuffs  belong  to  this  class  ; 
thus  the  red  fluorescent  dyestuffs  called  eur /iodines  are  amido-derivatives  of 
naphthophenazine,  C6H4[N2]C10H6,  while  the  eurhodoles  are  corresponding  hydroxy- 
derivatives.  Toluylene  red,  is  dimethyldiamidotoluphenazlne, 

NH2C6H2(CH3)[N2]C6H3N(CH3)2. 

The  indulines  and  safranines  are  dyestuffs  which  may  be  regarded  as  derived 
from  azoniums,  i.e.,  the  ammonium  bases  corresponding  with  the  tertiary  amines, 
the  azines,  such  as  C6H4  :  [N'NCH3C1] :  C6H4.  The  indulines  are  mostly  blue  dye- 
stuffs  made  by  heating  ^-amido-azo-compounds  with  monamines  and  an  acid, 
thus — 

NK,C6H4N  :  NC6H5  +  H2NC6H5  =  NH  :  C6H3^  ~)C6H4  +  NH3  +  H2. 

They  are  of  three  kinds  ;  the  benzindulenes,  having  the  above  formula  derived  from 
phenazine  ;  the  rosindulenes,  derived  from  naphthophenazine  ;  and  the  naphthin- 
dulines,  derived  from  naphthazine,  C10H6[N2]C10H6. 

The  safranines  are  diamido-derivatives  of  the  azonium  salts  and  maybe  classified 
like  the  indulines.  Tolusafranine,  NH2C6H2(CH3) :  [N'N(C2H5)C1]  :  C6H3NH2, 
the  commercial  red  dyestuff  called  safranine,  is  made  by  oxidising  a  mixture  of 
£>-toluylenediamine,  o-toluidine  and  aniline. 

577.  Pyrone,  O/  No,  is  the  only  other  six-membered  ring  to  which 

N/~1TT    .     /^TT/ 

Uxl  .  Uil 

attention  can  be  called  ;  it  is  a  neutral  substance  obtained  by  heating  comanic 
acid,  C5H302'C02H.  See  meconic  acid  (p.  622). 

URIC  ACID  AND  THE  ALKALOIDS. 

578.  Uric  acid  and  its  derivatives. — Although  these  are  strictly 
heteronucleal  compounds,  they  are  more  nearly  related  to  open-chain 
compounds  than  are  the  substances  just  considered  ;  however,  their 
connection  with  the  vegetable  bases,  originally  all  classed  together  as 
alkaloids,  warrants  their  discussion  at  this  place. 

Uric  acid,  or  lithic  acid,  C5H4N403,  or  C2(CO)3(NH)4.— Uric  acid  is 
generally  prepared  from  the  excrement  of  the  boa-constrictor  (serpent's 


UKIC  ACID. 

urine  from  the  Zoological  Gardens),  which  consists  chiefly  of  acid 
ammonium  urate,  H(NH4)C3H2N4O3 ;  this  is  dissolved  by  boiling  with 
dilute  potash,  which  expels  NH3,  and  converts  it  into  normal  potassium 
urate,  K2C5H2N403;  by  passing  C02  through  this,  the  sparingly  soluble 
add  potassium  urate,  HKC5H2N403,  is  precipitated  ;  this  is  washed, 
dissolved  in  hot  water,  and  decomposed  by  HC1,  which  precipitates  the 
uric  acid.  Human  urine  also  yields  uric  acid  in  small  crystals  when 
concentrated  by  evaporation,  mixed  hot  with  a  little  HC1,  and  set  aside  ; 
the  crystals  are  much  tinged  with  urinary  colouring-matter,  and  may 
be  purified  by  dissolving  in  potash  and  treating  as  above  ;  healthy  urine 
yields,  at  most,  one  thousandth,  by  weight,  of  the  acid. 

Guano,  the  partly  decomposed  excrement  of  sea-birds,  contains  much 
uric  acid,  which  may  be  extracted  from  it  by  boiling  it  with  a5-per-cent. 
solution  of  borax,  and  adding  HC1  to  the  filtered  solution. 

Uric  acid  is  a  white  crystalline  powder,  appearing  under  the  micro- 
scope in  peculiar  modifications  of  the  rhombic  prism.  It  is  very 
sparingly  soluble  in  water,  requiring  1800  parts  of  boiling  water  and 
14,000  parts  of  cold  water;  and  it  is  insoluble  in  alcohol  and  ether,  but 
dissolves  in  glycerine  and  in  alkaline  liquids. 

When  heated,  it  is  carbonised  and  decomposed,  emitting  odours  of  NH3  and 
HCN  ;  urea  and  cyanuric  acid  are  also  found  among  the  products.  Strong  H2S04, 
heated  with  uric  acid,  dissolves  it  without  blackening,  and,  on  cooling,  deposits 
crystals  containing  2H2S04  ;  water  separates  uric  acid  from  them.  Nitric  acid 
dissolves  uric  acid  easily  when  gently  warmed,  effervescing  from  escape  of  N,  C02, 
and  oxides  of  nitrogen.  On  evaporating  the  solution,  the  yellow  residue  becomes 
red  when  further  heated.  This  residue  is  a  mixture  of  several  oxidation-products 
of  uric  acid,  and  assumes  fine  purple  colours  when  treated  with  NH3  or  KOH 
(murexide  test).  Uric  acid  is  a  reducing-agent  ;  it  precipitates  cuprous  oxide  from 
alkaline  cupric  solutions,  and  reduces  silver  nitrate  to  the  metallic  state,  if  a  little 
Na2C03  is  added. 

When  uric  acid  is  heated  with  strong  hydriodic  acid  in  a  sealed  tube 
to  i6o°-i7o°  C.,  it  yields  glycocine,  CH2NH2'C02H,  and  the  products 
of  decomposition  of  urea,  viz.,  NH3  and  C02.  Conversely,  if  glycocine 
be  heated  with  excess  of  urea  to  230°,  uric  acid  is  formed — 

CH2NH2'C02H  +  3CO(NH2)2  =  C2(CO)3(NH)4  +  3NH8  +  2H20. 

Urea  is  found  among  the  products  of  distillation  and  oxidation  of 
uric  acid.  The  acid  character  of  uric  acid  is  feeble,  and  its  salts  are,  for 
the  most  parb,  sparingly  soluble;  it  is  dibasic. 

Acid  sodium  urate,  HNaC5H2N403,  occurs  in  the  gouty  concretions  termed  chalk- 
stones,  and  sometimes  as  a  deposit  from  urine. 

The  acid  ammonium  urate  is  the  buff  or  pink  deposit  so  often  formed  in  urine  on 
cooling  ;  it  disappears  on  gently_ warming  ;  the  colour  does  not  belong  to  the  salt 
itself.  Acid  lithium  urate,  HLiU,  is  the  most  soluble  urate,  requiring  370  parts  of 
cold  and  40  parts  of  boiling  water,  whilst  the  sodium  salt  requires  uoo  parts  cold 
and  124  parts  boiling,  and  the  ammonium  salt  requires  1600  parts  of  cold  water. 

Uric  acid  and  urates  are  very  common  constituents  of  urinary  calculi.  They  are 
also  found  in  minute  quantity  in  blood  and  some  other  animal  fluids,  and  in  the 
.solid  parts  of  some  animals. 

There  is  no  evidence  that  uric  acid  contains  *COOH  groups,  or  even 
•OH  groups  ;  it  probably  owes  its  acid  character  to  the  presence  of  :  NH 
groups,  which,  as  has  been  already  explained  (p.  669),  impart  acid 
properties  to  compounds  containing  them.  When  lead  urate  is  heated 
with  methyl  iodide,  dimethyl  uric  acid,  containing  two  methyl  groups 
in  place  of  two  H  atoms,  is  obtained.  This  is  also  a  dibasic  acid, 


PURINE. 


showing  that  it  must  still  contain  two  NH  groups,  and  when  its 
lead  salt  is  heated  with  methyl  iodide,  tetramethyluric  acid  is  obtained. 
When  these  methyl  uric  acids  are  decomposed,  the  N  appears  as 
methylamme  ;  hence  each  of  the  methyl  groups  is  directly  united  to 
a  nitrogen  atom,  in  which  case  there  must  have  been  four  NH 
groups  in  the  original  uric  acid.  The  various  decompositions  of  uric 
acid,  described  below,  indicate  that  it  contains  three  carbon  atoms 
directly  united,  and  that  at  least  two  of  its  NH  groups  must  be  attached 
directly  to  a  CO  group  (for  urea,  00(NH2)2,  is  a  product  of  its  decom- 
position). These  considerations  have  led  to  the  structural  formula  for 
uric  acid  — 


/NH-COONEL 
CO/  \CO. 

XNH  -  C-NB/ 


This  formula  represents  uric  acid  as  a  diureide,  a  ureide  being  a  com- 
pound which  may  be  supposed  to  be  formed  by  condensation  of  urea 
with  a  dibasic  acid.  Thus  parabanic  acid  (v.i.)  may  be  regarded  as 
formed  from  urea  and  oxalic  acid  :  — 

NH2        COOH  NH-CO 


C°NH2+COOH  NH-CO 

It  will  be  seen  that  uric  acid  contains  two  urea  residues,  but  the  acid  of 
which  it  is  a  diureide  is  not  known.  The  view  is  supported,  however, 
by  the  fact  that  most  of  its  derivatives  are  of  the  ureide  form. 

/N  :  CH-ONEL 

579.  Purine,  CH/  ..        ^CH>  is  obtained  from  uric  acid  by  treating  it 

with  POC13  whereby  it  becomes  trichloropurine,  which  yields  successively  diiodo- 
2)ii  fine  and  purine  when  treated  with  HI  and  Zn-dust.  It  melts  at  216°  C.,  is  very 
soluble  in  water  and  is  both  an  acid  and  a  base.  The  orientation  of  the  nucleus 

1657 
common  to  uric  acid  and  purine  will  be  understood  from  the  scheme  2  — 

3      49 

580.  When  uric  acid  is  added  by  degrees  to  strong  nitric  acid,  it  dissolves  with 
effervescence,  caused  by  liberation  of  C02  and  N,  and  the  liquid  becomes  hot.     On 

/NH-COV 

cooling,  it  deposits  octahedral  crystals  of  alloxan,  C0<  >CO,  or  mesoxalyl- 

X-X 


•urea,  which  stains  the  skin  pink,  and  gives  an  intense  purple  colour  with  ferrous 
sulphate  and  a  trace  of  potash.  The  octahedral  crystals  contain  lAq,  but  it  may 
be  crystallised  in  prisms  with  4Aq. 

When  alloxan  is  boiled  with  baryta-water,  it  deposits  the  barium  salt  of 
alloxanic  acid  ;  C303(NH)2CO  +  H20  =  NHa'CO'NH'COOl-OOOH,  If  the  boiling  be 
long  continued,  the  products  are  urea  and  (the  barium  salt  of)  mesoxalic  acid  — 

NHa-CO-NHtCOVCOaH  +  2HOH  =  CO(NH2)2  +  C(OH)2(C02H)2. 
By  hydrogenising  alloxan  by  passing  H2S  through  its  boiling  solution,  it  is  converted 
into  dialuric  acid,  or  tartromjl-urea,  CO/  \CHOH.     Dialuric  acid  crystal- 


Uses  in  needles  which  absorb  oxygen  when  exposed  to  air,  and  are  converted  into 
alloxa-ntin,  C8H4N407,  with  loss  of  2H20.     This  body  is  also  precipitated  together 
with  sulphur,  when  H2S  is  passed  into  a  cold  solution  of  alloxan,  when  the  d 
acid  formed  at  first  reacts  with  the  excess  of  alloxan,  and  the  alloxantm,  being 
nearly  insoluble  in  cold  water,  is  removed  from  the  further  action  of  t      H2b. 

Alloxantin  is  precipitated  on  mixing  solutions  of  alloxan  and  dialuric  acid 
that  it  is  a  diureide  formed  from  these  two  ureides  by  loss  of  one  mol.  H2O.    When 


772  OXALUPJC  ACID. 

uric  acid  is  dissolved  in  hot  dilute  nitric  acid,  alloxantin  is  the  chief  product,  and 
its  preparation  may  be  combined  with  that  of  alloxan  by  treating  the  cooled 
mother-liquor  from  the  alloxan  with  H2S,  and  boiling  the  precipitate  with 
water,  which  extracts  the  alloxantin  and  deposits  it,  on  cooling,  in  prisms  con- 
taining 3Aq.  It  has  an  acid  reaction,  and  produces  a  fine  violet  precipitate  with 
baryta-water,  which  is  bleached  by  boiling,  being  converted  into  the  alloxanate 
and  dialurate.  Ferric  chloride  and  a  trace  of  ammonia  give  a  blue  colour  with 
alloxantin.  It  becomes  red  when  exposed  to  air  containing  ammonia.  On 
adding  ammonium  chloride  to  a  hot  saturated  solution  of  alloxantin,  it  becomes 
first  purple  and  then  colourless,  depositing  a  crystalline  precipitate  of  uramil 

/NH-CCK 
(murexari)  or  dialuramide.  C0<  >CHNH2,  and  leaving  alloxan  in  solution. 


If  an  ammoniacal  solution  of  uramil  be  mixed  with  an  ammoniacal  solution  of 
alloxan,  a  purple  solution  is  formed  which  deposits  crystals,  with  a  green 
metallic  lustre,  of  murexide,  or  acid  ammonium  purpurate,  NH4.C8H4N506.H20, 
the  constitution  of  which  is  uncertain,  but  the  formula  is  the  sum  of  one  mole- 
cule of  uramil,  one  of  alloxan,  and  one  of  ammonia.  Since  alloxan  and  uramil 
are  both  produced  when  uric  acid  is  evaporated  with  nitric  acid,  it  is  easy  to 
account  for  the  purple  colour  produced  by  treating  the  residue  with  ammonia. 

Murexide  is  also  formed  by  heating  alloxantin  to  100°  C.  in  a  current  of 
ammonia-gas,  when  water  is  eliminated,  and  by  boiling  uramil  with  water  and 
HgO,  when  an  atom  of  oxygen  from  the  latter  acts  on  2  mol.  of  uramil,  yielding 
murexide  and  water.  Murexide  is  sparingly  soluble  in  cold  water,  and  insoluble 
in  alcohol  and  ether.  Potash  dissolves  it  with  a  rich  purple  colour.  Acids  bleach 
it,  apparently  producing  uramil. 

When  alloxantin  is  heated  with  strong  H2S04,  at  100°  C.,  as  long  as  S02  is 
evolved,  it  is  converted  into  barbituric  acid,  or  malonyl-urea,  which  is  also  obtained 
synthetically  by  heating  urea  with  nialonic  acid  and  phosphorus  oxy  chloride  — 

/CO-NIL 
3CH2(CO-OH)2  +  3CO(NH2)2  +  2POC13  =  3CH2/  \CO  +  2PO(OH)3  +  6HCI. 

L/L/-N  xi 

Barbituric  acid  is  sparingly  soluble  in  cold  water.  "When  boiled  with  alkalies,  it 
yields  malonic  acid  and  urea.  Amido-barbituric  acid  is  identical  with  uramil. 

/NH'CO 

Parabanic  acid,  or  oxalyl-urea,  C0<          •     ,  is  the  chief  product  of  the  more 

XNH-CO 

violent  oxidation  of  uric  acid,  and  is  prepared  by  gradually  adding  uric  acid  to 
6  parts  of  HN03  (sp.  gr.  1.3)  at  70°  C.,  evaporating  to  dryness  on  the  steam-bath, 
and  re-crystallising  from  water.  It  forms  prisms  which  are  strongly  acid,  .dissolve 
in  alcohol,  but  not  in  ether.  It  is  a  dibasic  acid  ;  its  solution  gives,  with  silver 
nitrate,  a  characteristic  crystalline  precipitate  of  CO:N2Ag2(C202).H2O.  When 
boiled  with  dilute  acids,  parabanic  acid  yields  urea  and  oxalic  acid,  and  it  may  be 
synthesized  from  these  substances  in  the  presence  of  phosphorus  oxychloride. 
Most  oxidising-agents  convert  uric  into  parabanic  acid. 

Oxaluric  acid,  NH2'CONH'COC02H,  is  formed  when  parabanic  acid  is  boiled 
with  NH3,  ammonium  oxalurate  crystallising  in  needles  after  cooling.  If  these  be 
dissolved  in  hot  water,  HC1  precipitates  oxaluric  acid  as  a  crystalline  powder. 
This  acid  has  the  same  relation  to  parabanic  acid  as  alloxanic  acid  has  to  alloxan  — 

Alloxan       .         .     N2H2(CO)4  I    Parabanic  acid         .     N2H2(CO)3 

Alloxanic  acid    .     N2H3(CO)3'C02H         |     Oxaluric  acid  .         .     N2H3(CO)2-C02H 

A  small  quantity  of  ammonium  oxalurate  may  be  extracted  from  urine  by 
animal  charcoal  ;  after  having  served  for  the  filtration  of  a  large  volume  of  urine, 
the  charcoal  is  well  washed  with  water,  and  boiled  with  alcohol,  which  leaves  the 
oxalurate  mixed  with  colouring-matter,  when  evaporated. 

Oxaluramide,  N2H3(CO)2'CO']SI"H2,  is  metameric  with  ammonium  parabanate, 
CO-N2H(NH4)-C202,  and  is  obtained  by  heating  that  salt  to  100°  C. 

Dimethyl-parabanle  acid,  CO-N2(CH3)2'C202,  or  cholestrophane,  is  formed  when 
silver  parabanate  is  heated  with  methyl  iodide.  It  is  interesting  from  having 
been  originally  obtained  by  the  oxidation  of  caffeine  (see  Caffeine). 

The  principal  immediate  products  of  the  oxidation  of  uric  acid  in  solution 
have  been  seen  to  be  alloxan,  parabanic  acid,  and  urea  ;  but,  when  an  alkaline 


SYNTHESIS  OF  URIC   ACID. 

*  ^^afstWA 

be  precipitated  by  HC1  ;  C^^+zttM+T^C  H$?  ""' 


ija^iK^^ 

C^ACalZMNMtM)  +  2(CN-NH2)(^«m^)  J?aSSSS  ftowioooun  4-  O 

Some  alloxan  is  formed  at  the  same  time  by  the  J^^^IEU^ 
antm,  which  thus  serves  as  the  necessary  reducing-agent 

Uric  acid  has  been  synthesised  by  the  following  reactions  :— 

Action  of  urea  on  ethyl  aceto-acetate  yields  methyl  uracyl 


NJTCO 

Action  of  HN03  on  this  yields  nitrouracylcarboxylic  acid  CO/NH  C(C° 

XNH-CO 

By  heating  with  lime  this  yields  nitrouracyl  .  CO/N        H 

XNH-COX 

NH' 

By  reduction  this  yields  isobarbituric  acid      .        .        .  CO/ 

XNH-CO 

NTT  'POTT 

By  oxidation  this  yields  isodialuric  acid         .        .        .  CO/ 

XNH-CO-X 
which  yields  uric  acid  when  warmed  with  urea  and  H2S04. 

581.  Theoretically,  the  parent  of  uric  acid  is  purine  (p.  771),  from  which  are  also 
derived  the  bases  — 


c      HH.COC.NH  HN:C 

XNH  -  ON   4  NH  _  C-N 

Xanthine.  Guaniue. 


c     NH-CO.C.NH 

^N  --  C-N    ^  ^N  ____  C-N    '' 

Hypoxanthine.  Adenine. 

These,  like  uric  acid,  are  products  of  degradation  of  the  animal  organism  and  are 
also  present  in  some  vegetable  products,  such  as  the  juice  of  the  beet  root.  They 
are  all  obtainable  from  uric  acid  through  trichloropurine  (r.  purine,  p.  771),  which 
yields  these  four  bases  by  different  reactions.  Guanine  is  converted  into  xanthine 
and  adenine  into  hypoxanthine  by  HN02. 

Guanine,  C5H5N50,  is  extracted  from  guano  (the  excrement  of  sea-fowl)  by 
boiling  it  with  lime  and  water,  and  boiling  the  undissolved  residue  with  NaOH, 
which  dissolves  the  guanine  and  uric  acid  ;  these  are  precipitated  by  acetic  acid, 
and  the  guanine  dissolved  out  by  hydrochloric  acid,  and  precipitated  by  NH3.  It 
is  amorphous,  insoluble  in  water  and  alcohol,  and  is  at  once  a  feeble  di-acid  base 
and  dibasic  acid.  It  gives  the  murexide  reaction,  and  when  oxidised  by  KC103  and 
HC1,  it  yields  C02,  parabanic  acid,  and  guanidine  — 

C5H5N50  +  03  +  H20  =  C02  +  C3H2N203  +  C(NH)(NH2)2. 

Guanine  is  found  in  the  pancreas  of  the  horse,  in  gouty  deposits  in  pigs,  in  the 
excrement  of  spiders  and  the  scales  of  bleak.  It  is  formed,  together  with  xan- 
thine and  sarcine,  when  yeast  is  allowed  to  decompose  in  water  at  35°  C. 


774  ALKALOIDS. 


Xanthine,  C5H4N402,  is  prepared  by  the  action  of  nitrous  acid  on  guanine  ; 
C5H5N50  +  HN02  =  C5H4N402  +  H20  +  N2.  It  forms  minute  white  crystals  sparingly 
soluble  in  water,  insoluble  in  alcohol,  dissolved  by  alkalies,  and  reprecipitated  by 
acids.  It  gives  the  murexide  reaction.  Its  crystalline  salts  with  acids  are  decom- 
posed by  water.  Its  ammoniacal  solution  yields,  with  AgN03,  a  gelatinous 
precipitate  containing  C5H2Ag2N402.H20,  which,  when  treated  with  CH3I,  yields 
theobromine  (q.r.). 

Xanthine  occurs  in  certain  rare  urinary  calculi,  and,  in  small  quantity,  in  urine, 
in  the  liver,  pancreas,  spleen,  and  brain  ;  also  in  guano  and  yeast. 

Sarcine,  or  hypoxanthine,  C5H4N40,  exists  in  extract  of  meat,  amounting  to  about 
0.6  per  cent.,  and  may  be  precipiated  from  the  mother-liquor  of  the  extraction 
of  creatine  (p.  ^676)  by  boiling  with  cupric  acetate.  The  brown  precipitate  is 
dissolved  in  HN03  and  precipitated  by  AgN03,  which  forms  an  insoluble  compound 
from  which  the  sarcine  may  be  extracted  by  decomposing  with  H2S  and  boiling 
with  much  water.  It  crystallises  in  minute  needles,  and  is  more  soluble  than 
xanthine,  though  it  forms  a  less  soluble  hydrochloride.  It  is  feebly  basic  arid 
acid.  Nitric  acid  oxidises  it  to  xanthine.  Sarcine  is  generally  found  together 
with  xanthine,  and  occurs  in  many  parts  of  the  animal  body,  especially  in  marrow. 

Adenine,  C5H5N5,  found  in  the  pancreas  of  the  ox  and  in  tea,  crystallises  in 
lustrous  laminae  (with  3H20)  and  is  soluble  in  water. 

Gamine,  C7H8N403,  is  also  found  in  extract  of  meat,  and  much  resembles 
xanthine  and  sarcine.  Nitric  acid  or  bromine-water  oxidises  it  to  sarcine. 

582.  The  Alkaloids. — These  compounds  possess  particular  interest 
for   the  chemist,   on  account  of  their  powerful  action  on  the  animal 
economy,  many  of  them  being  the  active  principles  of  the  medicinal   or 
poisonous  plants  from  which  they  are  extracted.     Hitherto  few  of  them 
have  been  prepared  artificially,  though  the  study  of  their  properties  in- 
dicates that  they  are  ammonia-derivatives.     They  all  contain  nitrogen, 
but  rarely  more  than  two  atoms  in  a  molecule,  though  there  may  be 
twenty  or  thirty  carbon-atoms ;  they  all  contain  oxygen  with  the  excep- 
tion of  coniine,    nicotine,  and  sparteine,   which   are   volatile   liquids. 
Most  of  them  refuse  to  sublime  without  partial  decomposition,  which 
unfits  them  for  ranking  as  amines;  they  dissolve  sparingly  in  water, 
which  renders  it  unlikely  that  they  are  ammonium  bases,  and  brings 
them  nearer  to  the  amides,  which  many  of  them  also  re.semble  in  their 
feebly  basic  character.     The  alkaloids  are  soluble  in  alcohol,  and  their 
solutions  are  generally  alkaline  and  bitter.     Their  salts  are  formed,  like 
those  of  ammonia,  by  the  direct  union  of  the  base  and  the  acid,  with- 
out separation  of  water,  and,  as  a  rule,  the  salts  are  soluble  in  water. 
The  hydrochlorides  of  the  alkaloids  resemble  those  of  all  amines,  as 
well  as  the  chlorides  of  the  alkali-metals  and  the  ammonium  bases,  in 
forming  crystalline  double  salts  with  platinic  chloride,  mercuric  chloride. 
and  auric  chloride.     Most  of  the  alkaloids  may  be  precipitated  from 
their  solutions  by  iodine  dissolved  in  potassium  iodide,  by  potassio-mer- 
curic  iodide,  by  potassio-bismuthic  iodide,  by  picric  acid,  tannin,  meta- 
tungstic  acid,  and  phosphomolybdic  acid. 

583.  Xanthine -alkaloids. — The  alkaloids,  theobromine  and  caffeine^ 
are  methyl  derivatives  of  xanthine  : — 

/  NH-CO-ON(CH3\                                   /N(CH3)-CO-C-N(CH3X 
C0<                ..            3\CH.                   CO/                     ..  3y\CH. 

XN(CH3)-C'N XN(CH3) C-N 

Theobromine,  or  3  :  y-dimethylxanthine.  Caffeine,  or  i  :  3  :  y-trimethylxanthine. 

Theobromine,  C7H8N402,  is  extracted  from  the  seeds  of  the  cacao  tree  (Tlieolroma 
cacao),  which  grows  in  Demerara.  These  are  known  as  cocoa-nibs,  and  are  the  raw 
material  of  cocoa  and  chocolate.  The  cocoa-beans  contain  1-2  per  cent,  of  theo- 
bromine, which  may  be  extracted  from  them  in  the  same  way  as  caffeine  (which  it 


CAFFEINE. 

inuch  resembles)  from  tea  or  coffee.     When  treated  with  KC10,  and  HC1  it  yields 
methy  alloxan  and  methyl-urea.     When   theobromine  is  dissolved  in  ammo 
and  boiled  with  silver  nitrate,  a  white  precipitate  of  Mwth^™}%  £i£^™ 
is  obtained,  and  when  this  is  heated  with  methyl  iodide,  it  yields  S-2u£S& 
or  cafteme.     Theobromine  is  similarly  obtained  from  silver  xanthine  (p.  774) 

Caffeine  or  theine,  C8H]0N402,  is  extracted  from  a  plant  of  Gin- 
chonaceous  order,  the  coffee-tree  (Caffea  arabica),  the  seeds  of  which 
contain  about  1.5  per  cent,  of  caffeine.  It  is  also  found  in  the  leaves  - 
but  those  of  the  tea-plant  (Thea)  yield  more  of  it,  the  proportion  in  the' 
dried  leaf  varying  from  2  to  4  per  cent.  To  prepare  caffeine,  tea-dust  is 
boiled  with  water  to  extract  all  the  soluble  matter,  which  amounts  to 
about  30  per  cent.,  and  consists  of  tannin,  cafteine,  aromatic  oil,  and 
other  bodies.  The  decoction  is  filtered,  mixed  with  excess  of 'lead 
acetate,  which  precipitates  the  tannin,  again  filtered,  the  lead  precipitated 
by  H2S,  and  the  filtrate  from  the  lead  sulphide  evaporated  to  a  small 
bulk,^when  the  caffeine  crystallises  and  maybe  purified  by recrystallij-a- 
tion  from  alcohol. 

The  waste  tea-leaves  which  have  been  exhausted  in  the  tea-pot  yield  a  consider- 
able proportion  of  caffeine  when  treated  in  this  way.  Caffeine  may  be  similarly 
extracted  from  ground  unroasted  coffee-beans.  It  may  be  sublimed  from  tea-leaves 
or  coffee-beans  by  gently  heating  them  in  an  evaporating-dish  covered  with  a  dial- 
glass  ;  one  of  the  best  processes  for  obtaining  it  is  to  precipitate  decoction  of  tea 
with  tribasic  lead  acetate,  to  evaporate  the  filtrate  to  dryness,  on  the  steam-bath, 
at  last,  and  to  cautiously  heat  the  dry  residue  in  an  evaporating-dish,  when  the 
caffeine  sublimes  on  to  the  cover. 

Caffeine  is  contained  in  several  plants  which  are  used  in  various  places  for 
chewing  or  preparing  drinks.  Paraguay  tea  is  made  from  the  leaves  of  one  of  the 
llicacece,  or  Holly  order,  the  Ilex  'paraguayemis,  and  is  drunk,  under  the  names  of 
mate  and  congonka,  in  Paraguay,  Brazil,  Chili  and  Peru.  The  leaves  contain  caffeine. 
Another  beverage  containing  caffeine  is  used  by  the  Indians  of  Brazil  and  called 
Guarana,  being  prepared  from  the  seeds  of  the  Paullinia  sorMlis,  a  tree  of  the  Soap- 
wort  order,  to  which  the  horse-chestnut  belongs.  The  kola-nut,  or  seeds  of  Cola 
acuminata,  used  as  food  and  medicine  by  the  natives  of  West-Central  Africa, 
contains  about  2  per  cent,  of  caffeine. 

Caffeine  crystallises  in  fine  silky  needles  (with  iH20).  It  becomes 
anhydrous  at  100°  C.  and  then  melts  at  233°  C.,  and  sublimes  unde- 
composed.  It  dissolves  in  90  parts  of  cold  water,  yielding  a  bitter 
solution,  which  is  not  alkaline.  It  is  soluble  in  alcohol  and  ether,  and 
more  easily  in  benzene  and  chloroform. 

Caffeine  is  a  very  feeble  base,  its  salts  being  decomposed  by  water. 
The  hydrochloride,  C8H10N4O2.HC1.2Aq,  crystallises  from  strong  hydro- 
chloric acid  in  prisms,  which  leave  pure  caffeine  at  100°  C.  The 
sulphate,  C8H10N4O2.H2SO4,  is  obtained  in  needles  by  adding  dilute 
sulphuric  acid  to  a  hot  alcoholic  solution  of  caffeine.  The  acetate  is 
C8H10N408(C2H102)2. 

Chlorine-water  (or  HC1  +  KC103)  converts  caffeine  into  amalic  acid,  or  tetra- 
methyl  alloxantin,  C8(CH3)4lsr407.Aq.  In  the  presence  of  air,  water,  and  ammonia, 
this  yields  murexoln,  or  tetramethyl  murexide,  C8(CH3)4N506(NH4),  which  crystal- 
lises from  hot  water  in  scarlet  prisms  with  a  golden  lustre.  The  test  for  caffeine 
is  based  on  this :  dissolve  it  in  strong  HC1,  add  a  crystal  of  potassium  chlorate, 
and  evaporate  to  dryness.  A  red  residue  is  left,  which  becomes  purple  with 
ammonia,  and  is  bleached  by  potash. 

The  final  product  of  the  action  of  chlorine-water  on  caffeine  is  cholestrophane 
(p.  772).  When  long  boiled  with  baryta-water,  caffeine  is  converted  into  cajfei 
dine,  C7H12N40,  which  is  a  stronger  base  than  caffeine — 

C8H10N402  +  Ba(OH)2  =  C7H12N40  +  BaC03. 


776  NICOTINE. 

Theophyllin  or  i  :  3-dimethylxanthine  accompanies  caffeine  in  tea ;  it 
melts  at  264°  C. 

584.  Pyridine-alkaloids. — The  alkaloids  piperine,  coniine,  and  nico- 
tine, are  derivatives  of  pyridine. 

Piperine,  or  piperidine  piper  ate,  CnH902'CONC5H10,  bears  the  same  relationship 

/0\ 

to  piperic  acid,  CH,/    >C6H3'CH  :  CH'CH  :  CH'C02H,   that   acetamide  bears   to 
XT 

acetic  acid,  the  piperidine  (p.  766)  residue,  -NC5H10,  behaving  like  the  ammonia 
residue,  'NH2.  It  is  a  feeble  base  extracted  by  alcohol  from  white  pepper,  the  ripe 
fruit  of  Piper  nigrum  (the  unripe  fruit  is  black  pepper).  It  crystallises  in  prisms 
(m.-p.  128°  C.),  which  are  insoluble  in  water,  but  soluble  in  ether.  The  alcoholic 
solution  tastes  hot.  When  boiled  with  potash  it  yields  piperidine,  and  potassium 
piperate.  It  dissolves  in  H2SO4,  cone,  with  a  red  colour. 

Coniine.  or  2-norntal-propyl  piperidine,  C5H9(C3H7)NH,  is  extracted  from  the 
seeds  of  hemlock  (Conium  maculatuni)  by  crushing  them  and  distilling  with  weak 
KOH.  The  distillate,  which  contains  NH3  and  coniine,  is  neutralised  with  H2S04, 
concentrated  by  evaporation,  and  mixed  with  alcohol  to  precipitate  the  (NH4)2S04. 
On  evaporating  the  filtrate  and  distilling  with  strong  KOH,  coniine  distils  with 
water,  upon  the  surface  of  which  it  floats.  It  is  dehydrated  with  dried  K2C03, 
and  fractionated. 

Coniine  has  a  strong  odour  of  mice  ;  its  sp.  gr.  is  0.89,  and  it  boils  at  167°  C. 
It  is  sparingly  soluble  in  cold  water,  giving  an  alkaline  solution.  It  dissolves  in 
alcohol  and  ether.  When  exposed  to  air,  it  becomes  brown,  and  evolves  NH3. 
Oxidising-agents,  such  as  nitric  and  chromic  acids,  convert  it  into  butyric  acid. 
When  coniine  is  heated  in  a  sealed  tube  with  CH3I,  it  exchanges  H  for  CH3,  show- 
ing it  to  be  a  secondary  monamine,  NH(C8H16)".  The  methylconiine,  NCH3(C8H16)", 
sometimes  occurs  in  hemlock.  It  combines  with  CH3I  to  form  a  crystalline 
coniine-methylium  iodide,  N(C8H16)"(CH3)2I,  which  yields  a  caustic  base  when 
decomposed  by  AgOH.  Hemlock  also  contains  another  base,  conhydrine,  C8H17NO, 
crystallising  in  plates. 

Coniine  has  been  obtained  artificially  by  the  action  of  sodium  on  an  alcoholic 
solution  of  ally l-pyri dine,  C5H4(C3H5)N,  a  liquid  product  of  the  action  of  paraldehyde 
upon  picoline,  C5H4(CH3)N.  The  base  obtained  in  this  way,  however,  is  optically 
inactive  ;  when  its  tartrate  is  fractionally  crystallised,  it  is  split  up  into  a  leevo- 
base  and  a  dextro-base  (cf,  p.  606)  ;  the  latter  is  coniine. 

Paraconiine,  C8H15,N,  propyl  tetrahydropyridine,  is  obtained  by  distilling  the 
product  of  the  action  of  alcoholic  ammonia  on  butyric  aldehyde — 

2C3H7CHO  +  NH3  =  H20  +  C8H17NO 

(dibutyraldine)  ;  C8H17NO  =  H20  +  C8H15N  (paraconiine).  This  base  is  very  similar 
to  coniine,  and,  like  it,  a  powerful  narcotic  poison,  but  is  optically  inactive,  and 
appears  to  be  a  tertiary  monamine. 

Nicotine,  C10H14K2,  is  found  chiefly  as  malate,  in  the  seeds  and  leaves 
of  tobacco,  Nicotiana  tabacum,  a  plant  of  the  order  of  Atropacese, 
many  of  which,  especially  deadly  nightshade,  thorn-apple,  henbane,  and 
mandrake,  yield  narcotic  poisons.  Nicotine  is  extracted  from  tobacco 
leaves  by  digesting  them  with  very  dilute  H2S04,  evaporating  to  a  small 
bulk,  and  distilling  with  excess  of  KOH.  The  distillate  is  shaken  with 
ether,  the  ethereal  layer  is  drawn  off,  the  ether  distilled,  and  the 
nicotine  placed  in  contact  with  quick-lime  to  remove  the  water,  and 
distilled  in  a  current  of  hydrogen,  since  it  is  decomposed  when  distilled 
in  air  at  the  ordinary  pressure. 

Nicotine  is  colourless  when  freshly  prepared,  but  soon  becomes  brown 
in  air.  It  smells  strongly  of  tobacco,  has  sp.  gr.  i.oi,  and  boils  at 
247°  C.  It  is  soluble  in  water,  alcohol,  and  ether;  its  solution  is  alka- 
line. It  is  a  di-acid  base,  but  its  salts  do  not  crystallise  well.  When 
heated  with  ethyl  iodide,  it  behaves  as  a  tertiary  amine,  yielding 


TOBACCO.  jjj 

nicotine-ethyliumdi-iodide,  N2(C10H14)"(C2H5)2T2,  which  yields  the  cor- 
responding  caustic  base  when  decomposed  by  AgOH. 

By  oxidation  with  chromic  acid,  nicotine  yields  nicotinic  acid  (wrltl'm,--- 
carboxylic  acid}  C5H4(C02H)N  which  yields  pyridine,  when  distilled  with  lime  ' 

Nicotine   is   a-pyridyl-w-methyltetrahydropyrrol,   being  obtainable  by  a  some- 
what  complex  series  of  reactions  from  the  amide  of  nicotinic 
acid  by  introduction  of  a  pyrrol  group  in  place  of  the  ru  .PTT 

CONH2  group.  CH3N/CH2CH2 

Virginia  tobacco   contains  more  nicotine    than    other  CH  'CH 

varieties,  the  alkaloid  amounting  to  nearly  7  per  cent,  of 
the  weight  of  the  leaf  dried  at  212°  F.,  whilst  the  Maryland  /C  =  CH 

and    Havana   varieties  contain    only    2   or   3   per    cent.         HC<^  \N 

Tobacco  is  remarkable  for  the  very  large  amount  of  ash 
which  it   leaves  when   burnt,    amounting   to   about   one-  Nicotine, 

fifth  of  the  weight  of  the  dried  leaf,  and  containing  about 

one-third  of  K2C03,  resulting  from  the  decomposition  of  the  malate,  citrate,  and 
nitrate  of  potassium  during  the  combustion.  The  latter  salt  is  frequently  present 
in  larger  quantity  than  is  found  in  most  other  leaves  and  aids  the  combustion,  for 
which  purpose  it  is  sometimes  added  ;  but  it  is  often  present  only  in  very  small 
proportion  and  the  burning  quality  of  the  tobacco  is  not  impaired  by  its  absence. 

Cigars  are  made  directly  from  the  moistened  tobacco  leaves  which  may  or  may 
not  have  undergone  a  fermentation  ;  but  Snuff,  after  being  moistened,  is  subjected, 
in  large  heaps,  to  a  fermentation  extending  over  18  or  20  months,  when  it  becomes 
alkaline  from  the  development  of  (NH^COg  (by  the  putrefaction  of  the  vegetable 
albumin  in  the  leaf)  and  of  a  minute  quantity  of  free  nicotine,  which  imparts  the 
peculiar  pungency  to  this  form  of  tobacco.  The  aroma  of  the  snuff  appears  to  be 
due  to  the  production  of  a  peculiar  volatile  oil  during  the  fermentation.  The 
proportion  of  nicotine  in  snuff  is  only  about  2  per  cent.,  being  one-third  of  that 
found  in  the  unfermented  tobacco  ;  and  a  great  part  of  this  exists  in  the  snuff  in 
combination  with  acetic  acid,  which  is  also  a  result  of  the  fermentation. 

585.  iSparteine,  C15H26N2,  is  a  narcotic  alkaloid  extracted  from  the  common  broom 
(Spartium  scopariwni)  by  digestion  with  weak  sulphuric  acid  and  decomposing  the 
sulphate  by  distilling  with  potash.     It  is  liquid,  heavier  than  water,  boiling  at 
311°  C.     It  is  sparingly  soluble  in  water,  giving  an  alkaline  solution  with  a  bitter 
taste.     It  smells  rather  like  aniline,  and  becomes  brown  when  exposed  to  air.     It 
acts  as  a  di-acid  base,  and  appears  to  be  a  tertiary  di-amine. 

586.  Tropine- alkaloids. — Atropine,  hyoscyamine  and  cocaine  are  derivatives  of 
a  base   tr opine   which  behaves  as   a   i-methyl-4-hydroxypiperidine  wherein  the 
2-  and  s-C  atoms  are  linked  by  a  -CHa'CHa  group.   Atropine  and  hyoscyamine  are 
isonieric  forms  of  a  salt  of  this  base  with  tropic  acid  or  a-phenylhydr  acrylic  acid. 


CH9'CH- 


NCHo    CH(OH) 


NCH,     CH-OCO-CH(C6H5)-CH2OH. 


CH2'CH CH2  CH2-CH CH2 

Tropine.  Atropiue. 

Tropine,  C8H15NO,  is  a  crystalline  base  melting  at  62°  C.  and  boiling  at  263°  C., 
obtained  by  hydrolysis  of  atropine. 

Atropine   and  hyoscyamine,    C^H^NOg,  are  physical  isomerides  associated  in 
several  plants  of  the  order  Solanacea,  the  former  particularly  in  deadly  night- 
shade  (Atropa   belladonna)    and   thorn-apple   (Datura  stramonium),   the    latter 
especially  in ,  hyoscyamus   (henbane).      Both    alkaloids  have    the  characterist 
(mydnatic)  effect  of  dilating  the  pupil  of  the  eye. 

Atropine  is  obtained  by  expressing  the  sap  from  the  flowers  of  belli 
heating  it  to  90°  C.  to  coagulate  albumin,  filtering,  adding  KOH  to  liberate  the 
base,  and  shaking  with  chloroform,  which  collects  it  and  sinks  to  the  bottom    T 
chloroform  is  distilled,  and  the  atropine  recrystalhsed  from  alcohol      I 
prisms,  fusing  at  115°  C.,  sparingly  soluble  in  cold  water,  and  having  a  bitter  burn- 
ing  taste  and   a  very   poisonous    action.    Atropine    is  optically  inactive    and 
hyoscyamine    lajvo-rotatory,  but  the  laevo-atropine   obtained  by  resolving   1 
inactive  form  is  not  identical  with  hyoscyamine. 


77  8  OPIUM — MOKPHIA. 

Solanine,  C42H87N016,  is  contained  in  plants  of  the  same  order,  especially  in 
Solatium  nigrum  and  in  the  shoots  of  potatoes  (Solatium  tuberosu-ni)  which  have  been, 
kept  in  a  cellar  during  winter.  To  extract  it,  the  plant  is  digested  with  weak 
sulphuric  acid,  and  the  solution  precipitated  with  ammonia.  It  crystallises  from 
alcohol  in  prisms,  which  are  nearly  insoluble  in  water.  It  gives  a  red  solution 
when  heated  with  sulphuric  acid  and  alcohol. 

Cocaine,  C17H21N04,  is  extracted  from  the  leaves  of  Erythroxylon  coca,  a 
Peruvian  stimulant.  It  crystallises  in  prisms,  melts  at  98°  C.  and  dissolves  in 
alcohol.  It  is  Isevo-rotatory  and  is  a  valuable  local  anaesthetic,  for  which  purpose 
the  hydrochloride  is  sold.  When  hydrolysed  cocaine  yields  tropine  carboxylic 
acid  or  ecgonine,  benzoic  acid  and  methyl  alcohol.  It  "is,  therefore,  a  benzoate 
of  methyl  tropine  carboxylate,  and  may  be  represented  by  substituting  the  benzoic 
acid  residue  for  that  of  tropic  acid,  and  C02CH3  for  H  in  the  3-position  of  the- 
piperidine  ring,  in  the  formula  for  atropine  (v.s.^). 

587.  Opium- alkaloids. — Opium  (OTTOS,  juice)  is  obtained  from  the 
Papaver  somniferum,  or  opium-poppy,  cultivated  in  Turkey,  Egypt, 
India,  and  other  Oriental  countries.  A  few  days  after  the  poppy-flower 
has  fallen,  incisions  are  made  in  the  poppy-head,  when  a  milky  juice 
exudes.  After  twenty-four  hours  this  becomes  a  soft  solid  mass  of 
brown  colour,  and  is  scraped  off  and  wrapped  in  leaves  for  the  market. 
Opium  contains  about  25  per  cent,  of  a  gummy  substance,  20  per  cent, 
of  ill-defined  organic  matters,  a  little  caoutchouc,  resin,  oil,  and  water, 
and  variable  proportions  of  a  large  number  of  alkaloids,  of  which  mor- 
phine, narcotine,  papaverine,  and  narceine  are  the  most  abundant. 
Little  is  known  of  the  constitution  of  morphine,  but  the  investigation, 
of  narcotine,  papaverine,  and  narceine  has  been  more  fruitful ;  the 
results,  however,  are  too  complex  for  discussion  here. 

Laudanum  is  supposed  to  contain  about  7  parts  by  weight  of  opium 
in  100  measures  of  proof  spirit. 

Morphine,  or  morphia,  C17H.9!N03,  is  extracted  from  opium  (which 
contains  6-15  per  cent.)  by  steeping  it  in  warm  water,  which  dissolves 
the  meconate  and  sulphate  of  morphine,  straining,  and  adding  CaCl2, 
which  precipitates  calcium  meconate.  The  filtered  solution  is 
evaporated  to  a  small  bulk  and  set  aside,  when  the  hydrochlorides  of 
morphine,  codeine,  and  oxymorphine  crystallise.  These  are  dissolved 
in  water,  and  the  morphine  precipitated  by  adding  ammonia.  It  is 
recrystallised  from  alcohol  in  prisms  (with  iH20),  which  become  anhy- 
drous and  melt  at  120°  C.  It  is  almost  insoluble  in  water,  requiring 
T  0,000  parts  of  cold  and  500  parts  of  boiling  water,  and  nearly 
insoluble  in  ether  and  chloroform,  both  of  which  dissolve  most  other 
alkaloids. 

Morphine  is  soluble  in  ethyl  acetate  (acetic  ether)  and  in  aniyl  alcohol,  either  of 
which  may  be  employed  to  extract  it  from  an  aqueous  solution.  Even  ether  may 
be  employed  to  extract  morphine  from  an  alkaline  solution,  if  shaken  with  it 
immediately  after  adding  the  alkali,  and  before  the  morphine  has  precipitated. 
Morphine  differs  from  most  other  alkaloids  by  being  very  soluble  in  potash  ;  if 
a  drop  of  weak  potash  be  stirred  with  solution  of  a  salt  of  morphine,  the  alkaloid  is. 
precipitated,  but  it  is  redissolved  by  a  very  little  more  potash.  Ammonia  does  not 
easily  redissolve  it  unless  NH4C1  be  present. 

Morphine  behaves  like  a  tertiary  monarnine  ;  it  contains  two  OH  groups  and 
resembles,  in  some  reactions,  a  phenol-alcohol.  Its  solutions  are  alkaline,  and  it 
combines  with  acids,  like  ammonia. 

Morphine  hydrochloride,  C17H19N03.HC1,  or  muriate  of  morphia,  is  the  chief  form 
in  which  morphine  is  used  in  medicine.  It  crystallises  in  needles  with  3Aq,  and  i& 
easily  soluble  in  water  and  alcohol.  Morphine  meconate,  the  most  soluble  of  the 
salts,  is  also  used  in  medicine. 


NARCOTINE. 

Morphine  and  its  salts  act  as  powerful  narcotic  poisons;  they  are  easily 
identified  by  giving  a  blue  colour  with  ferric  chloride  (purple  in  the  case  of  meconate^ 
and  a  golden  yellow  with  strong  nitric  acid.  Morphine  acts,  in  many  cases  as  a 
reducmg-agent  ;  it  liberates  iodine  from  iodic  acid  in  solution  ;  it  reduces  potassium 
ferricyanide  to  ferrocyanide,  and  precipitates  silver  when  boiled  with  silver 
nitrate.  When  distilled  with  potash,  morphine  yields  methylamine. 

Morphine  perwdide,  C17H19N03I4,  is  obtained  as  a  brown  precipitate  when  solu- 
tion of  iodine  in  KI  is  added  to  morphine  hydrochloride. 

Apomorphine,  C17H17N02,  is  formed  when  morphine  is  heated  with  a  large 
excess  of  strong  HC1  for  some  hours,  at  150°  C. ;  C17H19N03  =  C17HnNO  +  H0O. 
From  the  hydrochloride  thus  obtained,  Na^CC^  precipitates  apomorphine  as  "an 
amorphous  powder,  rapidly  turning  green  in  air,  and  then  dissolving  in  ether  with 
a  pink  colour.  It  is  much  more  soluble  in  alcohol  and  ether  than  is  morphine, 
and  is  a  powerful  emetic,  even  when  injected  under  the  skin. 

Codeine,  codeia,  or  methyl  morphine,  C17H18(CH3)N03,  is  obtained  from  opium 
by  adding  potash  or  soda  to  the  ammoniacal  filtrate  from  the  morphine.  It 
may  be  purified  by  crystallisation  from  ether.  Codeine  has  been  obtained  from 
morphine  by  heating  it  with  methyl  iodide  in  alcoholic  solution. 

Codeine  melts  at  150°  C.  and  is  easily  soluble  in  hot  water,  alcohol,  and  ether. 
It  crystallises  from  ether  in  anhydrous  octahedra,  and  from  water  in  rhombic 
prisms,  which  contain  Aq.  The  crystals  fuse  under  water.  It  is  a  narcotic  poison, 
though  less  powerful  than  morphine,  and  amounts  in  opium  to  only  about  0.5  per 
cent.  It  is  strongly  alkaline,  gives  no  colour  with  ferric  chloride,  and  does 
not  reduce  iodic  acid  like  morphine.  It  is  a  tertiary  monamine.  When  heated  with 
caustic  alkalies,  it  yields  methylamine  and  trimethylamine.  Heated  with  strong 
HC1  at  150°  C.,  it  yields  apomorphine  and  methyl  chloride. 

Narcotine,  C^H^NOf,  is  extracted  by  digesting  with  acetic  acid  the  residue 
left  after  exhausting  opium  with  water.  The  narcotine  is  dissolved  and  is 
precipitated  on  adding  NH3.  It  crystallises  from  alcohol  in  prisms,  which  contain 
Aq.,  but  like  morphine,  is  almost  insoluble  in  water  ;  it  dissolves  in  ether,  however, 
which  extracts  it  from  powdered  opium,  leaving  the  morphine.  Narcotine  is 
insoluble  in  potash,  and  melts  at  176°  C.  It  is  a  very  feeble- base,  not  alkaline, 
dissolving  in  acids,  but  not  forming  well-defined  salts.  It  has  a  narcotic  effect,  but 
is  not  nearly  so  poisonous  as  morphine.  Opium  contains  usually  about  I  per 
cent,  of  narcotine,  and  the  presence  of  this  drug  is  more  easily  detected  by  testing 
for  narcotine  than  for  morphine,  on  account  of  the  solubility  of  the  former 
in  ether.  The  material  to  be  tested  is  extracted  with  ether,  the  latter  evaporated, 
the  residue  dissolved  in  dilute  HC1,  and  a  little  euchlorine-water  added  (made  by 
adding  strong  HC1  to  a  weak  solution  of  KC103  till  it  has  a  bright  yellow  colour, 
and  adding  water  till  it  is  pale  yellow)  ;  this  produces,  with  narcotine,  a  yellow 
colour  in  the  cold,  becoming  pink  on  boiling  and  adding  more  of  the  euchlorine 
water. 

When  narcotine  is  long  boiled  with  water  it  yields  a  new  base,  cotarnine, 
C12H15N04  (m.-p.  132°  C.  )  soluble  in  water,  and  meconine  or  5  :6-dimethoxyph- 

CO 

thaUd^(CB.sO).2CQE^       \0,  (pM^/de  being  the  lactone  of  I  :  2-methylbenzoic 
CH2 

acid).  Meconine  is  sparingly  soluble  in  water  and  melts  at  102°  C.  It  occurs  in 
opium  to  the  extent  of  i  per  cent.  Cotarnine  appears  to  be  an  oxy-derivative  of 
/<-methylisoquinoline,  containing  a  methoxy-group.  When  reduced  it  yields  hydro- 
cotarnine,  C12H15N03,  and  when  this  is  heated  with  opianic  acid,  an  oxidation 
product  from  nieconine,  (CH30)2C6H4(CHOH)(C02H),  and  H2S04,  uowrcotiw  is 
formed.  This  melts  at  194°  C.  and  is  coloured  red  by  strong  H2S04.  *rom  thest 
reactions  it  is  concluded  that  narcotine  is  a  meconinehi/drocotarniii<<. 

Thebaine,  C17H15(OCH3)*NO,  is    contained  in  opium  in  small  proportion; 
remains  in  the  solution  from  which  the  hydrochlorides  of  morphine  and  codeine 
have   crystallised.     This   solution  is   mixed    with  ammonia,   which  precipitates 
thebaine  together  with  some  narcotine  ;  the  precipitate  is  dissolved  in  a  h 
acetic  acid,  and  the  narcotine  precipitated  by  tribasic  lead  acetate. 
is  precipitated  from  the  filtrate  by  dilute  sulphuric  acid,  after  which  ammo 
is  added  to  precipitate  the  thebaine.     This  alkaloid,  like  morphine,  is  msolubh 
water,  but  dissolves  in  alcohol  and  ether,  and  crystallises  in  plates  ;  m.-p.  193  ^ 
It  is  insoluble  in  alkalies.    Its  alcoholic  solution  is  alkaline.      Thebaine  gives 


7^0  QUININE. 

a  blood-red  solution  with  strong  sulphuric  acid.  When  heated  with  hydrochloric 
acid,  it  yields  an  isomeride,  thebenine,  which  gives  a  blue  colour  with  sulphuric 
acid.  Thebaine  is  very  poisonous,  producing  tetanic  convulsions. 

Narceine,  C^H^NOg,  remains  in  the  solution  from  which  the  thebaine  and 
narcotine  have  been  precipitated  by  NH3.  This  is  mixed  with  lead  acetate,  to 
precipitate  the  rest  of  the  narcotine,  filtered,  the  lead  removed  by  H2S04,  the 
filtrate  neutralised  by  NH3,  and  evaporated,  when  the  narceine  crystallises, 
leaving  meconine  in  solution,  which  may  be  extracted  by  shaking  with  ether. 
Narceine  crystallises  from  water  in  prisms  with  3Aq  ;  it  is  soluble  in  alcohol, 
but  not  in  ether.  It  is  a  narcotic  poison.  Iodine  colours  its  solution  blue.  It  is 
also  formed  by  heating  narcotine  methoiodide  with  KOH  solution. 

Papaverine,  or  tetramethoxy~benzyluoqiiinoline,  (CH30)2C9H4N'CH2C6H3(OCH:3)o, 
is  contained,  in  small  proportion,  in  the  precipitate  produced  by  excess  of  KOH 
in  the  aqueous  solution  of  opium.  The  precipitate  is  dissolved  in  ether,  and 
shaken  with  dilute  acetic  acid  ;  the  lower  layer  then  contains  the  acetate  of 
narcotine,  thebaine,  and  papaverine  ;  these  are  again  precipitated  by  KOH  and 
treated  with  oxalic  acid,  which  leaves  the  acid  papaverine  oxalate  undissolved. 
Papaverine  is  sparingly  soluble  in  water,  but  dissolves  in  hot  alcohol  and  ether.  It 
gives  a  violet-blue  solution  with  strong  H2S04.  Its  poisonous  properties  appear  to 
be  feeble.  It  melts  at  148°  C. 

588.  Cinchona-alkaloids. — The  plants  of  the  natural  order  Cin- 
chonacece  are  remarkable  for  their  medicinal  properties.  Conspicuous 
among  them  are  cinchona,  which  furnishes  quinine  ;  the  coffee-tree,  which 
yields  caffeine  ;  and  the  ipecacuanha,  which  produces  emetine. 

Cinchona,  or  Peruvian  bark,  is  obtained  chiefly  from  the  districts 
around  the  Andes,  and  owes  its  valuable  febrifuge  qualities  to  the 
presence  of  certain  alkaloids,  of  which  the  most  important  are — 


Quinine     . 
Conquinine 


Cinchonine      .        .     C19H22N20 
Cinchonidine  .         ,     C1QHooN00 


Quinamine 

Of  these,  quinine  and  cinchonine  are  by  far  the  most  important.  The  different 
species  of  cinchona  yield  a  bark  containing  these  alkaloids  in  different  proportions. 
The  yellow  bark  yields  from  2  to  3  per  cent,  of  quinine,  and  only  0.2  or  0.3 
of  cinchonine  ;  the  red  bark,  about  2  per  cent,  of  quinine  and  i  per  cent,  of 
cinchonine  ;  and  the  pale  or  grey  bark  about  0.8  per  cent,  of  quinine  and  2  per 
cent,  of  cinchonine.  The  alkaloids  exist  in  combination  with  quinic  acid  and 
with  a  variety  of  tannin  known  as  quinotannic  acid. 

Quinine,  C,0H24N2O2,  is  prepared  by  boiling  the  bruised  bark  with 
diluted  hydrochloric  acid,  and  mixing  the  filtered  solution  with  lime 
diffused  through  water,  until  it  is  alkaline.  The  precipitate,  containing 
quinine,  cinchonine,  and  colouring-matter,  is  filtered  oft'  and  boiled 
with  alcohol,  which  dissolves  both  the  alkaloids,  leaving  the  excess  of 
lime  undissolved.  A  part  of  the  alcohol  is  then  recovered  by  distilla- 
tion, and  the  solution  neutralised  with  sulphuric  acid,  boiled  with 
animal  charcoal  till  decolorised,  and  filtered.  On  standing,  quinine 
sulphate  crystallises  out,  leaving  the  cinchonine  sulphate  in  solution. 
The  quinine  sulphate  is  dissolved  in  water,  and  decomposed  by 
ammonia,  which  precipitates  the  quinine. 

Quinine  crystallises  in  prisms  containing  3Aq,  which  dissolve  in  1900 
parts  of  cold  water  and  easily  in  alcohol,  ether,  and  chloroform  ;  when 
anhydrous  it  melts  at  117°  C.  Its  solutions  are  alkaline,  and  bitter. 
It  appears  to  be  a  tertiary  di-amine,  because,  when  heated  with  the 
iodides  of  alcohol  radicles,  it  yields  iodides  which  furnish  ammonium 
bases  when  decomposed  by  AgOH  ;  thus,  methyl  iodide  gives 
C20H24N202*CH3I,  which  yields  the  alkaline  hydroxide, 
C20H24N202-CH3-OH. 


CINCHOXINE.  7gj 

Quinine  is  characterised  by  exhibiting  a  beautiful  blue  fluorescence 
when  dissolved  m  dilute  sulphuric  acid,  and  by  producing  a  fine  green 
colour  when  its  dilute  acid  solutions  are  mixed  with  a  little  chlorine   or 
bromine-  or  euchlorine-water  (see  p.  779),  and  afterwards  with  ammonia 
The  green  colour  is  due  to  the  thalleiochin,  formed  by  the  reaction— 
CaoH^NaOa  +  NH3  +  04  =  C^H^O,. 

Quinine  is  a  di-acid  base,  but  it  sometimes  forms  salts  in  which  it  is  monacid  • 
P  w  vn  *Sni  hy^r?chlo^d«  5  C20H24N202.2HC1  is  converted  by  water  into 
C2oH,yX202.  HC1,  which  crystallises  in  needles  of  the  formula  2(C00HolN9(X,  HCH  lAa 

^i-mal  quinine  sulphate,  C2oH24N202.H2S04.7Aq,  is  soluble  "in  u  parts  of  cold 
water,  but  the  basic  sulphate,  (CaoHa4N9Oa)a.HaSO4.8Aq)  requires  780  parts  of  cold 
water  to  dissolve  it.  This  is  the  quinine  salt  generally  used  in  medicine  •  it  forms 
very  light  silky  needles,  which  dissolve  easily  in  dilute  sulphuric  acid,  forming 
the  acid  sulphate,  CaftH04NaO2.(HaSO^a.7Aq,  which  is  very  soluble. 

Quinine  is  very  slightly  soluble  in  potash,  and  sparingly  in  ammonia,  though  it 
is  more  soluble  in  NH3  than  is  any  other  cinchona  alkaloid.  If  normal  quinine 
sulphate  be  dissolved  in  strong  acetic  acid,  warmed,  and  an  alcoholic  solution  of 
iodine  added  gradually,  thin  rectangular  plates  are  deposited  on  cooling  having 
the  formula  (C20H24N202)4.(H2S04)3.(HI)2.l4.6H20.  These  crystals  (herapathite,  or 
artificial  tourmaline)  are  bronze  green  by  reflection,  but  transmit  light  of  a  pale 
olive  colour,  which  is  perfectly  polarised,  like  that  transmitted  by  tourmaline,  so 
that,  if  another  plate  be  laid  upon  the  first,  no  light  is  transmitted  when  their 
principal  axes  are  at  right  angles. 

Quinidine,  or  conquinine,  C^H^N^,  is  isoineric  with  quinine,  and  is  extracted 
from  a  brown  substance  called  quinoidine,  or  amorphous  quinine,  which  is  obtained 
from  the  mother-liquors  of  quinine  sulphate  and  is  sold  as  a  cheap  substitute  for 
quinine.  It  is  also  obtained  in  quantity  from  some  of  the  inferior  varieties  of 
cinchona,  such  as  Cinchona  cordifolia,  which  yields  the  Carthagena  bark.  Quin- 
idine  forms  larger  prismatic  crystals  than  quinine,  and  these  contain  only  2Aq. 
Its  salts  are  more  soluble  than  those  of  quinine,  and  they  are  strongly  dextro- 
rotatory for  polarised  light,  whilst  those  of  quinine  are  la?vo-rotatory. 

Quinicine,  also  isomeric  with  quinine,  is  formed  by  heating  quinine  or  quinidine 
with  dilute  sulphuric  acid  to  130°  C.  It  is  resinous,  but  its  salts  crystallise.  It:v 
solutions  are  feebly  dextro-rotatory. 

Cinchonine,  CjgHgoNgO,  remains  as  sulphate  in  the  mother-liquor  from  quinine 
sulphate  (r.s.),  and  may  be  precipitated  by  ammonia.  It  is  almost  insoluble  in 
water,  and  sparingly  soluble  in  alcohol.  Ether  scarcely  dissolves  it,  and  is  used 
to  distinguish  it  from  quinine.  It  crystallises  from  hot  alcohol  in  anhydrous 
prisms,  which  have  an  alkaline  reaction.  It  melts  at  225°  C.  and  sublimes  in 
hydrogen.  The  salts  of  cinchonine  are  more  soluble  than  those  of  quinine,  and 
give  a  much  more  voluminous  precipitate  with  ammonia,  which  is  insoluble  in 
a  large  excess,  and  is  not  cleared  up  by  shaking  with  ether,  as  in  the  case  of 
quinine. 

Cinchonine  sulphate,  (C19H22]Sr.20)2.H2S04.2Aq,  fuses  when  heated,  evolving  an 
aromatic  odour  and  becoming  red.  Solution  of  cinchonine  sulphate  is  less 
strongly  fluorescent  than  one  of  quinine  sulphate.  Cinchonine  also  differs  from 
quinine  in  yielding  solutions  which  are  strongly  dextro-rotatory. 

Cinchonidine  is  isomeric  with  cinchonine,  but  is  strongly  lasvo-rotatory. 

Cinchonicine,  another  isomeride,  resembles  quinicine  in  origin  and  properties. 

When  quinine,  cinchonine,  and  their  isomerides  are  fused  with  KOH,  they  yield 
the  quinoline  bases,  indicating  that  they  are  closely  connected  with  quinoline. 
The  tarry  odour  on  heating  cinchonine  is  probably  due  to  these.  Thus  both 
cinchonine  and  quinine  are  supposed  to  contain  the  quinoline  group,  the  former 
being  C9H6N-C10H15(OH)N,  and  the  latter  (CH30)C9H5N'C10H15(OH)N. 

Emetine,  C30H40N205,  is  a  little-known  base  extracted  from  the  root  of  Cephaelis 
ipecacuanha,  a  cinchonaceous  plant  much  used  in  medicine. 

589.  Strychnos- alkaloids. — Strychnine  and  brucine  are  obtained 
from  nux-vomica,  the  seeds  of  the  tropical  plant,  Strychnos  nux-vomica, 
from  false  anyostura  bark*  which  is  the  bark  of  the  same  tree,  and  from 

*  True  angostura  bark  is  obtained  from  Galipea  officinalis  and  G.  cusparia,  belonging  to. 
the  order  Rutaceae.  It  is  used  as  a  febrifuge. 


782  STRYCHNINE. 

Ignatia  amara,  or  St.  Ignatius'  bean.  Nux-vomica,  or  crow-Jig,  contains 
about  i  per  cent,  of  strychnine  and  i  per  cent,  of  brucine. 

Strychnine,  C21H22N20,,  is  extracted  from  the  crushed  seeds  of  nux- 
•vomica  by  boiling  them  with  very  dilute  HCL  The  solution  is  mixed 
-with  milk  of  lime,  and  the  precipitate  filtered  off  and  boiled  with  alcohol, 
which  dissolves  the  strychnine  and  brucine,  and  deposits  the  strychnine 
first  when  evaporated.  The  mother-liquor  is  neutralised  with  HN03, 
when  strychnine  nitrate  crystallises  out,  leaving  brucine  nitrate  in 
.solution.  Both  alkaloids  are  Isevo-rotatory. 

Strychnine  crystallises  in  rhombic  prisms,  soluble  in  7000  parts  of 
water,  and  melting  at  284°  C.  It  is  insoluble  in  ether  and  in  absolute 
alcohol,  but  dissolves  in  dilute  alcohol.  It  is  very  soluble  in  chloroform, 
which  is  the  best  agent  for  collecting  it  from  aqueous  solutions.  Its 
intensely  bitter  taste  is  very  remarkable,  and  may  be  imparted  to  one 
million  parts  of  water  (one  grain  in  fourteen  gallons).  Its  alcoholic 
solution  is  alkaline,  and  it  is  a  monacid  tertiary  base,  combining  with 
methyl  iodide  to  form  strychnine-methylium  iodide,  N2C21H2209.CH3I, 
which  yields  the  corresponding  hydroxide  base  when  decomposed  by 
AgOH.  But  this  ammonium  base  is  not  bitter,  nor  poisonous  unless 
injected  under  the  skin,  when  it  induces  paralysis.  Strychnine  is 
extremely  poisonous,  giving  rise  to  tetanic  convulsions.  Potash  pre- 
cipitates strychnine  from  its  solution  in  acids,  and  an  excess  does  not 
dissolve  it ;  the  precipitate  by  ammonia  dissolves  in  excess,  but  the 
strychnine  crystallises  out  after  a  time.  The  smallest  particle  of  strych- 
nine may  be  identified  by  dissolving  it  in  strong  sulphuric  acid  and 
adding  a  minute  fragment  of  potassium  bichromate,  which  produces  a 
fugitive  blue-violet  colour. 

When  strychnine  is  warmed  with  dilute  HN03,  it  gives  a  faint  pink  solution, 
which  becomes  scarlet  on  adding  a  particle  of  powdered  KC103  ;  NH3  changes  this 
to  brown,  and,  on  evaporating  to  dryness,  the  residue  is  green  and  dissolves  in 
water  to  a  green  solution,  changed  to  orange  by  KOH,  and  becoming  green  again 
with  HN03.  Euchlorine- water  (p.  779),  or  bromine-water,  added  to  a  solution  of 
strychnine  in  HC1,  gives,  on  boiling,  a  fine  red  colour,  bleached  by  excess,  and 
returning  when  boiled. 

One  of  the  N-atoms  in  strychnine  is  the  tertiary  ammonia  nitrogen  ;  the  other 

/CO  /COOH 

appears  to  be  in  the  form  of  a  lactam  group  (p.  674)  <  •      which  becomes  < 

^N  ^NH 

yielding  stry clinic  acid,  when  strychnine  is  heated  with  sodium  ethoxide.     When 

,N(CH3)I 
the  methylium  iodide  (see  above)  is  treated  with  AgOH,  the  grouping  ^_CO 

^NH 
K(CH)3 

becomes  ^-CO 
NH 

Brucine,  C23H26N204,  is  precipitated  by  KOH  from  the  solution  of  brucine 
nitrate  obtained  in  the  extraction  of  strychnine.  It  is  more  soluble  in  water  and 
alcohol  than  strychnine  is,  and  crystallises  in  prisms  with  4Aq,  melting  at  178°  C. 
when  anhydrous.  Like  strychnine,  it  is  nearly  insoluble  in  ether.  It  is  intensely 
bitter  and  strongly  basic.  HN03  dissolves  it  with  a  fine  red  colour,  which  becomes 
violet  on  adding  stannous  chloride.  Both  strychnine  and  brucine  yield  quinoline 
bases  when  distilled  with  KOH  ;  indicating  their  relationship  with  quinoline.  The 
proportion  of  methyl  alcohol  obtainable  from  brucine  by  distilling  it  with  Mn02 


VERATRINE.  783 

and  H2S04  shows  that  it  contains  2(OCH3)  ;  it  may,  therefore,  be  regarded  ai 
dimethoxy-strychnine. 

590.  Aconitine,  C33H43N012,  is  extracted  from  the  root  of  Aconltinn  nunellus  a 
plant  of  the  Ranunculaceous  or  Buttercup  order,  known  as  monk's  /umd.  1,1  HP  rocket 
-and  wolfs  bane.  The  root  has  often  been  scraped  and  eaten  by  mistake  for  //»/•«/•- 
radish  (Cochlearia  armoracia,  a  cruciferous  plant),  but  the  two  roots  are  reallv 
very  unlike,  and  the  scrapings  of  monk's  hood  become  pink  when  exposed  to  air 
while  those  of  horse-radish  remain  white.  To  extract  the  aconitine,  the  scrapings 
of  the  root  are  boiled  with  amyl  alcohol  ;  the  solution  is  shaken  with  dil.  H2SO  , 
which  extracts  the  aconitine,  and  the  aqueous  liquid  is  neutralised  with  Na^CO 
The  aconitine  thus  precipitated  is  crystallised  from  ether.  It  crystallises  from 
alcohol  in  anhydrous  plates  (rn.-p.  188°  C.),  and  forms  well-defined  salts.  Aconitine 
is  one  of  the  most  poisonous  alkaloids,  and,  as  yet,  no  trustworthy  chemical  test 
for  it  is  known,  so  that  the  toxicologist  is  obliged  to  place  a  little  of  the  suspected 
substance  on  the  tongue,  when  aconotine  produces  a  numbing,  tingling  feeling, 
lasting  for  some  time.  When  heated  with  potash,  aconitine  yields  potassium 
Tsenzoate  and  aconine,  C2gH41NOn.  The  preparations  sold  as  aconitine  are  often 
impure  bases  of  very  variable  quality. 

Pseudaconitine,  C36H49N012  +  H20,  is  a  poisonous  alkaloid  obtained  from  Aconltinn 
/erox,  an  Indian  plant  of  the  same  natural  order.  Heated  with  potash,  it  yields 
pseudaconine,  C^H^NOg,  and  the  potassium  salt  of  dimethyl  dihydroxybenzoic 
(or  dimethyl  protocatechuic)  acid. 

Veratrine,  C37H53NOn,  is  extracted  from  the  root  of  white  hellebore  (Veratrum. 
album*),  and  from  the  seeds  of  Veratrum  sabadilla,  plants  of  the  natural  order  Col- 
chicacefe.  The  alkaloid  is  present  in  very  minute  quantity.  It  is  extracted  by 
digesting  the  root  with  alcohol  containing  a  little  tartaric  acid,  evaporating  the 
alcohol  from  the  filtered  solution,  dissolving  the  residue  in  water,  liberating  the 
alkaloid  by  caustic  soda,  and  shaking  with  ether,  which  dissolves  it.  The  ethereal 
layer  leaves  the  alkaloid  when  evaporated.  Veratrine  is  characterised  by  its 
power  to  cause  violent  sneezing  when  a  particle  of  the  powder  is  drawn  into  the 
nose.  It  dissolves  in  HC1,  and  the  solution  becomes  red  when  gently  heated. 
Strong  H2S04  gives  a  yellow  solution  passing  into  carmine-red,  and  becoming 
purple  with  bromine-water.  Cevadine,  C32H49N09,  is  another  alkaloid  which 
causes  sneezing,  and  is  extracted  from  Cevadilla  seeds  (Veratrum  sabadl/la'). 
Veratralbine,  C^H^NOg  ;  jervine,  C26H37N03  ;  pseudojervine,  C^H^NC^  ;  and  rubi- 
j  err  hie,  C26H43N02,  are  also  extracted  from  the  Veratrums.  These  plants  are 
chiefly  used  for  poisoning  vermin. 

JBebeerine,  C]9H21N03,  is  extracted  from  the  bark  of  the  bibiru-tree,  a  tree  of  the 
Laurel  order,  which  grows  in  British  Guiana,  and  yields  the  green-heart  wood 
used  in  shipbuilding,  because  it  resists  the  attacks  of  marine  animals.  It 
is  amorphous,  insoluble  in  water,  but  soluble  in  alcohol.  The  sulphate, 


MeKitpermwm  fenestratuni),  both  belonging  to  the  Menispermacea?.  Berberine 
crystallises  in  yellow  needles  with  5^Aq,  and  forms  yellow  salts.  It  is  soluble  in 
water. 

591.  Hydrastin,  C21H21]Sr06,  (m.-p.  132°  C.)  is  an  alkaloid  of  constitution  similar 
to  that  of  narcotine  also  obtained  from  barberry. 

Physostigmine,  or  eserine,  C15H21N3p2,  is  obtained  from  the  Calabar  bean,  the  seed 
of  a  Papilionaceous  plant.  It  is  sparingly  soluble  in  water,  but  dissolves  in  alcohol, 
is  strongly  alkaline,  and  very  poisonous.  It  has  the  property  of  contracting  the 
pupil  of  the  eye. 

Colchici-ne,  C^H^NOg,  occurs  in  meadow  saffron,  Colchicum  autumnale  (belonging 
to  the  same  order  as  the  Veratrums)  ;  much  used  as  a  remedy  in  gout.  It  is  a 
very  feeble  base,  soluble  in  water  and  alcohol,  and  does  not  crystallise. 

Cytisine,  CnHi4N20,  is  the  poisonous  alkaloid  contained  in  the  seeds  of  Gytimi 
laburnum,  a  Papilionaceous  plant. 

Chelidonine,  C^H^NOg,  has  been  extracted  from  celandine  (Chehdonnnn,  M^M), 
a  plant  of  the  Poppy  order. 

Delphinine,  CooH,5N06,  is  the  poisonous  alkaloid  contained  in  larkspur  or  staves- 
acre  (Delphinium  staphisagria),  the  seeds  of  which  are  used  for  destroying  vermin 
(aconite  belongs  to  the  same  order). 

Pilocarpine,  CUH16N202,  is  extracted  from  the  leaves  of  Pilocarpms  pennatijolnt*. 


784  MELTING-POINTS. 

a  plant  of  the  Eue  order.     The  base  itself  is  not  crystalline,  but  the  hydrochloride 
and  nitrate  are  crystalline  salts,  which  are  used  in  medicine. 

Jaborandine,  C10H12N203,  is  another  alkaloid  obtained  from  the  same  source. 

PHYSICAL  PROPERTIES  OF  ORGANIC  COMPOUNDS. 

592.  In  investigating  the  chemical  structure  of  the  molecules  of 
organic  bodies,  much  assistance  is  derived  from  the  observation  of  their 
physical  properties,  among  which  the  following  are  the  most  im- 
portant : — 

(1)  The  fusing -point  of  a  solid,  the  boiling-poinfoi  a  liquid,  and  the 
specific  gravity  of  a  vapour. 

(2)  The  specific  volume  of  a  liquid,  obtained  by  dividing  its  molecular 
weight  by  its  specific  gravity  (calculated  for  the  temperature  at  which 
the  liquid  boils). 

(3)  The  optical  properties  of  a  liquid,  or  of  a  solid  body  in  solution  ; 
especially  the  action  on  polarised  light,  the  refractive  power,  the  absorp- 
tion spectrum,  and  the  magnetic  rotatory  power  deduced  from  its  action 
on  a  ray  of  polarised  light  when  under  the  influence  of  magnetism. 

593.  Fusing-points  of  organic  compounds. — In  order  that  a  solid  may  fuse, 
it  must  first  attain  to  a  degree  of  temperature  called  the  fitting-point  of  the  solid, 
and  must  then  have  a  certain  amount  of  motion  imparted  to  its  molecules  by  the 
transformation  (into  motion)  of  an  amount  of  heat  which  is  termed  latent  heat  or 
heat  of  fusion.  This  motion  enables  the  molecules  to  circulate  more  or  less  freely 
among  themselves,  and  to  extend  themselves  in  a  horizontal  plane. 

The  fusing-point,  as  indicated  by  the  thermometer,  therefore,  is  the  temperature 
at  which  the  molecules  become  capable  of  converting  the  heat  subsequently 
acquired  into  the  motion  proper  to  the  liquid  condition.  This  temperature  will 
depend  upon  the  constitution  of  the  molecules,  which  regulates  their  relation  to 
adjacent  molecules. 

If  the  cohesion  which  limits  the  motion  of  molecules  in  a  solid  mass  be  similar 
in  character  to  the  gravitation  which  limits  the  motion  of  masses  of  matter,  it 
will  be  greater  among  those  molecules  which  have  the  larger  mass,  that  is,  the 
highest  molecular  weight,  and  these  should  have  the  highest  fusing-points,  since 
a  larger  amount  of  progressive  motion  (or  temperature)  must  be  imparted  to  them 
to  render  them  capable  of  acquiring  the  freedom  of  motion  proper  to  the  liquid 
condition.  But  it  is  by  no  means  true  that  the  fusing-point  is  always  higher 
when  the  molecular  weight  is  greater  ;  for  palmitin,  with  a  molecular  weight  of 
806,  fuses  at  63°  C.,  while  urea,  with  a  molecular  weight  of  60,  fuses  at  130°  C. 
It  may  be  stated,  however,  that  in  the  case  of  homologous  series,  the  fusing- 
point  generally  rises  as  the  molecular  weight  increases  ;  thus  the  paraffin  and  olefine 
hydrocarbons  are  liquids  until  they  contain  sixteen  atoms  of  carbon.  The  sub- 
stitution of  HO  for  H  tends  to  raise  the  fusing-point,  so  that  the  paraffin  alcohols 
containing  more  than  seven  carbon-atoms  are  solids,  and  this  is  also  the  case  with 
the  aldehydes. 

In  the  case  of  the  metameric  paraffin  derivatives  the  fusing-point  is  generally 
higher  in  those  compounds  which  contain  most  carbon  in  the  form  of  CH3  ;  thus, 
pseudo-valeric  or  tertiary  valeric  acid,  C(CH3)3-C02H,  fuses  at  about  35°  C.,  while 
normal  valeric  acid,  CH3[CH2]3'C02H,  fuses  at  -59°  C.  Again,  tertiary  butyl- 
alcohol,  C(CH3)3-OH,  fuses  at  25°  C.  ;  and  normal  butyl-alcohol,  CH3[CH2]3'OH,  is 
liquid  even  below  o°  C. 

In  the  benzene-hydrocarbons,  the  substitution  of  CH3  for  H  raises  the  fusing- 
point  ;  thus,  toluene,  C6H5'CH3,  and  xylene,  C6H4(CH3)2,  are  liquids  ;  but  durene, 
C6H2(CH3)4,  fuses  at  80°  C.  In  these  also,  when  they  have  the  same  molecular 
weight,  the  fusing-point  rises  with  the  number  of  methyl  groups  directly  united 
to  carbon  ;  for  example,  amyl-toluene,  C^HyfCKy^CHg,  is  liquid,  while  hexamethyl- 
benzene,  C6(CH3)6,  is  solid,  fusing  at  164°  C.  Even  in  compounds  which  are 
strictly  isomeric,  the  position  of  the  component  radicles  will  affect  the  fusing- 
point,  the  para-compound  having  generally  the  highest  fusing-point  ;  thus,  ortho- 
xylene  and  meta-xylene  are  liquids,  but  pa'ra-xylene  is  a  solid  fusing  at  15°  C. 


BOILING-POINTS.  785 

594.  Boiling-points  of  organic  compounds.— The  boiling-point  of  a  liquid  U 
that  temperature  at  which  its  molecules  are  capable  of  converting  heat  into  motion 
sufficient  to  enable  them  to  overcome  entirely  the  attraction  holding  them  to  each 
other,  and  to  extend  themselves  in  all  directions  through  space.  Under  ordinary 
conditions,  their  extension  is  impeded  by  the  pressure  of  the  atmosphere  upon 
the  surface  of  the  liquid,  so  that,  for  experimental  work,  the  boiling-point  is  that 
temperature  at  which  the  molecules  are  capable  of  acquiring  sufficient  motion  to 
overcome  a  pressure  of  760  millimetres  of  mercury  (at  o°  C.).  Since  the  boiling- 
point  refers  to  a  certain  standard  of  external  work,  it  exhibits  a  more  definite 
relation  to  the  constitution  of  the  molecules  than  is  the  case  with  the  fusing-point. 
In  homologous  series,  the  boiling-point  increases  with  the  molecular  weight,  but 
the  increase  due  to  each  addition  of  CH2  varies  in  different  series.  It  is  most 
uniform  in  the  normal  primary  alcohols  of  the  paraffin  series  (p.  565),  where  each 
addition  of  CH2  increases  the  boiling-point,  on  the  average,  by  19.5°  C.  In  the 
series  of  aldehydes  derived  from  these  alcohols  (p.  583),  the  increase  in  boiling- 
point  is  also  fairly  regular,  but  it  averages  26.2°  for  each  addition  of  CH2.  In  the  - 
corresponding  acids,  the  increase  is  much  less  uniform,  but  the  average  increase 
is  about  19°.  In  the  single  ketones  (p.  624),  the  mean  increase  in  boiling-point  for 
each  CH2  added  is  20.5°.  In  the  simple  ethers,  the  increase  is  26°. 

In  the  homologous  series  of  hydrocarbons,  the  increase  in  boiling-point  for  each 
addition  of  CH2  is  irregular,  but  generally  diminishes  as  the  number  of  carbon- 
atoms  increases.  Those  hydrocarbons  of  the  paraffin  and  olefine  series  which  contain 
the  same  number  of  carbon-atoms  exhibit  a  similarity  in  their  boiling-points  : — 

Paraffins     C5H12  37°       C6H14  69°       C7H16  98°       C8H18  125°       C16HW  288° 
Olefines        C5H10  35°       C6H12  69°       C7H14  99°      C8H16  123°      CwHa  275° 

The  isologous  hydrocarbons  of  the  acetylene  series  have  higher  boiling-pointy 
and  those  of  the  benzenes  are  higher  still — 

Acetylenes   C5H8  45°      C6H10  80°      C7H12  106°      C8HU  133°      C10H18  165° 
Benzenes  ...  C6H6  8o'i°   C7H8  111°      C8H10  142°      C10H14  196° 

The  substitution  of  HO  for  H  in  the  conversion  of  the  paraffin  hydrocarbons  into 
alcohols  increases  the  boiling-point  greatly,  but  in  a  ratio  which  decreases  in  nearly 
the  same  proportion  in  which  the  molecular  weight  of  the  alcohol  increases — 

Hydrocarbons        C5H12      37°      C6H14      69°      C7H16      98°      C8H18      125° 
Alcohols    .        .    C5H12Oi37°     C6H140  157°     C7H160 170°     C8H180    191° 

A  similar  increase  in  boiling-point  is  produced  by  the  substitution  of  HO  for  H 
in  the  conversion  of  an  aldehyde  into  an  acid — 

Aldehydes      C2H40      20.8°      C3H60      48°      C4H80      74°      C5H100     103° 
Adds         .    C2H402  118-3°      C3H602 140.7°    C4H802  162°      C5H1002   186° 

Metameric  bodies  which  belong  to  the  same  class  often  have  nearly  the  same 
boiling-points— e.g.,  propione,  C2H5-CO'C2H5  101°  ;  methyl-propyl  ketone, 
CH3-CO-C3H7  102°. 

But  this  is  not  the  case  when  they  belong  to  different  classes— e.g.,  methyl-ethyl 
ketone,  CH3-CO'C2H5  81°  ;  methyl-allyl  ether,  CH3-0-C3H5  46°. 

The  ethereal  salts  have  lower  boiling-points  than  the  acids  which  are  metameric 
with  them— e.g.,  methyl  formate,  CH3'CH02  36° ;  acetic  acid,  H-C2H302  118  . 

In  the  isomeric  hydrocarbons,  the  normal  compound  has  the  highest  boiln 
point,  which  falls  as  the  number  of  methyl  groups  increases  ;  thus,  normal  butane, 
H3C[CH.2]2CH3,  is  liquefied  at  i°  C.,  while  iso-butane,  H3C'CH(CH3)-CH3,  remain 

^Th" boiling-point  is  lowered,  in  these  isomeric  hydrocarbons,  by  the  substitution 
of  ethyl  and  methyl  for  hydrogen,  and  is  lowest  in  those  compounds  in  which 
carbon  is  united  to  the  compound  radicles  only.     The  same  tendency  is  observe 
in  the  isomeric  olefines  ;  thus  amylene,  H3C[CH2]2CH  :  CH*  boils  at  73  ,  and  wo- 
amylene,  (H3C)2C  :  CH(CH3)  at  35°. 

The  normal  primary  alcohols  have  the  highest  boiling-points,  then  come  the 
iso-alcohols,  while  the  secondary  and  tertiary  alcohols  have  the  lowest  boiling- 
points.  The  same  may  be  said  of  the  aldehydes  and  acids. 

When  any  other  element  or  group  is  substituted  for  hydrogen  in  an  orgams 
compound,  the  boiling-point  is  raised,  and  if  more  than  one  atom  of  hydrogen  be 
displaced,  the  boiling-point,  in  the  isomerides  thus  produced  will 


786  SPECIFIC   VOLUMES. 

be  higher  where  the  substituting  radicles  are  at  the  greatest  distance  from 
•each  other.  Thus,  ethylidene  dichloride,  H3C'CHC12,  boils  at  58°  ;  whilst  ethene 
dichloride,  C1H2C>CH.,C1,  does  not  boil  till  85°.  Again,  dibromo propane, 
H3C'CBr2-CH3.  boils  ftt  114°;  propene  dibromide,  H3C'CHBrCH2Br,  at  142°  ;  and 
trimethene  dibromide,  BrH2C'CH2'CH2Br,  at  above  160°.  Ortho-cresol, 
€6H4CH3-OH  (i  :  2),  boils  at  190°  ;  meta-cresol  (i  :  3)  at  195°  ;  and  para- 
•cresol  (1:4)  at  198°.  Ortho-chloraniline,  C6H4C1'NH2  (i  :  2),  boils  at  207°  ; 
meta-chloraniline  (1:3)  at  230°;  and  para-chloraniline  (i  14)  at  231°.  Diamido- 
toluene,  C6H3(CH3)(NH2)2  (i  :  2 :  3),  boils  at  270°  ;  and  (i  :  2  :  4)  at  280°.  Further 
investigation  of  the  boiling-points  of  isomerides  is  necessary  fully  to  establish  this 
law. 

595.  Specific  volumes  of  organic  liquids. — It  has  been  seen  that  the 
specific  volumes  of  the  vapours  of  organic  compounds,  obtained  by  dividing  the 
molecular  weight  by  the  vapour-density,  are  in  all  cases  alike  ;  but  this  is  not  the 
case  with  the  specific  volumes  of  liquids,  which  depend  upon  the  attraction  exerted 
between  their  molecules,  which  must  of  course  vary  with  the  nature  of  the  mole- 
cules themselves.  Since,  at  their  respective  boiling-points,  all  liquids  are  in  a 
similar  condition  in  regard  to  the  further  effect  of  heat  upon  them,  it  might  be 
expected  that  their  molecular  weights,  divided  by  their  specific  gravities  (at  the 
boiling-point),  would  yield  quotients  bearing  some  definite  relation  to  each  other, 
since  these  quotients  represent  the  molecular  volumes  of  the  compounds  in  the 
liquid  state  (at  the  boiling-point)  ;  that  is,  the  relative  (or  specific)  volumes, 
within  which  the  motions  of  each  molecule  are  restricted,  or  the  space  in  which 
each  molecule  keeps  free  from  other  molecules. 

The  molecular  volume  of  water,  calculated  in  this  way,  is  18*8  ;  that  of  methyl 
alcohol  is  42.  Then  CH40  -  H.20  =  CH2  ;  and  42  -  18.8  =  23.2,  which  is  the  increase 
in  molecular  volume,  due  to  the  addition  of  CH2  to  H20.  The  molecular  volume 
of  ethyl-alcohol  is  62.5,  or  higher  than  that  of  methyl -alcohol  by  20.5,  which 
represents  the  increase  due  to  CH2.  The  molecular  volume  of  acetic  acid  is  64, 
and  that  of  formic  acid  42,  giving  22  as  the  increase  due  to  CH2.  The  mean 
of  the  three  values  is  21.9,  and  this  is  almost  exactly  the  difference  in  the  molecular 
volumes  calculated  for  the  homologous  acids,  from  formic  to  valeric. 

At  one  time  it  was  stated  with  confidence  that  the  molecular  volume  depends  on 
the  number  and  nature  of  the  atoms  contained  in  the  molecule  rather  than 
on  their  grouping  ;  thus,  ethyl  acetate,  CH3*COOC2H5,  has  the  same  molecular 
volume  as  its  metameride,  butyric  acid,  C3H7'COOH.  Recently,  much  doubt  has 
been  cast  on  this  statement ;  and  it  has  been  asserted  that,  instead  of  the  molecular v 
volume  being  the  sum  of  the  atomic  volumes,  it  depends  on  the  manner  in  which 
the  atoms  are  united.  The  following  is  the  evidence  in  favour  of  the  older  view. 

Octane,  C8H18,  has  a  molecular  volume=i87,  and  if  we  deduct  from  this 
(CH2)8=i76,  the  difference,  u,  represents  the  molecular  volume  of  H2,  giving  5.5 
for  the  atomic  volume  of  hydrogen.  Cymene,  C10H14,  has  the  molecular  volume  187, 
which  differs  from  (CH2)7,  or  22  x  7,  by  33,  which  represents  the  increase  in 
molecular  volume  due  to  C3,  and  gives  1 1  for  the  atomic  volume  of  carbon. 

By  deducting  the  volume  of  H2  (n)  from  that  of  H20  (18.8),  7.8  is  obtained  for 
the  atomic  volume  of  oxygen. 

From  these  values  the  specific  volumes  of  many  molecules  may  be  calculated 
and  are  found  to  agree  very  nearly  ;  with  those  obtained  by  dividing  the  molecular 
weight  by  the  specific  gravity  of  the  liquid  at  its  boiling-point ;  for  example — 
Methyl  alcohol,  CH40,  gives         1 1  +  (5.5  x  4)  +7.8=  40.8  instead  of  42 
Ethyl         „         C2H60    „     (n  x  2) +  (5. 5x6) +7.8=  62.8         „  62.5 

Ether         „         C4H100  „  (11  x  4) +  (5.5.  x  10)4-7.8=106.8,  which  is  correct. 
Phenol       „         C6H60    „      (11  x  6)  + (5.5  x  6)4-7.8=  106.8      „  „ 

But  formic  acid,  CH202,  the  specific  volume  of  which  is  41.5,  gives  only  37.6  as 
the  sum  of  n  +  (5.5  x  2)  +  (7.8  x  2). 

Again,  acetone,  C3H60,  with  a  specific  volume  =  77.6,  gives  only  73.8  (which 
agrees  with  that  found  for  allyl-alcohoi,  also  C3H60)  by  the  addition  of 
(11x3)  +  (5.5x6)  +  7.8 

The  structural  formula  of  acetone  is  (CH3)2'C:  0,  the  oxygen  being  doubly 
linked  to  a  carbon  atom,  whilst  in  the  alcohols,  ethers,  and  phenols  it  is  only 
singly  linked  to  a  carbon  atom. 

Deducting  from  the  specific  volume  of  acetone  (77.6)  that  of  C3H6  (66),  there  re- 
mains 1 1. 6  as  the  atomic  volume  of  oxygen,  when  doubly  linked  to  a  carbon  atom. 


OPTICAL  PROPERTIES   OF  ORGANIC   COMPOUNDS.  787 

Formic  acid  contains  a  singly  linked  and  a  doubly  linked  oxygen  atom  •  her 
its  molecular  volume  should  be  the  sum  of  u  +(5.5  x  2)  +  7.8+  1^6  =  4 4 which  is 
very  nearly  correct. 
ofAcetic  acid,   H3C(C:  0)OH,    gives   (5.5  x4)  +  (n  x  2)  +  7.8+ 11.6  =  63.4,  instead 

The  specific  volume  of  an  atom  of  nitrogen  singly  linked 'to  carbon,  as  in  methyl- 
amme,  H.C-NH,   1B  23;  but  when  trebly  linked  to  carbon,  as  in  methyl  cyanide, 


r*        '       ,       Wen   rey     ne    to  carbon'  as  ^  methyl  cyanide, 
— C=N,  its  specific  volume  is  17. 

Sulphur,  singly  linked  to  carbon,  has  the  specific  volume  23  ;  but  when  doubly 
linked,  it  is  28.6.  The  specific  volume  of  chlorine  is  22.8,  of  bromine  27  8  and  of 
iodine  37.5 

rn.There^r?  man?1  ex.cfPtions  to  the  simple  laws  of  specific  volume  here  set  forth. 
Thus,  ethylene  chloride,  C1H2C.CH2C1,  and  ethylidene  chloride,  H3OCHC1-  which 
have  the  calculated  specific  volume  89.5,  give,  by  experiment,  respectively  8^4 
and  88.96,  a  difference  too  great  to  be  ascribed  to  experimental  errors.  Benzene  and 
some  other  members  of  the  aromatic  group,  also  exhibit  considerable  deviation 
the  observed  specific  volumes  being  lower  than  those  calculated. 

596.  Optical  properties  of  organic  compounds.— Since  the  phenomena  of 
light  depend  upon  the  waves  excited  in  the  asther  which  fills  the  spaces  between 
the  molecules  of  matter,  the  motions  of  these  molecules  must  exert  an  influence 
upon  the  optical  properties  of  the  substances  which  they  compose. 

The  molecular  conditions  which  regulate  the  colour  of  compounds,  by  enabling 
them  to  absorb  certain  of  the  waves  composing  white  light,  and  to  reflect  or  trans- 
mit others,  are  not  as  yet  understood,  but  colour  is  most  commonly  associated 
with  high  molecular  weight.  (See  also  Qu'monoid  structure,  p.  721.) 

Much  attention  has  been  devoted  to  the  comparison  of  the  refractive  powers  of 
liquid  organic  compounds,  that  is,  to  the  amount  of  deviation  from  its  original 
path  which  a  wave  of  light  suffers  in  passing  through  the  liquid  in  any  direction 
except  that  perpendicular  to  the  surface.  The  full  discussion  of  this  subject 
requires  the  study  of  optics,  but  it  may  be  stated  that  from  the  amount  of  devia- 
tion is  calculated  the  specific  refractive  power  of  the  liquid,  which  is  closely  con- 
nected with  the  nature  of  its  molecules.  The  molecular  refractive  energy,  or 
refraction-equivalent,  is  found  by  multiplying  the  molecular  weight  by  the  specific 
refractive  power.  Compounds  which  have  the  same  molecular  weight  and  belong 
to  the  same  or  to  nearly  related  classes  of  organic  compounds,  generally  have 
nearly  the  same  refraction-equivalent ;  thus,  the  number  for  methyl  acetate, 
CH3-C2H302,  is  28.78  and  that  for  ethyl  formate,  C2H5'CH02,  is  28.61.  Butyl- 
alcohol,  C4H9'OH,  gives  36.11,  and  ether,  C2H5'0-C2H5,  36.26.  Polymeric  bodies 
have  refraction-equivalents  nearly  proportionate  to  their  molecular  weights  ;  thus, 
aldehyde,  C2H40,  has  the  refraction-equivalent  18.5,  butyric  acid,  C4H802,  36.6, 
.and  paraldehyde,  C6H1203,  52.5.  In  the  homologous  alcohols  and  acids  derived 
from  the  paraffin  hydrocarbons,  the  refraction-equivalent  increases  by  about  7.6 
for  each  addition  of  CH2  ;  thus,  acetic  acid,  C.2H402,  having  the  refraction-equiva- 
lent 21. i,  oananthic  acid  should  give  21.11  +  (7.6  x  5)  =  59-i,  which  nearly  agrees 
-with  that  observed,  59.4. 

By  a  method  similar  to  that  explained  in  the  case  of  specific  volumes,  the 
refraction-equivalents  to  the  elements  may  be  calculated,  and  they  are  found  to  be, 
for  the  wave-length  corresponding  with  the  yellow  sodium  line,  for  carbon  4-71?  f°r 
hydrogen  1.47,  for  oxygen  singly  linked  to  carbon,  2.65,  and  for  oxygen  doubly 
linked,  3.33.  From  these  numbers  the  refraction-equivalent  of  a  liquid  may  be 
calculated  from  its  formula,  as  in  the  case  of  its  specific  volume,  and  the  result 
agrees  very  nearly,  in  a  great  many  cases,  with  that  obtained  by  experiment.  But 
there  is  sufficient  deviation  to  indicate  that  the  grouping  of  the  atoms,  as  well  as 
their  nature  and  number,  influences  the  refraction-equivalent.  Thus,  in  the 
terpenes,  the  observed  equivalent  exceeds  that  calculated  by  the  constant  number  3, 
while  in  the  benzenes  the  excess  amounts  to  6.  It  would  appear  that  when  a 
carbon  atom  is  doubly  linked  to  another  carbon  atom,  its  refraction-equivalent 
is  5.71  instead  of  4.71,  so  that  the  six  doubly-linked  carbon  atoms  in  the  benzene 
ring  would  explain  the  excess  in  the  refraction-equivalent. 

When  liquids  having  different  refraction-equivalents  are  mixed,  the  refraction- 
equivalent  of  the  mixture  is  the  sum  of  those  of  its  constituents,  so  that  the 
proportions  in  which  these  are  present  may  be  calculated. 


788 


ABSORPTION   SPECTRA. 


The  rotation  of  the  plane  of  polarised  light  (p.  542)  affords  another  optical 
method  of  investigating  the  constitution  of  organic  substances. 

The  angle  of  rotation,  in  the  case  of  any  given  substance,  varies  directly  as  the 
strength  of  the  solution,  its  specific  gravity,  and  the  length  of  the  column  of  liquid 
through  which  the  light  passes.  For  different  substances,  the  angle  of  rotation  also 
varies  with  the  specific  rotatory  power,  which  is  found  by  dividing  the  angle 
of  rotation  by  the  product  obtained  by  multiplying  together  the  weight  of 
the  substance  in  one  gramme  of  the  liquid,  the  specific  gravity  of  the  liquid,  and  the 
length  of  the  column  in  decimetres.  For  example,  a  beam  of  polarised  light 
was  passed  through  a  tube  with  glass  ends,  0.50  decimetre  long,  filled  with 
turpentine,  of  specific  gravity  (at  the  temperature  of  the  experiment)  0.8712,  and  it 
was  requisite  to  turn  the  analyser  16°  in  the  opposite  direction  to  the  hand  of 
a  watch  in  order  to  prevent  light  from  reaching  the  eye  of  the  observer.  This 

would  give  for  the   specific   (laevo)  rotatory  power,  =  36.7.      It   is 

i  x  0.8712x0.5 

evident  that  if  the  specific  rotatory  power  of  a  substance  be  known,  a  calculation 
like  this  would  give  the  weight  contained  in  each  gramme  of  the  solution,  and  this 
is  turned  to  account  in  the  saccharimeter  for  determining  the  proportion  of  sugar 
in  a  solution. 

This  rotatory  power  is  found  most  commonly  in  vegetable  and  animal  products 
and  their  immediate  derivatives,  as  will  have  been  seen  in  the  description  of 
such  bodies,  and  it  has  been  pointed  out  that  it  depends  upon  some  peculiarity 
in  the  structure  of  the  molecule.  Recent  observations  render  it  probable  that 
much  information  will  be  derived  from  the  study  of  circular  polarisation  with 
respect  to  the  true  configuration  of  molecules,  as  has  been  indicated  at  p.  605. 

All  liquids  exhibit  some  rotatory  power  for  polarised  light  when  they  are  under 
the  influence  of  a  powerful  (electro)  magnet,  and  the  amount  of  the  rotation,, 
compared  with  that  produced  by  water  under  the  same  conditions,  is  called  the 
magnetic  rotatory  power.  The  molecular  magnetic  rotation  obtained  by  multiplying 
the  rotatory  power  by  the  molecular  weight,  and  dividing  by  the  specific  gravity  of 
the  liquid,  exhibits  a  definite  relation  to  the  composition  of  the  molecule,  and 
increases  by  1.023  f°r  each  addition  of  CH2  in  homologous  series.  Proceeding  on 
the  same  principle  as  in  the  case  of  specific  volumes  (p.  786),  the  atomic  mag- 
netic rotatory  power  of  carbon  is  found  to  be  0.515,  that  of  hydrogen,  0.254,  of 
singly  linked  oxygen,  0.194,  and  of  doubly  linked  oxygen,  0.263,  and  from  these, 
in  many  cases,  the  molecular  magnetic  rotatory  power  of  compounds  may  be 
calculated,  or  conversely,  a  knowledge  of  the  rotatory  power  may  be  applied  to 
determine  a  molecular  formula. 

597.  Absorption  spectra  of  organic  compounds  for  chemical  rays. — The  light 
emanating  from  the  sun  and  from  the  electric  spark  is  accompanied  by  many 
other  waves  whose  period  of  vibration  is  so  short  that  they  produce  no  impression 
upon  the  eye,  or  upon  the  thermometer,  and  are  only  detected  by  their  power  of 
chemically  decomposing  the  salts  of  silver  and  other  photographic  materials.  The 
shortness  of  these  waves  causes  them  to  suffer  a  greater  amount  of  deviation 
or  refraction  than  the  luminous  waves  when  the  light  is  passed  through  a  prism,, 
so  that  their  effects  are  chiefly  perceived  in  that  part  of  the  spectrum  which  lies 
beyond  the  violet  light,  and  is  usually  termed  the  ultra-violet.  Many  substances 
which  are  perfectly  transparent  are  able  to  intercept  a  large  proportion  of  these 
actinic  waves,  as  they  are  termed,  and  are  said  to  be  adiactinic,  whilst  those  which 
transmit  them  freely  are  diactinic. 

Rock  crystal,  or  quartz,  is  much  more  diactinic  than  glass,  and  lenses  and 
prisms  of  this  material  are  used  in  experiments  upon  this  subject,  the  light  of  a 
stream  of  electric  sparks  being  allowed  to  pass  through  the  slit  of  a  spectroscope 
(p.  328),  through  a  cell  with  quartz  sides  containing  the  liquid  under  examina- 
tion, then  through  a  quartz  lens  and  prisms  and  afterwards  received  upon  a  sensi- 
tive photographic  plate  upon  which  that  portion  of  the  ultra-violet  waves  which 
has  passed  through  leaves  its  impression. 

It  has  been  shown,  by  such  experiments,  that  the  normal  alcohols  derived  from 
the  paraffins  are  highly  diactinic,  and  that  the  corresponding  acids  are  somewhat 
less  so,  absorbing  more  of  the  highly  refrangible  waves  remote  from  the  violet 
end  of  the  spectrum  ;  the  diactinic  character  decreasing,  in  both  acids  and  alcohols, 
as  the  molecular  weight  increases.  Benzene  and  its  derivatives  are  highly  adiactinic,. 


ABSORPTION  SPECTRA.  789 

and,  when  employed  in  strong  solutions,  are  often  capable  of  absorbing  all  the 
ultra-violet  waves  ;  but  when  diluted  to  a  certain  extent  with  water  or  alcohol, 
they  allow  some  of  the  waves  to  pass,  and  produce  photographs  of  spectra  exhibiting 
absorption-bands  due  to  this  selective  absorption.  Since  isomeric  benzene  derivatives 
exhibit  very  different  absorption-bands,  the  selective  absorption  must  be  due  to 
vibrations  within  the  molecules,  while  the  general  absorption,  which  varies  with 
the  molecular  weight,  is  caused  by  the  vibration  of  the  molecules  themselves. 
There  is  very  strong  evidence  that  the  absorption-bands  in  the  ultra-violet  spectrum 
are  exhibited  only  by  those  compounds  in  which  the  carbon  atoms  form  closed 
chains,  as  in  benzene  (p.  542),  and  naphthalene  (p.  552),  in  which  there  are  three 
pairs  of  doubly  linked  carbon  atoms. 

Starch,  glucose,  saccharose,  diastase,  and  gelatine  are  highly  diactinic,  and  show 
no  absorption-bands,  while  albumin,  casein,  and  serin  exhibit  absorption-bands  in 
dilute  solution. 

The  photographic  absorption-spectra  afford  a  most  accurate  method  of  identi- 
fying organic  substances,  and  a  most  delicate  test  of  their  purity,  since  the 
absorption-bands  are  visible  in  solutions  of  extreme  dilution. 


ON  SOME  OF  THE 

USEFUL  APPLICATIONS  OF  THE  PRINCIPLES  OF 
ORGANIC  CHEMISTRY. 

DESTRUCTIVE   DISTILLATION   OF   COAL. 

598.  An  extraordinary  progress  has  been  made  by  chemistry  since  the  intro- 
duction of  the  manufacture  of  coal-gas.  No  other  branch  of  manufacture  has 
brought  into  notice  so  many  compounds  not  previously  obtained  from  any  other 
source,  and  above  all,  offering,  at  first  sight,  so  very  little  promise  of  utility,  as 
to  press  urgently  upon  the  chemist  the  necessity  for  submitting  them  to  investi- 
gation. 

Although  many  important  additions  to  chemical  knowledge  have  resulted  from 
the  labours  of  those  who  have  engaged  in  devising  f,he  best  methods  of  obtaining 
the  coal-gas  itself  in  the  state  best  fitted  for  consumption,  far  more  benefit  has 
accrued  to  the  science  from  investigations  into  the  nature  of  the  secondary  pro- 
ducts of  the  manufacture,  the  removal  of  which  was  the  object  to  be  attained  in 
the  purification  of  the  gas. 

Of  the  compounds  of  carbon  and  hydrogen,  very  little  was  known  previously  to 
the  introduction  of  coal-gas  ;  and  although  the  liquid  hydrocarbons  composing 
coal-naphtha  were  originally  obtained  from  other  sources,  the  investigation  of 
their  chemical  properties  has  been  greatly  promoted  by  the  facility  with  which 
they  may  be  obtained  in  large  quantities  from  that  liquid.  The  most  important 
of  these  hydrocarbons,  benzole  or  benzene,  was  originally  procured  from  benzoic 
acid  ;  but  it  would  have  been  impossible  for  it  to  have  fulfilled  its  present  useful 
purposes  unless  it  had  been  obtained  in  abundance  as  a  secondary  product  in  the 
manufacture  of  coal-gas  ;  for,  leaving  out  of  consideration  the  various  uses  to 
which  benzene  itself  is  devoted,  it  yields  the  nitrobenzene  so  much  used  in  per- 
fumery, and  from  this  we  obtain  aniline,  from  which  many  of  the  most  beautiful 
dyes  have  been  prepared. 

The  naphthalene  found  so  abundantly  in  coal-tar  possesses  a  peculiar  interest,  as 
having  formed  the  subject  of  the  classical  researches  by  which  Laurent  was  led  to 
propose  the  doctrine  of  substitution,  which  has  since  thrown  so  much  light  upon 
the  constitution  of  organic  substances. 

We  are  also  especially  indebted  to  coal-tar  for  our  acquaintance  with  the  very 
interesting  and  rapidly  extending  class  of  volatile  alkalies,  of  which  the  above- 
mentioned  aniline  is  the  chief  representative,  and  for  phenic  or  carbolic  acid, 
from  which  are  derived  the  large  number  of  substances  composing  the  phenyl 
series. 

The  retorts  in  which  the  distillation  of  coal  is  effected  are  made  of  fire-clay, 
generally  having  the  form  of  a  flattened  cylinder,  and  arranged  in  sets  of  three  or 
five,  heated  by  the  same  coal-fire  or  gas  furnace  (Fig.  284).  The  coal  is  thrown  on 
to  the  red-hot  floor  of  the  retort,  as  soon  as  the  coke  from  the  previous  distillation 
has  been  raked  out ;  the  mouth  of  the  retort  is  then  closed  with  an  iron  plate 
luted  with  clay.  An  iron  pipe  rises  from  the  upper  side  of  the  front  of  the  retort 
projecting  from  the  furnace,  and  is  curved  round  at  the  upper  extremity,  which 
passes  into  the  side  of  a  much  wider  tube,  b,  called  the  hydraulic  main,  running 
above  the  furnaces,  at  right  angles  to  the  retorts,  and  receiving  the  tubes  from  all 
of  them.  This  tube  is  always  kept  half  full  of  the  tar  and  water  condensed  from 


GAS  MANUFACTURE. 


791 


the  gas,  and  below  the  surface  of  this  liquid  the  delivery  tubes  from  the  retorts 
are  allowed  to  dip,  so  that,  although  the  gas  can  bubble  freely  through  the  liquid, 
as  it  issues  from  the  retort,  none  can  return  through  the  tube  whilst  the  retort  is 
open  for  the  introduction  of  a  fresh  charge. 

Exhausters  are  used  in  most  gas-works,  to  prevent  the  pressure  in  the  retort 
from  exceeding  that  of  the  atmosphere,  thus  diminishing  loss  by  leakage,  and 
quickly  removing  the  gas  from  the  injurious  effect  of  the  hot  retort. 

The  aqueous  portion  of  the  liquid  deposited  in  the  hydraulic  main  is  known  as 
the  ammoniacal  liquor,  from  its  consisting  chiefly  of  a  solution  of  various  salts 
of  ammonium,  the  chief  of  which  is  the  carbonate ;  sulphide,  cyanide  and  sulpho- 
cyanide  of  ammonium  are  also  found  in  it. 

*  From  the  hydraulic  main  the  gas  passes  into  the  condenser,  e,  which  is  composed 
of  a  series  of  bent  iron  tubes  kept  cool  either  by  the  large  surface  which  they 
expose  to  the  air.  or  sometimes  by  a  stream  of  cold  water.  In  these  are  deposited, 
in  addition  to  water,  any  of  the  volatile  hydrocarbons  and  ammonium  salts  whioh 
may  have  escaped  condensation  in  the  hydraulic  main.  Even  in  the  condenser 
the  removal  of  the  ammoniacal  salts  is  not  complete,  so  that  it  is  usually  necessary 
to  pass  the  gas  through  a  scrubber  or  case  containing  fragments  of  coke,  over 
which  a  stream  of  water  is  allowed  to  trickle,  in  order  to  absorb  the  remaining 
ammoniacal  vapours. 


Fig.  284.— Manufacture  of  coal-gas. 

The  tar  which  condenses  in  the  hydraulic  main  is  a  very  complex  mixture,  of 
which  the  following  are  some  of  the  leading  components  :— 


NEUTRAL  HYDROCARBONS. 

Liquid. 
Benzene 
Toluene. 
Xylene. 
Isocumene. 

Solid. 

Naphthalene. 
Anthracene. 
Chrysene. 
Pyrene. 


ALKALINE  PRODUCTS. 

Ammonia. 

Aniline. 

Picolire. 

Quinoline. 

Pyridine. 

ACID  PRODUCTS. 
Carbolic  acid. 
Kresylic. 
Rosolic. 
Acetic. 


792 


PURIFICATION  OF  COAL-GAS. 


The  gas  is  now  passed  through  the  lime-purifier,  /,  which  is  an  iron  bex  with 
shelves  on  which  dry  slaked  lime  is  placed  in  order  to  absorb  the  carbonic  acid 
gas,  sulphuretted  hydrogen,  and  carbon  bisulphide. 

A  great  many  other  methods  have  been  devised  for  the  purification  of  the  gas 
from  sulphuretted  hydrogen,  but  none  appears  to  be  so  efficacious  and  economical 
as  that  which  consists  in  passing  the  gas  over  hjdrated  iron  oxide*  mixed  with 
sawdust  (which  is  employed  to  prevent  the  material  from  caking). 

The  action  oil  the  sulphuretted  hydrogen  on  the  ferric  oxide  is  represented  by 
two  equations  (i)  Fe2O3  +  H2S  =  2FeO  +  H20  +  S;  (2)Fe203  +  3H2S  =  2FeS  +  3H20  +  S; 
and  the  circumstance  which  especially  conduces  to  the  economy  of  the  process 
is  the  facility  with  which  the  ferrous  sulphide  and  oxide  may  be  reconverted  into 
the  ferric  oxide  by  mere  exposure  to  the  action  of  atmospheric  oxygen  ;  for 
2FeS  +  O3  =  Fe203  +  S2,  thus  reviving  the  power  of  the  mixture  to  absorb  sul- 
phuretted hydrogen.  Accordingly,  the  material  is  periodically  exposed  to  the 
action  of  air  ;  or,  as  is  sometimes  practised,  a  small  quantity  of  air  is  admitted 
into  the  purifier  together  with  the  gas  ;  this  reconverts  the  ferrous  sulphide  and 
oxide  into  ferric  oxide,  and  the  oxidation  is  attended  with  enough  heat  to  convert 
into  vapour  any  benzene  which  may  have  condensed  in  the  purifying  mixture,  and 
of  which  the  illuminating  value  would  otherwise  be  lost.  The  same  purifying 
mixture  may  thus  be  employed  to  purify  a  very  large  quantity  of  gas,  until  the 
separated  sulphur  (55  per  cent.)  has  increased  its  bulk  to  an  inconvenient  extent, 
when  the  spent  oxide  is  burnt  for  making  vitriol  (p.  225).  The  process  for 
removing  the  carbon  bisulphide  vapour  is  mentioned  at  p.  241. 

The  purified  gas  is  passed  into  the  gasometers,  g,  from  which  it  is  supplied  for 
consumption. 

In  the  manufacture  of  coal-gas,  attention  is  requisite  to  the  temperature  (1800° 
to  2000°  F.),  at  which  the  distillation  is  effected,  for,  if  it  be  too  low,  the  solid  and 
liquid  hydrocarbons  will  be  formed  in  too  great  abundance,  not  only  diminishing 
the  volume  of  the  gas,  but  causing  much  inconvenience  by  obstructing  the  pipes. 
On  the  other  hand,  if  the  retort  be  too  strongly  heated,  the  vapours  of  volatile 
hydrocarbons,  as  well  as  the  olefiant  gas  and  marsh  gas,  may  undergo  decompo- 
sition, depositing  their  carbon  upon  the  sides  of  the  retort,  in  the  form  of  gas- 
carbon,  and  leaving  their  hydrogen  to  increase  the  volume  and  dilute  the  illu- 
minating power  of  the  gas. 

These  effects  are  well  exemplified  in  the  following  table,  which  contains 
analyses  of  the  gas  collected  at  different  periods  of  the  distillation  : — 


In  100  volumes. 

After  10  mins. 

After  i^  hours. 

After  3^  hours. 

After  5^  hours. 

Sulphuretted  hydro- 

gen 

1.30 

1.42 

0.49 

0.  II 

Carbon  dioxide 

2.21 

2.09 

1.49 

1.50 

Hydrogen 

20.10 

38.33 

52.68 

67.12 

Carbon  monoxide     . 

6.19 

5.68 

6.21 

6.12 

Marsh  gas 

57.38 

44-03 

33-54 

22.58 

Illuminants    (see    p. 

161)       . 

10.62 

5.98 

3-04 

1.79 

Nitrogen  . 

2.  2O 

2.47 

2-55 

0.78 

Much  advantage  is  said  to  be  gained  by  mixing  the  coal  with  a  certain  propor- 
tion of  lime,  which  diminishes  the  sulphur  in  the  gas  and  increases  the  yield  of 
ammonia. 

One  of  the  most  useful  of  the  secondary  products  of  the  coal-gas  manufacture 
is  the  ammonia,  and  this  process  has  been  already  noticed  as  a  principal  source 
of  the  ammoniacal  salts  found  in  commerce. 

Next  in  the  order  of  usefulness  stands  the  coal-tar,  which  deserves  attentive 
consideration,  not  only  on  that  account,  but  because  the  extraction  of  the  various 
useful  substances  from  this  complex  mixture  affords  an  excellent  example  of 


*  Browii  haematite  (bog-  ore)  is  frequently  employed. 


COAL-TAR  DYES. 


793 


proximate  organic  analysis,  that  is,  of  the  separation  of  an  organic  mixture  into 
its  immediate  components. 

For  the  separation  of  the  numerous  volatile  substances  contained  in  coal-tar 
advantage  is  taken  of  the  difference  in  their  boiling-points. 

A  large  quantity  of  the  tar  is  distilled  in  an  iron  retort,  when  water  passes  over, 
holding  salts  of  ammonia  in  solution,  and  accompanied  by  a  brown  oily  offensive 
liquid  which  collects  upon  the  surface  of  the  water.  This  is  a  mixture  of  the 
hydrocarbons,  which  are  lighter  than  water,  viz.,  benzene,  toluene,  xylene,  and 
isocumene,  all  having  a  specific  gravity  of  about  0.85.  100  parts  of  the  tar  yield, 
at  most,  10  parts  of  this  light  oil. 

As  the  distillation  proceeds  and  the  temperature  rises,  a  yellow  oil  distils  over, 
which  is  heavier  than  water,  and  sinks  in  the  receiver.  This  oil,  commonly  called 
dead  oil,  is  much  more  abundant  than  the  light  oil,  amounting  to  one-fourth 
of  the  weight  of  the  tar,  and  contains  those  constituents  of  the  tar  which  have  a 
high  specific  gravity  and  boiling-point,  particularly  naphthalene,  aniline,  quino- 
line,  and  carbolic  acid.  The  proportion  of  naphthalene  in  this  oil  increases  with 
the  progress  of  the  distillation,  as  would  be  expected  from  its  high  boiling-point, 
so  that  the  last  portions  of  the  oil  which  distil  over  become  nearly  solid  on  cool- 
ing. When  this  is  the  case,  the  distillation  is  generally  stopped,  and  a  black 
viscous  residue  is  found  in  the  retort,  which  constitutes  pitch,  and  is  employed 
for  the  preparation  of  Brunswick  black  and  of  asphalt  for  paving. 

The  light  oil  which  first  passed  over  is  rectified  by  a  second  distillation,  and  is 
then  sent  into  commerce  under  the  name  of  coal-naphtha,  a  quantity  of  the  heavy 
oil  being  left  in  the  retort,  the  lighter  oils  having  lower  boiling-points. 

This  coal-naphtha  may  be  further  purified  by  shaking  it  with  sulphuric  acid, 
which  removes  several  of  the  impurities,  whilst  the  pure  naphtha  collects  on  the 
surface  when  the  mixture  is  allowed  to  stand.  When  this  is  again  distilled  it 
yields  the  rectified  coal-naphtha. 

The  distillation  of  cannel  coal,  and  of  various  minerals  nearly  allied  to  coal,  at 
low  temperatures,  is  now  extensively  carried  on  for  the  manufacture  of  paraffin 
and  paraffin  oil  (see  Paraffin). 

Coal-tar  dyes. — The  first  dye  ever  manufactured  from  aniline  on  a  large  scale 
was  that  known  as  mauve,*  or  aniline  purple,  which  is  obtained  by  dissolving  ani- 
line in  diluted  sulphuric  acid,  and  adding  solution  of  bichromate  of  potash,  when 
the  liquid  gradually  becomes  dark-coloured,  and  deposits  a  black  precipitate  which 
is  filtered  off,  washed,  boiled  with  coal-naphtha  to  extract  a  brown  substance,  and 
afterwards  treated  with  hot  alcohol,  which  dissolves  the  mauve.  The  chemical 
change  by  which  the  aniline  has  been  converted  into  this  colouring-matter  cannot 
at  present  be  clearly  traced,  but  the  basis  of  the  colour  has  been  found  to  be  a 
substance  which  has  the  composition  C^H^^  and  has  been  termed  mauvdine.  It 
forms  black  shining  crystals,  resembling  specular  iron  ore,  which  dissolve  in 
alcohol,  forming  a  violet  solution,  and  in  acids,  with  production  of  the  purple 
colour.  Mauveine  combines  with  the  acids  to  form  salts  ;  its  alcoholic  solution 
even  absorbs  carbonic  acid  gas.  The  hydrochloride  of  mauveine,  C^R^N^Hd, 
forms  prismatic  needles  with  a  green  metallic  lustre. 

Very  brilliant  red  dyes  are  obtained  from  commercial  aniline  by  the  action  of 
carbon  tetrachloride,  stannic  chloride,  ferric  chloride,  cupric  chloride,  mercuric 
nitrate,  corrosive  sublimate,  and  arsenic  acid.  It  will  be  noticed  that  all  these 
agents  are  capable  of  undergoing  reduction  to  a  lower  state  of  oxidation  or  chlori- 
nation,  indicating  that  the  chemical  change  concerned  in  the  transformation  of 
aniline  into  aniline-red  is  one  in  which  the  aniline  is  acted  on  by  oxygen  or 
chlorine.  The  easiest  method  of  illustrating  the  production  of  aniline  red  on  the 
small  scale  consists  in  heating  a  few  drops  of  aniline  in  a  test-tube  with  a  frag- 
ment of  corrosive  sublimate  (mercuric  chloride),  which  soon  fuses  and  acts  upon 
the  aniline  to  form  an  intensely  red  mass  composed  of  aniline  red,  calomel,  and 
various  secondary  products.  By  heating  this  mixture  with  alcohol,  the  red  dye  is 
dissolved,  and  a  skein  of  silk  or  wool  dipped  into  the  liquid  becomes  dyed  of  a 
fine  red,  which  is  not  removed  by  washing. 

On  the  large  scale,  magenta  (as  aniline  red  is  commonly  termed)  is  gene 
prepared  by  heating  aniline  to  about  320°   F.  (160°  C.)  with  arsenic  acid    when  a 
dark  semi-solid  mass  is  obtained,  which  becomes  hard  and  brittle  on  cooling,  and 
exhibits  a  green  metallic  reflection.     This  mass  contains,  in  addit 

*  French  for  marshmallow,  iii  allusion  to  the  colour  of  the  flower. 


794  ANILINE   DYES. 

red,  several  secondary  products  of  the  action,  and  arsenious  acid.  On  boiling  it 
with  water,  a  splendid  red  solution  is  obtained,  and  a  dark  resinous  or  pitchy 
mass  is  left.  If  common  salt  be  added  to  the  red  solution  as  long  as  it  is  dis- 
solved, the  bulk  of  the  colouring-matter  is  precipitated  as  a  resinous  mass,  which 
may  be  purified  from  certain  adnering  matters  by  drying  and  boiling  with  coal- 
naphtha.  The  red  colouring-matter  is  the  arsenate  of  a  colourless  organic  base, 
which  has  been  called  rosaniline  (p.  722).  If  the  red  solution  of  arsenate  of 
rosaniline  be  decomposed  with  calcium  hydroxide  suspended  in  water,  a  pinkish 
precipitate  is  obtained,  which  consists  of  rosaniline  mixed  with  calcium  arsenate, 
and  the  solution  entirely  loses  its  red  colour  (cf,  p.  722). 

By  treating  the  precipitate  with  a  small  quantity  of  acetic  acid,  the  rosaniline 
is  converted  into  rosaniline  acetate  (C20H19N3.C2H4O2),  forming  a  red  solution,  which 
may  be  filtered  off  from  the  undissoived  calcium  arsenate.  On  evaporating  the 
solution  to  a  small  bulk,  and  allowing  it  to  stand,  the  acetate  is  obtained  in 
crystals  which  exhibit  the  peculiar  green  metallic  lustre  of  the  wing  of  the  rose- 
beetle,  characteristic  of  the  salts  of  rosaniline.  This  salt  is  the  commonest  com- 
mercial form  of  magenta  ;  its  colouring  power  is  extraordinary,  a  very  minute 
particle  imparting  a  red  tint  to  a  large  volume  of  water.  Silk  and  wool  easily 
extract  the  whole  of  the  colouring-matter  from  the  aqueous  solution,  becoming 
dyed  a  fast  and  brilliant  crimson  ;  cotton  and  linen,  however,  have  not  so  strong 
an  attraction  for  it,  so  that  if  a  pattern  be  worked  in  silk  upon  a  piece  of  cambric, 
which  is  then  immersed  in  a  solution  of  magenta  and  afterwards  washed  in  hot 
water,  the  colour  will  be  washed  out  of  the  cambric  ;  but  the  red  silk  pattern  will 
be  left. 

Water  dissolves  but  little  rosaniline  ;  alcohol  dissolves  it  abundantly,  forming  a 
deep  red  solution.  Kosaniline  forms  two  classes  of  salts  with  acids,  those  with 
i  molecule  of  acid  (monacid  salts)  being  crimson,  and  those  with  three  molecules 
(triacid  salts)  having  a  brown  colour.  Thus,  if  colourless  rosaniline  be  dissolved 
in  a.little  dilute  hydrochloric  acid,  a  red  solution  is  obtained,  which  contains  the 
monacid  rosaniline  hydrochloride,  C20H19N3.HC1  ;  but  if  an  excess  of  hydrochloric 
acid  be  added,  the  red  colour  disappears,  and  a  brown  solution  is  obtained,  from 
which  the  triacid  hydrochloride.  C20H19N3.3HC1,  may  be  crystallised  in  brown  red 
needles. 

For  experimental  illustration  of  the  properties  of  rosaniline,  the  liquid  obtained 
by  boiling  a  solution  of  the  acetate  with  a  slight  excess  of  lime  diffused  in  water, 
and  filtering  while  hot,  is  very  well  adapted.  The  solution  has  a  yellow  colour, 
and  may  be  preserved  in  a  stoppered  bottle  without  alteration.  If  air  be  breathed 
into  it  through  a  tube,  the  liquid  becomes  red  from  production  of  rosaniline  car- 
bonate. Characters  painted  on  paper  with  a  brush  dipped  in  the  solution  are 
iavisible  at  first,  but  gradually  acquire  a  beautiful  rose  colour. 

The  other  properties  of  rosaniline  will  be  found  described  at  p.  722. 

Aniline-yelloiv,  or  cJirysanilinc  (from  %pi)creos,  golden),  is  found  among  the  secondary 
products  obtained  in  the  preparation  of  aniline  red.  It  forms  a  bright  yellow 
powder,  resembling  chrome-yellow,  and  having  the  composition  C^H-^Ng.  It 
is  nearly  insoluble  in  water,  but  dissolves  in  alcohol.  Chrysaniline  has  basic 
properties,  and  dissolves  in  acids,  forming  salts.  On  dissolving  it  in  diluted 
hydrochloric  acid,  and  mixing  the  solution  with  the  concentrated  acid,  a  scarlet 
crystalline  precipitate  of  chrysaniline  hydrochloride  (C20H17N3.2HC1)  is  obtained, 
which  is  insoluble  in  strong  hydrochloric  acid,  but  very  soluble  in  water.  A 
characteristic  feature  of  chrys-aniline  is  the  sparing  solubility  of  its  nitrate. 
Even  from  a  dilute  solution  of  the  hydrochloride,  nitric  acid  precipitates  chrys- 
aniline nitrate  (C2oHl7N3.HN03)  in  ruby -red  needles. 

Aniline-blue  is  produced  as  described  on  p.  723. 

The  hydrochloride  is  an  ordinary  commercial  form  of  aniline-blue  ;  it  has  a 
brown  colour,  refuses  to  dissolve  in  water,  but  yields  a  fine  blue  solution  in 
alcohol. 

DYEING   AND   CALICO-FEINTING. 

599.  The  object  of  the  dyer  being  to  fix  certain  colouring-matters  permanently 
in  the  fabric,  his  processes  would  be  expected  to  vary  with  the  nature  of  the  latter 
and  of  the  colour  to  be  applied  to  it.  In  order  that  uniformity  of  colour  and  its 
perfect  penetration  into  the  fibre  may  be  obtained,  it  is  evident  that  the  colouring- 
matter  must  always  be  employed  in  a  state  of  solution  ;  and  it  must  be  rendered 


DYEING. 

fast,  or  not  removable  by  washing,  by  assuming  an  insoluble  condition  in  the 
fibre. 

The  simplest  form  of  dyeing  is  that  in  which  the  fibre  itself  forms  an  insoluble 
compound  with  the  colouring-matter.  Thus,  if  a  skein  of  silk  be  immersed  in  a 
solution  of  indigo  in  sulphuric  acid,  it  removes  the  whole  of  the  colouring-matter 
from  the  liquid,  and  may  then  be  washed  with  water  without  losing  colour  •  but 
if  the  same  experiment  be  tried  with  cotton,  the  indigo  will  not  be  withdrawn 
from  the  solution,  and  when  the  cotton  has  been  well  squeezed  and  rinsed  with 
water,  it  will  become  white  again.  It  may  be  stated  generally,  that  the  animal 
fabrics  (silk  and  wool)  will  absorb  and  retain  colouring-matters  with  much 
greater  facility  than  vegetable  fabrics  (cotton  and  linen).  In  the  absence  of  so 
powerful  an  attraction  between  the  fibre  and  the  colouring-matter,  it  is  usual  to 
impregnate  the  fabric  with  a  mordant  or  substance  having  an  attraction  for  the 
colour,  and  capable  of  forming  an  insoluble  combination  with  it,  so  as  to  retain  it 
permanently  attached  to  the  fabric.  Thus,  if  a  piece  of  cotton  be  boiled  in  a 
solution  of  acetate  of  alumina,  the  alumina  will  be  precipitated  in  the  fibre  ;  and 
if  the  cotton  be  then  soaked  in  solution  of  cochineal  or  of  logwood,  the  red 
colouring-matter  will  form  an  insoluble  compound  (or  lake)  with  the  alumina,  and 
the  cotton  will  be  dyed  of  a  fast  red  colour. 

Another  method  of  fixing  the  colour  in  the  fabric  consists  in  impregnating 
the  latter  with  two  or  more  liquids  in  succession,  by  the  admixture  of  which 
the  colour  may  be  produced  in  an  insoluble  state.  If  a  piece  of  any  stuff  be 
soaked  in  solution  of  ferric  chloride,  and  afterwards  in  potassium  terro- 
cyanide,  the  Prussian  blue  which  is  precipitated  in  the  fibre  will  impart  a  fast 
blue  tint. 

An  indispensable  preliminary  step  to  the  dyeing  of  any  fabric  is  the  removal  of 
all  natural  grease  or  colouring-matter,  which  is  effected  by  processes  varying  with 
the  nature  of  the  fibre,  and  is  preceded,  in  the  cases  of  cotton  and  woollen 
materials  which  are  to  receive  a  pattern,  by  certain  operations  of  shaving  and 
singeing  for  removing  the  short  hairs  from  the  surface. 

From  linen  and  cotton,  the  extraneous  matters  (such  as  grease  and  resin)  are 
generally  removed  by  weak  solutions  of  carbonate  of  potassium  or  of  sodium, 
and  the  fabrics  are  afterwards  bleached  by  treatment  with  chloride  of  lime 
(p.  183). 

But  since  the  fibres  of  silk  and  wool  are  much  more  easily  injured  by  alkalies  and 
by  chlorine,  greater  care  is  requisite  in  cleansing  them.  Silk  is  boiled  with  a 
solution  of  white  soap  to  remove  the  gum,  as  it  is  technically  termed  ;  but  the 
natural  grease,  suint  or  yolk,  is  extracted  from  wool  by  soaking  at  a  moderate  tem- 
perature in  a  weak  bath  either  of  soap  or  of  ammoniacal  (putrefied)  urine.  Both 
silk  and  wool  are  bleached  by  sulphurous  acid  (p.  220). 

Among  the  red  dyes  the  most  important  are  madder,  alizarine,  Brazil  wood, 
cochineal,  lac,  and  the  aniline  reds. 

In  dyeing  red  with  madder  or  Brazil  wood,  the  linen,  cotton,  or  wool  is  first 
mordanted  by  boiling  in  a  solution  containing  alum  and  bitartrate  of  potash, 
when  it  combines  with  a  part  of  the  alumina,  and  on  plunging  the  stuff  into  a  hot 
infusion  of  madder,  the  colouring-matter  forms  an  insoluble  combination  with 
that  earth. 

To  dye  Turkey-red,  the  stuff  is  also  mordanted  with  alum,  but  has  previously 
to  undergo  several  processes  of  treatment  with  oil  and  with  galls,  the  necessity  p 
which  is  satisfactorily  established  in  practice,  though  it  is  not  easy  to  explain 
their  action.     The  colour  is  finally  brightened  by  boiling  the  stuff  with  chloi 
of  tin. 

Woollen  cloth  is  dyed  scarlet  with  lac  or  cochineal,  having  been  fin-t  mordant* 
by  boiling  in  a  mixture  of  perchloride  of  tin  and  bitartrate  of  potash. 

The  aniline  colours  (see  p.  794)  are  employed  for  dyeing  silk  and  wool,  ei 
without  any  mordant  or  with  the  help  of  albumin. 

Slues  are  generally    dyed  with  indigo  (p.  761),  or  with  Prussian  blue ;  m  tl 
latter  case  the  stuff  is  steeped  successively  in  solutions  of  a  salt  of  peroxide  01 
iron  and  of  potassium  ferrocyanide.     Aniline  blue  is  also  much  employed 
and  woollen  fabrics.  ...  •, 

The  principal  yellow  dyes  are  weld,  quercitron,  fustic,  annatto,  chrysamline,  ai 
lead   chromate.     For    the   first   four   colouring-matters   aluminous  mordants  are 
generally  applied.     Lead  chromate  is  produced  in  the  fibre  of  the  stuff,  which 11 
soaked  for  that  purpose,  first  in  a  solution  of  acetate  or  nitrate  of  lead,  and  1 


796  CALICO-FEINTING. 

in  potassium   chromate.     Carbazotic   or  picric  acid   (p.  711)   is  also  sometimes 
employed  as  a  yellow  dye. 

In  dyeing  blacks  and  broivns,  the  stuffs  are  steeped  first  in  a  bath  containing 
some  form  of  tannin  (p.  610),  such  as  infusion  of  galls,  sumach,  or  catechu,  and 
afterwards  in  a  solution  of  salt  of  iron,  different  shades  being  produced  by  the 
addition  of  indigo,  of  copper  sulphate,  &c. 

The  art  of  calico  printing  differs  from  that  of  dyeing  in  that  the  colour  is  re- 
quired to  be  applied  only  to  certain  parts  of  the  fabric  so  as  to  produce  a  pattern 
or  design  either  of  one  or  of  several  colours. 

A  common  method  of  printing  a  coloured  pattern  on  a  white  ground  consists  in 
impressing  the  pattern  by  passing  the  stuff  under  a  roller,  to  which  an  appropriate 
mordant  thickened  with  British  gum  (p.  736)  is  applied.  The  stuff  is  then 
dunged — i.e.,  drawn  through  a  mixture  of  cow-dung  and  water,  which  appears  to 
act  by  removing  the  excess  of  the  mordant,  and  afterwards  immersed  in  the  hot 
dye-bath,  when  the  colour  becomes  permanently  fixed  to  the  mordanted  device, 
but  may  be  removed  from  the  rest  of  the  stuff  by  washing. 

If  the  pattern  be  printed  with  a  solution  of  acetate  of  iron,  and  the  stuff  im- 
mersed in  a  madder-bath,  a  lilac  or  black  pattern  will  be  obtained  according  to 
the  strength  of  the  mordant  employed.  By  using  acetate  of  alumina  as  a  mordant, 
the  madder-bath  would  give  a  red  pattern. 

A  process  which  is  the  reverse  of  this  is  sometimes  employed,  the  pattern  being 
impressed  with  a  resist,  that  is,  a  substance  which  will  prevent  the  stuff  from 
taking  the  colour  in  those  parts  which  have  been  impregnated  with  it.  For 
example,  if  a  pattern  be  printed  with  thickened  tartaric  or  citric  acid,  and  the 
stuff  be  then  passed  through  an  aluminous  mordant,  the  pattern  will  refuse  to 
take  up  the  alumina,  and  subsequently  the  colour  from  the  dye-bath.  Or  a 
pattern  may  be  printed  with  nitrate  of  copper,  and  the  stuff  passed  through 
a  bath  of  reduced  indigo  (p.  762),  when  the  nitrate  of  copper  will  oxidise  the 
indigo,  and,  by  converting  it  into  the  blue  insoluble  form,  will  prevent  it  from 
sinking  into  the  fibre  of  those  parts  to  which  the  nitrate  has  been  applied,  whilst 
elsewhere  the  fibre,  having  become  impregnated  with  the  white  indigo,  acquires  a 
fast  blue  tint  when  exposed  to  the  air. 

Sometimes  the  stuff  is  uniformly  dyed,  and  the  colour  discharged  in  order 
to  form  the  pattern.  A  white  pattern  is  produced  upon  a  red  (madder)  or  blue 
(indigo)  ground  by  printing  with  a  thickened  acid  discharge,  and  passing  the  stuff 
through  a  weak  bath  of  chloride  of  lime,  which  removes  the  colour  from  those 
parts  only  which  were  impregnated  with  the-  acid  (p.  183).  By  adding  lead 
nitrate  to  the  acid  discharge,  and  finally  passing  the  stuff  through  a  solution  of 
potassium  chromate,  a  yellow  pattern  (lead  chromate)  may  be  obtained  upon  the 
madder-red  ground.  By  applying  nitric  acid  as  a  discharge,  a  yellow  pattern  may 
be  obtained  upon  an  indigo  ground  (p.  91). 

Very  brilliant  designs  are  produced  by  mordanting  the  stuff  in  a  solution  of 
stannate  of  potassium  or  sodium  (p.  453),  and  immersing  it  in  dilute  sulphuric 
acid,  which  precipitates  the  stannic  acid  in  the  fibre. 

When  the  thickened  colouring-matters  are  printed  on  in  patterns  and  steamed 
an  insoluble  compound  is  formed  between  the  colour  and  the  stannic  acid. 

It  is  evident  that,  by  combining  the  principles  of  which  an  outline  has  just  been 
given,  the  most  varied  parti-coloured  patterns  may  be  printed. 

TANNING. 

600.  When  infusion  of  nut-galls  is  added  to  a  solution  of  gelatine,  the  latter 
combines  with  the  tannic  acid,  and  a  bulky  precipitate  is  obtained.  If  a  piece  of 
skin,  which  has  approximately  the  same  ultimate  composition  as  gelatine,  be 
placed  in  the  infusion  of  nut-galls,  it  will  absorb  the  whole  of  the  tannic  acid 
and  become  converted  into  leather,  which  is  much  tougher  than  the  raw  skin, 
less  permeable  by  water,  and  not  liable  to  putrefaction. 

The  first  operation  in  the  conversion  of  hides  into  leather,  after  they  have  been 
cleansed,  consists  in  soaking  them  for  three  or  four  weeks  in  pits  containing  lime 
and  water,  which  saponifies  the  fat  and  loosens  the  hair.  The  same  object  is 
sometimes  attained  by  allowing  the  hides  to  enter  into  putrefaction,  when  the 
ammonia  produced  has  the  same  effect  as  the  lime.  The  loosened  hair  is  then 
scraped  off,  and  the  hides  are  soaked  in  water,  which  removes  adhering  lirne.  A 
further  effect  of  the  lime  is  to  open  the  pores  of  the  skin,  so  as  to  fit  it  to  receive 


TANNING. 

the  tanning  liquid ;  if  lime  have  not  been  used,  a  dilute  acid  should  be  employed 
to  effect  the  same  purpose. 

The  tanning  material  generally  employed  for  hides  is  the  infusion  of  oak  bark 
which  contains  querci-tannic  acid,  very  similar  in  properties  to  tannic  acid  The 
hides  are  soaked  in  an  infusion  of  oak  bark  for  about  six  weeks  being  passed  in 
succession  through  several  pits,  in  which  the  strength  of  the  infusion  is  gradually 
increased.  They  are  then  packed  in  another  pit  with  alternate  layers  of  coarsely 
ground  oak  bark  ;  the  pit  is  filled  with  water  and  left  at  rest  for  three  months 
when  the  hides  are  transferred  to  another  pit  and  treated  in  the  same  way  •  but 
of  course,  the  position  of  the  hides  will  now  be  reversed— that  which  was  upper- 
most, and  in  contact  with  the  weakest  part  of  the  tanning  liquor,  will  now  be  at 
the  bottom.  After  the  lapse  of  another  three  months  the  hide  is  generally  found 
to  be  tanned  throughout,  a  section  appearing  of  a  uniform  brown  colour.  It  has 
now  increased  in  weight  from  30  to  40  percent.  The  chemical  part  of  the  process 
being  thus  completed,  the  leather  is  subjected  to  certain  mechanical  operations 
to  give  it  the  desired  texture.  For  tanning  the  thinner  kinds  of  leather,  such  as 
morocco,  a  substance  called  sumach  is  used,  which  consists  of  the  ground  shoots 
of  the  Rhus  coriaria,  and  contains  a  large  proportion  of  tannic  acid. 

Morocco  leather  is  made  from  goat  and  sheep  skins,  which  are  denuded  of  hair 
by  liming  in  the  usual  way,  but  the  adhering  lime  is  afterwards  removed  by 
means  of  a  bath  of  sour  bran  or  flour.  In  order  to  tan  the  skin  so  prepared,  it  is 
sewn  up  in  the  form  of  a  bag,  which  is  filled  with  infusion  of  sumach,  and  allowed 
to  soak  in  a  vat  of  the  infusion  for  some  hours.  A  repetition  of  the  process,  with 
a  stronger  infusion,  is  necessary  ;  but  the  whole  operation  is  completed  in  twenty- 
four  hours.  The  skins  are  now  washed  and  dyed,  except  in  the  case  of  red 
morocco,  which  is  dyed  before  tanning,  by  steeping  it  first  in  alum  or  chloride  of 
tin,  as  a  mordant,  and  afterwards  in  infusion  of  cochineal.  Black  morocco  is 
dyed  with  acetate  of  iron,  which  acts  upon  the  tannic  acid.  The  aniline  dyes  are 
now  much  employed  for  dyeing  morocco. 

The  kid  of  which  gloves  are  made  is  not  actually  tanned,  but  submitted  to  an 
elaborate  operation  called  taiving,  the  chief  chemical  features  of  which  are  the 
removal  of  the  excess  of  lime,*  and  opening  the  pores  of  the  skin  by  means  of  a 
sour  mixture  of  bran  and  water,  in  which  lactic  acid  is  the  agent  ;  and  the  sub- 
sequent impregnation  of  the  porous  skin  with  aluminium  chloride,  by  steeping  it 
in  a  hot  bath  containing  alum  and  common  salt.  The  skins  are  afterwards 
softened  by  kneading  in  a  mixture  containing  alum,  flour,  and  the  yoke  of  eggs. 
The  putrefaction  of  the  skin  is  as  effectually  prevented  by  the  aluminium  chloride 
as  by  tanning. 

Wash-leather  and  buckskin  are  not  tanned,  but  s/tamoyed,  which  consist  in 
sprinkling  the  prepared  skins  with  oil,  folding  them  up,  and  stocking  them  under 
heavy  wooden  hammers  for  two  or  three  hours.  When  the  grease  has  been  well 
forced  in,  they  are  exposed  in  a  warm  atmosphere,  to  promote  the  drying  of  the 
oil  by  absorption  of  oxygen  (p.  798).  These  processes  having  been  repeated  the 
requisite  number  of  times,  the  excess  of  oil  is  removed  by  a  weak  alkaline  bath, 
and  the  skins  are  dried  and  rolled.  The  buff  colour  of  wash-leather  is  imparted 
by  a  weak  infusion  of  sumach. 

Parchment  is  made  by  stretching  lamb  or  goat  skin  upon  a  frame,  removing  the 
hair  by  lime,  and  scraping,  as  usual,  and  afterwards  rubbing  with  pumice-stone, 
until  the  proper  thickness  is  acquired. 

OILS  AND  FATS. 

601.  A  very  remarkable  feature  in  the  history  of  the  fats  is  the  close  resem- 
blance in  chemical  composition  and  properties  which  exists  between  them, 
whether  derived  from  the  vegetable  or  the  animal  kingdom.  They  all  contain 
two  or  more  neutral  substances  which  furnish  glycerine  when  saponified,  together 
with  some  of  the  acids  of  the  acetic  series  or  of  series  closely  allied  to  it. 

One  of  the  most  useful  vegetable  fatty  matters  is  palm,  oil,  which  is  extracts 
by  boiling  water  from  the  crushed  fruit  of  the  Elau  t/nmsr/txix,  an  African  palm. 
It  is  a  semi-solid  fat,  which  becomes  more  solid  when  kept,  since  it  then  und 
goes  a  species  of  fermentation,  excited  apparently  by  an  albuminous  substance 
contained  in  it,  in  consequence  of  which  the  palmitin  (C^H^O^is  conver 

*  Tolysulphides  of  sodium  or  calcium  are  sometimes  employed  for  removing  the  hair. 


OILS. 

glycerine  and  palmitic  acid.  The  bleaching  of  palm  oil  is  effected  by  the  action 
of  a  mixture  of  sulphuric  or  hydrochloric  acid  and  potassium  dichromate,  which 
oxidises  the  yellow  colouring-matter. 

Cocoa-nut  oil  is  also  semi-solid,  and  is  remarkable  for  the  number  of  acids  of  the 
acetic  series  which  it  yields  when  saponified — viz.,  caproic,  caprylic,  rutic,  lauric, 
myristic,  and  palmitic. 

These  fats  are  chiefly  used  in  the  manufacture  of  soap  and  candles. 

Salad  oil,  0t  sweet  oil(olire  oil),  is  obtained  by  crushing  olives,  and  an  inferior 
kind  which  is  used  for  soap  is  obtained  by  boiling  the  crushed  fruit  with  water. 
When  exposed  to  a  temperature  of  about  32°  F.  a  considerable  portion  of  the  oil 
solidifies  ;  this  solid  portion  is  generally  called  margarin  (C54H104O6)  ;  it  is  much 
less  soluble  in  alcohol  than  stearin  is,  though  more  so  than  palmitin.  When  saponi- 
fied, margarin  yields  glycerine  and  margaric  acid  (C17H3402).  This  acid  appears  to 
be  really  composed  of  stearic  and  palmitic  acids,  into  which  it  may  be  separated 
by  repeated  crystallisation  from  alcohol,  when  the  palmitic  acid  is  left  in  solution. 
The  fusing-point  of  margaric  acid  is  140°  F.,  that  of  stearic  being  159°,  and  that 
of  palmitic,  144°,  but  a  mixture  of  10  parts  of  palmitic  with  i  part  of  stearic  acid 
fuses  at  140°. 

That  portion  of  the  olive  oil  which  remains  liquid  below  32°  F.  consists  of  olein 
(C57H104O6).2,  and  forms  nearly  three-fourths  of  its  weight. 

It  is  well  known  that  salad*  oil  becomes  rancid  and  exhales  a  disagreeable  odour 
after  being  kept  for  some  time.  This  appears  to  be  due  to  a  fermentation  similar 
to  that  noticed  in  the  case  of  palm  oil,  originally  started  by  the  action  of  atmo- 
spheric oxygen  upon  albuminous  matters  present  in  the  oil  ;  the  neutral  fatty 
matters  are  thus  partly  decomposed,  as  in  saponification  ;  their  corresponding 
acids  being  liberated,  and  giving  rise  (in  the  case  of  the  higher  members  of  the 
acetic  series,  such  as  caproic  and  valerianic)  to  the  disagreeable  odour  of  rancid 
oil.  By  boiling  the  altered  oil  with  water,  and  afterwards  washing  it  with  a  weak 
solution  of  soda,  it  may  be  rendered  sweet  again. 

Almond  oil,  extracted  by  a  process  similar  to  that  employed  for  olive  oil,  is  also 
very  similar  in  composition  ;  but  colza  oil  (rape  oil),  obtained  from  the  seeds  of  the 
Srassicaoleifera,  contains  only  half  its  weight  of  olein,  and  hence  solidifies  more 
readily  than  the  others. 

Colza  oil  is  largely  used  for  burning  in  lamps,  and  undergoes  a  process  of  puri- 
fication from  the  mucilaginous  substances  which  are  extracted  with  it  from  the 
seed,  and  leave  a  bulky  carbonaceous  residue  when  subjected  to  destructive  dis- 
tillation in  the  wick  of  the  lamp.  To  remove  these,  the  oil  is  agitated  with  about 
2,  per  cent,  of  oil  of  vitriol,  which  carbonises  the  mucilaginous  substances,  but 
leaves  the  oil  untouched.  When  the  carbonaceous  flocks  have  subsided,  the  oil  is 
drawn  off,  washed  to  remove  the  acid,  and  filtered  through  charcoal. 

Linseed  oil,  obtained  from  the  seeds  of  the  flax  plant,  is  much  richer  in  olein 
than  any  of  the  foregoing,  exhibiting  no  solidification  till  cooled  to  15°  or  20°  F. 
below  the  freezing-point.  It  exhibits,  however,  in  a  far  higher  degree,  a  tendency 
to  become  solid  when  exposed  to  the  air,  which  has  acquired  for  it  the  name  of 
a  drying  oil,  and  renders  it  of  the  greatest  use  to  painters.  This  solidification  is 
attended  with  absorption  of  oxygen,  which  occurs  so  rapidly  in  the  case  of  linseed 
oil  that  spontaneous  combustion  has  been  known  to  take  place  in  masses  of  rag 
or  tow  which  have  been  smeared  with  it.* 

The  tendency  of  linseed  oil  to  solidify  by  exposure  is  much  increased  by  heat- 
ing it  with  about  ^V-h  of  litharge,  or  TVth  of  black  oxide  of  manganese;  these 
oxides  are  technically  known  as  dryers,  and  oil  so  treated  is  called  boiled  linseed 
oil.  The  action  of  these  metallic  oxides  is  net  well  understood. 

The  strong  drying  tendency  of  linseed  oil  is  supposed  to  be  due  to  a  peculiarity 
in  the  olein,  which  is  said  not  to  be  ordinary  olein,  but  to  furnish  a  different 
acid,  linoleic  acid,  when  saponified.  When  linseed  oil  is  exposed  for  some  time  to 
a  high  temperature,  it  becomes  viscous  and  treacly,  and  is  used  in  this  state  for 
the  preparation  of  printing  ink.  If  the  viscous  oil  be  boiled  with  dilute  nitric 
acid,  it  is  converted  into  artificial  caoutchouc,  which  is  used  in  the  manufacture  of 
surgical  instruments.  This  property  appears  to  be  connected  with  the  drying 
qualities  of  the  oil. 

Castor  oil,  obtained  from  the  seeds  of  Ricinus  communis,  also  yields  a  peculiar 

*  During1  the  oxidation,  a  volatile  compound  is  formed  which  resembles  acrolein  in  smell, 
and  colours  unsized  paper  brown.  It  has  been  suggested  that  the  brown  colour  and  musty 
smell  of  old  books  may  be  due  to  the  oxidation  of  the  oil  in  the  printing-ink. 


BUTTER. 

acid  when  saponified,  termed  ricinoUie  (H-C18H33O:j),  containing  one  more  atom 
of  oxygen  than  o.eic  acid,  which  it  much  resembles.  The  destructive  distillation 
of  castor  oil  yields  cenantliic  add  (iTC7H1302)  and  temnthol,  or  cenanthn-  ,//,/,.// ,/«fe 
(C7H140),  and  by  distilling  it  with  caustic  potash,  caprylic  alcohol  (C.H..O)  is 
obtained.  As  in  the  case  of  olive  oil,  the  cold-drawn  castor  oil,  which  is  expressed 
from  the  seeds  without  the  aid  of  heat,  is  much  less  liable  to  become  rancid 
Castor  oil  is  much  more  soluble  in  alcohol  than  is  any  other  of  the  fixed  oils 

The  various  fish  oils,  such  as  seal  and  whale  oil,  also  consist  chiefly  of  olein 
and  appear  to  owe  their  disagreeable  odour  to  the  presence  of  certain  volatile 
acids,  such  as  valerianic. 

Cod-liver  oil  appears  to  contain,  in  addition  to  olein  and  stearin,  a  small  quan- 
tity of  acetin  (C9H14O6),  which  yields  acetic  acid  and  glycerine  when  saponified. 
Some  of  the  constituents  of  bile  have  also  been  traced  in  it,  as  well  as  minute 
quantities  of  iodine  and  bromine. 

Butter  contains  about  half  its  weight  of  solid  fat,  which  consists  in  great  part 
of  palmitin  and  stearin,  but  contains  also  butin,  which  yields  glycerine  and  bufir 
acid  (H-C20H390.2)  when  saponified.  The  liquid  portion  consists  chiefly  of  olein. 
Butter  also  contains  small  quantities  of  butyrin,  caproin,  and  caprin,  which 
yield,  when  saponified,  glycerine  and  butyric  (H'C4H702),  caproic  (H-C6HnO.,), 
and  capric  (H'OpH^Oa)  acids,  distinguished  for  their  disagreeable  odour.  Fresh 
butter  has  very  little  odour,  being  free  from  these  volatile  acids,  but  if  kept  for 
some  time,  especially  if  the  casein  of  the  milk  has  been  imperfectly  separated  in 
its  preparation,  spontaneous  resolution  of  these  fats  into  glycerine  and  the  volatile 
disagreeable  acids  occurs.  By  salting  the  butter  this  change  is  in  great  measure 
prevented.  Margarine,  the  butter  substitute,  is  made  from  the  less  solid  portion 
of  mutton  suet. 

The  fat  of  the  sheep  and  ox  (suet,  or,  when  melted,  tallow)  consists  chiefly  of 
stearin,  whilst  in  that  of  the  pig  (lard)  olein  predominates  to  about  the  same 
extent  as  in  butter.  Palmitin  is  also  present  in  these  fats.  Benzoated  lard  con- 
tains some  gum  benzoin,  which  prevents  it  from  becoming  rancid. 

Human  fat  contains  chiefly  olein  and  margarin  (or,  if  we  do  not  admit  the 
independent  existence  of  the  latter,  palmitin  and  stearin). 

Sperm  oil,  which  is  expressed  from  the  spermaceti  found  in  the  brain  of  the 
sperm  whale,  owes  its  peculiar  odour  to  the  presence  of  a  fat  which  has  been 
called  phocen'm,  but  which  appears  to  be  valerin,  as  it  yields  glycerine  and 
valerianic  acid  (H -0511902)  when  saponified. 

The  beautiful  solid  crystalline  fat,  known  as  spermaceti  or  cetin,  differs  widely 
from  the  ordinary  fatty  matters,  for  when  saponified  (which  is  not  easily  effected), 
it  yields  no  glycerine,  but  in  its  stead  cetyl  alcohol  (p.  570). 

The  soap  prepared  from  spermaceti,  when  decomposed  by  an  acid,  yields  palm- 
itic acid  (H-C16H3102). 

Ambergris,  used  in  perfumery,  is  a  fatty  substance  found  in  the  intestines  of 
the  spermaceti  whale.  Boiling  alcohol  extracts  from  it  about  80  per  cent,  of 
ambrein. 

Chinese  wax,  the  produce  of  an  insect  of  the  Cochineal  tribe,  is  analogous  in  its 
chemical  constitution  to  spermaceti.  When  saponified  by  fusion  with  caustic 
potash,  it  yields  cerotin,  or  ceryl  alcohol  (C^H^'OH),  and  ceroticacid(E.'Cy,E.mO.,). 
Cerotic  acid  is  also  contained  in  ordinary  bees'-wax,  from  which  it  may  be 
extracted  by  boiling  alcohol,  and  crystallised  as  the  solution  cools.  It  forms 
about  two-thirds  of  the  weight  of  the  wax.  Cerotic  acid  is  found  among  the 
products  of  oxidation  of  paraffin  by  chromic  acid. 

Sees' -wax  also  contains  about  one-third  of  its  weight  of  myricin  (C^H^O.,),  a 
substance  analogous  to  spermaceti,  which  yields,  when  saponified,  palmitic  acid 
and  melissin,  or  myricyl  alcohol  (C30H61'OH).  The  colour,  odour,  and  tenacity 
of  bees'-wax  appear  to  be  due  to  the  presence  of  a  greasy  substance  called  Offvfei*, 
which  forms  about  -fa  of  the  wax,  and  has  not  been  fully  examined.  The  tree  wax 
of  Japan  is  said  to  be  pure  palmitin. 

Wax  is  bleached  for  the  manufacture  of  candles,  by  exposing  it  in  thin  strips  or 
ribands  to  the  oxidising  action  of  the  atmosphere,  or  by  boiling  it  with  nitrate  of 
soda  and  sulphuric  acid.     Chlorine  also  bleaches  it,  but  displaces  a  portion  of  the 
hydrogen  in  the  wax,  taking  its  place  and  causing  the  evolution  of  hydroc 
acid  vapours  when  the  wax  is  burnt. 

The  following  table  includes  the  principal  fatty  bodies  and  their  c< 
acids,  with  their  f  using-points  : — 


8oo 


MANUFACTUEE  OF  SOAP. 


Neutral 
Fats. 

Formula. 

Chief 
Source. 

Fusing- 
point, 
Fahr. 

Fatty 
Acids. 

Formula. 

Fusing- 
point, 
Fahr. 

Stearin 

CWHuflOg 

Tallow 

125°  to  157° 

Stearic 

Qw^gs^a 

!59° 

Palmitin 

C^lHggOg 

Palm  oil 

114°  to  145° 

Palmitic 

C16H3202 

144° 

Margarin 

^54^104^6 

Olive  oil 

116° 

Margaric 

C]7H3402 

140° 

Olein 

^57^104^6 

n 

Below  32° 

Oleic 

C18H3400 

40° 

Cetin 

C32H64°2 

Spermaceti 

120° 

Palmitic 

Ci6H3202 

144° 

Myriciu 

C46H92°2 

Bees'  -wax 

162° 

?5 

CHEMISTRY  OF  SOAP. 

602.  The  manufacture  of  soap  affords  an  excellent  instance  of  a  process  which 
was  in  use  for  centuries  before  anything  was  known  of  the  principles  upon  which 
it  is  based,  for  it  was  not  till  the  researches  of  Chevreul  were  published  in  1813 
that  any  definite  ideas  were  entertained  with  respect  to  the  composition  of  the 
various  fats  and  oils  from  which  soaps  are  made. 

The  investigations  of  Chevreul  are  conspicuous  among  the  labours  which  have 
contributed  in  so  striking  a  manner  to  the  rapid  advancement  of  chemistry  during 
the  nineteenth  century  ;  undertaken  when  the  chemistry  of  organic  substances  had 
scarcely  advanced  beyond  the  dignity  of  an  art,  when  the  principles  of  classifica- 
tion were  almost  entirely  empirical,  and  hardly  any  research  had  been  published 
which  would  serve  as  a  model,  these  investigations  reflect  the  remarkable  sagacity 
and  accuracy  of  their  author. 

The  sense  of  our  obligation  to  this  eminent  chemist  is  further  increased,  when 
we  remember  that  the  ultimate  analysis  of  organic  substances  was  then  effected 
by  a  very  difficult  and  laborious  process,  whilst  the  doctrine  of  combining  pro- 
portions was  so  imperfectly  understood,  that  it  could  afford  but  little  assistance 
in  confirming  or  interpreting  the  result  of  analysis. 

All  soaps  are  formed  by  the  action  of  the  alkalies  upon  the  oil  and  fats. 

In  the  manufacture  of  soap,  potash  and  soda  are  the  only  alkalies  employed,  the 
former  for  soft,  the  latter  for  hard  soaps. 

The  fatty  matters  used  by  the  soap-maker  are  chiefly  tallow,  palm  oil,  coco- 
nut oil,  and  kitchen  stuff,  for  hard  soaps,  and  seal  oil  and  whale  oil  for  soft 
soaps. 

In  the  manufacture  of  hard  soap,  the  alkali  is  prepared  by  decomposing  or 
caustifying  sodium  carbonate  (soda-ash)  with  slaked  lime,  Na2CO3  +  Ca(OH)2  = 
CaC03  +  2NaOH,  the  clear  solution  of  sodium  hydroxide,  or  soda-ley,  being  drawn 
off  from  the  insoluble  calcium  carbonate. 

The  tallow  is  at  first  boiled  with  a  weak  soda-ley,*  because  the  soap  which  is 
formed  is  insoluble  in  a  strong  alkaline  solution,  and  would  enclose  and  protect  a 
quantity  of  undecom posed  tallow  ;  in  proportion  as  the  saponification  proceeds, 
stronger  leys  are  added,  until  the  whole  of  the  grease  has  disappeared.  In  order 
to  separate  the  soap  which  is  dissolved,  advantage  is  taken  of  the  insolubility  of 
soap  in  solution  of  salt  ;  a  quantity  of  common  salt  being  thrown  into  the  boiler, 
the  soap  rises  to  the  surface,  when  the  spent  ley  is  drawn  off  from  below,  and  the 
soap  transferred  to  iron  moulds  that  it  may  harden  sufficiently  to  be  cut  up  into 
bars. 

In  order  to  understand  the  chemistry  of  this  process,  it  is  necessary  to  know 
that  tallow  contains  two  fatty  substances,  one  of  which,  stearin^  (C57H110O6),  is 
solid,  and  the  other,  ole'tn  (C57H10406),  liquid,  the  quantity  of  stearin  being  about 
thrice  that  of  olein. 

When  these  fats  are  acted  upon  by  soda,  they  undergo  decomposition,  furnish- 
ing stearic  and  oleic  acids,  which  combine  with  the  soda  to  form  soap,  whilst  a 
peculiar  sweet  substance,  termed  glycerine,  passes  into  solution  ;  the  nature  of  the 
decomposition  in  each  case  will  be  understood  from  the  following  equations — 

*  Soap  is  now  sometimes  made  by  the  action  of  the  sodium  carbonate  upon  the  fat,  thus 
saving-  the  expense  of  caustifying  (Morfit's  process), 
f  Sre'ap,  tallow. 


SOAP  AND  CANDLES.  8OI 

C3H5-(C18H350)3-03  +  3NaOH  =  3Na(C18HM0)0  +  C3H803 
.Stearin.  Sodium  stearate.       Glyceriae. 


C3H5-(C18H330)3-03  +  3NaOH  =  3Na(C18H:aO)0  +  C,H80, 

Olem-  Sodium  o'leate.       Glycerine  ; 

so  that  the  soap  obtained  by  boiling  tallow  with  soda  is  a  mixture  of  the  sodium- 
stearate  with  about  a  third  of  its  weight  of  sodium  oleate  and  20  to  to  per  cent 
of  water. 

Palm    oil  is   composed  chiefly   of  palmitin   (CKHK09)t  a  solid  fat  which   is 
resolved,  by  boiling  with  soda,  into  sodium  palmitate  (palm  oil  soap)  and  gly- 
cerine ;  C3H5-(C16H310)3-03  +  3NaOH  =  3Na(C16H310)0  +  C3H803 
Palmitin.  Sodium  palmitate.     Glycerine. 

In  the  fish  oils  the  predominant  constituent  is  olein,  so  that  when  boiled  with 
potassium  hydroxide,  they  yield  potassium  oleate  (KC18H3302),  which  composes  the 
chief  part  of  soft  soap. 

Castile  soap  is  made  from  olive  oil,  which  contains  olein  and  a  solid  fat  known 
as  margarln.  The  latter  appears  to  be  really  composed  of  palmitin  and 
stearin,  so  that  the  Castile  soap  is  a  mixture  of  oleate,  palmitate,  and  stearate 
of  sodium. 

The  peculiar  appearance  of  mottled  soap  is  caused  by  the  irregular  distribution 
of  a  compound  of  the  fatty  acid  with  oxide  of  iron,  which  arranges  itself  in  veins 
throughout  the  mass.  If  the  soap  contained  too  much  water,  so  as  to  render  it 
very  fluid  when  transferred  to  the  moulds,  this  iron  compound  would  settle  down 
to  the  bottom,  leaving  the  soap  clear,  so  that  the  mottled  appearance  is  often 
regarded  as  an  indication  that  the  soap  does  not  contain  an  undue  proportion  of 
water  ;  it  is  imitated,  however,  by  stirring  into  the  pasty  soap  some  ferrous 
sulphate  and  a  little  impure  ley  containing  sodium  sulphide,  so  as  to  produce  the 
dark  sulphide  of  iron  by  double  decomposition.* 

In  the  manufacture  of  yellow  soap,  in  addition  to  tallow  and  palm  oil,  a  con- 
siderable proportion  of  common  rosin  (see  p.  560)  is  added  to  the  soap  shortly 
before  it  is  finished.  Soft  soap  is  not  separated  from  the  water  by  salt  like  hard 
soap,  but  is  evaporated  to  the  required  consistency.  Transparent  soaps  are 
obtained  by  drying  hard  soap,  dissolving  it  in  hot  spirit  of  wine,  and  pouring  the 
strong  solution  into  moulds  after  the  greater  part  of  the  spirit  has  been  distilled 
off.  Silicated  soap  is  a  mixture  of  soap  with  silicate  of  soda.  Glycerine  soap  is 
prepared  by  heating  the  fat  with  alkali  and  a  little  water  at  about  400°  F.  for  two 
or  three  hours,  and  running  the  mass  at  once  into  moulds.  It  is,  of  course,  a 
mixture  of  soap  and  glycerine. 

The  proportion  of  water  in  soap  is  very  variable,  some  specimens  containing 
between  70  and  80  per  cent.  The  smallest  proportion  is  about  30  per  cent. 

The  theory  of  saponification,  stated  above,  has  received  the  strongest  confirma- 
tion within  the  last  few  years,  by  the  synthetic  production  of  the  fats  from 
glycerine  and  the  fatty  acids  formed  in  their  saponification. 

CANDLES. 

603.  Since  tallow  fuses  at  about  100°  F.,  and  stearic  acid  not  below  159°,  it  is 
evident  that,  independently  of  other  considerations,  the  latter  would  be  better 
adapted  for  the  manufacture  of  candles,  for  such  candles  would  never  soften  at 
the  ordinary  atmospheric  temperature  in  any  climate,  and  would  have  much  less 
tendency  to  gutter  in  consequence  of  the  excessive  fusion  of  the  fuel  around  the 
base  of  the  wick.  The  gases  furnished  by  the  destructive  distillation  of  stearic 
acicl  in  the  wick  of  the  candle  burn  with  a  brighter  flame  than  those  produced 
from  tallow.  Accordingly,  the  manufacture  of  stearin  (or  more  correctly,  stearic 
acid)  candles  f  has  now  become  a  very  important  and  instructive  bram 


lnTheroriginal  method  of  separating  the  stearic  acid  from  tallow  on  the  large 
scale  consisted  in  mixing  melted  tallow  with  lime  and  water,  and  heating  tl 
mixture  for  some  time  at  212°  F.  by  passing  steam  through  it.  nf  „„,„:„„ 

The  tallow  was  thus  converted  into  the  insoluble  stearate  and  oleate  of  c 
which  was  drained  from  the  solution  containing  the  glycerine,  and  c 

•  A  soap  which  contains  more  than  30  per  cent,  of  water  is  said  not  to  admit  of  mottling. 
f  Composite  candles  are  made  of  a  mixture  of  stearic  and  palm 


802  SAPONIFICATION  BY  ACIDS. 

sulphuric  acid.  The  mixture  of  stearic  and  oleic  acids  thus  obtained  was  cast 
into  thin  slabs,  which  were  packed  between  pieces  of  coco-nut  matting,  and  well 
squeezed  in  a  hydraulic  press,  which  forced  out  the  oleic  acid,  leaving  the  stearic 
and  palmitic  acids  in  a  fit  state  for  the  manufacture  of  candles. 

The  separation  of  the  solid  fatty  acids  from  tallow  and  other  fats  may  also  be 
effected  by  the  action  of  sulphuric  acid,  a  process  extensively  applied  in  this 
•country  to  palm  and  coco-nut  oils.  These  fats  are  mixed  in  copper  boilers  with 
about  one-sixth  of  their  weight  of  concentrated  sulphuric  acid,  and  heated  by 
steam  at  about  350°  F.  for  some  hours,  when  part  of  the  glycerine  is  converted 
into  sulphoglyceric  acid  (C3H8O3'S03),  and  the  remainder  is  decomposed  by  the 
sulphuric  acid,  carbonic  and  sulphurous  acid  gases  being  disengaged,  whilst  a 
dark-coloured  mixture  of  palmitic,  stearic  and  oleic  acid  is  left.  A  part  of  the 
oleic  acid  becomes  converted  in  this  process  into  elaidic  acid,  which  has  the  same 
composition,  but  differs  from  oleic  acid  in  fusing  at  about  113°  F.,  so  that  the 
amount  of  solid  acid  obtained  by  this  process  is  much  increased.  This  mixture 
is  well  washed  from  the  adhering  sulphuric  and  sulphoglyceric  acids,  and  trans- 
ferred to  a  copper  still  into  which  a  current  of  steam  is  passed,  which  has  been 
raised  to  about  600°  F.  by  passing  through  hot  iron  pipes.  These  fatty  acids 
co  aid  not  be  distilled  alone  without  decomposition,  but  under  the  influence  of  a 
current  of  steam  they  pass  over  readily  enough,  leaving  a  black  pitchy  residue 
in  the  retort,  which  is  employed  in  making  black  sealing-wax,  and  for  other 
useful  purposes. 

The  distilled  fatty  acids  are  broken  up  and  pressed  between  coco-nut  matting 
to  remove  the  oleic  acid. 

One  great  advantage  of  this  process,  which  is  commonly,  though  incorrectly, 
styled  the  saponification  by  sulphuric  acid,  is  its  allowing  the  conversion  of  the 
worst  kinds  of  refuse  fat  into  a  form  fit  for  the  manufacture  of  candles  ;  thus,  the 
fat  extracted  from  bones  in  the  manufacture  of  glue,  and  that  removed  from  wool 
in  the  scoring  process,  may  be  turned  to  profitable  account. 

It  will  be  remarked  that  in  this  process  the  palmitic,  stearic,  and  oleic  acids 
are  formed  from  the  palmitin,  stearin,  and  olein  existing  in  the  fats,  by  the 
assimilation  of  the  elements  of  water  and  the  subsequent  separation  of  glycerine, 
just  as  in  the  ordinary  process  of  saponification  by  means  of  alkalies. 

Strictly  speaking,  the  action  appears  to  consist  of  two  stages  ;  for  when  con- 
centrated sulphuric  acid  is  allowed  to  act  upon  the  natural  fats  in  the  cold,  it 
combines  with  each  of  their  ingredients,  forming  the  acids  known  as  sulpho- 
stearic,  sulphopalmitic,  sulpholeic,  and  sulphoglyceric,  which  are  soluble  in 
water,  though  not  (with  the  exception  of  the  last)  in  water  containing  sulphuric 
acid. 

The  second  stage  consists  in  the  decomposition  of  the  sulpho-fatty  acids  by  the 
high  temperature  in  contact  with  steam,  the  sulphoglyceric  acid  having  been  in 
great  measure  decomposed  into  secondary  products  before  the  distillation  is  com- 
menced. 

Within  the  last  few  years,  the  extraction  of  the  solid  acids  from  the  natural 
fats  has  been  effected  by  a  process  known  as  saponification  by  steam,  which  allows 
the  glycerine  also  to  be  obtained  in  a  pure  state.  It  is  only  necessary  to  subject 
the  fat,  in  a  distillatory  apparatus,  to  the  action  of  steam,  at  a  temperature  of 
about  600°  F.,  to  cause  both  the  fatty  acids  and  the  glycerine  to  distil  over  ;  the 
former  may  be  separated  as  usual  into  solid  and  liquid  portions  by  pressure, 
whilst  the  glycerine,  which  is  obtained  in  aqueous  solution  below  the  layer  of 
fatty  acid?,  is  concentrated  by  evaporation,  and  sent  into  commerce  as  a  very 
sweet  colourless  viscid  liquid.  The  saponificaticn  of  palmitin,  for  instance,  by 
steam,  would  be  represented  by  the  equation — 

C3H5-(C]6H3102)3   +   3H20   =   3(H-C16H3102)    +   C3H5(HO)3 
Falmitin.  Palmitic  acid.  Glycerine. 


Potatoes. 

Wheat. 

Starch 

.       20.2 

60.8 

Water 

.     75.9 

12.  1 

Gluten         .         .         . 
Albumin 

2.3 

10.5    ;; 

2.O 

Dextrin  and  sugar 
Woody  fibre 

0.4 

10.5 
1.5 

Oily  matter 

O.2 

J 

Mineral  matter   . 

I.O 

MANUFACTURE   OF  STARCH.  803 

STARCH. 

604.  Starch  is  manufactured  chiefly  from  potatoes,  wheat,  and  rice,  the  solid 
portion  of  which  consists  chiefly  of  starch,  as  appears  in  the  following  result  of 
analysis : — 

Rice. 
83.0 

6.0 

1.0 

4-8 

O.I 
O.I 

IOO.O  IOO.O  IOO.O 

In  order  to  extract  the  starch,  the  potatoes  are  rasped  to  a  pulp,  which  is 
washed  upon  a  sieve  under  a  stream  of  water,  as  long  as  the  latter  is  rendered 
milky  by  the  starch  suspended  in  it,  the  woody  fibre  being  left  behind  upon  the 
sieve.  The  milky  liquid  is  allowed  to  settle,  and  the  clear  water  drawn  off  ;  the 
deposited  starch  is  then  stirred  up  with  fresh  water,  and  again  allowed  to  subside, 
this  process  being  repeated  as  long  as  the  water  is  coloured,  after  which  the  starch 
is  mixed  up  with  a  small  quantity  of  water,  and  passed  through  a  fine  sieve  to 
separate  mechanically  mixed  impurities  ;  it  is  finally  drained  and  dried,  first  in  a 
current  of  air,  and  afterwards  by  a  gentle  heat. 

Starch  cannot  be  extracted  from  wheat  so  easily  as  from  potatoes,  on  account 
of  the  much  larger  proportion  of  other  solid  matters  from  which  it  must  be 
separated. 

To  extract  the  starch,  the  coarsely  ground  wheat  is  moistened  with  water,  and 
allowed  to  putrefy,  as  it  easily  does,  in  consequence  of  the  alterable  character  of 
the  gluten  (which  contains  carbon,  hydrogen,  nitrogen,  oxygen,  and  sulphur)  ; 
the  putrefying  gluten  excites  fermentation  in  the  sugar  and  part  of  the  starch, 
producing  acetic  and  lactic  acids.  These  acids  are  capable  of  dissolving  the 
remainder  of  the  gluten,  which  may  then  be  washed  away  by  water,  the  subse- 
quent processes  being  similar  to  those  employed  in  the  extraction  of  potato 
starch. 

A  far  more  economical  and  scientific  method  of  extracting  the  starch  consists 
in  dissolving  the  gluten  by  means  of  a  weak  alkaline  solution,  which  leaves  the 
starch  untouched,  This  process  is  especially  applied  in  the  manufacture  of  starch 
from  rice  (p.  735). 

Arrowroot  is  the  starch  extracted  from  the  root  of  the  Maranta  arundinacea, 
and  of  some  other  tropical  plants. 

In  the  preparation  of  tapioca  and  sago,  the  starch  is  dried  at  a  temperature 
above  140°  F.,  so  that  it  loses  its  ordinary  farinaceous  appearance  and  becomes 
semi-transparent. 

Sago  is  manufactured  from  the  pith  of  certain  species  of  palm,  natives  of  the 
East  Indian  islands.  The  tree  is  split  so  as  to  expose  the  pith,  which  is  mixed 
with  water,  and  the  starch,  having  been  separated  from  the  woody  fibre  in  the 
usual  manner,  is  pressed  through  a  perforated  metallic  plate,  which  moulds  it 
into  small  cylinders  ;  these  are  placed  in  a  revolving  vessel  and  broken  into  rough 
spherical  grains,  which  are  steamed  upon  a  sieve  and  dried. 

Tapioca  is  obtained  from  the  roots  of  the  Jatropha  manihot,  a  native  of  America. 
The  roots  are  peeled  and  subjected  to  pressure,  which  squeezes  out  a  juice 
employed  by  the  Indians  to  poison  their  arrows,  and  containing  a  deleterious  sub- 
stance which  has  been  named  jatrophine.  When  the  juice  is  allowed  to  stand  n 
deposits  starch,  which  is  well  washed,  pressed  through  a  colander,  and  dned  at 

212°  F. 

Osw'ego,  or  corn-flour,  is  the  flour  of  Indian  corn  deprived  of  gluten  by  treat- 
ment with  a  weak  solution  of  soda. 

605.  MALTING.— The  tendency  of  starch  to  combine  with  the  elements  of  water 
and  pass  into  glucose  (p.  733)  is  of  immense  importance  in  the  chemistry  of  veg 
tation,  as  well  as  in  that  of  food.     It  is,  indeed,  the  chief  chemical  change  con- 
cerned in  the  development  of  living  from  inanimate  matter,  being  one  of  the  I 


804  GERMINATION   OF  SEEDS. 

processes  involved  in  the  germination  of  seed — the  first  step  in  the  production  of 
vegetables,  which  must  precede  the  animals  whose  food  they  compose. 

The  components  of  all  seeds  are  similar  to  those  of  wheat,  which  have  been 
enumerated  above  ;  if  the  seeds  be  perfectly  dried  immediately  after  the  removal 
from  the  parent  plant,  they  may  be  preserved  for  a  great  length  of  time  unchanged 
and  without  losing  the  power  of  germinating  under  favourable  circumstances. 
The  essential  conditions  of  germination  are  the  presence  of  air  and  moisture,  and 
a  certain  temperature,  which  varies  with  the  nature  of  the  seed.  These  conditions 
being  fulfilled,  the  seed  absorbs  oxygen  from  the  air,  and  evolves  carbonic  acid 
gas,  produced  by  the  combination  of  the  oxygen  with  the  carbon  of  one  or  more 
of  the  most  alterable  constituents  of  the  seed,  such  as  the  vegetable  albumin  or 
the  gluten.  This  process  of  oxidation  is  attended  with  evolution  of  heat,  which 
serves  to  maintain  the  seed  at  a  degree  of  warmth  most  favourable  to  germina- 
tion. The  component  particles  of  the  albumin  or  gluten,  having  been  set  in 
motion  by  the  action  of  the  atmospheric  oxygen,  induce  a  movement  or  chemical 
change  in  the  starch  with  which  they  are  in  contact,  causing  it  to  pass  into 
dextrin  and  glucose,  which,  unlike  the  starch,  are  perfectly  soluble  in  water, 
and  capable  of  affording  to  the  developing  shoot  the  carbon,  hydrogen,  and  oxygen 
which  it  requires  for  the  increase  of  its  frame.  The  production  of  glucose  and  of 
dextrin  in  germination  is  well  illustrated  by  the  sweet  gummy  character  of  the 
bread  made  from  sprouted  wheat,  and  is  turned  to  practical  account  in  the  process 
of  malting. 

During  the  germination  of  all  seeds  there  is  formed,  apparently  by  the  oxidation 
of  one  of  the  more  alterable  constituents,  a  peculiar  substance  containing  carbon, 
hydrogen,  nitrogen,  and  oxygen,  which  has  never  yet  been  obtained  from  any 
other  source,  and  is  characterised  by  its  remarkable  property  of  inducing  the 
conversion  of  starch  into  dextrin  and  grape-sugar.  This  substance  has  been 
termed  diastase  (Stcia-racm,  dissensions  ;  metaph.  fermentation),  but  has  never  yet 
been  obtained  in  a  state  of  sufficient  purity  to  enable  its  formula  to  be  satis- 
factorily determined.  It  may  be  extracted,  however,  from  malt,  by  grinding  it 
and  mixing  it  with  half  its  weight  of  warm  water,  which  dissolves  the  diastase  ; 
the  solution  squeezed  out  of  the  malt  is  heated  to  about  179°  F.,  filtered  from  any 
coagulated  albumin,  and  mixed  with  absolute  alcohol,  which  precipitates  the 
diastase  in  white  flakes.  One  part  of  diastase  dissolved  in  water  is  capable  of 
inducing  the  conversion  of  2000*  parts  of  starch  into  dextrin  and  grape-sugar,  the 
diastase  itself  being  exhausted  in  the  process.  A  temperature  of  about  150°  F.  is 
most  favourable  to  the  action  of  diastase,  which  may  be  arrested  entirely  by 
raising  the  liquid  to  the  boiling-point. 

The  great  importance  of  diastase  in  the  art  of  the  brewer  and  distiller  is  at 
once  apparent.  In  the  process  of  malting  barley,  the  grain  is  soaked  in  water, 
and  afterwards  spread  out  in  thin  layers  upon  the  floor  of  a  dark  room  (thus 
imitating  the  natural  condition  under  which  the  seed  germinates),  which  is  main- 
tained as  nearly  as  possible  at  a  constant  and  moderate  temperature  (between 
55°  and  62°  F.)  ;  spring  and  autumn  are,  therefore,  more  favourable  to  malting 
than  summer  and  winter.  It  soon  evolves  heat,  and  the  grains  begin  to  swell  ; 
in  the  course  of  twenty-four  hours  the  germination  commences,  and  the  radicle 
makes  its  first  appearance  as  a  whitish  protuberance  ;  the  grain  is  turned  two  or 
three  times  a  day,  in  order  to  equalise  the  temperature.  In  about  a  fortnight  the 
radicle  has  grown  to  about  half  an  inch,  by  which  time  a  sufficient  quantity  of 
diastase  has  been  formed.  In  order  to  prevent  the  germination  from  proceeding- 
further,  the  grain  is  killed  by  drying  it  at  a  temperature  of  90°  F.  on  perforated 
metallic  plates,  where  it  is  afterwards  heated  to  about  140°  F.,  so  as  to  render  it 
brittle,  after  which  it  is  sifted  in  order  to  separate  the  radicle,  which  is  now 
easily  broken  off.  This  radicle  is  found  to  contain  as  much  as  £  of  the  total 
quantity  of  the  nitrogen  present  in  the  barley,  so  that  the  malt  dust,  as  the  siftings 
are  called,  forms  a  valuable  manure. 

One  hundred  parts  of  barley  generally  yield  about  80  parts  of  malt,  but  a  part 
of  the  loss  is  due  to  water  present  in  the  barley,  so  that  100  parts  of  dry  barley 
yield  90  parts  of  malt  and  4  parts  of  malt  dust,  the  difference,  viz.,  6  parts. 
representing  the  weight  of  the  carbon  converted  into  carbonic  acid  gas,  of  the 
hydrogen  (if  any)  converted  into  water  during  the  germination,  and  of  soluble 
matters  removed  from  the  barley  in  steeping.  Malt  contains  about  T£¥  of  its. 

*  100,000,  according  to  more  modern  authorities. 


BREWING. 


the 


The  following  table  illustrates  the  change  in  composition  suffered  br  barley 
during  the  process  of  malting,  leaving  the  moisture  out  of  consideration  :- 


— 

Barley. 

After 
Steeping. 

14^  Days 
on  Floor. 

Malt  after 
Sifting. 

Malt  Dust. 

Sugar 
Starch     ) 

2.56 

I.56 

12.14 

II.  OI 

"•35 

Dextrin  j  ' 

80.42 

8l.I2 

70.09 

72.03 

43-68 

Woody  fibre 
Albuminous  matter  . 
Mineral  matter  . 

4-69 
9-03 
2.50 

5,22 

9.83 
2.27 

5-03 
10.39 

2-35 

4.84 

9-95 
2.17 

9.67 
26.90 
8.40 

IOO.OO 

IOO.OO 

100.00 

100.00 

100.00 

BREWING. 

606.  In  order  to  prepare  beer,  the  brewer  washes  the  ground  malt  with  water  at 
about  1 80°  F.,  for  some  hours,  when  the  diastase  induces  the  conversion,  into 
dextrin  and  sugar,  of  the  greater  part  of  the  starch  which  has  not  been  so 
changed  during  the  germination,  and  the  wort  is  ready  to  be  drawn  off  for  con- 
version into  beer.  The  undissolved  portion  of  the  malt,  or  brewers'  grains,  still 
contains  a  considerable  quantity  of  starch  and  nitrogenised  matter,  and  is 
employed  for  feeding  pigs. 

That  malt  contains  far  more  diastase  than  is  necessary  to  convert  its  starch 
into  sugar,  is  shown  by  adding  a  little  infusion  of  malt  to  the  viscid  solution  of 
starch,  and  maintaining  it  at  about  150°  F.  for  a  few  hours,  when  the  mixture 
will  have  become  far  more  fluid,  and  will  no  longer  be  coloured  blue  by  solution 
of  iodine.  In  distilleries,  advantage  is  taken  of  the  excess  of  diastase  in  malt, 
by  adding  three  or  four  parts  of  unmalted  grain  to  it,  when  the  whole  of  the 
starch  in  this  latter  is  also  converted  into  dextrin  and  sugar,  and  the  labour  and 
expense  of  malting  it  are  avoided. 

The  wort  obtained  by  infusing  malt  in  water  contains  not  only  glucose,  dextrin, 
and  diastase,  but  a  considerable  quantity  of  nitrogenised  matter  formed  from  the 
gluten  (or  albuminous  matter)  of  the  barley.  Before  subjecting  it  to  fermenta- 
tion it  is  boiled  with  a  quantity  of  hops,  usually  amounting  to  about  TV  of  the 
weight  of  the  malt  employed,  which  is  found  to  prevent,  in  great  measure,  the 
tendency  of  the  beer  to  become  sour  in  consequence  of  the  conversion  of  the 
alcohol  into  acetic  acid. 

The  hop  contains  about  10  per  cent,  of  an  aromatic  yellow  powder  called  lujwIiH, 
which  appears  to  be  the  active  portion,  and  contains  a  volatile  oil  of  peculiar 
odour,  together  with  a  very  bitter  substance. 

The  hopped  wort  is  run  off  into  a  vat,  where  it  is  allowed  to  deposit  the  undis- 
solved portion  of  the  hops,  and  the  clear  liquor  is  drawn  off  into  shallow  coolers, 
where  its  temperature  is  lowered  as  rapidly  as  possible  to  about  60°  F.,  the  cooling 
being  usually  hastened  by  cold  water  circulating  through  pipes  which  traverse 
the  coolers.  *  If  the  wort  be  cooled  too  slowly,  the  nitrogenised  matter  which  it 
contains  undergoes  an  alteration  by  the  action  of  the  air,  in  consequence  of  which 
the  beer  is  very  liable  to  become  acid. 

The  wort  is  now  transferred  to  the  fermenting  tun,  where  it  is  made  to  ferment 
by  the  addition  of  yeast,  usually  in  the  proportion  of  TJT  of  its  volume. 
*  Yeast  has  been  depicted  and  described  at  p.  562. 

The  yeast  cells  contain  a  substance  somewhat  resembling  albumin  enclosed 
a  thin  membrane,  the  composition  of  which  is  similar  to  that  of  cellulose.     Ihey 
also  contain  a  peculiar  nitrogenised  body   (iiwerUue)  resembling  diastase,  and 
capable  of  inducing  the  conversion  of  cane-sugar  (Cl2H^On]  into  glucose  (C6H,aO6). 
Accordingly,  when  yeast  is  added  to  a  solution  of  cane-sugar  the  liquid 


8o6 


COMPOSITION   OF   BEEES. 


to  increase  in  specific  gravity  (a  solution  of  cane-sugar  having  a  lower  density 
than  one  containing  an  equivalent  quantity  of  glucose)  previously  to  the  com- 
mencement of  fermentation,  and  the  application  of  tests  readily  proves  the 
presence  of  glucose  in  the  solution. 

The  glucose  then  undergoes  the  decomposition  known  as  alcoholic  fermentation, 
described  at  p.  562. 

During  the  fermentation,  the  yeast  cells  are  gradually  broken  up,  so  that  a  given 
quantity  of  yeast  is  capable  of  fermenting  only  a  limited  quantity  of  sugar.  On 
an  average  a  quantity  of  yeast  containing  between  two  and  three  parts  of  solid 
matter  is  required  to  complete  the  fermentation  of  100  parts  of  sugar.  The  solu- 
tion remaining  after  the  fermentation  is  found  to  contain  salts  of  ammonium, 
which  have  been  formed  at  the  expense  of  the  nitrogen  of  the  yeast. 

If  the  liquid  in  which  the  yeast  excites  fermentation  contains  nitrogenised 
matters  and  phosphates,  the  yeast-plant  grows,  and  its  quantity  increases ; 
thus  in  the  sweet  wort  from  malt,  the  yeast  is  nourished  by  the  altered  gluten 
and  by  the  phosphates,  so  that  it  increases  to  six  or  eight  times  its  original 
weight. 

If  yeast  be  heated  to  the  boiling-point  of  water,  the  plant  is  killed,  as  might  be 
expected,  and  loses  its  power  of  inducing  alcoholic  fermentation  ;  but  it  may  be 
dried  at  a  low  temperature,  or  by  pressure,  without  losing  its  fermenting  power, 
and  dried  yeast  is  an  article  of  commerce.  German  dried  yeast  is  produced  in  the 
fermentation  of  rye  for  making  Hollands. 

In  the  fermentation  of  beer,  the  yeast  is  carried  up  to  the  surface  by  the  effer- 
vescence due  to  the  escape  of  the  carbonic  acid  gas,  and  is  eventually  removed, 
in  order  to  be  employed  for  the  fermentation  of  fresh  quantities  of  wort.  When 
the  fermentation  has  proceeded  to  the  required  extent,  the  beer  is  stored  for 
consumption. 

It  will  be  seen  that  the  chief  constituents  of  beer  are  the  alcohol,  the  nitrogen- 
ised substance  derived  from  the  albuminous  matter  of  the  barley  and  not  con- 
sumed in  the  growth  of  the  yeast,  the  unaltered  glucose  and  dextrin,  the  brown 
or  yellow  colouring-matter  formed  during  the  fermentation,  the  essential  oil  and 
bitter  principle  of  the  hop. 

Beer  also  contains  acetic  acid  (formed  by  the  oxidation  of  the  alcohol, 
p.  590),  free  carbonic  acid,  which  gives  it  its  sparkling  character,  together  with 
the  lactic  and  succinic  acids  and  glycerine,  formed  as  secondary  products  of  the  fer- 
mentation, and  ammoniacal  salts  derived  from  the  yeast.  The  soluble  mineral 
substances  from  the  barley  are  also  present,  minus  the  phosphates  abstracted  by 
the  yeast. 

The  proportions  of  the  constituents  of  course  vary  greatly,  as  will  be  seen  from 
the  following  examples  : — 


Percentage. 

Allsopp's 
Ale. 

Bass's  Ale. 

Strong  Ale. 

WMtbread's 
Porter. 

Whitbread's 
Stout. 

Alcohol 

6.00 

7.00 

8.65 

4.20 

6.  CO 

Acetic  acid 

O.2O 

0.18 

0.  12 

0.19 

0.18 

Sugar     and    other  \ 
solid  matters        J 

5.00 

4.80 

6.60 

5-40 

6.38 

The  dark  colour  of  porter  and  stout  is  caused  by  the  addition  of  a  quantity  of 
high-dried  malt  which  has  been  exposed  to  so  high  a  temperature  in  the  kiln  as  to 
convert  a  portion  of  its  sugar  into  a  dark  brown  soluble  substance  called  caramel. 
The  peculiar  aroma  of  beer  is  probably  due  to  the  presence  of  acetic  ether,  pro- 
duced during  the  fermentation. 

In  some  cases,  when  the  operation  of  brewing  has  been  badly  conducted,  the 
beer  becomes  ropy,  or  undergoes  the  viscous  fermentation.  In  this  case  the  glucose 
suffers  a  peculiar  transformation,  resulting  in  the  production  of  a  mucilaginous 
substance  resembling  gum  in  its  composition.  This  change  may  be  induced  by 
yeast  which  has  been  boiled,  or  by  water  in  which  flour  or  rice  has  been  steeped. 
During  this  viscous  fermentation  a  part  of  the  glucose  is  often  converted  into 
mannite  (C6H1406). 


WINES.  8o; 


WINES  AND  SPIRITS. 

607.  Wine  is  essentially  composed  of  8  or  10  parts  of  alcohol  v 
water,  together  with  minute  quantities  of  certain  fragrant  ethcrT  of  colourfn 

addition  of  ferment  is  necessary,  the  i£ti^^£S££F  G££° 
juice  contains,  in  addition  to  grape-sugar,  vegetable  albumin,  potassium  tartnS 
and  the  usual  mineral  salts  found  in  vegetable  juices.     The  husks 
stalks  of  the  grape  contain  a  considerable  quantity  of  tann  n    tVrther'wUh 
certain  blue,  red,  and  yellow  colouring-matters. 

When  the  expressed  juice  remains  for  a  short  time  in  contact  with  th-  air 
the  germs  or  spores  of  yeast  (p.  562)  which  float  in  the  air  are  deposited  oi 
surface  of  the  juice,  at  the  expense  of  which  tbev  begin  to  grow  excit  ne 
the  vinous  fermentation  in  the  sugar,  and  a  scum  of  yeast  if  formed  2 
the  surface.  If  this  fermentation  takes  place  in  contact  with  the  husks  Jf 
the  dark  grapes,  the  alcohol  dissolves  the  colouring-matter,  and  a  red  wine 
results  ;  whilst  for  the  production  of  white  wines,  the  husks,  &c.,  are  separated 
previously  to  the  fermentation,  and  the  juice  is  exposed  as  little  as  possible  to 
triG  tiir. 


White  wines  are  rather  liable  to  become  ropy  from  viscous  fermentation  but 
this  is  prevented  by  the  addition  of  a  small  quantity  of  tannin,  which  precipitates 
the  peculiar  ferment.  The  tannin  for  this  purpose  is  extracted  from  the  husks 
and  stalks  of  the  grapes  themselves,  and  already  exists  in  red  wine. 

^  Red  wines,  such  as  port  and  claret,  are  often  very  astringent  from  the  tannin 
dissolved  out  of  the  husks,  &c.,  during  the  fermentation.  Port  wine,  when  freshly 
bottled,  still  retains  in  solution  a  considerable  quantity  of  acid  potassium  tartrate 
or  bitartrate  of  potash  (KHC4H4O6),  but  after  it  has  been  kept  some  time,  and 
become  more  strongly  alcoholic,  this  salt  is  deposited,  together  with  a  quantity 
of  the  colouring-matter,  in  the  form  of  a  crust  upon  the  side  of  the  bottle.  Thus 
a  dark,  fruity  port  becomes  tawny  and  dry  when  kept  for  a  sufficient  length  of 
time,  the  sugar  having  been  converted  into  alcohol. 

When  the  wine  contains  an  excess  of  tartaric  acid,  it  is  customary  to  add  to  it 
some  neutral  potassium  tartrate  (K2C4H406),  which  precipitates  the  acid  in  the 
form  of  bitartrate. 

The  preparation  of  champagne  is  conducted  with  the  greatest  care.  The  juice 
or  must  is  carefully  separated  from  the  marc  or  husks,  and  is  often  mixed  with 
I  per  cent,  of  brandy  before  fermentation.  After  about  two  months  the  wine  is 
drawn  off  into  another  cask,  and  clarified  with  isinglass  dissolved  in  white  wine, 
and  added  in  the  proportion  of  about  half  an  ounce  1040  gallons.  This  combines 
with  the  tannin  to  form  an  insoluble  precipitate,  which  carries  with  it  any  im- 
purities floating  in  the  wine.  After  another  interval  of  two  months,  the  wine  is 
again  drawn  off,  and  a  second  clarification  occurs  ;  and  in  two  months  more 
the  wine  is  drawn  off  into  bottles  containing  a  small  quantity  of  pure  sugar-candy 
dissolved  in  white  wine.  The  bottles,  having  been  securely  corked  and  wired, 
are  laid  down  upon  their  sides  for  eight  or  ten  months,  during  which  time  the 
fermentation  of  the  newly  added  sugar  happens,  and  the  carbonic  acid  pro- 
duced dissolves  in  the  wine,  whilst  a  quantity  of  yeast  is  separated.  In  order  to 
render  the  wine  perfectly  clear,  the  bottle  is  left  for  about  three  weeks  in  such  a 
position  that  the  deposit  may  subside  into  the  neck  against  the  cork,  which  is 
then  unwired  so  that  the  pressure  of  the  accumulated  carbonic  acid  gas  may  force 
it  out  together  with  the  deposit  ;  the  bottle,  having  been  rapidly  tilled  up  with 
white  wine,  is  again  corked,  wired,  covered  with  tinfoil,  and  sent  into  the  market. 
Pink  champagne  is  prepared  from  the  must  which  is  squeezed  out  of  the  marc 
after  it  has  cea&ed  to  run  freely,  and  contains  a  little  of  the  colouring-matter  of 
the  husk.  The  colour  is  also  sometimes  imparted  by  adding  a  little  tincture  of 
litmus. 

The  proportion  of  alcohol  in  wines  varies  greatly,  as  will  be  seen  from  the 
following  statement  of  the  weight  of  alcohol  in  100  parts  of  the  wine  :— 


8o8  SPIEITS. 


Port  .  .  .  .  15  to  17 
Sherry  .  .  .  14  to  16 
Champagne  .  .  11.5 


Claret   .         .         .         .        8  to  9 
Eudesheimer        .         .         7  to  8.5 


Sherry  contains  from  I  to  5  per  cent,  of  sugar,  port  from  3  to  7  per  cent.,  and 
Tokay  17  per  cent.  ;  in  the  last  case  the  sugar  is  increased  by  adding  some  of  the 
must,  concentrated  by  evaporation,  to  the  wine,  previously  to  bottling. 

The  bouquet  or  fragrance  of  wine  is  due  to  the  presence  of  certain  fragrant 
ethers  (ethereal  salts),  especially  of  oenanthic,  pelargonic  and  acetic  ether,  formed 
during  the  fermentation  or  during  the  subsequent  storing  of  the  wine.  It  is  to 
the  increased  quantity  of  such  fragrant  ether  that  the  superior  bouquet  of  many 
old  wines  is  due. 

Distilled  spirits. — The  varieties  of  ardent  spirits  are  obtained  from  fermented 
liquids  by  distillation,  so  that  they  consist  essentially  of  alcohol  more  or  less 
diluted  with  water,  and  flavoured  either  with  some  of  the  volatile  products  of  the 
fermentation,  or  with  some  essential  oil  added  for  the  purpose. 

Brandy  is  distilled  from  wine,  and  coloured  to  the  required  extent  with  burnt 
sugar  (caramel).  Its  flavour  is  due  chiefly  to  the  presence  of  cenanthic  ether  de- 
rived from  the  wine.  The  colour  of  genuine  pale  brandy  is  due  to  its  having  re- 
mained so  long  in  the  cask  as  to  have  dissolved  a  portion  of  brown  colouring- 
matter  from  the  wood,  and  is  therefore  an  indication  of  its  age.  Hence  arose  the 
custom  of  adding  caramel,  and  sometimes  infusion  of  tea,  to  impart  the  colour 
and  astringency  due  to  the  tannin  dissolved  from  the  wood  by  old  brandy. 

Whiskey  is  distilled  from  fermented  malt  which  has  been  dried  over  a  peat  fire, 
to  which  the  characteristic  smoky  flavour  is  due. 

Gin  is  also  prepared  from  fermented  malt  or  other  grain,  and  is  flavoured  with 
the  essential  oil  of  juniper,  derived  from  juniper  berries  added  during  the  distil- 
lation. 

Rum  is  distilled  from  fermented  molasses,  and  a.ppears  to  owe  its  flavour  to  the 
presence  of  butyric  ether,  or  of  some  similar  compound. 

Arrack  is  the  spirit  obtained  from  fermented  rice. 

Kirschwasser  and  maraschino  are  distilled  from  cherries  and  their  stones,  which 
have  been  crushed  and  fermented. 

Some  varieties  of  British  brandy  and  whiskey  are  distilled  from  fermented 
potatoes,  or  from  a  mixture  of  potatoes  and  grain,  when  there  distils  over,  together 
with  ordinary  alcohol,  especially  towards  the  end  of  the  distillation,  another  spirit 
belonging  to  the  same  class,  but  distinguished  from  alcohol  by  its  nauseous  and 
irritating  odour.  This  substance,  which  is  known  as  potato-spirit,  amylic  alcohol, 
or  fusel  oil  (C5H120),  also  occurs,  though  in  very  minute  quantity,  in  genuine  wine 
brandy.  The  manufacturers  of  spirit  from  grain  and  potatoes  remove  a  consider- 
able part  of  this  disagreeable  and  unwholesome  substance  by  leaving  the  spirit 
for  some  time  in  contact  with  wood-charcoal. 

BREAD. 

608.  The  chemistry  of  fermentation  is  intimately  connected  with  the  ordinary 
process  of  bread-making.  It  will  be  remembered  that  wheaten  flour  (p.  803) 
consists,  essentially,  of  starch  and  gluten,  with  a  little  dextrin  and  sugar.  On 
mixing  the  flour  with  a  little  water,  it  yields  a  dough,  the  tenacity  of  which  is 
due  to  the  gluten  present  in  the  flour.  If  this  dough  be  tied  up  in  a  piece  of 
fine  muslin,  and  kneaded  under  a  stream  of  water,  the  starch  will  be  suspended 
in  the  water,  and  will  pass  through  the  muslin,  whilst  the  gluten  will  remain 
as  a  very  tough  elastic  mass,  which  speedily  putrefies  if  exposed  to  the  air  in 
a  moist  state,  and  dries  up  to  a  brittle  horny  mass  at  the  temperature  of  boiling 
water. 

On  analysis,  gluten  is  found  to  contain  carbon,  hydrogen,  nitrogen,  and  oxygen, 
in  proportions  which  may  be  represented  by  the  empirical  formula  Co4H40N607, 
though  it  cannot  be  regarded  as  a  single  independent  substance,  but  as  a  mixture 
of  three  substances  very  closely  allied  in  composition. 

When  gluten  is  boiled  with  alcohol,  one  portion  refuses  to  dissolve,  and  has 
been  named  vegetable  fibrin,  from  its  resemblance  to  the  substance  forming  the 
muscles  of  animals.  When  the  solution  in  alcohol  is  allowed  to  cool,  it  deposits 
a  white  flocculent  matter,  very  similar  to  the  casein  which  composes  the  curd  of 
milk.  On  adding  water  to  the  cold  alcoholic  solution,  a  third  substance 


BREAD-MAKING.  809 

(tjlutin)  is  separated,  which  much  resembles  the  albumin  found  so  abundantly  in 
the  blood. 

The  presence  in  gluten  of  three  substances,  similar  to  the  three  principal 
components  of  the  animal  body,  leads  us  to  form  a  high  opinion  of  its  value  as  a 
nutritive  compound.  But  gluten  itself,  separated  from  the  flour  by  the  process 
above  described,  would  be  found  very  difficult  of  digestion,  on  account  of  its 
resistance  to  the  solvent  action  of  the  fluids  in  the  stomach  ;  indeed,  the  dough 
composed  of  flour  and  water  is  proverbially  indigestible  even  when  baked.  In 
order  to  make  it  fit  for  food,  it  must  be  rendered  spongy  or  porous,  so  as  to 
expose  a  larger  surface  to  the  action  of  the  digestive  fluids  of  the  body  ;  the  most 
direct  method  of  effecting 'this  is  the  one  adopted  in  the  manufacture  of  the 
aerated  bread,  and  consists  in  mixing  the  flour  with  water  which  has  been  highly 
charged,  under  pressure,  with  carbonic  acid  gas;  the  mixing  having  been  effected 
in  a  strong  closed  iron  vessel,  an  aperture  in  the  lower  part  of  this  is  opened, 
when  the  pressure  of  the  accumulated  gas  forces  the  dough  out  into  the  air,  and 
the  gas  which  has  been  imprisoned  in  the  dough  expands,  conferring  great 
porosity  and  sponginess  upon  the  mass  in  its  attempt  to  escape.  In  another 
process  for  preparing  unfermented  bread,  the  flour  is  mixed  with  a  little  bicar- 
bonate of  soda,  and  is  then  made  into  a  dough  with  water  acidified  with 
hydrochloric  acid  ;  the  latter,  decomposing  the  bicarbonate  of  soda,  liberates 
carbonic  acid  gas,  which  renders  the  bread  porous.  The  sodium  chloride  formed 
at  the  same  time  remains  in  the  bread.  In  the  preparation  of  cakes  and  pastry, 
the  same  object  is  sometimes  attained  by  adding  carbonate  of  ammonia  to  the 
dough  ;  when  heat  is  applied  in  the  baking,  the  salt  is  converted  into  vapour 
which  distends  the  dough. 

In  the  common  process  of  bread-making,  however,  the  carbonic  acid  gas 
destined  to  confer  sponginess  upon  the  dough  is  evolved  by  the  fermentation  of 
the  sugar  contained  in  the  flour  ;  the  latter  having  been  kneaded  with  the  proper 
proportion  (usually  about  half  its  weight)  of  water,  a  little  yeast  and  salt  are 
added,  and  the  mixture  is  allowed  to  stand  at  a  temperature  of  about  70°  F.  for 
some  hours.  The  dough  swells  or  rises  considerably  in  consequence  of  the  escape 
of  carbonic  acid  gas,  the  sugar  being  decomposed  into  that  gas  and  alcohol,  as  in 
ordinary  fermentation.  The  spongy  dough  is  then  baked  in  an  oven,  heated  to 
about  500°  F.,  when  a  portion  of  the  water  and  the  whole  of  the  alcohol  are 
expelled,  the  carbonic  acid  gas  being  also  much  expanded  by  the  heat,  and  the 
porosity  of  the  bread  increased.  The  granules  of  starch  are  much  altered  by  the 
heat,  and  become  far  more  digestible.  Although  the  temperature  of  the  inside  of 
the  loaf  does  not  exceed  212°  F.,  the  outer  portion  becomes  torrefied  or  scorched 
into  crust. 

Occasionally,  instead  of  yeast,  leaven  is  employed,  in  order  to  ferment  the 
sugar,  leaven  being  dough  which  has  been  left  in  a  warm  place  until  decomposi- 
tion has  commenced. 

The  passage  of  new  into  stale  bread  does  not  depend,  as  was  formerly  supposed, 
upon  the  drying  of  the  bread  consequent  upon  its  exposure  to  air,  but  it  is  a  true 
molecular  transformation  which  occurs  equally  well  in  an  air-tight  vessel,  and 
without  any  loss  of  weight.  It  is  well  known  that  when  a  thick  slice  of  stale 
bread  is  toasted,  which  dries  it  still  further,  the  crumb  again  becomes  soft  and 
spongy  as  in  new  bread  ;  and  if  a  stale  loaf  be  again  placed  in  the  oven,  it  is 
entirely  reconverted  into  new  bread. 

Wheaten  flour  is  particularly  well  fitted  for  the  preparation  of  bread  on  accour 
of  the  great  tenacity  of  its  gluten.     Next  to  wheat  in  this  respect  stands  rye, 
whilst  the  other  cereals  contain  a  gluten  so  deficient  in  tenacity  that  it  is  impos 
sible  to  convert  them  into  good  bread. 

Barley  bread  is  close  and  heavy,  since  its  nitrogenised  matter  is  chiefly  pre 
in  the  form  of  albumin,  which  does  not  vesiculate  like  gluten  during  the  tern 
tation.     Even  in  wheaten  flour  the  tenacity  of  the  gluten  is  liable  to  variation, 
and  in  order  to  obtain  good  bread  from  a  flour  the  gluten  of  which  is 
in  this  respect,   it  is  customary  to  employ  a  minute  proportion  oi  alum,     l 
addition   being  considered   unwholesome   by  some  persons,  it  would 
to   substitute    lime-water,  which  has  been  found   by  Liebig  to  have  a  si 
effect.     Sulphate  of  copper  improves  in  a  very  striking  manner  the  c 
the  bread  prepared  from  inferior  flour,  but  this  salt  is  far  more  obj 
than  alum. 


8 10  COMPOSITION   OF   COFFEE. 

TEA,  COFFEE,  ETC. 

609.  A  very  remarkable  instance  of  the  application  of  chemistry  to  explain  the 
use  of  widely  different  articles  of  diet  by  different  nations,  with  a  view  to  the 
production  of  certain  analogous  effects  upon  the  system,  is  seen  in  the  case  of 
coffee,  tea,  Paraguay  tea,  and  the  kola  nut  (of  Central  Africa),  which  are  very  dis- 
similar in  their  sensible  properties,  and  afford  little  or  no  gratification  to  the 
palate,  owing  what  attractions  they  possess  chiefly  to  the  presence,  in  each,  of 
one  and  the  same  active  principle  or  alkaloid,  which  has  a  special  effect  upon  the 
animal  economy.  This  alkaloid  is  known  as  caffeine  or  theine,  and  is  associated, 
in  the  three  articles  of  diet  mentioned  above,  with  various  substances,  which  give 
rise  to  their  diversity  in  flavour. 

The  raw  coffee-berry  presents,  on  the  average,  the  following  composition  : — 

100  parts  of  Raw  Coffee  contain — 

Woody  fibre 34.0 

Water         ..........  12.0 

Fat 12.0 

Sugar  and  gum  .........  15.5 

Legumin,  or  some  allied  substance 13.0 

Caffeine 1.5 

Caffeic  acid        .........  4.0 

Mineral  substances    ........  7.0 

When  the  raw  berry  is  treated  with  hot  water,  the  infusion,  which  contains  the 
sugar  and  gum,  the  legumin,  caffeine,  and  caffeic  acid  (C9H8O4),  has  none  of  the 
peculiar  fragrance  which  distinguishes  the  ordinary  beverage,  and  is  due  to  an 
aromatic  volatile  oily  substance  termed  caffeol  (C8H10O2)  formed  during  the  roast- 
ing to  which  the  berry  is  subjected  before  use.  This  volatile  oil,  which  is  present 
in  very  minute  quantify,  is  produced  from  one  of  the  soluble  constituents  of  the 
berry  (probably  from  the  caffeic  acid),  for  if  the  infusion  of  raw  coffee  be  evapo- 
rated to  dryness,  the  residue,  when  heated,  acquires  the  characteristic  odour  of 
roasted  coffee. 

Acetic  and  palmitic  acids  are  also  found  among  the  products  of  coffee-roasting. 

The  roasting  is  effected  in  ovens  at  a  temperature  rather  below  400°  F.,  when 
the  berry  swells  greatly,  and  loses  about  |  of  its  weight,  becoming  brittle,  and 
easily  ground  to  powder.  It  also  becomes  very  much  darker  in  colour,  from  the 
conversion  of  the  greater  part  of  its  sugar  into  caramel  (p.  732),  which  imparts 
the  dark  brown  colour  to  the  infusion  of  coffee.  If  the  roasting  be  carried  too 
far,  a  very  disagreeable  flavour  is  imparted  to  the  coffee,  by  the  action  of  heat 
upon  the  legumin  and  other  nitrogenised  substances  contained  in  the  berry. 

From  ico  parts  of  the  roasted  coffee,  boiling  water  extracts  about  20  parts, 
consisting  ftf  caffeine,  caffeic  acid,  caramel,  legumin,  a  little  suspended  fatty 
matter,  fragrant  volatile  oil  (caffeone),  and  salts  of  potassium  (especially  the  phos- 
phate). The  undissolved  portion  of  the  coffee  contains,  beside  the  woody  fibre,  a 
considerable  quantity  of  nitrogenised  (and  nutritious)  matter,  and  hence  the 
custom,  in  some  countries,  of  taking  this  residue  together  with  the  infusion. 

The  constituents  of  the  leaves  of  the  tea-plant  (Thea  sinensis)  exhibit  a  general 
similarity  to  those  of  the  coffee-berry.  In  the  fresh  leaf  we  find,  in  addition  to 
the  woody  fibre,  a  large  quantity  of  a  substance  containing  nitrogen,  similar  to 
legumin,  an  astringent  acid  similar  to  tannic  acid,  a  small  quantity  of  caffeine,  and 
some  mineral  constituents. 

The  aroma  of  tea  does  not  belong  to  the  fresh  leaf,  but  is  produced,  like  that  of 
coffee,  during  the  process  of  drying  by  heat,  which  develops  a  small  quantity  of 
a  peculiar  volatile  oil,  having  powerful  stimulating  properties.  The  freshly  dried 
leaf  is  comparatively  so  rich  in  this  oil  that  it  is  not  deemed  advisable  to  use  it 
until  it  has  been  kept  for  some  time. 

Green  and  black  tea  are  the  produce  of  the  same  plant,  the  difference  being 
caused  by  the  mode  of  preparation.  For  green  tea  the  leaves  are  dried  over  a 
fire  as  soon  as  they  are  gathered,  whilst  those  intended  for  black  tea  are  allowed 
to  remain  exposed  to  the  air  in  heaps  for  several  hours,  and  are  then  rolled  with 
the  hands  and  partially  dried  over  a  fire,  these  processes  being  repeated  three  or 
four  times  to  develop  the  desired  flavour.  The  black  colour  appears  to  be  due  to 
the  action  of  the  air  upon  the  tannin  present  in  the  leaf. 


ANIMAL   SUBSTANCES.  8ll 

black  tea 


varies  from 

leaves  contain  the  greater  part  of  the  legumin  and  a  considerable 
quan  ity  of  caffeine,  which  may  be  extracted  by  boiling  them  with  water,  and 
treating  the  decoction  as  at  p.  775. 

Cocoa  and  chocolate  are  prepared  from  the  cacao-nut,  which  is  the  seed  of 
fheolroma  cacao  and  is  i  characterised  by  the  presence  of  more  than  half  of  its 
weight  (minus  the  husk)  of  a  fatty  substance  known  as  cacao-butter,  and  consist- 
ing of  olem  and  stearin,  which  does  not  become  rancid  like  the  natural  fats 
generally.  The  cacao-nut  also  contains  a  large  quantity  of  starch,  a  nitrogenis-ed 
substance  resembling  gluten,  together  with  gum,  sugar  and  t/teobroHiine,  a  feeble 
base  very  similar  to  caffeine,  but  having  the  composition  C7H8N,0,. 

ihe  seeds  are  allowed  to  ferment  in  heaps  for  a  short  time,  Which  improves 
their  flavour,  dried  in  the  sun  and  roasted  like  coffee,  which  develops  the  peculiar 
aroma  of  cocoa.  The  roasted  beans  having  been  crushed  and  winnowed  to  sepa- 
rate the  husks,  are  ground  in  warm  mills,  in  which  the  fatty  matter  melts  and 
unites  with  the  ground  beans  to  a  paste,  which  is  mixed  with  sugar  and  pressed 
into  moulds.  In  the  preparation  of  chocolate,  vanilla  and  spices  are  also  added. 

From  the  composition  of  cocoa  and  chocolate  it  is  seen  that,  when  consumed, 
as  is  usual,  in  the  form  of  a  paste,  they  would  prove  far  more  nutritious  than  mere 
infusions  of  tea  and  coffee. 

ANIMAL  CHEMISTKY. 

610.  Our  acquaintance  with  the  chemistry  of  the  substances  composing  the 
bodies  of  animals  is  still  very  limited,  although  the  attention  of  many  accom- 
plished investigators  has  been  directed  to  this  branch  of  the  science.   The  reasons 
for  this    are   to    be    found,   first,  in  the  susceptibility  to  change  exhibited  by 
animal  substances  when  removed  from  the  influence  of  life  ;  and  secondly,  in  the 
absence,  in  such  substances,  of  certain  physical  properties  by  which  we  might  be 
enabled  to  separate  them  from  other  bodies  with  which  they  are  associated,  and 
to  verify  their  purity  when  obtained  in  a  separate  state.     Two  of  the  most  im- 
portant of  these  properties  are  volatility  and  the  tendency  to  crystallise.    When  a 
substance  can  suffer  distillation  without  change,  it  will  be  remembered  that  its 
boiling-point  affords  a  criterion  of  its  purity  ;  or  if  it  be  capable  of  crystallising, 
this  may  betaken  advantage  of  in  separating  it  from  other  substances  which 
crystallise  more  or  less  easily  than  itself,  and  its  purity  may  be  ascertained  from 
the  absence  of  crystals  of  any  other  form  than  that  belonging  to  the  substance. 
But  the  greater  number  of  the  components  of  animal  frames  can  neither  be  crys- 
tallised nor  distilled,  so  that  many  of  the  analyses  which  have  been  made  of  such 
substances  differ  widely  from  each  other,  because  the  analyst  could  never  be  sure 
of  the  perfect  purity  of  his  material  ;  and  even  when  concordant  results  have 
been  obtained  as  to  the  percentage  composition  of  the  substance,  the  formula 
deduced  from  it  has  been  of  so  singular  and  exceptional  a  character  as  to  cast 
very  strong  suspicion  upon  the  purity  of  the  substance. 

Accordingly,  the  chemical  formulae  of  a  great  many  animal  substances  are  per- 
fectly unintelligible,  conveying  not  the  least  information  as  to  the  position  in 
which  the  compound  stands  with  respect  to  other  substances,  or  the  changes 
which  it  might  undergo  under  given  circumstances. 

Animal  chemistry  is,  for  the  above  reasons,  in  a  very  backward  condition,  as 
compared  with  vegetable  and  mineral  chemistry,  though  an  observation  of  the 
progress  of  research  affords  us  the  consolation,  that  a  steady  advance  is  being 
made  towards  a  generalisation  of  the  facts  which  have  been  discovered,  especially 
by  deductive  reasoning  from  those  two  other  departments  of  the  science. 

611.  Milk.—  The  chemistry  of  milk  is  well  adapted  to  introduce  the  study  o: 
animal  chemistry,  because  that  liquid  contains  representatives  of  all  the  sub- 
stances which  make  up  the  animal  frame  ;   and  it  is  on  this  account 
occupies  so  high  a  position  among  articles  of  food. 

Although,  to  the  unaided  eye,  milk  appears  to  be  a  perfectly  homogeneo' 
fluid,  the  microscope  reveals  the  presence  of  innumerable  globules  floating  in  a 
transparent  liquid,  which  is  thus  rendered  opaque.     If  milk  be  very  viol 


8l2  MILK  AND   CHEESE. 

agitated  for  several  hours,  masses  of  an  oily  fat  (butter,  p,  799)  are  separated 
f i  om  it,  and  leave  the  liquid  transparent.  This  tat  was  originally  distributed 
throughout  the  milk,  in  minute  globules,  which  were  made  to  coalesce  by  the 
violent  agitation. 

For  the  preparation  of  butter,  it  is  usual  to  allow  the  milk  to  stand  for  some 
hours,  when  a  layer  of  cream  collects  upon  the  surface,  the  proportion  of  which  is 
very  variable,  but  is  generally  about  ^  of  the  volume  of  the  milk.*  The 
skimmed  milk  retains  about  half  of  the  fatty  matter.  This  cream  contains  about 
35  per  cent,  (by  weight)  of  fat,  3  per  cent,  of  casein,  and  water.  When  the  cream 
is  churned,  the  fat  globules  are  broken,  and  the  fat  unites  into  a  semi-solid  mass  of 
butter,  from  which  the  butter-milk  containing  the  casein  may  be  separated.  If  this 
be  not  done  effectually,  the  casein  which  is  left  in  the  butter,  being  a  nitrogenised 
substance,  will  soon  begin  to  decompose,  and  will  induce  a  decomposition  in  the 
butter  (p.  799),  resulting  in  the  formation  of  certain  volatile  aoids,  which  impart 
to  ic  a  rancid  and  offensive  taste  and  odour.  To  prevent  this,  salt  is  generally 
added  to  butter  which  has  been  less  carefully  prepared  in  order  to  preserve  the 
casein  from  decomposition.  Butter-milk  contains  about  one-fourth  of  the  fatty 
matter  of  the  milk. 

Pure  butter  is  essentially  a  mixture  of  stearin,  palniitin  and  olein  with  smaller 
quantities  of  other  fats,  such  as  butyrin,  caprin,  and  caproin  (p.  799). 

Fresh  milk  is  slightly  alkaline  to  test-papers,  but  after  a  short  time  it  acquires 
an  acid  reaction  ;  and  if  it  be  then  heated,  it  coagulates  from  the  separation  of 
the  casein.  This  spontaneous  acidification  of  milk  is  caused  by  the  fermentation 
of  the  sugar  of  milk,  which  results  in  the  production  of  lactic  acid. 

If  milk  be  maintained  at  a  temperature  of  about  90°  F.,  the  fermentation  results 
in  the  production  of  alcohol  and  carbonic  acid,  for  although  milk-sugar  is  not 
fermented  like  ordinary  sugar,  by  contact  with  yeast,  it  appears,  under  the 
influence  of  the  changing  casein  at  a  favourable  temperature,  to  be  converted 
first  into  grape-sugar  (p.  726),  and  afterwards  into  alcohol  and  carbonic  acid. 
The  Tartars  prepare  an  intoxicating  liquid,  which  they  call  koumiss,  by  the  fermen- 
tation of  milk. 

When  an  acid  is  added  to  milk,  the  casein  is  separated  in  the  form  of  curd,  in 
consequence  of  the  neutralisation  of  the  soda  which  retains  it  dissolved  in  fresh 
milk,  and  this  curd  carries  with  it,  mechanically,  the  fat  globules  of  the  milk, 
leaving  a  clear  yellow  ivhey. 

In  the  preparation  of  cheese,  the  milk  is  coagulated  by  means  of  rennet,  which 
is  prepared  from  the  lining  membrane  of  a  cali's  stomach.  This  is  left  in  contact 
with  the  warm  milk  for  some  hours,  until  the  coagulation  is  completed.  The  curd 
is  collected  and  pressed  into  cheeses,  which  are  allowed  to  ripen  in  a  cool  place, 
where  they  are  occasionally  sprinkled  with  salt.  The  peculiar  flavour  which  the 
cheese  thus  acquires  is  due  to  the  decomposition  of  the  casein,  giving  rise  to  the 
production  of  certain  volatile  acids,  such  as  butyric,  valerianic,  and  caproic, 
which  have  very  powerful  and  characteristic  odours.  If  this  ripening  be  allowed 
to  proceed  very  far,  ammonia  is  developed  by  the  putrefaction  of  the  casein,  and 
in  some  cases  the  ethers  of  the  above-mentioned  acids  are  produced,  at  the  expense 
probably  of  a  little  sugar  of  milk  left  in  the  cheese,  conferring  the  peculiar  aroma 
perceptible  in  some  varieties  of  it. 

The  different  kinds  of  cheese  are  dependent  upon  the  kind  of  milk  used  in  their 
preparation,  the  richer  cheeses  being,  of  course,  obtained  from  milk  containing  a 
large  proportion  of  cream  ;  such  cheese  fuses  at  a  moderate  heat,  and  makes  good 
toasted  cheese,  whilst  that  which  contains  little  butter  never  fuses  completely, 
but  dries  and  shrivels  like  leather.  Double  Gloucester  and  Stilton  are  made  from 
a  mixture  of  new  milk  and  cream  ;  Cheddar  cheese  is  made  from  new  milk  alone  ; 
Cheshire  and  American  cheeses  from  milk  robbed  of  about  one-eighth  of  its 
cream  ;  Dutch  cheese  and  the  Skim  Dick  of  the  midland  counties,  from  skimmed 
milk. 

The  characteristic  constituents  of  milk  are  the  casein  and  milk-sugar,  but  the 
proportions  in  which  these  are  present  vary  widely  not  only  with  the  animal  from 
which  the  milk  is  obtained,  but  with  the  food  and  condition  of  the  animal.  A 
general  notion  of  their  relative  quantities,  however,  may  be  gathered  from  the 
following  table : — 

*  The  separation  of  cream  is  now  effected,  in  large  dairies,  by  means  of  a  centrifugal 
separator,  making  several  thousand  revolutions  per  minute. 


BLOOD. 


813 


Cow. 

Ass. 

Goat. 

Woman. 

Water     . 
Fat         .... 
Casein    .... 
Albumin 

87.2 
3-7 
3-0 

89.6 

1-7 

0.7 

85-7 
4-8 
3-2 

87.4 
3-8 

I.O 

Milk-sugar 
Mineral  salts  . 

4-9 
0.7 

6.0 

4-5 
0.7 

6.1 
o-3 

The   soluble   salts  present   in  milk  include  the  phosphates  and  chlorides  of 
potassium  and  sodium,  whilst  the  insoluble  salts  are  the  phosphates  of  calcium 
magnesium,  and  iron.    All  these  salts  are  in  great  request  for  the  nourishment  of 
the  animal  frame. 

The  milk  supplied  to  consumers  living  in  towns  is  subject  to  considerable 
adulteration  ;  but  in  most  cases  this  is  effected  by  simply  removing  the  cream  and 
diluting  the  skimmed  milk  with  water,  a  fraud  which  is  not  easily  detected  as 
might  be  supposed,  by  determining  the  specific  gravity  of  the  milk,  for  since 
milk  is  heavier  than  water  (1.032  sp.  gr.),  and  the  fatty  matter  composing  cream 
is  lighter  than  water,  a  certain  quantity  of  cream  might  be  removed,  and  water 
added,  without  altering  the  specific  gravity  of  the  milk. 

The  simplest  method  of  ascertaining  the  quality  of  the  milk  consists  in  setting 
it  aside  for  twenty-four  hours  in  a  tall  narrow  tube  (lactometer  or  crcumometer) 
divided  into  100  equal  parts,  and  measuring  the  proportion  of  cream  which 
separates,  this  averaging,  in  pure  milk,  from  eleven  to  thirteen  divisions.  The 
measurement  of  the  cream  is  effected  in  fifty  minutes  by  using  a  centrifugal 
separator,  in  which  the  tube  containing  the  milk  is  placed  in  a  case  attached  to  a 
centrifugal  apparatus  making  1200  revolutions  per  minute.  By  shaking  milk 
with  a  little  potash  and  ether,  the  butter  may  be  dissolved  in  the  ether  which 
rises  to  the  surface,  and  if  this  be  poured  off  and  allowed  to  evaporate,  the  weight 
of  the  butter  may  be  ascertained  ;  or  the  milk  may  be  evaporated  by  a  steam 
heat,  and  the  fat  dissolved  by  treating  the  residue  with  ether.  The  amount  of 
fat  is  sometimes  found  by  taking  the  specific  gravity  of  the  ethereal  solution, 
and  referring  to  a  table  giving  the  corresponding  quantity  of  fat.  One  thousand 
grains  of  milk  should  give,  at  least,  27  or  28  grains  of  butter.  Since,  however, 
the  milk  of  the  same  cow  gives  very  different  quantities  of  cream  at  different 
times,  it  is  difficult  to  state  confidently  that  adulteration  has  been  practised. 
The  standard  usually  adopted  by  analysts  is  25  grains  of  fat  or  butter  and  90 
grains  of  "  solids  not  fat  "  in  1000  grains  of  milk. 

612.  Blood. — The  blood,  from  which  the  various  organs  of  the  body  directly 
receive  their  nourishment,  is  the  most  important,  as  well  as  the  most  complex,  of 
the  animal  fluids.  Its  chemical  examination  is  attended  with  much  difficulty,  on 
account  of  the  rapidity  with  which  it  changes  after  removal  from  the  body  of  the 
animal. 

On  examining  freshly  drawn  blood  under  the  microscope,  it  is  observed  to  pre- 
sent some  resemblance  to  milk  in  its  physical  constitution,  consisting  of  opaque 
flattened  globules  floating  in  a  transparent  liquid ;  the  globules,  in  the  case  of 
blood,  having  a  well-marked  red  colour.  % 

In  a  few  minutes  after  the  blood  has  been  drawn,  it  begins  to  assume  a  gela- 
tinous appearance,  and  the  semi-solid  mass  thus  formed  separates  into  a  red  solid 
portion  or  clot,  which  continues  to  shrink  for  ten  or  twelve  hours,  and  a  clear 
yellow  liquid  or  serum.  It  might  be  supposed  that  this  coagulation  is  due  to  the 
cooling  of  the  blood,  but  it,  is  found  by  experiment  to  take  place  even  more 
rapidly  when  the  temperature  of  the  blood  is  raised  one  or  two  degrees  after  it 
has  been  drawn  ;  and.  on  the  other  hand,  if  it  be  artificially  cooled,  its  coagula- 
tion is  retarded.  Indeed,  the  reason  for  this  remarkable  behaviour  of  the  blood 
is  not  yet  understood. 

If  the  coagulum  or  clot  of  blood  be  cut  into  slices,  tied  m  a  cloth,  and  well 
washed  in  a  stream  of  water,  the  latter  runs  off  with  a  bright  red  colour,  and  a 
tough  yellow  filamentous  substance  is  left  upon  the  cloth  ;  this  substance  is  called 
fibrin  and  its  presence  is  the  proximate  cause  of  the  coagulation  of  the  blood, 
for  if  the  fresh  blood  be  wel)  whipped  with  a  bundle  of  twigs  or  glass  rods,  the 


8 14  FLESH. 

fibrin  will  adhere  to  them  in  yellow  strings,  and  the  defibrinated  blood  will  no 
longer  coagulate  on  standing.  If  this  blood,  from  which  the  fibrin  has  been  ex- 
tracted, be  mixed  with  a  large  quantity  of  a  saline  solution  (for  example,  8  times 
its  bulk  of  a  saturated  solution  of  sodium  sulphate),  and  allowed  to  stand,  the 
red  globules  subside  to  the  bottom  of  the  vessel. 

These  globules  are  minute  bags  of  red  fluid,  enclosed  in  a  very  thin  membrane 
or  cell-wall,  and  if  water  were  mixed  with  the  defibrinated  blood,  since  its  specific 
gravity  is  lower  than  that  of  the  fluid  in  the  globules,  it  would  pass  through  the 
membrane  (by  osmosis},  and  so  swell  the  latter  as  to  break  it  and  disperse  the 
contents  through  the  liquid. 

The  red  fluid  contained  in  these  blood  globules  consists  of  an  aqueous  solution, 
containing  as  its  principal  constituents  a  substance  known  as  globulin,  which 
very  nearly  resembles  albumin,  and  the  peculiar  colouring-matter  of  the  blood, 
which  is  called  hee  matin. 

Beside  these,  the  globules  contain  a  little  fatty  matter  and  certain  mineral  con- 
stituents, especially  the  iron  (which  is  associated  in  some  unknown  form  with  the 
colouring-matter),  the  chlorides  of  sodium  and  potassium,  and  the  phosphates  of 
potassium,  sodium,  calcium,  and  magnesium. 

Though  the  quantities  of  these  constituents  are  not  invariable,  even  in  the 
same  individual,  the  following  numbers  may  be  taken  as  representing  the  average 
composition  of  these  globules  : — 

1000  parts  of  Blood  Globules  contain — 


Water       ....     688.00 
Globulin  .  .     282.22 


Hsematin .         .         .         .       16.75 
Fat 2.31 

The  Mineral  Substances  consist  of 


Organic  substances  of  un-\         , 

known  nature .         .       / 
Mineral  substances  *  .  8. 12 


Potassium         .         .         .       3.328 
Phosphoric  oxide  (P2O5)  .       1.134 


Sodium     ....       1.052 
Chlorine  .  1.686 


Oxygen      ....     0.667 
Calcium  phosphate    .         .     0.114 


Magnesium  phosphate       .     0.073 
Sulphuric  oxide  (S03)        .     0.066 

The  liquid  in  which  the  blood  globules  float  is  an  alkaline  solution  containing 
albumin,  fibrin  and  saline  matters  in  about  the  proportions  here  indicated. 

IOQQ  parts  of  Liquor  Sangulnis  contain — 


Water       ....  902.90 

Albumin   ....  78.84 

Fibrin       .         .         .         .  4.05 

Fat 1.72 


Organic  substances  of  un-\ 

known  nature          .       j      3-94 
Mineral  substances     .         -8.55 


The  Mineral  Substances  comist  of — 


Phosphoric  oxide  (P2O5)  .  0.191 

Sulphuric  oxide  (S03)  .  0.115 

Calcium  phosphate    .  .  0.311 

Magnesium  phosphate  .  0.222 


Sodium  .  .  .  .3.341 
Chlorine  ....  3.644 
Potassium  .  .  .  0.323 
Oxygen  ....  0.403 

The  alkaline  character  of  this  liquid  appears  to  be  due  to  the  presence  of  car- 
bonate and  phosphate  of  sodium. 

613.  Flesh. — The  fibrin  composing  muscular  flesh  contains  about  three-fourths 
of  its  weight  of  water,  a  part  of  which  is  due  to  the  blood  contained  in  the  vessels 
traversing  it,  and  another  part  to  the  juice  of  flesh,  which  may  be  squeezed  out  of 
the  chopped  flesh.  In  this  juice  of  flesh  there  are  certain  substances  which 
appear  to  play  a  very  important  part  in  nutrition.  The  liquid  is  distinctly  acid, 
which  is  remarkable  when  the  alkaline  character  of  the  blood  is  considered,  and 
contains  phosphoric,  lactic,  and  butyric  acid,  together  with  creatine  (p.  676), 
inosite  (p.  716),  and  saline  matters.  By  soaking  minced  flesh  in  cold  water  and 
well  squeezing  it  in  a  cloth,  a  red  fluid  is  obtained  containing  the  juice  of  flesh 
mixed  with  a  little  blood. 

The  saline  constituents  of  the  juice  of  flesh  are  chiefly  phosphates  of  potassium 
and  magnesium,  with  a  little  chloride  of  sodium.  It  is  worthy  of  notice  that 
potassium  is  the  predominant  alkali-metal  in  the  juice  of  flesh,  whilst  sodium 
predominates  in  the  blood,  especially  in  the  serum. 

*  Exclusive  of  the  iron  wbicli  is  associated  with  the  hasmatiii. 


URINE.  815 

According  to  Liebig,  the  acidity  of  the  juice  of  flesh  is  chiefly  due  to  the  acid 
phosphate  of  potassium,  KH2P04,  whilst  the  alkalinity  of  the  blood  is  caused  by 
sodium  phosphate,  Na2HPO4  ;  and  it  has  been  suggested  that  the  electric  currents 
which  have  been  traced  in  the  muscular  fibres  are  due  to  the  mutual  action 
between  the  acid  juice  of  flesh  and  the  alkaline  blood,  separated  only  by  thin 
membranes  from  each  other,  and  from  the  substance  of  the  muscles  and  nerves. 

The  average  composition  of  flesh  may  be  represented  as  follows  :  _ 

Water    ........     78 

Fibrin,  vessels,  nerves,  cells,  &c.    .         .         .17 

Albumin        .         .         .         .         .         .        .2.5 

Other  constituents  of  the  juice  of  flesh          .       2.5 

100.0 

Lieblcfs  extract  of  meat  is  prepared  by  exhausting  all  the  soluble  matters  from 
the  flesh  with  cold  water,  separating  the  albumin  by  coagulation  and  evaporating 
the  liquid  at  a  steam  heat  to  a  soft  extract.  It  contains  about  half  its  weight  of 
water,  40  per  cent,  of  the  organic  constituents  of  the  juice  of  flesh  (albumin 
excepted),  and  10  per  cent,  of  saline  matter. 

Cooking  of  meat.  —  A  knowledge  of  the  composition  of  the  juice  of  flesh  explains 
the  practice  adopted,  in  boiling  meat,  of  immersing  it  at  once  in  boiling  water, 
instead  of  placing  it  in  cold  water,  which  is  afterwards  raised  to  the  boiling- 
point.  In  the  latter  case,  the  water  would  soak  into  the  meat,  and  remove  the 
important  nutritive  matter  contained  in  the  juice  ;  whilst,  in  the  former,  the 
albumin  in  the  external  layer  of  flesh  is  at  once  coagulated,  and  the  water  is 
prevented  from  penetrating  to  the  interior.  In  making  soup,  of  course,  the 
opposite  method  should  be  followed,  the  meat  being  placed  in  cold  water,  the 
temperature  of  which  is  gradually  raised,  so  that  all  the  juice  of  flesh  may  be 
extracted  and  the  muscular  fibre  and  vessels  alone  left. 

The  object  to  be  attained  in  the  preparation  of  beef-tea  is  the  extraction  of  the 
whole  of  the  soluble  matters  from  the  flesh,  to  effect  which  the  meat  should  be 
minced  as  finely  as  possible,  soaked  for  a  short  time  in  an  equal  weight  of  cold 
water,  and  slowly  raised  to  the  boiling-point,  at  which  it  is  maintained  for  a  few 
minutes.  The  liquid  strained  from  the  residual  fibrin  contains  all  the  constituents 
of  the  juice  except  the  albumin,  which  has  been  coagulated. 

When  meat  is  roasted,  the  internal  portions  do  not  generally  attain  a  suffi- 
ciently high  temperature  to  coagulate  the  albumin  of  the  juice,  but  the  outside 
is  heated  far  above  212°  F.  ;  so  that  the  meat  becomes  impregnated  to  a  greater 
extent  with  the  melted  fat,  and  some  of  the  constituents  of  the  juice  in  this  part 
suffer  a  change,  which  gives  rise  to  the  peculiar  flavour  of  roast  meat.  The  brown 
sapid  substance  thus  produced  has  been  called  osmazomc,  but  nothing  is  really 
known  of  its  true  nature.  In  salting  meat,  for  the  purpose  of  preserving  it,  a 
great  deal  of  the  juice  of  flesh  oozes  out,  and  a  proportionate  loss  of  nutritive 
matter  is  sustained. 

614.  Urine  always  contains  a  large  proportion  of  alkaline  and  earthy  salts, 
especially  of  sodium  chloride,  phosphate  and  sulphate  of  potassium,  and  phos- 
phates of  calcium,  magnesium,  and  ammonium. 

The  average  composition  of  human  urine  may  be  thus  stated  :— 


Water     ,  ....... 

Urea       ..........          J4-23 

Uric  acid       .........  °-37 

Mucus    .......       .•        •        • 

Hippuric  acid,  creatinine,  ammonia,  colouring-matter.  \         I$JQ$ 

and  unknown  organic  matters       .        .        •        •) 
Chloride  of  sodium        ....... 

Phosphoric  oxide  (P205)        ...... 

Potash    .......... 

Sulphuric  oxide  (S03)    ......  £JJ 

Lime       ....••••• 

:.:.:••;    :    :    : 

999-94 


8l6  NOURISHMENT  OF  PLANTS. 

CHEMISTEY  OF  VEGETATION. 

615.  Comparatively  few  of  the  elements  enter  into  the  composition  of  plants^ 
and  of  those  that  do  so  only  ten  are,  according  to  our  present  knowledge,  abso- 
lutely essentialto  the  growth  of  the  jplants  ;  these  are  carbon,  hydr&gen,  oxygen, 
nitrogen,  sulpftur.  phospiiorus,  potassium,  calcrum,  magnesium,  and  for  plants 
containing  chlorophyll,  iron.  At  the  same  time  sodfum,  silicon,  and  chlorine 
are  invariably  present,  while  manganese,  fluorine,  and  minute  quantities  of  other 
elements  are  generally  to  be  found. 

The  carbon,  hydrogen,  and  oxygen  occur  in  all  the  organic  constituents  of  the 
plant.  The  nitrogen  occurs  in  the  albuminoids,  together  with  a  small  quantity 
of  the  sulphur  ;  also  in  the  amides,  alkaloids,  and  nitrates.  The  metals  occur  as 
phosphates,  nitrates,  sulphates,  and  vegetable  salts — chiefly  oxalates,  malates, 
tartrates,  and  citrates. 

The  carbon  is  derived  by  green  plants  from  the  carbon  dioxide  of  the  air,  while 
plants  destitute  of  chlorophyll  are  capable  of  deriving  carbon  from  organic  matter 
in  the  soil.  The  hydrogen  and  oxygen  are  derived  from  the  water  of  the  soil. 

The  source  from  which  the  plant  derives  its  nitrogen  has  long  been  a  subject  of 
discussion.  This  element,  as  it  exists  uncombined  in  the  air,  is  not  absorbed  by 
the  plant  to  any  appreciable  extent,  if  at  all ;  and  the' small  quantities  of  ammonia 
and  nitric  acid  in  the  air  are  quite  inadequate  to  furnish  the  necessary  supply  for 
any  extensive  growth.  The  conclusion  is  that  the  nitrogen  must  be  derived  from 
the  soil,  and  the  beneficial  effect  of  manuring  with  nitrates  and  ammonium  salts 
supports  this  view.  That  nitrates  are  absorbed  in  solution  by  plant  roots  is 
certain,  and  nitrates  are  always  fairly  abundant  in  a  fertile  soil  during  the  growing 
season,  being  produced  by  the  nitrification  (p.  87)  of  the  ammonia  derived  from 
decaying  vegetable  matter,  and  in  smaller  degree  from  the  rainfall ;  it  appears 
probable  also  that  ammonia  and  amide-like  substances  in  the  soil  can  be  absorbed 
to  some  extent  directly,  without  previous  nitrification.  The  old  observation  that 
the  nitrates  in  the  soil  will  not  account  for  all  the  nitrogen  in  a  leguminous  crop, 
and  that  such  crops  are  not  benefited  by  the  application  of  nitrogenous  manures 
to  the  same  extent  as  are  other  crops,  points  to  the  conclusion  that  legumes  have 
some  exceptional  source  of  nitrogen  at  their  disposal.  The  discovery  on  the  roots 
of  these  plants  of  tubercules  containing  organisms  which  appear  to  be  in  symbiosis 
(crtiv,  together  with  ;  /St'os,  life)  with  the  plant,  and  to  transform  nitrogen,  either  from 
organic  matter,  or  from  the  atmosphere,  into  nitrogenous  compounds  which  can 
be  absorbed  by  the  roots,  and  the  discovery  that  inoculation  with  some  soil  which 
is  productive  for  legumes  will  render  fertile  one  previously  barren  for  such  growth, 
are  recent  results  of  this  interesting  and  important  inquiry. 

The  sulphur  and  phosphorus  are  derived  by  the  plant  from  sulphates  and 
phosphates  in  the  soil,  while  the  other  constituent  elements  are  also  derived  from 
the  mineral  matter  of  the  soil. 

It  is  thus  seen  that  the  plant  takes  up  its  elements  in  a  highly  oxidised  con- 
dition, and  that  the  chemical  tendency  of  vegetables  is  to  reduce  to  a  lower  state 
of  oxidation  the  substances  presented  in  their  food,  whilst  animals  exhibit  a 
reciprocal  tendency  to  oxidise  the  materials  on  which  they  feed. 

Soil  is  disintegrated  rock,  so  that  its  composition  will  depend  largely  on  the 
nature  of  the  rock.  To  be  fertile  it  must  contain  all  the  elements  essential  for 
plant  growth  (save  carbon)  in  a  condition  available  for  absorption  by  the  roots. 
Rarely  more  than  i  per  cent,  of  the  soil  is  in  such  a  condition,  the  rest  serving 
to  support  the  plant  mechanically,  and  becoming  slowly  available  by  the  process 
of  weathering  (p.  128),  which  is  much  aided  by  ploughing,  draining,  and  the 
various  other  operations  of  the  farm. 

The  chief  constituents  of  a  soil  are  sand,  clay,  carbonate  of  lime,  and  humus. 
The  proportion  which  these  bear  to  each  other  greatly  influences  the  physical 
properties  of  the  soil,  and  consequently  its  fertility  and  cost  of  working.  It  is  also 
closely  connected  with  the  absorptive  \)ower  of  the  soil,  or  its  capability  of  fixing 
fertilising  matter ;  thus,  humus  retains  the  all-important  ammonia,  while  the 
hydrated  silicates,  including  clay,  fix  potash  and  phosphoric  acid,  from  any  solu- 
tion containing  these  which  may  filter  through  the  soil. 

The  first  three  of  the  above  constituents  need  no  comment  here.  Humus  is  the 
name  applied  to  the  organic  matter  in  the  soil ;  it  consists  of  the  brown  and  black 
substances  resulting  from  the  decay  of  previous  vegetation.  Sodium  carbonate 
dissolves  this  brown  humus  to  a  brown  solution,  from  which  an  acid  precipitates 


FARM- YARD   MANURE.  817 

a  brown  substance  having  a  faintly  acid  reaction,  and  therefore  termed  w////,V 
acid  (tt&MM,  an  elm)  ;  according  to  some,  the  humus  contains  a  portion  insoluble 
in  sodium  carbonate,  to  which  the  name  ulmin  has  been  given  Black  humus 
yields  by  the  same  treatment  humic  acid  and  hnmln.  Two  other  acids  crenic  and 
apocrewf,  the  former  convertible  into  the  latter  by  oxidation,  have  also  been 
obtained  from  the  humus,  and  these  have  been  found  in  mineral  waters  All 
these  substances  are  of  ill-ascertained  composition. 

The  humus  is  the  store  of  nitrogenous  matter,  which,  by  slow  nitrification 
becomes  available  for  the  plant. 

When  a  soil  comes  under  tillage,  the  crops  raised  upon  it  are  consumed  by 
animals,  and  often  removed  to  a  distance,  so  that  the  mineral  food  and  nitrogen 
contained  in  the  soil  are  by  degrees  exhausted,  and  unless  these  are  restored  the 
soil  becomes  barren.  To  restore  its  fertility  is  the  object  of  manuring,  which  con- 
sists in  adding  to  the  soil  substances  which  shall  serve  directly  as  plant-food,  or 
shall  so  modify  by  chemical  action  some  material  already  present  in  the  soil  as 
to  convert  it  into  an  available  form.  These  two  objects  are  often  attained  by  one 
and  the  same  manure. 

Manures  either  supply  all  the  necessary  plant-foods—when  they  are  termed 
general  manures— or  they  supply  some  food  which  is  especially  wanting  to  enable 
the  plant  to  nourish,  and  make  use  of  food  already  existing  in  the  soil,  or  perhaps 
to  excite  rapid  growth  at  a  critical  period  of  its  existence,  when  it  is  most  sensitive 
to  attacks  of  insects  or  vicissitudes  of  weather.  Such  are  termed  special  manures. 

Nitrogen,  phosphorus,  and  potassium  are  the  plant  foods  which  are  most  rapidly 
exhausted  and  most  generally  needed.  A  general  manure  is  accordingly  valued 
by  its  content  of  these  three  elements,  regard  being  had  to  the  condition  in 
which  they  exist ;  for,  if  they  are  soluble,  they  will  be  more  rapidly  and  thoroughly 
distributed  through  the  soil,  thus  becoming  immediately  available  as  food  ;  if,  on 
the  other  hand,  they  are  in  a  condition  not  so  available,  the  immediate  benefit  of 
the  manure  will  be  smaller,  but  it  will  last  over  a  longer  period,  the  constituents 
becoming  soluble  in  the  course  of  time. 

The  various  manures  can  receive  but  short  notice  here.  Of  general  manures 
the  most  valuable  is  farm-yard  manure,  consisting  of  the  solid  and  liquid  excre- 
ment of  the  farm  stock,  together  with  the  litter  used  to  absorb  the  liquid.  Its 
value  will  be  controlled  by  the  quality  and  quantity  of  this  litter  ;  by  the  nature 
of  the  animals  ;  the  richness  of  their  food  in  N,  P205,  and  K20 ;  whether  they  are  in 
active  work,  in  which  case  as  much  N,  P2O5  and  K20  is  voided  as  is  consumed  in 
the  food  ;  or  being  fattened,  milked,  or  shorn,  in  which  case  some  of  the  N,  P205, 
and  K2O  will  be  stored  in  the  carcase  or  removed  as  milk  or  wool.  But  its  value 
is  most  affected  by  its  after-treatment.  If  it  be  stacked,  exposed  to  rain,  and 
the  drainings  not  preserved,  much  soluble  N,  P205,  and  K20  will  be  lost,  which 
is  not  the  case  if  it  be  spread  directly  on  the  land.  Fresh  farmyard  manure  in  a 
heap  rapidly  becomes  rotten,  fermenting  and  losing  much  carbon  as  carbon  dioxide 
and  marsh  gas,  but  very  little  nitrogen.  It  thus  becomes  more  valuable,  as  it  is 
less  weighty  when  rotten  and  contains  more  of  its  N  and  P205  in  a  soluble  con- 
dition. ^Rotten  manure  contains  on  an  average  70  per  cent.  H20,  2.7  per  cent. 
true  ash,  0.6  per  cent.  N,  0.3  per  cent.  P2O5,  and  0.5  per  cent.  KoO. 

Seaweed  is  allowed  to  have  a  manurial  value  approaching  that  of  farmyard 
manure. 

Guano  (Peruvian),  the  dried  excrement  of  sea-birds,  contains,  when  it  has  been 
deposited  in  sheltered  places,  ammonium  urate  and  other  ammonium  salts  and 
nitrogenous  matter  (equivalent  in  all  to  12  per  cent.  N)  ;  and  the  presence  of 
calcium  phosphate  (26  per  cent.)  and  small  quantities  of  potassium  salts  render 
this  variety  a  valuable  general  manure.  If,  however,  the  guano  has  been  deposited 
in  exposed  places  (Mejillones),  its  nitrogen  has  been  lost,  and  it  becomes  a  special 
phospJiMtio  manure,  containing  about  70  per  cent,  of  calcium  phosphate. 

Animal  refuses  of  various  kinds  form  general  manures,  valuable  chiefly  for  their 
N,  and  vegetable  matters  will  of  course  restore  to  the  soil  those  mineral  consti- 
tuents which  they  have  previously  removed.  Rape  cake,  the  compressed  refuse  of 
the  colza-oil  factory,  is  a  general  manure  of  this  kind,  (,'reen  iminitnn'j  has  a 
special  value,  as  it  consists  in  keeping  covered  with  vegetation  soil  which  would 
otherwise  be  left  fallow  (and  lose  by  drainage),  and  then  ploughing-in  the  crop  ; 
as  this  is  generally  a  deep-rooted  one,  mineral  constituents  and  nitrogen  are 
thus  brought  up  from  the  subsoil  and  left  in  a  quickly  available  form  in  the  surface 
soil  for  the  use  of  shallower-rooted  crops. 

3  F 


8l8  CHEMICAL  MANURES. 

Special  manures  supply  either  nitrogen,  phosphorus,  potassium,  or  calcium,  and 
less  frequently  sulphur,  chlorine,  and  magnesium. 

The  term  nitrates  as  applied  to  manure  usually  implies  sodium  nitrate,  the 
potassium  salt  being  too  expensive  for  use.  Sodium  nitrate  supplies  nitrogen  in  a 
very  soluble,  and  therefore  readily  available,  form,  stimulating  rapid  growth. 
Its  solubility  renders  it  less  effective  in  wet  weather,  as  it  is  then  washed  through 
the  soil;  for  the  same  reason,  it  is  best  applied  as  a  top-dressing  after  growth  has 
begun.  As  the  sodium  is  not  taken  up  by  the  crop,  it  partly  remains  in  the  soil 
as  sodium  carbonate  and  silicate,  and  tends  to  render  it  stiff .  Ammojiium  sulphate 
also  supplies  nitrogen,  but  is  less  rapid  in  its  action,  and  better  fitted  for  wet 
weather  than  is  nitrate.  The  ammonia  rapidly  undergoes  nitrification,  and  the 
nitric  acid  formed  combines  with  the  lime  in  the  soil.  The  sulphuric  acid,  not 
being  used  by  the  plant,  also  combines  with  the  lime.  Both  these  lime  salts  tend 
to  get  washed  away,  so  that  this  manure  is  liable  to  remove  lime  from  the  soil. 
Diluted  gas  liquor  is  sometimes  used  as  a  manure  on  account  of  its  ammonia. 
Soot  owes  its  chief  value  to  its  i  or  2  per  cent,  of  ammonia. 

Bones  are  of  value  for  their  phosphates  (50  per  cent.)  and  their  nitrogen  (3.5 
percent.);  they  are  slow  in  action,  and  last  long.  Bone  ash  and  mineral  phos- 
phates (coprolites,  &c.),  all  of  which  contain  no  nitrogen,  are  occasionally  used 
finely  ground,  but  are  generally  employed  for  making  superphosphate  (p.  334). 
This  most  important  manure  is  valued  by  the  amount  of  monocalcium  phosphate 
which  it  contains,  though  the  manufacturer  insists  on  this  being  calculated  into 
tricalcium  phosphate  and  then  called  ' '  soluble  phosphate  "  or  "  phosphate  rendered 
soluble."  For  this  soluble  constituent,  which  should  average  18  to  20  per  cent,  in 
a  mineral  superphosphate,  is  rapidly  spread  through  the  soil  by  the  rain,  and  is 
there  reconverted  into  phosphates  which  are  insoluble  in  pure  water,  but  are  very 
finely  divided,  and  thus  easily  soluble  in  carbonic  acid,  and  available  as  food. 
Dissolved  hones  have  been  partially  converted  into  superphosphate  by  treatment 
with  sulphuric  acid,  and  of  course  contain  nitrogen.  Basic  slay,  or  Thomas  or 
Thomas- Gilchrist  slag  (p.  410),  is  now  employed  as  a  manure  on  account  of  its 
phosphorus  ;  it  must  be  used  in  a  very  fine  state  of  division.  It  contains  14  to 
19  per  cent,  of  P2O5,  chiefly  as  the  compound  4CaO.P.205,  which  is  more  soluble  in 
saline  solutions  than  is  3CaO.P2O5. 

Potassium  is  supplied  in  kainit  (p.  311),  which  contains  13  to  14  per  cent.  K20. 
Other  sources  of  this  element  are  carnallite,  wood  ashes,  beet-sugar  refuse,  and  the 
suint  or  yolli  of  raw  wool. 

Lime  as  used  by  the  agriculturist  includes  chalk,  caustic  lime,  and  slaked 
lime.  It  is  more  often  employed  for  attacking  the  constituents  of  the  soil 
than  as  a  direct  plant-food,  there  generally  being  enough  in  the  soil  for  that 
purpose.  Lime  neutralises  organic  acids  in  the  soil,  sweetening  it,  and  hastens 
the  decay  of  organic  matter,  rendering  the  N  available  and  furnishing  CO.,  as  a 
solvent  for  minerals.  Its  action  on  minerals  is  specially  serviceable  for  decom- 
posing injurious  iron  compounds  and  the  felspars,  rendering  the  K2O  of  these 
latter  available.  Some  limestones,  and  all  shells,  contain  small  quantities  of 
P2O5,  itself  valuable. 

Common  salt  is  chiefly  of  value  for  its  chemical  action  on  the  soil  and  for  de- 
stroying weeds  and  pests.  Sodium  chloride  is  always  brought  down  in  small 
quantity  from  the  air  by  the  rain. 

Gypsum  and  magnesium  sulphate  are.  occasionally  used  for  a  supply  of  sulphur. 

6 1 6.  In  some  cases  fertility  is  restored  to  an  apparently  exhausted  soil,  with- 
out the  addition  of  manure,  by  allowing  it  to  lie  fallow  for  a  time,  so  that,  under 
the  influence  of  air,  moisture,  and  frost,  such  chemical  changes  may  occur  in  it 
as  will  again  replenish  it  with  food  available  for  the  crops.  It  is  not  even 
necessary  in  all  cases  that  the  soil  should  be  altogether  released  from  cultivation  ; 
for,  even  though  it  may  refuse  to  feed  any  longer  one  particular  crop,  it  may 
furnish  an  excellent  crop  of  a  different  description,  and,  what  is  more  remark- 
able, it  may,  after  growing  two  or  three  different  crops,  be  found  to  have  regained 
its  power  of  nourishing  the  very  crop  for  which  it  was  before  exhausted.  Experi- 
ence of  this  has  led  to  the  adoption  of  a  system  of  rotation  of  crops,  by  which  a 
soil  is  made  to  yield,  for  example,  a  crop  of  barley,  and  then  successive  crops  of 
clover,  wheat,  turnips,  and  barley  again. 

The  possibility  of  this  rotation  is  partly  accounted  for  by  the  difference  in  the 
mineral  food  removed  by  different  crops  ;  thus,  turnips  and  clover  require  much 
potash  and  lime,  while  wheat  and  barley  require  much  phosphoric  acid,  so  that, 


GROWTH  OF  PLANTS'.  819 

in  alternating  the  turnips  and  clover  with  the  wheat  and  barley  there  may  be 
sufficient  time  for  some  of  the  locked-up  phosphoric  acid  of  the  soil  to  become 
available  as  food. 

Moreover,  the  farm  crops  appear  to  differ  in  their  capacity  for  feeding  on  the 
mineral  substances  present  in  the  soil  ;  thus,  there  may  be  phosphoric  acid  in  a 
soil  which  would  be  available  for  wheat,  but  perfectly  useless  for  turnips  which 
are  for  this  reason  always  greatly  benefited  by  manuring  with  superphosphate 
Again,  cereal  crops  are  more  benefited  by  application  of  nitrates  than  are  most 
other  crops. 

An  explanation  of  this  is  afforded  by  our  knowledge  of  the  difference  in  the 
depth  to  which  the  roots  of  various  crops  are  capable  of  penetrating  into  the  soil, 
and  consequently  of  drawing  a  supply  of  food  from  the  subsoil.  The  benefit  of 
rotation  is  also  partly  to  be  accounted  for  in  this  way.  For  where  the  residue  of 
the  preceding  deep-rooted  crop  is  allowed  to  remain  on  the  land,  the  surface  soil 
will  become  enriched  with  food  collected  from  the  subsoil,  and  tLus  rendered 
available  for  the  shorter-rooted  crop  when  the  residue  is  ploughed  up.  At  the 
same  time  the  opening  up  of  the  soil  to  different  depths,  caused  by  the  differently 
penetrating  roots,  prevents  the  formation  of  the  hard  layer,  or  pan,  which  gene- 
rally forms  at  the  limit  of  the  roots  if  the  same  crop  be  grown  continually. 

617.  Our  knowledge  of  the  chemical  operations  occurring  in  the  plant,  and 
resulting  in  the  elaboration  of  the  great  variety  of  vegetable  products,  is  very 
slight  indeed.  We  appear  to  have  sufficient  evidence  that  starch  and  sugar,  for 
example,  are  constructed  in  the  plant  from  carbonic  acid  and  water,  and  that 
albuminoids  result  from  the  interaction  of  the  same  compounds,  together  with 
nitric  acid,  or  ammonia,  and  certain  sulphates  and  phosphates  ;  but  the  inter- 
mediate steps  in  these  conversions  are  as  yet  unknown. 

All  seeds  contain  starch  or  fat  (or  both),  albuminoids,  and  mineral  matters, 
these  being  provided  for  the  nourishment  of  the  young  plant  till  its  organs  are 
sufficiently  developed  to  enable  it  to  procure  its  own  food  from  the  air  and  soil. 
The  necessary  conditions  for  germination  are  a  suitable  temperature  (best  at  28° 
to  34°  C.),  the  presence  of  free  oxygen,  and  moisture.  It  is  to  obtain  this  last 
that  the  seed  is  buried,  light  or  darkness  having  little  or  no  effect.  The  seed 
absorbs  water  and  oxygen  and  evolves  carbon  dioxide  ;  since  the  albuminous 
constituents  are  the  most  changeable  substances  present,  it  is  probably  these 
which  undergo  oxidation,  part  forming  diastase,  which  excites  the  conversion  of 
insoluble  starch  into  soluble  starch  and  sugar  ;  some  of  the  albuminoids  at  the 
same  time  become  soluble  amides.  The  water  absorbed  dissolves  these  altered 
substances  and  the  mineral  matters,  forming  the  sap  to  nourish  the  embryo. 
The  seed  swells,  and  the  integument  bursts,  the  radicle  growing  first  and  then  the 
plumule;  the  former  develops  into  the  root,  which  absorbs  the  mineral  constitu- 
ents and  nitrogen  in  aqueous  solution  from  the  soil,  while  the  latter,  as  the  sap 
ascends,  develops  the  leaves,  the  sugar  of  the  sap  becoming  converted  into  cellu- 
lose for  the  purpose.  Chlorophyll  is  then  developed,  and  the  decomposition  of 
carbon  dioxide  and  assimilation  of  carbon  begins.  As  the  roots  act  more  quickly 
than  the  leaves,  the  young  plant  is  relatively  richer  in  mineral  constituents  and 
nitrogen  than  is  the  mature  plant.  The  assimilation  of  carbon  and  decomposition 
of  carbon  dioxide  proceed  only  in  light,  the  volume  of  oxygen  evolved  being 
equal  to  that  of  the  carbon  dioxide  absorbed,*  so  that  the  formation  of  cellulose 
might  be  regarded  as  occurring  directly  by  the  action  of  the  carbon  dioxide  on 
the  water  of  the  sap,  thus  :—  6C02  +  5H20  =  C6H1005  +  012.  The  compounds  what- 
ever they  may  be,  that  are  formed  by  the  assimilating  process  are  altered  and 
rendered  soluble  by  a  process  of  oxidation  known  as  metobolu,  accompanied  by 
evolution  of  carbon  dioxide—  a  veritable  respiration,  in  fact,  which  goes  on  in  li; 
or  dark,  though  in  the  light  the  evolved  carbon  dioxide  is  masked  by  the  larger 
evolution  of  oxygen.  Osmosis  is  concerned  in  the  passage  of  the  soluble  matt 
from  cell  to  cell. 

By  growing  plants  in  water  in  which  one  particular  constituent  element  is  cor 
tained  in  very  small  proportion  or  is  absent,  it  has  been  ascertained  that  potassium 
is  concerned  in  the  formation  of  starch  and  other  carbohydrates  ;    calcium  in 
the  formation  of  cellulose  ;  iron  in  the  formation  of  chlorophyll  ;  chloi 


*  It  has  been  suggested  that  formic  aldehyde  is  first  produced, 
and  that  this  is  subsequently  polymerised  to  glucose,  C6H12O6.    The  recent  production  of 
acrose  from  formic  aldehyde  (p.  728)  supports  this  view. 


820  EIPENING  OF  FRUIT. 

translocation  of  starch ;  phosphorus,  sulphur,  and  nitrogen  in  the  formation  of 
albuminoids.  The  mission  of  calcium  is  also  shown  by  the  fact  that  wheat  has  a 
tendency  to  lay  or  lodge  where  the  soil  is  poor  in  this  element. 

In  annual  plants  the  formation  of  seed  is  carried  on  at  the  expense  of  the  rest 
of  the  plant,  which  becomes  exhausted,  starch  and  albuminoids  being  transferred 
to  the  seed.  In-jjbiennial  and  perennial  plants  the  advent  of  autumn  is  accompanied 
by  a  transference  of  food  from  the  stem  and  leaves  to  the  roots,  tubers,  or  pith, 
to  form  a  basis  for  growth  next  spring,  exhaustion  and  death  occurring  in  the 
case  of  biennial  plants  at  seed-time,  and  the  rotation  recurring  in  the  case  of 
perennials. 

618.  With  respect  to  the  ripening  of  fruit,  we  know  a  little  more  concerning 
the  chemical  changes  which  it  involves.  Most  fruits,  in  their  unripe  condition, 
contain  cellulose,  starch,*  and  some  one  or  more  vegetable  acids,  such  as  malic, 
citric,  tartaric,  and  tannic,  the  last  being  almost  invariably  present,  and  causing 
the  peculiar  roughness  and  astringency  of  the  unripe  fruit.  The  characteristic 
constituent  of  unripe  fruits,  however,  is  pectose,  a  compound  of  carbon,  hydrogen, 
and  oxygen,  the  composition  of  which  has  not  been  exactly  determined.  Pectose 
is  quite  insoluble  in  water,  but  during  the  ripening  of  the  fruit  it  undergoes  a 
change  induced  by  the  vegetable  acids,  and  is  converted  into  pectin  (C32H400.28), 
which  is  capable  of  dissolving  in  water,  and  yields  a  viscous  solution.  "  As  the 
maturation  proceeds,  the  pectin  itself  is  transformed  into  pectic  acid  (C^H^O^) 
&ndpectosic  acid  (C32H46O3i),  which  are  soluble  in  boiling  water,  yielding  solutions 
which  gelatinise  on  cooling.  It  is  from  the  presence  of  these  acids,  therefore, 
that  many  ripe  fruits  are  so  easily  convertible  into  jellies. 

Whilst  the  fruit  remains  green,  its  relation  to  the  atmosphere  appears  to  be  the 
same  as  that  of  the  leaves,  for  it  absorbs  carbon  dioxide  and  evolves  oxygen  ;  but 
when  it  fairly  begins  to  ripen,  oxygen  is  absorbed  from  the  air  and  carbon  dioxide 
evolved,  whilst  the  starch  and  cellulose  are  converted  into  sugar  under  the 
influence  of  the  vegetable  acids  (p.  726),  and  the  fruit  becomes  sweet.  The  con- 
version of  starch  and  cellulose  (C6H10O5)  into  sugar  (CeH^Oe)  would  simply  require 
the  assimilation  of  the  elements  of  water,  so  that  the  absorption  of  oxygen  and 
evolution  of  carbon  dioxide  are  probably  necessary  for  the  conversion  of  the 
tannic  and  other  acids  into  sugar.  For  example — 

C14H1009  +  H2O  +  012  =  C6H12O6  +  8C02. 
Tannic  acid.  Fruit-sugar. 

3C4H606  +  03  =  C6H1206  +  3H20  +  6C02. 
Tartaric  acid. 

When  the  sugar  has  reached  its  maximum,  the  ripening  is  completed  ;  and  if  the 
fruit  be  kept  longer,  the  oxidation  takes  the  form  of  ordinary  decay. 

A  change  in  composition,  similar  to  that  caused  by  ripening,  is  effected  by 
cooking  the  unripe  fruit. 

619.  The  scheme  of  natural  chemistry  would  not  be  complete  unless  provision 
were  made  for  the  restoration  of  the  constituents  of  plants,  after  death,  to  the 
atmosphere  and  soil,  where  they  might  afford  food  to  new  generations  of  plants. 
Accordingly,  very  shortly  after  the  death  of  a  plant,  if  sufficient  moisture  be 
present,  the  spores  of  ferments  acquired  from  the  air  begin  to  develop,  the  change- 
able nitrogenised  (albuminous)  constituents  begin  to  putrefy,  and  the  change  is 
communicated  to  the  other  parts  of  the  plant,  under  the  form  of  decay,  so  that 
the  plant  is  slowly  consumed  by  the  atmospheric  oxygen,  its  carbon  being  recon- 
verted into  carbonic  acid,  its  hydrogen  into  water,  and  its  nitrogen  into  ammonia, 
these  substances  being  then  transported  in  the  atmosphere  to  living  plants  which 
need  them,  while  the  mineral  constituents  of  the  dead  plants  are  washed  into  the 
soil  by  rain. 

Moist  wood  is  slowly  converted  by  decay  into  humus.  When  it  is  desired  to 
preserve  wood  from  decay,  it  is  impregnated  with  some  substance  which  shall 
form  an  unchangeable  compound  with  the  albuminous  constituents  of  the  sap. 
Kreasote  (p.  712)  and  corrosive  sublimate  (ky  uniting)  are  occasionally  used  for 
this  purpose,  the  wood  being  made  to  imbibe  a  diluted  solution  of  the  preserva- 
tive, either  by  being  soaked  in  it  or  under  pressure. 

In  Boucherie's  process  for  preserving  wood,  the  natural  ascending  force  of  the 
sap  is  ingeniously  turned  to  account  in  drawing  up  the  preservative  solution.  A 

*  Some  doubt  exists  as  to  the  presence  of  starch  in  fruit. 


DIGESTION.  32I 

large  incision  being  made  around  the  lower  Dart  of  tbp  fr.,nt  nf  *u« 
a  trough  of  clay  is  built  up  around  it,  SSffiSft  weak  soludof  oTsSfphS 
of  copper,  peracetate  of  iron,  or  calcium.  chloride.     Even  after  the  tree  has  bee 
felled,  it  may  be  made  to  imbibe  the  preserving  solution  wmlst  in  a  horTzont^ 
position  by  enclosing  the  base  of  the  trunk  in  an  impermeable  bag  suppHed  wfth 
the  liquid  from  a  reservoir.     The  impregnation  of  the  wood  with  such 


NUTEITION  OF  ANIMALS. 

•  620.  Between  the  chemistry  of  vegetable  and  that  of  animal  life  there  is  this 
fundamental  distinction,  that  the  former  is  eminently  constructive  and  the  latter 
destructive.  •  The  plant,  supplied  with  compounds  of  the  simplest  kind—  carbonic 
acid,  water,  and  ammonia—  constructs  such  complex  substances  as  albumin  and 
sugar  ;  whilst  the  animal,  incapable  of  deriving  sustenance  from  the  simpler 
compounds,  being  fed  with  those  of  a  more  complex  character,  converts  them 
eventually,  for  the  most  part,  into  the  very  materials  with  which  the  construc- 
tive work  of  the  plant  began.  It  is  indeed  true  that  some  of  the  substances 
deposited  m  the  animal  frame,  such  as  fibrin,  and  gelatinous  matter  rival  in  com- 
plexity many  of  the  products  of  vegetable  life  ;  but  for  the  elaboration  of  these 
substances,  the  animal  must  receive  food  somewhat  approaching  them  in  chemical 
composition.  It  is  to  this  nearer  resemblance  between  the  food  of  animals  and 
the  proximate  constituents  of  their  frames,  that  we  may  partly  ascribe  the  greater 
extent  of  our  knowledge  on  the  subject  of  the  nutrition  of  animals,  which  is, 
however,  far  from  being  complete. 

The  -idtlm-ate  elements  contained  in  the  animal  body  are  the  same  as  those  of  the 
vegetable,  but  the  proximate  constituents  are  far  more  numerous  and  varied. 

The  bones  containing  the  phosphates  and  carbonates  of  calcium  and  magnesium 
together  with  gelatinous  matter,  require  that  the  animal  should  be  supplied  with 
food  which,  like  bread,  contains  abundance  of  phosphates,  as  well  as  the  nitro- 
genised  matter  (gluten)  from  which  the  gelatinous  substance  may  be  formed.  In 
milk,  the  food  of  the  young  animal,  we  have  also  the  necessary  phosphates,  whilst 
the  casein  affords  the  supply  of  nitrogenous  matters. 

Muscular  flesh  finds,  in  the  gluten  of  bread  and  the  casein  of  milk,  the  nitro- 
genised  constituent  from  which  its  fibrin  might  be  formed  with  even  less  trans- 
formation than  is  required  for  the  gelatinous  matter  of  bone,  since  the  com- 
position of  fibrin,  gluten,  and  casein  is  very  similar.  The  albumin  and  fibrin  of 
the  blood  have  also  their  counterparts  of  the  gluten  and  casein  of  bread  and 
milk,  whilst  all  the  salts  of  the  blood  may  be  found  in  either  of  these  articles  of 
food. 

Bread  and  milk,  therefore,  may  be  taken  as  excellent  representatives  of  the  food 
necessary  for  animals,  and  the  same  constituents  are  received  in  their  flesh  diet  by 
animals  which  are  purely  carnivorous,  but  the  flesh  contains  them  in  a  more 
advanced  stage  of  preparation. 

It  is  natural  to  suppose  that  the  fat,  which  contains  no  nitrogen,  should  be 
supplied  by  those  constituents  of  the  food  which  are  free  from  that  element,  such 
as  the  starch  in  bread,  and  the  sugar  and  fat  in  milk. 

Before  the  food  can  be  turned  to  account  for  the  sustenance  of  the  body,  it 
must  undergo  digestion,  that  is,  it  must  be  either  dissolved  or  otherwise  reduced 
to  such  a  form  that  it  can  be  absorbed  by  the  blood,  which  it  accompanies  into 
the  lungs  to  undergo  the  process  of  respiration,  and  thus  to  become  fitted  to  serve 
for  the  nutrition  of  the  various  organs  of  the  body,  since  these  have  to  be  con- 
tinually repaired  at  the  expense  of  the  constituents  of  the  blood. 

The  first  step  towards  the  digestion  of  the  food  is  its  disintegration  effected  by 
the  teeth  with  the  aid  of  the  saliva,  by  which  it  should  be  reduced  to  a  pulpy  mass. 
The  saliva  is  an  alkaline  fluid  characterised  by  the  presence  of  a  peculiar  albumin- 
ous substance  called  ptyalin  (irrtfw,  to  spit),  which  easily  putrefies.  The  action  of 
saliva  in  mastication  is  doubtless  in  great  part  a  mechanical  one,  biit  it  is  possil 
that  its  alkalinity  assists  the  process  chemically,  by  partly  emulsifying  the  fatty 
portions  of  the  food.  The  ptyalin  also  acts  as  a  ferment,  converting  starch  into 
sugar.  This  disintegration  of  the  food  is  of  course  materially  assisted  by  the 
cooking  to  which  it  has  been  previously  subjected,  the  hard  and  fibrous  portions 
having  been  thereby  softened. 


822  PRODUCTION   OF  BLOOD. 

The  food  now  passes  to  the  stomach,  in  which  it  remains  for  some  time,  at  the 
temperature  of  the  body  (98°  F.),  in  contact  with  the  yastrlc  juice,  the  chief 
chemical  agent  in  the  digestive  process.  The  gastric  juice  which  is  secreted  by 
the  lining  membrane  of  the  stomach  is  an  acid  liquid,  containing  hydrochloric 
and  lactic  acids.  It  is  characterised  by  the  presence  of  a  peculiar  substance 
belonging  to  the  albuminous  class  of  bodies  which  is  called  pepsin  (TreVrw,  to 
digest),  and  possesses  the  remarkable  power  of  enabling  dilute  acids,  by  its  mere 
presence,  to  dissolve  such  substances  as  fibrin  and  coagulated  albumin,  which 
would  resist  the  action  of  the  acid  alone  for  a  great  length  of  time. 

An  imitation  of  the  gastric  juice  may  be  made  by  digesting  the  mucous  mem- 
brane of  the  stomach  for  some  hours  in  warm  very  dilute  hydrochloric  acid.  The 
acid  liquid  thus  obtained  is  capable  of  dissolving  meat,  curd,  &c.,  if  it  be  main- 
tained at  the  temperature  of  the  body.  The  pepsin  prepared  from  the  stomach 
of  the  pig  and  other  animals  is  sometimes  administered  medicinally  in  order  to 
assist  digestion. 

The  principal  change  which  the  food  suffers  by  the  action  of  the  gastric  juice 
is  the  conversion  of  the  fibrinous  and  albuminous  constituents  into  soluble  forms 
(peptones) ;  the  starch  is  also  partly  converted  into  dextrin  and  sugar,  but  the 
fatty  constituents  are  unchanged. 

The  food  which  has  thus  been  partially  digested  in  the  stomach  is  called  by 
physiologists  chyme,  and  passes  thence  into  the  commencement  of  the  intestines 
(the  duodenum),  where  it  is  subjected  to  the  action  of  two  more  chemical  agents, 
the  bile  and  the  pancreatic  juice. 

621.  Bile  consists  essentially  of  a  solution  of  two  salts  known  as  glycocholate 
and  taurocholate  of  sodium.  Both  glycocbolic  and  taurocholic  acids  are  resinous, 
and  do  not  neutralise  the  alkali,  so  that  the  bile  has  a  strong  alkaline  character. 
Another  characteristic  feature  of  this  secretion  is  the  large  proportion  of  carbon 
which  it  contains.  GlycucJiolic  acid  contains  67  per  cent,  of  carbon,  whilst  taut-o- 
c/tolic  acid  contains  61  per  cent. 

The  special  function  of  the  bile  in  the  digestion  of  the  food  has  not  been  ex- 
plained, but  from  its  strongly  alkaline  reaction  it  does  not  appear  improbable  that 
it  assists  in  the  digestion  of  fatty  substances. 

The  pancreatic  juice  is  another  alkaline  secretion  which  differs  from  the  bile  in 
containing  a  considerable  quantity  of  albumin,  and  is  very  putrescible.  Its  par- 
ticular office  in  digestion  appears  to  consist  in  promoting  the  conversion  of  the 
starchy  portions  of  the  food  into  sugar,  though  it  also  has  a  powerful  action 
upon  the  fats,  causing  them  to  form  an  intimate  mixture,  or  emulsion,  with 
water,  and  partly  saponifying  them.  The  digestion  of  the  starch  and  sugar  is 
completed  by  the  action  of  the  intestinal  fluid  in  the  further  passage  of  the  food 
through  the  intestines,  so  that  when  it  arrives  in  the  small  intestines,  all  the 
soluble  matters  have  become  converted  into  a  thin  milky  liquid  called  chyle,  which 
has  next  to  be  separated  mechanically  from  the  insoluble  portions,  such  as  woody 
fibre,  &c.,  which  are  excreted  from  the  body. 

This  separation  is  effected  in  the  small  intestines  by  means  of  two  distinct  sets 
of  vessels,  one  of  which  (the  mescnteric  reinfi)  absorbs  the  dissolved  starchy  por- 
tions of  the  food,  and  conveys  them  to  the  liver,  whence  they  are  afterwards 
transferred  to  the  right  auricle  of  the  heart.  The  other  set  of  vessels  (lacteals) 
absorbs  the  digested  fatty  matters,  and  conveys  them,  through  the  thoracic  duct, 
into  the  subclavian  vein,  and  thence  at  once  into  the  right  auricle  of  the  heart. 

From  the  right  auricle  this  imperfect  blood  passes  into  the  right  ventricle  of 
the  heart,  and  is  there  mixed  with  the  blood  returned  from  the  body  by  the  veins, 
after  having  fulfilled  its  various  functions  in  the  system.  The  mixture,  which  has 
the  usual  dark  brown  colour  of  venous  blood,  is  next  forced,  by  the  contraction 
of  the  heart,  into  the  lungs,  where  it  is  distributed  through  an  immense  number 
of  extremely  fine  vessels  traversing  the  lungs,  in  contact  with  the  minute  tubes 
containing  the  inspired  air,  so  that  the  venous  blood  is  only  separated  from  the 
air  by  very  thin  and  moist  membranes.  Through  these  membranes  the  dark 
venous  blood  gives  up  the  carbonic  acid  gas  with  which  it  had  become  charged 
by  the  oxidation  of  the  carbon  of  the  organs  in  its  passage  through  the  body,  and 
acquires,  in  return,  about  an  equal  volume  of  oxygen,  which  converts  it  into  the 
bright  crimson  arterial  blood.  In  this  state  it  returns  to  the  left  side  of  the  heart, 
whence  it  is  conveyed,  by  the  arteries,  to  the  different  organs  of  the  body.  The 
chemistry  of  the  changes  effected  and  suffered  by  the  blood  in  its  circulation 
through  the  body  is  very  imperfectly  understood.  One  of  its  great  offices  is  the 


RATIONAL  FEEDING. 

supply  of  the  oxygen  necessary  to  oxidise  the  components  of  the  various  organs 
and  thus  to  evolve  the  heat  which  maintains  the  body  at  its  high  temperature' 
The  results  of  the  oxidation  of  these  organs  are  undoubtedly  very  numerous  ' 
among  them  we  may  trace  carbonic,  sulphuric,  phosphoric,  lactic,  butvric  and 
uric  acids,  as  well  as  urea  and  some  other  substances.  The  destroyed  tissues  must 
at  the  same  time  be  renewed  by  the  deposition.,  from  the  blood,  of  fresh  particles 
similar  to  those  which  have  been  oxidised.  In  the  course  of  the  blood  through 
the  circulation,  the  above  products  of  oxidation  have  to  be  removed  from  it— the 
carbonic  acid  by  the  lungs  and  skin-  the  sulphuric,  phosphoric,  and  uric  acids 
and  the  urea,  by  the  kidneys. 

The  various  liquid  secretions  of  the  body,  such  as  the  bile,  the  saliva,  the  gastric 
juice,  &c.,  have  also  to  be  elaborated  from  the  blood  during  its  circulation  through 
the  arteries,  after  which  it  returns,  by  the  veins,  to  the  heart,  to  have  its  com- 
position restored  by  the  matters  derived  from  the  food,  and  to  be  reconverted 
into  arterial  blood  in  the  lungs. 

When  it  is  remembered  that  the  body  is  exposed  to  very  considerable  variations 
of  external  heat  and  cold,  a  question  occurs  as  to  the  provision  made  for  main- 
taining it  at  its  uniform  temperature.  This  is  effected  through  the  agency  of  the 
fat  which  is  deposited  in  all  the  organs  of  the  body.  Since  fatty  substances  in 
general  are  particularly  rich  in  carbon  and  hydrogen,  their  oxidation  within  the 
body  would  be  attended  with  the  production  of  more  heat  than  that  of  those  parts 
of  the  organs  which  contain  much  nitrogen  and  oxygen.  Accordingly,  when  the 
body  is  exposed  to  a  low  temperature,  a  larger  quantity  of  its  fat  is  consumed  by 
the  oxidising  action  of  the  blood,  and  a  corresponding  increase  occurs  in  the 
amount  of  heat  evolved,  thus  compensating  for  the  greater  loss  of  heat  suffered 
by  the  body  in  the  cooler  atmosphere.  Of  course,  in  cold  weather,  when  more 
oxygen  is  required  to  maintain  the  heat  of  the  frame,  a  larger  quantity  of  that 
gas  is  inhaled  at  each  breath,  on  account  of  the  higher  specific  gravity  of  the  air, 
in  addition  to  which  we  have  the  quickened  respiration  which  always  attends  ex- 
posure to  cold.  To  supply  this  extra  demand  for  carbon  and  hydrogen  in  cold 
weather,  we  instinctively  have  recourse  to  such  substances  as  fat,  starch,  sugar, 
&c.,  which  contain  them  in  large  proportion,  and  these  aliments,  free  from  nitro- 
gen, are  often  spoken  of  as  the  respiratory  constituents  of  food ;  whilst  flesh,  gluten, 
albumin,  &c.,  which  contain  nitrogen,  are  styled  the  plastic  elements  of  nutrition 
(7rXcur<ra>,  to  for  HI). 

Bearing  in  mind  that  the  food  has  a  two-fold  office— to  nourish  the  frame  and 
to  maintain  the  animal  heat — it  will  be  evident  that  a  judiciously  regulated  diet 
will  contain  due  proportions  of  these  nitrogenous  constituents,  such  as  albumin, 
fibrin,  and  casein,  which  serve  to  supply  the  waste  of  the  organs,  and  of  such 
non-nitrogenised  bodies  as  starch  and  sugar,  from  which  fat  may  be  elaborated 
to  sustain  the  bodily  warmth. 

Albuminoid  ratio. — The  proportion  which  these  two  parts  of  the  food  should 
bear  to  each  other  will,  of  course,  depend  upon  the  particular  condition  of  exist- 
ence of  the  animal.  Thus,  for  a  growing  animal  a  larger  proportion  of  the 
nitrogenised  or  plastic  portion  of  food  would  be  required  than  for  an  animal 
whose  growth  has  ceased  ;  and  animals  exposed  to  a  low  temperature  would 
require  more  of  the  non-nitrogenised  or  heat-giving  portion  of  the  food. 

Accordingly,  we  find  that  a  man  can  live  upon  a  diet  which  contains  (as  in  the 
case  of  wheaten  bread)  5  parts  of  non-nitrogenised  (starch  and  sugar)  to  i  part 
of  nitrogenised  food  (gluten) ;  whilst  an  infant,  whose  increasing  organs  require 
more  nitrogenised  material,  thrives  upon  milk,  in  which  this  amounts  to  i  part 
(casein)  for  every  4  parts  of  the  non-nitrogenised  portion  (milk-sugar  and  fat).  The 
inhabitants  of  cold  climates  consume,  as  is  well  known,  much  more  oil  and 
than  do  those  of  the  temperate  and  hot  regions. 

An  examination  of  the  composition  of  different  articles  of  food  affp 
explanation  of  the  custom  which  experience  has  warranted,  of  associating  par 
ticular  varieties  of   food.      Thus,  assuming  as  our  standard  of  comparison  tne 


All  muscular  or  mental  exertion  is  attended  with  a  corresponding  oxidation >  of 
the  tissues  of  the  frame,  just  as  each  movement  of  a  •^^J^^J^^J 
to  the  combustion  of  a  proportionate  quantity  of  coal 


824  DECAY  AFTEE  DEATH. 

such  exertion  both  creates  a  demand  for  food,  and  quickens  the  respiration  to 
obtain  an  increased  supply  of  oxygen. 

CHANGES  IN  THE  ANIMAL  BODY  AFTEE  DEATH. 

622.  After  the  death  of  animals,  just  as  after  that  of  plants,  a  change  occurs 
in  some  of  the  nitrogenous  constitutents,  attended  by  the  development  of 
living  organisms  of  a  very  low  order,  and  this  change  is  soon  communicated  to  all 
parts  of  the  body,  which  undergoes  a  putrefaction  or  metamorphosis,  of  which  the 
ultimate  results  are  the  conversion  of  the  carbon  into  carbonic  acid,  the  hydrogen 
into  water,  the  nitrogen  into  ammonia,  nitrous  and  nitric  acids,  and  the  sulphur 
into  sulphuretted  hydrogen  and  sulphuric  acid.  The  mineral  constituents  of  the 
animal  frame  then  mingle  with  the  surrounding  soil,  and  are  ready  to  take  part 
in  the  nourishment  of  plants,  which  construct  the  organic  components  of  their 
frames  from  the  carbonic  acid  and  ammonia  furnished  by  the  putrefaction  of  the 
animal,  and  then  serve  in  their  turn  as  sustenance  for  animals  whose  respiration 
supplies  the  air  with  carbonic  acid  gas  and  takes  in  exchange  the  oxygen  elimi- 
nated by  the  plant. 

The  functions  of  the  two  divisions  of  animate  nature  are,  therefore,  perfectly 
reciprocal,  and  this  relationship  must  be  regarded  as  the  foundation  of  economical 
agriculture.  If  it  were  possible  to  prevent  the  change  of  the  atmosphere,  it  is 
quite  conceivable  that  a  perpetual  succession  of  plants  and  animals  could  be  raised 
upon  a  given  farm,  without  any  importation  of  food,  provided  that  there  was  also 
no  exportation.  Or  even,  permitting  an  exportation  of  food,  the  succession  of 
plants  and  animals  raised  upon  the  same  land  might  be,  at  least,  a  very  long  one, 
if  the  solid  and  liquid  excrement  of  the  animals,  to  feed  whom  was  the  object  of 
this  exportation,  were  restored  to  the  land  upon  which  this  food  was  raised.  The 
explanation  of  this  is,  that  the  solid  and  liquid  excrements  of  the  animal  contain 
a  very  large  proportion  of  the  mineral  constituents  of  the  soil,  in  the  very  state  in 
which  they  are  best  fitted  for  the  assimilation  by  the  crop,  and  as  long  as  the  soil 
contains  the  requisite  supply  of  mineral  food,  the  plant  can  derive  its  organic 
constituents  from  the  atmosphere  itself. 

Forasmuch,  however,  as  the  vegetable  and  animal  food  produced  upon  a  farm 
is  generally  exported  to  feed  the  dwellers  in  towns,  whose  excrements  cannot, 
without  excessive  outlay,  be  returned  to  the  soil  whence  the  food  was  derived,  it 
becomes  necessary  for  the  agriculturist  to  purchase  farm-yard  manure,  guano, 
&c.,  in  order  to  prevent  the  exhaustion  of  his  soil.  A  great  manufacturing 
country,  in  which  the  majority  of  the  inhabitants  are  congregated  in  very  large 
numbers  around  a  few  centres  of  industry,  at  a  distance  from  the  land  under 
tillage,  is  thus  of  necessity  dependent  for  a  considerable  proportion  of  its  food 
upon  more  thinly  populated  countries  where  manufactures  do  not  flourish,  to 
which  it  exports  in  return  the  produce  of  the  labour  which  it  feeds. 

The  parts  of  the  frames  of  animals  differ  very  considerably  in  their  tendency 
to  putrefaction.  The  blood  and  muscular  flesh  undergo  this  change  most  readily, 
as  being  the  most  complex  parts  of  the  body,  whilst  the  fat  remains  unchanged 
for  a  much  longer  period,  and  the  bones  and  hair  will  also  resist  putre- 
faction for  a  great  length  of  time.  The  comparative  stability  of  the  fat  is 
observed  in  the  bodies  of  animals  which  have  been  buried  for  some  time  in  a 
very  wet  situation,  when  they  are  often  found  converted  almost  entirely  into  a 
mass  of  adijjocere,  consisting  of  the  palmitic  and  stearic  acids  derived  from  the 
fat. 

When  an  animal  body  is  thoroughly  dried,  it  may  be  preserved  unchanged  for 
any  length  of  time,  and  this  is  the  simplest  of  the  methods  adopted  for  the  pre- 
servation of  animal  food,  becoming  far  more  efficacious  when  combined  with  the 
use  of  some  antiseptic  substance,  such  as  salt,  sugar,  spice,  or  kreasote.  The 
preservative  effects  of  salt  and  sugar  are  sometimes  ascribed  to  the  attraction 
exerted  by  them  upon  moisture,  which  they  withdraw  from  the  flesh,  whilst  spices 
owe  their  antiseptic  power  to  the  essential  oils,  which  appear  to  have  a  specific 
action  in  arresting  fermentative  change,  a  character  which  also  belongs  to  krea- 
sote, carbolic  acid,  and  probably  to  other  substances  which  occur  in  the  smoke  of 
wood,  well  known  for  its  efficacy  in  curing  animal  matter.  Such  substances  are 
often  called  anti-zymotic  bodies ;  carbolic,  salicylic,  benzoic,  and  boric  acids  are 
classed  under  this  head. 

A  process  commonly  adopted  for  the  preservation  of  animal  and  vegetable  food 


ANTISEPTIC  PRESERVATION.  825 

-consists  in  heating  them  with  a  little  water  in  tin  canisters,  which  are  sealed  air- 
tight as  soon  as  the  steam  has  expelled  all  the  air,  and  if  the  organic  matter  be 
perfectly  fresh,  this  mode  of  preserving  it  is  found  very  successful,  though,  if 
putrefaction  has  once  commenced,  to  ever  so  slight  an  extent,  it  will  continue 
even  in  the  sealed  canister  quite  independently  of  the  air. 

Modern  experiments  have  disclosed  a  great  imperfection  in  our  acquaintance 
with  the  conditious  under  which  putrefaction  occurs,  and  indicate  the  presence 
in  the  atmosphere  of  some  minute  solid  particles  which  appear  to  be  minute  ova 
or  germs,  and  have  the  power  of  inducing  the  commencement'  of  this  change. 
It  has  been  found  that  milk,  for  example,  may  be  kept  for  a  very  considerable 
period  without  putrefying,  if  it  be  boiled  in  a  flask,  the  neck  of  which  is  after- 
wards loosely  stopped  with  cotton  wool,  whilst,  if  the  plug  of  cotton  wool  be 
omitted,  the  other  conditions  being  precisely  the  same,  putrefaction  will  set  in 
very  speedily. 

Perfectly  fresh  animal  matters  have  also  been  preserved  for  a  length  of  time  in 
that  state,  in  vessels  containing  air  which  has  been  passed  through  red-hot  tubes 
with  the  view  of  destroying  any  living  germs  which  might  be  present,  and  such 
substances  have  been  found  to  putrefy  as  soon  as  the  unpurified  air  was  allowed 
access  to  them. 

The  extremes  of  the  scale  of  animated  existence  would  appear  to  meet  here. 
The  highest  forms  of  organised  matter,  immediately  after  death,  serve  to  nourish 
some  of  the  lowest  orders  of  living  germs,  these  helping  to  resolve  the  complex 
matter  into  the  simpler  forms  of  carbonic  acid,  ammonia,  &c.,  which  are  returned 
to  the  atmosphere,  the  great  receptacle  for  the  four  chief  elements  of  living 
matter — carbon,  hydrogen,  nitrogen,  and  oxygen. 


INDEX. 


The  names  of  minerals  are  printed  in  italics. 


ABSINTHE,  745 

Absolute  boiling-point,  27 

Absorption  bauds,  331,  789 

spectra,  331,  789 
Acacia  catechu,  712 
Acenapb.tb.ene,  553 
Acetacetic  acid,  627 
ether,  643 
Acetal,  582 

Acetaldehyde  hydrazone,  583 
Acetamide,  667 
Acetamido-chloride,  668 
Acetanilide,  663,  667,  668 
Acetates,  592 
Acetic  acid,  590 

anhydrous,  593 
glacial,  59 1 
synthesis  of,  592 
aldehyde,  581 
anhydride,  593 
chloride,  639 
esters,  643 
ether,  643 
peroxide,  593 
series  of  acids,  588 
Acetification,  590 
Acetimido-ether,  668 
Acetimethylarnide,  660 
Aceto-acetic  acid,  626 
Acetol,  626 
Acetone,  625 

peroxide,  626 
propione,  624 
Acetones,  624 
Aceto-nitrile,  667,  699 
Acetophenoue,  626 
Aceturic  acid,  675 
Acetyl,  592 

bromide,  639 
carbamides,  671 
chloride,  639 
creosol,  713 
dioxide,  593 
hydrate,  600 
hydride,  581 
iodide,  639 
sulphide,  593 
urea,  671 
vanillic  acid,  713 
Acetylene,  137,  537 


Acetylene  detected  in  coal-gas,  162 
dichloride,  538 
formed  from  ethylene,  144 
heat  of  formation,  141 
preparation  of,  139 
prepared  from  ether,  139 
properties  of,  141 
series,  537 
synthesis  of,  137 
tetrachloride,  538 
Acetylglycocine,  675 
Acetylides,  537 
Achro-dextriu,  736 
Acid,  19,  35 

albumin,  750 
calcium  meconate,  622 
chlorides,  191 
egg-,  227 
potassium  malate,  618 

racemate,  620 
saccharate,  622 
radicles,  94,  592 
salts,  defined,  104 
Acids,  acetic  series,  593 
acrylic  series,  596 
anhydro,  261 
aromatic  series,  599 
basicity  of,  104 
benzoic  series,  585,  599 
classification  of,  104 
dibasic,  104 
lactic  series,  603 
monobasic,  104 

diatomic,  602 
organic,  586 
oxalic  series,  612 
polybasic,  104,  623 
sorbic  series,  599 
structure  of,  260 
tetrabasic,  104 
tribasic,  104 

volatile,  separation  of,  598 
Acidic  decomposition,  644 
Acidulous  waters,  61 
Aconine,  783 
Aconitic  acid,  623 
Aconitine,  783 
Acridine,  768 

yellow,  768 
Acridinium  derivatives,  768 


828 


INDEX. 


Acrolein,  577,  583 
Acrose,  728 
Acrylic  acid,  597 

aldehyde,  583 
series  of  acids,  583 
Actinic  rays,  172 
Acyclic  compounds,  526 
Adapter,  139 
Adipic  acid,  622 
Adipocere,  595 

Adjacent  substitution-products,  546 
Adjective  dyes,  683 
Aerated  bread,  809 
JEsculetin,  744 
jEsculin,  744 
Affinity,  coefficients  of,  311 

measurement  of,  304 
predisposing-,  312 
residual,  136 
After-damp,  125, 145 
Agate,  276 
Aich-metal,  482 

Air,  analysis  of,  by  eudiometer,  44 
nitric  oxide,  97 
phosphorus,  68 
aqueous  vapour  in,  68,  71 
atmospheric,  67 
burnt  in  coal-gas,  152 
composition  of,  68 
effect  of  combustion  on,  123 
exact  analysis  of,  69 
liquid,  71 
optically  pure,  71 
pump,  330 

tested  for  impurity,  124 
Alabaster,  367 

oriental,  58 
Alanine,  677 
Albite,  389 

Albumin  of  blood,  750 
eggs,  749 
vegetables,  750 

Albuminoid  ammonia,  502,  750 
compounds,  748 
ratio,  823 
Albuminoids,  748 
Albuminose,  750 
Alcarsin,  655 
Alcohol,  561 

absolute,  563 
acids,  596 
amines,  666 

chemical  constitution  of,  561 
methylated,  566 
properties  of,  563 
radicles,  565,  592 
synthesis  of,  561 
test  for,  564 
Alcoholates,  564 

Alcoholic  fermentation,  562,  806 
Alcohols,  561 

aromatic,  571 
boiling-points  of,  565 
classification  of,  561 
dihydric,  573 
distinguished,  568 
general  preparation  of,  569 
iso,  567 

monohydric,  565 
normal,  567 


Alcohols,  polyhydric,  578 
primary,  568 
secondary,  568 
tertiary,  568 
tetrahydric,  577 
trihydric,  575 
unsaturated,  570 
Aldehyde,  581 

acids,  579 
ammonia,  582 

chemical  constitution  of,  580 
condensation,  584 
resin,  i;82 
Aldehydes,  579 

aromatic,  584 

constitution  of,  579 

general  reaction    for  obtaining, 

580 

test  for,  582 
Aldol,  582 

condensation,  583 
Aid  oses,  724 
Aldoximes,  583 
Ale,  composition  of,  806 
Algaroth,  powder  of,  444 
Alizarates,  720 
Alizarin,  719 

artificial,  720 
blue,  767 
bordeaux,  721 
cyauine,  721 
Alkali  defined,  19 

manufacture,  345 
metals,  group  of,  359 
waste,  347 
•works,  171 
Alkaline  cupric  solution,  619 

earth  metals,  372 
Alkaloids,  774 
Alkides,  651,  656,  657 
Alkylanilines,  664 

acetates,  643 
benzenes,  548 
Alkyl  cyanurates,  704 
cyanides,  699 
radicles,  528 
sulphates,  641 

Alkylpiperidiuium  iodides,  766 
Alkylpyridines,  766 
Alkylpyridinium  iodides,  766 
Alkylquiuolinium  iodides,  767 
Allantoin,  773 
Allan turic  acid,  773 
Allophanamide,  671 
Allophanic  acid,  671 
Allotropy,  118 
Alloxan,  771 
Alloxanic  acid,  771 
Alloxautin,  771 
Alloys,  451 
Allyl-alcohol,  570 
bromide,  636 
chloride,  636 
cyanamide,  705 
ether,  631 
iodide,  636 
isothiocyanate,  705 
pyridine,  776 
sulphide,  573 
thiocyanate,  705 


INDEX. 


829 


Allyl-thio-urea,  705 

tricyanide,  623 
Allylene,  538 
Almond  cake,  584 

oil,  798 
Almonds,  584 
Aloes,  746 
Aloin,  746 
Aludels,  196,  496 
Alum,  386 

basic,  388 
burnt,  387 
concentrated,  386 
shale,  387 
Alumina,  388 
Aluminium,  383,  385 

acetate,  591 
bronze,  386,  481 
carbide,  145 
chloride,  389 
ethide,  657 
ethoxide,  564 
extraction,  384 
fluoride,  389 
group,  review  of,  393 
hydroxide,  388 
methide,  657 
phosphates,  390 
properties,  385 
silicates,  389 
silicide,  281 
sulphates,  386 
Alums,  234,  387 
Alunogen,  386 
Amalgam,  ammonium,  85 
electrical,  498 
sodium,  85 

Amalgamating  battery  plates,  14,  497 
Amalgamation  of  gold-ores,  514 

silver-ores,  489 
Amalgams,  498 
Amalic  acid,  775 
Amber,  560 
Ambergris,  799 
Ambrein,  799 
Amethyst,  276 
Amic  acids,  667,  672 
Amides,  105,  265,  658,  667 
Amidines,  668 
Amido-acetic  acid,  674 
acids,  658 
amid-acids,  673 
azobenzenes,  683 
barbituric  acid,  772 
benzene,  662 

sul  phonic  acid,  664,  679 
benzoic  acids,  678 
caproic  acid,  677 
chlorides,  668 
cinnamic  acid,  767 
dinitrophenol,  711 
ethyl-sulphonic  acid,  679 
glyceric  acid,  754 
isovaleric  acid,  677 
malonyl  urea,  772 
naphthalenes,  665 
nitroplieuols,  711 
paraxyliue,  665 
phenols,  711 
phenylacetic  acid,  679 


Amido-phenylamidoacridine,  768 
propiouic  acid,  677 
succinamic  acid,  678 
succinic  acid,  678 
sulphonic  acids,  679 
thiazole,  765 
toluene,  665 
Amidoformic  acid,  674 
Amidogen,  105 
Amidoximes,  669 
Amines,  658 

converted  into  guanidines,  672 
distinction  between,  660 
mixed,  660 
Ammelide,  704 
Ammeline  hydrochloride,  704 
Ammonia,  77 

absorbed  by  charcoal,  115 
action  of  chlorine  on,  175 

iodine  on,  201 
albuminoid,  502 
alum,  387 
bicarbonate,  356 
carbonate,  356 
combustion  of,  83 
decomposed  by  spark,  83 

chlorine,  84 
derivatives,  658 
dissolution  of,  in  water,  79 
formed  from  nitric  acid,  93 
gas,  dried,  79 
heat  of  dissolution,  79 
formation,  78 
vaporisation,  82 
identified,  79 
liquefied,  82 
Nessler's  test  for,  502 
nitrification  of,  87 
oxidation  of,  87 
preparation  of,  79 
salts,  354 
soda  process,  346 
solution,  8 1 
sources  of,  77,  78 
sulphate,  355 
volcanic,  352 

Ammoniacal  liquor,  78,  791 
Ammoniacum,  714 
Ammonia-meter,  81 
Ammonia  compounds,  66r 
Ammonide,  sulphuric,  354 
Ammonium,  354 

alum,  387 
amalgam,  85 
arsenite,  270 
bases,  658 
bromide,  357 
carbamate,  356,  672,  706 
carbonates,  355,  356 
chloride,  356 
cyanate,  702 
cyanide,  692 
disulphide,  357 
hydrate,  81 
iodide,  357 
isethiouate,  679 
isocyanate,  703 
molybdate,  435 
nitrate,  354 
nitrite,  355 


830 


INDEX. 


Ammonium   oxalate,  613 

parabanate,  772 
picrate,  711 
purpunte,  772 
suits,  354 
sulphate,  355 
sulphides,  357 

yellow,  357 
theory,  85 
thiocarbamate,  706 
thiocyanate,  703 
urate,  770 

Amorces  fulminantes,  255 
Amorphous  condition,  109,  268 

phosphorus,  253 
Amygdalic  acid,  744 
Amygdalin,  584,  744 
Amyl,  592 

acetate,  644 
alcohol,  569 
carbiuol,  569 
nitrite,  642 
valerate,  644 
Amylene,  536 
Amylethylic  ether,  629 
Amyloid,  738 
Amylose,  734 
Analysis,  6 

gravimetric,  6 

of  gaseous  hydrocarbons,  157 

organic,  520,  521 

calculation  of,  522,  523 
qualitative,  6 
quantitative,  6 
volumetric,  6 
Ananas  oil,  644 
Anatase,  456 
Ancaster  stone,  366 
Anethol,  632 
Angelic  acid,  597 
Anglesite,  460,  471 
Angostura  bark,  781 
Anhydride  denned,  32 
Anhydrides,  ethereal,  669 
Anhydrite,  368 
Anhydrous,  50 
Anilides,  663 
Anilido-acetic  acid,  675 
Anilido-acids,  664 
Aniline,  662 

blue,  723,  794 
colours,  721 
dyes,  721,  794 
oil,  665 

for  blue,  665 
red,  665 
safraniue,  665 
salts,  664 

sulphonic  acid,  664 
test  for,  664 
yellow,  683,  794 
Animal  charcoal,  in,  116 
chemistry,  811 
substances,  811 

Animals  and  plants,  reciprocity  of,  820 
changes  in,  after  death,  824 
nutrition  of,  821 
Animi  resin,  560 
Anions,  324 
Aniseed,  essential  oil  of,  586 


Anisic  acid,  608 
Anisic  aldehyde,  586 
Anisoil,  631 
Annatto,  747 
Anode,  14 
Anthracene,  553 

constitution  of,  554 
dichloride,  554,  637 
dihydride,  554 
Anthrachrysone,  721 
Anthracite,  159,  168 
Anthranil,  678 
Anthranilic  acid,  678 
Anthranol,  719 
Anthrapurpurin,  720 
Anthraquinoline,  767 
Anthraquiuone,  554,  719 

disulphonic  acid,  720 
Antiarin,  745 
Antichlore,  221,  235 
Anti-corrosive  caps,  186 
Antifebrine,  668 
Autimonates,  443 
Antimonic  acid,  443 

oxide,  443 
sulphide,  445 

Antimonietted  hydrogen,  444 
Antimonious  acid,  442 
Antimony,  441 

alkides,  656 

amorphous,  442 

ash,  443 

butter  of,  444 

chlorides,  444 

chlorosulphide,  445 

crocus  of,  441 

crude,  441 

detected,  441 

flowers  of,  442 

glass  of,  445 

grey  ore  of,  441 

liver  of,  446 

metallurgy  of,  441 

ores,  441 

oxides,  442 

oxychloride,  444 

oxysulphide,  445 

oxytrichloride,  445 

pentachloride,  445 

pentasulphide,  445 

potassio-tartrate,  442 

red  ore,  445 

regains  of,  441 

sulphate,  446 

sulphides,  445 

tested  for  impurity,  444 

trichloride,  444 

uses  of,  442 

vermilion,  237,  445 

white  ore,  442 
Antimonyl,  620 
Antipyrine,  764 
Antiseptics,  220,  246 
Antiseptic  preservation,  825 
Antitoxines,  750 
Anti-zymotics,  220,  824 
Ants,  acid  of,  589 
Apatite,  249,  369 
Apocrenic  acid,  817 
Apomorphine,  779 


INDEX. 


831 


Apple  oil,  644 

Aq.,  water  of  crystallisation,  53 

Aqua  fortis,  90 

regia,  191,  456 
Aquamarine,  383 
Aquate,  171 
Arabic  acid,  737 
Arabin,  737 
Arabinose,  725,  731 
Arabitol,  578 

Arachidic  (butic)  acid,  588 
Aragonite,  363 
Arbor  Dianae,  498 
Arbutin,  744 
Arc,  electric,  137 
Archil,  714 
Argand  lamp,  153 
Argillaceous  iron  ores,  396 
Argol,  333 
Argon,  76 

in  air,  68 
Argyrodite,  458 
Aromatic  acids,  599 

alcohols,  599 
aldehydes,  585 
esters,  645 
ethers,  631 
hydrocarbons,  549 
series,  549 
Arrack,  808 
Arrowroot,  735,  803 
Arsenates,  271,  352 
Arsendimethyl,  655 
Arsenetted  hydrogen,  272 
Arsenic,  265 

acid,  271 
anhydride,  271 
detected,  270,  272 
di-iodide,  274 

extracted  from  organic  matters,  274 
in  copper,  479 
native,  265 
oxides,  267 
pentasulphide,  275 
sulphides,  274 
tests  for,  270,  272 
tribromide,  274 
trichloride,  273 
trifluoride,  274 
tri-iodide,  274 
white,  267 
Arsenical  iron,  266 

nickel,  424 
Arsenical  paper  hangings,  270 

soap,  270 
Arsenides,  265 
Arsenio  di-ethyl,  655 
Arsenic  siderite,  272 
Arsenio  sulphides,  275 
triethyl,  655 
trimethyl,  655 
Arsenious  acid,  267 

chloride,  273 
iodide,  274 
oxide,  267 

crystalline,  268 
opaque,  268 
vitreous,  268 
Arseuites,  270 
Arsen-methyl  dichloride,  656 


Arsen-methyl  oxide,  656 
Arsiue,  272 
Artificial  indigo,  762 
musk,  650 
Asbestos,  373 

platinised,  98 
Ashes  of  coal,  113 
Asparagine,  678 
Asparagus,  678 
Aspartic  acid,  678 
Assafoetida,  714 

Assay  of  gold  by  cupellation,  ci6 
Astatki,  161 
Asymmetric-carbon  atoms,  605 

substitution-products,  1:46 
Atacamite,  485 
Atmolysis,  23 

Atmosphere,  composition  of,  68 
Atmospheric  air,  67 

germs,  71 
Atom  defined,  8 

-fixing  power,  573 
Atomic  heat,  296 
Atomicity,  299 
Atomic  theory,  287 

volumes,  304,  786 
weight,  10,  295 

determined,  46,  296 
Atoms,  286 
Atropic  acid,  601,  755 
Atropine,  601,  777 
Attraction,  chemical,  defined,  5 
Augite,  389 
Aurantia,  665 
Auric-chloride,  518 

cyanide,  697 

oxide,  518 
Auricyanides,  697 
Aurin,  723 

Aurothiosulphuric  acid,  519 
Aurous  chloride,  518 
cyanide,  697 
oxide,  518 

Autogenous  soldering,  226 
Auxochromes,  683 
Available  chlorine,  184 
Avidity  of  acids,  311 
Avogadro's  la\v,  289 
Azines,  768 
Azobenzene,  682 
Azo-compounds,  679-682 

dye-stuffs,  683 
Azoimide,  107 
Azoimides,  683 
Azoles,  764 
Azote,  75 
Azoniurns,  769 
Azoxybenzene,  682 
Azulmamide,  688 
Azulmic  acid,  688 
Azurite,  485 
Azyliues,  684 

BAKING  powders,  128 
Balloons,  24 

Balmain's  luminous  paint,  368 
Balsam  of  Peru,  561,  645 

Tolu,  561 
Balsams,  560 
Banca  tin,  448 


INDEX. 


Barbituric  acid,  772 

Barilla,  345 

Bar-iron,  best,  408 

crystalline,  408 
fibrous,  410 
manufacture,  404 

Barium,  359 

bromide,  361 
carbide,  361 
carbonate,  361 
chlorate,  361 
chloride,  361 
chromate,  432 
chromic  oxalate,  613 
di-oxide,  360 
ethoxides,  564 
hydroxide,  360 
hypophosphite,  260 
manganate,  428 
nitrate,  361 
oleate,  598 
oxide,  360 
peroxide,  360 
sulphate,  360,  361 
sulphide,  361 
sulpho-methylate,  641 
tannate,  610 
tungstate,  436 

Barley  sugar,  732 

Baryta,  360 

in  glass,  371 
sulphate,  361 
water,  361 

Baryto-calcite,  364 

Basalt,  365 

Base,  defined,  37 

Basic  bricks,  411 

Basicity  of  acids,  104 

Basic  oxides,  38 

process  (steel),  410 
salts,  104 
slag,  818 

Bassorin,  737 

Bathgate  coal,  529 

Bath  stone,  365 

Battery,  galvanic,  14,  323 

Baume's  flux,  339 

Bauxite,  385 

Bay  salt,  344 

Beans,  inosite  in,  716 

Bear,  436 

Bebeeriue,  783 

Beckmann's  apparatus,  320 

Beef-tea,  815 

Beehive  shelf,  20 

Beer,  composition,  806 
ropy,  806 
sparkling,  127 

Bees'  wax,  644,  799 

Behenic  acid,  588 

Belladonna,  777 

Bellite,  355 

Bell -metal,  452 

Bengal  saltpetre,  337 

Benzal  chloride,  584,  637 

Benzaldehyde,  584 

Benzaldoxime,  585 

Beuzamide,  668,  675 

Benzamido-acetic  acid,  675 

Benzene,  539 


Benzene   chlorides,  540 

constitution  of,  541 
dichloride,  540 
disulphonic  acid,  540,  713 
hexachloride,  540 
hexahydride,  541 
homologues  of,  548 
hydrocarbons,  general  preparation 

of>  549 
nucleus,  542 
orientation  of,  545,  547 
reactions  of,  540 
ring,  542 
series,  539 

substitution-products  of,  546 
sulphonic  acid,  540,  649 
tetrachloride,  540 
trisulphonic  acid,  540 
Benzcneazomethane,  682 
Benzidine,  666 

dye-stuffs,  684 
migration,  685 
Benzine,  528 
Benzindulenes,  769 
Benzoacetic  anhydride,  601 
Benzoates,  599 
Benzoated  lard,  799 
Benzoflavine,  768 
Benzofurfurane,  7^9 
Benzoic  acid,  600" 
alcohol,  599 
aldehyde,  584 
anhydride,  60 1 
chloride,  639 
ether,  645 
peroxide,  601 
series  of  acids,  599 
Benzoine,  585 
Benzoin  gum,  600 
Benzole,  539,  790 
Benzoline,  528 
Benzomercuramide,  668 
Benzometudiazines,  769 
Benzonitrile,  67;,  700 
Benzoparadiazine,  769 
Benzophenone,  626 
Benzopyrazoles,  765 
Benzopyrrol,  759 
Benzothiophen,  759 
Benzoquinone,  717 
Benzotrichloride,  637 
Benzoyl,  600 

azoiinide,  686 
chloride,  600,  639 
compounds,  600 
glycocine,  675 
hydrate,  600 
hydrazine,  686 
hydride,  600 
salicm,  743 
Benzyl,  600 

alcohol,  571,  709 
amine,  665,  700 
benzoate,  645 
bromide,  637 
chloride,  637 
cinnamate,  645 
cyanide,  700 
ether,  631 
hydrate,  600 


INDEX. 


Benzyl  hydride,  600 
Benzylidene — see  Beiizal 
Benzylideneaniliue,  768 
Berberiue,  783 

Bergamotte,  essential  oil  of  ccc 
Beryl,  383 
Beryllium,  382 
Bessemer's  process,  409 
Betaine,  661 
Betol,  712 
Bezoar-stones,  610 
Biborate  of  soda,  352 
Bicarbonate  of  soda,  348 
Bicarbonates,  130 
Bichromate,  430 
Biebrich  scarlet,  684 
Bile,  756,  822 

colouring-matters  of,  756 
constituents  of,  756 
Bilifuscin,  756 
Biliprasin,  756 
Bilirubin,  756 
Biliyerdin,  756 
Bioses,  731 
Biotite,  389 

Birch,  essential  oil  of,  551 
Bischofite,  375 
Biscuit  porcelain,  391 
Bismarck  brown,  684 
Bismuth,  438 

extraction  of,  439 
Bismuth  glance,. 440 
Bismuth  iodide,  440 
nitrate,  440 
Bismuth  ochre,  439 
Bismuth  gal  late,  610 
oxides,  439 
oxychloride,  440 
sulphide,  440 
telluride,  244 
trichloride,  440 
triethyl,  656 
trisnitrate,  440 
Bismuthic  acid,  440 
Bismuthite,  440 
Bisulphate  of  potash,  336 
Bisulphide  of  carbon,  238 
Bisulphites,  221 
Bisulphuret  of  carbon,  238 
Bitter  almond  oil,  584     * 
Bitter  principles,  745 
Bittern,  192,  344 
Bituminous  coal,  159,  168 
Biuret,  670 
Bixin,  747 
Black  ash,  345 
Black  band,  396,  397 
Black  dyes,  796 
Black-jack,  381 
lead,  109 

crucibles,  in 
Black  vitriol,  485 

wash,  502 
Blacking-,  231 
Blast-furnace,  397 

chemical  changes  in,  398 
gases,  399 
Blasting-gelatine,  647 

with  gunpowder,  341 
Bleaching  by  chloride  of  lime,  184 


833 


Bleaching  by  chlorine,  184 
ozone,  66 

sulphurous  acid,  210 
powder,  184 
Bleach  electrolytic,  icn 

killed,  220 
Blende,  377 
Blistered  steel,  412 
Block  tin,  449 
Blood,  755,  813 

absorption  spectrum  of,  756 
action  of  oxygen  on,  755 
aeration  of,  755,  813     s 
coagulation  of,  813 
crystals,  756 
deflbrinated,  814 
formation  of,  813 
globules,  814 
production  of,  822 
venous  and  arterial,  822 
Bloom  (iron),  407 
Blowers  in  coal  mines,  145 
Blowpipe,  cupellation  with,  466 
flame,  156 
hot  blast,  157 
oxyhydrogen,  48 
reduction  of  metals  by,  1 57 
table,  279 
Blue,  bricks,  392 
copperas,  484 
dyes,  723,  795 
fire  composition,  186 
flowers,  747 
John,  202 
malachite,  485 
metal  (copper),  478 
opal,  723 
oxide  of  molybdenum,  435 

tungsten,  436 
pill,  497 
pots,  in 
Prussian,  693 
stone,  484 
Thdnard's,  423 
Turnbull's,  695 
verditer,  484 
vitriol,  484 

water  of  copper-mines,  478 
writing-paper,  390 
Boghead  cannel,  529 
Boiler  fluids,  57,  270 

incrustations,  57 
scale,  57 
Boiling  meat,  815 

-point,  absolute,  29] 

denned,  63 
-points,  785 

of  alcohols,  565 
of  solutions,  320 
process  (iron),  408 
Bolivite,  440 
Bolsover  stone,  366 
Bone-ash,  249 

as  manure,  818 
black,  116 
oil,  766 
Bones  as  manure,  818 
composition,  249 
destructive  distillation,  116,  753 
dissolved,  818 

3G 


834 


INDEX. 


Boracic  (boric)  acid,  246 

vitreous,  246 
ether,  642 
lagunes,  246 
Boracite,  352 
Borates,  247 
Borax,  245,  352 

lake,  246 

vitrefied,  353 
Boric  acids,  245,  246 
anhydride,  245 
ether,  642 

Borneo  camphor,  560 
Borneol,  560 
Borofluoric  acid,  248 
Borofluorides,  248 
Boroglyceride,  647 
Boron,  245,  247 

alkides,  653 

amorphous,  247 

carbide,  248 

crystallised,  248 

diamond  of,  248 

ethide,  653 

graphitoid,  248 

methide,  653 

nitride,  248 

sulphide,  249 

trichloride,  248 

trifluoride,  248 
Botany  Bay  gum,  711 
Boucherie's  process,  820 
Bouquet  of  wines,  808 
Boyle's  fuming  liquor,    57 

law,  27 
Brain,  755 
Brandy,  808 
Brass,  482 
Brassidic  acid,  598 
Braunite,  426 
Brazilin,  748 
Brazil  wood,  713 
Bread,  808 

aerated,  809 

new  and  stale,  809 
Brewing,  805 
Bricks,  390 
Bright-iron,  402 
Brimstone,  208 
Brin's  oxygen  process,  39 
Britannia  metai,  451 
Brochantite,  485 
Brodie's  graphite,  in 
Bromacetylurea,  671 
Bromal,  638 
Bromamines,  662 
Bromanil,  718 
Bromanilines,  664 
Bromargyrite,  494 
Bromates,  194 
Bromhydrins,  636 
Bromic  acid,  194 
Bromine,  192 

aquate,  193 
chloride  of,  195 
Bromobenzene,  637 
Bromoform,  636 
Bromosuccinic  acid,  618 
Bronze,  441, 452,  481 

annealing  of,  452 


Bronze  coin,  441,  452,  481 

powder,  455 
Bronzing,  482 
Brookite,  456 

Brown  acid  (sulphuric),  228 
blaze,  382 
coal,  159 
dyes,  796 
hematite,  396 
Brucine,  782 
Brucite,  374 
Brunswick  green,  485 
Bubbles,  explosive,  42 
Buckskin,  797 
Bug-poison,  500 
Building  materials,  365 
stones,  365  -— ; 
Bullets,  rifle,  466 

shrapnel,  466 
Burner,  air-gas,  54 
Argand,  153 
Bunsen's,  154 
gauze,  156 
regenerative,  154 
ring,  6 1 
smokeless,  154 

Burnett's  disinfecting  fluid,  381 
Butalanine,  677 
Butane,  532 

normal,  532 
Butanes,  isomeric,  532 
Butene,  536 
Butic  acid,  799 
Butiu,  799 
Butine,  538 
Butter,  648,  799 
-milk,  812 
preparation  of,  812 
Butyl,  565 

alcohols,  568 
aldehyde,  583 
carbinol,  568 
isothiocyanate,  706 
Butylene,  536 
Butylic  alcohol,  569 

fermentation,  569 
normal,  569 
secondary,  568 
tertiary,  568 
Butyric  acid,  593 

aldehyde,  583 
ether,  644 
Butyrone,  625 

CACAO-BUTTER,  811 
Cacodyl,  655 

chloride,  655 

Cadaveric  alkaloids,  666,  750 
Cadaverine,  666 
Cadet's  fuming  liquor,  655 
Cadmia,  382 
Cadmium,  382 

salts,  382 
Caen-stone,  366 
Caesium,  359 

carbonate,  359 
Caffeic  acid,  611,  810 
Caffeidine,  775 
Cafleiue,  775,  810 
Caffeone,  810 


INDEX. 


835 


Caffeo-tannic  acid,  611 
Cairngorm-stones,  276 
Caking-coal,  117 
Calamine,  377 

electric,  377 
Calamus,  oil  of,  555 
Calcareous  waters,  57 

spar,  363 
Calcite,  363 
Calcium,  363 

acetate,  592 

action  on  water,  19 

arsenates,  369 

carbide,  370 

carbonate,  363 

chloride,  368^ 

citrate,  623""^ 

dioxide,  367 

disulphide,  217 

fluoride,  368 

hydrosulphides,  369 

hydroxide,  365 

hypochlorite,  183 

hyposulphite,  235 

iodate,  195 

malate,  618 

meconate,  622 

mesotartrate,  620 

nitrate,  367 

oxalate,  613 

oxide,  364 

oxychloride,  368 

pentasulphide,  217 

phosphates,  369 

phosphide,  263 

platinate,  507 

pyrophosphate,  369 

racemate,  620 

saccharate,  622 

silicates,  370 

succinate,  614 

sulphate,  367 

sulphide,  368 

superphosphate,  369 

tartrate,  619 
Calc-spar,  363 
Calculation,  chemical,  24 

of  formulae,  522 
Caliche,  197 
Calico-printing-,  796 
Calomel,  501 
Calorific  intensity,  165 

value,  163 
Calorimeter,  164 
Calorimetric  bomb,  164     . 
Calumba  root,  745 
Calumbin,  745 

Calvert's  disinfecting'  powder,  710 
Calx  chlorata,  185 
Cameoe,  276 
Camphanic  acid,  560 
Camphene,  557 
Camphor,  559 

artificial,  557 

oil  of,  559 
Camphoric  acid,  560 

peroxide,  557 
Camphoronic  acid,  560 
Camphors,  558 
Canarin,  703 


Candle,  chemistry  of,  150 

power,  I53, 162 
Candles,  801 
Cane-sugar,  731 
Cannel,  168 
Cannel-gas,  168 
Cantharidiu,  746 
Canton's  phosphorus,  368 
Caoutchene,  558 
Caoutchouc,  557 

artificial,  798 
vulcanised,  558; 
Cap  composition,  707 
Capric  ether,  644 
Caproic  acid,  594 

aldehyde,  583 
Caproin,  812 
Caprylic  acid,  594 
Capryl  alcohol,  570 

aldehyde,  583 
Caramel,  732 
Caramelan,  732 
Caraway,  essential  oil  of,  555 
Carbamates,  355 
Carbamic  acid,  356,  672 
Carbamide,  669 
Carbamides,  672 
Carbamines,  700 
Carbanilide,  671 
Carbazole,  667,  764 
Carbazotic  acid,  711 
Carbinols,  568 
Carbodiamine,  669 
Carbohydrates,  724 
Carbolic  acid,  709 
Carbon,  108 

atomicity,  522 

bisulphide,  238 

calorific  intensity,  166 
value,  163 

chlorides,  189 

combustion  of,  132 

determination  of,  521 

diamide-imide,  673 

dichloride,  190 

dioxide,  1 18  (see  also  Carbonic  acid 
gas) 

composition  of,  136 
liquid,  128 

properties  of,  121,  128 
solid,  129 
synthesis  of,  109 

disulphide,  238 

electrodes,  118 

heat  of  vaporisation  of,  130 

iodide,  201 

monoxide,   131    (see  also  Carbonic 

oxide) 

combuBtion  of,  133,  135 
composition  of,  136 

oxides,  118 

oxychloride,  190 

oxysulphide,  241 

pure,  preparation  of,  118 

sulphides,  241 

tetrabrouiide,  195 

tetrachloride,  189 

trichloride,  189 
Carbonado,  no 
Carbonate  of  lime  in  waters,  57 


836 


INDEX. 


Carbonates,  130 

alkaline,  360 
-Carbonic  acid,  127,  130 

gas,     118     (see    also    Carbon 

dioxide) 

absorption  by  water,  127 
decomposed  by  carbon,  132 
electric 

sparks,i3i 
potassium, 
131 

determined,  130 
evolved  by  plants,  119 
experiments  with,  122 
in  breathed  air,  125 
injurious  effects  of,  124 
liquefaction,  128 
sources,  119 
synthesis  of,  109 
anhydride,  35 
ether,  643 

oxide,  131  (see  also  Carbon  mon- 
oxide) 

absorbed,  486 
calorific  value,  166 
formed  in  fires,  132 
metallurgic  uses,  132 
poisonous  properties,  133 
preparation,  134 
properties  of,  134 
reduction  by,  135 
Carbonisation,  108 
Carbonising  fermentation,  158 
Car  bony  1  chloride,  190 
Carborundum,  282 
Carbostyril,  767 
Carbotriamine,  673 
Carboxyl,  586 

diamine,  669 

Carburetted  hydrogen,  144 
Carbylamine  reaction,  660 
Carbylamines,  700 
Carbyloxime,  706 
Carbyl  sulphate,  535 
Carmine,  748 

lake,  748 
red,  748 

Carminic  acid,  748 
Carnallite,  335,  373 
Carnelian,  276 
Carnine,  774 
Carotin,  747 

Carry's  freezing  apparatus,  81 
Carthamin,  747 
Cartilage,  754 
Carvacrol,  712 
Cascarilla.  oil  of,  555 
Case-hardening,  413 
Casein,  751 

vegetable,  752 
Cassel  green,  428 
yellow,  472 
Cassia,  oil  of,  585 
Cassiterite,  453 
Cast-iron,  397,  401 
grey,  402 
malleable,  403 
mottled,  402 
varieties  of,  402 
white,  402 


Castner's  process,  350 
Castor-oil,  798 
Cast  steel,  413 
Catalysis,  64 
Catechu,  609,  712,  715 
Cathode,  14,  324 
Cations,  324 
Cat's  eye,  276 
Caustic  alkali,  20 
lunar,  492 
potash,  333 
soda,  348 

Cavendish  eudiometer,  43 
Cedar-wood,  essential  oil  of,  555 
Cedriret,  716 
Celestine,  362 
Celluloid,  742 
Cellulo-nitrins,  739 
Cellulose,  734,  737, 738 

action  of  nitric  acid  on,  739 

animal,  743 

converted  into  sugar,  738 

cotton,  739 

hexanitrate,  739 

jute,  739 

solvent  for,  483,  738 

straw,  739 

Cement,  Portland,  366 
Roman,  366 
rust- joint,  212 
Scott's,  367 

Cementation  process,  411 
Cerasin,  737 
Cerebric  acid,  755 
Cerebrin,  755 
Ceresin,  529 
Cerite,  394,  459 
Cerium,  459 
Cerolein,  799 
Cerotic  acid,  799 
Cerotin,  570,  799 
Ceruse,  470 
Cerussite,  460,  470 
Ceryl  alcohol,  570,  799 
Ceryl  cerotate,  570,  644 
Cetin,  570,  799 
Cetyl  alcohol,  570 
Cetyl  palmitate,  570,  644 
Cevadilla  seeds,  783 
Cevadine,  783 
Ceylon  moss,  737 
Chalcedony,  276 
Chalk,  363 

in  waters,  56 
Chalkstones,  770 
Chalybeate  waters,  61,  416 
Chamber  acid,  227 
Chamomile,  essential  oil  of,  555 
Champagne,  808 

Chance's  sulphur  recovery  process,  347 
Charbon  roux,  113 
Charcoal,  in 

absorption  of  gases  by,  114 

action  of  steam  on,  133 

animal,  in,  116 

as  fuel,  117, 160 

ash, 114 

burning,  112 

decolorising  by,  116 

deodorising  by,  115 


INDEX. 


837 


Charcoal   for  gunpowder,  113 

oxidised  by  nitric  acid,  91 

prepared    at   diffei-ent    tempera- 
tures, 113 

retort,  114 

suffocation,  131 

wood,  in 
Charles'  law,  28 
Charring-  by  steam,  113 
Cheese,  812 
Chelidouic  acid,  623 
Chelidouine,  783 
Cheltenham  water,  61 
Chemical  affinity,  304 

measurement  of,  304 

calculations,  24 

change,  velocity  of,  310 

combination,  laws  of,  287 

influence  of  moisture 
on,  327 

energy,  static  method  of  measur- 
ing, 309 

equivalent  defined,  20,  289 

manures,  818 

properties  defined,  12 
Chessylite,  485 

Chevreul's  investigations,  800 
Chill-casting,  403 
Chimney,  hot  air,  for  lamps,  153 

ventilation  by,  126 
China  moss,  737 
Chinese  wax,  570,  648.  799 

white,  380 
Chinoline,  767 
Chitin,  754 
Chloracetamides,  668 
Chloracetic  acid,  638 
Chloral,  638 

alcoholate,  638 
hydrate,  638 
Chloralum,  389 
Chloramines,  662 
Chloranhydrides,  191 
Chloranil,  718 
Chlorauillic  acid,  718 
Chloranilines,  664 
Chloranthraceues,  638 
Chlorate  of  potash,  184 
Chlorates,  186 
Chlorhydrins,  646 

of  glycol,  646 
Chloric  acid,  184,  756 
Chloride  of  calcium  tube,  521 
lime,  183 
nitrogen,  190 
soda,  184 
Chlorine,  169 

bleaching  by,  175 

dioxide,  187 

disinfecting  by,  176 

experiments  with,  172 

group  of  elements,  205 

heptoxidf,  188 

hydrate  or  aquate,  171 

monoxide,  181 

he.it  of  formation,  181 

oxides,  181 

peroxide,  187 

water,  171 
Chloriodoform,  636 


Chlorisatins,  760 
Chlorite,  389 
Chlorites,  188 
Chlorobenzenes,  637 

benzole  chloride,  639 
chromic  acid,  434 
malaeic  acid,  640 

chloride,  640 
methylfonnate,  643 
naphthalenes,  552,  637 
phenols,  710 

phenol  sulphonic  acid,  715 
propionic  chloride,  639 
Chloroform,  530,  635 
Chlorofoi-moxime,  707 
Chlorophosphamide,  265 
Chlorophyll,  746 
Chloropicrin,  650,  711 
Chlorosulphuric  acid,  221 
Chlorous  acid,  188 
Chloroxalethyline,  6(39 
Chocolate,  8n 
Choke-damp,  125 
Cholesteramiue,  757 
Cholesterin,  757 
Cholesterol,  757 
Cholesteryl  chloride,  757 
Cholestrophane,  772,  775 
Cholic  acid,  756 
Choline,  666 
Chologlycholic  acid,  756 
Chondrin,  754 
Chromates,  432 

of  lead,  432 

potash,  431 
Chrome-alum,  433 

iron-ore,  417,  430 
yellow,  432 
Chromic  acid,  431 

anhydride,  431 
oxide,  431 
Chromites,  433 
Chromium,  430 

clilorides,  433 
dioxode,  433 
hydroxide,  433 
metallic,  431 
nitride,  434 
oxides,  431 
oxychloride,  434 
sulphate,  432 
sulphide,  434 
Chromogens,  683 
Chromyl  chloride,  434 
fluoride,  434 
Chrysaniline,  794 
Chrysean,  704 
Chrysene,  554 
Chrysoberyl,  383 
Chrysocolla,  485 
Chrysoidine,  684 
Chrystalliu,  751 
Churning,  812 
Chyme,  822 
Cigars,  777 
Cinchona  bark,  780 
Cinchonicine,  781 
Cinchonidine,  781 
Clnchouiue,  781 
Cinder,  159 


838 


INDEX. 


Cinnabar,  503 
Cinnamene,  550 
Cinnamic  acid,  60 1 

aldehyde,  585 

Cinnamon,  essential  oil  of,  585 
alcohol,  572 
cinnamate,  645 
Circulation  of  blood,  813 
Cisterns,  incrustations  in,  60 
Citraconic  acid,  616,  623 
Citrates,  623 
Citrenes,  555 
Citric  acid,  623 
Clarite,  275 
Clark's  process,  59 
Classes  of  organic  compounds,  525 
Classification  of  the  elements,  301 
Claus  kiln,  347 
Clay,  384,  390 

ironstones,  396,  397 
Cleveite,  77 
Clinker,  391 

Closed-chain  hydrocarbons,  538,  539 
Cloves,  essential  oil  of,  555 
Coal,  158 

ash  of,  1 60 
bituminous,  159 
brown,  159 
combustion  of,  159 
composition  of,  168 
distillation  of,  161,  790 
-dust  explosions,  148 
formation  of,  158 
-gas,  161 

enriching,  16? 
explosions  of,  145 
manufacture,  791 
purification,  238,  792 
sulphur  in,  161 
mines,  explosions  in,  148 

firedamp  of,  145 
-naphtha,  793 
stone,  1 60 

spontaneous  comoustion  of,  160 
-tars,  793 

bases,  793 

distillation  of,  539,  792 
dyes,  793 
varieties  of,  159 
Welsh,  160 
Coarse  copper,  479 

-metal  (copper),  476 
Cobalt,  421 

amine  compounds,  423 

arsenate,  266,  422 

arsenides,  422 

bloom,  266,  422 

chloride,  422 

cyanide,  692 

glance,  421 

hydroxide,  422 

nitrate,  422 

nitrite,  422 

chides,  421 

phosphate,  423 

py rites,  422 

salts,  422 

separated  from  nickel,  424 

silicate,  422 

sulphate,  422 


Cobalt  sulphides,  422 

ultramarine,  423 
vitriol,  422 
yellow,  422 
Cobalticyanides,  692 
Cocaine,  777 
Cocculus  indicus,  745 
Cochineal,  795 
Cocoa,  8n 

(gun)  powder,  340 
Cocoa-nut  oil,  648,  798 
Codeia,  779 
Codeine,  779 
Cod-liver  oil,  799 
Co-efficient  of  solubility,  54 
affinity,  311 
velocity,  312 
Coerulignone,  716 
Coffee,  composition,  810 

roasting,  810 
Coin-bronze,  452,  481 
Coke,  1 60 

action  of  steam  on,  133 
composition  of,  168 
Colchicine,  783 
Colcothar,  224,  417 
Cold-shortness,  408 
Collidine,  766 
Collodion,  742 

balloons,  742 
cotton,  742 
Colloids,  278 
Colophony,  560 
Colour- base,  722 
Coloured  fires,  186 
Colouring-matters,  animal,  756 

vegetable,  746,  747 
Columbite,  447 
Colza  oil,  798 
Combination,  chemical,  5 
laws  of,  287 

Combined  carbon  in  iron,  402 
Combining  proportions,  10 
Combustion  defined,  33 
furnace,  521 
in  oxygen,  32 
reciprocal,  48,  153 
temperature  of,  520 
tube,  521 

Comanic  acid,  769 
Comenic  acid,  622 
Common  salt,  343,  818 
Composition  tube,  466 
Compound  and  mixture,  6,  71 

defined,  3 
Concrete,  366 
Condensation,  531 

Condensation  products  of  acetone,  625 
Condenser,  Liebig's,  62 
Condurrite,  266 

Condy's  disinfecting  fluid,  428 
Congonha,  775 
Congo  red,  684 
Conhydrine,  776 
Coniferin,  745 
Coniferyl  alcohol,  745 
Couiine,  776 

-methylium  hydroxide,  776 

iodide,  776 
Conquiniue,  781 


INDEX. 


Conservation  of  energy,  305 

matter,  2 
Constitution  of  compounds,  102 

salts,  104,  105 

Contact  process  for  sulphuric  acid  manufac- 
ture, 230 
Converting-  furnace,  411 

vessel,  Bessemer's,  409 
Convolvulin,  745 
Convolrulinol,  745 
Cooking-  of  meat,  815 
Copal,  560 
Copper,  474 

acetate,  592 

aceto-arsenite,  271,  592 

acetylide,  139,  537 

action  of  ammonia  and  air  on,  483 
nitric  acid  on,  92 

alloys  of,  481 

amalgam,  498 

ammonio-sulphate,  485 

Ang-lesea,  478 

arsenite,  261,  484 

best  selected,  476 

blister,  476 

carbonates,  434,  484 

chlorides,  485 

cleaned,  481 

dry,  477 

effect  of  sea-water  on,  480 

electric  conductivity  of,  480 

emerald,  485 

extracted  in  laboratory,  479 

fusing- point,  480 

glance,  474 

hydrate,  483 

hydride,  483 

impurities  in,  479 

Lake  Superior,  480 

lead  in,  477 

metallurgy  of,  474 

moss,  476 

natire,  474 

nitride,  484 

ores,  474 

roasting,  474 

treatment  of,  for  silver,  489 

overpoled,  477 

oxides,  482 

oxychloride,  480,  485 

peacock,  474 

phosphates,  485 

phosphide,  487 

poling-,  477 

precipitate,  478 

properties  of,  480 

pyrites,  474,  487 

reduced  by  hydrogen,  46 

refining-,  477 

rose,  478 

sand,  474 
•"•silicates,  485 

smeltiug,  475,  476 

smoke,  475 

Spanish,  480 

subchloride,  486 

suboxide,  482 

sulphate,  484 

in  bread,  809 

sulphides,  486 


839 


Copper,  tinned,  453,  481 

tough-cake,  477 

uses  of,  481 

underpoled,  477 

verdigris,  481 

vessels  for  cooking,  481 

wet  extraction  of,  478 
Copperas,  418 

blue,  484 

Copper-zinc  couple,  21 
Coprolite,  369 
Coquimbite,  419 
Coral,  363 
Cordite,  647 
Coridine,  766 
Corn-flour,  803 
Corrosive  sublimate,  499,  coo 
Corundum,  388 
Cotarnine,  779 
Cotton,  737 

separated  from  wool,  738 
solvent  for,  483 
Coulomb,  325 
Coumarilic  acid,  759 
Coumarin,  759 
Coumarone,  759 
Crackers,  detonating,  708 
Cream,  812 

of  tartar,  333,  619 
Creasote,  712,  713 
Creatine,  676 
Creatiniue,  676 
Crenic  acid,  817 
Creoline,  712 
Cresol,  709,  712 
Critical  temperature,  29 
Croceo-cobalt  salts,  423 
Crocin,  747 

Crocus  of  antimony,  441 
Crookes'  discovery  of  thallium  .-73 
Croton  aldehyde,  537 
Croton-chloral,  638 
Crotonic  acid,  584,  597 

aldehyde,  584 
Crotononitrile,  705 
Crotonylene,  538 
Crow-fig,  782 
Crucibles,  black  lead,  TTI 
Cryohydrates,  53 
Cryolite,  389 
Cryoscopic  metl  od  310 
Cryptidine,  767 
Crystal  carbonate,  348 
Crystallisation,  50 
Crystals,  forms  of,  51 
Crystalloids,  278 

Crystals  from  vitriol  chambers,  225 
Cubebs,  essential  oil  of,  555 
Cudbear,  714 
Cumic  aldehyde,  585 
Cuminic  acid,  601 

aldehyde,  585 
Cuminol,  585 

Cummin,  essential  oil  of,  585 
Cupel-furnace,  465 
Cupellation  on  the  large  scale,  464 
small  scale,  465 
Cupric  acetate,  592 

aceto-arsenite,  592 
acid,  484 


840 


INDEX. 


Cupric  arsenite,  485 

carbonates,  485 
chloride,  485 
hydroxide,  484 
nitrate,  484 
oxide,  482 
phosphates,  485 
phosphide,  487 
silicates,  485 
sulphate,  484 
sulphide,  487 
tartrate,  619 
xanthate,  643 
Cuprocyanides,  696 
Cuprous  acetylide,  140,  537 
chloride,  140,  486 
hydrate,  483 
hydride,  483 
iodide,  486 
nitride,  484 
oxide,  483 
sulphide,  487 
xanthate,  240,  643 
Curcumin,  747 
Curd  of  milk,  751 
Curing-  fish  and  meat,  824        ^ 
Current,  electric,  14,  323 
Cutch,  609 

Cutting1  isinglass,  753 
Cyamelide,  702 

Cyanacetate  of  potassium,  614 
Cyanamide,  704 
Cyanethine,  700 
Cyanetholin,  705 
Cyanates,  702 
Cyanic  acid,  702 
Cyanides,  692 

of  hydrocarbon  radicles,  699 
Cyanin,  747 
Cyanines,  767 
Cyanite,  389 
Cyan-methine,  699,  769 
Cyano-benzene,  700 
Cyanogen,  687 

bromide,  698 
chloride,  698 
compounds,  686 
iodide,  698 
reactions  of,  688 
sulphide,  704 
Cyanmuramide,  704 
Cyanurates,  702 
Cyanuric  acid,  701 

chloride,  698 

Cyclic  compounds,  526,  538 
Cyclohexanes,  539 
Cylinder-charcoal,  113 
Cymene,  544 
Cymogene,  528 
Cytisine,  783 
Cytoblast,  755 

DAPHNETIN,  744 

Daphnin,  744 

Daturine,  777 

Davy  lamp,  146 

Deacon's  chlorine  process,  170 

Dead  oil  of  coal-tar,  793 

Decane,  528 

Decay,  119 


Decay  after  death,  824 

Decolorising'  by  charcoal,  116 

Decomposition  defined,  3 

Deflagrating  spoou,  34 

Deflagration,  338 

Dehydracetic  acid,  644 

Deliquescence,  53 

Delphinine,  783 

Densimeter,  341 

Density,  absolute,  341 
apparent,  341 

Deodorising-  by  charcoal,  115 
chlorine,  176 

Dephlogisticated  muriatic  acid,  176 

Derbyshire  spar,  202 

Dermatol,  610 

Desiccator,  232 

Desilverising  lead,  463 

Destructive  distillation  defined,  112 

Detonating  tubes,  186,  647 

Devitrification,  372 

Dextrin,  736 

Dextro-ethylidine  lactic  acid,  604 

Dextro-rotatory,  542,  619 
pinene,  557 

Dextrose,  726 

Dextrotartaric  acid,  619 

Dhil  mastic,  468 

Diabetes,  726 

Diacetyl,  627 

oxide,  593 

Diad  elements,  n 

Diallyl  sulphide,  705 

Dialuramide,  772 

Dialuric  acid,  771 

Dialyser,  278 

Dialysis,  277 

of  air,  70 

Diamides,  669 

Diamido-azobenzene,  684 

Diamidobenzene,  650,  666 

Diamidothiodipheuylamiue,  645 
diphenyl,  666 

Diamidogen,  106 

Diamidomiphthalines,  666 

Diamidotriphenylmethane,  722 

Diamines,  658,  665 

Diamond,  108 

black,  in 
combustion  of,  109 
specific  heat  of,  118 

Diamonds,  artificial,  no 

Diaspore,  388 

Diastase,  733,  804 

Diathermic,  239 

Diatomic  elements,  10 

Diazines,  768 

Diazo-acetamide,  680 
acetic  acid,  680 
amidobcnzene,  682 

compounds,  682 
amidonaphthaleue,  666 
benzene,  680 

butyrate,  68  r 
chloride,  682 
compounds,  68 1 
hydroxide,  68 1 
nitrate,  680 
potasso  oxide,  68 1 
sulphonic  acid,  683 


INDEX. 


841 


Diazo-compounds,  106,  637,  680 

diazoimides,  686 

dyestuffs,  684 

ethane,  680 

methane,  680 

reactions,  106,  68 1 
Diazonium  srilts,  68 1 
Diazotising-,  681 
Dibenzofurfurane,  759 
Dibenzoparadiazine,  769 
Dibeuzoparathiaziues,  768 
Dibenzoparoxazine,  768 
Dibenzopyrrol,  759 
Dibenzothiophen,  759 
Dibenzoyl  oxide,  601 
Dibenzyl,  551 

Dibromonitro-aceto-nitrile,  707 
Dibromo-nitro-phenyl-propionic  acid,  764 
Dibromopropanes,  544 
Dibutyraldine,  776 
Dichloracetone,  623 

cyanhydrate,  623 
Dichloracetonic  acid,  623 
Dichlorethene,  634 
Dichlorether,  631 
Dichlorhydrin,  646 
Dichlorobenzene,  540 
Dichloromethane,  530 
Dicinnainene,  550 
Dicyauimide,  704 
Dicyauacetonic  acid,  623 
Didymium,  394 
Diethyl,  653 

amine,  662 
glycol  ether,  631 
Diethylene-diamine,  666 
Diethylnitrosamine,  662 
Diethyloxamide,  669 
Diffusibility  of  g-ases,  25 

law  of,  25,  291 
measurement  of,  25 
Diffusion,  25 

tube,  25 
Diformin,  647 
Digallic  acid,  610 
Digestion,  821 
Digitalin,  745 
Dihydric  alcohols,  555 
Dihydropyrazoles,  764 
Dihydroxy  anthraquinoline,  768* 
benzaldehydes,  586 
benzenes,  712 
benzoic  acid,  609 
succinic  acid,  618 
toluene,  714 
Dihydroxyl,  106 
Diiodopurine,  771 
Dikakodyl,  656 
Diketones,  626 


Dimethyl,  530 
allo 


.  Joxantin,  752 
amido-azobenzene,  683 

benzine  sulphouic  acid,  683 

pyrimidiue,  769 

toluphenazine,  769 
amine,  659 
analine,  664 
-arsenic  acid,  655 
arsine,  656 
benzene,  549 


Dimethyl  furfurane,  758 
ketone,  625 
oxamide,  669 
oxide,  628 
parabanic  acid,  772 
Dimethoxyphthalide,  779' 
Dimorphous,  109,  268 
Dinaphthyl,  553 
Dinasfire  brickx,  392 
Dinitraniline,  664 
Dinitric  acid,  96 
Dinitrobeuzene,  540 
benzenes,  650 
phenol,  711 
Diolefines,  537 
Dioptase,  485 
Dioxindol,  760 
Diphenic  acid,  554 
Diphenyl,  550 

amiiie,  664 
guanidine,  673 
ketone  (beuzophenone),  626 
methane,  551 
methylpyrazole,  764 
oxide,  631 
sulphides,  710 
sulphone,  710 
-sulphurea,  672 
urea,  671 

Diphenyleue  methane,  551 
oxide,  764 
sulphide,  764 
Diplatinamiue,  508 
Diplatosamiue,  508 
Dippel's  oil,  753 
Dipropargyl,  539 
Dipyrotartracetoue,  619 
Disaccharides,  731 
Disacryl,  584 
Disazo-dyestuffs,  684 
Discharge  in  calico  printing,  183,694 
Disinfectant,  Cal vert's,  710 

MacDougall's,  710 

Disinfecting  by  chloride  of  lime,  184 
chlorine,  170 
ferric  chloride,  419 
permanganates,  429 
fluid,  Burnett's,  381 
Condy's,  428 

Disintegration  of  rocks,  128 
Displacement,  collection  of  gas  by,  29 
Dissociation,  301,  312 

effect  of  pressure  on,  301 
of  dissolved  molecules,  317 
sal-ammoniac,  86 
steam,  48 

vermilion  vapour,  504 
Disthene,  389 
Distillation,  62 

destructive  or  dry,  112 
fractional,  74,  529 
under  diminished  pressure,  595 
Distilled  sulphur,  208 

water,  61 
Diterpene,  555 
Dithionic  acid,  237 
Dithionous  acid,  237 
Diureides,  771 
Divalent  elements,  n 
Divi-divi,  609 


842 


INDEX. 


Dobereiner's  lamp,  506 
Dodecane,  528 
Dodecatoic  acid,  594 
Dolomite,  373 
Double  salts,  104 
Dough,  734,  808 
Dowucast  shaft,  88 
Dowson  gas,  163 
Dragon's  blood,  715 
Drummond  light,  48 
Dryers,  798 
Drying  gases,  46 

in  vacuo,  232 
-oils,  798 

over  oil  of  vitriol,  232 
Dry  rot,  738 
Ductility  of  copper,  480 
Dulcite,  579 
Dung  as  manure,  817 
Dust,  71 

explosions,  148 
Dutch  liquid,  148,  535,  634 

metal,  172 
Dyeing,  795 
Dyes,  683 

adjective,  683 

substantive,  683 
Dyestuffs,  acid,  683 
basic,  683 
Dynamite,  646 
Dyslysin,  756 

EARTHENWARE,  392 
'Earths,  alkaline,  372 
Earth's  crust,  composition  of,  5 
Eau  de  Javelte,  184 
Ebonite,  558 
Effervescence,  127 
Efflorescence,  52 
Egg-shells,  1 20 
Eikonogeu,  712 
Elaidic  acid,  598,  802 
Elastine,  677 
Elaterin,  746 
Elaterium,  746 
Elba  iron  ore,  356 
Electric  arc,  137 

furnace,  138 
Electrical  amalgam,  498 
pressure,  17 
quantity,  17 
tension,  17 
Electrising,  66 
Electro-chemical  list,  324 

equivalents,  325 
Electrodes,  14,  118 
Electro-gilding,  517 
Electrolysis  defined,  15,  323 

of  hydrochloric  acid,  16 
of  salts,  325 

of  sulphuric  acid,  15,  324 
of  water,  13.. 
Electrolytes,  323 
Electrolytic  bleach,  350 

dissociation,  327 
production  of   alkali  and  chlo- 
rine, 349 

Electro -negative  elements,  15 
plating,  490 
positive  elements,  15 


Electrons,  324 

Element  denned,  3 

Elements,  groups  of,  303 

Elemi-resin,  560 

Ellagic  acid,  610 

Embolite,  494 

Emerald,  382 

Emerald  green,  271,  485, 592 

Emery,  388 

Emetics,  620 

Emetine,  781 

Empirical  formulae,  522 

Ernpyreumatic,  555 

Emulsin,  584 

Enantiomorphous,  621 

Enantiotropes,  315 

Eudosmose,  814 

Endothermic,  96,  305 

Energy,  chemical,  304 

Eosins,  723 

Epsom  salts,  375 

Equivalent  defined,  20     •— ^ " 

Equivalents  of  acids  and  bases,  105   N 

Ergot  of  rye,  734  S 

Erucic  acid,  598 

Erythric  acid,  714 

Erythrite,  578 

Erythro-dextrin,  736 

Eserine,  783 

Essence  of  turpentine,  555 

Essential  oils,  555 

extraction  of,  555 
Esters,  640 

sulphuric,  641 
Ethal,  570 
Ethane,  524,  530 

constitution  of,  527 
Ethene,  535 

-alcohol,  574 
-diamines,  666 
-dibromide,  574,  635 
-dichloi'ide,  634 
-di-iodide,  635 
-naphthalene,  553 
Ether,  627 

chemical  constitution,  628 
decomposition  by  heat,  141 
properties  of,  629 
reactions  yielding,  630 
Ethereal  salts,  640,  645 
Etherification,  continuous,  629 

theory  of,  629 
Ethers,  631 

derivation  from  alcohols,  627 
mixed,  627 

perfuming  and  flavouring,  644,  645 
table  of,  628 
Ethine,  537 
Ethionic  acid,  535,  649 

anhydride,  535 
Ethoxides,  564 
Ethoxyl,  654 
Ethyl,  600 

acetamide,  667 
acetate,  643 
aceto-acetate,  644 
alcohol,  561 
aldehyde,  583 
allophanate,  671 
amine,  662 


INDEX. 


843 


Ethylamine  hydrochloride,  662 

ethyl  thiocarbonate,  706 
arsenite,  642 
benzoate,  645 
borate,  642 
boric  acid,  653 
bromide,  634 
butyrate,  644 
caprate,  644 
carbamate,  672 
carbamine,  701 
carbimide,  705 
carbinol,  569 
carbonate,  643 
chloride,  633 
cyanide,  699 
diazo-acetate,  680 
diethylacetoacetate,  644 
ether,  628 

ethylacetoacetate,  644 
fluoride,  634 
formamide,  701 
formate,  643 
hydride,  524,  530 
iodide,  634 
isocyanate,  705 
isocyanide,  701 
isothiocyanate,  706 
malonate,  645 
metaphosphate,  642 
mustard  oil,  706 
nitrate,  642 
nitrite,  642 
nitrosamine,  662 
orthocarbonate,  643 
oxalacetate,  645 
oxalate,  645 
oxamate,  669 
oxamide,  669 
oxysulphide,  573 
palmitate,  644 
pelargonate,  644 
phosphates,  642 
phosphines,  654 
phosphinic  acids,  654 
quinol  dicarboxylate,  718 
salicylate,  645 
silicates,  642 
sodaceto-acetate,  643 
sodethylacetoacetate,  644 
succiuyl  succinate,  718 
sulphates,  641 
sulphides,  573 
sulphinic  acid,  649 
sulphite,  648 
sulphone,  573 
sulphonic  acid,  648 
sulphuric  acid,  628 
thiocarbimide,  706 
ureas,  705 
Ethylates,  564 
Ethylene,  142,  535 

-diamine,  665, 

bromide,  535,  635 

chloride,  535,  634 

glycol,  574 

hydrate  chloride,  631 

iodide,  635 

lactic  acid,  607 

oxide,  631 


Ethylene  succinic  acid,  614 
Ethylidene  chloride,  635 

lactic  acid,  603 

succinic  acid,  614 
Ethylsulphuric  acid,  641 
Euchlorine,  188 

-water,  779 
Eudiometer,  Cavendish,  43 

siphon,  44 
Eudiometric  analysis  of  air,  44 

marsh-gas,  157 
Eupyrion  matches,  188 
Eurhodines,  769 
Euxanthic  acid,  747 
Euxanthine,  747 
Euxanthone,  747 

Evaporation,  influence  of  pressure  on,  313 
Even  numbers,  law  of,  523 
Evernic  acid,  714 
Everninic  acid,  714 
Exalgin,  668 
Excretions,  823 
Exitele,  442 
Exothermic,  96 
Explosions,  30,  42 

in  coal-mines,  145,  148 

sympathetic,  741 
Extinguishing  fires,  122 

FAGOTING,  407 
Fallowing,  818 
Faraday's  law,  325 
Farinose,  735 
Farm-yard  manure,  817 
Fast  colours,  795 

green,  714 
yellow,  712 
Fats,  648,  797 

f using-points  of,  850 
Fatty  acid  series,  587,  588,  644 
Fehling's  test,  619 
Felspar,  332,  384 
Fenchene,  557 
Fenchone,  560 
Fermentation,  119,  562 

acetous,  590 
alcoholic,  562 
arrested,  220,  563 
viscous,  578 
Ferrates,  418 
Ferric  acetate,  591 

acid,  418 

ammonio-citrate,  624 

benzoate,  600 

carbonate,  418 

chloride,  419 

citrate,  623 

cyanide,  693 

ferrocyanide,  693 

oxalate,  613 

oxide,  417 

oxychloride,  420 

phosphate,  419 

succiuate,  614 

sulphate,  419 
Ferricuui,  421 
Ferricyanides,  695 
Ferrite,  414 
Ferrocyanic  acid,  687 
Ferrocyanides,  687 


844 


INDEX. 


Ferrocyanogen,  687,  693 
Ferro-manganese,  403 
Ferrosoferric  oxide,  417 
Ferrosum,  421 
Ferrous  arsenate,  419 
chloride,  419 
carbonate,  418 
cyanides,  693 
ferricyanide,  695 
ferrocyauide,  693 
hydroxide,  416 
iodide,  419 
oxalate,  613 
oxide,  416 
phosphate,  419 
silicate,  419 
sulphate,  418 
sulphide,  420 
Ferrum  redactum,  416 
Ferruretted  chyazic  acid,  687 
Fibrin,  blood,  751 
muscle,  751 
vegetable,  752 
Fibrinogen,  751 
Fibroin,  754 
Filtration,  116 
Finery  cinder,  405 
Fire-bricks,  392 
-clay,  384 
-damp,  144 

indicator,  148 
Fires,  blue  flame  in,  132 
coloured,  186 
gas,  161 
Fish  oils,  799 

shells,  82 

Fittig's  reaction,  531,  549 
Fixing  photographic  prints,  236 
Flags,  Yorkshire,  365 
Flake-white,  440 
Flame,  analysis  of,  siphon,  152 
blowpipe,  156 
cause  of  luminosity  in,  152 
effect  of  pressure  on,  153 

wire  gauze  on,  151 
experiments  on,  151 
extinction  by  gases,  122 
oxidising  and  reducing,  156 
structure  of,  148 
temperature  of,  151 
Flames,  simple  and  compound,  149 

smoky,  154 

Flashing-point  of  oils,  528 
Flavin,  745 
Flavopurpurin,  721 
Flesh,  814 

juice  of,  676,  814 
sugar  of,  716 
flint,  276 

and  steel,  276 
Flints  dissolved,  353 
Florence  flask,  41 
Floss-hole,-  405 
Flowers  bleached,  220 
Fluoranthreue,  555 
Fluorene,  551 
Fluorescei'n,  714,  724 
Fluorescence,  724,  781 
Fluoric  acid,  202 
Fluoride  of  calcium,  202,  330 


Fluoride  of  silicon,  203 
Fluorides',  205 
Fluorine,  202 
Fluor  spar,  202,  368 
Flux,  398 

Baume's,  339 
Fog,  71 

Food,  plastic  constituents  of,  823 
preservation  of,  823 
respiratory  constituents  of,  823 
Forge-iron,  403 
Formaldehyde,  580 
Formaline,  580 
Formamides,  667 
Formates,  590 
Formic  acid,  589 

aldehyde,  580 
esters,  643 
ether,  643 
thio-aldehyd,  7015 
Formins,  647 
Formouitrile.  699 
Formose,  728 

Formula?,  axial  symmetrical,  616 
calculation  of,  46,  300 
empirical,  523 
graphic,  524 
molecular,  523 
plane  symmetrical,  616 
rational,  524 
structural,  524 
Formyldiphenylamiue,  768 
Fouling  of  guns,  342 
Foundry  iron,  403 
Fractional  distillation,  74,  529 

precipitation,  588 
Franklinite,  417 
Fraxin,  744 
Free-stone,  365 
Freezing  apparatus,  81,  82 

in  red-hot  crucibles,  219 
mixtures,  83,  356 
of  water,  63 
points  of  solution,  319 
French  chalk,  373 
Friction-tubes,  445 
Friedel  and  Craft's  reaction,  549 
Fructose,  727 
Fruit  essences,  644 

sugar,  727 

Fruits,  ripening  of,  820 
Fuchsiue,  722 
Fucose,  7215 
Fucusol,  586 
Fuel,  158 

calorific  intensity  calculated,  166 

value  calculated,  163 
composition  of,  168 
gaseous,  161 
Fuller's  earth,  384 
Fulminate  of  mercury,  706 

silver,  708 

Fulminates,  706,  708 
Fulminating  gold,  518,  697 
platinum,  507 
silver,  492     ^ 
Fulminic  acid,  707 
Fulminurates,  718 
Fulmiuuric  acid,  708 
Fumanyl  dichloride,  640 


INDEX. 


845 


Furnaric  acid,  615 

Fumarotd  structure,  616 

Fumaryl  dichloride,  640 

Fumigation  with  sulphurous  acid,  220 

Fuming-  sulphuric  acid,  224 

Fumitory,  615 

Funnel  tube,  22 

Fur  in  kettles,  57 

Furfural,  586 

Furfuramide,  586 

Furfurane,  622,  758 

Furfuryl  alcohol,  586 

Furnace,  electric,  138 
gas,  22 

regenerative,  167 
reverberatory,  132 

Furnaces,  theory  of,  167 

waste  of  heat  in,  167 

Furo-azoles,  764 

Fusco-cobalt  salts,  423 

Fusel  oil,  808 

Fusible  alloy,  439 

Fusing-points,  784 

of  fats,  800 

Fusion,  277 

Fustic,  715,  747 

Fuze,  electric,  487 

percussion,  255 

GADININE,  666 
Gadolinite,  394 
Gahnite,  417 
Galactonic  acid,  734 
Galactose,  727 
Galbanum,  714 
Galena,  459 
Gallein,  715 
Gallic  acid,  609 

synthesis  of,  610 
anhydride,  610 
Gallium,  392 
Gall-nuts,  610 
Gallocyanine,  768 
Galloflavin,  609 

tannic  acid,  610 
Gallstones,  757 
Galvanic  battery,  14 

cell,  323 

Galvanised  iron,  376 
Gambodic  acid,  745 
Gamboge,  714,  747 
Gangue,  398 
Ganister,  407 
Garlic,  essential  oil  of,  705 
Garnet,  389 
Garnierite,  424 
Gas-burners,  154 

carbon,  792 

composition  of,  161,  168 

cylinder,  29 

Dowson,  163 

explosions,  145 

fires,  161 

holder,  135 

jar,  34 

manufacture,  791 

Mond,  163,  168 

producer,  162,  168 

semi-water,  163 

valuation  of,  143 


Gas-water,  163,  168 
Gases,  analysis  of,  45,  157 

constitution  of,  27 

diffusion  of,  25 

effect  of  pressure  on,  27 

expansion  by  heat,  28 

good  and  bad,  28,  72 

in  waters,  54 

solubility  of,  315,  316 

effect  of  heat  on,  80 

pressure  on,  80 
Gasolene,  528 
Gastric  juice,  822 
Gaultheria,  oil  of,  645 
Gaylmsite,  364 
Gedge's  metal,  481 
Geissler  tube,  330 
Gelatin,  753 
Gelatine  dynamite,  647 
Gelose,  737 
Gentianin,  745 
Germanium,  458 
German  silver,  423,  481 
Germination,  804 
Germs  of  disease,  71 
Geysers,  277 
Gibbsite,  388 
Gilding,  517 

porcelain,  392 
Gin,  808 
Glass,  370 

Bohemian,  371 

bottle,  371 

coloured,  372 

composition  of,  370 

crown,  371 

etched,  204 

flint,  371 

-gall,  370 

of  antimony,  445 

plate,  371 

potash,  371 

silvered,  490 

soda,  370 

soluble,  353 

toughened,  372 

window,  370 
Glauberite,  351 
Glauber's  salt,  351 
Glaze  for  earthenware,  391 
Glazier's  diamond,  no 
Gliadin,  753 
Globulin,  750 
Glucinum,  382 
Glucoheptouic  acid,  728 
Glucoheptose,  728 
Glucol,  715 
Gluconic  acid,  729 
Glucosan,  726 
Glucosazone,  728 
Glucose,  725 

artificial,  726 
Glucoses,  725 

constitution  of,  729 
synthesis  of,  728 
Glucosides,  743 
Glucosone,  728 
Glue,  753 

liquid,  753 
Glutamic  acid,  752 


846 


INDEX. 


Glutaric  acid,  615 
Gluten,  734,  752 
Glyceric  acid,  607 

aldehyde,  584 
Glycerides,  647 
Glycerine,  576 

artificial  preparation  of,    76 
ether,  631 
soap,  801 
Glycerol,  576 

ethereal  salts  of,  645 
Glycerose,  584 
Glyceryl,  636 

arsenite,  647 
borate,  647 
phosphate,  647 
salts,  647 
tribromide,  636 
trichloride,  636 
tricyanide,  623 
trinitrate,  646 
Glycocholic  acid,  756,  822 
Glycociamine,  676 
Glycocine  (glycocoll)  (glycine),  674 

synthesis  of,  654 
Glycocyamidine,  676 
Glycogen,  736 
Glycol,  573,  574 

amide,  668 
chlorhydrin,  575 
dialdehyde,  575 
disodium,  575 
ethereal  salts  of,  646 
ethers,  645 
monosodium,  575 
Glycolide,  604 
Glycollic  acid,  602 
Glycols,  secondary,  573 

tertiary,  573 
Glycosine,  584 
Glycuronic  acid,  607 
Glycyphillin,  744 
Glycyrrhizic  acid,  746 
Glyoxal,  584 
Glyoxalic  acid,  607 
Glyoxalines,  765 
GlyoxyJic  acid,  607 
Glyoxyl  urea,  773 
Gneiss,  389 
Gold,  513 

arsenide,  519 

assay  by  cupellation,  516 

bronze,  436 

chloride,  518 

coin,  515 

crucible,  518 

cyanides,  697 

dissolved,  191 

extracted  from  silver,  514 

extraction,  513 

fulminating',  518 

identified,  93 

leaf,  517 

oxides,  518 

physical  properties  of,  517 

refining,  514 

removal  of  mercury  from,  497 

ruby,  254,  517 

salts  of,  518 

separated  from  silver  and  copper,  233 


Gold,  sodium-hyposulphite,  519 
standard,  515 
sulphides,  519 
testing,  516 
thread,  517 
Gongs,  452 
Goose-fat,  648 
Goulard's  extract,  592 
Grains,  brewers',  805 
Granite,  365 

disintegration  of,  365 
Granitic  rocks,  332,  365 
Granulated  zinc,  22 
Granulose,  735 
Grape-sugar,  726 
Grapes,  colouring- matter  of,  746 
Graphic  formula,  524 
Graphite,  no 

in  cast-iron,  no,  402 
Graphitic  acid,  in 
Graphitised  carbon,  118 
Green,  arsenical,  270 

borate  of  chromium,  433 

Brunswick,  485 

chrome,  433 

colour  of  plants,  746 

fire,  186 

flame  of  barium,  362 

boracic  acid,  247 
copper,  485 
thallium,  473 
hydroquinone,  719 
malachite,  485 
manuring,  817 
mineral,  485 
Kinmann's,  423 
salt  of  Magnus,  508 
vitriol,  418 

Grey  antimony  ore,  441 
copper  ore,  474 
iron,  402 
powder,  497 
Grinder's  waste,  411 
Gristle,  753 
Grotto  del  Cane,  121 
Groug-h  saltpetre,  337 
Grove's  battery,  14 
Growth  of  plants,  819 
Guaiacol,  713 
Guaiacum,  resin,  560,  713 
Guanidines,  672,  673 
Guanine,  673,  773 
Guano,  817 
Guignet's  green,  433 
Gulose,  727 
Gum  Arabic,  737 
Bassora,  737 
British,  736 
Senegal,  737 
tragacanth,  737 
Gums,  737 
Gum-sugar,  725,  737 
Gun-cotton,  647,  740 

compared  with  gunpowder,  742 

composition,  740 

explosion,  741 

manufacture,  740 

products  of  explosion  of,  742 

properties,  742 

pulp,  741 


INDEX. 


Gun-cotton,  reconversion  of,  740 
Gun-metal,  452,  481 
Gunpowder,  339 

brown,  340 

composition,  339 

explosion  of,  341 

explosion  under  pressure,  343 

influence  of  size  of  grain,  340 

manufacture,  340 

products  of  explosion,  341 

properties  of,  340 

smokeless,  339 

temperature  of  combustion,  341 

white,  186 
Gutta-percha,  585 
Gypsum,  367,  818 

H.^MATEIN,  748 

Haematin,  756 
Hcematite,  396 
Hsematoxylin,  748 
Haemin,  756 
Haemocyanin,  474 
Haemoglobin,  755 
Hair-dye,  237,  493 
Halogen  defined,  205 

derivatives,  632 

from  acids,  639 
from  aldehydes,  638 
of  closed-chain  hydro- 
carbons, 637 
of  open-chain  hydrocar- 
bons, 632 
propylenes,  636 
Halogens,  review  of,  205 
Haloid  salts,  205 
Hammer-slag-,  406 
Hard  metal,  452 
Hardness,  degrees  of,  58 

permanent  and  temporary,  58 
Hard  water,  55 
Hargreave's  soda  process,  346 
Hartshorn,  spirit  of,  81 
Hatchett's  brown,  694 
Hauerite,  430 
Hausmannite,  427 
Heat  and  temperature,  163,  164 
atomic,  296 
of  combustion,  163 
relation  to  chemical  attraction,  38,  306, 

307 

specific,  296 

units,  44 

Heating-  of  hay-ricks,  158 
Heats  of  formation  calculated,  307 
Heavy  metal  alkydes,  656,  657 
Heavy  lead  ore,  469 

spar,  360 
Helianthin,  683 
Helicin,  743 
Heliotropine,  586 
Helium,  77 
Hellebore,  745 
Helleborein,  745 
Hemimorphite,  377 
Hemiterpene,  556 
Hemlock,  776 
Henbane,  778 
Hepatic  waters,  61 
Heptamethylene,  539 


847 


Heptane,  528 

Heptoses,  728 

Heptylic  acid,  594 

Herapathite,  781 

Hesperidene,  556 

Hesperidin,  744 

Hesperitin,  744 

Heterocyclic  compounds,  757  761: 

Hexacetyl  cellulose,  739     ' 

condensed  nuclei  from, 

759 
Hexa-chlorobenzene,  540 

dieue,  537 

ethane,  189 

hydric  alcohol,  578 

hydropyrazine,  769 

hydropyridine,  766 

hydroxyanthraquinone,  610,  721 

hydro  xybenzene,  716 

nitro-diphenylamine,  665 
Hexagonal  crystals,  52 
Hexoses,  725 

stereo-  isomerism  of,  730 
Hexyl  alcohol,  570 

fermentation,  570 

butyrate,  570 

carbinol,  570 
Hexylic  acid,  594 
Hippurates,  675 
Hippuric  acid,  675 
Holmia,  394 
Homologous  series,  527 
Honey,  731 
Hopeite,  382 
Hop  substitute,  711,  745 
Hops,  805 

essential  oil  of,  555 
Hornblende,  389 
Horn-lead,  471 

quicksilver,  502 
silver,  493 

Horse-chestnut  bark,  744 
Hot  blast,  theory  of,  399 
Humic  acid,  817 
Humus,  816 
Hyacinth,  458 
Hydantoin,  671 
Hydramines,  665 
Hydrargyllite,  388 
Hydrargyrum  cum  creti,  497 
Hydrates,  53 
Hydraulic  cements,  366 

main,  790 
Hydrazine,  106 

hydrate,  107 
sulphate,  1 06 
Hydrazines,  684 

identified,  685 
Hydrazobenzene,  682 
Hydrazoic  acid,  107 
Hydrazones,  625 
Hydrazotoluene,  685 
Hydrazulmin,  688 
Hydrides  of  alcohol  radicles,  527 
Hydrindigotin,  762 
Hydriodic  acid,  200 
Hydroaromatic  hydrocarbons,  550 
Hydrobenzamide,  585 
Hydrobenzoin,  575 
Hydroboracite,  375 


848 


INDEX. 


Hydromic  acid,  194 
Hydrocarbons,  137,  526,  791 
cracking1,  151 

open-  and  closed-chain,  538 
Hydrocellulose,  738 
Hydrochloric  acid,  177 

action  of,  on  metals,  179 
analysis  of  oxides,  180 
electrolysis  of,  16,  180 
from  alkali  works,  178 
yellow,  178 

Hydrocobalticyanic  acid,  692 
Hydrocoerulignone,  717 
Hydrocotarnine,  779 
Hydrocyanic  acid,  690 

synthesis  of,  690 
tests  for,  691 

Hydrocyanocarbodiphenylimide,  763 
Hydroferricyanic  acid,  695 
Hydroferrocyanic  acid,  693 
Hydrofluoboric  acid,  248 
Hydrofluoric  acid,  202 
Hydrofluosilicic  acid,  284 
Hydrogel  form,  278 
Hydrogen,  21 

antimonide,  444 

arsenide,  271 

calorific  intensity  calculated,  166 

value,  163 
chloride,  177 

synthesis  of,  177 
combustion  of,  29,  30 
dioxide,  63 
experiments  with,  29 
heat  of  formation,  172 
identified,  15 
liquefaction  of,  74 
nitride,  107 
peroxide,  63 

tests  for,  64 
persulphide,  217 
phosphides,  262 
preparation,  21,  22 
properties  of,  23 
purification,  46 
selenietted,  243 
sulphide,  213 
Hydrogenium,  49 
Hydro-isatin,  761 
Hydrolysis,  265,743 


Hydronaphthalene,  553 

Hydronitroprussic  acid,  696 

Hydronitrous  acid,  107 

Hydroplatinocyanic  acid,  698 

Hydro-potassium  tartrate,  619 

Hydropyrrol,  759 

Hydroquinone,  714,  717,  718 

Hydroselenic  acid,  243 

Hydrosol  form,  278 

Hydrosulphuric  acid,  213 

tests  for,  216 

use  in  analysis,  215 

Hydrosulphurous  acid,  237 

Hydrotelluric  acid,  244 

Hydroterpenes,  551 

Hydroxides.  54 

Hydroxy-acetic  acid,  602 

Hydroxy-acids,  570,  601 

authranol,  719 


Hydroxy-acids,  azo-eompounds,  684 

benzaldehydes,  585,  586 
benzenes,  526,  708 
benzoic  acids,  608 
butyric  acids,  607,  644 
caproicxacid,  607,  677 
cyanogen  compounds,  701 
ethylajrfine,  666 
formifc  acid,  589 
indol,  760 
naalouic  acid,  617 
oleic  acid,  607 
phenyl  fatty  acids,  611 
propionic  acid,  603 
pyridines,  766 
quinoline,  767 ' 
succinic  acid,  618 
toluenes,  712 
toluic  acids,  609 
tricarballylic  acid,  623 

Hydroxyl,  54,  94 

amine,  103 

Hyoscyamine,  777 

Hypobromous  acid,  194 

Hypochlorites,  182 

Hypochlorous  acid,  182 

anhydride,  181 

Hyponitrites,  103 

Hyponitrous  acid,  103 

Hypophosphites,  260 

Hypophosphorous  acid,  260 

Hyposulphite  of  soda,  236,  352 

Hyposulphuric  (dithionic)  acid,  237 

Hyposulphurous  acid,  235 

Hypoxanthine,  774 

ICE,  63 

Iceland  spar,  363 
Illuminating  value,  162 
Imides,  649,  658 
Imidogen,  669 
Incandescent  burners,  458 
Incorporating  mill,  340 
Incrustation  on  charcoal,  157 
Incrustations  in  boilers,  57 
Indazoles,  765 
Indian  fire,  274 

ink,  748 

India-rubber,  557 
Indican,  761 
Indifferent  oxides,  38 
Indigo,  761 

artificial,  762 

blue,  761 

brown,  761 

copper,  487 

gluten,  761 

manufacture  of,  763 

red,  761 

reduced,  762 

salt,  764 

vat,  preparation,  762 

white,  762 
Indiglucin,  761 
Indigo  tin,  761 

sulphonic  acids,  762 
Indium,  393 
Indoaniliue,  718 
Indole,  759 
Indolinones,  760 


INDEX. 


849 


Indophenin,  758 
Imlophenol,  718 
Indophor,  760 
Indoxyl,  760 
Iiidoxylic  acid,  760 
Induction  coil,  17 
Induliues,  769 
Ingot  iron,  404 
Ink,  605 

blue,  693 

stains  removed,  182 
Inorganic  substances,  6 
Inosite,  716 

Instantaneous  light,  506 
Intramolecular  condensation,  531 
Intumescence,  353 
Inulin,  736 
Invert  sugar,  727 
lodamines,  662 
lodammonium  iodide,  201 
lodates,  199 
lodic  acid,  199 
Iodide  of  nitrogen,  201 
Iodides,  199 
Iodine,  195 

bromides,  202 
chlorides,  202 
green,  723 
oxides,  198 
scarlet,  502 
test  for,  197 
tincture  of,  197 
Iodised  starch-paper,  65 
lodobenzene,  637 
lodoform,  636 
lodopyrrol,  759 
lodosobenzene,  637 
lodoxybenzene,  637 
lonisation,  degree  of,  326 
Ions,  323 

IridkKplatinum  alloy,  512 
Iridium,  511 
Iron,  394 

acetate,  591 

action  of  acids  on,  93,  179,  416 

air  on,  376 
on  water,  21 

allotropic,  414 

amalgam,  498 

and  carbon,  403 

and  oxygen,  34 

atomic  weight  of,  420 

bar,  407 

carbide,  415 

carbonate,  396 

carbon  in,  403,  405 

carbonyls,  420 

cast,  401 

chemical  properties  of,  416 

chlorides,  419 

cold-short,  408 

critical  temperature  of,  414 

extraction  in  the  laboratory,  415 

fibre  in,  408 

galvanised,  376 

glance,  396 

grey,  402 

group  of  metals  reviewed,  434 

iodide,  419 

magnetic  oxide,  417 


Iron,  metallurgy  of,  396 
mottled,  402 
mould,  416,  738 
nitride,  420 
ores,  395 

calcining  or  roasting,  397 
oxides,  416 
passive  state  of,  416 
perchloride  of,  419 
phosphates,  419 
phosphorus  in,  409 
plates  cleansed,  450 
puddled,  404 

pure,  preparation  of,  416. 
Iron  pyrites,  396,  420 
Iron,  pyrophoric,  136 
red-short,  408 
refining,  404 
rusting,  416 
salts  of,  419 
sand,  396,  456 
scurf,  392 
smelting,  398 
specular,  396 
sulphates,  418 
sulphides,  214,  420 
sulphur  in,  401 
tincture  of,  419 
tinned,  450 
white,  402 
wire,  407 
wrought,  404 

direct  extraction,  415 
manufacture,  404 
Isatic  acid,  679 
Isatide,  761 
Isatin,  679,  760 

anilide,  763 
Isatoic  anhydride,  679 
Iserine,  456 

Isethionic  acid,  535,  649 
chloride,  679 
Isinglass,  753 
Isobarbituric  acid,  773 
Iso- butane,  532 
butylene,  536 
butyl  alcohol,  565,  569 
cholesterin,  757 
cumene,  791 
cyanates,  704 
cyanides,  760 
cyanuric  acid,  708 
dialuric  acid,  773 
di-morphism,  442 
Isomeric  alcohols,  567 
Isomerides,  533 
Isomerism,  533,  603,  605 

explanation  of,  533 
position,  544 
Isomorphism,  297 
Isoparaffins,  533 
pentane,  533 
phthalic  acid,  617 
prene,  556 
propyl  alcohol,  568 

benzoic  acid,  601 
carbinol,  568  . 

quinolene,  767 
Iso-succinic  acid,  614 
uric  acid,  773 


85° 


INDEX. 


Isotonic  solutions,  318 
Isoxazole,  765 
Is  ore t,  669 
Ctaconic  acid,  623 
Ivory,  artificial,  742 
black,  116 

•JABORANDINE,  784 

-Jalapin,  745 

Jalapinol,  745 

Jasper,  276 

•Jatrophiue,  803 

•Jellies,  fruit,  820 

•Jervine,  783 

•Jtt,  160 

Jet  for  burning'  gases,  30 

Jewellers'  rouge,  417 

Juniper,  essential  oil  of,  555 

Kainit,  375 
Kairine,  767 
Kairolin,  769 
Kakodyl,  655 

chloride,  655 

compounds,  655 

cyanide,  655 

oxide,  655  ' 

sulphide,  651} 

trichloride,  656 
Kakodylic  acid,  655 
Kaolin,  384 
Kassner's  process,  469 
Kekul6's  chain,  546 
Kelp,  195 
Keratin,  754 
Kermes  mineral,  446 
Kernel  roasting,  486 
Kerosene,  528 
Ketodihydropyrazoles,  764 
Ketols,  626 
Ketone-acids,  574,  626 

alcohols,  574,  626 
aldehydes,  574,  626 
Ketones,  624 

double,  624 
table  of,  624 

Ketonic  decomposition,  644 
Ketoses,  724 
Ketoximes,  625 
Kid,  797 
Kieselguhr,  646 
Kieserite,  375 
Kinetic  theory  of  gases,  291 

method  of  measuring  affinity,  312 
King's  yellow,  275 
Kino,  712,  715 
Kipp's  apparatus,  120 
Kirschwasser,  8oS 
Kish,  in 

Kjeldahl's  method,  521 
Kola  nut,  775,  810 
Kosine,  746 
Koumiss,  733 
Kousso,  746 
Kreasote,  712 
Kreatine — see,  Creatine 
Kresol,  712 
Kryolite,  389 
Kupfernickel,  424 
Krypton,  77 


Kyanising  wood,  820 
Kyanite,  389 

LAB,  752 
Lac,  748 
Lacquer,  748 
Lacquering-,  482 
Lactamide,  668 
Lactams,  678 
Lactarine,  752 
Lactates,  604 
Lactic  acid,  603 

anhydride,  603 
fermentation,  603 
Lactide,  603 
Lactims,  679 
Lactometer,  813 
Lactones,  627 
Lactose,  733 
Lactyl  chloride,  639 
Laevo-rotatory,  542,  621 
Laevotartaric  acid,  621 
Laevulosan,  728 
Laevulose,  727 
Lakes,  alumina,  388 
Lamp-black,  in 

without  flame,  506 
Lanarkite,  471 

Landsberger's  apparatus,  321 
Lanolin,  757 
Lanthanum,  391 
Lapis  lazuli,  389 
Lard,  648,  799 
Laudanum,  778 
Laughing  gas,  96 
Laurel  water,  691 
Laurie  acid,  594 

aldehyde,  583 
Laurite,  511 
Lauth's  violet,  768 
Lava,  389 
Law  of  even  numbers,  523 

constant  proportions,  7,  286 
multiple  proportions,  286 
reciprocal  proportions,  287 
periodic,  301 
thermochemistry,  305 
Lead,  459 

acetates,  591,  592 

action  of  acids  on,  467 
on  water,  60 

alkides,  656 

applications  of,  466 

argentiferous,  463 

arsenate,  471 

calcining,  462 

carbonates,  470,  472 

chlorides,  471 

chlorobromide,  472 

chlorosulphide,  472 

chromates,  432 

coiTosion  of,  467 

desilverising  process,  463 

dioxide,  469 

extraction  in  laboratory,  460 

fume,  461 

-glazed  earthenware,  468 

hard,  462 

hydroxide,  470 

improving  process,  462 


INDEX. 


Lead  in  cider,  &c.,  467 

in  water,  60 

iodide,  199,  472 

nialate,  618 

metallurgy  of,  461 

molybdate,  435 

nitrate,  470 

oleate,  598 

ores,  459 

oxides,  467 

in  glass,  371 

oxy chlorides,  471 

peroxide,  467 

persulphide  of,  472 

phosphate,  471 

plaster,  598 

poisoning,  47I 

propionate,  593 

propylate,  593 

pyrophorus,  467 

selenide,  472 

smelting,  461 

Spanish,  462 

sugar  of,  591 

sulphate,  471 

sulphides,  472 
tartrate,  467 

test  for,  6 1 
tetracetate,  469 

tetramethyl,  656 

tetrethyl,  656 
thiosulphate,  237 
tribasic  acetate,  592 
triethyl,  656 
uses,  466 
vanadate,  446 
Lead  vitriol,  471 
Leaden  cistern,  60 
coffins,  467 
Leadhillite,  471 
Leather,  797 
Leaven,  809 

Leblanc  alkali  process,  345 
Lecanoric  acid,  714 
Lecithin,  647,  755 
Legumin,  752 
Lemery's  volcano,  212 
Lemons,  essential  oil  of,  555 
Lepidine,  767 
Lepidolite,  358 
Leucaniline,  722 
Leucic  acid,  677 
Leucine,  677 
Leuco-base,  722 
Leucoue,  282 
Leuco-parurosanilme,  722 
Levulinic  acid,  627 
Libethenite,  485 

Lichens,  colouring-matters  from,  714 
Liebermann's  reaction,  710 
Liebig's  condenser,  61 

extract,  815 
Light,  action  on  silver  chloride,  236 

carburetted  hydrogen,  144 

oil  of  coal-tar,  539,  793 
Lignite,  159,  168 
Ligroin,  528 
Lime,  363 

action  on  soils,  818 
air-slaked,  365 


851 


Lime-burning,  364 

carbonate  in  waters,  56 

chloride  of,  183 

-kilns,  364 

-light,  48 

phosphates,  369 

purifier,  792 

•stone,  363 

sulphate,  367 

superphosphate,  369 

water,  365 
Limonene,  556 
Linde's  machine,  72 
Linen,  737 

Linoleic  acid,  599,  798 
Linolenic  acid,  599 
Linseed,  737 

oil,  798 

Liquation,  488 
Liquefaction  of  air,  73 
gases,  72 

Liquor  ammonia?,  76,  bi 
chlori,  171 
iodi,  197 
sanguinis,  814 

sodse  chloratae,  184 
Liquorice  root,  746 
Litharge,  468 
Lithia,  358 
Lithia-mica,  358 
Lithic  acid,  769 
Lithium,  358 

blowpipe  test  for,  358 
urate,  770 
Litmus,  714 
Loadstone,  396 
Loam,  384 
Logwood,  388,  748 
Looking-glasses  silvered,  497 
Lophin,  765 

Lucifer  matches,  254,  255 
Lugol's  solution,  197 
Luminosity  of  flames,  149 
Lunar  caustic,  492 
Lupulin,  805 
Luteo-cobalt  salts,  423 
Luteolin,  747 
Lutidine,  766 
Luting  for  crucibles,  378 

iron  joints,  212 
Lycopodium,  148 
Lysidine,  765 
Lysol,  712 

MACDOUG ALL'S  disinfectant,  710 
Maclurin,  747 
Madder,  720,  795 

-lakes,  720 
Magenta,  722,  793 

bronze,  436 

Magic  lantern,  oil  for,  559 
Magistral,  489 
Magnesia,  374 

calcined,  375 

citrate,  623 
Magnesia  limestone,  365,  374 

for  Duilding.  365 
Magnesite,  373 
Magnesium,  373 

action  on  water,  21 


INDEX. 


Magnesium,  ammonio- chloride,  376 

phosphate,  375 
ammonium  arsenate,  375 
borate,  375 
carbonate,  374 
chloride,  375 
citrate,  623 
fluoride,  205 
group,  review  of,  383 
hydroxide,  374 
methide,  657 
nitride,  374 
phosphates,  375 
silicates,  373 
silicide,  282 
sulphate,  375 

Magnet-fuse  composition,  487 
Magnetic  iron  ore,  396,  417 

pyrites,  420 

Magnetic  rotatory  power,  788 
Magnetite,  417 
Magnus'  green  salt,  508 
Malachite,  474 

green,  722 
Maleic  acid,  615 

Malemoid  and  fumaroid  structure,  616 
Malic  acid,  618 
Malonic  acid,  614 

ether,  645 
Malonyl  urea,  772 
Malt,  804 

-dust,  804 
high-dried,  806 
Malting,  803 
Maltose,  733 
Mandelic  acid,  609,  744 
Manganates,  428 
Manganese,  426 

binoxide,  427 
Manganese  black,  427 
blende,  430 
Manganese  bronze,  452 

carbonate,  426 
chlorides,  429 
dioxide,  426 
oxalate,  613 
oxides,  426 
peroxide,  426 
recovery,  429 
separated  from  iron,  430 
Manganese  spar,  426 
Manganese  sulphate,  430 
sulphide,  430 
Manganic  acid,  427 
Manganite,  427 
Manna,  578 

Australian,  734 
trehala.  734 
Mannitane,  579 
Mannite  (mannitol),  578 
glycertdes,  579 
Mannose,  579,  727 
Mannonic  acid,  578,  729 
Mannyl  hexanitrate,  578 
Mantle  of  flame,  152 
Mantles  for  Welsbach  burners,  155,  458 
Manures,  817 
Manuring,  817 
Maraschino,  808 
Marble,  363 


Marcasite  (iron  pyrites),  420 
Margaric  acid,  596,  798 
Margarin,  798 
Margarine,  799 
Marine  glue,  557 
Marking-ink,  492 
Marl,  384 
Marsh -gas,  144,  526 

series,  526 

Marsh's  test  for  arsenic,  272 
Martensite,  414 
Martius'  yellow,  712 
Mascagnine,  355 
Mashing,  805 
Mass,  action  of,  310 

active,  310 
Massicot,  468 
Matches,  184,  254 

safety,  255 

without  phosphorus,  254 
Mate,  775 
MatlocTcite,  471 
Matte,  476 
Mauve  dye,  793 
Mauveine,  793 
Meadow-sweet,  oil  of,  586 
Meal-powder,  340 
Meconates,  622 
Meconic  acid,  622 
Meconine,  779 

hydrocotaruine,  779 
Meerschaum,  373 
Melam,  704 
Melamine,  704 
Melaniline,  673 
Mel  em,  704 
Melezitose,  734 
Melissene,  799 
Melissyl  alcohol,  570 

palmitate,  570,  644 
Melitose,  734 
Mellite,  624 
Mellitic  acid,  624 
Mellone,  704 
Mellonides,  704 
Menaccanite,  456 
Mendeleeffs  law,  301 
Mendipite,  472 
Menthene,  557 
Menthol,  557 
Mercaptan,  572 
Mercaptides,  572 
Mercaptol,  626 
Mercerisation,  738 
Merchant  bar  iron,  407 

acetamide,  668 
Mercuric  chloride,  499 

cyanide,  697 

ethide,  657 

fulminate,  706 

iodide,  502 

methide,  656 

nitrate,  499 

oxycyanide,  697 

sulphate,  499 

sulphide,  502 

colloidal,  504 

Mercuroso-mercuric  iodide,  502 
Mercurous  acetate,  591 
chloride,  501 


INDEX. 


853 


Mercurous  cobalticyanide,  692 
iodide,  502 
nitrate,  499 
sulphate,  499 
sulphide,  502 
Mercury,  495 

alkides,  656 
allyl-hydroxide,  636 
iodide,  502,  636 
amido-chloriue,  501 
ammoniated  oxide,  499 
bichloride,  499 
chlorosulphide,  503 
diphenyl,  657 
ethyl  chloride,  657 

hydroxide,  657 
frozen,  129 
fulminate,  706 
metallurgy  of,  496 
methyl  chloride,  656 
nitric  oxide  of,  498 
nitride,  499 
oxides,  498 
phenyl  chloride,  657 

hydroxide,  657 
protonitrate,  499 

stains  removed  from  gold,  497, 498 
uses  of,  497 
volatility  of,  498 
yellow  oxide,  499 
Mesaconic  acid,  616 
Mesitylene,  549,  625 
Mesitylenic  acid,  601 
Mesityl  oxide,  625 
Meso-derivatives,  554 
Mesotartaric  acid,  620 
Mesoxalic  acid,  618,  771 
Mesoxalyl  urea,  771 
Metabolis,  819 
Metaboric  acid,  246 
Metacetonic  (propylic)  acid,  593 
Metacinnamene,  550 
Metacresol,  712 
Metacrolein,  584 
Metadiazine,  768 
Metadibroruobenzene,  547 
Metadihydroxy benzene,  714 
Metadinitrobenzeue,  650 
Metatrihydroxy benzene,  715 
Metal,  alkides,  656 

definition  of,  38 
Metaldehyde,  583 
Metalepsis,  174 
Meta-diazines,  768 
Metallic  isocyanates,  703 

thiocyanates,  704 
Metallurgy  of  copper,  475 
iron,  396 
lead,  461 
tin,  448 
zinc,  377 

Metals,  action  on  water,  19,  21 
chemistry  of,  332 
noble,  21 

relations  to  oxygen,  35 
Metal-slag  (copper),  476 
Metameric,  533 
Metantimonic  acid,  443 
Metaphenylinediamine,  666 
Metaphosphates,  258 


Metaphosphoric  acid,  258 
Metarabin,  737 
Metarsenic  acid,  271 
Metasilicic  acid,  278 
Metastannic  acid,  453 
Metastyrolene,  550 
Metatartaric  acid,  619 
Metatoluidine,  665 
Metaxylene,  549 
Meteoric  iron,  395 
Methane,  144,  526,  530 

constitution  of,  526 

heat  of  formation,  141 

preparation  of,  144,  530 
Methene  di-iodide,  635 

diphenyl,  664 
Methods  of  determining  molecular  weights, 

Methyl,  592 

acetate,  643 
acrylic  acid,  597 
alcohol,  565 
aldehyde,  580 
amine,  659 
aniline,  664 
anthranilate,  678 
arsenic  acid,  656 
arsine,  655 
benzenes,  548 
benzoic  acid,  601 
bromide,  633 
carbamides,  671 
carbamine,  700 

carbimide,  704 

chloride,  633 

coniine,  776 

cyanate,  704 

cyanide,  668,  699 

cyanurate,  704 

dihydroglyoxaline,  765 

diphenylamine,  664 

ether,  627 

ethylamine,  662 

ethyl  amylamine,  662 
aniline,  664 
ketone,  626 
urea,  705 

fluoride,  634 

forinainide,  667 

formate,  643 

formic  acid,  590 

glycocines,  674 

glycocyamidine,  676 

glycocyamine,  676 

glycolyl-guanidiue,  676 

guaiacol,  713 

guanidine,  676 

hydantoin,  677 

hydrate,  565 

indol,  760 

indoliu,  760 

iodide,  634 

isocyanate,  704 

isocyanide,  700 

methyl-salicylate,  645 

morphine,  779 

naphthalenes,  553 

nitramiue,  662 
nonyl  ketoue,  626 
orange,  683 


854 

Methyl  oxalate,  645 

para-oxy  ben  zoic  acid,  608 

phenol,  709,  712 

phenylamine,  664 

phosphines,  654 

phthalic  acid,  758 

propyl  carbinol,  560 

protocatechuic  acid,  609 

pyrocatechol,  713 

quinolines,  767 

salicylate,  645 

salicylic  acid,  645 

succinic  acid,  615 

sulphates,  641 

theobromine,  775 

uracyl,  773 

ureas,  705 

violet,  723 
Methylated  ether,  628 

spirit,  565,  628 
Methylene  iodide,  635 
Metric  system,  12 
Mica,  332,  384 
Microcosmic  salt,  259,  357 
Mildew,  71 
Milk,  811 

constituents  of,  812 
of  sulphur,  209 
skimmed,  812 
sug-ar,  812 
Mill-cake,  340 

furnace,  407 
Millon's  base,  499 

test,  750 

Millstone  grit,  365 
Mineral  cotton,  401 

green,  485 

kermes,  446 

silicates,  280 

waters,  61 

yellow,  472 
Mines,  ventilated,  126 
Minium,  467 
Mirbane  essence,  540 
Mirrors,  manufacture  of,  491,  497 
Mispickel,  266 
Mixture  defined,  6 
Moire  metallique,  453 
Molasses,  731 

Molecular  formulae,  522,  523 
heats,  297 
volumes,  301,  786 
weight,  292 

determination  of,  292, 

293»  3J9>  522 
Molecule,  definition,  8 
Molecules,  8,  286 

velocity  of,  25,  290 
vibrations  of,  290,  331 
Molybdenite,  435 
Molybdeaum,  435 

glance,  435 
metallic,  435 
Molybdic  acid,  435 

anhydride,  435 
ochre,  436 
oxide,  435 
Mona  copper,  478 
Monad  elements,  n 
Monamides,  667 


INDEX. 


Monamines,  658,  660 
Monatouiic  elements,  12 
Monazite  sand,  458 
Monethyl  glycol  ether,  631 
Mond  g-as,  163,  168 
Monkshood,  783 
Monobasic  acids,  98,  104,  588 
Mouochloracetamide,  668 
Monochlorether,  631 
Monochlorhydrin,  646 
Monochlorobenzene,  540 
methane,  633 
Monoclinic  crystals,  52 
Monoformin,  647 
Monohydric  alcohols,  561,  565 
Monoses,  728 
Mordants,  683,  795 
Morin,  747 

Moritannic  acid,  611,  747 
Morocco  leather,  797 
Morphine,  778 

hydrochloride,  778 

meconate,  778 

periodide,  779 
Morpholine,  666 
Mortar  for  building,  366 
Mosaic  gold,  455 
Mould,  71 

Mountain-ash  berries,  618 
Mucic  acid,  622 
Mucilage,  737 
Mucin,  754 
Muffle,  466 

Mulberry  calculus,  613 
Multiple  proportions,  286 
Mundic  (iron  pyrites),  420 
Muntz  metal,  481 
Murexan,  772 
Murexide,  770 
Murexoin,  775 
Muriate  of  morphia,  778 
Muriatic  acid,  169 
Muscarine,  666 
Muscovite,  389 
Musk,  artificial,  757 
Muslin,  uninflammable,  355,  436 
Mustard,  essential  oil  of,  705 
oil,  reaction  of,  706 
oil  test  for  primary  bases,  706 
Mycose,  734 
Mydatoxine,  666 
Mydine,  666 
Myosin,  751 
Myricin,  570,  644,  799 
Myristic  aldehyde,  583 
Myronic  acid,  705 
Myrosin,  705 
Myrtle,  essential  oil  of,  555 

NAPHTHA,  mineral,  528 
Naphthalene,  551 

chlorides,  552 

chloro -substitution     products, 

552 

disulphonic  acid,  649 
heat  of  combustion  of,  165 
nitro-substitutiou       products, 

552>  65<> 
rings,  552 
sulphonic  acid,  649 


INDEX. 


Naphthalene,  yellow,  712 
Naphthalic  acid,  617 
Naphthalidine,  665 
Naphthalines,  528,  539 
Naphtha  zine,  769 
Naphthendulines,  769 
Naphthoic  acid,  601 
Naphthol,  708,  712 

yellow,  712 

Naphthoquinolines,  767 
Naphtlioquinones,  719 
Naphthohydroquinone,  719 
Naph'hophenazine,  769 
Naphthylamine,  665 
Naphthyleue-diamine,  666 
Naphthyl-phenyl-ketone,  626 
Naples  yellow,  443 
Narceine,  780 
Narcotine,  779 
Nascent  condition,  102 
Natron,  348 
Neg-ative  change,  310 
Negative  pole,  14 
Neodyminm,  394 
Neon,  77 

Neo- paraffins,  533 
Neo-pentane,  533 
Neroli  oil,  678 
Nervous  substance,  755 
Nessler's  test,  502 
Nest  sugar,  734 
Neuridine,  666 
Neurine,  666 
Neutralisation,  19 
Newland's  law  of  octaves,  301 
Nickel,  423 

ammonium  sulphate,  425 

arsenical,  424 

arseniosulphide,  424 

blende,  424 

car  bony],  425 

cobalticyunide,  692 

cyanide,  692 

glance,  424 

metallurgy  of,  424 

oxides,  425 

steel,  415 

sulphate,  425 

sulphides,  425 
Nicotine,  770 

ethylinm  dihydroxide,  777 
Nicotinic  acid,  777 
Nightshade,  776 
Nil  album,  377 
Niobium,  447 
Nitramines,  662 
Nitranilines,  600,  664 
Nitrate,  89 
Nitrates,  95 

as  manure,  818 
formation  in  nature,  87 
Nitre,  337,  338 

action  on  carbon,  339 

cubic,  353 

-heaps,  337 
purified,  340 

refining,  338 
Nitric  acid,  89 

action  on  hydrochloric  acid,  191 
metals,  92 


Nitric  acid,  action  on  organic  bodies,  93 

turpentine,  74 
composition  of,  95 
formation  from  uir,  88 

ammonia,  86 
fuming,  90 
preparation,  89 
reduction,  products  of,  102 
test  of  strength,  90 
anhydride,  96 
esters,  642 
ether,  642 
nitrides,  107 
oxide,  96 
peroxide,  100 
Nitrification,  87 
Nitrifying  organism,  88 
Nitriles,  699 
Nitrites,  95,  100 
Nitro-benzene,  540,  650,  682 
chloroform,  650 
cinnamic  acid,  764 
compounds,  649 
copper,  101 
erythrite,  578 
ethene,  650 
mannite,  578 
methane,  650 
naphthalene,  650 
paraffins,  642,  649 
phenols,  711 

phenyl-lactomethyl  ketone,  764 
phenylamine,  664 
phenylpropiolic  acid,  761 
toluenes,  650 
Nitrogen,  74 

as  plant  food,  816 
bromide,  195 
bulbs,  521 

chemical  relations,  75 
chloride,  90 
chlorophosphide,  265 
determination,  521 
group  of  elements,  275 
iodide,  201 
liquefied,  73 
oxides,  88 
preparation,  75 
properties,  75 
sulphides,  241 

Nitrogeuised  bodies  identified,  116 
Nitroglycerine,  577,  646 
Nitrolic  acid,  567 
Nitro  metals,  100 
Nitrometer,  93 
Nitromuriatic  acid,  191 
Nitroprussides,  695 
Nitrosalicylic  acid,  743 
Nitrosamines,  660 
Nitroso-phenol,  718 

reaction,  660 

Nitro  substitution-products,  94 
Nitrosulphonic  acid,  191 
sulphuric  acid,  191 
Nitrosyl  chloride,  191 
sulphate,  191 
Nitrouracyl,  773 
Nitrous  acid,  99,  101 

formed  from  ammonia,  86 
anhydride,  98 


856 


INDEX. 


Nitrous  ether,  642 

oxide,  96 
Nitroxyl,  94,  100 

chloride,  192 
Nitryl  chloride,  192 
Nobel's  detonators,  647 
Nonane,  528 

Non-metallic  elements,  3 
Nonoses,  728 
Nonylic  acid,  594 

alcohol,  565 

Nordhausen  oil  of  vitriol,  224 
Normal  salt  defined,  104 
Normandy's  still,  62 
Nucleal  synthesis,  531 
Nucleiu,  754 
Nuggets,  513 

Nutmegs,  essential  oil  of,  555 
Nutrition  of  animals,  821 

plants,  816 
Nux  vomica,  781 

OCCLUSION  of  hydrogen,  49 
Ochres,  384 
Octane,  528 
Octoses,  728 
Octyl  acetate,  570 

alcohol,  570 
Octylic  acid,  594 
CEnanthic  acid,  594,  799 

aldehyde,  583,  799 
ether,  644 
Oil  of  cress,  700 

gaultheria,  608 

meadow-sweet,  585 

mignonette  root,  705 

mustard,  705 

nasturtium,  700 

rue,  594,  626 

spiraj  i,  586 

vitriol,  223 

manufacture,  225 

wine,  641 

winter-green,  608,  645 
Oils,  798 
Oleates,  598 
Olefiant  gas,  142,  534 
Olefine  hydrocarbons,  general  preparation  of, 

536 
Olennes,  534,  536 

structure  of,  534 
Oleic  acid,  598 
Olein,  598,  647,  798 
Oligist  iron  ore,  396 
Olive  oil,  648,  798 
Olivine,  375 
Onyx,  276 

Oolite  limestone,  363 
Oolitic  iron  ore,  396 
Opal,  276 

blue,  723 
Open-  and  closed-chain  hydrocarbons,  538 

hearth  process,  409 
Opianic  acid,  779 
Opium,  778 

alkaloids,  778 
Orange  chrome,  432 
Oranges,  essential  oil  of,  555 
Orcein,  715 
Orchella  weed,  578,  714 


Orcin,  or  orcinol,  704,  714 
Ore-furnace,  476 
Organic  acids,  586 

acid  radicles,  592 
analysis,  ultimate,  521 
chemistry,  6,  520 
compounds,  classified,  524,  525 
matter  identified,  108 
radicles,  524,  592 

Organic  compounds,  absorption  spectra,  788 
boiling-points  of,  785 
fusing-points  of,  784 
optical    properties    of, 

787 
physical  properties  of, 

784 
rotatury      polarisation 

of,  788 

specific  volume?,  786 
Organo-rnineral  compounds,  651 
Oriental  alabaster,  58 
Orientation  of  the  benzene-ring-,  545 
Orpiment,  red,  274 

yellow,  275 
Orsellinic  acid,  714 

Ortho-,  meta-,  and  para-compounds,  546 
acetic  acid,  643 
acids,  261 
boric  acitl,  247 
carbonic  aciu,  261 
cresol,  712 

dibroinobeuzene,  546 
formic  ether,  636 
phosphates,  258 
phosphoric  acid,  257 
silicic  acid,  278 
Orthotoluidine,  665 
Orthoclase,  389 
Osazones,  728 
Osmamines,  511 
Osmazome,  815 
Osmic  acid,  510 
Osmium,  510 
Osmosis,  316 
Osmotic  membrane,  317 
pressure,  316 

law  of,  318 
Osones,  728 
Oaotriazole,  765 
Ossein,  766 
Oswego,  803 
Oxalates,  613 
Oxalethylic  acid,  645 
Oxalethyline,  669 
Oxalic  acid,  612 

aldehyde,  584 
ether,  645 
Oxalouitrile,  699 
Oxalovinic  acid,  645 
Oxaluramide,  772 
Oxaluric  acid,  772 
Oxalyl  urea,  772 
Oxamethane,  669 
Oxamic  acid,  672 
Oxamide,  669,  672 
Oxatyl,  587 
Oxazines,  768 
Oxazoles,  764 
Ox- gall,  756 
Oxidation  defined,  32 


INDEX. 


857 


Oxidation  of  tissue  products,  823 
Oxides,  302 

indifferent,  49 

types  of,  302 
•Oxidising  agent,  91 


Oximes,  625 
Oxindol,  679 
Oxindole,  760 
Oxy-acids,  94 
Oxycalcium  light,  48 
Oxycellulose,  739 
Oxygen,  31 

blowpipe  flame,  157 

combustion  in,  33 

detected,  97 

determined,  44,  521 

extracted  from  air,  39,  74 

identified,  15 

liquefied,  73 

positive  and  negative,  67 

preparation,  38,  39 

properties,  31 

purification,  108 
Oxyhaemoglobin,  755 
Oxyhydrogen  blowpipe,  48 
Oxymorphiue,  778 
Oxymuriatic  acid,  177 
Oxynaphthylamine,  665 
Oxyphenic  acid,  713 
Ozokerite,  529 
Ozone,  65 

heat  of  formation,  66 
Ozonisation  by  phosphorus,  67 
Ozonised  air,  65 

oxygen,  66 
Ozonising  apparatus,  65 

PAINT,  blackened,  216 
luminous,  368 

Paintings,  effect  of  light  and  air  on,  216 
Palladamine  hydrochloride,  1509 
Palladium,  509 
Palmitic  acid,  594 

aldehyde,  583 
Palmitin,  647 
Palmitolic  acid,  599 
Palm  oil,  797 
Pancreatic  juice,  822 
Papaverine,  780 
Paper,  737 

action  of  nitric  acid  on,  739 
for  photographic  printing,  236 
Parabanic  acid,  772 
Parabin,  737 
Para-compounds,  546 
Paraconiine,  776 
Paracresol,  712 
Paracyanogen,  687 
Paradiazine,  769 
Paraffin,  527 

hydrocarbons,  526 

oil,  527 

series,  526 

wax,  529 
Paraffins,  iso-  or  secondary,  533 

neo-  or  tertiary,  533 

normal,  533 
Paraformaldehyde,  581 
Paraguay  tea,  775 


Paralactic  acid,  604 
Paraldehyde,  583 
Parainucic  acid,  622 
Paranthracene,  554 
Paratoluidine,  665 
Pararosaniline,  723 
Parchment,  797 

paper,  738 

size,  754 

vegetable,  738 
Paris  yellow,  472 
Parkes'  process,  464 
Parsley,  essential  oil  of,  555 
Partial  pressures,  law  of,  314 

saturation,  method  of,  588 
Parting  of  gold,  233 
Parvoline,  766 
Passive  state,  416 
Patchouli,  oil  of,  555 
Patent  yellow,  472 
Pattinsou's  process,  463 

oxy chloride,  471 
Paviin,  744 
Paving  stones,  365 
Pea  iron  ore,  396 
Peachwood,  748 
Pear  flavouring,  644 
Pearlash,  333 
Pearl  hardener,  368 
Pearls,  120 
Pearl-spar,  375 
Pearl  white,  440 
Peat-bog,  159 
Peat,  composition  of,  168 
Pectic  acid,  820 
Pectin,  820 
Pectose,  820 
Pectosic  acid,  820 
Pelargonic  acid,  594 

ether,  644 

Peuicillium  glaucum,  621 
Peutachlorobenzene,  540 
Pentad  elements,  n 
Pentamethylarsiue,  656 
Pentamethylene,  539 

diainine,  666 
Pentaue,  533 
Pentanes,  isomeric,  533 
Peutathionic  acid,  238 
Peutoses,  725 

Pepper,  essential  oil  of,  555 
Peppermint,  essential  oil  of,  557 
Pepsin,  750 
Peptones,  750 
Perchloracetic  ether,  643 
Perch  lorates,  187 
Perchlorethaue,  189 
Perchloric  acid,  187 
Perchlorinated  ether,  631 
Perchloronaphthalene,  552 
Perchrornic  acid,  433 
Percussion  cap  composition,  707 

fuse,  186,  188 
Perfume  ethers,  644 
Perfumes,  extraction  of,  555 
Periclase,  374 
Pericline,  389 
Periodates,  199 
Periodic  acid,  199 
Periodic  law,  301 


858  INDEX. 


Periodic  law,  applications  of,  304 
Perlite,  414 
Permanent  ink,  492 

white,  360 
Permanganates,  428 
Permanganic  acid,  428 
Perosmic  anhydride,  510 
Peroivskite,  456 
Persulphates,  235 
Persulphocyanic  acid,  703 
Persulphuric  acid,  235 

anhydride,  235 
Perthiocyanogen,  703 
Per-uranates,  437 
Peruvian  bark,  780 

saltpetre,  337 
Petalite,  358 
Petchiney  process,  348 
Petrifying  springs,  58 
Petrol,  528 

Petroleum,  144,  161,  528 
ether,  528 
oil,  528 
spirit,  528 
Pewter,  452 
Pharaoh's  serpent,  704 
Phase  rule,  315 
Phellandrene,  556 
Phenacetine,  711 
Phenanthraquinone,  721 
Pheuanthrene,  554 
Pheuanthridiue,  768 
Phenanthroline,  767 
Phenaziue,  769 
Phenetoi'l,  632 
Phenic  acid,  709 
Phenol,  708 

aquate,  710 

blue,  718 

properties  of,  710 

test  for,  710 
Phenols,  708 

converted  into  hydrocarbons,  710 
monohydric,  709 
Phenolic  acids,  608 

general  reactions  for  obtain- 
ing, 608 
Phenol-sulphonic  acid,  709,  712 

phthalein,  723 
Phenoxazine,  768 
Phenyl,  548 

acetate,  644 

acetic  acid,  700 

acetonitrile,  700 

acetylene,  550 

acrylic  acid,  601 

allyl  alcohol,  572 

amine,  662 

aniline,  664 

carbaniine,  701 

carbinol,  571 

chloride,  637 

cyanide,  675,  700 

dimethylpyrazolone,  764 

ethylene,  550 

ethyl  ether,  632 

formic  acid,  600 

glycocine,  675 

glycollic  acid,  609 

glyoxylic  acid,  627 


Phenyl  hydracrylic  acid,  777 
hydrate,  689,  709 
hydrazine,  684 
hydrosulphide,  710 
imide-amide,  686 
isocyanide,  701 
mercaptan,  710 
methyl  ether,  631 

pyrazolone,  764 
orthophosphate,  710 
phenol,  710 
phenyl,  550 
phosphine  oxides,  655 
phosphinee,  654 
phosphonium  iodides,  654 
phosphoric  acids,  710 
salicylate,  645 
sulphuric  acid  641 
Phenylene  blue,  719 
brown,  684 
diamine,  666 
Philosopher's  wool,  377 
Phlogistic  theory,  176 
Phlogiston,  176 
Phloramine,  716 
Phloretin,  744 
Phlorizein,  744 
Phlorizin,  715,  744 
Phloroglucol,  715 
Phlorol,  713 
Phocenin,  799 
Phorone,  625 
Phosgene  gas,  190 
Phosphamides,  265 
Phosphaniline,  654 
Phosphates,  258 
Phosphenyl  chlorides,  655 
Phosphenylic  acid,  655 
Phosphenylous  acid,  655 
Phosphides,  254 
Phosphine,  262,  654 
Phosphites,  259 
Phosphobenzene,  655 
Phosphodiamide,  265 

glyceric  acid,  647 
molybdate  of  ammonium,  435 
nitrile,  265 

Phosphonium  iodide,  263 
Phosphor-bronze,  452 
Phosphorescence,  251 
Phosphoric  acid,  256,  257,  258 

glacial,  257 
anhydride,  257 
Phosphorised  oil.  251 
Phosphorite,  249,  256,  369 
Phosphorous  acid,  259 

anhydride,  259 
Phosphorus,  249 

action  of  potash  on,  262 

of,  on  other  elements,  254 
allotropic  varieties,  252,  253 
amorphous,  252 
and  oxygen,  32 
bases,  654 
bromides,  264 
burnt  under  water,  188 
chlorides,  263 
cyanide,  704 
fluoride,  264 
fuse  composition,  255 


INDEX. 


859 


Phosphorus  iodides,  264 

match-bottle,  251 

oxides,  255 

oxychloride,  264 

pentachloride,  263 

red,  252 

sources  of,  249 

suboxide,  260 

sulphides,  264 

sulphochloride,  264 

tetroxide,  259 

trichloride,  263 

vitreous,  252 
Phosphoryl  chloride,  264 
Phosphotriamide,  265 
Phosphurets,  254 
Phosphuretted  hydrogen,  262 
Photographic  baths,  silver  recovered,  494 

printing,  236,  495 
Photo-reduction,  495 

salts,  494 
Phthalic  acids,  617 

anhydride,  617 
Phthalide,  779 
Phthalyl  dichloride,  640 
Phycite,  578 
Phyllocyanin,  746 
Phylloxanthiu,  746 
Physical  properties,  12 
Physostigmiue,  783 
Phytosterin,  757 
Picnometer,  81 
Picolines,  766 
Picramic  acid,  711 
Picrates,  711 
Picric  acid,  709,  711 
Picrotoxin,  745 
Pig-  iron,  399,  403 
Pilocarpine,  783 
Pimple  metal  (copper),  478 
Piuacones,  575 
Pine-apple  flavouring,  644 
Pinene,  557 
Pink  salt,  455 
Pins,  tinned,  451 
Pipe  clay,  384 
Piperazine,  666,  769 
Piperic  acid,  611,  776 
Piperidine,  766 
Piperine,  766,  776 
Piperonal,  586 
Pipette,  curved,  130 
Pit  charcoal,  114 
Pitch-blende,  437 
Plants,  793 

action  of,  on  carbon  dioxide,  119 
nutrition  of,  816 
Plaster  of  Paris,  367 
Plate-powder,  369 
Platiuamine,  508 
Platinates,  506 
Platinic  chloride,  506 

hydroxide,  506 
iodide,  509 
Platinicyanides,  697 
Platinised  asbestos,  98 
Platinochlorides,  507 
Platinocyanides,  697 
Platinoid  metals  reviewed,  512 
Platinous  chloride,  508 


Platinum,  504 

amalgam,  498 
ammonio-chloride,  508 
arsenide,  509 
black,  506 
chlorides,  507 
corroded,  245,  506 
crucible  heated,  277 
cyanides,  697 
fulminating,  507 
ores,  analysis,  512 

treatment  of,  504 
oxides,  506 
phosphide,  509 
properties  of,  505 
spongy,  505,  506 
stills,  228 
sulphides,  509 
tetrachloride,  507 
Platosamine,  508 
Pleonaste,  417 
Plumbago,  no 
Plumbite,  467 
Plumbous  oxide,  467 
Pneumatic  trough,  135 
Poison,  cumulative,  471 
Polarimeter,  543 
Polarised  light,  543,  788 
Pole,  negative  and  positive,  15 
Pollux,  359 
Polonium,  438 
Polychroite,  747 
Polyhalite,  375 

Polyhydroxy-monobasic  acids,  607 
Polymeric,  533 
Polymerides,  533 
Polymerism,  533 
Poplar,  oil,  of,  555 
Populin,  743 
Porcelain,  390 

glazed,  391 
painting,  391 
Porous  cell,  14,  26 
Porphyry,  365,  389 
Porter,  806 

Porter-Clark  process,  59 
Portland  cement.  366 

stone,  365 
Port  wine  crust,  807 

effect  of  keeping,  807 
Position-isomerism,  542,  544 
Positive  change,  310 

pole,  14 

Potash-albite,  389 
Potash,  332 

bichromate,  430 
bulbs,  521 
caustic,  333 
red  prussiate,  694 
Potassamide,  105 
Potassium,  332,  334 

action  on  water,  20 
antimonate,  443 
autimonyl  tartrate,  620 
antimony  oxalate,  613 
arsenite,  270 
aurate,  518 
auricyanide,  697 
aurocyauide,  697 
bicarbonate,  333 


86o 


INDEX. 


Potassium  bichromate,  430 
bisulphate,  336 
bitartrate,  333 
blowpipe,  test  for,  335 
bromate,  193 
bromide,  336 

calcium  chromic  oxalate,  613 
carbethylate,  643 
carbonate,  332 
carbovinate,  643 
chlorate,  184,  335 

heat  of   decomposition, 

186 

chloride,  335 
chlorochromate,  434 
chromate,  431 
chromic  oxalate,  613 
chromcyanide,  696 
cobaltic  nitrite,  422 
cobalticyauide,  692 
cobaltocyanide,  692 
cyanate,  702 
cyanide,  691 
dichromate,  430 
dimetantimonate,  443 
ferric  ferrocyanide,  693 
ferricyanide,  694 
ferrocyanide,  689 
ferrous  ferrocyanide,  694 
ferrous  oxalate,  613 
fluoride,  205,  336 
fulmiuurate,  708 
guaiacol,  713 
hydrate,  333 
hydride,  335 
hydroxide,  333 
iodate,  199,  336 
iodide,  199,  336 
isethionate,  679 
isocyanate,  702 
isothiocyanate,  703 
manganate,  428 
mang-anicyanide,  696 
manganocyanide,  696 
metantimonate,  443 
metastannate,  454 
myronate,  705 
nitrate,  337 
nitrite,  100 
nitroprusside,  696 
oleate,  598 
osmate,  511 
osmiamate,  511 
oxalates,  613 
oxides,  335 
perchlorate,  335 
permanganate,  428 
perosmate,  511 
peroxide,  335 
phenol,  710 
phenyl-sulphate,  641 
picrate,  711 
platinochloride,  507 
platinocyanide,  697 
pyrosulphate,  337 
quadroxalate,  613 
saccharate,  622 
silicofluoride,  285 
sulphates,  233,  336 
sulphides,  336 


Potassium  sulphocyanide.  703 
tannate,  610 
tartrate,  619 
tartryl-antimonite,  620 
test  for,  51 
thio-arsenite,  275 
thiocyanate,  703 
trichromate,  432 
tri-iodide,  336 
trithionate,  237 
urate,  770 

Potato,  composition  of,  803 
spirit,  569,  808 
starch,  803 

extraction  of,  803 
Pottery,  390 
Praseo-dymium,  394 

cobalt  salts,  423 
Press  cake,  340 
Pressure  of  gases,  27 
osmotic,  316 
partial,  law  of,  314 
Preston  salts,  355 
Primary  compounds,  568 
Producer,  163 
Producer-gas,  162 
Promethean  light,  188 
Proof  spirit,  564 
Propane,  531 

constitution  of,  527 
Propargyl  alcohol,  571 

chloride,  637 
Propene  dichloride,  576 

glycerol,  645 
Propeptone,  750 
Propine,  538 
Propinyl  alcohol,  571 
Propiolic  acid,  599 
Propione,  624 
Propionic  acid,  593 
Propionitrile,  699 
Propyl  alcohols,  569 
aldehyde,  583 
benzole  acid,  601 
carbinol,  569 
hydride,  531 

tetra-hydro-pyridine,  776 
Propylene,  536 
Propylic  acid,  593 
ether,  628 
Protagon,  755 
Proteids,  748 
Protein,  748 

Protocatechuic  acid,  609 
Proustite,  266 

Proximate  organic  analysis,  793 
Prussian  blue,  686,  693 

soluble,  693 
green,  695 

Prussiate  of  potash,  134,  689 
Prussic  acid,  687,  690 
Pseudaconine,  783 
Pseud  aconitine,  783 
Pseudobutylene,  536 
Pseudocarbons,  in 
Pseudojervine,  783 
Pseudonitrol,  569 
Pseudosulphocyanogen,  703 
Pseudourea,  671 
Psilomelane,  426 


INDEX. 


861 


Ptomaines,  666,  749 
Ptyalin,  735,  821 
Puddled  bars,  407 
steel,  408 
Puddling-,  404 
Pulvis  fulmiuans,  339 
Pumice  stone,  384 
Purbeck  stone,  366 
Purine,  771 
Purple  of  Cassius,  519 
Purpureo-cobalt  salts,  423 
Purpurin,  721 
Purree,  747 
Pus,  754 

Putrefaction,  119,  825 
Putrescine,  666 
Putty  powder,  454 
Pyrazine,  666 
Pyrazoles,  764 
Pyrazolidines,  765 
Pyrazolidones,  765 
Pyrazolines,  764 
Pyrazolones,  764 
Pyrene,  791 
Pyridine,  766 

bases,  766 

carboxylic  acid,  777 
dicar  boxy  lie  acid,  766 
series,  777 
Pyridones,  766 
Pyrimidines,  768 
Pyrites,  arsenical,  266 

burners,  226 

capillary,  425 

efflorescent,  224 

extraction  of  sulphur  from,  206 

Fahlun,  242 

iron,  396,  420 

magnetic,  420 

oxidation  in  air,  224 

radiated,  420 

spent,  478 

white,  224,  420 
Pyroacetic  spirit,  625 
Pyroarsenic  acid,  271 
Pyroboric  acid,  246 
Pyrocatechol,  609,  712 
Pyrocitric  acids,  616 
Pyrocomenic  acid,  622 
Pyrog-allic  acid,  715 
Pyrogallin,  715 
Pyrogallol,  610, 708,  715 

-phthalein,  715 
Pyroligneous  acid,  590 

ether,  566 
Pyrolusite,  426 
Pyromucic  acid,  622 

aldehyde,  586 
Pyrone,  769 
Pyrophoric  iron,  136 
Pyrophorus,  lead,  467 
Pyrophosphates,  258 
Pyrophosphoric  acid,  258,  260 
Pyroracemic  acid,  626 

aldehyde,  626 
Pyrosulphuric  acid,  222 
Pyrosulpimryl  chloride,  190 
Pyrotartaric  acid,  615 
Pyrotritartaric  acid,  758 
Pyroxanthin,  566 


Pyroxylic  spirit,  566 
Pyroxylin,  739 
Pyrro-azoles,  764 

di:izole,  765 

triazole,  765 
Pyrrol,  759 

-red,  759 
Pyrrolidine,  759 
Pyrrol  ine,  759 
Pyruvic  acid,  626 

QUADRATIC  crystals,  52 
Quadrivalent  elements,  n 
Quartation  of  gold,  516 
Quartz,  383 

artificial,  279 
Quassia,  745 
Quassiin,  745 
Quercetin,  745 
Quercitannic  acid,  611,  797 
Quercitrin,  745 
Quercitron,  795 
Quicklime,  53,  364 
Quicksilver,  495 
Quinaldine,  767 
Quinamine,  780 
Quinazoline,  769 
Quince  oil,  644 
Quinhydrone,  718 
Quinic  acid,  611,  717 
Quinicine,  781 
Quinidine,  781 
Quinine,  780 

amorphous,  781 
sulphates,  781 
Quinoidine,  781 
Quinol,  714,  717 

-dicarboxylJc  acid,  718 
Quinoline,  767 

bases,  767 

blue,  767 

cyanine,  767 

red,  767 

yellow,  767 
Quinolinic  acid,  767 
Quinone,  717 

chlorimidea,  718 
Quinones,  717 
Quinonoid  structure,  721 
Quinotannic  acid,  611 
Quinoxaline,  769 
Quinquivalent  elements,  n 

RACEMATES,  621 

Racemic  acid,  620 

Radiant  matter  spectroscopy,  330 

Radicles,  94,  168,  524 

alcohol,  568 

alkyl,  593 

aromatic,  548 

basylous,  359 

chlorous,  359 

organic,  524 
Radium,  438 
Raffinose,  725 
Raisins,  726 
Rancid  butter,  799 

oils,  798 

Raoult's  method,  319 
Rape-cake,  817 


862 


INDEX. 


Rare  earths,  394 
Rational  feeding,  823 
formulae,  524 
Reactions,  complete,  310 
reversible,  309 
Realgar,  274 
Reaumur's  porcelain,  372 
Reciprocal  combustion,  47 
Rectified  coal  naphtha,  793 
Rectified  spirit,  564 
Bed  antimony  ore,  445 

copper  ore,  474 

dyes,  795 

fire,  186 

haematite,  396 

lead,  468 

lead  ore,  432 

ochre,  396 

orpiment,  274 

oxide  of  manganese,  426 

paints,  503 

precipitate,  498 

prussiate  of  potash,  694 

sanders-wood,  748 

-shortness,  408 

silver  ore,  495 

sulphide  of  antimony,  237,  445 

zinc  ore,  379 
Redonda  phosphate,  390 
Reduced,  39 

Reducing  blowpipe  flame,  156 
Reduction  by  carbonic  oxide,  136 

on  charcoal,  157 
Refinery,  iron,  404 
Refraction  equivalent,  787 
of  saltpetre,  337 
Refractive  power,  787 
Refrigerator,  Carre's,  81 
Regenerative  cooling,  73 

heating,  167 
Regular  crystals,  52 
Regulus,  476 

of  antimony,  441 
Rennet,  752,  812 
Resins,  560 

Resists  (calico-priiiting),  796 
Resorcinol,  713 
Resorcin-phthalein,  714 

yellow,  684 
Resorufine,  768 
Respiration,  223,  821 
Retene,  554 
Retort,  6 1 

Reverberatory  furnace,  132 
Reversed  condenser,  575 
Reversible  reactions,  309 
Reverted  phosphate,  369 
Rhamnose,  725 
Rhamno-hexose,  727 
Rhigolene,  528 
Rhodium,  509     * 
Rhombic  crystals,  52 
Ribose,  725 
Rice,  803 

Ricinoleic  acid,  607,  799 
Rinmann's  green,  423 
Rising  of  bread,  809 
River-water,  54 
Roasting,  chlorinating,  478 
meat,  815 


Roasting  sulphides,  217 
Rochelle  salt,  619 
Rock  crystal,  276 

moss,  714 

oil,  528 

salt,  343 

Roman  cement,  366 
Rosaniline,  722 

acetate,  794 
salts,  722 

Roseo-cobalt  salts,  423 
Rosette  copper,  478 
Rosewood,  oil  of,  555 
Rosiclers,  495 
Rosin,  560 

soap,  801 

Rosindulenes,  769 
Rosocyanin,  747 
Rosolic  acid,  723 
Rotation  of  crops,  818 
Rouge,  747 
Ruberythric  acid,  720 
Rubidine,  766 
Rubidium,  358 
Rubijervine,  783 
Ruby,  388 

glass,  372 

Rue,  essential  oil  of,  594,  626 
Rufigallic  acid,  610,  721 
Ruhmkorfl's  induction-coil,  17 
Rum,  808 
Rust,  86,  416 

-joint  cement,  212 
Rusty  deposit  in  waters,  58 
Ruthenic  anhydride,  511 
Ruthenium,  511 
Rutic,  aldehyde,  583 
Rutile,  456 
Rutin,  745 
Rye-flour,  809 

SACCH ABATES,  622 
Saccharic  acid,  622 
Saccharides,  724 
Saccharimeter,  788 
Saccharine,  668 
Safety-lamp,  Davy's,  146 
Safflower,  747 
Saffron,  747 

bronze,  436 
Safranines,  769 
Sagapenum,  714 
Sago,  803 
Salad  oil,  798 
Sal-alembroth,  500 

ammoniac,  77,  356 
Sal-gemme,  343 
Saliciu,  743 
Salicyl  alcohol,  572 
aldehyde,  585 
chloride,  639 
Salicylates,  608 
Salicylic  acid,  608 

aldehyde,  585 

chloride,  639 
Saligenin,  743 
Saline  waters,  61 
Salipyrine,  765 
Saliretin,  743 
Saliva,  821 


INDEX. 


Salol,  645 
Sal-polychrest,  336 
prunelle,  338 
volatile,  356 
Salt  as  manure,  818 
cake,  345 
common,  343 
defined,  37  ^ 

electrolysis  of,  349 
-gardens  of  Marseilles,  344 
-glazing,  392 
of  lemons,  613 
of  sorrel,  613 
of  tartar,  619 
Salting  of  meat,  815 
Saltpetre,  337 

as  manure,  817 
cubical,  ^338 
-flour,  338 
impurities  in,  338 
made  from  sodium  nitrate,  337 
prismatic,  338 
properties,  338 
refining,  338 
tests  of  purity,  338 
Salt-radicles,  205 
Salts,  acid,  104  »-••"• 
basic,  104 

classification  of,  104 
constitution  of,  104 
double,  104 

electrolysis  of,  324^^-^" 
haloid,  205 
iron  of,  419 
normal,  104 
Samarskite,  394 
Sand,  276 

Sandarach  resin,  560 
Sandemeyer's  reaction,  681 
Sandstone,  365 

Cratgleith,  365 
Santalin,  747 
Santonic  acid,  745 
Santonin,  745 
Sap  of  plants,  819 
Saponification  by  steam,  802 

sulphuric  acid,  802 
of  ethereal  salts,  641 
theory  of,  802 
Saponin,  745 
Sappan  wood,  748 
Sapphire,  388 
Sarcine,  774 
Sarcolactic  acid,  604 
Sarcosine,  675 
Sassafras  nuts,  594 
Satin  spar,  363 
Saturated  compounds,  136 

hydrocarbons,  526 
solution,  50 

Savin,  essential  oil  of,  555 
Saxony  blue,  762 
Scale,  boiler,  57 
Scarnmony,  745 
Scandium,  394 
Scarlet  dyes,  795 
Scheele's  green,  270,  485 
Scheelite,  436 
Schlippe's  salt,  446 
Schultze's  pomler,  742 


863 


Schweitzer's  reagent  778 
Scotch  pebbles,  276 
Scott's  cement,  367 
Scrubber,  791 
Scurvy-grass,  oil  of,  706 
Seal  oil,  799 
Sea- water,  61 

extraction  of  salts  from,  344 
weed,  817 
Sebacic  acid,  598 
Secretion,  823 
Sedative  salt,  245 
Seeds,  composition,  804 
germination,  804 
Seignette's  salt,  619 
Sel  d'or,  518 

Selective  absorption,  780 
Selenic  acid,  243 
Selenides,  243 
Selenietted  hydrogen,  247 
Selenite,  367 
Selenium,  242 

dioxide,  243 
Selenophen,  758 
Self-burning  gas,  156 
Self-reduction,  460 
Sellaite,  205 
Seltzer  water,  61,  120 
Semidine  nigration,  685 
Semi- water  gas,  163 
Senarmontite,  442 
Separating  funnel,  143 
Sericin,  754 
Serin,  754 
Serpentine,  375 
Serum,  813 

albumin,  750 
Sesqui-terpenes,  556 
Shaft,  downcast  and  upcast,  126 
Shale  oils,  529 
Shamoying,  797 
Shear  steel,  412 

Sheep-dipping  composition,  270 
Shell-lac,  560,  748 
Sherry,  808 
Shoddy,  738 
Shot,  466 

Sicilian  sulphur,  207 
Side-chains,  550,  551 
Siderite,  418 
Siemen's  regenerative  furnace,  167 

-Martin  steel,  409 
Sienna,  384 

Signal-light  composition,  274 
Silica,  276 

amorphous,  279 
crystalline,  278 

dissolved  by  hydrofluoric  acid,  293 
gelatinous,  278 
Silicated  soap,  801 
Silicates,  280 

aluminium  of,  389 
Silicic  acid,  278 

ether,  642 
Silicium,  281 
Silico-acetic  acid,  654 

acetylene,  282 
chloroform,  283 
nonane,  653 
nonyl-alcohol,  653 


864 


INDEX. 


Silico-acetic  propionic  acid,  654 
Silicon,  276,  281 

alkides,  653 

amorphous,  281 

carbide,  282 

chloride,  282 

disulphide,  285 

ethide,  653 

ethylates,  653,  654 

fluorides,  283 

graphitoid,  281 

hydride,  282 

methide,  653 

nitride,  282 

organic  compounds  of,  653 

tetrabromide,  283 
Silicone,  282 
Silk-gelatin,  754 
Silver,  487 

acetamide,  668 
acetate,  591       ^' 
acetylide,  140,  537 
allotropic,  491 
amalgam,  498 
amalgamation  process,  489 
ammonio-nitrate,  493 
arsenate,  495 
arsenite,  270,  495 
bromide,  494 
carbonate,  493 
chlorides,  493 
chromates,  432 
cleaned,  215 
coin,  489 
colloidal,  490 
crucibles,  491 
cyanide,  696 
dendritic,  488 
detected  in  lead,  464 
extracted  by  amalgamation,  488 
from  copper  ores,  488 

lead,  463 
ferricyanide,  695 
ferrocyanide,  695 
fluoride,  495 
frosted,  489 
fulminate,  708 
fulminating,  492 
fusing-point,  491 
glance,  495 
hallides,  494 
hypouitrite,  103,  493 
hyposulphite,  236 
iodide,  199,  494 
meconate,  622 
metaphosphate,  258 
native,  488 
nitrate,  492 
nitride,  492 
nitrite,  493 
ore,  red,  495 

orthophosphate,  258,  495 
oxalate,  613 
oxides,  492 
oxidised,  489 
paracyanide,  696 
periodate,  199 
phosphate,  494 
photo-salts,  494 
plate,  490 


Silver,  pure,  preparation  of,  491 

pyrophosphate,  258 

refining,  464 

solder,  489 

sprouting  of,  491 

standard,  489 

sub-chloride,  493 

sulphantimomite,  495 

sulpharsenite,  495 

sulphates,  495 

sulphide,  495 

sulphite,  495 

tarnished,  215 

tartrate,  620 

thiosulphate,  236 

tree,  498 
Silvering,  490 
Simple  solution,  49 
Sinamiue,  705 
Siphon  eudiometer,  44 
Size,  754 
Skatole,  760 
Skraup's  method,  767 
Slag  blast-furnace,  400 
iron -refinery,  405 
lead-furnace,  461 
ore-furnace,  476 
puddling-f  urnace,  407 
refinery  (copper),  476 
roaster  (copper),  477 
Slaked  lime,  364 
Slaking'  of  lime,  53,  364 
Slate,  384 
Slow  port  fire,  339 
Smalt,  422 
Smelling-snlts,  355 
Smelting  tin  stone,  448 
SmitJisonite,  380 
Smoke,  159 
Smokeless  gas  burners,  154 

powder,  339 
Smut,  485 
Snow,  63 
Snuff,  777 
Soap,  800 

arsenical,  270 

Castile,  801 

glassmaker's,  372 

mottled,  801 

white  curd,  596 

yellow,  801 
Soda,  348 

action  on  hard  waters,  59 

ash,  346 

caustic,  348 

-lime,  521 

-lye,  348 

manufacture,  345 

washing,  348 

-waste,  315 

-water,  127 
Sodacetic  ether,  643 
Sodamide,  105 

Sedium  potassium  tartrate,  619 
Sodium,  343,  350 

acetate,  592 
acetylide,  537 
action  on  water,  20 
aluminate,  388 
amalgam,  85 


INDEX. 


Sodium,  ammonium  racemate,  621 

and  oxygen,  36 

anthrapurpurate,  720 

antimonites  of,  442 

arsenates,  352 

arsenite,  270 

aurocliloride,  518 

bicarbonate,  348 

borate,  352 

carbonates,  348 

Castner's  process,  350 

chlorate,  354 

chloride,  351 

dichromate,  431 

equivalent  weight,  20 

ethoxide,  564 

extraction,  350 

fluoride,  351 

fulminate,  708 

glycol,  574 

hydride,  351 

hydrosulphite,  237 

hydroxide,  348 

hypochlorite,  184 

hypophosphite,  260 
hyposulphite,  352 
line  in  spectrum,  329 
man  gam  te,  428 
metaphosphate,  259 
methoxide,  627 
nitrate,  353 
nitride,  107 
nitrite,  353 
nitromethane,  707 
nitroprusside,  695 
oleate,  598 
oxalate,  613 
palmitate,  801 
pentasulphide,  237 
periodate,  199 
permanganate,  429 
peroxide,  351 
phenol,  710 
phenoxide,  709 
phosphate,  352 
platinate,  507 
platiuochloride,  507 
potassium  alloy,  350 
propenoxides,  577 
pyroborate,  352 
pyrophcsphate,  352 
pyrosulphate,  351 
silicates,  353 
sodiolactate,  604 
stannate,  453 
stannite,  453 
stearate,  596 
sulphantimonate,  215 
sulpharseniate,  215 
sulphates,  351 
sulphides,  351 
sulphite,  221,  351 
sulphostannate,  217 
tetrathionate,  237 
thiochromite,  434 
thiophosphate,  352 
thiosulphate,  352 
tungstate,  436 
urate,  770 
zirconate,  458 


865 


Soffioni,  246 
Softening  waters.  59 
Soft  soap,  598,  801 

water,  55 

Soils,  absorptive  power  of,  816 
carbonic  acid  in,  81 
formation  of,  817 
impoverished,  817 
iron  in,  417 
Solanine,  778 
Solder,  452 

brazier's,  452 
silversmith's,  490 
Soluble  glass,  353 
Solution,  50,  316 
Solutions,  freezing-points  of,  320 
isetonic,  318 
nature  of,  316 
saline,  321 
solidified,  451 
vapour  pressure  of,  320 
Solvay's  process,  346 
Sombrerite,  369 
Soot,  159 

as  manure,  818 
Sorbic  acid,  599 
Sorbitol,  579 
Sorrel,  salt  of,  613 
Sovereign,  515 
Sozoidol,  712 
Spanish  black,  in 
Sparkling  wines,  127 
Sparteine  777 
Spathic  iron  ore,  396,  418 
Specific  gravity  of  gases,  24,  31,  293 
liquids,  63,  81 
solids,  63 

heat  and  atomic  weight,  297 
refractive  power,  787 
rotatory  power,  788 
volume,  786 
Spectroscope,  328 

use  of,  329 
Spectroscopy,  328 
Spectrum  analysis,  329 
Specular  iron  ore,  417 
Speculum  metal,  452,  481 
Speiss,  422 
Spelter,  379 
Spent  oxide,  478,  792 
Spermaceti,  799 
Sperm  oil,  799 
Spheroidal  state,  219 
Spices,  preservative  effect  of,  824 
Spiegeleisen,  403 
Spinelle,  388 
Spirit,  methylated,  565 
of  hart's  horn,  81 
of  salt,  169 
of  turpentine,  555 
of  wine,  563 
proof,  564 
Spirits,  807 
Spiritus  rectificatus,  564 

tenuior,  564 
Spodumene,  358 
Spongin,  754 
Spongy  platinum,  504 
Spontaneous  combustion,  33 
Sprengel's  pump,  70 

31 


866  INDEX. 

Springs,  petrifying,  58 
Spring  water,  55,  127 
Sprouting-  of  stiver,  491 
Stalactites  and  stalagmites,  58 
Standard  gold,  516 
Stannates,  453 
Stannic  acid,  454 

anhydride,  453 
arsenate,  456 
bromide,  455 
chloride,  455 
ethide,  657 
nitrate,  454 
oxide,  453 
phosphate,  456 
sulphate,  456 
sulphide,  455 
Stannous  chloride,  454 
ethide,  657 
nitrate,  454 
oxide,  453 
sulphide,  455 
Star  antimony,  441 
Starch,  734,  803 

animal,  736 
cellulose,  735 
commercial,  734 
extraction,  734 
iodised,  198 
manufacture  of,  802 
soluble,  735 
-sugar,  726 
varieties  of,  735,  803 
Stassfurtite,  375 
Stavesacre,  783 

Steam,  composition  by  volume,  45 
decomposed  by  c:irbon,  134 
chlorine,  174 
electric  sparks,  17 
heat,  1 8 

heat  of  formation  of,  307 
latent  heat  of,  307 
specific  gravity  calculated,  63 
Stearates,  596,  644 
Stearic  acid,  595 

aldehyde,  583 
Stearin,  595.  647 

caudles,  596 
Stearolic  acid,  599 
Steatite,  373 
Steel,  397 

annealing,  413 
Bessemer,  410 
blistered,  412 
cast,  413 
crucible,  413 

distinguished  from  iron,  41 
hard,  404,  410 
hardening,  410 
influence  of  impurities,  415 
manufacture,  410 
mild,  404,  409 
properties  of,  413 
shear,  412 
tempering,  414 
tungsten  in,  415 
Whitworth's,  413 
Stereochromy,  353 
Stereo-isornerides,  605 
Stereo-isomerism,  604,  620,  730 


Stereotype  metal,  439 
Sterro-metal,  482 
Stibines,  656 
Stibiopentamethyl,  656 
Stibiotriethyl,  656 
Stibiotrimethyl,  656 
Stibnite,  441 
Stilbeue,  551 
Still,  61 

Stone,  artificial,  354 
-coal,  160 
decayed,  366 
preservation  of,  366 
test  of  durability,  365 
-ware,  392 
Storax,  561,  645 
Stout,  806 
Straits  tin,  449 
Stramonium,  777 
Stream  tin  ore,  447 
Sti*ontia,  362 

-process  for  sugar-refining,  731 
Strontianite,  362 
Strontium,  362 

carbonate,  362 
chloride,  362 
dioxide,  362 
hydroxide,  362 
minerals,  362 
nitrate,  362 
sulphate.  362 
sulphide,  362 

Structural  formulae,  102,  524 
Strychnic  acid,  782 
Strychnine,  782 

methylium  hydroxide,  782 
Strychnos  alkaloids,  y  8  c 
Stubb,  555 
Stucco,  367 
Stupp,  555 
Styphnic  acid,  714 
Styracin,  645 
Styrolene,  550 
Suberic  acid,  615 
Sublimate,  corrosive,  499 
Sublimation,  78 
Sublimed  sulphur,  208 
Substantive  dyes,  683 
Substitution-products,  527 

rules  concerning,  547 
Succinamic  acid,  672 
Succiuamide,  669 
Succiuic  aciil,  614,  672 
anhydride,  614 
series  of  acids,  570,  611 
Succiuimide,  669 
Succino-dialdoxime,  759 
Succinyl  dichloride,  639 
Succussion,  228 
Sucrates,  732 
Sucrose,  731 
Sucrotetrauitrate,  733 
Suet,  648,  799 
Sugar,  731 

artificial,  727 
barley,  732 
beetroot,  731 
-candy,  731 
cane,  726,  731 
compounds  of,  732 


INDEX. 


867 


Sugar  extraction,  731 
-lime,  732 
loaf,  731 
maple,  731 
of  flesh,  716 
of  fruits,  725 
of  gelatine,  675 
of  lead,  592 
of  manna,  578 
of  milk,  727,  733,  812 
refining,  731 
starch,  726 
synthesis  of,  728 
uncrystallisable,  731 
Sugars,  724 

constitution  of,  727 
isomerism  among,  730 
synthesis  of,  728 
Suint,  333,  795 
Sulphamylic  acid,  629 
Sulphanilic  acid,  664 
Sulphonal,  626 
Sulpharsenntes,  275 
Sulphates,  206 
Sulphethylates,  641 
Sulphethylic  acid,  535,  628,  641 
Sulphides,  206 

action  of  air  on,  217 
formation  of,  212 
Sulphindigotic  acid,  175,  762 
Sulphindylic  aciJ,  762 
Sulphines,  573 
Sulphiuic  acids,  648 
Sulphites,  221 
Sulpho-     See  also  Thio 
Sulphobenzide,  710 

carbonates,  240 
carbonic  acid,  240 
cyanic  acid,  703 
cyanides,  703 
glyceric  acid,  646 
methylates,  641 
inetbylic  acid,  641 
palmitic  acid,  802 
phosphotriamide,  265 
stearic  acid,  802 
urea,  671 

vinic  acid,  535,  641 
Sulpholeic  acid,  802 
Sulphonal,  626 
Sulphouamides,  668 
Sulphones,  573 
Sulphonic  acids,  648 
Sulphur,  206,  479 
-acids,  217 
action  of  alkalies  on,  216 

lime  on,  217 
alcohols,  572 
allotropic  states  of,  212 
amorphous  or  insoluble,  210 
and  oxygen,  34 
bases,  217 
chlorides,  241,  242 
dimorphous,  210 
dioxide,  218 
distilled,  208 
ductile,  210 
electro-negative,  210 
positive,  210 
extraction,  207 


Sulphur,  extraction  from  soda-waste  ^7 

flowers  of,  208 

iodides,  242 

milk  of,  209 

occurrence  in  nature,  206 

octahedral,  211 

ores,  206 

oxides,  218 

plastic,  210 

prismatic,  211 

properties,  209 

recovered,  347 

refining,  208 

roll,  208 

rough,  208 

-salts,  217 

sesquioxide,  235 

sublimed,  208 

trioxide,  222 

uses,  209 

vapour  density,  213 
Sulphureous  waters,  61 
Sulphuretted  hydrogen,  213 
Sulphuric  acid,  223 

action  on  copper,  218 
fats,  802 
metals,  233 
organic  matters, 

anhydro-,  223 
anhydrous,  222 
composition  of,  233 
concentration,  228 
dihydrated,  232 
diluted,  turbidity  of,  232 
distillation  of,  228 
fuming,  223 
glacial,  232 

heat  evolved  in  diluting,  232 
manufacture,  225 

by  contact  pro- 
cess, 229 

monobydrated,  232 
Nordhausen,  223 
solidified,  232 
anhydride,  222 
ether,  628 

Sulphuring  casks,  220 
Sulphurous  acid,  219 

properties,  219 
anhydride,  218 
Sulphuryl,  221 

chloride,  221 
Sumach,  611,  797 
Superphosphate  of  lime,  369 
Supersaturated  solutions,  51 
Swedish  iron  ore,  396 
Sweet  oil,  798 

spirit  of  nitre,  642 
Syenite,  389 
Sylvestriue,  556 
Symbols,  4,  9 

Symmetrical  substitution-products,  546 
Sympathetic  ink,  53,  422 
Synaptase  (emulsiu),  584 
Synthesis,  6 

of  acids  of  the  acetic  series,  587 
organic  compounds,  141,  539 
water,  42 
Syntonin,  750 


868 


INDEX. 


TABASHEER,  277 
Tagilite,  485 
Talc,  373 
Tallow,  648,  799 
Taloses,  727 
Tank  liquor,  349 

waste,  345 
Tannates,  610 
Tannic  acid,  610 
Tannin,  611 
Tanning-,  797 
Tantalite,  447 
Tantalum,  447 
Tap-cinder,  407 
Tapioca,  803 

coal,  791 
Tartar,  618 

-emetic,  442,  620 
salt  of,  619 
Tartaric  acid,  619 

anhydride,  619 

properties  of,  619 

salts  of,  619 
Tartralic  acid,  619 
Tartrates,  619 
Tartrazine,  765 
Tartronic  acid,  617 
Tartronyl  urea,  771 
Tartryl  antim onions  acid,  620 

antimonites,  620 
Taurine,  679,  757 

synthesis  of,  679 
Taurocarbamic  acid,  679 
Taurocholic  acid,  756,  822 
Tautomerism,  701 
Tawing,  797 
Tea,  composition,  810 
Teeth,  artificial,  368 
Telluretted  hydrogen,  244 
Telluric  acid,  244 
Tellurides,  244 
Tellurium,  243 
Tellurous  acid,  244 
Temper  spoilt,  414 
Tempering,  colours  in,  414 
Tenacity  of  iron,  397 
Tennantite,  266 
Terbia,  394 
Terebenthene,  557 
Terephthalic  acid,  617 
Terne  plate,  450 
Terpenes,  555,  556 
Terpiuene,  556 
Terpineol,  559 
Terpin  hydrate,  559 
Terpinolene,  556 
Terra  japonica,  609 
Tertiary  alcohols,  568 

amines,  658 

benzene  ring,  716 

butyl  alcohol,  568 
Test-tube,  40 
Tetrachlorether,  631 
Tetrachlorobenzene,  540 

ethylene,  190 
hydroquinone,  718 
methane,  530 
quinone,  718 
Tetrad  elements,  12 
Tetrahydric  alcohols,  577 


Tetrahydropyrazoles,  765 

hydroxy-anthraquinoue,  721 
Tetramethyl-alloxantin,  775 

-ammonium  hydroxide,  661 

iodide,  659 
arsonium  hydroxide,  656 

iodide,  656 
benzene,  549 
methane,  533 
murexide,  775 
stiboniuin  hydroxide,  656 
thiouine,  768 

Tetramethoxyben  zylisoquinoliue,  780 
Tetramethylenindde,  759 
Tetrathionic  acid,  237 
Tetratomic  molecules,  300 
Tetrazines,  768 
Tetrazodiphenyl,  684 
Tetrazole,  765 
Tetrethyl  ammonium  hydroxide,  662 

iodide,  662 
Tetrethylium  hydroxide,  662 

iodides,  662 
Tetrethyl-phosphouium  hydroxide,  654 

iodide,  654 
Tetrolic  acid,  599 
Tetroses,  725 
Thalleiochin,  781 
Thalliue,  767 
Thallium,  473 

eth  oxide,  564 
Thebaine,  779 
Thebeuine,  780 
Theine,  775 
Thenard's  blue,  423 
Thenardite,  351 
Theobromine,  754 
Thennochemical  data,  305 

determination  of,  306 
application  of,  308 
Thermochemistry,  305 
Thiazines,  768 
Thiazoles,  764 
Thio-acetic  acid,  593 
-alcohols,  572 
aldehydes,  583 
antimonates,  446 
arsenates,  275 
arsenites,  275 
azoles,  764 
carbamic  acid,  672 
carbamide,  671 
carbanilide,  672 
carbimides,  703,  705 
carbonates,  240 
chromites,  434 
cyanic  acid,  702 
cyanates,  703 
cyanogen  compounds,  701 
diphenylamiue,  768 
ether,  573 
ethoxides,  572 
phenol,  710 

phosphoryl  chloride,  264 
resorcinol,  714 
sulphates,  235 
sulphuric  acid,  235 
Thionic  acids,  237 
Thionine,  768 
Thionyl,  221 


INDEX. 


Thionyl  chloride,  221 
Thiophen,  758 
Thiophosphates,  264 
Thio-stannates,  456 
Thio-sulphuric  acid,  235 
Thomas-Gilchrist  process,  410 

slag,  818 
Thoria,  458 
Thorium,  458 
Thorite,  458 
Thulia,  394 

Thyme,  essential  oil  of    ccc 
Thymol,  712 
Tiglic  acid,  597 
Tile  copper,  476 
Tiles,  392 
Tin,  447 

alkides,  657 
alloys  of,  451 
amalgam,  498 
binoxide,  453 
bisulphide,  455 
boiling,  454 
chlorides  of,  454 
crystals,  454 
dichloride,  454 
dimethyl  iodide,  657 
disulphide,  455 
dropped,  449 
foil,  449 
grain,  449 
grey,  450 
hexethide,  657 
impurities,  452 
metallurgy  of,  448 
nitromuriate.  455 
ores,  447 
oxides,  453 
oxychloride,  454 
plate,  450 
properties  of,  449 
protochloride,  454 
protosulphide,  455 
protoxide,  453 
pure,  449 

purification  of,  449 
pyrites,  456 
salts,  454 
sesquioxide,  454 
spots,  452 
stannate,  454 
stone,  447 
sulphides  of,  455 
tetrachloride,  455 
tetramethide,  657 
tetrethide,  657 
-tree,  455 

trimethyl-iodide,  657 
Tincal,  245,  352 
Tinned  iron,  450 
Tinning  brass,  451 

copper,  450 
Tinwhite  cobalt,  421 
Titanic  acid,  456 
iron,  396 
oxide,  456 
Titanium,  456 

salts,  457 
Toast,  736 
Tobacco,  777 


869 


Tokay,  808 

Tolane,  555 

Tolidine,  685 

Tolu,  essential  oil  of,  ccc 

Toluene,  549 

Toluic  acid,  601 

Toluidines,  665 

Tolusafrauine,  769 

Toluylene,  551 

reds,  760 
Tolyl,  548 

diphenylmethanc,  722 
Tolypyrine,  765 
Tonka- bean.  611 
Topaz,  205,  388 
Torbane-hill  mineral,  516 
Touch-paper,  339 
Touch-stone,  93 
Toughening  steel,  413 
Tourmaline,  205 

artificial,  781 
Tous-les-mois,  735 
Toxiues,  666 
Transition-point,  315 

of  iron,  414 
Trap-rock,  389 
Treacle,  731 
Tree-wax,  799 
Trehalose,  734 
Triacetin,  648 
Triad  elements,  12 
Triallyl  melamine,  705 
Triamidotolydiphenyl  carbinol,  721 
Triamidotriphenylmethane,  722 
Triamines,  658 
Triaziues,  768 
Triazoacetic  acid,  680 
Treborethyl,  653 
Tribromauilines,  664 
Tribromhy  driu,  636 
Tribromophenol,  710 
Tributyrm,  648 
Tricarballylic  acid,  623 

aniline,  664 
Trichlorhydriu,  636 
Trichlorobenzene,  540 

hydroquiuone,  718 
propane,  636 
puriue,  771 
pyrogallol,  715 
quinone  718 
Triclinic  crystals,  52 
Tricyanhydrin,  623 
Triethylamine,  662 
arsine,  273 
phosphiue,  654 
stibine,  656 

Triethylene  diamine,  666 
Trigonal  crystals,  52 
Trihydric  alcohols,  575 
Trihydroxy-anthraquinone,  721 
benzene,  715 
benzoic  acids,  609 
triphenyl-carbiuol,  723 
methane,  722 
Tri-iodo-methane,  636 
Trilauriu,  648 
Trimesic  acid,  624 
Trimethylamine,  659,  661 
arsine,  655 


8;o 


INDEX. 


Trimethylstibine,  656 

vinyl  ammonium  hydroxide,  666 
Trinitro-cellulose,  724 
phenol,  711 
phloroglucol,  716 
resorcin,  714 

Trinitrosophloroglucol,  716 
Triolein,  648 
Trioses,  725 
Tripalmitin,  648 
Triphane,  358 
Triphenylamine,  665 
Triphenylglyoxaline,  765 
Triphenylmethane,  551 

carboxylic  acid,  722 
dyestuffs,  721 
rosaniline,  723 
Triple  phosphate,  375 
Trithionic  acid,  237 
Trivalent  elements,  n 
Trona,  348 
Tropic  acid,  777 
Tropine,  777 
Tungstates,  436 
Tungsten,  436 
Tungstic  acid,  436 

hydrated,  436 
Tungstoborates,  436 
Tunicin,  743 
Turacine,  474 

Turbith  or  turpeth  mineral,  499 
Turkey  red,  795 
Turmeric,  747 

action  of  boric  acid  on,  247 
Turn  bull's  blue,  695 
Turner's  yellow,  472 
Turpentine,  555 

action  of  nitric  acid  on,  93 
hydrocarbons,  555 
in  chlorine,  175 
Turpethin,  745 
Turquoise,  390 
Tuyere  pipes,  397 
Type  furniture  alloy,  463 
metal,  399,  453,  466 
Types  of  chemical  compounds,  168 
Typical  oxides,  302 
Tyrosin,  678 
Tyrotoxicon,  68 1 

ULMIC  acid,  739,  817 
Ultramarine,  artificial,  390 
green,  390 
yellow,  432 
Unit  of  heat,  44 

volume  and  weight,  10,  12 
Umbelliferone,  714 
Umber,  384 
Unsaturated  compounds,  136 

hydrocarbons,  534 
Upcast  shaft,  126 
Urainil,  772 
Uranium,  437 
Uranyl,  437 
U  rates,  770 
Urea,  669 

artificial  formation,  670 

derivatives  of,  671 

extraction  from  urine,  670 

hydrochloride,  670 


Urea  nitrate,  670 
oxalate,  670 
Ureas,  compound,  671 
Ureides,  671,  771 
Urethane,  672 
Uric  acid,  769 

action  of  nitric  acid  on,  771 

synthesis  of,  773 
Urine,  composition,  815 
Uroxanic  acid,  773 
Uvinic  acid,  758 
Uvitic  acid,  758 

VACUUM-PANS,  731 
vessel,  73 
Valency,  n,  297 
Valentinite,  442 
Valerian,  essential  oil  of,  555 

root,  594 

Valerianic  acid,  594 
Valeric  acid,  594 

aldehyde,  583 
Valerin,  799 
Vanadic  acid,  446 
Vanadium,  446 
Vanillic  acid,  609 
Vanillin,  745 
Van't  Hoff's  law,  318 
Vapour-densities,  292 

density  determined,  293 

pressure  of  solutions,  320 
Varnishes,  560 
Vaseline,  529 
Vegetable  brimstone,  148 

colouring-matters,  746 
parchment,  738 
Vegetation,  chemistry  of,  816 
Velocities  of  molecules,  25,  291 
Venetian  red,  417 
Venice  turpentine,  555 
Ventilation,  125 
Veratralbine,  783 
Veratric  acid,  713 
Veratrine,  783 
Veratrol,  713 
Verdigris,  592 
Verditer,  484 
Vermilion,  503 
Vert  de  Guignet,  433 
Vesta  matches,  188 
Victoria  orange,  712 
Victor  Meyer's  apparatus,  293 
Vinasses,  66 1 
Vinegar,  composition  of,  591 

manufacture,  590,  591 
Vinyl  alcohol,  570 
chloride,  635 
Violet  bronze,  436 

Lauth's,  768 
Viridine,  766 
Viscose,  738 

Viscous  fermentation,  737,  806 
Vitriol,  231 

chambers,  226 
Vivianite,  419 
Volcanic  ammonia,  352 
Volt,  325 
Voltameter,  43 
Volumes,  law  of,  289 

standard,  10,  292 


INDEX. 


87I 


Vulcanised  rubber,  558 
Vulcanite,  558 

Wad,  426 

Walls,  efflorescence  on,  392 

Wash  leather,  797 

Watch-spring  burnt  in  oxygen,  37 

Water,  42 

action  on  metals,  21 
analysis,  60,  73 
chemical  relations  of,  49 
decomposed  by  battery,  13 

heat,  1 8 
distilled,  61 
electrolysis  of,  15,  324 
from  natural  sources,  54 
-gas,  134,  506 
hard,  55 

of  constitution,  53,  375 
crystallisation,  53 
oxygenated,  63 
physical  properties,  63 
purified,  60,  6 1 
soft,  55 

synthesis  of,  42,  45,  46 
tested,  60 
Waterproof  cloth,  557 

felt,  557 

Waters,  mineral,  61 
Water  vapour,  63 
Wavellite,  390 
Wax,  bees',  570,  644,  799 
bleached,  799 
Chinese,  590,  799 
Weld,  747 
Welding,  409 
Weldon's  chlorine  process,  170 

manganese  recovery  process,  170 
-Peciiiney  process,  348 
Well-water,  55 
Welsh  coal,  160 

Welsbach  incandescent  light,  154 
Wermuth,  745 
Whale  oil,  799 
Wheat,  803 

sprouted,  804 
Wheaten  flour,  808 
Whey,  812 
Whiskey,  808 
Whit?  antimony  ore,  442 
arsenic,  267 
gunpowder,  186,  339 
iron,  402 
lead,  460,  470 

manufacture,  470 
ore,  460 
metal,  475 
of  egg,  749 
precipitate,  500 

fusible,  501 
White  vitriol,  381 
Whitworth's  steel,  413 
Willesden  paper,  738 
Willow-bark,  743 
Windows,  crystals  on,  355 
Wine,  807 

Wines,  alcohol  in,  808 
Winter-green  oil,  645 
Wire-iron,  407 
Witherite,  359,  360 


Woad,  761 
Wolfram,  436,  447 
Wood  charcoal,  112 

combustion,  in 

composition,  168 

distillation,  112,  566 

for  gunpowder-charcoal,  113 

gum,  737 

kre  isote,  713 

-naphtha,  566 

preservation  of,  820 

-smoke,  824 

-spirit,  566 

-tar,  566 
Wood's  fusible  alloy,  439 
Worm,  6 1 
Worm-seed,  745 
Wormwood,  745 
Wort,  562,  805 
Wrought-iron,  404 
Wulfenite,  435 

XANTHATES,  643 
Xanthic  acid,  643 
Xanthine,  774 
Xantho-cobalt  salts,  423 
X  mthogen  persulphide,  643 
Xanthroproteic  acid,  750 
Xanthosiderite,  272 
Xenon,  77 
Xylene,  549 
Xylidine,  665 
Xylyl,  548 
Xylonite,  742 
Xylose,  725 

YEAST,  562,  805 
Yellow  casscl,  472 

chrome,  432 

dyes,  795 

fast,  683 

fire,  350 

Indian,  747 

ochre,  396 

orpiment,  275 

Paris,  472 

prussiate  of  potash,  689 

Turner's,  472 

ultramarine,  432 
Ytterbium,  394 
Yttrium,  394 

ZAFFRE,  423 
Zeisel's  method,  631 
Zinc,  376 

acet.ite,  592 

alkides,  651 

amalgam,  498 

amalgamated,  498 

amide,  653 

arsenide,  272 

arsenite,  270 

boiling-point,  377 

carbonate,  380 

chloride,  380 

cyanide,  692 

diamine,  380 

ethoxide,  653 

distilled,  378 


872 

Zinc  dust,  380 
ethide,  651 
ethyl,  651,  652 
extraction,  377 
ferrocyanide,  694 
granulated,  22 
hydrosulphite,  23 
hydroxide,  380 
impurities  in,  379 
lactate,  604 
mercaptide,  653 
metallurgy  of,  379 
methide,  653 
methyl,  653 


INDEX. 


Zinc  nitride,  380 

ores,  377 

oxide,  380 

oxychloride,  377 

phosphate,  382 

removal  of  lead  from,  379 

silicate,  382 

sulphate,  381 

sulphide,  381 

white,  380 
Zircon,  458 
Zirconia,  458 
Zirconium,  458 
Zymase,  584 


Printed  by  BALLANTVNE,  HANSON  &  Co. 
London  &  Edinburgh 


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